阅读说明：本技术 基于逆变器侧电流反馈的直流有源滤波器谐振抑制方法 (DC active filter resonance suppression method based on inverter side current feedback ) 是由 窦文雷 周荔丹 黄琛 姚钢 于 2021-10-09 设计创作，主要内容包括：一种基于逆变器侧电流反馈的直流有源滤波器谐振抑制方法,通过建立直流有源滤波系统的等效电路进行系统谐振特性分析,根据系统谐振特性设计逆变器侧电流反馈有源阻尼的传递函数,即采用霍尔电流传感器对逆变器侧电流进行采样,获得采样电流后乘以逆变器侧电流反馈有源阻尼的传递函数,再与原电流环的输出以负反馈的形式叠加得到控制信号,再将控制信号经载波脉宽调制,得到PWM驱动信号控制开关管通断,从而完成有源阻尼过程,实现谐振抑制。本发明无需增加额外的传感器的同时减小了系统的体积,简化了硬件设计。(A direct current active filter resonance suppression method based on inverter side current feedback is characterized in that an equivalent circuit of a direct current active filter system is established to analyze system resonance characteristics, a transfer function of inverter side current feedback active damping is designed according to the system resonance characteristics, namely, a Hall current sensor is adopted to sample inverter side current, the sampled current is multiplied by the transfer function of the inverter side current feedback active damping, the sampled current and the output of an original current loop are superposed in a negative feedback mode to obtain a control signal, and the control signal is subjected to carrier pulse width modulation to obtain a PWM (pulse width modulation) driving signal to control the on-off of a switching tube, so that the active damping process is completed, and resonance suppression is realized. The invention reduces the volume of the system without adding additional sensors and simplifies the hardware design.)

1. A resonance suppression method of a direct current active filter system is characterized in that system resonance characteristic analysis is carried out by establishing an equivalent circuit of the direct current active filter system, and a transfer function of inverter side current feedback active damping is designed according to the system resonance characteristic to realize resonance suppression;

the active damping is specifically realized by: the method comprises the steps of sampling current at the side of an inverter by using a Hall current sensor, multiplying the sampled current by a transfer function of current feedback active damping at the side of the inverter after obtaining the sampled current, superposing the sampled current and the output of an original current loop in a negative feedback mode to obtain a control signal, and carrying out carrier pulse width modulation on the control signal to obtain a PWM (pulse width modulation) driving signal to control the on-off of a switching tube, thereby completing the active damping process.

2. The method of claim 1, wherein the dc active filter system comprises: direct current bus, two active full-bridge converters, direct current active filter and direct current load, wherein: the input side of the DAB converter is connected with the direct current bus, the output side of the DAB converter is connected with the direct current side of the direct current active filter, and the output side of the direct current active filter is filtered by the LC filter and then is connected with a load in parallel through the blocking capacitor.

3. The resonance suppression method of the dc active filter system according to claim 2, wherein the dc active filter is a diode midpoint clamped three-level topology, and specifically comprises: the active filter comprises eight switching tubes, two blocking capacitors and a second-order LC filter which is composed of an output filter inductor and an output filter capacitor and is used for filtering switching frequency harmonics in output current of the active filter.

4. The method of claim 1, wherein the system resonance characteristics include: resonant frequency of low frequency resonant peakAnd the resonant frequency of the high-frequency resonance peak is Both resonance peaks are suppressed by the transfer function of the active damping loop.

5. The method of claim 1, wherein the transfer function of the active damping isWherein: k_ADLGain factor, omega, for active damping₀Lower angular frequency, k, of the DC-APF passband₀Is a constant.

Technical Field

The invention relates to a technology in the field of direct current active filtering, in particular to a direct current active filter resonance suppression method based on inverter side current feedback active damping.

Background

The existing direct current active filter is connected to the grid through a DC blocking capacitor through an LC filter, and has two resonance peaks of low frequency and high frequency, so that oscillation is easy to occur, and instability of a system is caused. The traditional active damping method based on grid-connected current high-frequency component feedback can realize the suppression of a high-frequency resonance peak without additionally adding a sensor, but has no suppression effect on a low-frequency resonance peak, and if the resonant frequency of a system is slightly shifted after the active damping is introduced, the suppression of the high-frequency resonance peak by the method is also influenced; if the resonance frequency of the system is greatly deviated, the dynamic response and the stability of the system are influenced, so that the existing method has the contradiction between resonance suppression and system stability.

Disclosure of Invention

The invention provides a direct current active filter resonance suppression method based on inverter side current feedback, aiming at the problems of wide frequency domain resonance caused by an LC filter, a blocking capacitor and power grid impedance in the prior art and the contradiction between resonance suppression and system stability in the existing active damping method based on grid-connected current high-frequency component feedback.

The invention is realized by the following technical scheme:

the invention relates to a resonance suppression method of a direct current active filter system, which is characterized in that an equivalent circuit of the direct current active filter system is established to analyze the resonance characteristics of the system, and a transfer function of current feedback active damping at the side of an inverter is designed according to the resonance characteristics of the system to realize resonance suppression.

The active damping is specifically realized by: the method comprises the steps of sampling current at the side of an inverter by using a Hall current sensor, multiplying the sampled current by a transfer function of current feedback active damping at the side of the inverter after obtaining the sampled current, superposing the sampled current and the output of an original current loop in a negative feedback mode to obtain a control signal, and carrying out carrier pulse width modulation on the control signal to obtain a PWM (pulse width modulation) driving signal to control the on-off of a switching tube, thereby completing the active damping process.

The direct current active power filter system comprises: a direct current bus, a dual active full bridge (DAB) converter, a direct current active filter (DC-APF), and a direct current load, wherein: the input side of the DAB converter is connected with the direct current bus, the output side of the DAB converter is connected with the direct current side of the direct current active filter, and the output side of the direct current active filter is filtered by the LC filter and then is connected with a load in parallel through the blocking capacitor.

The dc active filter is a diode Neutral Point Clamped (NPC) three-level topology structure, and specifically includes: the active filter comprises eight switching tubes, two blocking capacitors and a second-order LC filter which is composed of an output filter inductor and an output filter capacitor and is used for filtering switching frequency harmonics in output current of the active filter.

The resonance characteristics of the system include: resonant frequency of low frequency resonant peakAnd the resonant frequency of the high-frequency resonance peak isBoth resonance peaks are suppressed by the transfer function of the active damping loop.

The transfer function of the active damping isWherein: k_ADLGain factor, omega, for active damping₀Lower angular frequency, k, of the DC-APF passband₀Is a constant.

Technical effects

The invention analyzes the resonance characteristic of the system, andbased on the transfer function G of the designed active damping ring_{A L}(s), the problem of system wide frequency domain oscillation possibly caused by the existence of two low-frequency and high-frequency resonance peaks in the direct current active filter is integrally solved, so that the system can suppress resonance on a software layer without adding an additional sensor, the hardware design of the system is simplified, and the hardware cost of the system is reduced; meanwhile, the resonance frequency of the system is not greatly deviated after the method is introduced, so that the method has small influence on the amplitude-frequency and phase-frequency characteristics of the system in the pass band of the DC-APF, and the original compensation effect of the DC-APF can be well maintained.

Drawings

FIG. 1 is a schematic diagram of an embodiment of an active filter;

FIG. 2 is a schematic diagram of an equivalent model of FIG. 1 in the s-domain;

FIG. 3 is a frequency domain plot of the equivalent virtual impedance of the resonance suppression method of the embodiment;

fig. 4 is a bode diagram of the system before and after the active damping method according to the present invention is introduced into the embodiment.

Detailed Description

As shown in fig. 1, the dc active filter system according to this embodiment includes: direct current bus, direct current load, direct current active filter, DAB converter and controller, wherein: the input end and the output end of the DAB converter are respectively connected with the direct current bus and the direct current side of the active filter to provide stable direct current side voltage for the active filter, and the output end of the direct current active filter is adopted to pass through an inductor L_fAnd a capacitor C_fForm a second-order LC filter and a DC blocking capacitor C_iThen the current is connected in parallel with the DC load to be compensated, thereby improving the current flowing through the load and further improving the voltage on the load.

The embodiment relates to a resonance suppression method based on the direct current active filter system, which is characterized in that a Hall current sensor is used for sampling the current on a direct current bus, and all harmonic components i in the system are obtained through low-pass filtering_d(ii) a And then a Hall current sensor is used for sampling the side inductive current i of the inverter_cAs a negative feedback signal.

As shown in fig. 2(a), the reference current signal i obtained after low-pass filtering is obtained_dAnd inverter side current i_cPerforming negative feedback on the difference, and sending the error signal to the current tracking control module G_i(s) obtaining an output signal u_i(ii) a At the same time i_cAnd active damping transfer function G_ADL(s) multiplying to obtain an output signal u_a. Will u_iAnd u_aAfter subtracting, sending the data to a carrier pulse width modulation module (K in the figure)_pwmModule), a control signal for controlling the on and off of the switch tube of the active filter can be obtained, and the output voltage of the active filter is u₁Then passes through LC filter and DC blocking capacitor C_i1And C_i2And an inductance L_SThen obtaining the final compensating current i_c(s). Damping the active G_ADLThe feedback point of(s) is moved to 1/(sL)_f) I.e. an equivalent block diagram as shown in fig. 2(b), it can be seen that the resonance suppression method based on the inverter-side current feedback is essentially based on the filter inductance L_fOn top of an impedance Z_eqL(s). Equivalent virtual impedance Z_eqL(s) and active damping transfer function G_ADLThe relation of(s) is G_ADL(s)＝Z_eqL(s)/K_pwm。

As shown in fig. 3, the frequency domain characteristic diagram of the equivalent virtual impedance is shown. Equivalent resistance R_eqL(j ω) decreases from a maximum value to 0 and then starts increasing; and equivalent reactance X_eqL(j ω) is capacitive at low frequencies, R_eqLThe time when (j ω) ═ 0 also becomes 0, and then becomes perceptual. Within the passband of the DC-APF, the equivalent resistance is kept to be a small value all the time, so that the influence on the gain of the system is small; the equivalent reactance remains inductive at all times and thus facilitates the cancellation of ripple in the output current. At the low-frequency harmonic peak and the high-frequency harmonic peak, the system keeps larger resistance, so that the harmonic peak is suppressed.

As shown in fig. 4, is a bode plot of the system before and after the introduction of the present method. Therefore, after the active damping is added, the two damping peaks are inhibited, in the passband of the DC-APF, the amplitude-frequency characteristic of the system after the active damping is almost completely consistent with that of the original system, and the phase-frequency characteristic has smaller offset, so that the compensation effect of the DC-APF in the passband before and after the active damping is added is ensured. It can be seen from the amplification at the high frequency resonance peak that the resonance frequency after the active damping is added has only a small shift, which is beneficial to the dynamic response of the stability of the system.

In this embodiment, the direct current active filter system is built under the environment of MATLAB/Simulink, and when the system resonates, if a resonance suppression strategy is not added, the total harmonic distortion of the load current reaches 0.19%; if a traditional resonance suppression strategy based on grid-connected current high-frequency component feedback is added, the system cannot suppress a low-frequency resonance peak, but can suppress a high-frequency resonance peak, and at the moment, the total harmonic distortion of the load current becomes 0.16%; if the resonance suppression strategy based on inverter side current feedback provided by the embodiment is added, low-frequency and high-frequency resonance peaks are effectively suppressed, and the total harmonic distortion of the load current is reduced to 0.02%.

In conclusion, the inverter-side current feedback-based active damping method provided by the invention can effectively inhibit low-frequency and high-frequency resonance when the resonance frequency is deviated slightly, and does not need an additional sensor. The equivalent resistance of the inverter side current feedback active damping method keeps low resistance in a pass band of a DC-APF, and is high resistance at a resonance peak, so that the stability and the dynamic performance of an original system are ensured on the basis of resonance inhibition, and the resonance inhibition of a wide frequency domain is realized.

The foregoing embodiments may be modified in many different ways by those skilled in the art without departing from the spirit and scope of the invention, which is defined by the appended claims and all changes that come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.