CN110336476B - Closed-loop zero-sequence voltage optimal injection method for cascaded H-bridge converters - Google Patents

Abstract

The invention discloses a closed-loop zero-sequence voltage optimal injection method for cascaded H-bridge converters. The method is applied to interphase power control of cascaded H-bridge converters, which can expand the adjustment range of cascaded H-bridge interphase power and improve the The utilization rate of the DC bus voltage of the converter, and the closed-loop control is used to prevent over-modulation after the three-phase modulation wave is injected into the zero-sequence voltage. Its characteristics are: obtaining the original modulation wave of the cascaded H-bridge three-phase and the fundamental frequency component V _{zero, f} of the zero-sequence signal; then sending the modulation signal into the overmodulation component extraction function f _ext respectively to obtain the overmodulation component extraction signal D ^over ; Then pass the D ^over signal through the low-pass filter transfer function, gain coefficient and fundamental frequency notch filter, respectively, to obtain the zero-sequence signal component V _{zero, h} for suppressing overmodulation; finally V _{zero, h} and the zero-sequence signal fundamental frequency The components V _zero,f are added to obtain the optimized zero-sequence voltage V _zero,op , which is injected into the original modulation wave, corresponding to the output of the switching signal.

Description

Closed-loop zero-sequence voltage optimal injection method for cascaded H-bridge converters

technical field

The invention relates to the technical field of converters, in particular to a closed-loop zero-sequence voltage optimal injection method. Specifically, the method is applied to the phase-to-phase power control of cascaded H-bridge converters, which can expand the zero-sequence voltage injection range and improve the conversion efficiency. The utilization rate of the DC bus voltage of the converter is improved, and the over-modulation occurs after the three-phase modulated wave is injected into the zero-sequence voltage in the form of closed-loop control.

Background technique

Converter technology is a technology that converts electrical energy from DC to AC or AC to DC, and plays an important role in today's industrial applications. The cascaded H-bridge converter is widely used in high-voltage and high-power energy supply applications. , control the switching state of the switch tube, so that the input/output current waveform is approximately sinusoidal. Because the three-phase cascaded H-bridge converter is composed of cascaded H-bridge module units, the output power of each module unit needs to be balanced, which is divided into phase-to-phase power balance and intra-phase power balance. For phase-to-phase power balance, the industry usually uses a specific zero-sequence signal to be injected into the three-phase modulation signal to flexibly adjust the output power of each phase. After the zero-sequence voltage is injected, the amplitude of the modulated signal may exceed the amplitude of the carrier wave, resulting in an overmodulation problem. At this time, the power balance of the cascaded H-bridge and the power quality of the output current cannot meet the requirements.

SUMMARY OF THE INVENTION

Aiming at the problem that the amplitude of the modulated signal may exceed the amplitude of the carrier after the zero-sequence voltage injection, and overmodulation occurs, the present invention proposes a closed-loop zero-sequence voltage optimal injection method for cascaded H-bridge converters. Through the designed closed-loop control algorithm , generate an irregular zero-sequence voltage including the corresponding fundamental frequency component, and reduce the amplitude of the modulated signal after the zero-sequence voltage is injected, thereby expanding the interphase power adjustment range of the cascaded H-bridge.

The purpose of this invention is to realize through the following technical solutions:

The closed-loop zero-sequence voltage optimal injection method for cascaded H-bridge converters includes the following steps:

(1) Obtaining the three-phase original modulation waves _da , _db , and dc of the _cascaded H-bridge through the current controller;

(2) Obtain the zero-sequence voltage amplitude E _zero and the phase angle θ _zero to be injected through the phase-to-phase power controller, and use the zero-sequence voltage amplitude and phase angle to generate the zero-sequence signal fundamental frequency component V _zero,f , the calculation formula is:

V _{zero, f} = E _zero sin(ω _f t+θ _zero ) (1-1)

where ω _f is the cutoff frequency, and t is the sampling time;

将

和

相加得到信号D^over，过调制成分提取函数D^over表达式为：(3) Send the signals da , _db , and _dc to the overmodulation component extraction function _{f ext} respectively to obtain the waveform of the overmodulation component

Will

and

The signal D ^over is obtained by adding, and the overmodulation component extraction function D ^over is expressed as:

where d _i (i=a, b, c) is the original three-phase modulated wave, and threshold is the overmodulation threshold of the modulated wave, which is 0.95;

(4) Pass the D ^over obtained in step (3) through the low-pass filter transfer function G _f (s), the gain coefficient K and the fundamental frequency trap G _trap (s), respectively, to obtain the zero-sequence signal component for suppressing overmodulation V _{zero, h} ; where G _f (s) is the low-pass filter transfer function, and its expression is:

where ω _cut is the cut-off angular frequency of the first-order low-pass filter, and s is a variable in the complex frequency domain;

(5) Add the V _{zero, h} obtained in step (4) and the fundamental frequency component V _{zero, f} of the zero-sequence signal obtained in step (2) to obtain the optimized zero-sequence voltage V _{zero, op} , and the optimized zero-sequence voltage V _{Zero and op} are injected into the original modulated waves da , _db , and _{dc to obtain switching signals Sa , S b , and} S _{c .}

Further, steps (2) to (5) together constitute a three-phase output power control structure, and the corresponding transfer function formula of the control structure is:

V _{zero, h} = [f _ext (d _a )+f _ext (d _b )+f _ext (d _c )] · G _f (s) · K · G _trap (s) (1-5)

ω _c is the cut-off angular frequency of the notch filter, and ω ₀ is the angular frequency corresponding to the power frequency;

ω _cut is the cut-off angular frequency of the first-order low-pass filter;

V _{zero, op} = V _{zro, f} + V _{zero, h} (1-8)

S _a =d _a +V _{zero, op} (1-9)

S _b =d _b +V _{zero, op} (1-10)

S _c =d _c +V _{zero, op} (1-11)

Compared with the prior art, the beneficial effects brought by the technical solution of the present invention are:

The invention is applied to the phase-to-phase power control of the cascaded H-bridge converter, omits the complicated trigonometric function calculation, and directly through the proportional-integral control of the power error, can realize the rapid generation of the optimized irregular zero-sequence voltage with a low calculation amount; The overmodulation extraction function reduces the amplitude of the modulated signal after zero-sequence voltage injection, reduces the occurrence of overmodulation, and thus expands the interphase power adjustment range of the cascaded H-bridge; at the same time, the closed-loop control can improve the accuracy and precision of the interphase power control, It has certain engineering practical significance.

Description of drawings

FIG. 1 is a schematic diagram of a topology structure of a three-phase cascaded H-bridge grid-connected converter in the implementation of the present invention.

2a is a schematic diagram of the control structure of the three-phase cascaded H-bridge grid-connected converter in the implementation of the present invention.

FIG. 2b is a structural diagram of a zero-sequence voltage optimization controller in the implementation of the present invention.

FIG. 3 is a grid-side voltage waveform diagram of the present invention.

Figure 4a shows the grid-side current waveform when the three-phase power is balanced and equal.

Figure 4b shows the grid-side current waveform that uses the closed-loop zero-sequence voltage injection method to achieve three-phase power redistribution and balance.

Fig. 4c is a grid-side current waveform that realizes the redistribution and balance of three-phase power using the closed-loop zero-sequence voltage optimal injection method proposed by the present invention.

FIG. 5a is a diagram showing the effect of three-phase power control under the condition that the three-phase powers are balanced and equal.

Figure 5b is a diagram showing the effect of three-phase power control in which three-phase power is redistributed and balanced by the closed-loop zero-sequence voltage injection method.

Fig. 5c is a diagram showing the effect of three-phase power control in which three-phase power is redistributed and balanced by adopting the closed-loop zero-sequence voltage optimal injection method proposed by the present invention.

FIG. 6a is the output modulation signal waveform of the cascaded H-bridge converter under the condition that the three-phase powers are balanced and equal.

Fig. 6b is the output modulation signal waveform of the cascaded H-bridge converter in the case of adopting the closed-loop zero-sequence voltage injection method to realize the three-phase power redistribution and balance.

FIG. 6c shows the output modulation signal waveform of the cascaded H-bridge converter when the three-phase power is redistributed and balanced by adopting the closed-loop zero-sequence voltage optimal injection method proposed by the present invention.

FIG. 7a is a waveform diagram of the zero-sequence voltage V _zero,f injection before the present invention is adopted.

FIG. 7b is a waveform diagram of zero-sequence voltage V _{zero, op} injection after adopting the closed-loop zero-sequence voltage optimal injection method proposed by the present invention.

Detailed ways

The specific embodiments of the present invention for power balancing of cascaded H-bridge converters will be described below with reference to the diagrams, so that those skilled in the art can better understand the present invention. Taking a cascaded H-bridge converter operating in grid connection as an example, FIG. 1 is a schematic diagram of a topology structure of a specific implementation of the present invention under this working condition, and FIGS. 2 a and 2 b are schematic diagrams of a control structure. As shown in Figure 1, the cascaded converter is composed of H-bridge converter module units with the same structure. Connect to the medium and high voltage grid. Since the power emitted by each module is different, and the three-phase grid-connected current needs to be balanced, it is necessary to inject a zero-sequence signal into the three-phase modulation signal to ensure that the three-phase output power meets the requirements and maintains the three-phase current balance. When the power difference between the phases is large, the injected zero-sequence signal amplitude is large, and a certain phase over-modulation may occur. At this time, the present invention needs to be applied to suppress the over-modulation of the three-phase modulation signal, while ensuring that the current and power quality is not affected.

The basic steps of the present invention for power control of cascaded H-bridge converters are as follows:

Step 1: Obtain the three-phase original modulation waves _da , _db , and dc of the _cascaded H-bridge through the current controller.

Step 2: Obtain the zero-sequence voltage amplitude E _zero and the phase angle θ _zero to be injected through the phase-to-phase power controller, and use the zero-sequence voltage amplitude and phase angle to generate the zero-sequence signal fundamental frequency component V _{zero, f} , and add it to the step (1) In the obtained three-phase original modulated waves d _a , _{db , and d c , signals D a , D b , and D c are generated , and} the calculation formula is:

V _{zero_f} =E _zero sin(ω _f ·t+θ _zero ) (1-1)

D _a =V _{zero, f} +d _a (1-2)

D _b =V _{zero, f} +d _b (1-3)

D _c =V _{zero, f} +d _c (1-4)

where ω _f is the cutoff frequency and t is the sampling time.

将其相加得到信号D^over。过调制成分提取函数f_ext(x)表达式为：Step 3: Send the signals da , _db , and _dc to the overmodulation component extraction function _{f ext} (x) respectively to obtain the waveform of the overmodulation component

Adding these results in the signal D ^over . The overmodulation component extraction function f _ext (x) is expressed as:

T is any limit of x.

Therefore, the overmodulation component extraction function D ^over is expressed as:

threshold is the modulated wave overmodulation threshold, generally 0.95.

Step 4: Pass the D ^over obtained in Step 3 through the low-pass filter transfer function G _f (s), the gain coefficient K and the fundamental frequency trap G _trap (s), respectively, to obtain the zero-sequence signal component V _zero for suppressing overshoot _{, h} . where G _f (s) is the low-pass filter transfer function, and its expression is:

where ω _cut is the cut-off angular frequency of the first-order low-pass filter.

Step 5: Add V _{zero, h} obtained in step 4 and the fundamental frequency component V _{zero, f} of the zero-sequence signal obtained in step 2 to obtain _an optimized zero-sequence voltage V _{zero, op} , and inject it into the original modulating wave da, In _db and _dc , the signals _Sa , _Sb , and _Sc are obtained, which are output corresponding to the driving signals.

The steps 2 to 5 together constitute a three-phase output power control structure, and the corresponding transfer function formula of the control structure is:

V _{zero, h} = [f _ext (d _a )+f _ext (d _b )+f _ext (d _c )] · G _f (s) · K · G _trap (s) (1-7)

ω _c is the cut-off angular frequency of the notch filter, and ω ₀ is the angular frequency corresponding to the power frequency

V _{zero, op} = V _{zero, f} + V _{zero, h} (1-10)

S _a =d _a +V _{zero, op} (1-11)

S _b =d _b +V _{zero, op} (1-12)

S _c =d _c +V _{zero, op} (1-13)

Step 6: Build the simulation model shown in FIG. 1 with Matlab/Simulink, and verify the zero-sequence voltage optimal injection method proposed by the present invention.

FIG. 3 is a grid-side voltage waveform diagram of the present invention, and FIGS. 4a to 4c are grid-side current waveform diagrams before and after applying the present invention. Fig. 4a is the grid-side current waveform when the three-phase power is balanced and equal, Fig. 4b is the grid-side current waveform when the three-phase power is redistributed and balanced by the closed-loop zero-sequence voltage injection method, and Fig. 4c is the grid-side current waveform proposed by the present invention. The closed-loop zero-sequence voltage optimal injection method realizes the three-phase power redistribution and balanced grid-side current waveform. It can be seen from Fig. 4a that the grid-connected current is in the same phase as the grid voltage, and the basic power balance control is realized. Figure 4b shows that the simple zero-sequence voltage injection method causes the distortion of the grid-connected current waveform due to the overmodulation problem of the H-bridge module, which affects the performance and reliability of the grid-connected device. The method can solve the overmodulation problem very well.

Figure 5a is a three-phase power control effect diagram when the three-phase power is balanced and equal, λ _a =λ _b =λ _c =1/3, P _a =P _b =P _c =2000W; Figure 5b is a zero-sequence voltage The effect diagram of the three-phase power control that realizes the three-phase power redistribution and balance by the injection method, λ _a = 0.333, λ _b = 0.234, λ _c = 0.433, P _a = 2000W, P _b = 1400W, P _c = 2600W; Figure 5c In order to use the closed-loop zero-sequence voltage optimal injection method to realize the three-phase power redistribution and balanced three-phase power control effect diagram, λ _a = 0.333, λ _b = 0.234, λ _c = 0.433, P _a = 2000W, P _b = 1400W, P _c =2600W.

Figure 6a shows the output modulation signal waveform of the cascaded H-bridge converter when the three-phase power is balanced and equal, and Figure 6b shows the cascaded H-bridge converter when the three-phase power is redistributed and balanced by the closed-loop zero-sequence voltage injection method Figure 6c shows the output modulated signal wave of the cascaded H-bridge converter when the three-phase power is redistributed and balanced by the closed-loop zero-sequence voltage optimal injection method proposed by the present invention. Given that V _dc = 130V, since the H-bridge output voltage peak V _p is usually below 3 V _dc , V _p = 3 V _dc only when the power imbalance increases to a critical point. It can be seen from the figure that there is an overmodulation problem in Figure 6b, while the closed-loop zero-sequence voltage optimal injection method can be used to control the modulation signal to be less than or equal to 3V _dc as shown in Figure 6c.

FIG. 7a is a waveform diagram of the zero-sequence voltage V _zero,f injection before using the present invention; FIG. 7b is a zero-sequence voltage V _zero,op injection waveform diagram after using the zero-sequence voltage optimal injection method proposed by the present invention.

In summary, the present invention discloses a closed-loop zero-sequence voltage optimal injection method, which is applied to the phase-to-phase power control of the cascaded H-bridge converter, which can expand the adjustment range of the phase-to-phase power of the cascaded H-bridge, and improve the DC bus voltage utilization rate of the converter. And the closed-loop control is used to prevent over-modulation after the three-phase modulated wave is injected into the zero-sequence voltage. It is a new zero-sequence voltage injection method worthy of promotion.

The present invention is not limited to the embodiments described above. The above description of the specific embodiments is intended to describe and illustrate the technical solutions of the present invention, and the above-mentioned specific embodiments are only illustrative and not restrictive. Without departing from the spirit of the present invention and the protection scope of the claims, those of ordinary skill in the art can also make many specific transformations under the inspiration of the present invention, which all fall within the protection scope of the present invention.

Claims (2)

1. The closed-loop zero-sequence voltage optimization injection method for the cascaded H-bridge converter is characterized by comprising the following steps of:

(1) obtaining three-phase original modulation wave d of cascade H bridge by current controller_a、d_b、d_c；

(2) Obtaining zero sequence voltage amplitude E to be injected through interphase power controller_zeroAnd phase angle theta_zeroGenerating fundamental frequency component V of zero sequence signal by using amplitude and phase angle of zero sequence voltage_zero，fThe calculation formula is as follows:

V_zero，f＝E_zerosin(ω_f·t+θ_zero) (1-1)

wherein ω is_fIs the cut-off frequency, t is the sampling time;

(3) will signal d_a、d_b、d_cAre fed separately into overmodulation component extraction functions f_extObtaining a waveform of an overmodulation component

Will be provided with

And

adding them to obtain a signal D^overOver-modulation component extraction function f_extThe expression is as follows:

wherein d is_i(i is a, b and c) is a three-phase original modulation wave, and threshold is a modulation wave overmodulation threshold which is 0.95;

(4) d obtained in the step (3)^overRespectively low-pass filtered transfer function G_f(s), gain factor K and fundamental trap G_trap(s) obtaining a zero sequence signal component V for suppressing overmodulation_zero，h(ii) a Wherein G is_f(s) is a low pass filter transfer function expressed as:

wherein ω is_cutThe cutoff angular frequency of the first-order low-pass filter, s is a variable of the complex frequency domain;

(5) v obtained in the step (4)_zero，hAnd (3) obtaining a zero sequence signal fundamental frequency component V in the step (2)_zero，fAdding to obtain optimized zero sequence voltage V_zero，opAnd will optimize the zero sequence voltage V_zero，opInjected into the original modulated wave d_a、d_b、d_cIn the step (2), a switching signal S is obtained_a、S_b、S_c。

2. The closed-loop zero-sequence voltage optimized injection method for the cascaded H-bridge converter according to claim 1, wherein the steps (2) to (5) jointly form a three-phase output power control structure, and the control structure corresponds to a transfer function formula as follows:

V_zero，h＝[f_ext(d_a)+f_ext(d_b)+f_ext(d_c)]·G_f(s)·K·G_trap(s) (1-5)

ω_cfor the trap to cut off the angular frequency, omega₀The angular frequency is corresponding to the power frequency;

ω_cutcut off the angular frequency for the first order low pass filter;

V_zero，op＝V_zero，f+V_zero，h (1-8)

S_a＝d_a+V_zero，op (1-9)

S_b＝d_b+V_zero，op (1-10)

S_c＝d_c+V_zero，op (1-11)。

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