CN103812107B - A kind of Mixed cascading seven level active filter based on complex controll - Google Patents

Abstract

The invention discloses a mixed cascaded seven-level active filter based on composite control. The invention comprises an H bridge hybrid cascaded main circuit (3), a sampling circuit (4), a control circuit (5) and a PWM modulation and isolation drive circuit (6); two H bridges in the H bridge hybrid cascaded main circuit (3) The DC side voltage ratio of the unit is 1:2; the control circuit (5) includes a main power signal generation module (7), a power compensation signal generation module (8), and a composite control module (9); the main power signal generation module (7) generates The main control signal, the power compensation signal generation module (8) generates the power compensation signal, and the composite control module (9) is used to generate the first control signal and the second control signal; the PWM modulation and isolation drive circuit (6) generates the final switching tube drive signal. Compared with the traditional equal-pressure cascaded active filter, the invention can output more levels when the number of units is the same, and improves the effect of harmonic compensation.

Description

A hybrid cascaded seven-level active filter based on composite control

technical field

The invention relates to a hybrid cascaded seven-level active filter based on composite control, which is suitable for various medium and high power occasions and belongs to the technical field of electric harmonic suppression.

Background technique

In recent years, power electronics technology and devices have been developed rapidly. While improving people's living standards, it also brings a large number of nonlinear loads to the power grid, especially the converters that work in switch mode. These nonlinear loads will generate a large number of harmonics and reactive power. If they are injected into the grid, the grid current and grid voltage will be distorted. In severe cases, it may threaten the safe operation of the grid. Therefore, the suppression and management of harmonics is very important. , is an important research topic in power electronics and other fields in recent years.

Active filter is a device that can dynamically suppress harmonics and compensate reactive power. It has the advantages of fast dynamic response, high reliability, and flexible compensation. It has a good application prospect and is favored and concerned by people. With the development of society, power electronics technology is gradually moving towards high-voltage and high-power applications. The first problem to be solved is the contradiction between the frequency of switching devices and the power level. In the past period of time, the application of multi-level converter technology in high-voltage and high-power applications has been well researched and developed. Multi-level topology can realize the direct application of low-voltage high-frequency switching devices to high-voltage and high-power applications. At the same time, the multi-level topology also has the advantages of less output voltage harmonics and less electromagnetic interference.

In recent years, the development of multilevel topologies is changing rapidly. AburtoV, SchneiderM, and MoranL, "Anactive power filter implemented with three-level NPC voltage-source inverter," IEEEPESC, 1997: 1121-1126 first applied the diode-clamped multi-level topology to the active power filter, which can effectively reduce the switching tube voltage Stress improves the compensation effect, but with the increase of the number of levels, the number of switching devices increases sharply, which will increase the size and cost of the system. In addition, this topology also has voltage balance problems, and the control is more complicated. J.S.LaiandF.Z.Peng, "Multilevelconverters-Anewbreedofpowerconverters," IEEETransactionsonIndustryApplications, 1996, 32(3): 2348-2356 proposed an equal-pressure H-bridge cascaded inverter topology, if this topology is applied to active filtering In the device, the number of output levels can be increased, the compensation effect can be improved, and it can be applied to high-voltage and high-power occasions, but when the number of required levels increases, the number of cascaded units will also increase greatly, which will make the system and control become easier. more complicated. How to use the same number of cascaded units to output more levels has practical significance for better improving the compensation effect. In response to this problem MiguelLopezG, LuisMoranT, and JoseEspinozaC, etal, "Performanceanalysisofahybridaasymmetricmultilevelinverterforhighvoltageactivepowerfilterapplications," IEEEIECON, 2003: 1050-1055 applies a hybrid cascaded multilevel topology of H-bridges with a binary relationship to the active power filter, This topology can output more levels with the same cascaded unit, and the compensation effect is better.

The control of the hybrid cascaded multilevel active filter is very important. How to obtain a good compensation effect under the premise of ensuring that the DC side voltage is stable at a predetermined mixing ratio is the focus and difficulty of the research. Most of the methods are aimed at the control of equal-voltage H-bridge cascading, and there are few studies on hybrid cascading control, such as using additional hardware devices to control the stability of the DC side voltage. Although this method can stabilize the DC side voltage at the required value, but at the same time it also increases the cost and volume of the system; it is also possible to control the voltage stability of the DC side by shifting the output waveform phase, but due to the limited range of the phase shift angle, the voltage stability of the H-bridge DC side is slow and the dynamic performance poor. ManjrekarMD, SteimerPK, and LipoTA, "Hybrid multilevel power conversion system: a competitive solution for high-power applications," IEEE Transactions on Industry Applications, 2000, 36 (3): 834-841 proposed to use a PWM rectifier composed of fully-controlled power devices to control the DC side voltage of the low-voltage unit for the hybrid cascaded topology. Stability, which will increase the complexity of system control, reduce the efficiency of the system, and increase the volume and cost of the system. MiguelLopezG, LuisMoranT, and JoseEspinozaC, etal, "Performanceanalysisofahybridaasymmetricmultilevelinverterforhighvoltageactivepowerfilterapplications," IEEEIECON, 2003: 1050-1055 did not use external equipment, but controlled the system through a hybrid control method, which achieved certain compensation effects, but the article did not It is not reliable to analyze the dynamic performance when the load changes suddenly.

Therefore, how to make the hybrid cascaded seven-level active filter obtain a good dynamic and static compensation effect and meet the requirements of high reliability without increasing the system cost and complexity has important research significance.

Contents of the invention

Purpose of the invention:

The purpose of the present invention is to propose a hybrid cascaded seven-level active filter based on composite control, in which the hybrid cascaded multi-level topology can better suppress power harmonics and can be applied to medium-high voltage and high-power occasions. Based on the characteristics of the topology itself, the present invention proposes a compound control method, which can not only control the DC side voltage of each unit to stabilize at a given value, but also obtain good dynamic and static compensation effects, and enable the system to operate with high reliability.

Technical solutions:

The present invention adopts following technical scheme:

A hybrid cascaded seven-level active filter based on composite control, including an H-bridge hybrid cascaded main circuit, a sampling circuit, a control circuit, and a PWM modulation and isolation drive circuit; the input of the H-bridge hybrid cascaded main circuit The terminals are respectively connected to the positive busbar of the AC grid and one end of the nonlinear load, and the output terminals are respectively connected to the negative busbar of the AC grid and the other end of the nonlinear load. The side circuit is connected to collect the sampled values of voltage and current; the control circuit includes a main power signal generation module, a power compensation signal generation module and a composite control module; the input terminal of the main power signal generation module, the first power compensation signal generation module One input end is respectively connected to the output end of the sampling circuit; the first output end of the main power signal generation module is connected to the second input end of the power compensation signal generation module, and the second output end of the main power signal generation module, the power compensation signal generation The output terminals of the module are respectively connected to the first and second input terminals of the composite control module; the output terminals of the composite control module are connected to the input terminals of the PWM modulation and isolation driving circuit; the output terminals of the PWM modulation and isolation driving circuit are mixed with the H bridge cascade main circuit connection;

The H-bridge hybrid cascaded main circuit includes an AC-side interface inductor L and two H-bridge units, wherein the two H-bridge units adopt a hybrid cascaded structure, which are respectively a low-voltage unit H1 and _a high-voltage unit _H2 , and the DC side voltage mixing ratio is 1:2;

The sampling circuit includes AC grid voltage sampling VT1, low-voltage unit DC side voltage sampling VT2, high-voltage unit DC side voltage sampling VT3, grid current sampling CT1, and compensation current sampling CT2; wherein the sampling value u _s of the AC grid voltage sampling VT1 The sampling value i _s of grid current sampling CT1 is input to the main power signal generating module; the sampling value u ₁ of the DC side voltage sampling VT2 of the low-voltage unit, and the sampling value u ₂ of the DC side voltage sampling VT3 of the high-voltage unit are respectively input to the main power signal generation module at the same time A power signal generation module, a power compensation signal generation module; the sampling value ic of the compensation current sampling _CT2 is input to the power compensation signal generation module.

Further, the above-mentioned main power signal generation module of the hybrid cascaded seven-level active filter based on composite control is used to generate the main control signal, and the process is as follows: the VT2 low-voltage unit DC side voltage sampling value u ₁ and VT3 The DC voltage sampling value u ₂ of the high-voltage unit is superimposed to obtain the total voltage U _dc of the DC side of the two cascaded units, which is compared with the given voltage reference U _dc ^* , and the error signal is sent to the voltage controller 1 to obtain the grid current reference The amplitude signal I _S of the signal i _S ^* ; the VT1 power grid voltage sampling value u _s is locked by the phase-locked loop PLL to generate a standard unit sinusoidal signal e _s with the same phase as the power grid voltage, and then the standard unit sinusoidal signal e _s Multiply the output _{IS of the voltage controller 1 to obtain the grid current reference signal i S *; CT1 grid current sampling value i S is compared with the grid current reference signal i S *} ^, _{and the} ^difference can be obtained through the current controller to obtain the main control signal p _m .

Further, the above-mentioned power compensation signal generation module of a hybrid cascaded seven-level active filter based on composite control is used to generate a power compensation signal, including the following steps: detecting the compensation current ic through the current transformer _CT2 ; according to the two The DC side total voltage U _dc of the cascaded unit and the DC side voltage mixing ratio of the cascaded unit are respectively obtained the DC side voltage reference values of the low voltage unit and the high voltage unit, and then the two DC side voltage reference values are respectively compared with the DC side voltage of the low voltage unit and the high voltage unit The sampling values u ₁ and u ₂ of the DC side voltage are compared, and the comparison results are respectively sent to the voltage controller 2 and the voltage controller 3 to obtain the voltage compensation signals Δu ₁ and Δu ₂ of the low voltage unit and the high voltage unit; the two voltage compensation signals are respectively Multiplied with the compensation current _ic , the result is Δp ₁ and Δp ₂ , that is, power compensation signal 1 and power compensation signal 2.

Further, the composite control module of the hybrid cascaded seven-level active filter based on composite control is used to generate the first control signal and the second control signal, specifically as follows: the main control signal p _m is adjusted accordingly and Calculate p _m1 (p _m1 =k ₁ p _m ) and p _m2 (p _m2 =k ₂ p _m ), that is, the main control signal 1 and the main control signal 2; add the main control signal 1 and the power compensation signal 1 to get the first A control signal p ₁ , the main control signal 2 and the power compensation signal 2 are added to obtain a second control signal p ₂ .

Sending the first control signal p ₁ and the second control signal p ₂ into the PWM modulation and isolation driving circuit can obtain the driving signals of the switching tubes of the two cascaded units.

Beneficial effect:

1. The topology of the active filter of the present invention adopts a hybrid cascaded structure of two H-bridges, which has the advantages of an equal-pressure H-bridge cascaded structure. In addition, this topology is compared with the equal-pressure H-bridge cascaded topology at the same level. In the case of the number of connected units, more levels can be output, which is beneficial to reduce the output harmonic content and improve the compensation effect;

2. The composite control module of the present invention integrates the main power signal generation module and the power compensation signal generation module. According to the actual situation, through the adjustment and optimization of the coefficients, it can provide corresponding power compensation for the DC side of the two cascaded units in real time to ensure For the stability of the DC side voltage of the two cascaded units, when the load changes suddenly, the control method can also quickly adjust the power compensation amount of the DC side of the two cascaded units, so that the DC side voltage quickly returns to a stable state. On the one hand, the control method can ensure that the system has good dynamic and static compensation performance; on the other hand, the control method has good adaptability to some uncertain factors, which greatly improves the reliability of the system.

Description of drawings

Fig. 1 is a structural diagram of a hybrid cascaded seven-level active filter based on composite control of the present invention.

Fig. 2 is a main circuit and control schematic diagram of a hybrid cascaded seven-level active filter based on compound control of the present invention.

Fig. 3 is the grid voltage, grid current, load current, compensation current and compensation voltage simulation waveforms applied to the 220V/50Hz power grid in the present invention.

Fig. 4 is a simulation waveform of the DC side voltage of the low-voltage unit and the steady-state voltage of the DC side of the high-voltage unit when the present invention is applied to a 220V/50Hz power grid.

Fig. 5 is a dynamic simulation waveform of the grid current, compensation current, and DC side voltage of two cascaded units applied to a 220V/50Hz grid when the present invention is suddenly loaded.

Labels in the figure: 1. AC power grid, 2. Non-linear load, 3. H-bridge hybrid cascade main circuit, 4. Sampling circuit, 5. Control circuit, 6. PWM modulation and isolation drive circuit, 7. Main power signal generation module, 8. a power compensation signal generation module, and 9. a composite control module.

specific implementation plan

Below in conjunction with accompanying drawing, the implementation of technical scheme is described in further detail:

Fig. 1 is a structural diagram of a hybrid cascaded seven-level active filter based on composite control of the present invention. As shown in Figure 1, active filter of the present invention comprises H-bridge hybrid cascaded main circuit 3, sampling circuit 4, control circuit 5 and PWM modulation and isolation drive circuit 6; Described H bridge hybrid cascaded main circuit 3 and The AC grid 1 is connected to the nonlinear load 2, and the input end of the sampling circuit 4 is respectively connected to the H-bridge hybrid cascaded main circuit 3 and the AC grid 1 side circuit for collecting sampled values of voltage and current; the control circuit 5 includes the main power Signal generation module 7, power compensation signal generation module 8 and composite control module 9; Wherein the input end of main power signal generation module 7, the first input end of power compensation signal generation module 8 are connected with the output end of sampling circuit 4 respectively; The first output end of the power signal generation module 7 is connected with the second input end of the power compensation signal generation module 8, and the second output end of the main power signal generation module 7 and the output end of the power compensation signal generation module 8 are respectively connected with the composite control module The first and second input ends of 9 are connected; the output end of composite control module 9 is connected with the input end of PWM modulation and isolation drive circuit 6; the output end of PWM modulation and isolation drive circuit 6 is mixed with H bridge cascaded main circuit 3 connect.

Fig. 2 is a main circuit and control schematic diagram of a hybrid cascaded seven-level active filter based on compound control of the present invention. As shown in Figure 2, the system consists of an AC grid 1, a nonlinear load 2, and an H-bridge hybrid cascaded main circuit 3, where the AC grid 1 emits an AC voltage, and the nonlinear load 2 is a current-type harmonic source that generates harmonic currents , the H-bridge hybrid cascaded main circuit 3 is composed of the AC side interface inductor L and two H-bridge units, wherein the two H-bridge units adopt a hybrid cascaded structure, which are the low-voltage unit H ₁ and the high-voltage unit H ₂ , and the DC side voltage of the two units The mixing ratio is 1:2. The input terminals of the two cascaded units are connected to the positive bus of the AC grid 1 and one end of the nonlinear load 2 through the interface inductor L, and the output terminals are directly connected to the negative bus of the AC grid 1 and the other end of the nonlinear load 2. . The sampling circuit 4 includes AC grid voltage sampling VT1, low-voltage unit DC side voltage sampling VT2, high-voltage unit DC side voltage sampling VT3, grid current sampling CT1, and compensation current sampling CT2. The control circuit 5 includes a main power signal generation module 7, a power compensation signal generation module 8 and a compound control module 9, and the input of the main power signal generation module 7 is the sampled values of VT1, VT2, VT3 and CT1, i.e. u _s , u ₁ , u ₂ and i _s , the output is the total voltage signal of the DC side and the main control signal, which are respectively connected to the power compensation signal generation module 8 and the composite control module 9; the input of the power compensation signal generation module 8 is the sampling value of VT2, VT3 and CT2, namely u ₁ , u ₂ and i _c , the outputs are power compensation signal 1 and power compensation signal 2, which are connected to composite control module 9; composite control module 9 inputs the main control signal output by main power signal generation module 7 and power compensation signal generation module 8 The output of the two power compensation signals is the first control signal and the second control signal, which are connected to the PWM modulation and isolation drive circuit 6; the input of the PWM modulation and isolation drive circuit 6 is the two control signals output by the composite control module 9, and the output is The driving signals of the switching tubes of the two H bridges are connected to the H bridge hybrid cascaded main circuit 3 .

In the main power signal generation module 7, the VT2 low-voltage unit DC side voltage sampling value u ₁ and the VT3 high-voltage unit DC side voltage sampling value u ₂ are used as two inputs of the adder B ₁ , and the output of the adder B ₁ is two cascaded The total voltage U _dc on the DC side of the unit, and use it as the negative input of the subtractor B ₂ , the voltage reference U _dc ^* as the positive input of the subtractor B ₂ , the output of the subtractor B ₂ as the input of the voltage controller 1, the voltage The output of the controller 1 is the magnitude signal I _S of the grid current reference signal i _S ^* , which is used as an input of the multiplier M ₁ , and the VT1 grid voltage sampling value u _s is input into the phase-locked loop PLL to obtain the same phase as the grid voltage The standard unit sinusoidal signal e _s is the phase information of i _S ^* , which is used as another input of the multiplier M ₁ , and the output of the multiplier M ₁ is the grid current reference signal i _S ^* , which is used as the positive signal of the subtractor B ₃ Input, CT1 grid current sampling value i _S is used as the negative input of subtractor B ₃ , the output of subtractor B ₃ is used as the input of the current controller, and the output of the current controller is the main control signal p _m .

In the power compensation signal generation module ₈ , the output Udc of the adder B1 in the main power signal generation module 7 is passed through the proportional link _k3 (the _DC side voltage mixing ratio of the two cascaded units is 1:2, here _k3 =1 /3), the output of the proportional link k ₃ and the DC side voltage u ₁ of the low-voltage unit are used as the negative and positive inputs of the subtractor B ₄ , the output of the subtractor B ₄ is used as the input of the voltage controller 2, and the output of the voltage controller 2 is the low voltage The unit voltage compensation signal Δu ₁ ; the output U _dc of the adder B ₁ in the main power signal generation module 7 passes through the proportional link k ₄ (according to the mixing ratio of the DC side voltage of the two cascaded units is 1:2, here k ₄ =2 / ₃ ), the output of the proportional link k4 and the high _- voltage unit DC side voltage u2 are used as the negative and positive inputs of the subtractor B5, the output of the subtractor B5 is used as the input of the voltage controller ₃ , and the output of the voltage controller ₃ is High-voltage unit voltage compensation signal Δu ₂ ; the CT2 compensation current sampling value _ic and the output Δu ₁ of the voltage controller 2 are used as the two inputs of the multiplier M ₂ , and the output of the multiplier M ₂ is Δp ₁ , which is the power compensation signal 1, The ic and the output Δu ₂ of the voltage controller ₃ are used as two inputs of the multiplier M ₃ , and the output of the multiplier M ₃ is Δp ₂ , that is, the power compensation signal 2 .

In the composite control module 9, the output of the main power signal generation module ₇ is used as the input of the proportional link _k1 and the proportional link k2 respectively, the output of the proportional link _k1 is p _m1 , which is the main control signal ₁ , and the output of the proportional link k2 is p _m2 is the main control signal 2; the main control signal p _m1 and the output Δp ₁ of the multiplier M ₂ in the power compensation signal generation module 8 are used as the two inputs of the adder B ₆ , and the output of the adder B ₆ is p ₁ , which is the first A control signal, the main control signal p _m2 and the output Δp2 _of the multiplier M3 in the power compensation signal generation module ₈ are used as _two inputs of the adder _B7 , and the output of the adder B7 is _p2 , which is the second control signal.

The acquisition of the _first control signal p1 and the second control signal _p2 of the present invention is obtained by the main control signal and the power compensation signal through a weighted operation, and its expression can be expressed as:

p ₁ =k ₁ p _m +Δp ₁ (1)

p ₂ =k ₂ p _m +Δp ₂ (2)

Among them, k ₁ and k ₂ are adjustable quantities. It can be seen from formulas (1) and (2) that when the DC side voltage of the two cascaded units deviates from a given value, the weighting coefficients k ₁ and k ₂ are adjusted as needed Corresponding adjustments can change the ratio of the power compensation signal in the first and second control signals, thereby changing the power compensation amount for each DC side. On the one hand, the DC side voltage of the two cascaded units can be quickly restored to a given value. On the other hand, by further optimizing the coefficients, large fluctuations in the DC side voltage can be avoided, and power tubes can be prevented from being damaged due to excessive voltage; when the load changes suddenly, the filter can also be adjusted in a short time by properly processing the weighting coefficients. Therefore, the active filter of the present invention has strong adaptability to the load and has good dynamic and static compensation performance.

Sending the first control signal p ₁ and the second control signal p ₂ into the PWM modulation and isolation driving circuit 6 can obtain the driving signals of the switching tubes of the low voltage unit and the high voltage unit.

The composite control of the present invention is essentially a control method in which the main control signal and the power compensation signal work in harmony, and each signal is flexibly optimized and processed according to different working states and actual conditions. When the filter works stably, the influence of the power compensation signal on the system is very small; when the DC side voltage of the two cascaded units deviates or the load changes suddenly, the system will be unstable at this moment, and the effect of the power compensation signal on the system will appear, through The optimal selection and design of the weighting coefficients k ₁ and k ₂ adjusts the active power that needs to be compensated on the DC side of each unit, so that the system can quickly recover and stabilize. Therefore, the system has strong load adaptability and good dynamic and static compensation performance. Reliability is greatly improved.

Under the MATLAB software environment, the present invention establishes a simulation model and analyzes the waveform. The simulation parameters are as follows: the grid voltage is 220V/50Hz, the nonlinear load is a single-phase uncontrolled rectifier bridge-connected resistive load (20Ω, 500mH), the inductance L of the APF AC side interface is 1.2mH, and the total voltage of the DC side of the active filter is 390V (u ₁ :u ₂ =1:2), the capacitance values of the DC side capacitors of the two cascaded units are both 1000 μF, and the triangular carrier frequency is 20 kHz.

Fig. 3 is the grid voltage, grid current, load current, compensation current and compensation voltage simulation waveforms applied to the 220V/50Hz power grid in the present invention. It can be seen from the figure that the grid current has almost no distortion, the phase is synchronized with the grid voltage, and the compensation voltage is seven levels. The simulation results show that the hybrid cascaded seven-level active filter has achieved a good compensation effect, which proves the The effectiveness and feasibility of the invention control method.

Fig. 4 is a simulation waveform of the DC side voltage of the low-voltage unit and the steady-state voltage of the DC side of the high-voltage unit when the present invention is applied to a 220V/50Hz power grid. It can be seen from the figure that the voltage ratio of the DC side of the two cascaded units is 1:2 and is stable at a given value, so it can be seen that the control method of the present invention can be used to control the hybrid cascaded active filter of different voltage units.

Fig. 5 is a dynamic simulation waveform of the grid current, compensation current, and DC side voltage of two cascaded units applied to a 220V/50Hz grid when the present invention is suddenly loaded. It can be seen from the simulation waveform that when the load suddenly increases, it only takes one cycle for the grid current to return to a steady state, and the DC side voltage fluctuates very little and can quickly return to a stable value. The simulation results show that: the control method of the present invention can make The system has good dynamic performance, strong adaptability to load changes, and high reliability.

Claims (2)

1. A hybrid cascaded seven-level active filter based on composite control, comprising H-bridge hybrid cascaded main circuit (3), sampling circuit (4), control circuit (5) and PWM modulation and isolation drive circuit ( 6); the input ends of the H-bridge hybrid cascaded main circuit (3) are respectively connected to one end of the AC grid (1) positive busbar and the non-linear load (2), and its output terminals are respectively connected to the AC grid (1) negative busbar It is connected to the other end of the nonlinear load (2), and the input end of the sampling circuit (4) is respectively connected to the H-bridge hybrid cascaded main circuit (3) and the side circuit of the AC power grid (1) for sampling voltage and current value; it is characterized in that: the control circuit (5) includes a main power signal generation module (7), a power compensation signal generation module (8) and a compound control module (9); wherein the input of the main power signal generation module (7) terminal and the first input end of the power compensation signal generation module (8) are respectively connected with the output end of the sampling circuit (4); the first output end of the main power signal generation module (7) is connected with the output end of the power compensation signal generation module (8) The second input end is connected, the second output end of the main power signal generation module (7) is connected with the first input end of the composite control module (9), the output end of the power compensation signal generation module (8) is connected with the composite control module (9) ) is connected to the second input end; the output end of the composite control module (9) is connected to the input end of the PWM modulation and isolation drive circuit (6); the output end of the PWM modulation and isolation drive circuit (6) is cascaded in combination with the H bridge The main circuit (3) is connected; The H-bridge hybrid cascaded main circuit (3) includes an AC-side interface inductor L and two H-bridge units, wherein the two H-bridge units adopt a hybrid cascaded structure, which are respectively a low-voltage unit H1 and _a high-voltage unit _H2 , and the DC side The voltage mixing ratio is 1:2; The sampling circuit (4) includes AC grid voltage sampling VT1, low voltage unit DC side voltage sampling VT2, high voltage unit DC side voltage sampling VT3, grid current sampling CT1 and compensation current sampling CT2; wherein the sampling of the AC grid voltage sampling VT1 The value u _s and the sampled value i _s of grid current sampling CT1 are input to the main power signal generation module (7); the sampled value u1 of the DC side voltage sampling VT2 of the low voltage unit and the sampled value u _of the DC side voltage sampling VT3 of the high voltage unit ₂ are simultaneously input to the main power signal generation module (7) and the power compensation signal generation module (8); the sampling value ic of the compensation current sampling _CT2 is input to the power compensation signal generation module (8). 2. a kind of hybrid cascaded seven-level active filter based on compound control according to claim 1, is characterized in that, described main power signal generation module (7) is used for producing main control signal, power compensation signal The generation module (8) is used to generate the power compensation signal, and the composite control module (9) is used to generate the first control signal and the second control signal, and the specific steps are as follows: Step A, superimpose the sampled value u ₁ of the DC side voltage of the VT2 low-voltage unit and the sampled value u ₂ of the DC side voltage of the VT3 high-voltage unit to obtain the total voltage U _dc of the DC side of the two cascaded units, and then compare it with the voltage reference U _dc * Comparison, the comparison result is sent to the voltage controller 1 to obtain a value signal I _S ; In step B, the sampled value u _s of the AC grid voltage of VT1 is sent to the phase-locked loop PLL to obtain the standard unit sinusoidal signal e _s in phase with the grid voltage, and the standard unit sinusoidal signal e _s is combined with the amplitude signal obtained in step A I _S is multiplied, and the result is the grid current reference signal i _S ^* ; Step C, sampling the actual grid current, i.e. the sampled value i _S of CT1, calculating the difference between the grid current reference signal i _S ^* obtained in step B and the sampled value of CT1 grid current i _S , and passing it through the current controller to obtain the main Control signal p _m ; step D, detecting compensation current ic through current transformer _CT2 ; Step E, according to the total voltage U _dc of the DC side of the two cascaded units and the mixing ratio k ₃ of the DC side voltage of the cascaded unit, the reference value of the DC side voltage of the low-voltage unit is obtained, and then compared with the sampling value u ₁ of the DC side voltage of the low-voltage unit. Send the result of the voltage controller 2 to get the voltage compensation signal Δu ₁ of the low-voltage unit; Step F, calculating the product of the voltage compensation signal _{Δu 1} of the low-voltage unit and the compensation current ic, and the result is Δp ₁ , which is the power compensation signal 1; Step G, according to the total voltage U _dc of the DC side of the two cascaded units and the mixing ratio k ₄ of the DC side voltage of the cascaded unit, the reference value of the DC side voltage of the high-voltage unit is obtained, and then compared with the sampling value u ₂ of the DC side voltage of the high-voltage unit. The result of sending the result into the voltage controller 3 can obtain the high-voltage unit voltage compensation signal Δu ₂ ; Step H, calculating the product of the voltage compensation signal _{Δu 2} of the high-voltage unit and the compensation current ic, and the result is Δp ₂ , which is the power compensation signal 2; In step I, the main control signal p _m is adjusted and calculated correspondingly to obtain p _m1 and p _m2 , p _m1 =k ₁ p _m , p _m2 =k ₂ p _m , that is, main control signal 1 and main control signal 2, Among them, k ₁ and k ₂ are adjustable quantities; Step J, the main control signal and the power compensation signal are coordinated with each other, the main control signal 1 and the power compensation signal 1 are superimposed to obtain the first control signal p ₁ , and the main control signal 2 and the power compensation signal 2 are superimposed to obtain the second control signal p ₂ .