CN114710027A - Unified temperature control strategy for flying capacitor type converter based on carrier rotation - Google Patents

Abstract

The invention provides a unified temperature control strategy of a flying capacitor type converter based on carrier rotation. The method comprises the following concrete steps: 1. on the basis of carrier laminated modulation, one or two base frequency periods are adopted as a rotation period according to the parity of the number of carriers in a single base frequency period, and the single rotation period is divided into a plurality of equal areas; 2. fixing the driving mode of the fully-controlled switch tube unchanged, keeping the positions of the corresponding carriers of the upper and lower bridge arms unchanged in one half area of each rotation period, and interchanging the spatial positions of the carriers in the other half area to generate fully-controlled switch tube driving signals which meet the requirements that two zero level states appear in pairs in one rotation period, the action time is equal, and all power devices are used in a balanced manner; 3. and outputting a driving signal of a specific fully-controlled switching tube according to the polarity characteristic of the current, and finally realizing the stabilization of the flying capacitor voltage, the balanced reduction of the loss and the junction temperature of all devices and the setting of no dead time.

Description

Unified temperature control strategy of flying capacitor converter based on carrier rotation

technical field

The invention belongs to the field of reliability research of high-power multi-level power electronic converters, in particular to a unified temperature control strategy based on carrier rotation for a flying capacitor type converter module.

Background technique

In recent years, with the development of power electronics technology and the continuous progress of industrial modernization, "Multilevel Converter" (Multilevel Converter) has received more and more attention in various fields of industrial applications. At present, there are mainly three topological structures of multi-level converters with more mature applications: diode clamping type, cascaded H-bridge type and flying capacitor type. Compared with the other two topologies, the flying-capacitor multilevel converter topology is based on the characteristics of capacitor clamping, which overcomes the inherent difficulty of balanced control of the DC side capacitor voltage of the diode-clamped converter and the fact that power switching devices cannot be used in a balanced manner. And there is no problem that cascaded H-bridge converters require multiple DC power supplies; in addition, flying capacitor converters also have the advantages of easy expansion of the number of levels, flexible control, and many redundant switch states, etc., and have been widely used. It is used in medium and high voltage frequency converters, active power filters, static var compensators and other fields.

The main problem of flying capacitor multilevel converters in practical applications is reliability. Flying capacitor multilevel converters belong to complex power electronic systems, and a large number of power switching devices used in them have greatly increased its failure probability. Many research literatures point out that the most frequent failures in power electronic systems are the failures of power switching devices, which are closely related to the junction temperature of the device, more precisely, the thermal stress and thermal cycling of the device. Therefore, reducing the thermal stress of the power switching device will effectively prolong the service life of the device, thereby improving the reliability of the entire power electronic system. In recent years, a large number of studies have explored thermal stress control methods for power switching devices in power electronic systems. These methods can be roughly divided into two categories. One is to reduce the thermal stress of the device by improving the external hardware of the device; the other method is called active temperature control strategy, which is generally regarded as a more efficient and cost-effective solution. The active temperature control strategy is usually to reduce the temperature by changing the operating parameters of the power switching device itself. For example, some literatures propose to reduce the switching loss of the power switching device by reducing the switching frequency to achieve the purpose of reducing the temperature of the device, but this method will significantly reduce the temperature. Add harmonics of the current, which is unacceptable in some applications. Some literatures propose the use of discontinuous pulse width modulation method to reduce the switching loss of power switching devices and achieve the purpose of lowering the temperature of the device, but this method will also significantly increase the current harmonics. Some literatures propose a temperature control method based on the working mechanism of periodically rotating power devices for fully-controlled H-bridge converters. This method does not consider the balance and stability of the flying capacitor voltage, so it cannot be applied to the flying capacitor type converter. In addition, as the main modulation scheme of the flying capacitor type converter, the carrier phase-shift modulation not only increases the harmonic content of the output voltage, but also has the problems of excessive use of power devices and excessive generation of zero-level states, which greatly increases the number of devices. The loss and junction temperature of the converter have extremely adverse effects on the output quality and reliability of the converter. So far, there has not been any satisfactory solution that enables the flying capacitor converter to reduce and uniformly distribute the temperature of all power switching devices under various operating conditions without affecting all the performance of the circuit. .

SUMMARY OF THE INVENTION

In order to solve the above problems, the present invention provides a unified temperature control strategy for a flying capacitor type converter based on carrier rotation. This control strategy is suitable for all operating conditions of the flying capacitor converter including rectification, inversion, and reactive power compensation. By using one or two fundamental frequency cycles as a rotation cycle, the upper and lower bridge arms are periodically rotated corresponding to the carrier. The space position and the implementation of outputting a specific switching device drive signal according to the positive and negative polarity of the input current maintain the stability of the flying capacitor voltage, realize the balanced reduction and uniform distribution of the loss and temperature of all power devices, and avoid deadlock. zone time settings.

The purpose of the present invention is achieved through the following technical solutions, which is characterized in that: on the basis of carrier stacking modulation, according to the parity of the number of carriers n ₁ in a single fundamental frequency period, m fundamental frequency periods are used as a rotation Period (m=1 or 2), a single rotation period is divided into _i equal areas, the number of carriers in each area is 2j, and each area can be divided into two equal sub-areas ia and _ib , each sub-region contains j equal carriers; the driving mode of the fixed full-control switch tube remains unchanged, and the spatial positions of the upper and lower bridge arms corresponding to the carriers c _U and c _D remain unchanged in all sub-regions i _a , and in all sub-regions i a The spatial positions of the carriers c _U and c _D are exchanged in the area i _b to generate all fully-controlled switches and freewheeling diodes that can satisfy the zero-level O ₁ and O ₂ states appearing in pairs in one rotation cycle and have an equal duration of action. The switching device driving signals G ₁ , G ₂ , G ₃ , and G ₄ are used for equalization in one rotation period; in order to avoid the setting of dead time in the pulse signal, according to the positive and negative of the current i _x,x=a,b,c The polarity outputs the drive signals G ₁ , G ₂ or G ₃ , G ₄ of the specific full-control switch tubes. When the current polarity is positive, the drive signals G ₃ and G ₄ corresponding to the full-control switches S ₃ and S ₄ are output. , when the current polarity is negative, the drive signals G ₁ and G ₂ corresponding to the fully-controlled switches S ₁ and S ₂ are output, and finally the stability of the flying capacitor voltage, the balanced use of all power devices and no dead time are realized. set up. Based on the control strategy provided by the present invention, the two zero-level states in the flying capacitor type converter can appear in pairs in one rotation period and have equal action time. It has equal charge and discharge time with the negative terminal. On the other hand, it balances and reduces the loss and junction temperature of all power devices, and effectively improves its reliability on the basis of ensuring the normal operation of the flying capacitor type converter. In addition, since there are no unnecessary switching devices involved in the work, the control strategy proposed in the present invention makes the flying capacitor type converter no longer affected by the dead time effect, and further improves its output quality.

是经高频滤波后u_xo,x＝a,b,c的低频分量，输入电流为i_x,x＝a,b,c。四个全控开关管的驱动信号分别为全控开关管S₁栅极驱动脉冲G₁，全控开关管S₂栅极驱动脉冲G₂，全控开关管S₃栅极驱动脉冲G₃，全控开关管S₄栅极驱动脉冲G₄。 _A unified temperature control strategy _of a flying capacitor converter based _on carrier rotation provided by the present invention is shown in FIG. S ₄ , four anti-parallel diodes D ₁ , D ₂ , D ₃ , D ₄ , a flying capacitor C _f and two voltage-stabilizing capacitors C ₁ , C ₂ , wherein the emitter of the fully controlled switch S ₁ is connected to the _The collector of S2 is connected to the collector of _S2 , the emitter _of S2 is connected to the collector _of S3, the emitter of _S3 is connected to the collector _of S4, the collector of _S1 and the emitter of S4 respectively form the positive terminal of the DC side The voltage between P and the negative terminal N of the DC side, and the voltage between the positive terminal P and the negative terminal N is E, and the connection point O of the voltage _- stabilizing capacitors _C1 and C2 provides the zero-point potential between the positive and negative terminals of the DC side. The AC side port voltage is u _xo,x=a,b,c ,

is the low-frequency component of u _xo,x=a,b,c after high-frequency filtering, and the input current is i _x,x=a,b,c . The driving signals of the four fully-controlled switch tubes are respectively the gate drive pulse G ₁ of the fully-controlled switch tube S ₁ , the gate drive pulse G ₂ of the fully-controlled switch tube S ₂ , the gate drive pulse G ₃ of the fully-controlled switch tube S ₃ , The gate drive pulse G _{4 of the fully controlled switch S 4 .}

The flying capacitor type converter can operate in rectification condition, capacitive reactive power compensation condition, inverter condition and inductive reactive power compensation condition. 4 and 5 show, respectively: positive level P state, negative level N state, and zero level O ₁ and O ₂ states. Define the direction of current i _{x, x = a, b, c} flowing into the converter as the positive direction. The following table presents the working mechanism of the power device corresponding to each level state and current flow direction. It can be seen that only the two zero-level states of O ₁ and O ₂ exist in the charging and discharging process of the flying capacitor C _f .

The stability of the flying capacitor voltage u _cf at E/2 is the basic condition for the normal operation of the converter, which requires the flying capacitor C _f to have equal charge and discharge durations for the P terminal and the N terminal. Figure 6 shows the distribution diagram of the zero-level state of the flying capacitor converter under the traditional carrier phase-shift modulation. It can be seen that the states of O ₁ and O ₂ appear alternately in a single fundamental frequency cycle and the action time is equal, so the carrier shift Phase modulation can naturally maintain u _cf =E/2, which becomes the main modulation strategy of the flying capacitor converter. However, carrier phase-shift modulation not only increases the harmonic content of the output voltage of the converter, but also has the problem of excessive use of power devices and excessive generation of zero-level states, which greatly increases the loss and junction temperature of the device, which is very important for the flying capacitor. The output quality and reliability of the type converter are adversely affected.

In view of the above problems, the present invention proposes a unified temperature control strategy for flying capacitor converters based on carrier rotation. The fundamental frequency period is a rotation period. The positions of the corresponding carriers of the upper and lower bridge arms are kept unchanged in one half of each rotation period, and the spatial positions of the carriers are exchanged in the other half of the area. Finally, a specific output is output according to the polarity characteristics of the input current. The driving signal of the switch tube realizes that the two zero-level O ₁ and O ₂ states appear in pairs in one rotation cycle and have an equal duration of action, which reduces the loss and junction temperature of each power device in a balanced manner, and avoids dead zones. Time setting, its implementation steps are as follows:

1) On the basis of carrier stacking modulation, it is defined that the carriers c _U and c _D corresponding to the upper and lower bridge arms are located on the positive and negative half axes of the vertical axis, respectively. According to the parity of the number of carriers n ₁ in a single fundamental frequency period, m Each fundamental frequency period is a rotation period (m=1 or 2), a single rotation period is divided into i equal areas, and the number of carriers in each area is 2j; at the same time, each area can be divided into two equal areas. sub-regions i _a and i _b , each sub-region contains j equal carriers; specifically,

When n ₁ is an even number, (m=1) fundamental frequency periods are used as a rotation period, and the number of carriers n ₁ in the rotation period can be decomposed into a prime factor to obtain n ₁ =2·i·j, at this time, the rotation period It is divided into i equal regions, the number of carriers in each region is 2j, and the number of regions in the positive and negative half cycles must be equal and even; at the same time, each region can be equally divided into two sub-regions i _a and i _b , each sub-region contains j equal carriers;

When n ₁ is an odd number, (m=2) fundamental frequency periods are used as a rotation period, and the number of carriers 2n ₁ in the rotation period can be decomposed into a prime factor to obtain 2n ₁ =2·i·j, at this time, the rotation period It is divided into i equal regions, and the number of carriers in each region is 2j; since n ₁ is odd, i and j are both odd, where i takes a larger odd value and j takes a smaller odd value; at the same time, each Each area can be equally divided into two sub-areas _ia and _ib , and each sub-area contains j equal carriers.

2) The driving mode of the fixed full-control switch tube remains unchanged, the spatial positions of the upper and lower bridge arms corresponding to the carriers c _U and c _D remain unchanged in all sub-regions i _a , and the carriers c _U and c D are exchanged in all sub-regions i _b . The spatial position of c _D , to generate a switching device drive that satisfies the zero-level O ₁ and O ₂ states appear in pairs in one rotation period and have equal action time, and all fully-controlled switches and freewheeling diodes are used equally in one rotation period Signals G ₁ , G ₂ , G ₃ , G ₄ ;

Specifically, in the modulation process, the power switch tubes of the upper and lower bridge arms are switched on and off by comparing the modulation wave u _ref with the corresponding carrier waves c _U and c _D of the upper and lower bridge arms. The specified driving mode is as follows:

When u _ref >c _U , drive the full _- control switch S1 to conduct, and the full _- control switch S4 to turn off;

When u _ref =c _U , drive the full _- control switch S1 to turn off, and the full _- control switch S4 to turn off;

When u _ref <c _U , the full-control switch S1 is driven to turn off, and the full _- control switch S4 is turned _on ;

When u _ref >c _D , the full-control switch S2 is driven to be turned _on , and the full _- control switch S3 is turned off;

When u _ref = _{c D} , the full-control switch S2 is driven to turn off, and the full _- control switch S3 is turned off;

When u _ref <c _D , the full-control switch S2 is driven to turn off, and the full _- control switch S3 is turned _on ;

Based on this driving method, the spatial positions of the upper and lower bridge arms corresponding to the carriers c _U and c _D are kept unchanged in all sub-regions i _a , and the spatial positions of the carriers c _U and c _D are exchanged in all sub-regions i _b , then the Generate the switching device driving signals G ₁ , G ₂ that satisfy the zero-level O ₁ and O ₂ states appear in pairs in one rotation period and have equal action time, and all fully-controlled switches and freewheeling diodes are used equally in one rotation period , G ₃ , G ₄ ;

Among them, when n ₁ is an even number, in the positive half cycle of a fundamental frequency cycle,

The duration of action of zero-level O ₂ in sub-region 1 _a = duration of action of zero-level O ₁ in sub-region (i/2) _b ;

The duration of action of zero-level O ₁ in sub-region 1 _b = duration of action of zero-level O ₂ in sub-region (i/2) _a ;

which is:

The duration of action of zero-level O ₂ in sub-region x _a = duration of action of zero-level O ₁ in sub-region [(i/2)+1-x] _b ;

The duration of action of zero-level O ₁ in sub-region x _b = duration of action of zero-level O ₂ in sub-region [(i/2)+1-x] _a ;

Similarly, in the negative half cycle of a fundamental frequency cycle,

Sub-region [( _i /2)+1] Action duration of zero-level O ₂ in sub-region i = Action duration of zero-level O ₁ in sub-region i _b ;

The duration of action of zero-level O ₁ in sub-region [( _i /2)+1] _b = duration of action of zero-level O ₂ in sub-region ia;

which is:

Sub-region [(i/2)+x] Action duration of zero-level O ₂ in _a = sub-region (i-x+1) Action duration of zero-level O ₁ in _b ;

The duration of action of zero-level O 1 in sub-region [(i/ ₂ )+x] _b = duration of action of zero-level O ₂ in sub-region (i-x+1) _a ;

It can be found that when n ₁ is an even number, the zero-level O ₁ and O ₂ states can appear in pairs in the positive and negative half cycles of a fundamental frequency cycle, respectively, with equal durations.

Similarly, when n ₁ is odd, within two fundamental frequency cycles,

The duration of action of zero-level O ₂ in sub-region 1 _a (within the first fundamental frequency period) = the duration of action of zero-level O ₁ in sub-region [(i-1)/2+1] _b (the second fundamental frequency period)

The duration of action of zero-level O ₁ in sub-region 1 _b (in the first fundamental frequency period) = the duration of action of zero-level O ₂ in sub-region [(i-1)/2+2] _a (the second fundamental frequency period)

which is:

The duration of action of zero-level O ₂ in sub-region x _a (within the first fundamental frequency period) = the duration of action of zero-level O ₁ in sub-region [(i-1)/2+x] _b (the second fundamental frequency period)

The duration of action of zero-level O ₁ in sub-region x _b (within the first fundamental frequency period) = the duration of action of zero-level O ₂ in sub-region [( _i -1)/2+x+1] (the second within the fundamental frequency period)

It can be found that when n ₁ is an odd number, the zero-level O ₁ and O ₂ states can also appear in pairs within two fundamental frequency cycles and have an equal duration of action.

In this way, based on the proposed control strategy, no matter whether _{n 1} is odd or even, there are always two corresponding sub-regions ia and _ib in a rotation period, which respectively contain O ₁ and O ₂ states with equal durations, and then realize The balance and stability of the flying capacitor voltage. At the same time, in the case of the same carrier frequency, compared with the traditional carrier phase-shift modulation strategy, the number of zero-level states in the proposed control strategy will be greatly reduced, and the loss and temperature of all power devices will be uniformly reduced and uniformly distributed. .

3) In order to avoid the setting of dead time in the pulse signal, output the drive signals G ₁ , G ₂ or G ₃ , G ₄ of the specific full-control switch tube according to the polarity characteristics of the current i _x,x=a,b,c ; When the current polarity is positive, the drive signals G ₃ and G ₄ corresponding to the fully controlled switches S ₃ and S ₄ are output, and when the current polarity is negative, the drive signals corresponding to the fully controlled switches S ₁ and S ₂ are output G ₁ and G ₂ , so that the unnecessary switches in each rotation cycle can be turned off, and finally the voltage of the flying capacitor is stabilized, all power devices are used in a balanced manner, and the setting of dead time is avoided.

且i_x,x＝a,b,c＞0时，变换器的电平状态包含P状态、O₁状态与O₂状态，此时仅需保留驱动信号G₃和G₄即可产生相应的电平状态；Specifically, when

And when i _x,x=a,b,c >0, the level state of the converter includes the P state, the O ₁ state and the O ₂ state. At this time, only the driving signals G ₃ and G ₄ need to be retained to generate the corresponding level state;

Level status Device working mechanism Only need to drive signals G₃ and G₄ P state D₁/D₂ on G₃=0, G₄=0 O₁ status D₁/S₃ on G₃=1, G₄=0 O₂ state D₂/S₄ on G₃=0, G₄=1

且i_x,x＝a,b,c＜0时，变换器的电平状态包含P状态、O₁状态与O₂状态，此时仅需保留驱动信号G₁和G₂即可产生相应的电平状态；when

And when i _x,x=a,b,c < 0, the level state of the converter includes the P state, the O ₁ state and the O ₂ state. At this time, only the driving signals G ₁ and G ₂ need to be retained to generate the corresponding level state;

Level status Device working mechanism Only need to drive signals G₁ and G₂ P state S₁/S₂ on G₁=1, G₂=1 O₁ status S₁/D₃ on G₁=0, G₂=1 O₂ state S₂/D₄ on G₁=1, G₂=0

且i_x,x＝a,b,c＜0时，变换器的电平状态包含N状态、O₁状态与O₂状态，此时仅需保留驱动信号G₁和G₂即可产生相应的电平状态；when

And when i _x,x=a,b,c < 0, the level state of the converter includes the N state, the O ₁ state and the O ₂ state. At this time, only the driving signals G ₁ and G ₂ need to be retained to generate the corresponding level state;

Level status Device working mechanism Only need to drive signals G₁ and G₂ N state D₃/D₄ on G₁=0, G₂=0 O₁ status S₁/D₃ on G₁=1, G₂=0 O₂ state S₂/D₄ on G₁=0, G₂=1

且i_x,x＝a,b,c＞0时，变换器的电平状态包含N状态、O₁状态与O₂状态，此时仅需保留驱动信号G₃和G₄即可产生相应的电平状态。when

And when i _x,x=a,b,c >0, the level state of the converter includes the N state, the O ₁ state and the O ₂ state. At this time, only the driving signals G ₃ and G ₄ need to be retained to generate the corresponding level status.

To sum up, when the current polarity is positive, the proposed control strategy selects to output the drive signals G ₃ and G ₄ corresponding to the specific fully-controlled switches S ₃ and S ₄ , and when the current polarity is negative, the proposed control strategy selects The drive signals G ₁ and G ₂ corresponding to the specific full-control switch tubes S ₁ and S ₂ are output. In this way, the control strategy proposed in the present invention can not only maintain the stability of the flying capacitor voltage, reduce the loss and temperature of each power device in a balanced manner, but also does not need to set dead time for the driving pulse, thereby avoiding the influence of the dead time effect on the output quality of the converter. Compared with the traditional carrier phase-shift modulation strategy, the proposed control strategy effectively improves the reliability and output quality of the flying capacitor converter.

In order to discuss the proposed control strategy in more detail, the proposed control strategy is described by taking the case where n ₁ shown in FIG. 7 is an even number and when n ₁ shown in FIG. 8 is an odd number as an example.

As shown in FIG. 7 , when n ₁ =12 is an even number, the implementation steps of the control strategy proposed by the present invention are as follows:

1) Define that the carriers c _U and c _D corresponding to the upper and lower bridge arms are located on the positive and negative semi-axes of the vertical axis, respectively. According to the number of carriers n ₁ =12 in a single fundamental frequency period, it is an even number, and (m=1) fundamental frequencies are used. The period is a rotation period, and the number of carriers n ₁ in the rotation period can be decomposed into a prime factor to obtain 12=2×4×1.5. At this time, the rotation period is divided into (i=4) equal areas. The number of carriers is (2j=3), and the number of regions i/2 in the positive and negative half cycles is an even number 2; at the same time, each region can be equally divided into two sub-regions i _a and i _b , each sub-region contains (j=1.5) equal carriers.

2) The driving mode of the fixed full-control switch tube remains unchanged, the spatial positions of the upper and lower bridge arms corresponding to the carriers c _U and c _D remain unchanged in all sub-regions i _a , and the carriers c _U and c D are exchanged in all sub-regions i _b . The spatial position of c _D , to generate a switching device drive that satisfies the zero-level O ₁ and O ₂ states appear in pairs in one rotation period and have equal action time, and all fully-controlled switches and freewheeling diodes are used equally in one rotation period Signals G ₁ , G ₂ , G ₃ , G ₄ .

Specifically, in the modulation process, the power switch tubes of the upper and lower bridge arms are switched on and off by comparing the modulation wave u _ref with the corresponding carrier waves c _U and c _D of the upper and lower bridge arms. The specified driving mode is as follows:

When u _ref >c _U , drive the full _- control switch S1 to conduct, and the full _- control switch S4 to turn off;

When u _ref =c _U , drive the full _- control switch S1 to turn off, and the full _- control switch S4 to turn off;

When u _ref <c _U , the full-control switch S1 is driven to turn off, and the full _- control switch S4 is turned _on ;

When u _ref >c _D , the full-control switch S2 is driven to be turned _on , and the full _- control switch S3 is turned off;

When u _ref = _{c D} , the full-control switch S2 is driven to turn off, and the full _- control switch S3 is turned off;

When u _ref <c _D , the full-control switch S2 is driven to turn off, and the full _- control switch S3 is turned _on ;

Based on this driving method, the spatial positions of the upper and lower bridge arms corresponding to the carriers c _U and c _D are kept unchanged in all sub-regions i _a , and the spatial positions of the carriers c _U and c _D are exchanged in all sub-regions i _b , then the Generate the switching device driving signals G ₁ , G ₂ that satisfy the zero-level O ₁ and O ₂ states appear in pairs in one rotation period and have equal action time, and all fully-controlled switches and freewheeling diodes are used equally in one rotation period , G ₃ , G ₄ ;

Among them, in the positive half cycle of a fundamental frequency cycle,

The duration of action of zero-level O ₂ in sub-region 1 _a = duration of action of zero-level O ₁ in sub-region (i/2=2) _b ;

The duration of action of zero-level O ₁ in sub-region 1 _b = duration of action of zero-level O ₂ in sub-region (i/2=2) _a ;

Similarly, in the negative half cycle of a fundamental frequency cycle,

Sub-region [(i/2)+1=3] Action duration of zero-level O ₂ in _a = sub-region (i=4) Action duration of zero-level O ₁ in _b ;

Sub-region [(i/2)+1=3] Action duration of zero-level O ₁ in _b = Action duration of zero-level O ₂ in sub-region (i=4) _a ;

It can be found that when n ₁ =12 is an even number, the zero-level O ₁ and O ₂ states can respectively appear in pairs in the positive and negative half cycles of a fundamental frequency cycle and have equal durations. Based on the proposed control strategy, there are always two corresponding sub-regions ia and _ib in _a rotation period, which respectively contain O ₁ and O ₂ states with equal durations, so as to achieve the balance and stability of the flying capacitor voltage. At the same time, in the case of the same carrier frequency, compared with the traditional carrier phase-shift modulation strategy, the number of zero-level states in the proposed control strategy will be greatly reduced, and the loss and temperature of all power devices will be uniformly reduced and uniformly distributed. .

3) In order to avoid the setting of dead time in the pulse signal, output the drive signals G ₁ , G ₂ or G ₃ , G ₄ of the specific full-control switch tube according to the polarity characteristics of the current i _x,x=a,b,c ; When the current polarity is positive, the drive signals G ₃ and G ₄ corresponding to the fully controlled switches S ₃ and S ₄ are output, and when the current polarity is negative, the drive signals corresponding to the fully controlled switches S ₁ and S ₂ are output G ₁ and G ₂ , so that the unnecessary switches in each rotation cycle can be turned off, and finally the voltage of the flying capacitor is stabilized, all power devices are used in a balanced manner, and the setting of dead time is avoided.

且i_x,x＝a,b,c＞0时，变换器的电平状态包含P状态、O₁状态与O₂状态，此时仅需保留驱动信号G₃和G₄即可产生相应的电平状态；Specifically, when

And when i _x,x=a,b,c >0, the level state of the converter includes the P state, the O ₁ state and the O ₂ state. At this time, only the driving signals G ₃ and G ₄ need to be retained to generate the corresponding level state;

Level status Device working mechanism Only need to drive signals G₃ and G₄ P state D₁/D₂ on G₃=0, G₄=0 O₁ status D₁/S₃ on G₃=1, G₄=0 O₂ state D₂/S₄ on G₃=0, G₄=1

且i_x,x＝a,b,c＜0时，变换器的电平状态包含P状态、O₁状态与O₂状态，此时仅需保留驱动信号G₁和G₂即可产生相应的电平状态；when

And when i _x,x=a,b,c < 0, the level state of the converter includes the P state, the O ₁ state and the O ₂ state. At this time, only the driving signals G ₁ and G ₂ need to be retained to generate the corresponding level state;

Level status Device working mechanism Only need to drive signals G₁ and G₂ P state S₁/S₂ on G₁=1, G₂=1 O₁ status S₁/D₃ on G₁=0, G₂=1 O₂ state S₂/D₄ on G₁=1, G₂=0

且i_x,x＝a,b,c＜0时，变换器的电平状态包含N状态、O₁状态与O₂状态，此时仅需保留驱动信号G₁和G₂即可产生相应的电平状态；when

And when i _x,x=a,b,c < 0, the level state of the converter includes the N state, the O ₁ state and the O ₂ state. At this time, only the driving signals G ₁ and G ₂ need to be retained to generate the corresponding level state;

Level status Device working mechanism Only need to drive signals G₁ and G₂ N state D₃/D₄ on G₁=0, G₂=0 O₁ status S₁/D₃ on G₁=1, G₂=0 O₂ state S₂/D₄ on G₁=0, G₂=1

且i_x,x＝a,b,c＞0时，变换器的电平状态包含N状态、O₁状态与O₂状态，此时仅需保留驱动信号G₃和G₄即可产生相应的电平状态。when

And when i _x,x=a,b,c >0, the level state of the converter includes the N state, the O ₁ state and the O ₂ state. At this time, only the driving signals G ₃ and G ₄ need to be retained to generate the corresponding level status.

To sum up, when the current polarity is positive, the proposed control strategy selects to output the drive signals G ₃ and G ₄ corresponding to the specific fully-controlled switches S ₃ and S ₄ , and when the current polarity is negative, the proposed control strategy selects The drive signals G ₁ and G ₂ corresponding to the specific full-control switch tubes S ₁ and S ₂ are output. In this way, the control strategy proposed in the present invention can not only maintain the stability of the flying capacitor voltage, reduce the loss and temperature of each power device in a balanced manner, but also does not need to set dead time for the driving pulse, thereby avoiding the influence of the dead time effect on the output quality of the converter. Compared with the traditional carrier phase-shift modulation strategy, the proposed control strategy effectively improves the reliability and output quality of the flying capacitor converter.

Further, when n ₁ =9 is an odd number as shown in FIG. 8 , the implementation steps of the control strategy proposed by the present invention are as follows:

1) Define that the carriers c _U and c _D corresponding to the upper and lower bridge arms are located on the positive and negative semi-axes of the vertical axis, respectively. According to the number of carriers n ₁ =9 in a single fundamental frequency period, it is an odd number, and (m=2) fundamental frequencies are used. The period is a rotation period, the number of carriers 2n ₁ in the rotation period can be decomposed into a prime factor to obtain 2×9=2×3×3, at this time, the rotation period is divided into (i=3) equal areas, each The number of carriers in the area is (2j=6); at the same time, each area can be equally divided into two sub-areas _ia and ib , and each sub-area contains (j ₌ 3) equal carriers.

2) The driving mode of the fixed full-control switch tube remains unchanged, the spatial positions of the upper and lower bridge arms corresponding to the carriers c _U and c _D remain unchanged in all sub-regions i _a , and the carriers c _U and c D are exchanged in all sub-regions i _b . The spatial position of c _D , to generate a switching device drive that satisfies the zero-level O ₁ and O ₂ states appear in pairs in one rotation period and have equal action time, and all fully-controlled switches and freewheeling diodes are used equally in one rotation period Signals G ₁ , G ₂ , G ₃ , G ₄ ;

Specifically, in the modulation process, the power switch tubes of the upper and lower bridge arms are switched on and off by comparing the modulation wave u _ref with the corresponding carrier waves c _U and c _D of the upper and lower bridge arms. The specified driving mode is as follows:

When u _ref >c _U , drive the full _- control switch S1 to conduct, and the full _- control switch S4 to turn off;

When u _ref =c _U , drive the full _- control switch S1 to turn off, and the full _- control switch S4 to turn off;

When u _ref <c _U , the full-control switch S1 is driven to turn off, and the full _- control switch S4 is turned _on ;

When u _ref >c _D , the full-control switch S2 is driven to be turned _on , and the full _- control switch S3 is turned off;

When u _ref = _{c D} , the full-control switch S2 is driven to turn off, and the full _- control switch S3 is turned off;

When u _ref <c _D , the full-control switch S2 is driven to turn off, and the full _- control switch S3 is turned _on ;

Based on this driving method, the spatial positions of the upper and lower bridge arms corresponding to the carriers c _U and c _D are kept unchanged in all sub-regions i _a , and the spatial positions of the carriers c _U and c _D are exchanged in all sub-regions i _b , then the Generate the switching device driving signals G ₁ , G ₂ that satisfy the zero-level O ₁ and O ₂ states appear in pairs in one rotation period and have equal action time, and all fully-controlled switches and freewheeling diodes are used equally in one rotation period , G ₃ , G ₄ ;

Among them, in two fundamental frequency cycles,

The action duration of zero-level O ₂ in sub-region 1 _a (in the first fundamental frequency period) = sub-region [(i-1)/2+1=2] The action duration of zero-level O ₁ in _b (the second within the fundamental frequency period)

The duration of action of zero-level O ₁ in sub-region 1 _b (in the first fundamental frequency period) = sub-region [(i-1)/2+2=3] The duration of action of zero-level O ₂ in sub-region _a (the second within the fundamental frequency period)

The duration of action of zero-level O ₂ in sub-region 2 _a (in the first fundamental frequency period) = sub-region [(i-1)/2+2=3] The duration of action of zero-level O ₁ in sub-region _b (the second within the fundamental frequency period)

It can be found that when n ₁ =9 is an odd number, the zero-level O ₁ and O ₂ states can also appear in pairs within two fundamental frequency periods and have an equal duration of action. Based on the proposed control strategy, there are always two corresponding sub-regions ia and _ib in _a rotation period, which respectively contain O ₁ and O ₂ states with equal durations, so as to achieve the balance and stability of the flying capacitor voltage. At the same time, in the case of the same carrier frequency, compared with the traditional carrier phase-shift modulation strategy, the number of zero-level states in the proposed control strategy will be greatly reduced, and the loss and temperature of all power devices will be uniformly reduced and uniformly distributed. .

3) In order to avoid the setting of dead time in the pulse signal, output the drive signals G ₁ , G ₂ or G ₃ , G ₄ of the specific full-control switch tube according to the polarity characteristics of the current i _x,x=a,b,c ; When the current polarity is positive, the drive signals G ₃ and G ₄ corresponding to the fully controlled switches S ₃ and S ₄ are output, and when the current polarity is negative, the drive signals corresponding to the fully controlled switches S ₁ and S ₂ are output G ₁ and G ₂ , so that the unnecessary switches in each rotation cycle can be turned off, and finally the voltage of the flying capacitor is stabilized, all power devices are used in a balanced manner, and the setting of dead time is avoided.

且i_x,x＝a,b,c＞0时，变换器的电平状态包含P状态、O₁状态与O₂状态，此时仅需保留驱动信号G₃和G₄即可产生相应的电平状态；Specifically, when

And when i _x,x=a,b,c >0, the level state of the converter includes the P state, the O ₁ state and the O ₂ state. At this time, only the driving signals G ₃ and G ₄ need to be retained to generate the corresponding level state;

Level status Device working mechanism Only need to drive signals G₃ and G₄ P state D₁/D₂ on G₃=0, G₄=0 O₁ status D₁/S₃ on G₃=1, G₄=0 O₂ state D₂/S₄ on G₃=0, G₄=1

且i_x,x＝a,b,c＜0时，变换器的电平状态包含P状态、O₁状态与O₂状态，此时仅需保留驱动信号G₁和G₂即可产生相应的电平状态；when

And when i _x,x=a,b,c < 0, the level state of the converter includes the P state, the O ₁ state and the O ₂ state. At this time, only the driving signals G ₁ and G ₂ need to be retained to generate the corresponding level state;

Level status Device working mechanism Only need to drive signals G₁ and G₂ P state S₁/S₂ on G₁=1, G₂=1 O₁ status S₁/D₃ on G₁=0, G₂=1 O₂ state S₂/D₄ on G₁=1, G₂=0

且i_x,x＝a,b,c＜0时，变换器的电平状态包含N状态、O₁状态与O₂状态，此时仅需保留驱动信号G₁和G₂即可产生相应的电平状态；when

And when i _x,x=a,b,c < 0, the level state of the converter includes the N state, the O ₁ state and the O ₂ state. At this time, only the driving signals G ₁ and G ₂ need to be retained to generate the corresponding level state;

Level status Device working mechanism Only need to drive signals G₁ and G₂ N state D₃/D₄ on G₁=0, G₂=0 O₁ status S₁/D₃ on G₁=1, G₂=0 O₂ state S₂/D₄ on G₁=0, G₂=1

且i_x,x＝a,b,c＞0时，变换器的电平状态包含N状态、O₁状态与O₂状态，此时仅需保留驱动信号G₃和G₄即可产生相应的电平状态。when

And when i _x,x=a,b,c >0, the level state of the converter includes the N state, the O ₁ state and the O ₂ state. At this time, only the driving signals G ₃ and G ₄ need to be retained to generate the corresponding level status.

Level status Device working mechanism Only need to drive signals G₃ and G₄ N state S₃/S₄ on G₃=1, G₄=1 O₁ status D₁/S₃ on G₃=1, G₄=0 O₂ state D₂/S₄ on G₃=0, G₄=1

To sum up, when the current polarity is positive, the proposed control strategy selects to output the drive signals G ₃ and G ₄ corresponding to the specific fully-controlled switches S ₃ and S ₄ , and when the current polarity is negative, the proposed control strategy selects The drive signals G ₁ and G ₂ corresponding to the specific full-control switch tubes S ₁ and S ₂ are output. In this way, the control strategy proposed in the present invention can not only maintain the stability of the flying capacitor voltage, reduce the loss and temperature of each power device in a balanced manner, but also does not need to set dead time for the driving pulse, thereby avoiding the influence of the dead time effect on the output quality of the converter. Compared with the traditional carrier phase-shift modulation strategy, the proposed control strategy effectively improves the reliability and output quality of the flying capacitor converter.

Description of drawings

1 is a block diagram of a unified temperature control strategy for a flying capacitor type converter based on carrier rotation of the present invention;

2 is a diagram of two current paths corresponding to the positive level P state of the flying capacitor type converter in the present invention;

3 is a diagram of two current paths corresponding to the negative level N state of the flying capacitor type converter in the present invention;

4 is a diagram of two current paths corresponding to the zero-level O ₁ state of the flying capacitor type converter in the present invention;

5 is a diagram of _two current paths corresponding to the zero-level O state of the flying capacitor type converter in the present invention;

6 is a zero-level distribution diagram of a flying capacitor type converter in the present invention based on a traditional carrier phase-shift modulation strategy;

7 is a zero-level distribution diagram of the flying capacitor type converter in the present invention based on the proposed control strategy (the number of carriers in a single fundamental frequency period is an even number);

Fig. 8 is the zero-level distribution diagram of the flying capacitor type converter in the present invention based on the proposed control strategy (the number of carriers in a single fundamental frequency period is an odd number);

9 is a structural diagram of a three-phase SVG unified temperature control strategy system based on carrier rotation according to an embodiment of the present invention;

10 is a step diagram of a unified temperature control strategy based on carrier rotation for an A-phase flying capacitor converter in an embodiment of the present invention;

11 is a waveform diagram of the flying capacitor voltage and the DC bus voltage of the A-phase unit based on the PLECS simulation software according to an embodiment of the present invention;

Fig. 12 is a phase A unit loss curve diagram based on PLECS simulation software according to an embodiment of the present invention;

13 is a temperature curve diagram of the A-phase unit based on PLECS simulation software according to an embodiment of the present invention;

14 is a waveform diagram of a low-frequency component of a three-phase AC side port voltage after high-frequency filtering based on PLECS simulation software according to an embodiment of the present invention;

15 is a three-phase input current waveform diagram based on PLECS simulation software according to an embodiment of the present invention;

Detailed ways

The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

As shown in FIG. 9 , the application of the flying capacitor converter in the three-phase common DC bus SVG topology is taken as an example. Among them, the phase voltages of the three-phase grid are u _sa , u _sb , and u _sc , the currents of the three-phase grid are _isa , _isb , and i _sc , the three-phase currents of the grid load are i _La , i _Lb , and i _Lc , and the three-phase SVG topology The input currents are i _a , i _b , and _ic , and the AC side port voltages are u _ao , u _bo , and u _co .

The flying capacitor converter topology consists of four fully controlled switches S ₁ , S ₂ , S ₃ , S ₄ , four anti-parallel diodes D ₁ , D ₂ , D ₃ , D ₄ , and a flying capacitor C _f and _two voltage _- stabilizing capacitors C ₁ and C ₂ , wherein the emitter of the fully _- controlled switch S1 is connected to the collector of S2, the emitter _of S2 is connected to the collector _of S3, and the emitter of S3 is connected to the collector of S3. _The collector of S4 is connected, the collector _{of S1} and the emitter of S4 respectively form the positive terminal P of the DC side and the negative terminal N of the DC side, the voltage between the positive terminal P and the negative terminal N is E, the voltage stabilization capacitor C The connection point O of ₁ and C ₂ provides the zero-point potential between the positive and negative terminals of the DC side. The driving signals of the four fully-controlled switch tubes are respectively the gate drive pulse G ₁ of the fully-controlled switch tube S ₁ , the gate drive pulse G ₂ of the fully-controlled switch tube S ₂ , the gate drive pulse G ₃ of the fully-controlled switch tube S ₃ , The gate drive pulse G _{4 of the fully controlled switch S 4 .}

的角度为90°。令基频频率为50Hz，开关频率为10kHz，如图10所示，上述实施例三相共直流母线SVG中A相飞跨电容型变换器基于载波轮换的统一温度控制策略包括以下步骤：Since the three-phase grid load is an inductive load, the flying capacitor-type converter will deliver advanced reactive power to the grid system in the capacitive reactive power compensation condition, and theoretically does not consume active power. Taking phase A as an example, the input current i _a is ahead of

The angle is 90°. Let the fundamental frequency be 50Hz and the switching frequency be 10kHz, as shown in Figure 10, the unified temperature control strategy of the A-phase flying capacitor converter based on carrier rotation in the three-phase common DC bus SVG in the above embodiment includes the following steps:

1) Define that the carriers c _U and c _D corresponding to the upper and lower bridge arms are located on the positive and negative half axes of the vertical axis, respectively. According to the number of carriers n ₁ =200 in a single fundamental frequency cycle, it is an even number, and (m=1) fundamental frequencies are used. The period is a rotation period, and the number of carriers n ₁ in the rotation period can be decomposed into a prime factor to obtain 200=2×20×5. At this time, the rotation period is divided into (i=20) equal areas, within each area The number of carriers is (2j=10), and the number of regions i/2 in the positive and negative half cycles is an even number of 10; at the same time, each region can be equally divided into two sub-regions i _a and i _b , each sub-region contains (j=5) equal carriers.

2) The driving mode of the fixed full-control switch tube remains unchanged, and the spatial positions of the upper and lower bridge arms corresponding to the carriers c _U and c _D remain unchanged in all sub-regions i _a , and the carriers c _U and c D are exchanged in all sub-regions i _b . The spatial position of c _D , to generate a switching device drive that satisfies the zero-level O ₁ and O ₂ states appear in pairs in one rotation period and have equal action time, and all fully-controlled switches and freewheeling diodes are used equally in one rotation period Signals G ₁ , G ₂ , G ₃ , G ₄ .

Specifically, in the modulation process, the power switch tubes of the upper and lower bridge arms are switched on and off by comparing the modulation wave u _ref with the corresponding carrier waves c _U and c _D of the upper and lower bridge arms. The specified driving mode is as follows:

When u _ref >c _U , drive the full _- control switch S1 to conduct, and the full _- control switch S4 to turn off;

When u _ref =c _U , drive the full _- control switch S1 to turn off, and the full _- control switch S4 to turn off;

When u _ref <c _U , the full-control switch S1 is driven to turn off, and the full _- control switch S4 is turned _on ;

When u _ref >c _D , the full-control switch S2 is driven to be turned _on , and the full _- control switch S3 is turned off;

When u _ref = _{c D} , the full-control switch S2 is driven to turn off, and the full _- control switch S3 is turned off;

When u _ref <c _D , the full-control switch S2 is driven to turn off, and the full _- control switch S3 is turned _on ;

Based on this driving method, the spatial positions of the upper and lower bridge arms corresponding to the carriers c _U and c _D are kept unchanged in all sub-regions i _a , and the spatial positions of the carriers c _U and c _D are exchanged in all sub-regions i _b , then the Generate the switching device driving signals G ₁ , G ₂ that satisfy the zero-level O ₁ and O ₂ states appear in pairs in one rotation period and have equal action time, and all fully-controlled switches and freewheeling diodes are used equally in one rotation period , G ₃ , G ₄ ;

Among them, in the positive half cycle of a fundamental frequency cycle,

The duration of action of zero-level O ₂ in sub-region 1 _a = duration of action of zero-level O ₁ in sub-region (i/2=10) _b ;

The duration of action of zero-level O ₁ in sub-region 1 _b = duration of action of zero-level O ₂ in sub-region (i/2=10) _a ;

which is:

The duration of action of zero-level O ₂ in sub-region x _a = duration of action of zero-level O ₁ in sub-region [(i/2)+1-x] _b ;

The duration of action of zero-level O ₁ in sub-region x _b = duration of action of zero-level O ₂ in sub-region [(i/2)+1-x] _a ;

Similarly, in the negative half cycle of a fundamental frequency cycle,

Sub-region [(i/2)+1=11] Action duration of zero-level O ₂ in _a = sub-region (i=20) Action duration of zero-level O ₁ in _b ;

Sub-region [(i/2)+1=11] Action duration of zero-level O ₁ in _b = Action duration of zero-level O ₂ in sub-region (i=20) _a ;

which is:

Sub-region [(i/2)+x] Action duration of zero-level O ₂ in _a = sub-region (i-x+1) Action duration of zero-level O ₁ in _b ;

The duration of action of zero-level O 1 in sub-region [(i/ ₂ )+x] _b = duration of action of zero-level O ₂ in sub-region (i-x+1) _a ;

It can be found that when n ₁ =200 is an even number, the zero-level O ₁ and O ₂ states can respectively appear in pairs in the positive and negative half cycles of a fundamental frequency cycle and have an equal duration of action. Based on the proposed control strategy, there are always two corresponding sub-regions ia and _ib in _a rotation period, which respectively contain O ₁ and O ₂ states with equal durations, so as to achieve the balance and stability of the flying capacitor voltage. At the same time, in the case of the same carrier frequency, compared with the traditional carrier phase-shift modulation strategy, the number of zero-level states in the proposed control strategy will be greatly reduced, and the loss and temperature of all power devices will be uniformly reduced and uniformly distributed. .

3) In order to avoid the setting of dead time in the pulse signal, output the drive signals G ₁ , G ₂ or G ₃ , G ₄ of the specific full-control switch tube according to the polarity characteristics of the current i _x,x=a,b,c ; When the current polarity is positive, the drive signals G ₃ and G ₄ corresponding to the fully controlled switches S ₃ and S ₄ are output, and when the current polarity is negative, the drive signals corresponding to the fully controlled switches S ₁ and S ₂ are output G ₁ and G ₂ , so that the unnecessary switches in each rotation cycle can be turned off, and finally the voltage of the flying capacitor is stabilized, all power devices are used in a balanced manner, and the setting of dead time is avoided.

且i_x,x＝a,b,c＞0时，变换器的电平状态包含P状态、O₁状态与O₂状态，此时仅需保留驱动信号G₃和G₄即可产生相应的电平状态；Specifically, when

And when i _x,x=a,b,c >0, the level state of the converter includes the P state, the O ₁ state and the O ₂ state. At this time, only the driving signals G ₃ and G ₄ need to be retained to generate the corresponding level state;

Level status Device working mechanism Only need to drive signals G₃ and G₄ P state D₁/D₂ on G₃=0, G₄=0 O₁ status D₁/S₃ on G₃=1, G₄=0 O₂ state D₂/S₄ on G₃=0, G₄=1

且i_x,x＝a,b,c＜0时，变换器的电平状态包含P状态、O₁状态与O₂状态，此时仅需保留驱动信号G₁和G₂即可产生相应的电平状态；when

And when i _x,x=a,b,c < 0, the level state of the converter includes the P state, the O ₁ state and the O ₂ state. At this time, only the driving signals G ₁ and G ₂ need to be retained to generate the corresponding level state;

Level status Device working mechanism Only need to drive signals G₁ and G₂ P state S₁/S₂ on G₁=1, G₂=1 O₁ status S₁/D₃ on G₁=0, G₂=1 O₂ state S₂/D₄ on G₁=1, G₂=0

且i_x,x＝a,b,c＜0时，变换器的电平状态包含N状态、O₁状态与O₂状态，此时仅需保留驱动信号G₁和G₂即可产生相应的电平状态；when

And when i _x,x=a,b,c < 0, the level state of the converter includes the N state, the O ₁ state and the O ₂ state. At this time, only the driving signals G ₁ and G ₂ need to be retained to generate the corresponding level state;

Level status Device working mechanism Only need to drive signals G₁ and G₂ N state D₃/D₄ on G₁=0, G₂=0 O₁ status S₁/D₃ on G₁=1, G₂=0 O₂ state S₂/D₄ on G₁=0, G₂=1

且i_x,x＝a,b,c＞0时，变换器的电平状态包含N状态、O₁状态与O₂状态，此时仅需保留驱动信号G₃和G₄即可产生相应的电平状态。when

And when i _x,x=a,b,c >0, the level state of the converter includes the N state, the O ₁ state and the O ₂ state. At this time, only the driving signals G ₃ and G ₄ need to be retained to generate the corresponding level status.

Level status Device working mechanism Only need to drive signals G₃ and G₄ N state S₃/S₄ on G₃=1, G₄=1 O₁ status D₁/S₃ on G₃=1, G₄=0 O₂ state D₂/S₄ on G₃=0, G₄=1

To sum up, when the current polarity is positive, the proposed control strategy selects to output the drive signals G ₃ and G ₄ corresponding to the specific fully-controlled switches S ₃ and S ₄ , and when the current polarity is negative, the proposed control strategy selects The drive signals G ₁ and G ₂ corresponding to the specific full-control switch tubes S ₁ and S ₂ are output. In this way, the control strategy proposed in the present invention can not only maintain the stability of the flying capacitor voltage, reduce the loss and temperature of each power device in a balanced manner, but also does not need to set dead time for the driving pulse, thereby avoiding the influence of the dead time effect on the output quality of the converter. Compared with the traditional carrier phase-shift modulation strategy, the proposed control strategy effectively improves the reliability and output quality of the flying capacitor converter.

Example: Simulation result analysis.

The SVG unified temperature control strategy model of the three-phase common DC bus based on carrier rotation is built in the PLECS simulation software, and the traditional carrier phase-shift modulation strategy and the proposed control strategy are compared and simulated. The total simulation time is 30s, and the simulation parameters as shown in the table below.

parameter value power voltage 110Vrms/50Hz DC side capacitor voltage 200V On-off level 10kHz IGBT devices IKW30N60T ambient temperature 25℃

Figure 11 shows the waveforms of the flying capacitor voltage and the DC bus voltage in the A-phase unit of the PLECS simulation software. It can be seen that in the proposed control strategy, the flying capacitor voltage can be more quickly stabilized at 200V, which is half of the voltage across the PN side of the DC side; the voltages of the two stabilizing capacitors are also balanced at 200V. The control strategy can realize the normal operation of the flying capacitor converter.

Figure 12 and Figure 13 show the loss and temperature curves of the A-phase unit of the PLECS simulation software, respectively. It can be seen that when the three-phase SVG works with the traditional carrier phase-shift modulation strategy, the loss of the power switching device in the A-phase unit and The temperatures were all raised, wherein the average losses and average temperature of the power switching devices S ₁ , S ₂ , S ₃ , S ₄ were raised to 12.2W and 91.5°C. In the proposed control strategy, all power switching devices achieve balanced and effective loss reduction and cooling, the average loss is stable at 8.8W, and the average temperature is stable at 72.9°C.

与输入电流i_a,i_b,i_c的波形图。其中，传统载波移相调制策略和所提控制策略下

和i_a的THD如下表所示。可以发现，由于受到死区时间效应的影响，传统载波移相调制策略中

包含基波分量和低次谐波分量，而所提控制策略中

仅存在基波分量，所提控制策略有效地提升了飞跨电容型变换器的输出质量。Figure 14 and Figure 15 show the low-frequency components of the three-phase SVG AC side port voltages u _ao , u _bo , and u _co after high-frequency filtering in the PLECS simulation software, respectively.

and the waveform diagram of the input current i _a , i _b , _ic . Among them, under the traditional carrier phase-shift modulation strategy and the proposed control strategy

The THD of and _ia are shown in the table below. It can be found that due to the influence of the dead time effect, the traditional carrier phase-shift modulation strategy

contains fundamental components and low-order harmonic components, and the proposed control strategy

Only the fundamental component exists, and the proposed control strategy effectively improves the output quality of the flying capacitor converter.

It can be clearly seen from the above simulation results that the unified temperature control strategy based on carrier rotation proposed in the present invention effectively reduces and balances the loss and temperature of the power switching device in the three-phase SVG flying capacitor type unit, and avoids the pulse signal The setting of the middle dead time can effectively improve the reliability and current quality of the flying capacitor converter.

The above embodiments are only exemplary embodiments of the present invention, and are not intended to limit the present invention, and the protection scope of the present invention is defined by the claims. Those skilled in the art can make various modifications or equivalent replacements to the present invention within the spirit and protection scope of the present invention, and such modifications or equivalent replacements should also be regarded as falling within the protection scope of the present invention.

Claims (4)

1. the unified temperature control strategy of the flying capacitor type converter based on carrier rotation, is characterized in that, comprises the following steps: 1) On the basis of carrier stacking modulation, according to the parity of the number of carriers n ₁ in a single fundamental frequency period, m fundamental frequency periods are used as a rotation period (m=1 or 2), and a single rotation period is divided into i Equal area, the number of carriers in each area is 2j, and at the same time, each area can be divided into two equal sub-areas _ia and _ib , and each sub-area contains j equal carriers; 2) The driving mode of the fixed full-control switch tube remains unchanged, the spatial positions of the upper and lower bridge arms corresponding to the carriers c _U and c _D remain unchanged in all sub-regions i _a , and the carriers c _U and c D are exchanged in all sub-regions i _b . The spatial position of c _D , to generate a switching device that can satisfy the zero-level O ₁ and O ₂ states appear in pairs in one rotation period and have equal duration of action, and all fully-controlled switches and freewheeling diodes are used equally in one rotation period. drive signals G ₁ , G ₂ , G ₃ , G ₄ ; 3) In order to avoid the setting of dead time in the pulse signal, output the drive signal G ₁ , G ₂ or G ₃ , G ₄ of the specific full-control switch tube according to the positive and negative polarities of the current i _{x, x=a, b, c} , when the current polarity is positive, the drive signals G ₃ and G ₄ corresponding to the fully controlled switches S ₃ and S ₄ are output, and when the current polarity is negative, the drive signals corresponding to the fully controlled switches S ₁ and S ₂ are output Signals G ₁ and G ₂ , ultimately achieve the stability of the flying capacitor voltage, the balanced use of all power devices, and the setting of no dead time. 2. the unified temperature control strategy of the flying capacitor type converter based on carrier rotation according to claim 1, it is characterized in that: in step 1, on the basis of carrier wave stacking modulation, define the corresponding carrier wave c _U of upper and lower bridge arms and c _D are respectively located on the positive and negative half axes of the vertical axis. According to the parity of the number of carriers n ₁ in a single fundamental frequency period, m fundamental frequency periods are used as a rotation period (m=1 or 2), and a single rotation period is used. It is divided into i equal areas, and the number of carriers in each area is 2j; at the same time, each area can be divided into two equal sub-areas i _a and _ib , and each sub-area contains j equal carriers; land, When n ₁ is an even number, (m=1) fundamental frequency periods are used as a rotation period, and the number of carriers n ₁ in the rotation period can be decomposed into a prime factor to obtain n ₁ =2·i·j, at this time, the rotation period It is divided into i equal regions, the number of carriers in each region is 2j, and the number of regions in the positive and negative half cycles must be equal and even; at the same time, each region can be equally divided into two sub-regions i _a and i _b , each sub-region contains j equal carriers; When n ₁ is an odd number, (m=2) fundamental frequency periods are used as a rotation period, and the number of carriers 2n ₁ in the rotation period can be decomposed into a prime factor to obtain 2n ₁ =2·i·j, at this time, the rotation period It is divided into i equal regions, and the number of carriers in each region is 2j; since n ₁ is odd, i and j are both odd, where i takes a larger odd value and j takes a smaller odd value; at the same time, each Each area can be equally divided into two sub-areas _ia and _ib , and each sub-area contains j equal carriers. 3. the unified temperature control strategy of the flying capacitor type converter based on carrier rotation according to claim 1, it is characterized in that: in step 2, the driving mode of the fixed full-control switch tube is unchanged, in all sub-regions i _a Keep the spatial positions of the upper and lower bridge arms corresponding to the carriers c _U and c _D unchanged, exchange the spatial positions of the carriers c _U and c _D in all sub-regions i _b , and generate the zero-level O ₁ and O ₂ states in one rotation The switching device driving signals G ₁ , G ₂ , G ₃ , G ₄ appear in pairs in the cycle and have equal action time, and all fully-controlled switching tubes and freewheeling diodes are used in a balanced cycle in one rotation cycle; Specifically, in the modulation process, the power switch tubes of the upper and lower bridge arms are switched on and off by comparing the modulation wave u _ref with the corresponding carrier waves c _U and c _D of the upper and lower bridge arms. The specified driving mode is as follows: When u _ref >c _U , drive the full _- control switch S1 to conduct, and the full _- control switch S4 to turn off; When u _ref =c _U , drive the full _- control switch S1 to turn off, and the full _- control switch S4 to turn off; When u _ref <c _U , the full-control switch S1 is driven to turn off, and the full _- control switch S4 is turned _on ; When u _ref >c _D , the full-control switch S2 is driven to be turned _on , and the full _- control switch S3 is turned off; When u _ref = _{c D} , the full-control switch S2 is driven to turn off, and the full _- control switch S3 is turned off; When u _ref <c _D , the full-control switch S2 is driven to turn off, and the full _- control switch S3 is turned _on ; Based on this driving method, the spatial positions of the upper and lower bridge arms corresponding to the carriers c _U and c _D are kept unchanged in all sub-regions i _a , and the spatial positions of the carriers c _U and c _D are exchanged in all sub-regions i _b , then the Generate the switching device driving signals G ₁ , G ₂ that satisfy the zero-level O ₁ and O ₂ states appear in pairs in one rotation period and have equal action time, and all fully-controlled switches and freewheeling diodes are used equally in one rotation period , G ₃ , G ₄ ; Among them, when n ₁ is an even number, in the positive half cycle of a fundamental frequency cycle, The duration of action of zero-level O ₂ in sub-region 1 _a = duration of action of zero-level O ₁ in sub-region (i/2) _b ; The duration of action of zero-level O ₁ in sub-region 1 _b = duration of action of zero-level O ₂ in sub-region (i/2) _a ; which is: The duration of action of zero-level O ₂ in sub-region x _a = duration of action of zero-level O ₁ in sub-region [(i/2)+1-x] _b ; The duration of action of zero-level O ₁ in sub-region x _b = duration of action of zero-level O ₂ in sub-region [(i/2)+1-x] _a ; Similarly, in the negative half cycle of a fundamental frequency cycle, Sub-region [( _i /2)+1] Action duration of zero-level O ₂ in sub-region i = Action duration of zero-level O ₁ in sub-region i _b ; The duration of action of zero-level O ₁ in sub-region [( _i /2)+1] _b = duration of action of zero-level O ₂ in sub-region ia; which is: Sub-region [(i/2)+x] Action duration of zero-level O ₂ in _a = sub-region (i-x+1) Action duration of zero-level O ₁ in _b ; The duration of action of zero-level O 1 in sub-region [(i/ ₂ )+x] _b = duration of action of zero-level O ₂ in sub-region (i-x+1) _a ; It can be found that when n ₁ is an even number, the zero-level O ₁ and O ₂ states can appear in pairs in the positive and negative half cycles of a fundamental frequency cycle, respectively, and the duration of action is equal; Similarly, when n ₁ is odd, within two fundamental frequency cycles, The duration of action of zero-level O ₂ in sub-region 1 _a (within the first fundamental frequency period) = the duration of action of zero-level O ₁ in sub-region [(i-1)/2+1] _b (the second fundamental frequency period) The duration of action of zero-level O ₁ in sub-region 1 _b (in the first fundamental frequency period) = the duration of action of zero-level O ₂ in sub-region [(i-1)/2+2] _a (the second fundamental frequency period) which is: The duration of action of zero-level O ₂ in sub-region x _a (in the first fundamental frequency period) = the duration of action of zero-level O ₁ in sub-region [(i-1)/2+x] _b (the second fundamental frequency period) The duration of action of zero-level O ₁ in sub-region x _b (within the first fundamental frequency period) = the duration of action of zero-level O ₂ in sub-region [( _i -1)/2+x+1] (the second within the fundamental frequency period) It can be found that when n ₁ is an odd number, the zero-level O ₁ and O ₂ states can also appear in pairs within two fundamental frequency periods and have an equal duration of action; In this way, based on the proposed control strategy, no matter whether _{n 1} is odd or even, there are always two corresponding sub-regions ia and _ib in a rotation period, which respectively contain O ₁ and O ₂ states with equal durations, and then realize The balance of the flying capacitor voltage is stable; at the same time, in the case of the same carrier frequency, compared with the traditional carrier phase-shift modulation strategy, the number of zero-level states in the proposed control strategy will be greatly reduced. The temperature will be uniformly reduced and uniformly distributed. 4. the unified temperature control strategy of the flying capacitor type converter based on carrier rotation according to claim 1, is characterized in that: in step 3, in order to avoid the setting of dead time in the pulse signal, according to current i _{x, x =} The polarity characteristics of _{a, b, c} output the drive signals G ₁ , G ₂ or G ₃ , G ₄ of the specific fully-controlled switch tubes; when the current polarity is positive, output the corresponding fully-controlled switches S ₃ and S ₄ The drive signals G ₃ and G ₄ , when the current polarity is negative, output the drive signals G ₁ and G ₂ corresponding to the fully-controlled switches S ₁ and S ₂ , so that the unnecessary switches in each rotation cycle can be In the off state, the voltage of the flying capacitor is finally stabilized, all power devices are used in a balanced manner, and the setting of dead time is avoided; Specifically, when

And when i _x,x=a,b,c >0, the level state of the converter includes the P state, the O ₁ state and the O ₂ state. At this time, only the driving signals G ₃ and G ₄ need to be retained to generate the corresponding level state; Level status Device working mechanism Only need to drive signals G₃ and G₄ P state D₁/D₂ on G₃=0, G₄=0 O₁ status D₁/S₃ on G₃=1, G₄=0 O₂ state D₂/S₄ on G₃=0, G₄=1 when

And when i _x,x=a,b,c < 0, the level state of the converter includes the P state, the O ₁ state and the O ₂ state. At this time, only the driving signals G ₁ and G ₂ need to be retained to generate the corresponding level state; Level status Device working mechanism Only need to drive signals G₁ and G₂ P state S₁/S₂ on G₁=1, G₂=1 O₁ status S₁/D₃ on G₁=0, G₂=1 O₂ state S₂/D₄ on G₁=1, G₂=0 when

And when i _x,x=a,b,c < 0, the level state of the converter includes the N state, the O ₁ state and the O ₂ state. At this time, only the driving signals G ₁ and G ₂ need to be retained to generate the corresponding level state; Level status Device working mechanism Only need to drive signals G₁ and G₂ N state D₃/D₄ on G₁=0, G₂=0 O₁ status S₁/D₃ on G₁=1, G₂=0 O₂ state S₂/D₄ on G₁=0, G₂=1 when

And when i _x,x=a,b,c >0, the level state of the converter includes the N state, the O ₁ state and the O ₂ state. At this time, only the driving signals G ₃ and G ₄ need to be retained to generate the corresponding level state; Level status Device working mechanism Only need to drive signals G₃ and G₄ N state S₃/S₄ on G₃=1, G₄=1 O₁ status D₁/S₃ on G₃=1, G₄=0 O₂ state D₂/S₄ on G₃=0, G₄=1 To sum up, when the current polarity is positive, the proposed control strategy selects to output the drive signals G ₃ and G ₄ corresponding to the specific fully-controlled switches S ₃ and S ₄ , and when the current polarity is negative, the proposed control strategy selects Output the drive signals G ₁ and G ₂ corresponding to the specific fully-controlled switches S ₁ and S ₂ ; in this way, the proposed control strategy can not only maintain the stability of the flying capacitor voltage, reduce the loss and temperature of each power device in a balanced manner, but also eliminate the need for driving pulses The dead time is set to avoid the effect of dead time on the output quality of the converter. Compared with the traditional carrier phase-shift modulation strategy, the proposed control strategy effectively improves the reliability and output quality of the flying capacitor converter.

Images