CN117394708A - Current mode PWM rectifier control system and method suitable for unbalanced input - Google Patents

Abstract

The present invention belongs to the technical field of PWM rectification control, and proposes a current-mode PWM rectifier control system and method suitable for input unbalanced input, which mainly includes: first, obtaining the change in equivalent input resistance of each phase when the input voltage is unbalanced; secondly, according to the input voltage When the input voltage is unbalanced, the equivalent input resistance of each phase changes, and the equivalent conduction time Ta, Tb and Tc of each phase within an input voltage cycle are adjusted to realize the change of the three-phase input current ia, ib and ic under the unbalanced input voltage. balance. The present invention does not require additional hardware equipment and can realize the input current balance of the current-mode PWM rectifier under the condition of unbalanced input voltage while reducing the output current ripple.

Description

Current mode PWM rectifier control system and method suitable for unbalanced input

Technical field

The present invention relates to the technical field of PWM rectifier control, and in particular to a current-mode PWM rectifier control system and method suitable for unbalanced input.

Background technique

The conversion of alternating current into direct current is called rectification, also called AC-DC conversion. A rectifier circuit is a circuit that converts AC power supply voltage into DC power supply voltage. Rectifier circuits are widely used in electric vehicle charging, DC transmission systems, aerospace and other fields. According to the different energy storage components on the output side, PWM rectifiers can be divided into voltage-type rectifiers and current-type rectifiers. The voltage-type PWM rectifier has high energy storage efficiency, low loss, fast dynamic response, and convenient control. Its technology is relatively mature. Current-mode PWM rectifiers use inductors as energy storage components and have made great achievements in active power filtering, reactive power compensation, superconducting energy storage, motor speed regulation, renewable energy grid-connected power generation, induction heating power supplies, electronic loads, etc. Good application.

In practical applications, three-phase current-mode PWM rectifiers sometimes inevitably work under unbalanced input voltage conditions, or the three-phase input voltage sampling ratio is biased. If a traditional control scheme is used, the three-phase current-mode PWM rectifier is designed with voltage balance as a constraint. The phase current type PWM rectifier will produce even-numbered and odd-numbered non-characteristic harmonics on its DC side and AC side respectively. These low-order non-characteristic harmonics will cause harmonic pollution to the power grid, deteriorating the performance of the rectifier, and in severe cases It may even burn out the rectifier equipment.

Among current-mode PWM rectifier modulation methods, the existing twelve-sector spatial pulse width modulation method has high DC voltage or current utilization, flexible and diverse digital implementation methods, and the lowest switching loss. It has always been the best choice for current-mode PWM rectifier modulation. method of choice. However, under the condition of unbalanced grid voltage, the existing twelve-sector space vector modulation method will cause serious distortion and imbalance in the input current, resulting in a large number of odd harmonics and subsequently a large amount of reactive power, which will It causes serious pollution to the power grid, affects the normal operation of other equipment in the power grid, and the output voltage will also contain a large number of even harmonics, resulting in excessive output voltage ripple.

Contents of the invention

The object of the present invention is to provide a current mode PWM rectifier control system and method suitable for input imbalance, which can suppress the input current imbalance caused by the grid voltage imbalance and reduce the DC side output current ripple.

The technical solution adopted by the present invention to solve the technical problem is:

On the one hand, the present invention provides a current mode PWM rectifier control system suitable for input unbalance, including:

The three-phase input voltage equivalent resistance change acquisition unit is used to obtain the change in the equivalent input resistance of each phase when the input voltage is unbalanced;

The three-phase input current balance control unit under unbalanced input voltage is used to adjust the equivalent conduction time Ta, Tb and Tc of each phase within an input voltage cycle based on the change in the equivalent input resistance of each phase when the input voltage is unbalanced. Adjust to achieve the balance of the three-phase input currents ia, ib and ic under unbalanced input voltage.

On the other hand, the present invention also provides a current-mode PWM rectifier control method suitable for input unbalance, which is applied to the current-mode PWM rectifier control system suitable for input unbalance, including the following steps:

Obtain the change in equivalent input resistance of each phase when the input voltage is unbalanced;

According to the change of the equivalent input resistance of each phase when the input voltage is unbalanced, the equivalent conduction time Ta, Tb and Tc of each phase within an input voltage cycle are adjusted to achieve the three-phase input current ia, ib under the unbalanced input voltage. and IC balance.

As a further optimization, the change in the equivalent input resistance of each phase is represented by the resistance change coefficients Ka, Kb and Kc of each phase. The resistance change coefficients Ka, Kb and Kc for the Nth input voltage period are represented by the N-1th Represented by the equivalent conduction time Ta, Tb and Tc of each phase of an input voltage cycle;

The method of obtaining the change in equivalent input resistance of each phase when the input voltage is unbalanced includes the following steps:

Integrate the three-phase modulated wave signal in the N-1 input voltage period to obtain the equivalent conduction time Ta, Tb and Tc of each phase in the N-1 input voltage period;

The equivalent resistance of each phase resistor in the Nth input voltage cycle is distributed according to the equivalent conduction time of each phase in the N-1th cycle, that is, Ka:Kb:Kc=Ta:Tb:Tc;

Keep Kc=1, and get the resistance change coefficient of each phase in the Nth period Ka=Ta/Tc, Kb=Tb/Tc, Kc=1.

As a further optimization, the resistance change coefficients Ka, Kb and Kc of each phase in the first input voltage cycle are initialized to 1.

As a further optimization, the resistance change coefficients Ka, Kb and Kc for the N-th input voltage period are represented by the equivalent conduction times Ta, Tb and Tc of each phase for the N-1th input voltage period. For the N-1th input voltage period The conduction time Ta, Tb and Tc of each phase in each cycle are integrated and calculated as a reference to correct the Ka, Kb and Kc of the Nth cycle.

As a further optimization, the calculation formula of the three-phase input currents ia, ib and ic is:

In the formula, Ua, Ub, Uc represent the input phase voltage of each phase, Ra, Rb, Rc are the equivalent input resistance of each phase, R represents the average input resistance of each phase when the three-phase input is completely balanced, Ka, Kb and Kc represent the equal input resistance of each phase. Effective input resistance change coefficient.

As a further optimization, the three-phase input currents ia, ib and ic are balanced under unbalanced input voltage. The specific implementation method is:

The equivalent conduction time Ta, Tb and Tc of each phase within an input voltage cycle is proportional to the input voltage Ua, Ub, Uc. The equivalent input resistance change coefficient Ka of each phase is calculated using the equivalent conduction time Ta, Tb and Tc of each phase. , Kb and Kc, so that the equivalent input resistance change coefficients Ka, Kb and Kc of each phase change with the input voltages Ua, Ub, Uc, thereby making the three-phase input currents ia, ib and ic have equal amplitudes, realizing the three-phase input currents ia, Balance of ib and ic.

As a further optimization, the equivalent conduction times Ta, Tb and Tc of each phase within an input voltage cycle are adjusted by adjusting the action time of each vector of space vector pulse width modulation.

As a further optimization, adjusting the equivalent conduction time Ta, Tb and Tc of each phase within an input voltage cycle by adjusting the action time of each vector of space vector pulse width modulation includes the following steps:

Divide the three-phase input voltage on the input side into sectors according to 30 electrical degrees per sector, and divide the three-phase input voltage period into 12 sectors in the counterclockwise direction;

Determine the current vector acting in the sector by inputting the sectors where the voltages Ua, Ub and Uc are located;

Calculate the action time of each current vector in the sector based on the output voltage, input voltages Ua, Ub and Uc and the resistance change coefficients of each phase Ka, Kb and Kc of the current input voltage cycle;

According to the action time of each current vector, a three-phase modulated wave signal is generated;

Compare the three-phase modulated wave signal with the triangular carrier signal Ut. When the value of the three-phase modulated wave is greater than the triangular carrier signal Ut, the driving signal of the switch tube on the corresponding bridge arm is generated to be 1. The value of the three-phase modulated wave is less than or equal to the triangular carrier wave. When the signal Ut is generated, the driving signal of the switch tube on the corresponding bridge arm is 0.

The beneficial effects of the present invention are: through the above-mentioned current-mode PWM rectifier control system and method suitable for input unbalanced input, the equivalent input resistance of each phase within an input voltage cycle can be controlled according to the change of the equivalent input resistance of each phase when the input voltage is unbalanced. The conduction times Ta, Tb and Tc are adjusted to achieve the balance of the three-phase input currents ia, ib and ic under unbalanced input voltage. In the present invention, the input current can be kept balanced and has low distortion, will not generate a large amount of odd harmonics, and will not generate a large amount of reactive power, thereby avoiding serious pollution to the power grid and not affecting the normal operation of other equipment in the power grid. , and effectively reduces the output voltage ripple.

Description of the drawings

Figure 1 is a schematic system structure diagram of a current mode PWM rectifier control system suitable for unbalanced input according to Embodiment 1 of the present invention;

Figure 2 is a flow chart of a current mode PWM rectifier control method suitable for unbalanced input in Embodiment 2 of the present invention;

Figure 3 shows the variation of the resistance change coefficient of each phase with the input voltage cycle in Embodiment 2 of the present invention;

Figure 4 shows the input three-phase current waveform under the traditional twelve-sector space vector modulation method in Embodiment 2 of the present invention;

Figure 5 shows the input three-phase current waveform under the current-mode PWM rectifier control method suitable for unbalanced input under the same power, load, and circuit topology conditions in Embodiment 2 of the present invention;

Figure 6 shows the DC side output current waveform using the existing modulation method under the same power, load, and circuit topology conditions in Embodiment 2 of the present invention;

Figure 7 is a DC side output current waveform corresponding to Figure 6 in Embodiment 2 of the present invention, under the same power, load, and circuit topology conditions, using a current-mode PWM rectifier control method suitable for input unbalance.

Detailed ways

In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments These are some embodiments of the present invention, rather than all embodiments. The components of the embodiments of the invention generally described and illustrated in the figures herein may be arranged and designed in a variety of different configurations.

Example 1

This embodiment provides a current-mode PWM rectifier control system suitable for unbalanced input, including:

The three-phase input voltage equivalent resistance change acquisition unit is used to obtain the change in the equivalent input resistance of each phase when the input voltage is unbalanced;

The three-phase input current balance control unit under unbalanced input voltage is used to adjust the equivalent conduction time Ta, Tb and Tc of each phase within an input voltage cycle based on the change in the equivalent input resistance of each phase when the input voltage is unbalanced. Adjust to achieve the balance of the three-phase input currents ia, ib and ic under unbalanced input voltage.

See Figure 1, in which the current-mode PWM rectifier topology includes an input (AC side) LC filter structure composed of an inductor Lin and a capacitor Cin, which serves to filter out the harmonics of the current switching frequency on the grid side of the rectifier; it is composed of a fully controlled switch tube The three-phase rectifier bridge is composed of a switch tube and a diode in series, which can improve the voltage reverse blocking ability of the device; the output inductor Lo plays a role in maintaining the stability of the output current; the freewheeling diode can maintain the continuity of the output inductor Lo current; output Capacitor Co plays the role of stabilizing the output voltage.

In this embodiment, if equivalent voltage control is adopted, the equivalent voltage cannot be obtained directly by using the equivalent action time Ta, Tb and Tc of each phase, and the control process is relatively more complicated. Therefore, an equivalent resistance control strategy is adopted to control the input voltage at an input voltage. Within the cycle, the ratio of the equivalent resistance of each phase is the same as the ratio of the equivalent action time of each phase. Therefore, if the equivalent resistance control strategy is adopted, the equivalent action time Ta, Tb and Tc can obtain the equivalent resistance change coefficients Ka, Kb and Kc of each phase.

Example 2

Based on Embodiment 1, this embodiment provides a current mode PWM rectifier control method suitable for input unbalanced input. The flow chart is shown in Figure 2. The method includes the following steps:

S1. Obtain the change in equivalent input resistance of each phase when the input voltage is unbalanced;

S2. According to the change in the equivalent input resistance of each phase when the input voltage is unbalanced, adjust the equivalent conduction time Ta, Tb and Tc of each phase within an input voltage cycle to achieve the three-phase input current ia under the unbalanced input voltage. , ib and ic balance.

In this embodiment, the equivalent input resistance change coefficients Ka, Kb and Kc of each phase are indirectly obtained by calculating the equivalent action time of each phase in each input voltage cycle. Therefore, it is necessary to calculate the equivalent input resistance change coefficients Ka, Kb and Kc of each phase in the N-1th input voltage cycle. The equivalent action time of each phase is calculated to obtain the equivalent resistance change coefficients Ka, Kb and Kc of the Nth input voltage cycle. In this embodiment, through the periodic equivalent resistance strategy, the resistance change coefficients Ka, Kb, and Kb can be continuously updated, and a balanced three-phase input current can be obtained after reaching a steady state.

In this embodiment, the change in the equivalent input resistance of each phase is represented by the resistance change coefficients Ka, Kb and Kc of each phase. The resistance change coefficients Ka, Kb and Kc for the Nth input voltage period are represented by the N-th Represented by the equivalent conduction time Ta, Tb and Tc of each phase in one input voltage cycle;

Obtaining the change in equivalent input resistance of each phase when the input voltage is unbalanced may include the following steps:

Step 1. Integrate the three-phase modulated wave signal in the N-1 input voltage period to obtain the equivalent conduction time Ta, Tb and Tc of each phase in the N-1 input voltage period;

Step 2. The equivalent resistance of each phase resistor in the Nth input voltage cycle is distributed according to the equivalent conduction time of each phase in the N-1th cycle, that is, Ka: Kb: Kc = Ta: Tb: Tc;

Step 3. Keep Kc=1, and obtain the resistance change coefficient of each phase in the Nth period Ka=Ta/Tc, Kb=Tb/Tc, Kc=1.

In the actual application process, the resistance change coefficients Ka, Kb and Kc of each phase in the first input voltage period are all initialized to 1; and, for the resistance change coefficients Ka, Kb and Kc in the Nth input voltage period, the resistance change coefficients Ka, Kb and Kc of the Nth input voltage period are determined by the N-th It is represented by the equivalent conduction time Ta, Tb and Tc of each phase in one input voltage cycle, and the integral calculation of the conduction time Ta, Tb and Tc of each phase in the N-1th cycle is used as a reference to correct the Nth Ka, Kb and Kc of the period.

It should be pointed out that the calculation formula of the three-phase input currents ia, ib and ic is:

In the formula, Ua, Ub, Uc represent the input phase voltage of each phase, Ra, Rb, Rc are the equivalent input resistance of each phase, R represents the average input resistance of each phase when the three-phase input is completely balanced, Ka, Kb and Kc represent the equal input resistance of each phase. Effective input resistance change coefficient.

The specific implementation method of achieving the balance of the three-phase input currents ia, ib and ic under unbalanced input voltage is as follows:

The equivalent conduction time Ta, Tb and Tc of each phase within an input voltage cycle is proportional to the input voltage Ua, Ub, Uc. The equivalent input resistance change coefficient Ka of each phase is calculated using the equivalent conduction time Ta, Tb and Tc of each phase. , Kb and Kc, so that the equivalent input resistance change coefficients Ka, Kb and Kc of each phase change with the input voltages Ua, Ub, Uc, thereby making the three-phase input currents ia, ib and ic have equal amplitudes, realizing the three-phase input currents ia, Balance of ib and ic.

Preferably, the equivalent conduction time Ta, Tb and Tc of each phase within one input voltage period can be adjusted by adjusting the action time of each vector of space vector pulse width modulation.

Specifically, adjusting the equivalent conduction time Ta, Tb and Tc of each phase within an input voltage cycle by adjusting the action time of each vector of space vector pulse width modulation may include the following steps:

a. Divide the three-phase input voltage on the input side into sectors according to 30 electrical degrees per sector, and divide the three-phase input voltage cycle into 12 sectors in the counterclockwise direction;

b. Determine the current vector acting in the sector by inputting the sectors where the voltages Ua, Ub and Uc are located;

c. Calculate the action time of each current vector in the sector based on the output voltage, input voltage Ua, Ub and Uc and the resistance change coefficients Ka, Kb and Kc of each phase in the current input voltage cycle;

d. Generate three-phase modulated wave signals according to the action time of each current vector;

e. Compare the three-phase modulated wave signal with the triangular carrier signal Ut. When the value of the three-phase modulated wave is greater than the triangular carrier signal Ut, the driving signal of the switch tube on the corresponding bridge arm is generated to be 1, and the value of the three-phase modulated wave is less than or equal to When the triangular carrier signal Ut is generated, the driving signal generated for the switch tube on the corresponding bridge arm is 0.

In the actual application process, the duration of each operating mode of the rectifier can be calculated based on the output voltage, input voltage Ua, Ub and Uc and the resistance change coefficients Ka, Kb and Kc of each phase of the current input voltage cycle, which specifically include:

The calculation formula for the action time of each current vector is as follows:

Sector 12,1:

Sector 2, 3:

Sector 4, 5:

Sector 6, 7:

Sector 8, 9:

Sector 10, 11:

In the formula, T1, T2, T3, T4, T5, T6 and T0 respectively represent the action time of the current vectors I1, I2, I3, I4, I5, I6 and I0, Ts represents the switching period, Ka, Kb and Kc represent each Phase equivalent resistance change coefficient, Uo represents the DC side output voltage, Ua, Ub and Uc represent the three-phase input voltage respectively.

Figure 3 shows the change coefficient of each phase resistance with the input voltage cycle in this embodiment. It can be seen from Figure 3 that every other input voltage cycle, under the condition of maintaining Kc=1, the values of Ka and Kb will change. It is updated with the equivalent action time of each phase.

Figure 4 shows the input three-phase current waveform when the input voltage is unbalanced under the traditional twelve-sector space vector modulation method. It can be seen from the waveform in Figure 4 that the three-phase input current is asymmetrical at this time, and the The amplitude difference is large, and the three-phase current amplitude variance reaches 0.3262.

Figure 5 shows the input three-phase current waveform under the current-mode PWM rectifier control method suitable for unbalanced input under the same power, load, and circuit topology conditions in this embodiment. It is simulated and verified according to the hardware design and modulation method in the specific implementation process. , it can be seen from Tu 5 that the symmetry of the three-phase input current is better, the variance of the three-phase current amplitude is reduced to 0.0137, the current harmonic content is small, and the harmonic pollution caused to the input power supply is smaller.

Figures 6 and 7 show the DC side output current using the traditional twelve-sector space vector modulation method and the current-mode PWM rectifier control method suitable for input unbalance under the same power, load, and circuit topology conditions in this embodiment. Waveforms, comparing the waveforms in Figure 6 and Figure 7, it can be seen that when the current mode PWM rectifier control method suitable for input unbalance proposed in this embodiment is used, the output current ripple is smaller and the output power quality is high.

Therefore, this embodiment introduces the resistance variation coefficient of each phase into the control process of the current-mode PWM rectifier under unbalanced input to eliminate the serious distortion and distortion of the input current caused by the traditional twelve-sector space vector modulation under unbalanced input conditions. The problem of excessive output voltage ripple reduces the serious pollution to the power grid and avoids affecting the normal operation of other equipment in the power grid. Therefore, the current mode PWM rectifier control method algorithm proposed in this embodiment is suitable for input unbalanced It is simple and easy to implement without additional hardware equipment. It can achieve input current balance when the input voltage of the current-mode PWM rectifier is unbalanced, while effectively reducing the output current ripple.

The above are only preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and changes. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention shall be included in the protection scope of the present invention.

Claims (9)

1. A current-mode PWM rectifier control system adapted for input imbalance, comprising:

the three-phase input voltage equivalent resistance change acquisition unit is used for acquiring the change of each phase of equivalent input resistance when the input voltage is unbalanced;

and the three-phase input current balance control unit under the unbalance of the input voltage is used for adjusting the equivalent on time Ta, tb and Tc of each phase in one input voltage period according to the change of the equivalent input resistance of each phase when the input voltage is unbalanced, so as to realize the balance of the three-phase input currents ia, ib and ic under the unbalance of the input voltage.

2. A control method for a current-mode PWM rectifier suitable for input unbalance, applied to the control system for a current-mode PWM rectifier suitable for input unbalance according to claim 1, comprising the steps of:

acquiring the change of each equivalent input resistance when the input voltage is unbalanced;

according to the change of the equivalent input resistance of each phase when the input voltage is unbalanced, the equivalent on time Ta, tb and Tc of each phase in one input voltage period is adjusted, and the balance of three-phase input currents ia, ib and ic under the input voltage unbalance is realized.

3. The control method for a current-mode PWM rectifier adapted for input unbalance according to claim 2, wherein the change in the effective input resistance per time is represented by respective phase resistance change coefficients Ka, kb, and Kc, and the resistance change coefficients Ka, kb, and Kc for the nth input voltage period are represented by respective effective on-times Ta, tb, and Tc for the N-1 th input voltage period;

the method for acquiring the change of the equivalent input resistance of each phase when the input voltage is unbalanced comprises the following steps:

integrating the three-phase modulated wave signals in the N-1 th input voltage period to obtain equal effective on-time Ta, tb and Tc of the N-1 th input voltage period;

the equivalent resistance of each phase of resistance of the nth input voltage period is distributed according to the equivalent on time of each phase of the (N-1) th period, namely Ka: kb: kc=ta: tb: tc;

maintaining kc=1, the respective phase resistance change coefficients ka=ta/Tc, kb=tb/Tc, kc=1 in the nth period are obtained.

4. A control method for a current-mode PWM rectifier adapted to an input imbalance according to claim 3, wherein each of the phase resistance change coefficients Ka, kb and Kc of the 1 st input voltage period is initialized to 1.

5. A control method for a current-mode PWM rectifier adapted to an input unbalance according to claim 3, wherein the resistance change coefficients Ka, kb and Kc for the nth input voltage period are represented by respective equivalent on-times Ta, tb and Tc for the N-1 th input voltage period, and the integral calculation is performed for the respective phase on-times Ta, tb and Tc for the N-1 th period as a reference, thereby correcting the Ka, kb and Kc for the nth period.

6. The control method for a current-mode PWM rectifier adapted for input unbalance according to claim 2, wherein the three-phase input currents ia, ib and ic are calculated as:

where Ua, ub, uc represent input phase voltages of each phase, ra, rb, rc are equal effective input resistances of each phase, R represents an average input resistance of each phase at the full balance of three-phase input, and Ka, kb, and Kc represent equal effective input resistance change coefficients of each phase.

7. The method for controlling a PWM rectifier adapted for unbalanced input of claim 6, wherein the balancing of the three phase input currents ia, ib and ic under unbalanced input voltage is implemented by:

the equal effective on-time Ta, tb and Tc in one input voltage period is in direct proportion to the input voltage Ua, ub and Uc, the equal effective on-time Ta, tb and Tc is used for calculating the equal effective input resistance change coefficient Ka, kb and Kc, the equal effective input resistance change coefficient Ka, kb and Kc changes along with the input voltage Ua, ub and Uc, and the three-phase input current ia, ib and ic are further equal in amplitude value, so that the balance of the three-phase input current ia, ib and ic is realized.

8. The control method for a current-mode PWM rectifier adapted for input imbalance according to claim 2, wherein the equivalent on-times Ta, tb and Tc of each phase in one input voltage period are adjusted by adjusting the space vector pulse width modulation respective vector on-times.

9. The method for controlling a PWM rectifier adapted for input imbalance according to claim 8, wherein said adjusting the equivalent on-times Ta, tb and Tc of each phase in an input voltage cycle by adjusting the space vector pulse width modulation on-times of each vector comprises the steps of:

dividing the input side three-phase input voltage into sectors according to 30 electric angles, and dividing the period of the three-phase input voltage into 12 sectors according to the anticlockwise direction;

determining a current vector acting in a sector through the sector in which the input voltages Ua, ub and Uc are positioned;

calculating the acting time of each current vector in the sector according to the output voltage, the input voltages Ua, ub and Uc and the phase resistance change coefficients Ka, kb and Kc of the current input voltage period;

generating a three-phase modulated wave signal according to the action time of each current vector;

and comparing the three-phase modulated wave signal with the triangular carrier signal Ut, generating a driving signal corresponding to the switching tube on the bridge arm as 1 when the value of the three-phase modulated wave is larger than the triangular carrier signal Ut, and generating a driving signal corresponding to the switching tube on the bridge arm as 0 when the value of the three-phase modulated wave is smaller than or equal to the triangular carrier signal Ut.