CN102570476B - Repetitive-control-based method for controlling compensation current of DSTATCOM (Distribution Static Synchronous Compensator) - Google Patents

Abstract

The invention discloses a DSTATCOM compensation current control method based on repetitive control, including: (1) collecting grid voltage, load current and compensation current; (2) extracting current instructions from the load current; Repeat control and PI control, and then output voltage command to DSTATCOM. The present invention enables DSTATCOM to realize static error-free tracking of low-order harmonics including the fundamental wave, improves the compensation accuracy of DSTATCOM, increases the compensation bandwidth of DSTATCOM; improves the compensation ability and precision of DSTATCOM under unbalanced load conditions, and enables DSTATCOM to have Harmonic compensation and suppression capabilities reduce the use of passive filters on the outlet side of DSTATCOM, and improve the harmonic performance of DSTATCOM compensation current, reduce output harmonics, and reduce pollution to the grid.

Description

A DSTATCOM compensation current control method based on repetitive control

technical field

The invention belongs to the technical field of reactive power compensation, and in particular relates to a compensation current control method based on repetitive control DSTATCOM.

Background technique

In recent years, with the rapid development of industrial technology, the degree of social electrification has been continuously improved. In the power grid, especially in the distribution network, various large-capacity induction motors, special motors and other reactive loads, electric arc furnaces, large rolling mills, electric locomotives and other various Impulsive, fluctuating unbalanced loads, increasing capacity, power electronic devices and complete sets of devices and other nonlinear loads are widely used. The operation and use of these devices not only consume a lot of reactive power, but also generate a lot of harmonics, which seriously pollute the power grid and reduce the power grid The use efficiency affects the quality and reliability of power supply, causing various complex precision instruments and electrical equipment sensitive to power quality to fail to work normally. In response to the above quality problems, a large number of harmonic suppression and reactive power compensation equipment aimed at improving the power quality of distribution networks have emerged. Distribution network static synchronous compensators (DSTATCOM) are used as transmission line static synchronous compensators (STATCOM) in power distribution The new application in the grid can continuously and quickly adjust the size and nature of reactive power injected into the grid, compensate load reactive power and harmonics, stabilize the voltage of the public access node (PCC), and improve the power quality of the distribution network; Compared with static var compensator (SVC), DSTATCOM has attracted wide attention due to its fast reactive power adjustment capability, wider operating range, good current output performance, smaller device size and cost, etc. In addition, the cascaded structure The DSTATCOM can easily achieve high voltage and large capacity through simple series connection of power modules, which is very suitable for the application of medium voltage distribution network level (6kV-10kV).

The control strategy of the output current of the DSTATCOM AC side is a core technology related to the performance of the equipment. Traditional control methods such as current hysteresis control, PI control, deadbeat control, etc., cannot meet the continuously improving power quality requirements of users and the relevant national regulations. The industry has strict standards for the grid connection of power equipment, and in the harsh and complex grid environment of the power distribution system, the efficient, reliable and normal operation of the device itself cannot be guaranteed. Through the search of the existing technical literature, it is found that the DSTATCOM high-performance current control strategy has been widely studied and applied for the purpose of improving the output current performance and quality of the device, reducing the pollution to the power grid, and improving the reliability of the device.

Tang Jie and Luo An et al. proposed a fuzzy adaptive The PI control strategy improves the flexibility and robustness of device control, and has fast dynamic response and small overshoot when the load fluctuates; however, this method belongs to open-loop control for the output current of the device, and cannot guarantee that the output current of DSTATCOM is stable and without difference Tracking instructions, for unbalanced loads, harmonic loads, grid voltage waveform distortion has no ability to control.

Tu Chunming, Li Hui and others analyzed the impact of grid voltage asymmetry on D-STATCOM and its suppression (Journal of Electrotechnical Society, 2009, (10): 114-121) which analyzed the influence of grid voltage asymmetry on D-STATCOM. Due to the influence of voltage output characteristics, a method to suppress the third harmonic output of the device by changing the switching function is proposed to improve the output characteristics of the device; however, the structure of the controller is complex, and the control performance is affected by the negative sequence detection of the grid voltage. This method does not solve the problem of grid voltage. The problem of ensuring the output performance of the device and the accuracy of harmonic load tracking during distortion.

Tan Tianyuan, Jiang Qirong and others proposed a set of triangular wave comparison based on the article titled "Control method of three-level DSTATCOM device based on current tracking control" (Power System Automation, 2007, (4): 61-65). The current direct tracking strategy of the three-level converter can reduce the command tracking error and the fluctuation of the switching frequency of the switching device to a certain extent, but this strategy makes the switching frequency of the device low, the output filter design is large, and the steady-state error cannot be eliminated.

Wu Chunhui, Jiang Qirong and others proposed a switch based on selective harmonic elimination in the article titled "An Optimization Method for Three-level Specific Harmonic Elimination Pulse Width Modulation" (Power Electronics Technology, 2005, (5)) The angle optimization calculation method enables the inverter output to obtain better harmonic characteristics at a lower switching frequency. However, under the influence of large-capacity impact loads in the distribution network, the voltage of the access node has large fluctuations. Due to the influence of detection error and delay, the response speed is slow, and the specific harmonic elimination bandwidth is limited, it is impossible to track the harmonic load without static error, and the work performance is poor under the grid imbalance and distortion.

In addition, some DSTATCOM nonlinear control based on advanced control theory, adaptive deadbeat control, etc. do not have high requirements on the accuracy of the system model, and can adaptively change the system parameters to obtain higher compensation accuracy, but due to the controller design Complexity, poor real-time performance, lagging response, and limited switching frequency make it difficult to be widely used in engineering. Therefore, none of the existing DSTATCOM current control strategies can take into account good harmonic output performance, precise steady-state control accuracy, superior dynamics, and strong adaptability to load and grid voltage disturbances.

Contents of the invention

In view of the above-mentioned technical defects in the prior art, the present invention provides a DSTATCOM compensation current control method based on repetitive control, which can significantly improve the reactive power compensation accuracy and harmonic suppression capability of DSTATCOM.

A compensation current control method based on repetitively controlled DSTATCOM, comprising the steps of:

(1) Collect the grid voltage signal, load current signal and compensation current signal of DSTATCOM in the current sampling period;

(2) Extract the load current signal according to the phase of the grid voltage signal to obtain the active shaft current command and the reactive shaft current command; perform dq transformation on the compensation current signal according to the phase of the grid voltage signal (synchronous Rotational coordinate transformation) to obtain the active axis compensation current component and the reactive axis compensation current component;

(3) The active shaft current command and the active shaft compensation current component are used as input, and the active shaft current command is subtracted from the active shaft compensation current component to obtain the current error signal; the internal model update is performed on the current error signal to obtain the internal model update current error Signal; Compensate the internal model update current error signal to obtain a current error correction signal;

(4) Superimpose the current error signal on the current error correction signal to obtain a corrected current error signal; perform PI (proportional integral) adjustment on the corrected current error signal to obtain a voltage command signal; delay the voltage command signal , get the delayed voltage command signal of the active shaft;

(5) Let the reactive shaft current command and the reactive shaft compensation current component be used as input, and according to the signal processing methods in steps (3) and (4), obtain the delayed voltage command signal of the reactive shaft; delay the active shaft After the voltage command signal and the voltage command signal after the delay of the reactive shaft are subjected to dq inverse transformation (synchronous rotation coordinate inverse transformation), they are sent to DSTATCOM to control the compensation current of DSTATCOM.

In the step (2), the process of extracting the instruction of the load current signal is: performing dq transformation on the load current signal according to the phase of the grid voltage signal to obtain the d-axis load current component and the q-axis load current component. The q-axis load current component is the reactive axis current command; the high-pass filter is performed on the d-axis load current component to obtain the active shaft current command.

The active shaft current command is the load harmonic active current; the reactive shaft current command includes the load fundamental wave reactive current and the load harmonic reactive current.

In the step (3), the internal model of the current error signal is updated according to the following equation;

U(i)=E(i)+QE(i-n)

Among them: U(i) is the internal model update current error value of the i-th sampling point in the internal model update current error signal, E(i) is the current error value of the i-th sampling point in the current error signal, and E(i-n) is the current The current error value of the i-nth sampling point in the error signal, Q is the attenuation coefficient, and n is the number of sampling points in a fundamental cycle.

In the step (3), the internal model update current error signal is compensated according to the following equation;

Y(i)=f(z)U(i-n+k)

Among them: Y(i) is the current error correction value of the i-th sampling point in the current error correction signal, U(i-n+k) is the internal model update of the i-n+k sampling point in the internal model update current error signal Current error value, f(z) is the second-order low-pass filter function, n is the number of sampling points of a fundamental wave cycle, and k is the number of compensation points.

The beneficial technical effect of the present invention is:

(1) Enable DSTATCOM to realize static error-free tracking of low-order harmonics including the fundamental wave, improve the compensation accuracy of DSTATCOM, and increase the compensation bandwidth of DSTATCOM.

(2) Make DSTATCOM have harmonic compensation and suppression capabilities, reduce the use of passive filters on the outlet side of DSTATCOM, and improve the harmonic performance of DSTATCOM compensation current, reduce output harmonics, and reduce pollution to the grid. It reduces the heating of DSTATCOM's own filter reactor and DC side support capacitor and other components, reduces the design capacity, improves the capacity utilization rate, and saves the cost and floor space of DSTATCOM.

(3) The compensation ability and accuracy of DSTATCOM under the condition of unbalanced load are improved, so that DSTATCOM can compensate single-phase or unbalanced load, and the application range of DSTATCOM is broadened.

(4) The harmonic performance of DSTATCOM compensation current in the case of grid voltage distortion is improved, and the stability of DSTATCOM is improved.

(5) On the premise of improving the steady-state precision, the control method of the present invention has superior dynamic performance.

(6) The control method of the present invention is simple in design and can be fully digitally realized by a piece of DSP without increasing device cost, with high integration and good reliability.

Description of drawings

Fig. 1 is a schematic flow chart of the steps of the method of the present invention.

Figure 2 is a schematic diagram of the use status of DSTATCOM.

FIG. 3 is a schematic flow chart of command extraction in the present invention.

Fig. 4 is a flow diagram of repetitive control and PI control in the present invention.

FIG. 5 is a schematic diagram of frequency characteristics of a closed-loop transfer function of a traditional PI regulation system.

FIG. 6 is a schematic diagram of the frequency characteristics of the closed-loop transfer function of the PI regulation system after repeated control compensation in the present invention.

Fig. 7(a) is a waveform diagram of grid voltage and compensation current when inductive reactive power is injected into the grid.

Figure 7(b) is the spectrum diagram of the compensation current when inductive reactive power is injected into the grid.

Fig. 8(a) is a waveform diagram of grid voltage and compensation current when capacitive reactive power is injected into the grid.

Figure 8(b) is the spectrum diagram of the compensation current when capacitive reactive power is injected into the grid.

Fig. 9(a) is a waveform diagram of switching grid voltage and compensation current from inductive reactive power to capacitive reactive power.

Fig. 9(b) is a waveform diagram of switching grid voltage and compensation current from capacitive reactive power to inductive reactive power.

Fig. 10(a) is a waveform diagram of grid voltage and grid current under uncompensated conditions.

Figure 10(b) is the spectrum diagram of the grid current without compensation.

Fig. 11(a) is a waveform diagram of grid voltage and grid current under the condition of traditional PI control compensation.

Fig. 11(b) is the spectrum diagram of grid current under the condition of traditional PI control compensation.

Fig. 12(a) is a waveform diagram of grid voltage and grid current under the condition of control and compensation of the present invention.

Fig. 12(b) is a frequency spectrum diagram of the grid current under the control and compensation condition of the present invention.

Detailed ways

In order to describe the present invention more specifically, the compensation current control method of the present invention will be described in detail below in conjunction with the accompanying drawings and specific embodiments.

As shown in Figure 1, a DSTATCOM compensation current control method based on repetitive control includes the following steps:

(1) Collect grid voltage, load current and compensation current.

Gather the grid voltage signal, the load current signal and the compensation current signal of DSTATCOM in the current sampling period; Fig. 2 is the usage status diagram of DSTATCOM in the present embodiment; Wherein, U is the grid voltage signal, I _L is the load current signal, and I _C is A compensation current signal; in this embodiment, the sampling period is 100 μs.

(2) Extract the current command from the load current.

As shown in Figure 3, the phase of the grid voltage signal is extracted by using the phase-locked loop, and the load current signal is transformed by dq according to the phase of the grid voltage signal to obtain the d-axis load current component I _Ld and the q-axis load current component I _Lq , q The shaft load current component I _Lq is the reactive shaft current command I _refq ; the d-axis load current component I _Ld is high-pass filtered to obtain the active shaft current command I _refd .

Wherein, the active shaft current command I _refd is the load harmonic active current; the reactive shaft current command I _refq includes the load fundamental wave reactive current and the load harmonic reactive current.

According to the symmetrical component method, any form of three-phase load current can be expressed as the superposition form of the fundamental positive sequence, negative sequence components and harmonic components shown in the following formula. Usually, the zero sequence component is effectively suppressed by the delta connection of the distribution network transformer , can be ignored.

If the phase of the three-phase grid voltage obtained through the phase-locked loop is ωt, then through the following coordinate transformation matrix,

${\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; abc</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; dq</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; 3</span>}}\left[\begin{array}{ccc}\mathrm{<span\; class="notranslate">\; sin</span>}\mathrm{<span\; class="notranslate">\; \&omega;t</span>}& \mathrm{<span\; class="notranslate">\; sin</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&omega;t</span>}<span\; class="notranslate">\; -</span>\frac{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}}{\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; )</span>& \mathrm{<span\; class="notranslate">\; sin</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&omega;t</span>}<span\; class="notranslate">\; +</span>\frac{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}}{\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; )</span>\\ \mathrm{<span\; class="notranslate">\; cos</span>}\mathrm{<span\; class="notranslate">\; \&omega;t</span>}& \mathrm{<span\; class="notranslate">\; cos</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&omega;t</span>}<span\; class="notranslate">\; -</span>\frac{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}}{\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; )</span>& \mathrm{<span\; class="notranslate">\; cos</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&omega;t</span>}<span\; class="notranslate">\; +</span>\frac{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}}{\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; )</span>\end{array}\right]$

Transform the above current expression into the dq synchronous rotating coordinate system to get:

Through coordinate transformation, the three-phase fundamental AC of load current is decomposed into DC active and reactive components on the d-axis and q-axis, and the load unbalanced component is converted into the second harmonic component. The load harmonic component is based on the harmonic positive and negative sequence Converted to the harmonic component of the original harmonic order plus or minus one.

Similarly, the dq transformation is performed on the compensation current signal I _C according to the phase of the grid voltage signal to obtain the active axis compensation current component I _Cd and the reactive axis compensation current component I _Cq .

(3) Carry out repetitive control and PI control according to the current command, and then output the voltage command to DSTATCOM.

As shown in Figure 4, the active shaft current command I _refd and the active shaft compensation current component I _Cd are used as input, and the active shaft current command is subtracted from the active shaft compensation current component to obtain the current error signal; the current error signal is calculated according to the following equation The internal model is updated to obtain the internal model update current error signal;

U(i)=E(i)+QE(i-n)

Among them: U(i) is the internal model update current error value of the i-th sampling point in the internal model update current error signal, E(i) is the current error value of the i-th sampling point in the current error signal, and E(i-n) is the current The current error value of the i-nth sampling point in the error signal, Q is the attenuation coefficient, and n is the number of sampling points in one fundamental wave cycle; in this embodiment, Q=0.98, n=200.

Compensate the internal model update current error signal according to the following equation to obtain the current error correction signal;

Y(i)=f(z)U(i-n+k)

$\mathrm{<span\; class="notranslate">\; f</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; z</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; A</span>}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; Bz</span>}}^{<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; Az</span>}}^{<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 2</span>}}}{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; Cz</span>}}^{<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; Z</span>}}^{<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 2</span>}}}$

Among them: Y(i) is the current error correction value of the i-th sampling point in the current error correction signal, U(i-n+k) is the internal model update of the i-n+k sampling point in the internal model update current error signal Current error value, f (z) is a second-order low-pass filter function, and k is the number of compensation points; in the present embodiment, k=4; the damping ratio of the second-order low-pass filter is 0.67, and the cut-off frequency is 2.3KHz, so A =0.2151, B=0.4301, C=0.359, D=0.2193.

Superimpose the current error signal on the current error correction signal to obtain a corrected current error signal; perform PI adjustment on the corrected current error signal according to the following equation to obtain a voltage command signal;

P(i)=g(z)W(i)

$\mathrm{<span\; class="notranslate">\; g</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; z</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; E.</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; Fz</span>}}^{<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}}{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; z</span>}}^{<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}}$

Among them: P(i) is the voltage value of the i-th sampling point in the voltage command signal, W(i) is the current error value of the i-th sampling point in the corrected current error signal, and g(z) is the PI adjustment function; In an embodiment, E=4.071, F=4.065.

Delay the voltage command signal (delay for one sampling period) to obtain the delayed voltage command signal of the active shaft.

In the same way, let the reactive shaft current command and the reactive shaft compensation current component be used as input to obtain the delayed voltage command signal of the reactive shaft; the delayed voltage command signal of the active shaft and the delayed voltage command of the reactive shaft The signal is sent to DSTATCOM after dq inverse conversion to control the compensation current of DSTATCOM.

The design of the compensator takes the inner-loop closed-loop transfer function as the controlled object to perform amplitude and phase compensation. The frequency characteristic of the typical inner-loop closed-loop transfer function after traditional PI adjustment is shown in Figure 5; it can be seen that after compensation, there is a large phase lag in the middle and low frequency bands within 1kHz of the frequency characteristic, which seriously affects the harmonic tracking of DSTATCOM ability and output harmonic performance, and there is a large phase shock in the mid-frequency band, and the amplitude attenuation is small, which is not conducive to the stability of the system.

However, the frequency characteristics of the inner-loop closed-loop transfer function after compensation and PI adjustment in this embodiment are shown in Figure 6; it can be seen that the control after compensation achieves zero amplitude attenuation and zero phase shift in the middle and low frequency bands, and improves the compensation accuracy of DSTATCOM. At the same time, the unstable frequency point of the phase shock shifts with the high frequency, and the amplitude attenuation increases significantly, which ensures the stability of DSTATCOM.

In order to further verify the beneficial effects of the inventive method, the DSTATCOM of a three-phase star-connected H-bridge cascaded structure is incorporated into a three-phase grid whose line voltage effective value is 1316V; the power property defines the positive direction with DSTATCOM absorbing reactive power, Then the nature of DSTATCOM injecting reactive power into the grid is opposite to that of DSTATCOM absorbing reactive power.

According to this embodiment, the inductive and capacitive effective values are respectively given as 56.58A reactive current command, so that DSTATCOM injects a given reactive power into the grid, records the C-phase grid voltage U _s and the device output current _Ic through an oscilloscope, and uses Wavestar software analyzes the compensation current of DSTATCOM, and equivalently verifies the performance of reactive power compensation. The experimental results are shown in Figure 7 and Figure 8. Among them, the output current tracking error in Figure 7 is 1.03%, and the total harmonic content (THD) is 0.58%; the output current tracking error in Figure 8 is 0.71%, and the total harmonic content (THD) is 0.96%.

Experimental results show that regardless of whether the device outputs inductive reactive power or capacitive reactive power, this embodiment has high command tracking accuracy and output current harmonic performance.

To further verify the dynamic performance of this embodiment, the reactive current commands injected by DSTATCOM into the grid are switched from RMS inductive 42.43A to capacitive 56.58A and capacitive 42.43A to inductive 56.58A, and the dynamic process of switching is captured by an oscilloscope. Record the phase C grid voltage U _s and the device output current I _c , and the experimental results are shown in Figure 9. It can be seen that due to the introduction of current command feedforward, this embodiment inherits the superior dynamic performance of traditional single PI control, and has a fast response speed. When reactive power commands of different natures are switched within a large range, the control module responds quickly within 1ms , the compensation current smoothly transitions from one steady state to another.

Under the control of PI and PI+REP, the harmonic compensation capability of DSTATCOM is compared and verified. The harmonic load is a three-phase half-bridge uncontrolled rectification pure resistance circuit, and the load resistance is nominally 42.5Ω. This implementation method is used to collect the load current and extract the harmonic Wave compensation instruction to perform load compensation. Record C-phase grid voltage U _s and grid current I _s with an oscilloscope, and use wavestar software to analyze the waveform. The results are shown in Table 1 and Figures 10, 11 and 12.

Table 1

It can be seen that compared with single PI compensation, the sine degree of grid current after PI+REP compensation in this embodiment is significantly improved, and the FFT data analysis results show that the harmonic content of grid current under PI+REP compensation is significantly lower than With single PI compensation, the total harmonic content (THD) of grid current is reduced by 94.8% compared with that before compensation, the residual harmonic content of grid current is less than 1.4%, and the total harmonic suppression rate is 60% higher than that of single PI control. The harmonic suppression rate is above 80%, which fully proves the harmonic suppression ability of PI plus repetition control strategy.

Claims (4)

1. the Compensating Current Control Method of the DSTATCOM based on repeating to control, comprise the steps:

(1) gather the compensating current signal of mains voltage signal, load current signal and the DSTATCOM in current sampling period;

(2) according to the phase place of mains voltage signal, described load current signal is carried out to instruction fetch, obtain meritorious shaft current instruction and idle shaft current instruction; According to the phase place of mains voltage signal, described compensating current signal is carried out to the dq conversion, obtain meritorious axle offset current component and idle axle offset current component;

(3) the meritorious shaft current instruction of order and meritorious axle offset current component, as input, make meritorious shaft current instruction deduct meritorious axle offset current component, obtain current error signal; Current error signal is carried out to the internal mold renewal, obtain internal mold and upgrade current error signal; Internal mold is upgraded to current error signal and compensate, obtain the current error corrected signal;

(4) make described current error signal superimposed current error correction signal, obtain revised current error signal; Revised current error signal is carried out to the PI adjusting, obtain voltage command signal; Voltage command signal is carried out to time delay, obtain the voltage command signal after meritorious axle time delay;

(5) make idle shaft current instruction and idle axle offset current component as input, according to the signal processing method of step (3) and (4), obtain the voltage command signal after idle axle time delay; Voltage command signal after meritorious axle time delay and the voltage command signal after idle axle time delay are carried out being delivered to DSTATCOM after the dq inverse transformation, to control the offset current of DSTATCOM.

2. the Compensating Current Control Method of the DSTATCOM based on repeating to control according to claim 1, it is characterized in that: in described step (2), the process of load current signal being carried out to instruction fetch is: according to the phase place of mains voltage signal, load current signal is carried out to the dq conversion, obtain d axle load current component and q axle load current component, described q axle load current component is idle shaft current instruction; Described d axle load current component is carried out to high-pass filtering, obtain meritorious shaft current instruction.

3. the Compensating Current Control Method of the DSTATCOM based on repeating to control according to claim 1, is characterized in that: in described step (3), according to following equation, current error signal is carried out to the internal mold renewal;

U(i)=E(i)+QE(i-n)

Wherein: U (i) upgrades the current error value for the internal mold that internal mold upgrades i sampled point in current error signal, the current error value that E (i) is i sampled point in current error signal, the current error value that E (i-n) is i-n sampled point in current error signal, Q is attenuation coefficient, the sampling number that n is a primitive period.

4. the Compensating Current Control Method of the DSTATCOM based on repeating to control according to claim 1, is characterized in that: in described step (3), according to following equation, internal mold is upgraded to current error signal and compensate;

Y(i)=f(z)U(i-n+k)

Wherein: the current error correction value that Y (i) is i sampled point in the current error corrected signal, U (i-n+k) upgrades the current error value for the internal mold that internal mold upgrades i-n+k sampled point in current error signal, f (z) is the second-order low-pass filter function, the sampling number that n is a primitive period, k is compensation points.

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