CN204992594U - Reactive power compensator based on novel many level of modularization topological structure - Google Patents

Abstract

Reactive power compensator based on novel many level of modularization topological structure, it relates to a high pressure, high -power reactive power compensator. The utility model discloses an it is limited and to the problem that the suppression ability is not enough of circulation in high pressure high -power field compensation in order to solve prior art. The utility model discloses a three -phase AC power supply, hinder the sense load, the MMC transverter, signal detection circuit, control circuit and drive circuit, the MMC transverter includes the same parallel connection's of three structure bridge arm, every bridge arm includes last bridge arm and lower bridge arm about point symmetry in the bridge arm and series connection, go up the bridge arm including the inductance of establishing ties each other, a plurality of half -bridge units and a H bridge unit, go up the inductance of bridge arm and the inductance series connection of lower bridge arm, the mid point of the three bridge arm of transverter passes through the wire and links between three -phase AC power supply and load. The utility model discloses it is not only can the compensation network idle, solve the unbalanced three phase of system problem, support grid voltage in addition, restrain the effect of circulation.

Description

Based on the reactive power compensator of novel modularized many level topological structure

Technical field

The utility model relates to a kind of reactive power compensator, is specifically related to the reactive power compensator based on novel modularized multilevel converter, belongs to high-power reactive power compensation technology field.

Background technology

Along with the extensive application of power converter and nonlinear load, in electrical network, create a large amount of idle and harmonic waves.Utilize STATCOM to carry out reactive power compensation and harmonics restraint, the requirement that electrical network is energy-conservation, fall damage can not only be met, but also be conducive to the improvement of grid supply quality.

At present, common many level topological structure mainly contains three kinds: diode clamp type, striding capacitance type and H bridge cascade connection type.Diode clamp type and striding capacitance type structure, along with the increase of level number, required switching device and clamp capacitor quantity can increase greatly, be unfavorable for the translation circuit realizing more high level, and capacitance voltage are not easily balanced, applies and is restricted.H bridge cascade structure, when the current-unbalance that three-phase exports, can not transmit meritorious energy between brachium pontis, be difficult to the capacitor voltage balance realized between three-phase module.

Utility model content

The purpose of this utility model compensates problem that is limited and rejection ability deficiency to circulation in order to solve prior art in high-power field.

The technical solution of the utility model is: based on the reactive power compensator of novel modularized many level topological structure, comprise three-phase alternating-current supply, resistance sense load, converter, control circuit, signal deteching circuit and drive circuit, described converter comprises three identical brachium pontis be connected in parallel of structure, each brachium pontis comprises about point symmetry in brachium pontis and the upper brachium pontis be connected in series and lower brachium pontis, described upper brachium pontis comprises the inductance of series connection mutually, some half-bridge cells and a H-bridge unit, the inductance of upper brachium pontis and the inductance of lower brachium pontis are connected in series, the mid point of converter three brachium pontis is connected between three-phase alternating-current supply and resistance sense load by conductor in parallel, the input of signal deteching circuit connects the output of three-phase alternating-current supply respectively, the input of resistance sense load, the output of converter, converter three brachium pontis, each half-bridge cells of converter and H-bridge unit, the input of the output connection control circuit of signal deteching circuit, the output of control circuit is connected by drive circuit and converter.

Described control circuit comprises phase-shifting carrier wave controller, first control unit and the second control unit, the output of the first control unit and the output of the second control unit all connect with phase-shifting carrier wave controller, described first control unit comprises the first comparator, second comparator, 3rd comparator, 4th comparator, 5th comparator, one PI controller, 2nd PI controller, 3rd PI controller, first coordinate converter, second coordinate converter, first reactor and the second reactor, first comparator, one PI controller, second comparator, 2nd PI controller and the 3rd comparator access the first coordinate converter after connecting successively, 4th comparator, 3rd PI controller and the 5th comparator access the first coordinate converter after connecting successively, the output of the first coordinate converter connects phase-shifting carrier wave controller, the output of phase-shifting carrier wave controller connects drive circuit, the output of described converter connects the second coordinate converter, first output of the second coordinate converter connects the second comparator and the second reactor respectively, the output of the second reactor connects the 3rd comparator, another output of second coordinate converter connects the 4th comparator and the first reactor respectively, the output of the first reactor connects the 5th comparator, two parallel controllers are adopted to control respectively the power model of converter and full-bridge modules, improve the control efficiency of system, make system cloud gray model more stable, first control unit is for controlling the power model part of converter, first control unit carries out balance to the capacitance voltage of the power model of converter and controls while control converter load current.

Described second control unit comprises the 6th comparator, 7th comparator, 8th comparator, 9th comparator, first proportional controller, second proportional controller, 4th PI controller, 5th PI controller sum functions module, 6th comparator, first proportional controller, 7th comparator, 4th PI controller and the second proportional controller access the 9th comparator after connecting successively, 8th comparator, 5th PI controller sum functions module accesses the 9th comparator after connecting successively, the output of the 9th comparator connects described phase-shifting carrier wave controller, circulation is controlled by the output voltage controlling full-bridge modules, namely by adopting rational control strategy, in full-bridge modules, insert suitable voltage can suppress circulation, not only circulation is suppressed by independently control unit, achieve the Balance route to full-bridge modules capacitance voltage simultaneously.

Described control circuit comprises DSP module and FPGA module, the output of DSP module connects FPGA module, the output of FPGA module connects drive circuit, described first control unit and the second control unit are integrated in DSP module, and described phase-shifting carrier wave controller is integrated in FPGA module, adopt the control mode of DSP+FPGA, DSP is as computing and control section, FPGA is used for producing PWM ripple, substantially increases control, arithmetic speed like this, reduces the response time of whole device.

The described reactive power compensator based on novel modularized many level topological structure comprises zero cross detection circuit, described zero cross detection circuit comprises voltage sensor, comparison circuit and optocoupler, the input of voltage sensor connects the output of three-phase alternating-current supply, the output of voltage sensor connects the input of comparison circuit, the output of comparison circuit accesses DSP module by optocoupler, makes reactive power compensator achieve phase locking process to line voltage.

Described signal deteching circuit comprises current detecting and modulate circuit, described current detecting and modulate circuit comprise current sensor and opto-coupler chip, the output of current sensor connects opto-coupler chip, reduces the antijamming capability of the delayed and raising detection signal that current sample link causes.

Described drive circuit comprises level shifting circuit and driving chip, and the input of level shifting circuit is the input of drive circuit, and the output of level shifting circuit connects driving chip, and the output of driving chip is the output of drive circuit.

The control method of the described reactive power compensator based on novel modularized many level topological structure, specifically comprises: adopt the i based on instantaneous reactive power theory _p-i _qelectric current testing detects electric current; Half-bridge cells and full bridge unit are controlled respectively, obtain pwm control signal, definition half-bridge cells is power model, full bridge unit is full-bridge modules, the control of described power model comprises and to control the capacitor voltage equalizing of power model and based on the Double closed-loop of voltage and current of Feedforward Decoupling, and the control of full-bridge modules comprises the inhibitory control of the circulation of and whole reactive power compensator balanced to full-bridge modules capacitance voltage.

Described capacitor voltage equalizing controls to comprise voltage between phases balance and controls and the control of independent voltage balance, and described voltage between phases control balancing is made as: outer voltage is the mean value making every phase 2N power model capacitance voltage with the set-point U of power model capacitance voltage _refdiffer from, poor with the circulation of this phase after PI regulates, as the command signal that average voltage controls after electric current loop proportion adjustment, be defined as u _aj, wherein, j=a, b, c, described in with circulation i _cirexpression formula be respectively:

${\stackrel{\‾}{U}}_c=\frac{1}{2N}\underset{j=1}{\overset{2N}{\Σ}}{U}_{cj}$

$i_{cir}=\frac{1}{2}(i_P+i_N)$

Individual capacitor voltages control balancing is made as: the capacitance voltage U detecting every mutually upper and lower brachium pontis power model _cji, by the set-point U of the capacitance voltage of itself and power model _refcompare, through proportion adjustment, then be multiplied with corresponding bridge arm current, through the correction of sign function, obtain the instruction u that every mutually upper and lower brachium pontis independent voltage balance controls _bPjand u _bNj.Adopt capacitance voltage grading control strategy, guarantee each module capacitance electric voltage equalization, achieve good reactive power compensation, voltage stabilizing, all pressure and loop current suppression effect.

The feed forward decoupling control strategy of the described Double closed-loop of voltage and current based on Feedforward Decoupling is:

$\left[\begin{array}{c}{x}_1\\ x_2\end{array}\right]=\left[\begin{array}{c}{K}_1({i_d}^{*}-i_d)+\frac{K_1}{T_1}\∫({i_d}^{*}-i_d)dt\\ K_2({i_q}^{*}-i_q)+\frac{K_2}{T_2}\∫({i_q}^{*}-i_q)dt\end{array}\right]$

Wherein, x ₁, x ₂for intermediate variable, K ₁, K ₂for proportionality coefficient, T ₁, T ₂for integral coefficient, i _dand i _qbe respectively the current component of the dq reference axis that converter exports, i _d ^*and i _q ^*be respectively the active current in load and reactive current component;

Described Double closed-loop of voltage and current comprises: by given direct voltage U _refcompare with Converter DC-side capacitance voltage, regulate through voltage PI, it exports the set-point i as active current _d ^*, load current obtains reactive current set-point i through coordinate transform, negate process _q ^*; By the three-phase current i that converter exports _abci is obtained through coordinate transform _dand i _q, by i _dand i _qrespectively with i _d ^*, i _q ^*compare, regulate through electric current loop PI, obtain the output voltage V expected _cd, V _cq; To V _cd, V _cqcarry out inverse transformation obtain rest frame under three-phase modulations ripple, are obtained pwm control signal after the triangular carrier that this three-phase modulations ripple and phase-shifting carrier wave controller are produced.

Described full-bridge modules capacitance voltage balancing procedure comprises: the set-point V of each mutually upper and lower brachium pontis full-bridge modules capacitance voltage _{h, ref}compare with the actual capacitance voltage of full-bridge modules, through PI controller, after it exports and is multiplied by the sign function of this bridge arm current, by the full-bridge submodule voltage given value V generated _{r, ref}with obtain PWM ripple after triangular carrier, wherein, r=P, N, drive corresponding power switch pipe in full-bridge modules, carry out charge and discharge control, realize the equilibrium of full-bridge modules capacitance voltage to the electric capacity of full-bridge submodule;

Described loop current suppression process comprises: compared with the reference value of circulation respectively by each phase circulation, now the reference value i of circulation _{cir, ref}=i _dc/ 3, the result obtained forms the voltage adjustment signal of a full-bridge modules by a proportional controller, and this voltage adjustment signal is divided into 2 parts, is added in respectively on the voltage signal of this mutually upper and lower brachium pontis full-bridge modules.For three alternate circulation problems, propose a kind of novel topological structure increasing H bridge module, by independently control unit, realize the effective suppression to circulation.

The utility model compared with prior art has following effect: the utility model not only can compensation network idle, resolution system three-phase imbalance problem, support line voltage in addition, suppress the effect of circulation, three phase feedback currents that described detecting signal unit detection of grid three-phase voltage, load-side three-phase current, converter export, the capacitance voltage of each module of DC side and the bridge arm current of three-phase, then, to detect that feedback quantity carries out computing and adjustment in control circuit, obtain pwm control signal; Finally, control signal is carried out power amplifier with power switch pipe in the modules driving converter, make converter export corresponding offset current, realize reactive power compensation.In the New Topological of the utility model design, every mutually upper and lower brachium pontis adds 1 H-bridge unit, and the H-bridge unit in whole like this three-phase system has 6.Converter is made up of half-bridge cells and H-bridge unit, and wherein half-bridge cells module is for controlling the first-harmonic load current in brachium pontis, and H-bridge unit as voltage correction module for suppressing circulation.Adopt the i based on instantaneous reactive power theory _p-i _qelectric current testing, the method has good real-time, can accurately detect the size of active current in electrical network and reactive current, improves the stability of system.Converter of the present utility model has obvious advantage relative to traditional multilevel converter, can realize reactive power, harmonic wave and unbalanced comprehensive compensation, it exports as many level, close to sine wave, harmonic content is little, select suitable control algolithm can reduce the switching frequency of power tube, reduce switching loss.

Accompanying drawing explanation

Fig. 1, entire system block diagram;

Fig. 2, novel MMC converter topological structure circuit diagram;

The equivalent control model schematic of Fig. 3, STATCOM;

Fig. 4, voltage between phases balance controls schematic diagram;

Fig. 5, independent voltage balance controls schematic diagram;

Fig. 6, loop current suppression device operation principle schematic diagram;

The working state schematic representation of Fig. 7, module, wherein (a) is input state, and (b) is excision state, and (c) is blocking;

The equivalent model schematic diagram of Fig. 8, Three phase MMC topological structure;

Fig. 9, Detecting Reactive Current block diagram;

Figure 10, meritorious, reactive current control block diagram;

Figure 11, Feedforward Decoupling equivalent control block diagram;

The control block diagram of Figure 12, STATCOM voltage and current double closed-loop;

Figure 13, STATCOM system main-control block diagram;

The fundamental diagram of Figure 14, controller 2;

Figure 15, zero cross detection circuit figure;

Figure 16, current detecting and modulate circuit circuit diagram thereof;

Figure 17, isolated drive circuit circuit diagram;

Figure 18, main program flow chart;

Figure 19, capture interrupt flow chart;

Figure 20, T1 interruption subroutine flow chart;

A phase voltage, current waveform figure before Figure 21, compensation;

A phase voltage, current waveform figure after Figure 22, compensation;

A phase current waveform figure before Figure 23, compensation;

A phase current waveform figure after Figure 24, compensation;

A phase module capacitance voltage waveform after Figure 25, balance control;

Three phase circulation waveforms before Figure 26, suppression;

Three phase circulation waveforms after Figure 27, suppression.

Embodiment

Accompanying drawings embodiment of the present utility model, reactive power compensator based on novel modularized many level topological structure of the present utility model, comprise three-phase alternating-current supply, resistance sense load, MMC converter, control circuit, signal deteching circuit and drive circuit, described MMC converter comprises three identical brachium pontis be connected in parallel of structure, each brachium pontis comprises about point symmetry in brachium pontis and the upper brachium pontis be connected in series and lower brachium pontis, described upper brachium pontis comprises the inductance of series connection mutually, some half-bridge cells and a H-bridge unit, the inductance of upper brachium pontis and the inductance of lower brachium pontis are connected in series, the mid point of MMC converter three brachium pontis is connected between three-phase alternating-current supply and resistance sense load by conductor in parallel, the input of signal deteching circuit connects the output of three-phase alternating-current supply respectively, the input of resistance sense load, the output of MMC converter, MMC converter three brachium pontis, each half-bridge cells of MMC converter and H-bridge unit, the input of the output connection control circuit of signal deteching circuit, the output of control circuit is connected by drive circuit and MMC converter, half-bridge cells module is for controlling the load fundamental current in brachium pontis, H-bridge unit as voltage correction module for suppressing circulation, signal deteching circuit, detection of grid three-phase voltage, load-side three-phase current, three phase feedback currents that MMC exports, the capacitance voltage of each submodule of DC side and the bridge arm current of three-phase, then, will detect that feedback quantity carries out computing and adjustment in a control unit, obtain pwm control signal, finally, control signal is carried out power amplifier to drive power switch pipe in MMC submodule, make converter export corresponding offset current, realize reactive power compensation.

The topological structure of the modular multilevel MMC converter of present embodiment has common DC bus, three alternate energy can flow mutually, when electrical network distorts, reactive power, harmonic wave and unbalanced comprehensive compensation can be realized, high modularization, is easy to Redundancy Design, and exports as many level, close to sine wave, harmonic content is little.

Half-bridge module is called power model, and H-bridge unit is called full-bridge modules.As shown in Figure 2, SM is half-bridge module, each half-bridge module is made up of two IGBT with reverse fly-wheel diode and 1 storage capacitor C, each half-bridge module has two kinds of on off states, control the break-make of module in each phase, the output voltage of module can be made to form the output voltage of 2N+1 level by superposition.

As shown in Figure 7, in figure, arrow shows the flow direction of electric current to the power model operating state of MMC converter.Shown power model has three kinds of operating states:

1) T ₁(D ₁) open, T ₂(D ₂) turn off as input state, as schemed shown in (a) in Fig. 7;

2) T ₁(D ₁) turn off, T ₂(D ₂) open as excision state, as schemed shown in (b) in Fig. 7;

3) T ₁and T ₂all turn off as blocking, as schemed shown in (c) in Fig. 7;

If s _ifor the switch function of the power model of MMC converter, can be expressed as

The then equivalent output voltage u of each power model _ocan be expressed as

u _o＝s _iV _d(2)

HB is H-bridge unit, has 3 kinds of on off states, the switch function s of shown MMC full-bridge modules _i, s _i∈ {-1,0,1}, s _ivalue determine the polarity of H-bridge unit output voltage.

As shown in Figure 8, wherein, DC side electric current is i to the equivalent model of Three phase MMC converter power topological structure _dc, on three-phase, bridge arm current is respectively i _aP, i _bP, i _cP, under three-phase, bridge arm current is respectively i _aN, i _bN, i _cN, three-phase output current is respectively i _a, i _b, i _c.

For a phase, according to KCL Circuit theory, a phase output current can be expressed as

i _a＝i _aP-i _aN(3)

If the circulation of a phase brachium pontis is i _{cir, a}, because the circuit structure of upper and lower brachium pontis is identical, then have

$j_{aP}=i_{cir,a}+\frac{i_a}{2}---\left(4\right)$

$i_{aN}=i_{cir,a}-\frac{i_a}{2}---\left(5\right)$

Formula (5) and (6) are added, obtain

$i_{cir,a}=\frac{1}{2}(i_{aP}+i_{aN})---\left(6\right)$

The current i of three-phase MMC DC bus _dcfor a, b, c tri-phase circulation sum, namely

i _dc＝i _cir,a+i _cir,b+i _cir,c(7)

Due to three-phase symmetrical, three phase circulation i _{cir, j}can be expressed as

$i_{cir,j}=\frac{i_{dc}}{3}+{i_{zj}}^{*}---\left(8\right)$

In formula, i _zj ^*two frequency multiplication negative phase-sequence alternating current components in circulation, wherein, j=a, b, c, convolution (4), (5) can obtain with (8):

$i_{aP}=\frac{i_{dc}}{3}+\frac{i_a}{2}+{i_{zj}}^{*}---\left(9\right)$

$i_{aN}=\frac{i_{dc}}{3}-\frac{i_a}{2}+{i_{zj}}^{*}---\left(10\right)$

Composite type (9) and (10), the two frequency multiplication negative phase-sequence alternating components that can obtain a phase circulation are

${i_{zj}}^{*}=\frac{1}{2}(i_{aP}+i_{aN})-\frac{i_{dc}}{3}---\left(11\right)$

MMC converter power module can be equivalent to controlled voltage source V _jr, wherein, j=a, b, c; R=P, N, then bridge output voltage V in a phase _aPwith the output voltage V of lower brachium pontis _aNcan be expressed as

$V_{aP}=\underset{i=1}{\overset{N}{\Σ}}{S}_i{V}_d---\left(12\right)$

$V_{aN}=\underset{i=N+1}{\overset{2N}{\Σ}}{S}_i{V}_d---\left(13\right)$

In the equivalent model of Fig. 8, the output voltage of full-bridge modules is V _{h, jr}, with the mid point of DC bus-bar voltage for reference, the three-phase voltage that MMC system exports is V _j, the equivalent resistance of each brachium pontis is R _e, according to KVL Circuit theory, can obtain

$\frac{U_d}{2}-V_{aP}-V_{H,aP}-V_a=R_e{i}_{aP}+L\frac{{\mathrm{di}}_{aP}}{dt}---\left(14\right)$

$\frac{U_d}{2}-V_{aN}-V_{H,aN}+V_a=R_e{i}_{aN}+L\frac{{\mathrm{di}}_{aN}}{dt}---\left(15\right)$

Formula (14) and (15) are added, then convolution (4) is to (6), can obtain:

$2L\frac{{\mathrm{di}}_{cir,a}}{dt}+2R_e{i}_{cir,a}=(U_d-V_{aP}-V_{aN})-(V_{H,aP}+V_{H,aN})---\left(16\right)$

As can be seen from formula (16), can by controlling the output voltage (V of full-bridge modules _{h, aP}+ V _{h, aN}) size and voltage difference (U _d-V _aP-V _aN) equal thus reach and eliminate the object of circulation.

Formula (15) is deducted formula (14), can obtain

$V_a=\frac{1}{2}(V_{aN}-V_{aP})+\frac{1}{2}(V_{H,aN}-V_{H,aP})+\frac{R_e}{2}(i_{aN}-i_{aP})+\frac{L}{2}(\frac{{\mathrm{di}}_{aN}}{dt}-\frac{{\mathrm{di}}_{aP}}{dt})---\left(17\right)$

From formula (17), the output voltage of full-bridge modules on MMC does not almost affect, and reason has two: first, the output voltage grade of full-bridge modules relative to MMC system output voltage be very little; Secondly, the voltage that control full-bridge modules inserts each mutually upper and lower brachium pontis is equal, therefore (V in formula (17) _{h, aP}-V _{h, aN})/2 one can be similar to regards 0 as, the not output voltage of influential system.

Described control circuit comprises phase-shifting carrier wave controller, first control unit and the second control unit, the output of the first control unit and the output of the second control unit all connect with phase-shifting carrier wave controller, and described first control unit comprises the first comparator 1, second comparator 3, 3rd comparator 5, 4th comparator 7, 5th comparator 9, one PI controller 2, 2nd PI controller 4, 3rd PI controller 8, first coordinate converter 6, second coordinate converter 12, first reactor 10 and the second reactor 11, first comparator 1, one PI controller 2, second comparator 3, 2nd PI controller 4 and the 3rd comparator 5 access the first coordinate converter, the 4th comparator 7 after connecting successively, 3rd PI controller 8 and the 5th comparator 9 access the first coordinate converter 6 after connecting successively, the output of the first coordinate converter 6 connects phase-shifting carrier wave controller, the output of phase-shifting carrier wave controller connects drive circuit, the output of described MMC converter connects the second coordinate converter, first output of the second coordinate converter connects the second comparator 3 and the second reactor 11 respectively, the output of the second reactor 11 connects the 3rd comparator 5, another output of second coordinate converter connects output connection the 5th comparator 9 of the 4th comparator 7 and the first reactor 10, first reactor 10 respectively.

Described second control unit comprises the 6th comparator 13, 7th comparator 15, 8th comparator 18, 9th comparator 21, first proportional controller 14, second proportional controller 17, 4th PI controller 16, 5th PI controller 19 sum functions module 20, 6th comparator 13, first proportional controller 14, 7th comparator 15, 4th PI controller 16 and the second proportional controller 17 access the 9th comparator 21 after connecting successively, 8th comparator 18, 5th PI controller 19 sum functions module 20 accesses the 9th comparator 21 after connecting successively, the output of the 9th comparator 21 connects described phase-shifting carrier wave controller.

The modulation technique of the present embodiment adopts phase-shifting carrier wave control strategy.

Described control circuit comprises DSP module and FPGA module, the output of DSP module connects FPGA module, the output of FPGA module connects drive circuit, described first control unit and the second control unit are integrated in DSP module, described phase-shifting carrier wave controller is integrated in FPGA module, the DSP control module of the present embodiment with the TMS320F2812 of TI company for core, DSP module and FPGA module cooperation realize load-side current sample, offset current is sampled, capacitance voltage is sampled, bridge arm current is sampled, current/voltage double-closed-loop control, the functions such as CPS-SPWM ripple generation, auxiliary circuit is by Switching Power Supply, the compositions such as protective circuit.

The described reactive power compensator based on novel modularized many level topological structure comprises zero cross detection circuit, described zero cross detection circuit comprises voltage sensor 22, comparison circuit 23 and optocoupler 24, the input of voltage sensor 22 connects the output of three-phase alternating-current supply, the output of voltage sensor 22 connects the input of comparison circuit 23, and the output of comparison circuit 23 accesses DSP module by optocoupler 24.The employing voltage Hall module CHV-25P of present embodiment reduces to about 5V A phase voltage amplitude, then one is produced with electrical network with square-wave signal frequently by comparison circuit 23, its rising edge overlaps with the zero crossing of a phase forward voltage, and the time difference of two rising edges is the cycle of electrical network a phase voltage.

Reactive power compensator based on novel modularized many level topological structure comprises current detecting and modulate circuit, described current detecting and modulate circuit comprise current sensor 25, optical isolation amplifier 26 and operational amplifier 27, the output of current sensor 25 connects optical isolation amplifier 26, the output concatenation operation amplifier 27 of optical isolation amplifier 26, the output of operational amplifier 27 is the output of current detecting and modulate circuit, the utility model adopts current Hall module CHB-25NP at a high speed to realize three-phase current detection, and utilize optical isolation amplifier 26 to isolate, to improve the antijamming capability of detection signal, the model of the optical isolation amplifier that present embodiment adopts is HCPL7840, the model of operational amplifier 27 is LF358, operational amplifier 27 adds to the output voltage of optocoupler HCPL7840, and 2V's is biased.

Described drive circuit comprises level shifting circuit and driving chip, the input of level shifting circuit is the input of drive circuit, the output of level shifting circuit connects driving chip, the output of driving chip is the output of drive circuit, the isolated drive circuit of the reactive power compensator of present embodiment as shown in figure 17, the pwm signal sent by FPGA is after level conversion, give driving chip 2SD315A, this chip has the isolation voltage of 4000VAC, be provided with short circuit and overcurrent protection function, the mode of operation of 2SD315A is set to on-line operation pattern, two control signals can be inputted like this in INA and INB two pins, and two power tubes can be driven simultaneously.

Based on the control method of the reactive power compensator of novel modularized many level topological structure, specifically comprise: adopt the i based on instantaneous reactive power theory _p-i _qelectric current testing detects electric current; Due to idle be the set-point that current compensation controls with the detected value of harmonic current, the effect directly affecting STATCOM with the performance of Harmonic currents detection compensate so idle, adopts the i based on instantaneous reactive power theory _p-i _qelectric current testing, has good real-time, can accurately detect the size of active current in electrical network and reactive current, is undelayed substantially when detecting fundamental reactive current.

Due to i _p-i _qharmonic currents detection method only needs the angle information of three-phase transient current and a phase line voltage, and thus external signal testing circuit is simple.In addition, i _p-i _qdetection method adopts inner reference sinusoidal signal, directly uses system voltage information to participate in computing, is not subject to electrical network voltage distortion or asymmetricly affects.

First, by threephase load current i _a, i _b, i _cunder transforming to dq coordinate system, namely

$\left[\begin{array}{c}{i}_d\\ i_q\\ i_0\end{array}\right]=C_{2s/2r}{C}_{3s/2s}\left[\begin{array}{c}{i}_a\\ i_b\\ i_c\end{array}\right]=T_{abc-dq}\left[\begin{array}{c}{i}_a\\ i_b\\ i_c\end{array}\right]---\left(18\right)$

Wherein, T _abc-dqfor transformation matrix of coordinates is

In formula, ω t is the anglec of rotation with synchronized, is realized by phase-locked loop (PLL).

Fig. 9 is System Reactive Power and Harmonic currents detection schematic diagram, the load current i in figure _a, i _b, i _ccomponent i under formula (18) conversion obtains dq coordinate _d, i _q.From instantaneous reactive power theory, after coordinate transform, obtain meritorious, reactive current component i in load _d, i _q, after low-pass filtering treatment, obtain reflected load current first harmonics component respectively by i _d, i _qwith make meritorious, the idle component i that difference obtains reflecting harmonic wave _d-hrm, i _q-hrm.By above i _d-hrm, i _q-hrmand i _qcombine, three kinds of electric currents with practical significance can be formed, respectively: (1) i _d-hrm+ i _q-hrm, be harmonic wave in load; (2) i _q, be reactive current component in load; (3) i _q+ i _d-hrm, be the idle and harmonic wave in load.

The control method of the described reactive power compensator based on novel modularized many level topological structure comprises and controlling respectively power model and full-bridge modules, the control of power model comprises and to control the capacitor voltage equalizing of power model and based on the Double closed-loop of voltage and current of Feedforward Decoupling, and the control of full-bridge modules comprises the suppression of the circulation of and whole reactive power compensator balanced to full-bridge modules capacitance voltage.

The capacitor voltage equalizing of described power model controls to comprise voltage between phases balance and controls and the control of independent voltage balance, and described voltage between phases control balancing is made as: outer voltage is the mean value making every phase 2N power model capacitance voltage with the set-point U of power model capacitance voltage _refdiffer from, poor with the circulation of this phase after PI regulates, as the command signal that average voltage controls after electric current loop proportion adjustment, be defined as u _aj, described in with circulation i _cirexpression formula be respectively:

${\stackrel{\‾}{U}}_c=\frac{1}{2N}\underset{j=1}{\overset{2N}{\Σ}}{U}_{cj}$

$i_{cir}=\frac{1}{2}(i_P+i_N)$

Individual capacitor voltages balance controls as shown in Figure 5, detects the module capacitance voltage U of every mutually upper and lower brachium pontis _cji, by the set-point U of itself and module capacitance voltage _refcompare, through proportion adjustment, then be multiplied with corresponding bridge arm current, because bridge arm current is influential for the discharge and recharge of module capacitance, need sign function revised be increased: as bridge arm current i in this phase _pduring >0, sign function is just, gets 1; Work as i _pduring <0, sign function is negative, gets-1.Lower brachium pontis and upper brachium pontis similar, finally obtain the instruction u that every mutually upper and lower brachium pontis independent voltage balance controls _bPjand u _bNj.

The current control method of STATCOM system can divide directly and indirect control two classes.Direct control directly controls the output current of converter, mainly contains Hysteresis control and triangle wave control; Indirect control STATCOM is equivalent to a controlled alternating-current voltage source, indirectly controls output current by the amplitude and phase place regulating inverter output voltage.Through comparing discovery, Direct Current Control wants to reach desirable control effects, just needs very high switching frequency, causes switching loss to increase, therefore be unsuitable for applying in great power conversion circuit system, therefore the utility model adopts the current indirect control method based on Feedforward Decoupling.

By the Analysis of Equivalent Circuit to system, the loss of whole current transformer is equivalent to fixed resistance R, and linked reactor and line inductance are equivalent to inductance L, and inverter output voltage is many level staircase waveform, harmonic content is little, therefore can ignore harmonic wave and only consider its fundametal compoment; Think system three-phase symmetrical, ac output voltage and capacitance voltage linear.For star connection, under abc coordinate system, can be obtained by Kirchoff s voltage current law:

$L\frac{d}{dt}\left[\begin{array}{c}{i}_a\\ i_b\\ i_c\end{array}\right]=\left[\begin{array}{c}{v}_{sa}\\ v_{sb}\\ v_{sc}\end{array}\right]-\left[\begin{array}{c}{v}_{ca}\\ v_{cb}\\ v_{cc}\end{array}\right]-R\left[\begin{array}{c}{i}_a\\ i_b\\ i_c\end{array}\right]---\left(20\right)$

DC bus capacitor instantaneous power is sTATCOM direct current with exchange both sides energy conservation relation, can obtain:

${\mathrm{NCu}}_{dc}\frac{{\mathrm{du}}_{dc}}{dt}=v_{ca}{i}_a+v_{cb}{i}_b+v_{cc}{i}_c---\left(21\right)$

In formula, N is the total electric capacity number of DC side, again due to i _a, i _b, i _cthe electric current sent in the STATCOM moment, v _sa, v _sb, v _scfor certain moment line voltage value, v _ca, v _cb, v _ccfor the STATCOM moment sends magnitude of voltage, C is capacitance, u _dcfor the voltage on electric capacity, and:

$\left\{\begin{array}{c}{v}_{sa}=\sqrt{2}{U}_{s}sin\left(\mathrm{\&omega;}t\right)\\ v_{sb}=\sqrt{2}{U}_{s}sin(\mathrm{\&omega;}t-\frac{2}{3}\mathrm{\&pi;})\\ v_{sc}=\sqrt{2}{U}_{s}sin(\mathrm{\&omega;}t+\frac{2}{3}\mathrm{\&pi;})\end{array}\right.---\left(22\right)$

$\left\{\begin{array}{c}{v}_{ca}={\mathrm{Mu}}_{dc}sin(\mathrm{\&omega;}t-\mathrm{\&delta;})\\ v_{cb}={\mathrm{Mu}}_{dc}\sin (\mathrm{\&omega;}t-\frac{2}{3}\mathrm{\&pi;}-\mathrm{\&delta;})\\ v_{cc}={\mathrm{Mu}}_{dc}sin(\mathrm{\&omega;}t+\frac{2}{3}\mathrm{\&pi;}-\mathrm{\&delta;})\end{array}\right.---\left(23\right)$

Must under abc coordinate by (20) to (23), the Mathematical Modeling calculating STATCOM is:

$\left\{\begin{array}{c}\frac{{\mathrm{di}}_a}{dt}=\sqrt{2}{U}_{S}sin\left(\mathrm{\&omega;}t\right)-{\mathrm{Mu}}_{dc}sin(\mathrm{\&omega;}t-\mathrm{\&delta;})-{\mathrm{Ri}}_a\\ \frac{{\mathrm{di}}_b}{dt}=\sqrt{2}{U}_{S}sin(\mathrm{\&omega;}t-\frac{2}{3}\mathrm{\&pi;})-{\mathrm{Mu}}_{dc}sin(\mathrm{\&omega;}t-\frac{2}{3}\mathrm{\&pi;}-\mathrm{\&delta;})-{\mathrm{Ri}}_b\\ \frac{{\mathrm{di}}_c}{dt}=\sqrt{2}{U}_{S}sin(\mathrm{\&omega;}t+\frac{2}{3}\mathrm{\&pi;})-{\mathrm{Mu}}_{dc}sin(\mathrm{\&omega;}t+\frac{2}{3}\mathrm{\&pi;}-\mathrm{\&delta;})-{\mathrm{Ri}}_c\\ \frac{{\mathrm{du}}_{dc}}{dt}=\frac{M}{NC}\&lsqb;i_{a}sin(\mathrm{\&omega;}t-\mathrm{\&delta;})+i_{b}sin(\mathrm{\&omega;}t-\frac{2}{3}\mathrm{\&pi;}-\mathrm{\&delta;})+i_{c}sin(\mathrm{\&omega;}t+\frac{2}{3}\mathrm{\&pi;}-\mathrm{\&delta;})\&rsqb;\end{array}\right.---\left(24\right)$

Introduce dq conversion, formula (24) becomes under rotating coordinate system:

$\begin{array}{c}\frac{d}{dt}\left[\begin{array}{c}{i}_d\\ i_q\end{array}\right]=\frac{d}{dt}\left(T_{abc-dq}\left[\begin{array}{c}{i}_a\\ i_b\\ i_c\end{array}\right]\right)=T_{abc-dq}\frac{d}{dt}\left[\begin{array}{c}{i}_a\\ i_b\\ i_c\end{array}\right]+\frac{{\mathrm{dT}}_{abc-dq}}{dt}\left[\begin{array}{c}{i}_a\\ i_b\\ i_c\end{array}\right]\\ =T_{abc-dq}\frac{d}{dt}\left[\begin{array}{c}{i}_a\\ i_b\\ i_c\end{array}\right]+\mathrm{\&omega;}\left[\begin{array}{c}{i}_d\\ i_q\end{array}\right]=\left[\begin{array}{cc}-\frac{R}{L}& \mathrm{\&omega;}\\ -\mathrm{\&omega;}& -\frac{R}{L}\end{array}\right]\left[\begin{array}{c}{i}_d\\ i_q\end{array}\right]+\frac{1}{L}\left[\begin{array}{c}{v}_{sd}-v_{cq}\\ v_{sq}-v_{cq}\end{array}\right]\end{array}---\left(25\right)$

In formula, v _sd, v _sq, v _cd, v _cqbe respectively the dq component of line voltage and STATCOM output voltage, i _d, i _qfor the dq component of STATCOM output current.Due to U _soverlap with d axle, therefore have following formula to set up:

$\left[\begin{array}{c}{v}_{sd}\\ v_{sq}\end{array}\right]=\sqrt{3}{U}_s\left[\begin{array}{c}1\\ 0\end{array}\right],\left[\begin{array}{c}{v}_{cd}\\ v_{cq}\end{array}\right]=\frac{\sqrt{3}}{2}{\mathrm{Mu}}_{dc}\left[\begin{array}{c}1\\ 0\end{array}\right]\left[\begin{array}{c}cos\mathrm{\&delta;}\\ sin\mathrm{\&delta;}\end{array}\right]---\left(26\right)$

Wherein: δ is the phase difference of STATCOM output voltage and line voltage, M is modulation ratio, U _sfor line voltage.Selection controlled quentity controlled variable is the dq axle component v of the output voltage of STATCOM _cdand v _cq, due to δ=tg ^-1(v _cd/ v _cq), by will change the Power Exchange of STATCOM and electrical network to the control of M and δ, thus bucking-out system is idle.STATCOM output voltage v can be obtained according to formula (21) _cd, v _cqexpression formula:

$\left[\begin{array}{c}{v}_{cd}\\ v_{cq}\end{array}\right]=\left[\begin{array}{c}{v}_{sd}\\ v_{sq}\end{array}\right]+\left[\begin{array}{cc}-R& \mathrm{\&omega;}L\\ -\mathrm{\&omega;}L& -R\end{array}\right]\left[\begin{array}{c}{i}_d\\ i_q\end{array}\right]-L\frac{d}{dt}\left[\begin{array}{c}{i}_d\\ i_q\end{array}\right]---\left(27\right)$

Gained merit according to formula (27), reactive current control block diagram as shown in Figure 10.Can obviously find out, STATCOM system is a typical coupled system, i _d, i _qbe coupled by reactor, the change of STATCOM output voltage can have influence on the change of output current, and dq axle influences each other, and is unfavorable for controlling.By taking certain measure to dq decoupler shaft, control can be made more simple, and current transformation becomes DC quantity after dq axle, is regulated can realize floating adjustment by conventional linear PI.

Feed forward decoupling control strategy is as follows, introduces intermediate variable x ₁, x ₂:

$\left\{\begin{array}{c}{x}_1=v_{sd}-v_{cd}+{\mathrm{\&omega;Li}}_q\\ x_2=v_{sq}-v_{cq}+{\mathrm{\&omega;Li}}_d\end{array}\right.---\left(28\right)$

Can be obtained by (27) and (28):

$\frac{d}{dt}\left[\begin{array}{c}{i}_d\\ i_q\end{array}\right]=\left[\begin{array}{cc}-R/L& 0\\ 0& -R/L\end{array}\right]---\left(29\right)$

$\left[\begin{array}{c}{x}_1\\ x_2\end{array}\right]=\left[\begin{array}{c}{K}_1({i_d}^{*}-i_d)+\frac{K_1}{T_1}\&Integral;({i_d}^{*}-i_d)dt\\ K_2({i_q}^{*}-i_q)+\frac{K_2}{T_2}\&Integral;({i_q}^{*}-i_q)dt\end{array}\right]---\left(30\right)$

Wherein, K ₁, K ₂for proportionality coefficient, T ₁, T ₂for integral coefficient, i _dand i _qbe respectively the current component of the dq reference axis that MMC converter exports, i _d ^*and i _q ^*be respectively the set-point of active current in load and reactive current component;

As shown in figure 11, by this conversion, the current design of dq axle is become two PI controllers, its output is exactly intermediate variable x ₁, x ₂, so just can realize the uneoupled control of dq shaft current.

As shown in figure 12, STATCOM system is made up of outer voltage and current inner loop described Double closed-loop of voltage and current, and wherein, outer voltage is the capacitance voltage controlling DC side, makes it keep constant, given direct voltage U _refcompare with Converter DC-side capacitance voltage, regulate through voltage PI, it exports as active current set-point i _d ^*, load current obtains reactive current set-point i through coordinate transform, negate process _q ^*; By the three-phase current i that converter exports _abci is obtained through coordinate transform _dand i _q, with i _d ^*, i _q ^*compare, regulate through electric current loop PI, obtain the output voltage V expected _cd, V _cq; To V _cd, V _cqcarry out coordinate inversion obtain rest frame under three-phase modulations ripple, pwm control signal is obtained after the triangular carrier produced with phase-shifting carrier wave controller, corresponding power switch pipe in MMC module is driven through power amplifier, thus the amplitude of control STATCOM output voltage and phase place, reach the object of compensating reactive power.

Described full-bridge modules capacitance voltage balancing procedure comprises: the set-point V of each mutually upper and lower brachium pontis full-bridge modules capacitance voltage _{h, ref}compare with the actual capacitance voltage of full-bridge modules, through PI controller, after it exports and is multiplied by the sign function of this bridge arm current, by the full-bridge modules voltage given value V generated _{r, ref}with obtain PWM ripple after triangular carrier, wherein, r=P, N, drive corresponding power switch pipe in full-bridge modules, carry out charge and discharge control, realize the equilibrium of full-bridge modules capacitance voltage to the electric capacity of full-bridge modules;

Described loop current suppression process comprises: compared with the reference value of circulation respectively by each phase circulation, now the reference value i of circulation _{cir, ref}=i _dc/ 3, the result obtained forms the voltage adjustment signal of a full-bridge modules by a proportional controller, and this voltage adjustment signal is divided into 2 parts, is added in respectively on the voltage signal of this mutually upper and lower brachium pontis full-bridge modules.

The utility model realizes the programming of master controller DSP by the design of main program, capture interrupt subprogram and T1 cycle interruption subprogram.

The integrated planning of STATCOM systems soft ware has been come by program design, it is mainly configured the operational environment of dsp system, in system correlated variables initialization, each interrupt initialization, judge whether opens interrupters subprogram etc., then enter and receive and send in the circulation of data, wait for the generation of interrupt event simultaneously.When interruption is unlocked, temporarily stop major cycle, enter into corresponding interrupt service subroutine and carry out various computing and configuration pwm control signal.After having interrupted, return major cycle, continued to wait for the generation next time interrupted.Main program flow chart as shown in figure 18.

The design of capture interrupt subprogram is to realize digital phase-locked loop, with the frequency of detection of grid.The unlatching of capture interrupt subprogram is then that the rising edge produced by the zero crossing of a phase voltage signal is triggered.It should be noted that the frequency of electrical network is not unalterable 50Hz, but one among a small circle in fluctuation, therefore need to carry out one and limit and judge, concrete implementation method is as shown in figure 19.

The flow chart of T1 interruption subroutine as shown in figure 20; to complete in this subprogram the sampling of electric current and voltage, bridge arm current polarity judgement, with the communication of FPGA, submodule voltage protection, the calculating of active reactive and the calculating etc. of three-phase modulations ripple, the main algorithm of DSP module all completes in this subprogram.

Proof procedure:

For verification system reactive power compensation effect, Figure 21 be power network compensation before A phase voltage, current waveform, can find out, compensate before electric current obviously lag behind voltage; Figure 22 be compensate after A phase voltage and current waveform, phase voltage, current phase are consistent.Visible, the utility model has good compensation effect to idle.

For checking submodule capacitor voltage portfolio effect, in the upper and lower brachium pontis of a phase, the capacitance voltage of half-bridge submodule as shown in figure 25, can be seen, upper and lower brachium pontis submodule capacitor voltage is basically stable at 1000V, fluctuates at about 10V.Visible, the utility model has the equal pressure energy power of good submodule.

For verification system is to the rejection ability of circulation, Figure 26 gives and adopts three phase circulation waveforms before and after loop current suppression device, and Figure 27 is three phase circulation waveforms after adopting loop current suppression device, can find out that three phase circulations obtain effective suppression.Visible, the utility model has suppression circulation ability preferably.

Claims (6)

1. based on the reactive power compensator of novel modularized many level topological structure, comprise three-phase alternating-current supply, resistance sense load, converter, control circuit, signal deteching circuit and drive circuit, described converter comprises three identical brachium pontis be connected in parallel of structure, each brachium pontis comprises about point symmetry in brachium pontis and the upper brachium pontis be connected in series and lower brachium pontis, it is characterized in that: described upper brachium pontis comprises the inductance of series connection mutually, some half-bridge cells and a H-bridge unit, the inductance of upper brachium pontis and the inductance of lower brachium pontis are connected in series, the mid point of converter three brachium pontis is connected between three-phase alternating-current supply and resistance sense load by conductor in parallel, the input of signal deteching circuit connects the output of three-phase alternating-current supply respectively, the input of resistance sense load, the output of converter, converter three brachium pontis, each half-bridge cells of converter and H-bridge unit, the input of the output connection control circuit of signal deteching circuit, the output of control circuit is connected by drive circuit and converter.

2. according to claim 1 based on the reactive power compensator of novel modularized many level topological structure, it is characterized in that: described control circuit comprises phase-shifting carrier wave controller, first control unit and the second control unit, the output of the first control unit and the output of the second control unit all connect with phase-shifting carrier wave controller, described first control unit comprises the first comparator (1), second comparator (3), 3rd comparator (5), 4th comparator (7), 5th comparator (9), one PI controller (2), 2nd PI controller (4), 3rd PI controller (8), first coordinate converter (6), second coordinate converter (12), first reactor (10) and the second reactor (11), first comparator (1), one PI controller (2), second comparator (3), 2nd PI controller (4) and the 3rd comparator (5) access the first coordinate converter after connecting successively, 4th comparator (7), 3rd PI controller (8) and the 5th comparator (9) access the first coordinate converter (6) after connecting successively, the output of the first coordinate converter (6) connects phase-shifting carrier wave controller, the output of phase-shifting carrier wave controller connects drive circuit, the output of described converter connects the second coordinate converter, first output of the second coordinate converter connects the second comparator (3) and the second reactor (11) respectively, the output of the second reactor (11) connects the 3rd comparator (5), another output of second coordinate converter connects the 4th comparator (7) and the first reactor (10) respectively, the output of the first reactor (10) connects the 5th comparator (9).

3. according to claim 2 based on the reactive power compensator of novel modularized many level topological structure, it is characterized in that: described second control unit comprises the 6th comparator (13), 7th comparator (15), 8th comparator (18), 9th comparator (21), first proportional controller (14), second proportional controller (17), 4th PI controller (16), 5th PI controller (19) sum functions module (20), 6th comparator (13), first proportional controller (14), 7th comparator (15), 4th PI controller (16) and the second proportional controller (17) access the 9th comparator (21) after connecting successively, 8th comparator (18), 5th PI controller (19) sum functions module (20) accesses the 9th comparator (21) after connecting successively, the output of the 9th comparator (21) connects described phase-shifting carrier wave controller.

4. according to claim 2 based on the reactive power compensator of novel modularized many level topological structure, it is characterized in that: described control circuit comprises DSP module and FPGA module, the output of DSP module connects FPGA module, the output of FPGA module connects drive circuit, described first control unit and the second control unit are integrated in DSP module, and described phase-shifting carrier wave controller is integrated in FPGA module.

5. according to claim 1 based on the reactive power compensator of novel modularized many level topological structure, it is characterized in that: the described reactive power compensator based on novel modularized many level topological structure comprises zero cross detection circuit, described zero cross detection circuit comprises voltage sensor (22), comparison circuit (23) and optocoupler (24), the input of voltage sensor (22) connects the output of three-phase alternating-current supply, the output of voltage sensor (22) connects the input of comparison circuit (23), the output of comparison circuit (23) accesses DSP module afterwards by optocoupler (24).

6. according to claim 1 based on the reactive power compensator of novel modularized many level topological structure, it is characterized in that: described drive circuit comprises level shifting circuit and driving chip, the input of level shifting circuit is the input of drive circuit, the output of level shifting circuit connects driving chip, and the output of driving chip is the output of drive circuit.