CN102570476A - 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

A kind of Compensating Current Control Method based on the DSTATCOM that repeats to control

Technical field

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

Background technology

Along with the develop rapidly of industrial technology, social electrifing degree improves constantly in recent years, reactive load such as various big capacity induction motors, specific type of electric machine in the power distribution network especially in the electrical network; Various impacts, fluctuation unbalanced loads such as arc furnace, heavy (merchant) mill, electric locomotive, capacity constantly increases, and nonlinear loads such as power electronic device and the complete sets of equipment are used widely; The operation of these devices uses not only consumption idle in a large number; And produce a large amount of harmonic waves, the severe contamination electrical network reduces the electrical network service efficiency; Influence power supply quality and reliability, cause various sophisticated instruments and can't operate as normal the responsive power consumption equipment of the quality of power supply.To above-mentioned quality problems; Be intended to improve harmonic wave inhibition and the reactive-load compensation equipment emerge in multitude that distribution network electric energy quality is a purpose; Power distribution network STATCOM (DSTATCOM) can be through idle size and character continuous, that fast adjuster injects to electrical network, the idle harmonic of compensating load as the new application of transmission line STATCOM (STATCOM) in power distribution network; Stablize public access node (PCC) voltage, improve distribution network electric energy quality; (SVC) compares with traditional SVC; DSTATCOM is with its fast reactive regulating power, wideer range of operation, good electric current output performance; Advantages such as less device volume and cost have obtained extensive concern; The DSTATCOM of cascade structure realizes high-voltage large-capacityization easily through the simple series connection of power model in addition, is fit to very much the application of medium-voltage distribution network level (6kV-10kV).

The control strategy of DSTATCOM AC side output current; It is a core technology that concerns equipment performance; Traditional control method such as the control of current hysteresis ring, PI control, dead beat control etc.; Can't satisfy the strict standard that quality of power supply demand that the user improves constantly and national relevant industries are incorporated into the power networks to power equipment, and in the abominable complicated power grid environment of distribution system, install self efficient, reliable, normal work and also can't be guaranteed.Retrieval through 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 current control strategy is by broad research and application.

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); Improved the flexibility and the robustness of device control, dynamic response is fast when the fluctuation of load, and overshoot is little; But this method belongs to open loop control for the device output current, can't guarantee DSTATCOM output current stable state indifference ground trace command, and for unbalanced load, the load of harmonic wave property, the grid voltage waveform distortion does not have control ability.

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

People such as Tan Tianyuan and Jiang Qirong is " based on the control method of three level DSTATCOM devices of current tracking control " (Automation of Electric Systems at title; 2007; (4): proposed a cover in article 61-65) based on the triangular wave direct tracking strategy of three-level current transformer electric current relatively, to a certain degree reduced the fluctuation of instruction trace sum of errors switching device switching frequency, but this strategy has made that the device switching frequency is low; The output filter design is bigger, and steady-state error can't be eliminated.

People such as Wu Chunhui and Jiang Qirong proposes a kind of switch angle optimized calculation method based on selectivity harmonic elimination ripple in the article of " a kind of optimization methods of three level selective harmonic elimination pulse-width modulations " (power electronic technology, 2005, (5)); Make inverter output than obtaining harmonic characterisitic preferably under the low switching frequency; But this method is influenced down by big capacity impact load etc. in power distribution network, and access node voltage exists than great fluctuation process, owing to detect the influence that sum of errors is delayed time; Response speed is slow; And particular harmonic is eliminated limited bandwidth, can't floating follow the tracks of harmonic load, and service behaviour is poor under unbalanced power supply and the distortion.

Based on the DSTATCOM nonlinear Control of advanced control theory, self adaptation dead beat control etc. do not have too high requirement to the model accuracy of system more in addition, can self adaptation change system parameters; Obtain higher compensation precision; But because design of Controller 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 output performance, accurate steady state controling precision, superior dynamic and stronger load, line voltage disturbance adaptability.

Summary of the invention

To the above-mentioned technological deficiency of existing in prior technology, the invention provides a kind of Compensating Current Control Method based on the DSTATCOM that repeats to control, the reactive power compensation precision harmonic that can significantly improve DSTATCOM suppresses ability.

A kind of Compensating Current Control Method based on the DSTATCOM that repeats to control comprises the steps:

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

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

(3) meritorious shaft current instruction of order and meritorious axle offset current component make meritorious shaft current instruction deduct meritorious axle offset current component as input, obtain current error signal; Current error signal is carried out internal mold upgrade, obtain internal mold and upgrade current error signal; Internal mold is upgraded current error signal 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 PI (proportional integral) regulate, obtain voltage command signal; Voltage command signal is delayed time, obtain the voltage command signal after meritorious axle is delayed time;

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

In the described step (2); The process of load current signal being carried out instruction fetch is: the phase place according to mains voltage signal is carried out the dq conversion to load current signal; 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 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 the described step (3), according to following equation current error signal is carried out internal mold and upgrade;

U(i)＝E(i)+QE(i-n)

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

In the described step (3), according to following equation internal mold is upgraded current error signal and compensate;

Y(i)＝f(z)U(i-n+k)

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

Useful technique effect of the present invention is:

(1) makes 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 have 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; Reduced pollution, reduced the heating that DSTATCOM self filter reactor and DC side support elements such as electric capacity simultaneously, reduced design capacity electrical network; Improve the capacity utilance, saved cost and the floor space of DSTATCOM.

(3) improve compensation ability and the precision of DSTATCOM under 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 under line voltage distortion situation, improved the stability of DSTATCOM.

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

(6) control method simplicity of design of the present invention can be passed through the digital realization of a slice DSP, need not to increase installation cost, and integrated level is high, good reliability.

Description of drawings

Fig. 1 is the steps flow chart sketch map of the inventive method.

Fig. 2 is the user mode sketch map of DSTATCOM.

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

Fig. 4 repeats to control for the present invention and the schematic flow sheet of PI control.

Fig. 5 is the frequency characteristic sketch map of traditional PI regulating system closed loop transfer function.

Fig. 6 repeats the frequency characteristic sketch map of PI regulating system closed loop transfer function, after the control compensation for the present invention.

Fig. 7 (a) is an oscillogram from offset current to electrical network that inject idle line voltage down of perception and.

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

Fig. 8 (a) is an oscillogram from offset current to electrical network that inject line voltage under the capacitive reactive power and.

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

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

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

Figure 10 (a) is the oscillogram of line voltage and power network current under the not compensation situation.

Figure 10 (b) is the spectrogram of power network current under the not compensation situation.

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

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

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

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

Embodiment

In order to describe the present invention more particularly, Compensating Current Control Method of the present invention is elaborated below in conjunction with accompanying drawing and embodiment.

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

(1) gathers 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; Fig. 2 is the user mode figure of DSTATCOM in this execution mode; Wherein, U is a mains voltage signal, I _LBe load current signal, I _CBe compensating current signal; In this execution mode, the sampling period is 100 μ s.

(2) from load current, extract current-order.

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

If obtaining the three phase network voltage-phase through phase-locked loop is ω t, then through 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 gets:

Through coordinate transform; Load current three-phase first-harmonic is exchanged meritorious, the idle component of the direct current that resolves on d axle and the q axle; 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) repeat control and PI control according to current-order, and then instruct to the DSTATCOM output voltage.

As shown in Figure 4, the meritorious shaft current instruction of order I _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 internal mold and upgrade, obtain internal mold and upgrade current error signal;

U(i)＝E(i)+QE(i-n)

Wherein: U (i) upgrades the current error value of i sampled point in the current error signal for internal mold; E (i) is the current error value of i sampled point in the current error signal; E (i-n) is the current error value of i-n sampled point in the current error signal; Q is an attenuation coefficient, and n is the sampling number of a primitive period; In this execution mode, Q=0.98, n=200.

According to following equation internal mold is upgraded 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: Y (i) is the current error correction value of i sampled point in the current error corrected signal, and U (i-n+k) is the current error value of i-n+k sampled point in the internal mold renewal current error signal, and f (z) is the second-order low-pass filter function, and k is a compensation points; In this execution mode, 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 PI and regulate, obtain voltage command signal;

P(i)＝g(z)W(i)

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

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

Voltage command signal is delayed time (delaying time a sampling period), obtain the voltage command signal after meritorious axle is delayed time.

In like manner make idle shaft current instruction and idle axle offset current component as input, obtain the voltage command signal after idle axle is delayed time; Voltage command signal after voltage command signal after the meritorious axle time-delay and the idle axle time-delay is carried out being delivered to DSTATCOM after the dq inverse transformation, with the offset current of control DSTATCOM.

The design of compensator is a controlled device with interior ring closed loop transfer function,, carries out amplitude and phase compensation.Traditional PI is regulated the typical interior ring closed loop transfer function, in back, and its frequency characteristic is as shown in Figure 5; Can find out and have bigger phase lag at frequency characteristic 1kHz with interior medium and low frequency section after the compensation; Have a strong impact on harmonic wave follow-up control and the output harmonic wave performance of DSTATCOM; And have bigger 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 ring closed loop transfer function, is as shown in Figure 6 in the PI adjusting back, this execution mode compensation back; Can find out the null decay and the zero phase-shift of the control realization medium and low frequency section after overcompensation, improve the DSTATCOM compensation precision, the instability frequency point phase high frequency of phase place violent change is passed simultaneously, and amplitude attenuation significantly increases, and has guaranteed the stability of DSTATCOM.

For the further beneficial effect of checking the inventive method, be the three phase network of 1316V with the DSTATCOM and the lambda line voltage effective value of the H bridge cascade structure of a star-like connection of three-phase; Power nature absorbs idle definition positive direction with DSTATCOM, and then DSTATCOM injects idle character and DSTATCOM absorbs idle incompatibility to electrical network.

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

No matter the experimental result demonstration installs the idle still capacitive reactive power of output perception, and this execution mode all has very high instruction trace precision and output current harmonics performance.

Further verify the dynamic property of this execution mode; Make DSTATCOM switch to perceptual 56.58A to capacitive 56.58A and capacitive 42.43A from effective value perception 42.43A respectively to the referenced reactive current that electrical network injects; Catch the switching dynamic process through oscilloscope, record C phase line voltage U _sWith device output current I _c, experimental result is as shown in Figure 9.Can find out because the introducing of current-order feedforward; This execution mode has been inherited the superior dynamic property of traditional single PI control; Response speed is fast; When the idle instruction of heterogeneity during in intra in a big way, control module is response rapidly in 1ms, and what offset current was level and smooth carries out the transition to another stable state from a stable state.

The harmonic compensation ability of DSTATCOM compares checking under PI and PI+REP control; Harmonic load is that the three-phase half-bridge is not controlled rectification pure resistance circuit; Load resistance nominal 42.5 Ω use this execution mode to gather load current, extract harmonic compensation instruction carrying out load compensation.Through oscillograph recording C phase line voltage U _sWith power network current I _s, and utilize wavestar software to carry out the waveform analysis result like table 1 and Figure 10, shown in 11 and 12.

Table 1

Can find out; Compare with single PI compensation, the power network current sine degree after this execution mode PI+REP compensation obviously improves, and FFT data analysis result 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%, and total harmonic wave inhibiting rate exceeds 60% than single PI control; Each harmonic inhibiting rate below 25 times has proved fully that more than 80% PI adds the harmonic wave inhibition ability of repetition control strategy.

Claims (4)

1. the Compensating Current Control Method based on the DSTATCOM that repeats to control comprises the steps:

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

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

(3) meritorious shaft current instruction of order and meritorious axle offset current component make meritorious shaft current instruction deduct meritorious axle offset current component as input, obtain current error signal; Current error signal is carried out internal mold upgrade, obtain internal mold and upgrade current error signal; Internal mold is upgraded current error signal 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 PI regulate, obtain voltage command signal; Voltage command signal is delayed time, obtain the voltage command signal after meritorious axle is delayed time;

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

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

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

U(i)＝E(i)+QE(i-n)

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

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

Y(i)＝f(z)U(i-n+k)

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

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