CN103684021B - Inverter parallel control system - Google Patents

Abstract

The invention provides a kind of inverter parallel control system, this system comprises at least two inversion units that are connected in parallel to ac bus, each inversion unit comprises inverter, droop control module, reference voltage generation unit and fine-adjusting unit, also comprise: busbar voltage detecting unit and voltage to frequency adjustable ring, be used for according to frequency and the amplitude of the busbar voltage gathering, calculate unloaded output angle frequency values δ ω and unloaded output voltage amplitude δ E, and offer respectively the droop control module of each inversion unit; Droop control module is for calculating the frequency instruction value ω that exports to j inversion unit_jWith amplitude command value E_j, and offer reference voltage generation unit, to form reference voltage υ_ref. Inverter parallel control system provided by the present invention, regulates the voltage-regulation can effectively be adapted to the fluctuation of load time to the voltage-frequency of whole inversion system by setting up.

Description

Inverter parallel control system

Technical field

The present invention relates to Electrical Control Technology, relate in particular to a kind of inverter parallel control system.

Background technology

Along with the increase of urban traffic pressure, city rail vehicle becomes more and more important track traffic workTool. Subordinate inverter is as a part for light rail car, the operation of the reliability of its work to whole vehicleHave a great impact, how to improve power supply reliability extremely urgent.

Prior art is the demand that adapts to high power load, most of subordinate inverter Parallel Control that adoptsScheme, is connected in parallel by multiple inversion units, provides power supply to load. Subordinate inverter joint controlGenerally there is fluctuation of service and the large problem of circulation in scheme processed, prior art often in practiceAdopt voltage-frequency droop control strategy to export adjustment.

Contravarianter voltage-frequency droop control principle as shown in Figure 1, is connected in parallel to the each contrary of ac busBecome unit and comprise inverter 1, droop control module, reference voltage generation unit 3 and fine-adjusting unit 4.Inverter 1 is exactly can be by pulse width modulation (PulseWidthModulation is called for short PWM)The PWM inverter that control signal is controlled. Droop control module comprises power calculation unit 21With droop control unit 22.

The essence of voltage-frequency droop method control strategy is: each inversion unit detects the electricity that self exportsPressure value u and current value i; Calculate accordingly active-power P and reactive power Q; Based on droop characteristic songLine obtains output voltage frequency command value ω to be adjusted_iWith amplitude command value E_i; Then refer to according to frequencyThe value of order and amplitude command value, by adjusting the anti-phase fine setting inverter output voltage of pwm control signalAmplitude and frequency, thereby reach the reasonable distribution of meritorious and reactive power. , meritorious for outputHigh-power inversion unit, reduces its output frequency by frequency droop characteristic, gains merit thereby reduce itPower stage; The inversion unit that active power of output is little, increases its output frequently by frequency droop characteristicRate, thus its active power output increased; The inversion unit that output reactive power is large, under amplitudeVertical characteristic reduces its voltage magnitude, thereby reduces its output reactive power; Little contrary of output reactive powerBecome unit, raise its voltage magnitude by amplitude droop characteristic, thereby increase its output reactive power.Be that the less inversion unit of power output can increase its output according to voltage-frequency droop characteristic, and exportThe inversion unit that power is relatively many reduces its output accordingly, and this self-control process willBe sustained, until parallel system reaches minimum ring flow point. Because inversion unit internal resistance is very little,Its output external characteristic can compare " firmly ", very little amplitude or phase difference all can inversion unit in parallel itBetween produce very large system circulation. Thereby introduce the control of voltage-frequency droop method, will make its output specialProperty phase strain " soft ".

The output voltage frequency of inversion unit and amplitude change based on following formula (1):

$\left\{\begin{array}{c}{\mathrm{\ω}}_j={\mathrm{\ω}}_{0j}-m_j{P}_j\\ E_j=E_{0j}-n_j{Q}_j\end{array}(j=\mathrm{1,2},...,n)\right.---\left(1\right)$

Wherein, the quantity that n is inversion unit, ω_0jBe the unloaded output angle frequency of j inversion unit, E_0iForJ the unloaded output voltage amplitude of inversion unit, P_jBe the active power of output of j inversion unit, Q_jBe the output reactive power of j inversion unit, m_jBe the sagging of j inversion unit output angle frequencyCoefficient, n_jIt is the sagging coefficient of j inversion unit output amplitude.

So voltage-frequency droop control strategy can utilize above-mentioned formula (1) to calculate output voltageFrequency instruction value ω_iWith amplitude command value E_i。

But there is following defect in the voltage-frequency droop control method that prior art adopts: voltage-frequency droop control strategy be the power output of inversion unit is carried out among a small circle in part dynamically micro-Adjust, but cannot tackle the power adjusting of the fluctuation of load when larger, can not realize static error free.

Summary of the invention

The invention provides a kind of inverter parallel control system, the inverter merit when adapting to the fluctuation of loadRate regulates.

The invention provides a kind of inverter parallel control system, comprise and be connected in parallel at least two of ac busIndividual inversion unit, each described inversion unit comprises that inverter, droop control module, reference voltage generateUnit and fine-adjusting unit, is characterized in that, also comprises:

Busbar voltage detecting unit, for gathering the frequencies omega of busbar voltage from ac bus_MGAnd amplitudeE_MG；

Voltage to frequency adjustable ring, is connected with described busbar voltage detecting unit, for according to gather busThe frequency of voltage and amplitude, based on the unloaded output angle frequency values δ ω of following formula calculating droop control moduleWith the unloaded output voltage amplitude δ E of droop control module, and offer respectively the sagging control of each inversion unitMolding piece:

δω=k_pω(ω_MG ^*-ω_MG)+k_iω∫(ω_MG ^*-ω_MG)dt+Δωs

δE=k_pE(E_MG ^*-E_MG)+k_iE∫(E_MG ^*-E_MG)dt

Wherein, k_pω、k_iω、k_pEAnd k_iEBe respectively the control parameter of setting, ω_MG ^*For the interchange mother who setsLine electric voltage frequency value, E_MG ^*For the ac bus voltage magnitude of setting, the output that Δ ω s is synchronous pllValue;

Wherein, described droop control module, for calculating and export to j inversion list based on following formulaThe frequency instruction value ω of unit_jWith amplitude command value E_j, and offer reference voltage generation unit, to form ginsengExamine voltage u_ref：

$\left\{\begin{array}{c}{\mathrm{\ω}}_j={\mathrm{\ω}}_{0j}-m_j{P}_j\\ E_j=E_{0j}-n_j{Q}_j\end{array}\right.(j=\mathrm{1,2},......,n),$ Wherein, $\left\{\begin{array}{c}{\mathrm{\ω}}_{0j}=\mathrm{\δ\ω}\\ E_{0j}=\mathrm{\δE}\end{array}\right.$

Wherein, the quantity that n is inversion unit, ω_0jBe the unloaded output angle frequency of j inversion unit, E_0jBe the unloaded output voltage amplitude of j inversion unit, P_jBe the active power of output of j inversion unit,Q_jBe the output reactive power of j inversion unit, m_jBe j inversion unit output angle frequency underCoefficient, n hang down_jIt is the sagging coefficient of j inversion unit output amplitude.

Inverter parallel control system provided by the present invention, by set up voltage to whole inversion system-Frequency adjustment, the voltage-regulation can effectively be adapted to the fluctuation of load time.

Brief description of the drawings

Fig. 1 is contravarianter voltage-frequency droop control principle schematic diagram in prior art;

The structural representation of the inverter parallel control system that Fig. 2 provides for the embodiment of the present invention;

Virtual impedance circuit signal in the inverter parallel control system that Fig. 3 provides for the embodiment of the present inventionFigure.

Detailed description of the invention

The structural representation of the inverter parallel control system that Fig. 2 provides for the embodiment of the present invention, the present inventionThe inverter parallel control system that embodiment provides, comprises that to be connected in parallel at least two of ac bus 20 contraryBecome unit 10, the present embodiment is only to comprise that three inversion units 10 describe as example, other quantityInversion unit 10 is adopted in a like fashion and is connected.

Each inversion unit 10 comprises inverter 1, droop control module 2, reference voltage generation unit 3With fine-adjusting unit 4. Wherein, inverter 1 is typically the PWM inverter of pwm control signal control.Output voltage and the electric current of droop control module 2 specifically for gathering according to inversion unit 10 outputs, meterCalculate active power and reactive power, then the droop characteristic based on frequency and amplitude is determined frequency instructionValue and amplitude command value, parameter acquisition, power calculation and sagging feature calculation process all can be with reference to Fig. 1 institutesThe prior art of showing realizes. Reference voltage generation unit 3 is for according to frequency instruction value and amplitude instructionReference voltage is calculated and produced to value. Fine-adjusting unit 4 specifically can comprise Voltage loop and electric current loop, i.e. voltage electricityThe two Closed Loop Control Units of stream, for according to reference voltage, and the output voltage that feeds back of inverter 1 and defeatedGo out electric current, determine voltage quantities to be regulated and electric current variable, and change accordingly pwm control signal,Adjust the output voltage of inverter, the Voltage loop in fine-adjusting unit 4 and electric current loop adjustment process can be based onThere is technology to realize, in the present invention, this is not limited.

On the basis of technique scheme, the inverter parallel control system of the present embodiment further comprises:Busbar voltage detecting unit 30 and voltage to frequency adjustable ring 40.

Wherein, busbar voltage detecting unit 30, for gathering the frequencies omega of busbar voltage from ac bus 20_MGWith amplitude E_MG; Voltage to frequency adjustable ring 40 is connected with busbar voltage detecting unit 30, adopts for basisFrequency and the amplitude of the busbar voltage of collection, calculate droop control module based on following formula (2) and (3)Unloaded output angle frequency values δ ω and the unloaded output voltage amplitude δ E of droop control module, and point you can well imagineSupply with the droop control module 2 of each inversion unit 10:

δω=k_pω(ω_MG ^*-ω_MG)+k_iω∫(ω_MG ^*-ω_MG)dt+Δωs（2）

δE=k_pE(E_MG ^*-E_MG)+k_iE∫(E_MG ^*-E_MG)dt（3）

Wherein, k_pω、k_iω、k_pEAnd k_iEBe respectively the control parameter of setting, conventionally can be tied by technical staffClose experience and experimental result presets. ω_MG ^*For the ac bus electric voltage frequency value of setting, E_MG ^*For the ac bus voltage magnitude of setting, the output valve that Δ ω s is synchronous pll, synchronous pll is used forKeep the Phase synchronization between different inversion units, make it by the frequency values of controlling inversion unit outputPhase synchronization, genlock technology is prior art, has considered that synchronous pll is to frequency in the present embodimentOverall control effect.

Voltage to frequency adjustable ring is that all inversion units are carried out to the link that entirety is controlled, unloaded output angular frequencyRate value δ ω and unloaded output voltage amplitude δ E offer respectively the droop control module of each inversion unit. RespectivelyThe droop control module of inversion unit, except according to existing droop control policy calculation, also needs to consider emptyCarry output angle frequency values δ ω and unloaded output voltage amplitude δ E. , the droop control of j inversion unitModule is specifically for calculating the frequency instruction value ω that exports to j inversion unit based on following formula (4)_jWith amplitude command value E_j, and offer reference voltage generation unit, to form reference voltage υ_ref：

$\left\{\begin{array}{c}{\mathrm{\ω}}_j={\mathrm{\ω}}_{0j}-m_j{P}_j\\ E_j=E_{0j}-n_j{Q}_j\end{array}\right.(j=\mathrm{1,2},....,n),$ Wherein $\left\{\begin{array}{c}{\mathrm{\ω}}_{0j}=\mathrm{\δ\ω}\\ E_{0j}=\mathrm{\δE}\end{array}\right.---\left(4\right)$

Wherein, the quantity that n is inversion unit, ω_0jBe the unloaded output angle frequency of j inversion unit, E_0jForJ the unloaded output voltage amplitude of inversion unit, P_jBe the active power of output of j inversion unit, Q_jBe the output reactive power of j inversion unit, m_jBe the sagging of j inversion unit output angle frequencyCoefficient, n_jIt is the sagging coefficient of j inversion unit output amplitude. The unloaded output angle frequencies omega of inversion unit_0jWith the unloaded output voltage amplitude E of inversion unit_0jCome from respectively voltage to frequency adjustable ring output δ ω andδE。

By more known with existing droop control formula (1), the embodiment of the present invention is at existing droop controlBasis on, further set up overall electric voltage frequency control, be equivalent to amplitude and frequency secondary adjustJoint, adjusts whole inverter parallel control system can be adapted to the fluctuation of load time, makes it rapidMeet the demand of the fluctuation of load.

In the above embodiment of the present invention, preferably between reference voltage generation unit 3 and fine-adjusting unit 4, connectBe connected to virtual emotional resistance 5, can connect by comparator 6. And calculate and set based on following formula (5)Inverter output voltage value, adjust for fine-adjusting unit 4:

u₀ ^*=u_ref-Z_vir(s)i₀（5）

Wherein, u_o ^*For the inverter output voltage value of setting; u_refFor the output of reference voltage generation unit;Z_vir(s) be virtual emotional resistance value; i_oFor the output current value of inverter.

Between virtual emotional resistance 5 and reference voltage generation unit 3, also dispose low pass filter 7,For processing based on following formula (6) the reference voltage υ that reference voltage generation unit 3 is exported_ref：

$u_0*=u_{\mathrm{ref}}\left(s\right)-L_{\mathrm{vir}}s\frac{{\mathrm{\ω}}_p}{s+w_p}{i}_0---\left(6\right)$

Wherein, Z_vir(s)=L_virs，ω_pFor the break angular frequency of low pass filter.

In embodiments of the present invention, preferably virtual emotional resistance and low pass filter adopt respectively and are integrated with controlThe controller of algorithm processed is realized. Both can make the output impedance of inverter be perception without setting up hardware, fullThe precondition of afc voltage-frequency droop control strategy, ensures accuracy and the reliability controlled.

Be provided with the circuit of perceptual virtual impedance as shown in Figure 3. Be equivalent in inverter output end and referenceThe perceptual virtual impedance of having connected between voltage. As shown in Figure 3, because each inverter output of parallel connection hindersAnti-difference, and output impedance is all resistive under normal circumstances, the output impedance of shunt chopper like thisAffect the power-sharing precision of parallel system, when serious, even can have influence on based on active power and idleThe theory of the droop characteristic control that power is adjusted. In order to reduce the shadow of inverter output impedance to parallel systemRing, really do not seal in impedance at the output of inverter again, can in inverter system, add one long-rangeIn the virtual impedance of inverter output impedance. Namely make the output current of inverter with the shape of impedance voltage dropFormula deducts from its reference voltage.

Formula (5) can directly apply in the parallel system of linear load, still, and when load is non-lineWhen shape load, undoubtedly can be by output harmonic wave electric current drawing-in system, thus make to contain in inverter reference voltageThere is harmonic wave, finally strengthened the harmonic content of inverter output voltage; While is due to the frequency of harmonic currentHigher, in identical virtual inductor situation, can produce larger impedance voltage drop, reduce too much outputThe control accuracy of voltage. In order to overcome these deficiencies, can be by output current first by a low pass filterIts harmonic wave of filtering, obtains reference voltage by formula (6).

The embodiment of the present invention provides the course of work of inverter parallel control system as follows:

First, the interior ring droop control of each inversion unit, calculates by the electric current and voltage that self is exportedGo out active power and reactive power, then produce voltage and frequency instruction value, after the effect of virtual impedance ringVoltage magnitude by Voltage loop and electric current loop fine setting self and frequency realize the reasonable distribution of bearing power;Wherein, the effect of virtual impedance ring is to ensure that inverter output impedance is perceptual, and feels by configurationProperty virtual impedance value ensures that each inverter output impedance is consistent. Throw at inverter switching or heavy loadWhen cutting, iff the control and regulation of hanging down on the lower, output voltage has impact, easily produces circulation. AndVoltage to frequency adjustable ring add the impact that can reduce voltage, suppress inverter switching or heavy load and throwThe circulation producing while cutting.

As the above analysis, the embodiment of the present invention provides a kind of inverter parallel control system, shouldSystem can be used as the subordinate inverter of light rail train power supply, certainly, also can be widely used in various inversionsThe situation of device power supply. This inverter parallel control system has many advantages:

1, by setting up voltage to frequency adjustable ring, make the basis at voltage-frequency droop control strategyUpper, the fluctuation of load further reflecting according to ac bus voltage, can overall feedback arrive each inversion listIn unit, regulate rapidly, made up droop control strategy and only carried out the local deficiency of fine setting among a small circle,Can successfully manage the power adjusting of the fluctuation of load when larger, realize static error free.

2, the output impedance of existing inverter depends primarily on circuit and Qi Nei ring control strategy, oftenBe not perceptual, and the precondition that this and voltage-frequency droop control strategy are set up is disagreed, voltageIt is perceptual that the precondition of-frequency droop control strategy requires the output impedance of inverter. The present invention is realExecute example by set up virtual emotional resistance at inverter output end, make inverter output end present senseProperty impedance, meets the requirement of droop control strategy. Meanwhile, the embodiment of the present invention can adopt control algolithmRealize virtual emotional resistance, the output current that makes inverter with the form of impedance voltage drop from reference voltageMiddle removal. So not only meet impedance requirements, and also increased the body of inverter without setting up hardwareAmass and weight.

3, above-mentioned scheme of setting up virtual emotional resistance, can also reduce inverter output impedance and lineThe anti-impact on voltage-frequency droop control strategy of roadlock, reduces the generation of circulation.

The inverter parallel control system that the embodiment of the present invention provides, by the droop control plan traditionalOn basis slightly, improve, increase amplitude-frequency adjustment ring and virtual impedance ring, can solve output resistanceThe circulation problem that before and after the anti-inconsistent circulation problem causing and heavy load switching, voltge surge causes, therebyFor vehicle provides high-quality and reliable accessory power supply. The greatly raising power supply reliability of degree, presses downCirculation processed, the shortcoming of those control programs before overcoming.

Finally it should be noted that: above each embodiment is only in order to technical scheme of the present invention to be described, but not rightIts restriction; Although the present invention is had been described in detail with reference to aforementioned each embodiment, this area commonTechnical staff is to be understood that: its technical scheme that still can record aforementioned each embodiment is modified,Or some or all of technical characterictic is wherein equal to replacement; And these amendments or replacement, andDo not make the essence of appropriate technical solution depart from the scope of various embodiments of the present invention technical scheme.

Claims (3)

1. an inverter parallel control system, comprises three inversion units that are connected in parallel to ac bus, everyIndividual described inversion unit comprises inverter, droop control module, reference voltage generation unit and fine-adjusting unit,It is characterized in that, also comprise:

Busbar voltage detecting unit, for gathering the frequencies omega of busbar voltage from ac bus_MGAnd amplitudeE_MG；

Voltage to frequency adjustable ring, is connected with described busbar voltage detecting unit, for according to gather busThe frequency of voltage and amplitude, based on the unloaded output angle frequency values δ ω of following formula calculating droop control moduleWith the unloaded output voltage amplitude δ E of droop control module, and offer respectively the sagging control of each inversion unitMolding piece:

δω＝k_pω(ω_MG ^*-ω_MG)+k_iω∫(ω_MG ^*-ω_MG)dt+Δωs

δE＝k_pE(E_MG ^*-E_MG)+k_iE∫(E_MG ^*-E_MG)dt

Wherein, k_pω、k_iω、k_pEAnd k_iEBe respectively the control parameter of setting, ω_MG ^*For the interchange mother who setsLine electric voltage frequency value, E_MG ^*For the ac bus voltage magnitude of setting, the output that Δ ω s is synchronous pllValue;

Wherein, described droop control module, for calculating and export to j inversion list based on following formulaThe frequency instruction value ω of unit_jWith amplitude command value E_j, and offer reference voltage generation unit, to form ginsengExamine voltage u_ref：

$\left\{\begin{array}{c}{\mathrm{\ω}}_j={\mathrm{\ω}}_{0j}-m_j{P}_j\\ E_j=E_{0j}-n_j{Q}_j\end{array}\right.,(j=1,2,......,n),$ Wherein, $\left\{\begin{array}{c}{\mathrm{\ω}}_{0j}=\mathrm{\δ}\mathrm{\ω}\\ E_{0j}=\mathrm{\δ}E\end{array}\right.$

Wherein, the quantity that n is inversion unit, ω_0jBe the unloaded output angle frequency of j inversion unit, E_0jBe the unloaded output voltage amplitude of j inversion unit, P_jBe the active power of output of j inversion unit,Q_jBe the output reactive power of j inversion unit, m_jBe j inversion unit output angle frequency underCoefficient, n hang down_jIt is the sagging coefficient of j inversion unit output amplitude;

Between reference voltage generation unit and fine-adjusting unit, be connected with virtual emotional resistance, and based on followingFormula calculates the inverter output voltage value of setting, and adjusts for fine-adjusting unit:

u₀ ^*＝u_ref-Z_vir(s)i₀

Wherein, u_o ^*For the inverter output voltage value of setting; u_refFor the output of reference voltage generation unit;Z_vir(s) be virtual emotional resistance value; i_oFor the output current value of inverter.

2. inverter parallel control system according to claim 1, is characterized in that:

Between described virtual emotional resistance and reference voltage generation unit, also dispose low pass filter,Based on the reference voltage u of following formula manipulation reference voltage generation unit output_ref：

$u_0*=u_{ref}\left(s\right)-L_{vir}s\frac{{\mathrm{\ω}}_p}{s+w_p}{i}_0$

Wherein, Z_vir(s)＝L_virs，ω_pFor the break angular frequency of low pass filter.

3. inverter parallel control system according to claim 2, is characterized in that: described virtualEmotional resistance and low pass filter adopt respectively the controller that is integrated with control algolithm to realize.