CN212114790U

CN212114790U - Active power filter

Info

Publication number: CN212114790U
Application number: CN202020601334.5U
Authority: CN
Inventors: 肖婷婷; 张舒麒; 徐瑞东
Original assignee: China University of Mining and Technology CUMT
Current assignee: China University of Mining and Technology CUMT
Priority date: 2020-04-21
Filing date: 2020-04-21
Publication date: 2020-12-08
Anticipated expiration: 2030-04-21

Abstract

The utility model discloses an active power filter, including two looks coordinate system conversion module (204), low pass filter (205), three looks coordinate system conversion module (206), subtracter (213), PR controller module (214), PWM module (207), IGBT drive circuit (209), power unit (210) and APF module (215) that connect gradually, wherein, the PWM module input links to each other with PR controller module output, and the APF module output passes through reactor (211) and links to each other with a generating line of electric wire netting. The utility model discloses need not extra sensor and acquire filter capacitor voltage, current loop stability is high, can improve harmonic current detection precision, reduces and detects the distortion, improves harmonic current compensation effect, solves APF's harmonic resonance problem.

Description

Active power filter

Technical Field

The utility model relates to a wave filter specifically is an active power filter, belongs to power quality control technical field.

Background

In recent years, with the increase of power demand, the power grid structure is more and more complex, and the harmonic problem is more and more serious. The APF is a highly efficient harmonic compensation device that receives much attention because of its ability to constantly compensate for harmonics, whereas a passive filter cannot, and in addition, the APF is faster in response and has a high-precision harmonic compensation ability. The LCL filter is an important component of the APF, and has a more significant filtering effect than the L output filter, and since the resonance point in the LCL filter affects the stability of the system, it is important to study the damping control strategy of the LCL filter.

Common damping strategies can be divided into two categories: the active power filter is a voltage source inverter in a current mode, and the output current of the active power filter is generated by the action of the output voltage of the inverter on an output inductor. The active damping strategy has recently become a hot point of research because it can suppress resonance without power loss by changing the system structure, can compensate for harmonic and reactive power with both frequency and magnitude change, can make up for the disadvantages of passive filters, and obtains better compensation characteristics than passive filters.

There are several active damping strategies on the market, one of which is to calculate and predict the inductor voltage on the converter side in order to eliminate the resonance phenomenon of the LCL filter, then obtain the high frequency component from the high pass filter and set a proportional feedback loop in front of the controller. However, the process of induced voltage prediction involves numerical differentiation, which may introduce high frequency noise, which is only applicable in active rectifier applications, and if applied to APF systems, the high frequency noise problem becomes more severe for multiple harmonics, making this approach difficult to implement.

Some researchers have proposed a method using voltage feedback with capacitors, but in the parameter selection process, accurate equivalent impedance parameters of the power grid are required, and in addition, an additional sensor is required to obtain the voltage of the filter capacitors and repeatedly calculate the parameters of the lead-lag link, and the method is not suitable for practical application.

There is also a current loop control method for stabilizing the LCL filter using the first order delay inherent in digital control, which does not require an additional sensor, only requires a compensation current check, and is simple in operation and low in cost. But the stability of the current loop is not very high, which leads to a severe phase delay, although more time delay is applied and a low pass filter may improve the system stability. In addition, adding a corresponding phase delay compensation to the controller involves a complex operation, with less obvious effects.

The above active damping strategy implements several different LCL filter resonance suppression methods, but they all have corresponding disadvantages, and therefore, damping suppression needs to be further optimized.

Disclosure of Invention

Problem to above-mentioned prior art exists, the utility model provides an active power filter need not extra sensor and acquires filter capacitor voltage, and current loop stability is high, can improve harmonic current detection precision, reduces and detects the distortion, improves harmonic current compensation effect.

The utility model relates to an active power filter, including detecting and control module, drive module, power unit and APF module, wherein, detect and include with control module:

the two-phase coordinate system transformation module is used for transforming the three-phase load current into a two-phase load current under a two-phase coordinate system, namely a d-q coordinate system, wherein the two-phase coordinate system and a voltage vector in the circuit synchronously rotate;

the low-pass filter is used for filtering harmonic component currents of d and q components in the two-phase load current output by the two-phase coordinate system conversion module to obtain a fundamental current component;

the three-phase coordinate system transformation module is used for transforming the fundamental component current processed by the low-pass filter into fundamental component current of three-phase load current under a three-phase (A-B-C) coordinate system;

the subtractor is configured to subtract the fundamental component current output by the three-phase load current and the three-phase coordinate system transformation module 206 to obtain a harmonic current;

the input end of the PR controller module is connected with the output end of the subtracter and used for subtracting the capacitance current fed back by the virtual resistor from the output of the PR controller inside the PR controller module so as to attenuate the resonance peak value of the APF; a PR controller inside the PR controller module is used for tracking a sinusoidal signal with a specified frequency in the load current;

the input end of the PWM module is connected with the output end of the RP controller module, and the output end of the PWM module is connected with the input end of the power unit through the driving module and used for generating a pulse width modulation signal of the power unit 210 for controlling the active power filter;

the output end of the power unit is connected with the input end of the APF module, and the output end of the APF module is connected with one bus of the power grid through the reactor.

Compared with the prior art, the utility model has the advantages of it is following:

1. the utility model discloses a coordinate transformation, low pass filter realize the accurate detection harmonic current, utilize PWM module 207 to produce power unit 210's control signal. The virtual resistor is adopted to restrain the harmonic peak of the APF, so that the APF harmonic resonance suppression device is more energy-saving compared with a passive damping strategy, has better universality and practicability compared with strategies such as a notch filter and the like, not only has the characteristics of accurately detecting and filtering harmonic current, but also effectively solves the harmonic resonance problem of the APF.

2. The utility model discloses the fundamental component that will obtain feeds back harmonic current detection link, has reduced the detection distortion, has improved harmonic current compensation effect.

3. The utility model discloses harmonic current directly obtains by the three-phase load, need not do any calculation, has avoided the deviation of rounding in the calculation process, has improved harmonic current's detection precision.

4. The utility model discloses added algorithm time delay compensation function in three-phase coordinate transform module, compensated the produced time delay of software algorithm to it is more accurate to make fundamental current fundamental component.

5. The utility model discloses a PR controller satisfies stability, steady state performance and dynamic behavior through adjusting proportional gain and integral gain, comes the disturbance that the suppression frequency fluctuation brought for APF through adjusting cut-off frequency, has solved the problem of coordinate transformation, realizes easily.

Drawings

FIG. 1 is a diagram of the virtual resistance strategy equivalent control structure of the present invention;

FIG. 2 is a block diagram of the present invention;

fig. 3 is the utility model discloses active power filter emulation filtering effect show based on virtual resistance strategy.

In the figure: 202. the circuit comprises a current transformer, 203, a rectifying nonlinear load, 204, a two-phase coordinate system conversion module, 205, a low-pass filter, 206, a three-phase coordinate system conversion module, 207, a PWM module, 209, an IGBT driving circuit, 210, a power unit, 211, a reactor, 213, a subtractor, 214, a PR controller module, 215 and an APF module.

Detailed Description

The present invention will be further explained with reference to the accompanying drawings.

As shown in fig. 1, for the virtual resistance strategy equivalent control structure diagram, ADSV (virtual circuit strategy) only needs to introduce one k ═ L in the LCL circuit₁/(C_fR_d) The proportional loop is simple and easy to implement.

Compared with a passive damping method, the active damping method does not need to introduce actual resistance, does not increase the power loss of the system, and improves the efficiency of the APF system. The principle of the virtual resistance method is as follows: the method realizes resonance suppression by replacing the function of an actual damping resistor through a control algorithm, and in terms of hardware, the method needs to add a group of sensors on a capacitance branch circuit to detect capacitance current.

Shown in fig. 1 is a virtual resistor-and-capacitor approach, the solid line portion is a control block diagram of the system without introducing a parallel virtual resistor,

the three components form an LCL module. Electric current

Into the PR controller, into the LCL module, and finally out, wherein the capacitor

Current of (2) is divided by a dotted line

The proportional element of (2) feeds back to the voltage setting.

As shown in fig. 2, which is a structural block diagram of the present invention, the present invention relates to an active power filter, which comprises a detection and control module, an IGBT driving circuit 209, a power unit 210 and an APF module 215, wherein the detection and control module comprises a two-coordinate transformation module 204, a low pass filter 205, a three-coordinate transformation module 206, a subtractor 213, a PR controller module 214 and a PWM module 207;

the output end of the two-term coordinate transformation module 204 is connected with the input end of a low-pass filter 205, the output end of the low-pass filter 205 is connected with the input end of a three-term coordinate transformation module, the output end of the three-term coordinate transformation module is connected with the input end of a subtracter 213, the output end of the subtracter 213 is connected with the input end of a PR controller module 214, the output end of the PR controller module 214 is connected with the input end of a PWM module 207, the output end of the PWM module 207 is connected with the input end of an IGBT driving circuit 209, the output end of the IGBT driving circuit 209 is connected with the input end of a power unit 210, the output end of the power.

The two-phase coordinate system transformation module 204 is configured to transform the three-phase load current into a two-phase load current in a two-phase coordinate system, that is, a d-q coordinate system, where the two-phase coordinate system rotates synchronously with a voltage vector in the circuit;

a low-pass filter 205, configured to filter out harmonic component currents of the d and q components in the two-phase load current output by the two-phase coordinate system transformation module 204, so as to obtain a fundamental current component;

a three-phase coordinate system transformation module 206, configured to transform the fundamental component current processed by the low-pass filter 205 into a fundamental component current of a three-phase load current in a three-phase a-B-C coordinate system;

the subtractor 213 is configured to subtract the fundamental component current output by the three-phase load current and the three-phase coordinate system transformation module 206 to obtain a harmonic current;

a PR controller module 214, the input end of which is connected with the output end of the subtracter 213, for subtracting the capacitance current fed back by the virtual resistor from the output of the PR controller inside the PR controller module to attenuate the resonance peak value of the APF; a PR controller inside the PR controller module 214 is used for tracking a sinusoidal signal with a specified frequency in the load current, that is, a harmonic current to be compensated to the power grid;

a PWM module 207 for generating a pulse width modulated signal for controlling the power unit 210 of the active power filter.

When the three-phase load current transformer works, the power grid supplies power to the rectifying nonlinear load 203, the current transformer 202 samples three-phase load currents ILa, ILb and ILc, and I is converted into I through the two-phase coordinate system conversion module 204_LThe three-phase load current is converted into a two-phase load current, the harmonic component of the two-phase load current is filtered by the low-pass filter 205 module 205 to obtain a fundamental component current, the two-phase load current is converted into a fundamental component current of the three-phase load current by the three-phase coordinate system conversion module 206, the fundamental current component of the three-phase load current ILa, ILb and ILc is removed by the subtractor 213 to obtain a three-phase harmonic current, and the output current of the APF module 215 is subtracted to be used as a given input of a PR controller in the PR controller module 214, and the PR controller is used for tracking a sinusoidal signal with a given frequency in the load current, namely, the. The PR controller module 214 has two functions, that is, it includes a PR controller, and subtracts the capacitance current fed back by the virtual resistor from the output of the PR controller to attenuate the resonance peak of the APF, and uses the obtained output signal as the given signal of the PWM generating module 207, the PWM generating module 207 obtains the modulation wave by using the PWM modulation technique, and uses the modulation wave as the input signal of the IGBT driving circuit 209, the control signal output by the IGBT driving circuit 209 is used to control the output of the power unit 210, and finally injects the specified compensation current to the power grid through the APF module 215 and the reactor 211 in sequence, so as to achieve the purpose of compensating the harmonic and reactive power of the power grid, improving the power quality, and enhancing the reliability and stability of the power grid.

As shown in fig. 3, which is a diagram of a simulation result of the system, in an embodiment of the present invention, a set of simulation data parameters is input into the simulation system, and the simulation parameters related to each device in fig. 1 are as follows: equivalent inductance L of grid_S0.1 mH; inverter side inductor L₁Is 2 mH; network side inductor L₂0.784 mH; filteringCapacitor C_f5 μ F. System simulation AC voltage U_SIs 380v,50 HZ; other simulation parameters also include: DC voltage measurement U_dc750V, and the switching frequency f is 10 kHZ; the load resistance R of the rectifier bridge is 4 omega;

as can be seen from fig. 3, the current distortion rate of the simulation network side of the active power filter based on the virtual resistance strategy is 1.82%, and the filtering effect is significant.

Claims

1. An active power filter comprising a detection and control module, a drive module, a power unit (210), and an APF module (215), wherein the detection and control module comprises:

the two-phase coordinate system transformation module (204) is used for transforming the three-phase load current into a two-phase load current under a two-phase coordinate system, namely a d-q coordinate system, wherein the two-phase coordinate system and a voltage vector in the circuit synchronously rotate;

the low-pass filter (205) is used for filtering harmonic component currents of d and q components in the two-phase load current output by the two-phase coordinate system transformation module (204) to obtain a fundamental current component;

a three-phase coordinate system transformation module (206) for transforming the fundamental component current processed by the low-pass filter (205) into the fundamental component current of the three-phase load current in the three-phase coordinate system;

the subtracter (213) is used for subtracting the fundamental component current output by the three-phase load current and the three-phase coordinate system transformation module (206) to obtain harmonic current;

a PR controller module (214) with an input end connected with the output end of the subtracter (213) and used for subtracting the capacitance current fed back by the virtual resistor from the output end of the PR controller inside the PR controller module to attenuate the resonance peak value of the APF; a PR controller internal to the PR controller module (214) for tracking a sinusoidal signal of a specified frequency in the load current;

the input end of the PWM module (207) is connected with the output end of the RP controller module, and the output end of the PWM module is connected with the input end of the power unit (210) through the driving module and used for generating a pulse width modulation signal of the power unit (210) for controlling the active power filter;

the output end of the power unit (210) is connected with the input end of the APF module (215), and the output end of the APF module (215) is connected with one bus of the power grid through the reactor (211).

2. An active power filter according to claim 1, characterized in that the driving module is an IGBT driving circuit (209).