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

Abstract

The invention discloses a repetitive-control-based method for controlling a compensation current of a DSTATCOM (Distribution Static Synchronous Compensator). The method comprises the following steps of: (1) acquiring a grid voltage, a load current and the compensation current; (2) extracting current commands from the load current; and (3) carrying out repetitive control and PI (Proportional-Integral) control according to the current commands, and then, outputting voltage commands to the DSTATCOM. According to the repetitive-control-based method for controlling the compensation current of the DSTATCOM, the no-static-error tracking of the low-order harmonics, comprising fundamental harmonics, of the DSTATCOM can be achieved, the compensation accuracy of the DSTATCOM is improved, the compensation bandwidth of the DSTATCOM is increased, and the compensation capability and accuracy of the DSTATCOM with unbalanced loads are improved, so that the DSTATCOM can have harmonic compensation and suppression capabilities, the use of passive filters at the outlet side of the DSTATCOM is reduced, the harmonic performance of the compensation current of the DSTATCOM is improved, the harmonic output is reduced, and the pollution to a power grid is reduced.

Description

The Compensating Current Control Method of a kind of DSTATCOM based on repeating to control

Technical field

The invention belongs to the reactive power compensation technology field, be specifically related to the Compensating Current Control Method of a kind of DSTATCOM based on repeating to control.

Background technology

In recent years along with the develop rapidly of industrial technology, society's electrifing degree improves constantly, especially various large capacity induction motors in power distribution network in electrical network, the reactive loads such as specific type of electric machine, arc furnace, heavy (merchant) mill, the various impacts such as electric locomotive, the fluctuation unbalanced load, capacity constantly increases, the nonlinear load such as power electronic device and the complete sets of equipment is used widely, the operation of these devices is used not only consumption idle in a large number, and produce a large amount of harmonic waves, the severe contamination electrical network, reduce the electrical network service efficiency, affect power supply quality and reliability, cause various complex precise instruments and can't work to the power consumption equipment of quality of power supply sensitivity.For above-mentioned quality problems, being intended to improve harmonic wave inhibition and the reactive-load compensation equipment that distribution network electric energy quality is purpose emerges in multitude, Distribution Static Compensator (DSTATCOM) is as the new application of transmission line STATCOM (STATCOM) in power distribution network, can be by idle size and character continuous, that fast adjuster injects to electrical network, compensating load is idle and harmonic wave, stablize public access node (PCC) voltage, improve distribution network electric energy quality; With traditional Static Var Compensator (SVC), compare, DSTATCOM is with its fast reactive regulating power, wider range of operation, good electric current output performance, the advantages such as less device volume and cost get the attention, the DSTATCOM of cascade structure, by the simple series connection of power model, easily realizes high-voltage large-capacity in addition, is applicable to very much the application of medium-voltage distribution network level (6kV-10kV).

The control strategy of DSTATCOM AC output current, it is a core technology that concerns equipment performance, traditional control method is as Hysteresis Current control, PI control, dead beat control etc., can't meet quality of power supply demand and the national relevant industries strict standard grid-connected to power equipment that the user improves constantly, and in distribution system in severe complicated power grid environment, install self efficient, reliable, normal work and also can't be guaranteed.Retrieval by the prior art document is found, to improve device output current Performance and quality, reduces the pollution to electrical network, and improving device reliability is that purpose DSTATCOM high-performance electric flow control policy is widely studied and applied.

The people such as Tang Jie and Luo An is " the fuzzy self-adaption PI control strategy of distribution static synchronous compensator " (electrotechnics journal at title, 2008, (2): proposed a kind of fuzzy self-adaption PI control strategy in article 120-126), flexibility and robustness that device is controlled have been improved, when the fluctuation of load, dynamic response is fast, and overshoot is little; But the method belongs to open loop for the device output current to be controlled, can't guarantee DSTATCOM output current stable state indifference ground trace command, for unbalanced load, harmonic wave load, the grid voltage waveform distortion does not have control ability.

The people such as Tu Chunming and Li Hui is " the asymmetric impact analysis to D-STATCOM of line voltage and inhibition " (electrotechnics journal at title, 2009, (10): analyzed the asymmetric impact on the DSTATCOM voltage output characteristics of line voltage in article 114-121), proposed, by changing 3 subharmonic of switch function restraining device output, to improve the method for device output characteristic; But the controller architecture complexity, control performance is detected by the line voltage negative phase-sequence to be affected, the problem of assurance device output performance and harmonic wave load tracking precision when the method does not solve the line voltage distortion.

The people such as Tan Tianyuan and Jiang Qirong is " control methods of the three level DSTATCOM devices of controlling based on current tracking " (Automation of Electric Systems at title, 2007, (4): proposed a set of direct tracking strategy of three-level current transformer electric current based on triangle wave in article 61-65), to a certain degree reduced the fluctuation of instruction trace error and switching device switching frequency, but this strategy makes the device switching frequency low, the output filter design is larger, and steady-state error can't be eliminated.

The people such as Wu Chunhui and Jiang Qirong is " a kind of optimization methods of three level selective harmonic elimination pulse-width modulations " (power electronic technology at title, 2005, (5) a kind of switch angle optimized calculation method based on the selectivity harmonic wave eliminating is proposed in article), make inverter output than obtaining harmonic characterisitic preferably under low switching frequency, but the method is subject under large capacity impact load etc. affects in power distribution network, there is larger fluctuation in access node voltage, due to the impact that detects error and time delay, response speed is slow, and particular harmonic is eliminated limited bandwidth, can't floating follow the tracks of harmonic load, and the lower service behaviour of unbalanced power supply and distortion is poor.

DSTATCOM nonlinear Control based on advanced control theory more in addition, self adaptation dead beat control etc. do not have too high requirement to the model exactness of system, can self adaptation change system parameters, obtain higher compensation precision, but, because the controller design is complicated, real-time is poor, response lag, the switching frequency finiteness problem is difficult to extensive use in engineering.Therefore, existing DSTATCOM Current Control Strategy all can't be taken into account good harmonic wave performance, accurate steady state controling precision, superior dynamic and stronger load, grid disturbances adaptability.

Summary of the invention

For the existing above-mentioned technological deficiency of prior art, the invention provides the Compensating Current Control Method of a kind of DSTATCOM based on repeating to control, can significantly improve reactive power compensation precision and the harmonic inhibition capability of DSTATCOM.

The Compensating Current Control Method of a kind of 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 dq conversion (synchronously rotating reference frame 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(proportional integral) regulate, 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 and the voltage command signal after idle axle time delay after meritorious axle time delay are carried out being delivered to DSTATCOM after dq inverse transformation (synchronously rotating reference frame inverse transformation), to control the offset current of DSTATCOM.

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.

Described meritorious shaft current instruction is load harmonic wave active current; Described idle shaft current instruction comprises load fundamental reactive current and load harmonic wave reactive current.

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.

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.

Useful technique effect of the present invention is:

(1) make DSTATCOM realize that the floating comprise the first-harmonic low-order harmonic follows the tracks of, improved the compensation precision of DSTATCOM, increased the compensation bandwidth of DSTATCOM.

(2) make DSTATCOM there is harmonic compensation and inhibition ability, reduced the use of DSTATCOM outlet side passive filter, and improved the harmonic performance of DSTATCOM offset current, reduced output harmonic wave, reduce the pollution to electrical network, reduced the heating of the elements such as DSTATCOM self filter reactor and DC side Support Capacitor simultaneously, reduced design capacity, improve the capacity utilance, saved cost and the floor space of DSTATCOM.

(3) improve compensation ability and the precision of DSTATCOM in the unbalanced load situation, made DSTATCOM can compensate single-phase or unbalanced load, widened the scope of application of DSTATCOM.

(4) improve the harmonic performance of DSTATCOM offset current in line voltage distortion situation, improved the stability of DSTATCOM.

(5), under the prerequisite improved at stable state accuracy, control method dynamic property of the present invention is superior.

(6) control method simplicity of design of the present invention, can pass through the digital realization of a slice DSP, and without increasing installation cost, integrated level is high, good reliability.

The accompanying drawing explanation

The steps flow chart schematic diagram that Fig. 1 is the inventive method.

The use view that Fig. 2 is DSTATCOM.

The schematic flow sheet that Fig. 3 is instruction fetch of the present invention.

Fig. 4 is that the present invention repeats the schematic flow sheet of controlling and PI controls.

The frequency characteristic schematic diagram that Fig. 5 is traditional PI regulating system closed loop transfer function.

Fig. 6 is the frequency characteristic schematic diagram that the present invention repeats PI regulating system closed loop transfer function, after control and compensation.

Fig. 7 (a) injects the oscillogram of the idle lower line voltage of perception and offset current to electrical network.

Fig. 7 (b) injects the spectrogram of the idle lower offset current of perception to electrical network.

Fig. 8 (a) injects the oscillogram of line voltage under capacitive reactive power and offset current to electrical network.

Fig. 8 (b) injects the spectrogram of offset current under capacitive reactive power to electrical network.

Fig. 9 (a) is from the idle oscillogram to capacitive reactive power switching line voltage and offset current of perception.

The oscillogram that Fig. 9 (b) is idle switching line voltage and offset current from the capacitive reactive power to the perception.

The oscillogram that Figure 10 (a) is line voltage and power network current in not compensation situation.

The spectrogram that Figure 10 (b) is power network current in not compensation situation.

Figure 11 (a) is the oscillogram of line voltage and power network current in employing conventional PI control compensation situation.

Figure 11 (b) is for adopting the spectrogram of power network current in conventional PI control compensation situation.

Figure 12 (a) is the oscillogram of line voltage and power network current in employing control and compensation situation of the present invention.

Figure 12 (b) is for adopting the spectrogram of power network current in control and compensation situation of the present invention.

Embodiment

In order more specifically to describe the present invention, below in conjunction with the drawings and the specific embodiments, Compensating Current Control Method of the present invention is elaborated.

As shown in Figure 1, the Compensating Current Control Method of a kind of DSTATCOM based on repeating to control, comprise the steps:

(1) gather line voltage, load current and offset current.

Gather the compensating current signal of mains voltage signal, load current signal and the DSTATCOM in current sampling period; The use state diagram that Fig. 2 is DSTATCOM in present embodiment; Wherein, U is mains voltage signal, I _LFor load current signal, I _CFor compensating current signal; In present embodiment, the sampling period is 100 μ s.

(2) extract current-order from load current.

As shown in Figure 3, utilize phase-locked loop to extract the phase place of mains voltage signal, 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 I _LdWith q axle load current component I _Lq, q axle load current component I _LqBe idle shaft current instruction I _RefqTo d axle load current component I _LdCarry out high-pass filtering, obtain meritorious shaft current instruction I _Refd.

Wherein, meritorious shaft current instruction I _RefdBe load harmonic wave active current; Idle shaft current instruction I _RefqComprise load fundamental reactive current and load harmonic wave reactive current.

According to symmetrical component method, the threephase load ammeter of arbitrary form can be shown to the form of the fundamental positive sequence shown in following formula, negative sequence component and harmonic component stack, zero-sequence component effectively suppresses by the wiring of power distribution network transformer triangle usually, can not consider.

If obtaining the three phase network voltage-phase by phase-locked loop is ω t, by following transformation matrix of coordinates,

$T_{\mathrm{abc}-\mathrm{dq}}=\frac{2}{3}\left[\begin{array}{ccc}\sin \mathrm{\ωt}& \sin (\mathrm{\ωt}-\frac{2\mathrm{\π}}{3})& \sin (\mathrm{\ωt}+\frac{2\mathrm{\π}}{3})\\ \cos \mathrm{\ωt}& \cos (\mathrm{\ωt}-\frac{2\mathrm{\π}}{3})& \cos (\mathrm{\ωt}+\frac{2\mathrm{\π}}{3})\end{array}\right]$

Above-mentioned current expression is transformed under the dq synchronous rotating frame and can obtains:

By coordinate transform, load current three-phase first-harmonic is exchanged to the direct current resolve on d axle and q axle is meritorious, idle component, the laod unbalance component changes into second harmonic component, and the load harmonic component changes into former harmonic number plus-minus harmonic component once according to the harmonic wave positive-negative sequence.

In like manner, according to the phase place of mains voltage signal to compensating current signal I _CCarry out the dq conversion, obtain meritorious axle offset current component I _CdWith idle axle offset current component I _Cq.

(3) according to current-order, repeated to control and PI control, and then to the instruction of DSTATCOM output voltage.

As shown in Figure 4, the meritorious shaft current instruction I of order _RefdWith meritorious axle offset current component I _CdAs input, make meritorious shaft current instruction deduct meritorious axle offset current component, obtain current error signal; According to following equation, current error signal is carried out to the internal mold renewal, obtain internal mold and upgrade current error signal;

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; In present embodiment, Q=0.98, n=200.

According to following equation, internal mold is upgraded to current error signal and compensate, obtain the current error corrected signal;

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

$f\left(z\right)=\frac{A+{\mathrm{Bz}}^{-1}+{\mathrm{Az}}^{-2}}{1-{\mathrm{Cz}}^{-1}+{\mathrm{Dz}}^{-2}}$

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, and k is compensation points; In present embodiment, k=4; The damping ratio of second-order low-pass filter is 0.67, and cut-off frequency is 2.3KHz, thus A=0.2151, B=0.4301, C=0.359, D=0.2193.

Make current error signal superimposed current error correction signal, obtain revised current error signal; According to following equation, revised current error signal is carried out to the PI adjusting, obtain voltage command signal;

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

$g\left(z\right)=\frac{E-{\mathrm{Fz}}^{-1}}{1-z^{-1}}$

Wherein: the magnitude of voltage that P (i) is i sampled point in voltage command signal, the current error value that W (i) is i sampled point in revised current error signal, g (z) is the PI adjustment function; In present embodiment, E=4.071, F=4.065.

Voltage command signal is carried out to time delay (sampling period of time delay), obtain the voltage command signal after meritorious axle time delay.

In like manner make idle shaft current instruction and idle axle offset current component as input, 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.

It is controlled device that interior ring closed loop transfer function, is take in the design of compensator, carries out amplitude and phase compensation.Ring closed loop transfer function, in traditional PI is typical after regulating, its frequency characteristic is as shown in Figure 5; Can find out and at frequency characteristic 1kHz, with interior medium and low frequency section, exist larger phase place to lag behind after compensation, have a strong impact on harmonic track ability and the output harmonic wave performance of DSTATCOM, and have larger phase place violent change at Mid Frequency, and amplitude attenuation is very little, is unfavorable for the stable of system.

And the frequency characteristic of the rear interior ring closed loop transfer function, of the rear PI adjusting of present embodiment compensation as shown in Figure 6; Can find out that control after overcompensation realizes null decay and the zero phase-shift of medium and low frequency section, improve the DSTATCOM compensation precision, the instability frequency point phase high frequency of phase place violent change passing simultaneously, amplitude attenuation significantly increases, and has guaranteed the stability of DSTATCOM.

In order further to verify the beneficial effect of the inventive method, by the DSTATCOM of the H bridge cascade structure of a star-like connection of three-phase the three phase network that the lambda line voltage effective value is 1316V; Power nature absorbs the Reactive power definition positive direction with DSTATCOM, and DSTATCOM injects idle character and DSTATCOM absorbs idle incompatibility to electrical network.

According to present embodiment, given perception and capacitive effective value are the 56.58A referenced reactive current respectively, DSTATCOM are injected given idle to electrical network, by oscillograph recording C phase line voltage U _sWith device output current I _c, and utilize wavestar software to be analyzed the offset current of DSTATCOM, and equivalence checking reactive power compensation performance, experimental result is as shown in Figure 7 and Figure 8.Wherein, in Fig. 7, the output current tracking error is 1.03%, and total relative harmonic content (THD) is 0.58%; In Fig. 8, the output current tracking error is 0.71%, and total relative harmonic content (THD) is 0.96%.

No matter the experimental result demonstration, install the idle or capacitive reactive power of output perception, and present embodiment all has very high instruction trace precision and output current harmonics performance.

Further verify the dynamic property of present embodiment, the referenced reactive current that makes respectively DSTATCOM inject to electrical network is switched to perceptual 56.58A to capacitive 56.58A and capacitive 42.43A from effective value perception 42.43A, catch the switching dynamic process by oscilloscope, record C phase line voltage U _sWith device output current I _c, experimental result as shown in Figure 9.Can find out the introducing due to the current-order feedforward, present embodiment has been inherited traditional single PI and has been controlled superior dynamic property, fast response time, when the idle instruction of heterogeneity is switched in a big way, control module is response rapidly in 1ms, and what offset current was level and smooth is transitioned into another stable state from a stable state.

Under PI and PI+REP control, the harmonic compensation ability of DSTATCOM compares checking, harmonic load is that the three-phase half-bridge is not controlled the rectification pure resistor element circuit, load resistance nominal 42.5 Ω, use present embodiment to gather load current, extracts the harmonic compensation instruction and carry out load compensation.By oscillograph recording C phase line voltage U _sWith power network current I _s, and utilize wavestar software to carry out the waveform analysis result as shown in table 1 and Figure 10,11 and 12.

Table 1

Can find out, with single PI compensation, compare, power network current sine degree after present embodiment PI+REP compensation obviously improves, and the FFT data results shows, power network current each harmonic content under the PI+REP compensation is starkly lower than single PI compensation, power network current total harmonic distortion (THD) reduces 94.8% before compensating, the residual harmonic content of power network current is less than 1.4%, total harmonic wave inhibiting rate is controlled and is exceeded 60% than single PI, each harmonic inhibiting rate below 25 times is more than 80%, sufficient proof PI add the harmonic inhibition capability of 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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