CN113937986B - Method, device and equipment for detecting direct-current voltage of cascaded H-bridge power module - Google Patents

Abstract

The invention provides a method, a device and equipment for detecting direct-current voltage of a cascaded H-bridge power module, wherein the method comprises the following steps: acquiring alternating current of a current conversion chain acquired by a current transformer on the current conversion chain of the cascaded H bridge, and acquiring the current stage of a power module on the current conversion chain; when the power module is in an uncontrolled stage, calculating the direct current of the power module according to the alternating current of the converter chain; when the power module is in a control stage, acquiring a switch state matrix of each switch of the power module, and calculating direct current of the power module according to the switch state matrix and alternating current of a current conversion chain; and calculating the direct current voltage of the power module according to the direct current of the power module. The invention provides a new method for indirectly detecting the direct-current voltage of the power module of the cascaded H bridge based on the alternating current of the converter chain, the calculation precision of the method is irrelevant to the number of the power modules, the method is not influenced by the number of the power modules, and the method can be applied to a high-voltage system and has wider applicability.

Description

Method, device and equipment for detecting DC voltage of cascaded H-bridge power modules

technical field

The present invention relates to the field of electric power technology, in particular to a method, device and equipment for detecting the DC voltage of a cascaded H-bridge power module.

Background technique

Chain STATCOM is an advanced reactive power compensation equipment, which is widely used in power quality compensation of new energy power stations. Cascaded H-bridges are the most common structure of chained STATCOMs. Ensuring that the DC voltage of each power module is stable is a necessary condition for the operation of the device. Therefore, during the specific operation, it is generally necessary to detect the DC voltage of the power module.

The traditional solution is to install a DC voltage sensor on each power module, so the chain STATCOM often needs to install dozens of sensors. Adding sensors increases equipment cost and introduces additional measurement losses. And when a sensor of a power module fails, the entire equipment may be shut down. Therefore, the indirect detection technology without DC voltage sensor has a great effect on improving the economy and reliability of the chain STATCOM.

In the prior art, the DC voltage of the cascaded H-bridge power modules is generally detected indirectly based on a potential transformer (PT) on the commutation chain. However, when there are many power modules, the PT sampling error will cause a large Moreover, if the number of power modules increases, the calculation time will increase rapidly, resulting in a large delay. Therefore, the calculation accuracy of the existing indirect detection method is greatly affected by the number of power modules and the sampling accuracy, and it is difficult to apply to high-voltage systems.

SUMMARY OF THE INVENTION

Based on this, the purpose of the present invention is to provide a method, device and device for detecting the DC voltage of a cascaded H-bridge power module, so as to solve at least one technical problem in the background art.

A method for detecting a DC voltage of a cascaded H-bridge power module according to an embodiment of the present invention, the method includes:

obtaining the AC current of the commutation chain collected by the current transformer on the commutation chain of the cascaded H-bridge, and obtaining the current stage of the power module on the commutation chain;

When the power module is in the non-control phase, calculating the DC current of the power module according to the AC current of the commutation chain;

When the power module is in the control stage, obtain a switch state matrix of each switch of the power module, and calculate the DC current of the power module according to the switch state matrix and the AC current of the commutation chain;

The DC voltage of the power module is calculated according to the DC current of the power module.

In addition, the method for detecting the DC voltage of a cascaded H-bridge power module according to the above-mentioned embodiment of the present invention may also have the following additional technical features:

Further, when the power module is in the non-control phase, the DC current of the power module satisfies the conditional formula:

i _cj ( t )=| i _r ( t )|

Wherein, i _cj ( t ) represents the DC current of the power module , and _ir ( t ) represents the AC current of the commutation chain.

Further, when the power module is in the control stage, the DC current of the power module satisfies the conditional formula:

，ΔT为计算步长，C为所述功率模块当中直流电容的容量，R ₁-R ₄分别为所述功率模块四个开关的阻值，当开关导通时阻值为R _on 、关断时阻值为R _off ，四个开关的导通关断状态通过所述开关状态矩阵确定，i _cj （t）代表所述功率模块的直流电流，i _r （t）代表所述换流链的交流电流，V _dcj （t-ΔT）= V _dcj （t _k-1），V _dcj （t _k-1）为等效历史电压源。in,

, ΔT is the calculation step size, C is the capacity of the DC capacitor in the power module, R ₁ - R ₄ are the resistance values of the four switches of the power module, respectively, when the switches are turned on, the resistance value is R _on , and when the switches are turned off The time resistance value is R _off , the on and off states of the four switches are determined by the switch state matrix, i _cj ( t ) represents the DC current of the power module, and i _r ( t ) represents the commutation chain AC current, Vdcj ( t - ΔT ) _{= Vdcj(tk-1), Vdcj(tk-1 ) is the} equivalent historical _voltage source .

Further, the DC voltage v _dcj ( t ) of the power module satisfies the conditional formula:

Among them, V _dcj ( t _{k -1} ) is the equivalent historical voltage source, which satisfies the conditional formula:

。

.

Wherein, k represents the sampling times of the current transformer.

Further, after the step of calculating the DC voltage of the power module according to the DC current of the power module, the method further includes:

According to the current stage of the power module, a corresponding error formula is used to calculate the calculation error of the DC voltage of the power module;

The calculation parameter of the DC voltage of the power module is adjusted according to the calculation error.

Further, when the power module is in a steady state operation stage, the error formula is:

In the formula, ΔT is the calculation step size, C is the capacity of the DC capacitor in the power module, Δv _dcj is the calculation error of the DC voltage of the power module, i _cj ( t - ΔT ) represents the power corresponding to the time t - ΔT DC current of the module.

Further, when the power module is in the transient operation stage or the control stage, the error formula is:

，ΔT为计算步长，C为所述功率模块当中直流电容的容量。In the formula, Δv _dcj ( t _k ) is the calculation error of the DC voltage of the power module corresponding to the k -th sampling time, ε ₂ is the sampling relative error of the current transformer, and i _cj ( t _k ) represents the k -th sampling time The DC current of the power module corresponding to the time,

, ΔT is the calculation step size, and C is the capacity of the DC capacitor in the power module.

A device for detecting the DC voltage of a cascaded H-bridge power module according to an embodiment of the present invention, the device includes:

an information acquisition module, configured to acquire the alternating current of the commutation chain collected by the current transformer arranged on the commutation chain of the cascaded H-bridge, and to acquire the current stage of the power module on the commutation chain;

a current calculation module, configured to calculate the DC current of the power module according to the AC current of the commutation chain when the power module is in the non-control phase; obtain the power when the power module is in the control phase a switch state matrix of each switch of the module, and calculate the DC current of the power module according to the switch state matrix and the AC current of the commutation chain;

A voltage calculation module, configured to calculate the DC voltage of the power module according to the DC current of the power module.

The present invention also provides a computer-readable storage medium on which a computer program is stored, and when the program is executed by a processor, the above-mentioned method for detecting the DC voltage of a cascaded H-bridge power module is implemented.

The present invention also provides a device for detecting the DC voltage of a cascaded H-bridge power module, which includes a memory, a processor, and a computer program stored in the memory and running on the processor. When the processor executes the program, the The above-mentioned method for detecting the DC voltage of a cascaded H-bridge power module.

Compared with the prior art, the DC voltage of the cascaded H-bridge power modules is indirectly detected based on the AC current of the commutation chain. The increase in the number of modules affects the calculation accuracy and calculation response time, and can be applied to high-voltage systems with wider applicability.

Description of drawings

1 is a typical topology diagram of a chained STATCOM provided by an embodiment of the present invention;

Fig. 2 is a monitoring point location diagram of a chained STATCOM provided by an embodiment of the present invention;

3 is a flowchart of a method for detecting a DC voltage of a cascaded H-bridge power module in the first embodiment of the present invention;

4 is an equivalent circuit diagram of a power module in an uncontrolled phase provided by an embodiment of the present invention;

5 is an equivalent circuit diagram of a power module in a control stage provided by an embodiment of the present invention;

6 is a flowchart of a method for detecting a DC voltage of a cascaded H-bridge power module in a second embodiment of the present invention;

FIG. 7 is a comparison diagram of DC voltage results in an uncontrolled charging stage with ΔT = 500 us provided by an embodiment of the present invention;

FIG. 8 is a comparison diagram of DC voltage results in an uncontrolled charging stage with ΔT = 50 us provided by an embodiment of the present invention;

FIG. 9 is a comparison of the DC voltage results in the +20A steady-state operation stage with ΔT = 500 us provided by an embodiment of the present invention;

FIG. 10 is a comparison of the DC voltage results in the +20A steady-state operation stage with ΔT = 50 us provided by the embodiment of the present invention;

FIG. 11 is a comparison of the DC voltage results in the transient stage from -20A to +20A for ΔT = 500 us provided by an embodiment of the present invention;

FIG. 12 is a comparison of DC voltage results in the transient stage from -20A to +20A for ΔT = 50 us provided by an embodiment of the present invention;

FIG. 13 is a graph of the actual measurement result of the DC voltage in the transient stage from -20A to +20A provided by an embodiment of the present invention;

14 is a comparison diagram of DC voltage results in a transient stage from -20A to +20A provided by an embodiment of the present invention;

15 is a schematic structural diagram of a device for detecting the DC voltage of a cascaded H-bridge power module in a third embodiment of the present invention;

16 is a schematic structural diagram of a device for detecting the DC voltage of a cascaded H-bridge power module according to a fourth embodiment of the present invention.

The following specific embodiments will further illustrate the present invention in conjunction with the above drawings.

Detailed ways

In order to facilitate understanding of the present invention, the present invention will be described more fully hereinafter with reference to the related drawings. Several embodiments of the invention are presented in the accompanying drawings. However, the present invention may be embodied in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete.

It should be noted that when an element is referred to as being "fixed to" another element, it can be directly on the other element or intervening elements may also be present. When an element is referred to as being "connected" to another element, it can be directly connected to the other element or intervening elements may also be present. The terms "vertical," "horizontal," "left," "right," and similar expressions are used herein for illustrative purposes only.

Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The terms used herein in the description of the present invention are for the purpose of describing specific embodiments only, and are not intended to limit the present invention. As used herein, the term "and/or" includes any and all combinations of one or more of the associated listed items.

The following embodiments can be applied to the chained STATCOM system shown in Fig. 1. Fig. 1 shows a typical topology of chained STATCOMs (cascaded H-bridges), including three commutation chains in total, in which each A smoothing reactor is connected in series with the commutation chain, and the inductance value is L. The inverter voltages of the commutation chains are u _ca , u _cb , and u _cc , and the currents of the three commutation chains are i _ab , i _bc , and i _ca , respectively. In Figure 1, FB corresponds to the H-bridge sub-module, that is, the power module. Each power module includes 4 switches and a DC capacitor C. The switches are specifically insulated gate bipolar transistors (Insulated Gate Bipolar Transistor, referred to as IGBT for short). ). Among them, the four IGBTs are sequentially numbered as T ₁ , T ₂ , T ₃ and T ₄ , and the diodes connected thereto are sequentially numbered as D ₁ , D ₂ , D ₃ and D ₄ . Taking the AB commutation chain as an example, the voltage of the DC capacitor of the jth power module is defined as v _{d cj} , the current of the DC capacitor is defined as id _cj , and the inverter voltage of the power module is defined as u _Hj , j =1,2 ,3,… N , where the DC voltage of the power module is the voltage of the DC capacitor of the power module, that is, the voltage of the DC capacitor of the cascaded H-bridge power module is actually detected.

At present, the DC voltage of the cascaded H-bridge power module is generally detected indirectly based on the voltage transformer (PT) on the commutation chain. The layout of the voltage transformer (PT) is shown in Figure 2. The specific principles are as follows:

First, according to the parameters of the chained STATCOM module shown in Table 1 below, we can get:

（1）

(1)

Table 1:

Taking phase A as an example, the inverter voltage of the commutation chain and the capacitor voltage of the power module satisfy:

（2）

(2)

The capacitor voltage will not change abruptly in a short time, that is:

（3）

(3)

Then by looking for N linearly independent switching states in a short time, we can get

（4）

(4)

Among them, u _ca , u _cb , and u _cc are the inverter voltages of the commutation chain, and _Skj is the switching state.

make

（5）

(5)

Then formula (4) can be changed to:

U=SV (6)

If the rank of the switch state matrix S satisfies rank(S)=N , then the necessary determinant, according to Crammer's rule:

V=S ^-1 U (7)

Then the DC voltage of all power modules can be solved for a short period of time.

The PT sampling error will have a great impact on the indirect detection accuracy. Assume that the PT sampling relative error is ε ₁ .

，则：According to formula (2), the modulation ratio is introduced

,but:

（8）

(8)

The condition that the voltages of the individual power modules in normal operation are approximately equal is used here.

Then the absolute value of the PT measurement is

（9）

(9)

In the extreme case, these calculation errors are all reflected in the calculation result of a certain power module. At this time, the relative error of the DC voltage of the power module is:

（10）

(10)

During stable operation, 0< m <1, according to the standard ε ₁ ≤2%, generally ε ₁ =1%.

When N= 3, η <3%, and the allowable error of DC voltage is generally 10%, so this test method is effective.

When N= 3, η <12%, the maximum error has exceeded the allowable range of DC voltage.

Therefore, for the existing indirect detection scheme, the PT sampling error will cause a large indirect detection error when there are many power modules.

；一般采用LU分解法、Cholesky分解法或者QR分解法进行求逆运算，这些算法的计算复杂度也为

。因此，间接检测算法的计算复杂度满足The calculation delay generally uses the Gauss elimination method to obtain the rank of the matrix, and its computational complexity is

; Generally, LU decomposition method, Cholesky decomposition method or QR decomposition method are used for inversion operation, and the computational complexity of these algorithms is also

. Therefore, the computational complexity of the indirect detection algorithm satisfies

（11）

(11)

Assuming that the basic calculation time for one time is T ₁ , the calculation time T _N for one time of N power modules can be approximated as

（12）

(12)

Then the calculation time of 12 power modules is about 64 times that of 3 power modules. If the number of power modules increases, the calculation time will increase rapidly, resulting in a large delay.

To find N linearly independent switching states, it needs to be calculated at least N times, then the delay T _d satisfies

（13）

(13)

Typical value T ₁ ≈ 1us .

N=3 , T _d >81us ; N=12 , T _d ≥20.1ms . At this time, the delay has exceeded 1 power frequency cycle, so the establishment of formula (3) cannot be guaranteed, and the equation will not be solved accurately.

Therefore, the current method of indirectly detecting the DC voltage of cascaded H-bridge power modules based on PT is difficult to apply to high-voltage systems because its calculation accuracy is greatly affected by the number of power modules and sampling accuracy. Therefore, the present application indirectly detects the DC voltage of the cascaded H-bridge power modules based on the AC current of the commutation chain. The calculation accuracy of this method is independent of the number of power modules and is not affected by the number of power modules, and can be applied to high-voltage systems. The specific scheme of the new method will be described in detail in the following examples.

Example 1

Referring to FIG. 3 , a method for detecting the DC voltage of a cascaded H-bridge power module in the first embodiment of the present invention is shown, and the method specifically includes steps S01 to S04.

Step S01: Acquire the AC current of the commutation chain collected by the current transformer on the commutation chain of the cascaded H-bridge, and obtain the current stage of the power module on the commutation chain.

Among them, as shown in FIG. 2 , a diagram of the arrangement position of a current transformer (CT for short) on the commutation chain is shown, which is different from the arrangement position of a traditional PT. The current stage of the power module includes an uncontrolled stage and a controlled stage. In the specific implementation, the current transformer will sample the AC current of the commutation chain every preset time, and the preset time is the calculation step size ΔT. DC.

Step S02, when the power module is in the non-control phase, calculate the DC current of the power module according to the AC current of the commutation chain.

Specifically, the uncontrolled phase is the charging phase, that is, the charging phase through the diode. In the uncontrolled phase, the direction of i _cj is irreversible, ignoring the IGBT, and the diode is equivalent to a small resistance R _Dj , then the equivalent circuit of the power module in the uncontrolled charging phase is shown in Figure 4. Among them, the commutator represents the conversion of negative voltage/negative current into positive voltage/negative current. Therefore, at this time, the DC current of the power module satisfies the conditional formula:

i _cj ( t ) = | i _r ( t ) | (16)

Wherein, i _cj ( t ) represents the DC current of the power module , and _ir ( t ) represents the AC current of the commutation chain.

Step S03, when the power module is in the control stage, obtain the switch state matrix of each switch of the power module, and calculate the DC current of the power module according to the switch state matrix and the AC current of the commutation chain. current.

In the control stage, the IGBT and the diode can be equivalent to adjustable resistance, and the circuit of the equivalent power module can be obtained as shown in Figure 5. At this time, the DC current of the power module is solved according to the node voltage method, that is, the DC current of the power module satisfies the conditional expression:

，ΔT为计算步长，C为所述功率模块当中直流电容的容量，R ₁-R ₄分别为所述功率模块四个开关的阻值，当开关导通时阻值为R _on 、关断时阻值为R _off ，四个开关的导通关断状态通过所述开关状态矩阵确定，i _cj （t）代表所述功率模块的直流电流，i _r （t）代表所述换流链的交流电流；下面，将针对上述表1中功率模式在控制阶段下的正常运行的四种开关状态矩阵S _kj 的状态，分别对该公式进行求解，其中四种开关状态分别通过不同S _kj 值（1，0， -1，0对应两种状态）来区分标识，具体地：in,

, ΔT is the calculation step size, C is the capacity of the DC capacitor in the power module, R ₁ - R ₄ are the resistance values of the four switches of the power module, respectively, when the switches are turned on, the resistance value is R _on , and when the switches are turned off The time resistance value is R _off , the on and off states of the four switches are determined by the switch state matrix, i _cj ( t ) represents the DC current of the power module, and i _r ( t ) represents the commutation chain AC current; below, the formula will be solved for the states of the four switch state matrices S _kj of the normal operation of the power mode in the above table 1 in the control stage, wherein the four switch states are determined by different values of S _kj ( 1, 0, -1, 0 correspond to two states) to distinguish the identification, specifically:

When Skj ₌ 1, R ₁ = R ₄ = R _on , R ₂ = R ₃ = R _off , then

（17）

(17)

When Skj ₌ 0 , then

（18）

(18)

In practice, R _off is large, so at this time

When Skj ₌ -1 , then

（19）

(19)

Step S04: Calculate the DC voltage of the power module according to the DC current of the power module.

，其拉式变换表达式为Specifically, according to the voltage formula of the capacitor

, and its pull transformation expression is

，功率模块直流电压的表达式为：According to the bilinear transformation method, it is assumed that the calculation step size is

, the expression of the DC voltage of the power module is:

（14）

(14)

，则等效历史电压源

为：In formula (14), define the equivalent calculated resistance

, then the equivalent historical voltage source

for:

（15）

(15)

Wherein, k represents the sampling times of the current transformer, t _k represents the k-th sampling time, _{and icj} ( t _k ) represents the DC current of the power module corresponding to the k -th sampling time.

For indirect detection, ΔT is controllable. The capacitance C is known, and the influence of the capacitance value by the environment can be ignored. If the initial DC voltage of the power module is known, that is, the DC voltage of the power module at the start of detection is known, and the DC current icj ( t ) of the power module is known, v _dcj ( t ) can be solved _iteratively . That is, by synthesizing formulas (14), (15) and (16), the DC voltage v _dcj ( t ) of each power module in the uncontrolled phase can be obtained. By synthesizing formulas (14) (15) and (17)-(19), the DC voltage v _dcj ( t ) of each power module in the control stage can be obtained.

To sum up, the method for detecting the DC voltage of the cascaded H-bridge power module in the above-mentioned embodiments of the present invention indirectly detects the DC voltage of the cascaded H-bridge power module based on the AC current of the commutation chain. It is not affected by the number of power modules, and will not affect the calculation accuracy and calculation response time due to the increase in the number of power modules. It can be applied to high-voltage systems and has wider applicability.

Embodiment 2

Referring to FIG. 6 , a method for detecting the DC voltage of a cascaded H-bridge power module in a second embodiment of the present invention is shown, and the method specifically includes steps S11 to S16 .

In step S11, the AC current of the commutation chain collected by the current transformer on the commutation chain of the cascaded H-bridge is obtained, and the current stage of the power module on the commutation chain is obtained.

Step S12, when the power module is in the non-control phase, calculate the DC current of the power module according to the AC current of the commutation chain.

Step S13, when the power module is in the control stage, obtain the switch state matrix of each switch of the power module, and calculate the DC current of the power module according to the switch state matrix and the AC current of the commutation chain. current.

Step S14: Calculate the DC voltage of the power module according to the DC current of the power module.

Step S15, according to the current stage of the power module, using a corresponding error formula to calculate the calculation error of the DC voltage of the power module.

Step S16, adjusting the calculation parameter of the DC voltage of the power module according to the calculation error.

Among them, since the calculation error of the DC voltage detection method of the cascaded H-bridge power module is only related to the calculation step size ΔT, it is only necessary to adjust the calculation step size ΔT to make the final error within the allowable range.

When the power module is running in a steady state, i _cj will not change abruptly, and the error is due to the difference in the output results caused by the delay of ΔT . Then the error can be evaluated by the increment of the current term, i.e.

（20）

(20)

In the formula, ΔT is the calculation step size, C is the capacity of the DC capacitor in the power module, Δv _dcj is the calculation error of the DC voltage of the power module, i _cj ( t - ΔT ) represents the power corresponding to the time t - ΔT DC current of the module. This means that the larger the calculation step ΔT , the larger the error.

When the power module is in the transient operation stage, the CT sampling is susceptible to the interference of harmonics and other factors, resulting in sampling errors. Assuming that the relative error of CT sampling is ε ₂ , it is also generally ε ₂ =1% according to the standard. The initial time is t ₀ , and the next time t ₁ = t ₀ + Δ T . According to formula (16), we can get

（21）

(twenty one)

_At time t1 , there is

（22）

(twenty two)

According to formulas (14) and (15) at time t ₂ , we can get

（23）

(twenty three)

_At time t3 , then

It is not difficult to prove by induction

（25）

(25)

When the H-bridge power module is in normal operation, the charging current is approximately equal to the discharging current, so

so

（26）

(26)

，ΔT为计算步长，C为所述功率模块当中直流电容的容量；In the formula, Δv _dcj ( t _k ) is the calculation error of the DC voltage of the power module corresponding to the k -th sampling time, ε ₂ is the sampling relative error of the current transformer, and i _cj ( t _k ) represents the k -th sampling time The DC current of the power module corresponding to the time,

, ΔT is the calculation step size, C is the capacity of the DC capacitor in the power module;

When the power module is in the control stage, since the iterations are still performed according to formulas (14) and (15), and according to formulas (17)-(19), there are still

（27）

(27)

This formula is only different from formula (21) by constant coefficient, so its calculation method is the same as formula (22)-(26), and the conclusion is also similar, that is,

（28）

(28)

，则公式（28）变为generally

, then formula (28) becomes

（29）

(29)

。如果ΔT=500us，根据

，其计算误差大约是ΔT=50us的十倍。That is, it is consistent with the conclusion of formula (26). Therefore, compared with the existing indirect detection algorithm, the error brought by the proposed algorithm due to PT sampling has nothing to do with the number of modules, and the maximum error is

. If ΔT=500us , according to

, the calculation error is about ten times that of ΔT=50us .

It can be seen that the new fast indirect detection method of the DC voltage of the cascaded H-bridge power module can be applied to the uncontrolled and controlled phases with less error.

The following experiments and simulation analysis are carried out to verify the novel fast indirect detection method of the DC voltage of the cascaded H-bridge power module proposed by the present invention:

First, a simulation and experimental platform is built according to the parameters of the cascaded H-bridge system of N power modules in Table 2 below.

Table 2:

The simulation results are shown in Figure 7-Figure 12. The simulation settings are as follows: (1) The uncontrolled charging stage is set to charge with a soft-start resistor before 0.4s and bypass the soft-start resistor for 0.4s; (2) +20A steady-state operation Phase, the initial DC voltage is set to 36V, 0.25s input to the chain STATCOM to run at +20A; (3) From -20A to +20A transient stage, the initial DC voltage is set to 36V, 0.25s to input the chain STATCOM to run at -20A , 1.0s moment suddenly changed to +20A transient operation stage. Figures 7 and 8 are the comparison of the DC voltage results in the uncontrolled charging stage with ΔT = 500 us and ΔT = 50 us respectively. Comparing the two schemes with the calculation step length of 500 us and 50 us, it can be obtained that when ΔT = 500 us , The absolute error is 0.2V, and the relative error is 0.5%; at 50us, the absolute error is about 0.02V, and the relative error is 0.05%; Figure 9 and Figure 10 are ΔT = 500 us and ΔT = 50 us at +20A steady state The comparison of the DC voltage results in the running phase shows that due to the influence of sampling error and delay, the absolute error of the existing algorithm reaches 55V, and the relative error is 152.8%. When ΔT = 500 us , the absolute error is 0.2V and the relative error is 0.5 %; at 50us, the absolute error is about 0.02V, and the relative error is 0.05%; Figure 11 and Figure 12 are the comparison of the DC voltage results in the transient stage from -20A to +20A with ΔT =500 us and ΔT =50 us , respectively. It can be obtained that when ΔT = 500 us , the absolute error is 0.2V, and the relative error is 0.5%; when ΔT = 50 us , the absolute error is about 0.02V, and the relative error is 0.05%.

In addition, an experimental comparison was also carried out. In the experimental platform of this experiment, a total of 12 H-bridge power modules were installed on 6 boards on each layer, and a total of 36 in the three layers. The worst working condition is from -20A to +20A temporarily. In the state stage, only the data of this stage are recorded in the experiment. The experimental design is: first implement the proposed algorithm into the DSP board through programming, the DSP obtains the PWM state, AC current and other information of all 12 channels, so the proposed algorithm can be used to calculate the DC voltage value of the first module of phase A , set the calculation step size to 50us through the interrupt; then set the initial value of the running state of the DSP to -20A, set it to +20A at a certain moment, sample the actual DC voltage through the oscilloscope and record it, and use the CAN bus to sample and record the whole process at this moment The calculated results; finally, the two results were imported and compared using MATLAB. The experimental results are shown in Figure 13-Figure 14. Figure 13 and Figure 14 are the measured results and results of the DC voltage in the transient phase from -20A to +20A, respectively. The curve in Figure 13 is the 36V DC voltage curve, and the proposed algorithm is in 50us. When the step size is used, the absolute error is about 0.3V, and the relative error is 0.83%. Although the sampling causes additional errors, the relative error still meets the national standard within 2%.

It can be seen that the experimental results are consistent with the simulation results, indicating that the proposed new indirect detection algorithm based on the AC CT sampling of the commutator chain is superior to the indirect detection algorithm based on the AC PT sampling of the converter chain.

Embodiment 3

Another aspect of the present invention also provides a device for detecting the DC voltage of a cascaded H-bridge power module. Please refer to FIG. 15 , which shows the device for detecting the DC voltage of a cascaded H-bridge power module in the third embodiment of the present invention. The device includes:

The information acquisition module 11 is used for acquiring the alternating current of the commutation chain collected by the current transformer arranged on the commutation chain of the cascaded H bridge, and acquiring the current stage of the power module on the commutation chain;

The current calculation module 12 is used to calculate the DC current of the power module according to the AC current of the commutation chain when the power module is in the non-control phase; when the power module is in the control phase, obtain the a switch state matrix of each switch of the power module, and calculate the DC current of the power module according to the switch state matrix and the AC current of the commutation chain;

The voltage calculation module 13 is configured to calculate the DC voltage of the power module according to the DC current of the power module.

Further, in some optional embodiments of the present invention, when the power module is in the non-control phase, the DC current of the power module satisfies the conditional formula:

i _cj ( t )=| i _r ( t )|

Wherein, i _cj ( t ) represents the DC current of the power module , and _ir ( t ) represents the AC current of the commutation chain.

Further, in some optional embodiments of the present invention, when the power module is in the control stage, the DC current of the power module satisfies the conditional formula:

，ΔT为计算步长，C为所述功率模块当中直流电容的容量，R ₁-R ₄分别为所述功率模块四个开关的阻值，当开关导通时阻值为R _on 、关断时阻值为R _off ，四个开关的导通关断状态通过所述开关状态矩阵确定，i _cj （t）代表所述功率模块的直流电流，i _r （t）代表所述换流链的交流电流。in,

, ΔT is the calculation step size, C is the capacity of the DC capacitor in the power module, R ₁ - R ₄ are the resistance values of the four switches of the power module, respectively, when the switches are turned on, the resistance value is R _on , and when the switches are turned off The time resistance value is R _off , the on and off states of the four switches are determined by the switch state matrix, i _cj ( t ) represents the DC current of the power module, and i _r ( t ) represents the commutation chain Alternating current.

Further, in some optional embodiments of the present invention, the DC voltage v _dcj ( t ) of the power module satisfies the conditional formula:

Among them, V _dcj ( t _{k -1} ) is the equivalent historical voltage source, which satisfies the conditional formula:

Wherein, k represents the sampling times of the current transformer.

Further, in some optional embodiments of the present invention, the apparatus further includes:

An error calculation module, configured to calculate the calculation error of the DC voltage of the power module by using a corresponding error formula according to the current stage of the power module;

A parameter adjustment module, configured to adjust the calculation parameter of the DC voltage of the power module according to the calculation error.

Further, in some optional embodiments of the present invention, when the power module is in a steady state operation stage, the error formula is:

In the formula, ΔT is the calculation step size, C is the capacity of the DC capacitor in the power module, Δv _dcj is the calculation error of the DC voltage of the power module, i _cj ( t - ΔT ) represents the power corresponding to the time t - ΔT DC current of the module.

Further, in some optional embodiments of the present invention, when the power module is in a transient operation stage or a control stage, the error formula is:

，ΔT为计算步长，C为所述功率模块当中直流电容的容量。In the formula, Δv _dcj ( t _k ) is the calculation error of the DC voltage of the power module corresponding to the k -th sampling time, ε ₂ is the sampling relative error of the current transformer, and i _cj ( t _k ) represents the k -th sampling time The DC current of the power module corresponding to the time,

, ΔT is the calculation step size, and C is the capacity of the DC capacitor in the power module.

The functions or operation steps implemented by the foregoing modules and units when executed are substantially the same as those in the foregoing method embodiments, and will not be repeated here.

Embodiment 4

In another aspect of the present invention, a device for detecting the DC voltage of a cascaded H-bridge power module is also provided. Please refer to FIG. 16 , which shows the device for detecting the DC voltage of a cascaded H-bridge power module in the fourth embodiment of the present invention, including: The memory 20, the processor 10, and the computer program 30 stored in the memory and running on the processor, when the processor 10 executes the computer program 30, the above-mentioned method for detecting the DC voltage of a cascaded H-bridge power module is implemented .

Wherein, the processor 10 may be a central processing unit (Central Processing Unit, CPU), a controller, a microcontroller, a microprocessor or other data processing chips in some embodiments, and is used for running the program codes stored in the memory 20 or Processing data, such as implementing access restriction procedures, etc.

The memory 20 includes at least one type of readable storage medium, including flash memory, hard disk, multimedia card, card-type memory (eg, SD or DX memory, etc.), magnetic memory, magnetic disk, optical disk, and the like. In some embodiments, the memory 20 may be an internal storage unit of the device for detecting the DC voltage of the cascaded H-bridge power module, such as a hard disk of the device for detecting the DC voltage of the cascaded H-bridge power module. In other embodiments, the memory 20 may also be an external storage device of a device for detecting the DC voltage of a cascaded H-bridge power module, for example, a plug-in hard disk or a smart memory card equipped on the device for detecting the DC voltage of a cascaded H-bridge power module. (Smart Media Card, SMC), secure digital (SecureDigital, SD) card, flash memory card (Flash Card), etc. Further, the memory 20 may also include both an internal storage unit of a device for detecting the DC voltage of a cascaded H-bridge power module and an external storage device. The memory 20 can not only be used to store application software and various types of data installed in the DC voltage detection equipment of the cascaded H-bridge power modules, but also can be used to temporarily store data that has been output or will be output.

It should be pointed out that the structure shown in FIG. 16 does not constitute a limitation on the detection device for the DC voltage of the cascaded H-bridge power module. In other embodiments, the detection device for the DC voltage of the cascaded H-bridge power module may include a Fewer or more components are shown, or some components are combined, or a different arrangement of components.

Embodiments of the present invention further provide a computer-readable storage medium, on which a computer program is stored, and when the program is executed by a processor, implements the above-mentioned method for detecting the DC voltage of a cascaded H-bridge power module.

Those skilled in the art will appreciate that logic and/or steps represented in flowcharts or otherwise described herein, for example, may be considered an ordered listing of executable instructions for implementing logical functions, may be embodied in in any computer-readable medium for use by an instruction execution system, apparatus, or device (such as a computer-based system, a system including a processor, or other system that can fetch and execute instructions from an instruction execution system, apparatus, or device), or Used in conjunction with these instruction execution systems, apparatus or devices. For the purposes of this specification, a "computer-readable medium" can be any device that can contain, store, communicate, propagate, or transport the program for use by or in connection with an instruction execution system, apparatus, or apparatus.

More specific examples (non-exhaustive list) of computer readable media include the following: electrical connections with one or more wiring (electronic devices), portable computer disk cartridges (magnetic devices), random access memory (RAM), Read Only Memory (ROM), Erasable Editable Read Only Memory (EPROM or Flash Memory), Fiber Optic Devices, and Portable Compact Disc Read Only Memory (CDROM). In addition, the computer readable medium may even be paper or other suitable medium on which the program may be printed, as the paper or other medium may be optically scanned, for example, followed by editing, interpretation, or other suitable medium as necessary process to obtain the program electronically and then store it in computer memory.

It should be understood that various parts of the present invention may be implemented in hardware, software, firmware or a combination thereof. In the above-described embodiments, various steps or methods may be implemented in software or firmware stored in memory and executed by a suitable instruction execution system. For example, if implemented in hardware, as in another embodiment, it can be implemented by any one or a combination of the following techniques known in the art: Discrete logic circuits, ASICs with suitable combinational logic gates, Programmable Gate Arrays (PGA), Field Programmable Gate Arrays (FPGA), etc.

In the description of this specification, description with reference to the terms "one embodiment," "some embodiments," "example," "specific example," or "some examples", etc., mean specific features described in connection with the embodiment or example , structure, material or feature is included in at least one embodiment or example of the present invention. In this specification, schematic representations of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the particular features, structures, materials or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.

The above-mentioned embodiments only represent several embodiments of the present invention, and the descriptions thereof are specific and detailed, but should not be construed as a limitation on the scope of the patent of the present invention. It should be pointed out that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can also be made, which all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention should be subject to the appended claims.

Claims (7)

1. A method for detecting a DC voltage of a cascaded H-bridge power module is characterized by comprising the following steps:

acquiring alternating current of a current conversion chain acquired by a current transformer on the current conversion chain of the cascaded H bridge, and acquiring the current stage of a power module on the current conversion chain;

when the power module is in an uncontrolled stage, calculating the direct current of the power module according to the alternating current of the current conversion chain;

when the power module is in a control stage, acquiring a switch state matrix of each switch of the power module, and calculating direct current of the power module according to the switch state matrix and alternating current of the converter chain;

calculating the direct current voltage of the power module according to the direct current of the power module;

when the power module is in an uncontrolled stage, the direct current of the power module satisfies a conditional expression:

i _cj （t）=| i _r （t）|

wherein,i _cj （t) Represents the direct current of the power module,i _r （t) An alternating current representative of said converter chain;

when the power module is in a control stage, the direct current of the power module meets the conditional expression:

wherein,

，ΔTin order to calculate the step size,Cis the capacity of the dc capacitor in the power module,R ₁-R ₄the resistance values of the four switches of the power module are respectively, and when the switches are switched on, the resistance values areR _on Resistance value of at turn-offR _off The on-off states of the four switches are determined by the switch state matrix,i _cj （t) Represents the direct current of the power module,i _r （t) Represents the alternating current of said converter chain,V _dcj （t-ΔT）=V _dcj （t _k-1），V _dcj （t _k-1) Is an equivalent historical voltage source,krepresenting the sampling times of the current transformer;

DC voltage of the power modulev _dcj （t) The conditional expression is satisfied:

wherein,V _dcj （t _k-1) The equivalent historical voltage source satisfies the conditional expression:

wherein,krepresenting the number of samples taken by the current transformer.

2. The method for detecting the direct-current voltage of the cascaded H-bridge power module according to claim 1, wherein the step of calculating the direct-current voltage of the power module according to the direct current of the power module is followed by the step of:

calculating the calculation error of the direct-current voltage of the power module by adopting a corresponding error formula according to the current stage of the power module;

and adjusting the calculation parameters of the direct current voltage of the power module according to the calculation error.

3. The method for detecting the direct-current voltage of the cascaded H-bridge power module according to claim 2, wherein when the power module is in a steady-state operation stage, the error formula is as follows:

in the formula,ΔTin order to calculate the step size,Cis the capacity of the dc capacitor in the power module,Δv _dcj is the calculation error of the dc voltage of the power module,i _cj （t-ΔT) Representst-ΔTThe time corresponds to the direct current of the power module.

4. The method for detecting the direct-current voltage of the cascaded H-bridge power module according to claim 2, wherein when the power module is in a transient operation stage or a control stage, the error formula is as follows:

in the formula,Δv _dcj （t _k ) Is as followskThe calculation error of the dc voltage of the power module corresponding to the sub-sampling time,ε ₂is the relative error of sampling of the current transformer,i _cj （t _k ) Represents the firstkThe power module direct current corresponding to the sub-sampling time,

，ΔTin order to calculate the step size,Cthe capacity of the direct current capacitor in the power module.

5. A detection device for detecting DC voltage of a cascaded H-bridge power module is characterized by comprising:

the information acquisition module is used for acquiring alternating current of a current conversion chain acquired by a current transformer arranged on the current conversion chain of the cascade H bridge and acquiring the current stage of a power module on the current conversion chain;

the current calculation module is used for calculating the direct current of the power module according to the alternating current of the commutation chain when the power module is in an uncontrolled stage; when the power module is in a control stage, acquiring a switch state matrix of each switch of the power module, and calculating direct current of the power module according to the switch state matrix and alternating current of the converter chain;

the voltage calculation module is used for calculating the direct current voltage of the power module according to the direct current of the power module;

when the power module is in an uncontrolled stage, the direct current of the power module satisfies a conditional expression:

i _cj （t）=| i _r （t）|

wherein,i _cj （t) Represents the direct current of the power module,i _r （t) An alternating current representative of said converter chain;

when the power module is in a control stage, the direct current of the power module meets the conditional expression:

wherein,

，ΔTin order to calculate the step size,Cis the capacity of the dc capacitor in the power module,R ₁-R ₄the resistance values of the four switches of the power module are respectively, and when the switches are switched on, the resistance values areR _on Resistance value of at turn-offR _off The on-off states of the four switches are determined by the switch state matrix,i _cj （t) Represents the direct current of the power module,i _r （t) Represents the alternating current of said converter chain,V _dcj （t-ΔT）=V _dcj （t _k-1），V _dcj （t _k-1) Is an equivalent historical voltage source,krepresenting the sampling times of the current transformer;

DC voltage of the power modulev _dcj （t) The conditional expression is satisfied:

wherein,V _dcj （t _k-1) The equivalent historical voltage source satisfies the conditional expression:

wherein,krepresenting the number of samples taken by the current transformer.

6. A computer-readable storage medium, on which a computer program is stored, which, when being executed by a processor, carries out a method for detecting a dc voltage of a cascaded H-bridge power module according to any one of claims 1 to 4.

7. A device for detecting dc voltage of a cascaded H-bridge power module, comprising a memory, a processor and a computer program stored in the memory and executable on the processor, wherein the processor executes the computer program to implement the method for detecting dc voltage of a cascaded H-bridge power module according to any one of claims 1 to 4.

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