CN114884046A - Multi-low-order harmonic current self-adaptive suppression method based on impedance editing - Google Patents

Abstract

A self-adaptive suppression method for multiple low-order harmonic currents based on impedance editing relates to the field of power harmonic suppression, a large amount of low-frequency harmonic currents exist in a microgrid direct-current bus, and the low-frequency harmonic currents flow to a DC-DC converter at a source end, so that the service life of a direct-current power supply is shortened, the efficiency of the DC-DC converter is reduced, the tracking of the maximum power point of a photovoltaic system is influenced, and the realization of soft switching of the converter is influenced. Meanwhile, the frequency and the content of each low-frequency ripple in the direct current bus may also fluctuate along with the load. Compared with the traditional ripple suppression control method, the harmonic content and frequency in the bus current are extracted through fast Fourier analysis, and then the current harmonic with the content exceeding a threshold value is suppressed. The dynamic performance of the system is not influenced while the low-frequency current harmonic is dynamically suppressed. The self-adaptive low-frequency harmonic current suppression method does not need additional electric elements, reduces the system cost and improves the system efficiency.

Description

An Adaptive Suppression Method for Multi-Low-Order Harmonic Current Based on Impedance Editing

technical field

The invention relates to the field of power supply harmonic suppression, in particular to a multi-low order harmonic current adaptive suppression method based on impedance editing.

Background technique

Low-frequency harmonic currents can be seen everywhere in power supply systems used in industrial production, and have no small impact on them. Hydrogen production from new energy has become one of the most popular research projects at present. The so-called new energy hydrogen production means that the renewable energy system is directly rectified by the AC-DC converter and then supplies power to the electrolysis device to produce hydrogen, or the AC-DC converter and the DC-DC converter work together to supply power to the hydrogen production device. . Among them, the bipolar AC-DC converter has a wide output voltage adjustment range, a higher power factor, and a better hydrogen production effect. However, the generated low-order ripple affects the conversion efficiency of the front-stage renewable energy equipment, and also easily damages the latter-stage hydrogen production equipment. In addition, in the distributed renewable energy (DERs) module in the microgrid system, since multiple DC-DC and DC-AC converters are connected to the DC bus, the second harmonic current generated by the single-phase inverter and the third harmonic current are generated by the single-phase inverter. The third and fifth harmonic currents generated by the unbalanced phase converter will flow into the DC bus side in large quantities. These low-frequency harmonic currents flow into DERs through DC-DC converters, reducing energy conversion efficiency and shortening equipment life. At the same time, a large amount of low-frequency ripple will increase the conduction loss, increase the size of the input filter, and deteriorate the power quality. Therefore, it is of great practical significance to suppress the low-frequency current ripple.

The proposed low-frequency harmonic current suppression methods are divided into two categories. The first is to add additional low frequency harmonic suppression circuits. The most common method is to incorporate a large electrolytic capacitor on the DC bus side or to add an LC resonant circuit whose resonant frequency is twice the fundamental frequency to suppress secondary current harmonics. The method is simple and convenient, but the electrolytic capacitors required to achieve the suppression effect are bulky and short-lived, reducing the power density and efficiency of the system. Active power filter is used to compensate the low frequency harmonic current of the DC bus by injecting the same amplitude and opposite phase harmonic current into the DC bus. The harmonic suppression effect of this method is good, but the cost is high, and there are additional component losses. Absorbing low-frequency harmonics by connecting a bidirectional DC-DC converter or a power decoupling circuit in parallel at the DC bus end will increase the complexity of the system and reduce the system efficiency. The second type is to realize the suppression of low-frequency harmonic currents by adopting appropriate control methods for the power-side converters. This method does not require the addition of additional electronic devices, so there is no additional loss while suppressing harmonic currents. Chinese patent CN102843020B discloses a method for suppressing the second harmonic current of a front-stage converter in a two-stage inverter and its control circuit. Together with the inductor current sampling signal passing through the follower, it is used as the feedback signal of the current regulator, and together with the voltage regulator signal, a regulation signal is generated and sent to the PWM modulator. The control method has a simple structure, is convenient to implement, and can effectively suppress the input secondary ripple current. . However, it is not considered that the output voltage frequency is not stable at the power frequency in actual operation, and directly using twice the power frequency as the characteristic frequency will lead to poor actual suppression effect and poor dynamic performance. Chinese patent CN111293869A discloses a method for suppressing the second harmonic current of the inductor current feedback path of a two-stage inverter power supply. On the basis of the voltage and current double closed-loop control strategy, an inverter input current i _inv feedforward path is added. Improve the dynamic performance of the system, so that the system has the ability to suppress the second harmonic current, and also has excellent dynamic performance. However, this paper only suppresses the second harmonic current, and in actual DC microgrid applications, there are often three-phase unbalanced AC loads at the load end, which means that there may be more than second harmonic current components at the DC bus end. , and these harmonic contents are also non-negligible.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide an adaptive suppression method for multiple low-order harmonic currents based on impedance editing.

The technical scheme of the present invention is to suppress the low-frequency harmonic current of the DC power supply of the micro-grid system through control.

The control system of the present invention is composed of a DC power supply, a front-stage DC-DC converter, and various types of converters in the back-stage; the DC power supply is provided by a new energy power generation device, a fuel cell, etc.; the front-stage DC-DC converter outputs The terminal contains an LC circuit or a DC-DC conversion circuit similar to an LC circuit; the post-stage converter includes a DC-DC converter, a single-phase inverter, a three-phase inverter, and the like.

The new energy power generation device includes a wind energy power generation device, a photovoltaic power generation device, a hydrogen energy power generation device, a biochemical energy power generation device, and the like.

The present invention increases the output impedance of the DC-DC converter at h times (h takes 2-8) fundamental frequency by feeding back the current i _Lb of the inductor L and the DC bus voltage u _bus at both ends of the capacitor C _bus .

The present invention includes the following steps:

1) In each sampling period, sample the current i _Lb and the DC bus voltage u _bus of the inductor L _b in the LC circuit in the DC-DC converter;

2) Perform fast Fourier analysis on the inductor current i _Lb to obtain the content m _h and frequency f _h of each low-frequency ripple current; then perform fast Fourier analysis on the voltage u _bus to obtain the bus voltage harmonic content m After ' _h and frequency _f'h , logically discriminate the voltage and current harmonic content and frequency, and output logical signals _yh and _y'h ;

减去直流母线电压采样值

先与信号y′_h进行逻辑或运算，再乘上比例谐振传递函数K_R(s)；同样的，DC-DC变换器LC电路中电感L的电流采样值

先与信号y_h进行逻辑或运算，再与带通滤波器传递函数B_R(s)相乘；其中，比例谐振传递函数的表达式为：3) Reference voltage of DC-DC converter

Subtract DC bus voltage sample value

First perform a logical OR operation with the signal y' _h , and then multiply it by the proportional resonance transfer function K _R (s); similarly, the current sampling value of the inductor L in the DC-DC converter LC circuit

First perform a logical OR operation with the signal y _h , and then multiply it with the transfer function _BR (s) of the band-pass filter; among them, the expression of the proportional resonance transfer function is:

In the formula, K _r is the proportional coefficient, f _b1 is the passband bandwidth of the band-pass filter, and f _h is the center resonant frequency of the band-pass filter; the expression of the transfer function of the band-pass filter is:

In the formula, _rh is the gain of the band-pass filter, and f _b2 is the pass-band bandwidth of the band-pass filter;

与电感电流采样值为

反馈量为H₁和H₂，其表达式分别为：Set the bus voltage sampling value as

and the inductor current sampling value is

The feedback quantities are H ₁ and H ₂ , and their expressions are:

减去H₁和H₂，即

得到第一个参考电压

Reference voltage for DC-DC converters

Subtract H ₁ and H ₂ , i.e.

get the first reference voltage

相减，即

得到电压误差 u_Δ；4) Compare the DC bus voltage sampled value with the first reference voltage

subtract, i.e.

get the voltage error u _Δ ;

5) Multiply the transfer function G _v (s) of the voltage controller by the error u _Δ , and the transfer function of the voltage controller is:

Among them, K _P is the proportional coefficient of the voltage controller, and K _i is the integral coefficient of the voltage control;

再将占空比经过驱动电路后输送到DC-DC变换器的开关管(MOSFET、IGBT)中，控制DC-DC变换器的输出电压，实现低频谐波电流的抑制。6) Multiply the product with the transfer function G _d (s) for discretization, and then compare it with the triangular carrier to obtain the duty cycle

Then, the duty cycle is sent to the switch tube (MOSFET, IGBT) of the DC-DC converter after passing through the driving circuit, and the output voltage of the DC-DC converter is controlled to realize the suppression of low-frequency harmonic current.

In step 2), the logic judgment is mainly: when the ratio of the h-th harmonic current amplitude m _h to the inductive current DC component m ₀ is greater than the allowable value of the harmonic content, the corresponding output is 1, otherwise the output is 0; at the same time, The ratio of the h-th harmonic voltage amplitude m' _h to the DC component of the capacitor voltage m' ₀ is compared with the voltage ripple factor threshold u _th ; when the former is greater than the latter, the corresponding output is 1, and the output is 0 when it is smaller; the output is 0 It means that the component of the h-order harmonic current is small enough to not be suppressed, and the output is 1 to suppress the h-order harmonic current.

下截止频率为

In step 6), the method for suppressing the low-frequency harmonic current may be: the value range of K _r is 0<K _r <1, the value of f _o should be the frequency of the corresponding order current harmonic, K _R ( s) is a constant value, and B _R (s) is a time variable, the upper cutoff frequency of the band-pass filter is

The lower cutoff frequency is

The basic principle of the invention is that the controller constituted by the corresponding control method can dynamically change the output impedance of the DC-DC converter at the corresponding harmonic frequency according to the content and frequency of the low-frequency current ripple in the DC bus. The use of single-phase AC loads and three-phase unbalanced AC loads in the microgrid system will generate power pulsations at the secondary, tertiary and above fundamental frequencies, thereby returning a low-frequency harmonic current to the DC power supply. From the perspective of impedance, as long as the output impedance of the source DC-DC converter is large enough at the corresponding sub-resonant frequency, the low-frequency current harmonics of the DC-side power supply will be absorbed by the bus capacitor, so that the low-frequency current ripple in the bus can be obtained. inhibition.

The present invention does not require additional circuit devices, can suppress the current of low-frequency harmonics (harmonic components with a frequency lower than 400hz when the power frequency is 50hz) to less than 4%, and solves the efficiency brought by adding additional devices in the traditional solution. Reduce, increase in size, increase in cost, decrease in power density and other issues. The traditional control method can only target specific current harmonics of a fixed frequency, while the present invention extracts the inductive current of the source converter and the busbar voltage of the DC microgrid and decomposes it by fast Fourier transform to obtain the harmonic currents and busbars of each order. The content and frequency of the harmonic voltage, according to the content of the current harmonic and the content of the voltage harmonic, determine whether the ripple is suppressed or not, and then dynamically adjust the center frequency of the band-pass filter according to the obtained harmonic current frequency to achieve Suppression of low frequency current harmonics.

Compared with the prior art, the present invention has the following beneficial effects:

1) The present invention realizes the suppression of the low-frequency harmonic current of the DC side power supply without adding additional electronic devices, improves the stability of the system, improves the efficiency of the system, increases the power density of the system, reduces the cost, and has better harmonics. Inhibitory effect.

2) In the present invention, the inductor current and the DC bus voltage are fed back to the input terminal through the band-pass filter for comparison with the reference voltage, and then the duty cycle of the active switching device of the front-stage DCDC converter is controlled, thereby increasing the impedance of the DC bus terminal. Z _dc-dc , so that the low-frequency harmonic current flows into the capacitor C _bus at the bus terminal, eliminating its influence on the DC power supply. Compared with the existing control method, the method of collecting the inductor current and passing it through a high-pass filter has higher stability.

3) In the present invention, after the inductor current and the DC bus voltage are collected, the harmonic content is extracted through fast Fourier analysis, and it is determined whether filtering is required.

Description of drawings

Figure 1 shows a typical DC microgrid system consisting of a DC power supply, a front-stage DC-DC converter, and various back-stage converters.

Figure 2 is an equivalent schematic diagram of a DC microgrid system.

FIG. 3 is a block diagram of a control system for suppressing low-frequency harmonic currents according to the present invention.

Figure 4 is a Bode plot of a high pass filter.

Figure 5 is a Bode plot of a multiband pass filter.

Fig. 6 is the control flow chart of the multi-band-pass filter.

Figure 7 is a block diagram of a time-varying bandpass filter.

Fig. 8 is the waveform diagram of the actual current ripple suppression experiment. In Figure 8, curve 1 is 200V/div, curve 2 is 20V/div, curve 3 is 100V/div, and curve 4 is 4.00A/div.

Detailed ways

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

The technical solution of the embodiment of the present invention is to suppress the low-frequency harmonic current of the DC power supply of the microgrid system through control.

The embodiment of the control system of the present invention is composed of a DC power supply, a front-stage DC-DC converter, and various types of converters at the rear stage; the DC power supply is provided by a new energy power generation device, a fuel cell, etc.; the front-stage DC-DC converter The output end of the converter contains an LC circuit or a DC-DC conversion circuit similar to the LC circuit; the latter-stage converter includes a DC-DC converter, a single-phase inverter, a three-phase inverter, and the like.

The new energy power generation device includes a wind energy power generation device, a photovoltaic power generation device, a hydrogen energy power generation device, a biochemical energy power generation device, and the like.

In the embodiment of the present invention, the output impedance of the DC-DC converter at h times (h is 2-8) of the fundamental frequency is increased by feedback of the current i _Lb of the inductor L and the DC bus voltage u _bus at both ends of the capacitor C _bus .

Referring to FIG. 1 , the control system of the present invention is a typical DC microgrid system composed of a DC power supply, a DC-DC converter at the front stage, and various types of converters at the rear stage. The DC power supply U _in provides electrical energy, which is boosted by the front-stage boost chopper (Boost) circuit, and then passes through the inverter circuit to form a 50Hz sinusoidal AC power to supply power to the AC load.

Referring to Figure 2, the system shown in Figure 1 is equivalent to a DC source and an AC source whose frequency is h times the fundamental frequency (h takes 2-8). The low-frequency harmonic current generated by the AC current source is fed back to the DC source through the Boost circuit, so the low-frequency harmonic current will be generated on the DC voltage source side.

Further, the output impedance Z _dc-dc of the front-stage DC-DC converter is changed to a high impedance at h times the fundamental frequency through a corresponding control method, and the harmonic current of the corresponding order will flow into the capacitor C _bus . Therefore, the output current i _in of the DC power supply will contain very little low frequency harmonic current.

Referring to FIG. 3 , according to the system control block diagram for realizing low-frequency current harmonic suppression proposed by the present invention, its specific implementation method is as follows:

In each sampling period, the current i _Lb of the inductor L _b and the DC bus voltage u _bus across the capacitor C _bus are sampled by the sensor, and the sampling result is input into the DSP, and the data is processed in the next step.

Perform fast Fourier analysis on the inductor current i _Lb to obtain the content m _h and frequency f _h of each low-frequency ripple current; then perform fast Fourier analysis on the voltage u _bus to obtain the bus voltage harmonic content m′ _h and frequency f′ _h . Then logically discriminate the harmonic content and frequency of the voltage and current, and output the logical signals y _h and y′ _h .

减去直流母线电压采样值

与逻辑判别信号 y′_h相乘后，再与电压反馈回路多次带通滤波器传递函数K_R(s)相乘，得到反馈量H₁。其中，电压反馈回路多次带通滤波器传递函数K_R(s)的表达式为：Further, the reference voltage of the DC-DC converter

Subtract DC bus voltage sample value

After multiplied by the logic discrimination signal y' _h , and then multiplied by the transfer function K _R (s) of the voltage feedback loop multiple band-pass filters to obtain the feedback quantity H ₁ . Among them, the expression of the transfer function K _R (s) of the multiple band-pass filter of the voltage feedback loop is:

In the above formula, K _r is the proportional coefficient, its value is less than 1 but greater than 0, f _b is the passband bandwidth of the band-pass filter, and f _o is the center resonant frequency of the band-pass filter.

与逻辑判别信号y_h相乘后，再与带通滤波器传递函数B_R(s)相乘，得到反馈量H₂。其中，电感电流反馈回路多次带通滤波器传递函数B_R(s)的表达式为：Further, the current sampling value of the inductor L in the DC-DC converter LC circuit

After multiplying with the logic discrimination signal y _h , and then multiplying with the transfer function _BR (s) of the band-pass filter to obtain the feedback quantity H ₂ . Among them, the expression of the transfer function _BR (s) of the multiple band-pass filter of the inductor current feedback loop is:

In the above formula, _rh is the gain of the multiple bandpass filter in the inductor current feedback loop. When designing, it is necessary to ensure that the current part at each h times the fundamental frequency can pass, and the value range of r _h should be adjusted according to the actual effect.

下截止频率为

为了兼顾带通滤波器的分辨率和动态性能，品质因数Q取1。The K _R (s) is a constant value, and B _R (s) is a time variable, and the upper cutoff frequency of the bandpass filter is

The lower cutoff frequency is

In order to take into account the resolution and dynamic performance of the band-pass filter, the quality factor Q is set to 1.

减去H₁和H₂，得到第一个参考电压

其中，各反馈量H₁、H₂表达式为：Further, the reference voltage of the DC-DC converter

Subtract H ₁ and H ₂ to get the first reference voltage

Among them, the expressions of each feedback quantity H ₁ and H ₂ are:

与第一个参考电压

相减，即

得到电压误差u_Δ，然后将误差u_Δ与电压控制器的传递函数G_v(s)相乘。电压控制器的传递函数为：Further, the sampled value of the DC bus voltage is

with the first reference voltage

subtract, i.e.

The voltage error u _Δ is obtained, then the error u _Δ is multiplied by the transfer function G _v (s) of the voltage controller. The transfer function of the voltage controller is:

In the above formula, K _P is the proportional coefficient of the voltage controller, and its value range is 0.1<K _P <10; K _i is the integral coefficient of the voltage control, and its value range is 0.1<K _i <1.

Further, after the product is multiplied by the discretized transfer function G _d (s) for discretization, it is compared with the triangular carrier to obtain the duty ratio d. After passing through the driving circuit, it is sent to the switch tube (MOSFET, IGBT) of the DC-DC converter to control the output voltage of the DC-DC converter and realize the suppression of the second harmonic current.

或电流

反馈到参考电压端时，参考电压只会添加交流分量，不会影响其直流部分。与高通滤波器的幅频特性曲线相比，如图4所示，引入多带通滤波器的端口阻抗仅在各个h倍基频处体现为高阻抗，在其他频率下均有不同程度衰减，确保了对应次谐波电流的抑制效果。同时，带通滤波器在各个h倍基频处的相移近似为 0，提高了系统的稳定性。然而，采用这种方法消除低频谐波分量，最多需要设计14个带通滤波器。若14个带通滤波器同时工作，会导致系统控制计算时间增加，动态性能差。Referring to Figure 5, according to the Bode diagram of the multi-band-pass filter shown, only the voltage and current components of each h-fold fundamental frequency can pass through, and the DC part is filtered out. Therefore the voltage

or current

When fed back to the reference voltage terminal, the reference voltage will only add an AC component and will not affect its DC portion. Compared with the amplitude-frequency characteristic curve of the high-pass filter, as shown in Figure 4, the port impedance introduced into the multi-band-pass filter is only reflected as high impedance at each h times the fundamental frequency, and has different degrees of attenuation at other frequencies. The suppression effect of the corresponding sub-harmonic current is ensured. At the same time, the phase shift of the band-pass filter at each h times the fundamental frequency is approximately 0, which improves the stability of the system. However, using this method to eliminate low-frequency harmonic components requires the design of up to 14 bandpass filters. If 14 band-pass filters work at the same time, it will lead to increased system control calculation time and poor dynamic performance.

进行逻辑或运算。经过上述流程，能够有效判断含量较高的低次谐波分量，再使能对应次的带通滤波器工作，减少运算量，提高动态响应。Referring to FIG. 6, it is a block diagram of the control flow of the adaptive multi-pass filter. First, the detected inductor current and voltage current are subjected to fast Fourier analysis to make two logical outputs y _h and y′ _h . Then, the inductor current and the bus voltage harmonic content are judged respectively. When the ratio of the h-th harmonic current amplitude m _h to the inductor current DC component m ₀ is greater than 4%, the output of y _h is 1, otherwise the output is 0. At the same time, when the ratio of the h-th harmonic voltage amplitude m' _h to the DC component of the capacitor voltage m' ₀ is greater than the voltage ripple factor threshold u _th , the output of y' _h is 1, otherwise it is 0. When the output is 0, it means that the component of the h-order harmonic current is small enough, and when the output is 1, the h-order harmonic current is suppressed. Finally, y _h and y′ _h are respectively related to the inductor current i _Lb , the capacitor voltage

Perform a logical OR operation. Through the above process, the low-order harmonic components with high content can be effectively judged, and then the band-pass filter of the corresponding order can be enabled to work, reducing the amount of calculation and improving the dynamic response.

Figure 7 is a block diagram of a time-varying bandpass filter, where u is used as the input and y is used as the output. Different from the traditional band-pass filter, which selects a fixed characteristic frequency, the time-varying band-pass filter dynamically adjusts the characteristic frequency value according to the change of the fundamental frequency by performing fast Fourier analysis on the inductor current, reducing the bandwidth of the band-pass filter and improving the filtering effect. dynamic performance of the device.

Figure 8 is the waveform diagram of the DC side power supply current i _in and the inverter output voltage when the Boost circuit adopts the proposed control method when the inverter loads are different. It can be seen that the low-order harmonic current in the current i _in is affected by inhibition. The Fourier analysis results show that the second harmonic current accounts for 2.89% of the DC component, and the third harmonic current accounts for about 1.71%. Therefore, the control method proposed by the present invention has an excellent suppressing effect on the low-order harmonic current.

To sum up, the present invention can realize the suppression of the low-frequency harmonic current of the DC power supply in the microgrid system, and the suppression effect is good, and there is no loss caused by additional circuits. Compared with the traditional low-frequency harmonic current suppression method, it has the advantages of good stability and high operation efficiency.

The above description is only a preferred embodiment of the present invention, but the protection scope of the present invention is not limited to this. Substitutions should be covered within the protection scope of the present invention. Therefore, the protection scope of the present invention should be subject to the protection scope of the claims.

Claims (3)

1. A self-adaptive suppression method of multi-low-order harmonic current based on impedance editing is characterized in that a control system consists of a direct-current power supply, a front-stage DC-DC converter and various rear-stage converters; the direct current power supply is provided by a new energy power generation device and a fuel cell; the output end of the front-stage DC-DC converter comprises an LC circuit or a DC-DC conversion circuit similar to the LC circuit; the post converter comprises a DC-DC converter, a single-phase inverter and a three-phase inverter;

the method comprises the following steps:

1) at each sampling period, the inductance L in the LC circuit in the DC-DC converter is measured _b Current i of _Lb And the DC bus voltage u _bus Sampling is carried out;

2) for the inductive current i _Lb Performing fast Fourier analysis to obtain the content m of each low-frequency ripple current _h And frequency f _h (ii) a Voltage u of another pair _bus Performing fast Fourier analysis to obtain the content m 'of the harmonic wave of the bus voltage' _h And frequency f' _h Then, the harmonic content and frequency of the voltage and the current are subjected to logicDiscriminating and outputting logic signal y _h 、y′ _h ；

3) Reference voltage of DC-DC converter

Subtracting DC bus voltage sampling value

And signal y 'first' _h Performing logical OR operation, and multiplying by proportional resonant transfer function K _R (s); similarly, the current sampling value of the inductor L in the LC circuit of the DC-DC converter

First AND signal y _h Performing logical OR operation, and then transferring function B with band-pass filter _R (s) multiplication; wherein, the expression of the proportional resonance transfer function is:

in the formula, K _r Is a proportionality coefficient, f _b1 Is the passband bandwidth of the bandpass filter, f _h Is the center resonance frequency of the band-pass filter; the expression for the band pass filter transfer function is:

in the formula, r _h Is the gain of a band-pass filter, f _b2 The passband bandwidth of the bandpass filter;

setting the sampling value of the bus voltage as

The inductor current has a sampling value of

The feedback quantity is H ₁ And H ₂ The expressions are respectively:

reference voltage of DC-DC converter

Minus H ₁ And H ₂ I.e. by

Obtaining a first reference voltage

4) The DC bus voltage sampling value and the first reference voltage are compared

By subtraction, i.e.

Obtain the voltage error u _Δ ；

5) By error u _Δ Transfer function G with voltage controller _v (s) the transfer function of the voltage controller is:

wherein, K _P Is the proportionality coefficient of the voltage controller, K _i Is an integral coefficient of voltage control;

6) multiplying the product with a transfer function G _d (s) multiplying, discretizing, and comparing with a triangular carrier to obtain the duty ratio

And then the duty ratio is transmitted to a switching tube (MOSFET, IGBT) of the DC-DC converter after passing through a driving circuit, the output voltage of the DC-DC converter is controlled, and the suppression of low-frequency harmonic current is realized.

2. The adaptive suppression method for multiple low-order harmonic currents based on impedance editing according to claim 1, characterized in that in step 2), the logic judgment is: when h harmonic current amplitude m _h And the direct current component m of the inductor current ₀ When the ratio is greater than the harmonic content tolerance value, the corresponding output is 1, otherwise the output is 0; meanwhile, h harmonic voltage amplitude m' _h And capacitor voltage DC component m' ₀ Ratio and voltage ripple factor threshold u _th Comparing; when the former is larger than the latter, the corresponding output is 1, and when the former is smaller than the latter, the output is 0; an output of 0 indicates that the component of the h-th harmonic current is small enough and does not need to be suppressed, and an output of 1 suppresses the h-th harmonic current.

3. The adaptive suppression method for multiple low-order harmonic currents based on impedance editing as claimed in claim 1, wherein in step 6), the suppression method for the low-order harmonic currents is: k _r Has a value range of 0 < K _r ＜1，f _o Should be taken to be the frequency, K, of the corresponding order current harmonic _R (s) is a constant value, and B _R (s) is a time variable and the upper cut-off frequency of the band-pass filter is

Lower cut-off frequency of

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