CN103227581B - Inverter parallel harmonic wave ring current restraining method for controlling harmonic wave droop - Google Patents

Abstract

The invention discloses an inverter parallel harmonic wave ring current restraining method for controlling harmonic wave droop. The method comprises a harmonic wave droop control, a power droop control and a voltage control. During the harmonic wave droop control, feature subharmonic power is detected through a rapid Fourier FFT (fast fourier transform algorithm) commutation fractional frequency, according to a harmonic wave droop feature, and a feature subharmonic reference voltage output by an inverter is calculated; and during the power droop control, the fundamental wave reference voltage is calculated, the feature subharmonic reference voltage and the fundamental wave reference voltage are combined into the reference voltage output by the inverter, the output voltage distortion of the inverter is effectively reduced, the inter-harmonic ring current of the inverter is controlled, and the power accurate allocation is realized. The inverter parallel harmonic wave ring current restraining method provided by the invention can be used for solving the problems that when a large number of non-linear loads are switched on the parallel system, the voltage distortion of a system is serious, a harmonic wave ring current is magnified and the like, the inverter parallel harmonic wave ring current restraining method is effectively applied to an industry special power supply, a UPS (uninterrupted power supply) and a distributed energy system.

Description

A kind of inverter parallel harmonic circulating current inhibition method of harmonic wave droop control

Technical field

The present invention relates to a kind of inverter parallel harmonic circulating current inhibition method in multi-inverter parallel system field, particularly harmonic wave droop control in distributed power generation, UPS, special power supply.

Background technology

In order to utilize more fully distributed power generation and regenerative resource (as wind energy, solar energy, tidal energy etc.), adopt the form of micro-electrical network to organize its access, and with isolated island or grid-connected form operation, become the study hotspot in current generation of electricity by new energy field.Because raising and the power electronic device of load capacity are held quantitative limitation, distributed power source generally adopts the mode of inverter parallel to access micro-electrical network.Therefore, the stable parallel running of inverter will greatly improve whole volume and the reliability of micro-grid system.

For multi-inverter parallel there is not the equal flow problem of inverter in distortion situation with linear load, output voltage in operation, and virtual impedance technology is suggested and is applied in multi-inverter parallel control system.By introducing virtual impedance, redesign inverter equivalent output impedance and become resistive or perceptual, and according to the characteristics design droop control device of equivalent output impedance, at Fundamental wave suppression circulation with realize power and accurately reached good control effect aspect distribution.

But the high frequency action of switching tube during inverter parallel, nonlinear-load and containing the power distribution network of harmonic wave etc., all may impact inverter output voltage, make inverter output voltage produce distortion, and between inverter, produce harmonic circulating current, affect power between inverter and accurately distribute.Now, if adopt again virtual impedance art designs inverter equivalent output impedance to become resistive or perceptual, cannot suppress harmonic circulating current between inverter, realize power between inverter and accurately distribute, can not get well controlling effect.

Summary of the invention

Technical problem to be solved by this invention is, not enough for prior art, a kind of inverter parallel harmonic circulating current inhibition method of harmonic wave droop control is provided, solve existing method and be applied to multi-inverter parallel system band nonlinear-load when operation, inverter output voltage produces distortion, cause producing between inverter harmonic circulating current, the low problem of power division precision between inverter.

For solving the problems of the technologies described above, the technical solution adopted in the present invention is: a kind of inverter parallel harmonic circulating current inhibition method of harmonic wave droop control, comprise the multi-inverter parallel system with nonlinear-load, described multi-inverter parallel system comprises the inverter that several are in parallel, and described inverter comprises DC power supply, inverter circuit, LC filter circuit, line impedance, processor, Drive Protecting Circuit; Described DC power supply, inverter circuit, LC filter circuit connect successively, and described LC filter circuit is by line impedance incoming transport bus; Described processor input is connected with described LC filter circuit; Described processor output is connected with described Drive Protecting Circuit input; Described inverter circuit comprises two brachium pontis in parallel, and described brachium pontis is composed in series by two full-control type power devices, and described Drive Protecting Circuit drives the full-control type power device in described inverter circuit, and the method is:

1) in the starting point in each sampling period, processor is by LC filter circuit filter capacitor voltage u _owith filter capacitor current i _c, line current i _osample respectively and process;

2) by LC filtering circuit capacitor voltage u _oafter 90 ° of phase shifts, with line current i _omultiply each other and obtain virtual instantaneous reactive power q, LC filtering circuit capacitor voltage u _owith line current i _omultiply each other and obtain instantaneous active power p;

3) instantaneous active power p obtains inverter fundamental active power average value P through digital low-pass filtering, and virtual instantaneous reactive power q obtains inverter First Harmonic Reactive Power mean value Q through digital band pass filtering;

4) to the unloaded output reference voltage amplitude of inverter E ^*, unloaded reference angle frequencies omega ^*, fundamental active power average value P, First Harmonic Reactive Power mean value Q carry out power droop control, calculates first-harmonic reference voltage u _r1;

5) instantaneous active power p and virtual instantaneous reactive power q are carried out to fast Fourier transform FFT, obtain the active power average value P of inverter h subharmonic _hwith reactive power mean value Q _h;

6) to the unloaded reference angle frequencies omega of inverter ^*active power average value P with h subharmonic _h, reactive power mean value Q _hcarry out the computing of h subharmonic droop control, obtain the effective value E of inverter output h subharmonic reference voltage _hand angular frequency _h;

7) by the effective value E of h subharmonic reference voltage _hand angular frequency _hthe synthetic h subharmonic reference voltage u that obtains _rh;

8) by h subharmonic reference voltage u _rhwith first-harmonic reference voltage u _r1superpose, obtain inverter output reference voltage u _r;

9) introduce virtual resistance R _v, by inverter output reference voltage u _rdeduct line current i _owith virtual resistance R _vproduct, obtain LC filtering circuit capacitor voltage reference value u ^* _r;

10) LC filtering circuit capacitor voltage reference value u ^* _rwith LC filter circuit filter capacitor voltage u _othrough quasi-resonance, control, obtain the reference value i of LC filtering circuit capacitor electric current _c ^*;

11) the reference value i of LC filtering circuit capacitor electric current _c ^*with filter capacitor current i _cthrough ratio, regulate and obtain SPWM modulating wave d, SPWM modulating wave and triangular carrier carry out bipolarity modulation, obtain the duty cycle signals of full-control type power device, through Drive Protecting Circuit, control opening and turn-offing of full-control type power device.

In described step 3), the expression formula of inverter fundamental active power average value P, First Harmonic Reactive Power mean value Q is:

$\{\begin{array}{c}P=\frac{{\mathrm{\ω}}_o}{s+{\mathrm{\ω}}_o}p\\ Q={\mathrm{\ω}}_o\frac{s}{(s+{\mathrm{\τ}}^{-1})(s+{\mathrm{\ω}}_o)}q\end{array},$

Wherein, ω<sub TranNum="137">o</sub>for the cut-off frequency of wave digital lowpass filter, τ is the sagging time constant of transient state, 0.95<τ<1.05, and s is complex frequency.

In described step 4), first-harmonic reference voltage u _r1computing formula is:

$u_{\mathrm{<figure-callout\; id="1"\; label="r"\; filenames="HDA00003171139400021.png"\; state="\{\{state\}\}">r</figure-callout>}1}=\sqrt{2}(E^{*}-n_{1}P)\sin \left(({\mathrm{\&omega;}}^{*}+m_{1}Q)t\right)$

Wherein, m ₁and n ₁sagging coefficient for power droop control.

In described step 6), the effective value E of h reference harmonic voltage of inverter output _hand angular frequency _hcomputing formula be:

$\left\{\begin{array}{c}{\mathrm{\&omega;}}_h={\mathrm{h\&omega;}}^{*}-m_h{Q}_h\\ E_h=-n_h{P}_h\end{array},\right.$

Wherein, m _hand n _hsagging coefficient for h subharmonic.

In described step 7), h subharmonic reference voltage u _rhcomputing formula is:

$u_{\mathrm{rh}}=\sqrt{2}{E}_h\sin (\mathrm{h\&omega;t}+{\mathrm{\&phi;}}_h)$

Wherein, h is harmonic number, and ω is first-harmonic angular frequency,

starting phase angle for h reference harmonic voltage.

In described step 10), the transfer function that quasi-resonance is controlled is:

$G\left(s\right)=k_p+\frac{2k_r{\mathrm{\&omega;}}_{\mathrm{<figure-callout\; id="2"\; label="c\; s\; s"\; filenames="HDA00003171139400022.png"\; state="\{\{state\}\}">c</figure-callout>}}s}{s^{}}$

Wherein, k<sub TranNum="163">p</sub>and k<sub TranNum="164">r</sub>be respectively proportionality coefficient and the resonance gain of quasi-resonance controller, 3<k<sub TranNum="165">p</sub><5,100<k<sub TranNum="166">r</sub><150, ω<sub TranNum="167">c</sub>for cut-off frequency, s is complex frequency.

The sagging Coefficient m of h subharmonic _hand n _hcomputing formula be respectively:

$m_h={\mathrm{<figure-callout\; id="1"\; label="m"\; filenames="HDA00003171139400021.png"\; state="\{\{state\}\}">m</figure-callout>}}_1\frac{\mathrm{hQ}}{Q_h},$ $U_o\left(\mathrm{THD}\right)=\frac{\left|Z_{\mathrm{oh}}\left(\mathrm{hj\&omega;}\right)\right|I_{\mathrm{oh}}}{(1+n_h{I}_{\mathrm{oh}})E^{*}},$

Wherein, h is harmonic number, m ₁and n ₁for the sagging coefficient of power droop control, U _o(THD) be the aberration rate of inverter output voltage, Z _o(hj ω) is the impedance of h subharmonic, I _oheffective value for h subharmonic current.Actual, choose in process the sagging coefficient n of harmonic wave _hchoosing should be as far as possible bigger than normal.

Compared with prior art, the beneficial effect that the present invention has is: the present invention proposes a kind of inverter parallel harmonic circulating current inhibition method of harmonic wave droop control, comprise harmonic wave droop control, power droop control and voltage control.Harmonic wave droop control, by fast Fourier transform FFT frequency division detected characteristics subharmonic power, according to harmonic wave droop characteristic, calculates the harmonics reference voltage of inverter output; Power droop control calculates first-harmonic reference voltage; Both are synthetic as inverter output reference voltage, thereby effectively reduce inverter output voltage distortion, suppress harmonic circulating current between inverter, realize power and accurately distribute.The problems such as when the invention solves nonlinear-load and accessing parallel system in a large number, system voltage distortion is serious, harmonic circulating current increase, can effectively be applied to industrial special power supply, UPS, distributing-supplying-energy system.

Accompanying drawing explanation

Fig. 1 is one embodiment of the invention multi-inverter parallel system configuration schematic diagram;

Fig. 2 is one embodiment of the invention harmonic wave droop control and power droop control structured flowchart;

Fig. 3 is that one embodiment of the invention inverter output voltage encircles control block diagram more;

Fig. 4 is the simulation waveform figure of the inverter parallel circulation inhibition method of one embodiment of the invention harmonic wave droop control; Fig. 4 (a) is circulation oscillogram between ac bus voltage waveform and inverter; Fig. 4 (b) is ac bus output voltage waveforms spectrum analysis figure.

Embodiment

Figure 1 shows that one embodiment of the invention multi-inverter parallel system configuration schematic diagram, comprise the inverter that several are in parallel.Described multi-inverter parallel system comprises the inverter that several are in parallel; described inverter comprises DC power supply, inverter circuit, LC filter circuit, line impedance, sampling and control circuit, Drive Protecting Circuit (seeing utility model patent " a kind of high frequency light photovoltaic grid-connected system ", [ZL201120462487.7]).Described DC power supply, inverter circuit, LC filter circuit connect successively, and described LC filter circuit is by line impedance incoming transport bus; Described sampling is connected with described LC filter circuit with control circuit input; Described sampling is connected with described Drive Protecting Circuit input with control circuit; Described inverter circuit comprises two brachium pontis in parallel, and described brachium pontis is composed in series by two full-control type power devices, and described Drive Protecting Circuit drives the full-control type power device in described inverter circuit.Full-control type power device adopts IGBT.Sampling consists of sample peripheral circuit and microprocessor with control circuit, and wherein, sampling peripheral circuit completes sampling and the filtering of voltage, current signal and processes.Microprocessor adopts dsp controller.Inductance L and capacitor C form inverter circuit AC filter circuit, are used for the high-frequency harmonic that filtering inverter circuit AC produces.U _dcfor current transformer DC voltage, u _invfor AC side of converter voltage, i _ofor line current, i _lfor inductive current, i _cfor capacitance current, u _ofor output filter capacitor voltage.

In Fig. 1, Z _linebe line impedance, comprise line resistance R _linewith line reactance X _line, i.e. Z _line=R _line+ X _line.

The inverter parallel harmonic circulating current inhibition method of harmonic wave droop control of the present invention is as follows:

1) in the starting point in each sampling period, sampling and control circuit are by inverter output filter capacitor voltage u _owith filter capacitor current i _c, line current i _osample respectively and process;

2) by LC filtering circuit capacitor voltage u _oafter 90 ° of phase shifts, with line current i _omultiply each other and obtain virtual instantaneous reactive power q, LC filtering circuit capacitor voltage u _owith line current i _omultiply each other and obtain instantaneous active power p;

3) instantaneous active power p obtains fundamental active power average value P through digital low-pass filtering, and virtual instantaneous reactive power q obtains First Harmonic Reactive Power mean value Q through digital band pass filtering;

4) the unloaded output reference voltage amplitude of inverter E ^*, unloaded reference angle frequencies omega ^*, fundamental active power average value P, reactive power mean value Q carry out power droop control, calculates first-harmonic reference voltage u _r1, its computing formula is:

$u_{\mathrm{<figure-callout\; id="1"\; label="r"\; filenames="HDA00003171139400021.png"\; state="\{\{state\}\}">r</figure-callout>}1}=\sqrt{2}(E^{*}-n_{1}P)\sin \left(({\mathrm{\&omega;}}^{*}+m_{1}Q)t\right)$

Wherein, m ₁and n ₁sagging coefficient for power droop control;

5) instantaneous active power p and virtual instantaneous reactive power q are carried out to fast Fourier transform (FFT), can obtain the active power average value P of h subharmonic _hwith reactive power mean value Q _h;

6) the unloaded reference angle frequencies omega of inverter ^*active power average value P with h subharmonic _h, reactive power mean value Q _hcarry out the computing of h subharmonic droop control, obtain the effective value E of inverter output h subharmonic reference voltage _hand angular frequency _h;

7) by the effective value E of h subharmonic reference voltage _hand angular frequency _hthe synthetic h subharmonic reference voltage u that obtains _rh;

8) by h subharmonic reference voltage u _rhwith first-harmonic reference voltage u _r1superpose, obtain inverter output reference voltage u _r;

9) introduce virtual resistance R _v, by inverter output reference voltage u _rdeduct line current i _owith virtual resistance R _vproduct, obtain LC filtering circuit capacitor voltage reference value u ^* _r;

10) u ^* _rwith inverter output voltage u _othrough quasi-resonance (QPR), control, obtain the reference value i of LC filtering circuit capacitor electric current _c ^*;

11) the reference value i of LC filtering circuit capacitor electric current _c ^*with filter capacitor current i _cthrough ratio, regulate and obtain SPWM modulating wave d, SPWM modulating wave and triangular carrier carry out bipolarity modulation, obtain the duty cycle signals of full-control type power device, through Drive Protecting Circuit, control opening and turn-offing of full-control type power device.

Fig. 2 is harmonic wave droop control device structured flowchart.Only consider the impact of line impedance, inverter is equivalent to voltage source E ∠ δ and equivalent output impedance Z _o∠ θ series connection.Traditional power analysis method is often voltage source load equivalent, and active power and reactive power that now inverter is transferred to load by transfer impedance are expressed formula because of the difference difference of inverter output impedance type, and corresponding droop control equation is also different.When inverter equivalent output impedance becomes perceptual, resistive and capacitive, power delivery equation and droop control equation are as shown in the table:

Table 1 power expression and droop control equation

In table, E _i ^*and ω _i ^*be respectively unloaded output reference voltage amplitude, unloaded reference angle frequency, i represents i platform inverter, ω _ifor first-harmonic angular frequency.

When load equivalent is current source, inverter actual output voltage:

${\stackrel{\&CenterDot;}{U}}_o=E\&angle;\mathrm{\&delta;}-Z_o{I}_o\&angle;\mathrm{\&theta;}=E\cos \mathrm{\&delta;}-Z_o{I}_o\cos \mathrm{\&theta;}+j(E\sin \mathrm{\&sigma;}-Z_o{I}_o\sin \mathrm{\&theta;})---\left(1\right)$

Active power and reactive power that inverter is transferred to load by output impedance are respectively

$\left\{\begin{array}{c}P={\mathrm{EI}}_o\cos \mathrm{\&delta;}-Z_{\mathrm{<figure-callout\; id="2"\; label="o\; I\; o"\; filenames="HDA00003171139400022.png"\; state="\{\{state\}\}">o</figure-callout>}}{I_o}^{}{{}_{}}^2\cos \mathrm{\&theta;}\\ Q={\mathrm{EI}}_o\sin \mathrm{\&delta;}-Z_{\mathrm{<figure-callout\; id="2"\; label="o\; I\; o"\; filenames="HDA00003171139400022.png"\; state="\{\{state\}\}">o</figure-callout>}}{I_o}^{}{{}_{}}^2\sin \mathrm{\&theta;}\end{array}\right.---\left(2\right)$

Wherein, δ is the phase difference of inverter output voltage and electric current, when δ is very little, has

$\left\{\begin{array}{c}P\&ap;{\mathrm{EI}}_o-Z_{\mathrm{<figure-callout\; id="2"\; label="o\; I\; o"\; filenames="HDA00003171139400022.png"\; state="\{\{state\}\}">o</figure-callout>}}{I_o}^{}{{}_{}}^2\cos \mathrm{\&theta;}\\ Q\&ap;{\mathrm{EI}}_o\mathrm{\&delta;}-Z_{\mathrm{<figure-callout\; id="2"\; label="o\; I\; o"\; filenames="HDA00003171139400022.png"\; state="\{\{state\}\}">o</figure-callout>}}{I_o}^{}{{}_{}}^2\sin \mathrm{\&theta;}\end{array}\right.---\left(3\right)$

According to formula (3), no matter, for the output impedance of which kind of characteristic, active power is relevant with voltage, and reactive power is relevant with phase angle.Therefore, be different from the situation that load equivalent is voltage source, when load equivalent is current source, the design of droop control device does not rely on the characteristic of inverter equivalent output impedance, under any circumstance, all only has a kind of droop control equation:

$\left\{\begin{array}{c}{\mathrm{\&omega;}}_i={\mathrm{\&omega;}}^{*}-m_i{Q}_i\\ E_i=E^{*}-n_i{P}_i\end{array}\right.---\left(4\right)$

This makes to control for inverter parallel easier, especially when needs design harmonic wave droop control device and improve inverter output voltage aberration rate, does not spend the characteristic of judgement inverter output impedance under each secondary frequencies and distinguishes CONTROLLER DESIGN.

Can proper P=0 by formula (2), during Q=0:

E=Z _oI _o，δ=θ （5）

This condition is identical without the condition of harmonic component with inverter actual output voltage.Can be for ensuing harmonic wave droop control device design.

Inverter actual output voltage harmonic component u _oh=0, the harmonic wave pressure drop on inverter equivalent output impedance equals the harmonic component of inverter output reference voltage, has formula (5) to set up.When setting E ^*=0, ω ^*during=h ω, can obtain harmonic wave droop control equation:

$\left\{\begin{array}{c}{\mathrm{\&omega;}}_h={\mathrm{h\&omega;}}^{*}-m_h{Q}_h\\ E_h=-n_h{P}_h\end{array}---\left(6\right)\right.$

Voltage magnitude as shown in Figure 2, in harmonic wave droop control, in voltage magnitude control channel, only there is a proportional component, so can exist static receiver error and make load harmonic voltage U when stable state _ohcan not be entirely 0(close to 0).

Consider the inverter output equivalent circuit under single frequency, according to Kirchhoff's law, harmonic voltage amplitude U _ohcan be approximately:

U _oh≈E _h-|Z _o(hjω)|I _oh （7）

By formula (6) substitution above formula, have:

U _oh≈-n _hU _ohI _oh-|Z _o(hjω)|I _oh （8）

That is:

$U_{\mathrm{oh}}\&ap;-\frac{\left|Z_o\left(\mathrm{hj\&omega;}\right)\right|I_{\mathrm{oh}}}{1+n_h{I}_{\mathrm{oh}}}---\left(9\right)$

Voltage distortion rate now can be approximately:

$U_o\left(\mathrm{THD}\right)=\frac{\left|Z_{\mathrm{oh}}\left(\mathrm{hj\&omega;}\right)\right|I_{\mathrm{oh}}}{(1+n_h{I}_{\mathrm{oh}})E^{*}}---\left(10\right)$

From formula (10), can find out voltage distortion rate and output impedance Z _o(hj ω) is directly proportional, with sagging coefficient n _hbe inversely proportional to.Therefore under the prerequisite of system stability, sagging coefficient n _hlarger, voltage distortion rate is lower, and harmonic suppression effect is better.When design inverter equivalent output impedance, should make as far as possible output impedance Z simultaneously _o(hj ω) is little.

Sagging Coefficient m _hwith power droop control Coefficient m ₁choose relevant.The frequency droop degree being defined under fundamental frequency is

${\mathrm{\&gamma;}}_1=\frac{m_{1}Q}{\mathrm{\&omega;}}---\left(11\right)$

The frequency droop degree γ under h subfrequency _hshould equal the sag under fundamental frequency, have

${\mathrm{\&gamma;}}_h=\frac{m_h{Q}_h}{\mathrm{h\&omega;}}={\mathrm{\&gamma;}}_1=\frac{m_{1}Q}{\mathrm{\&omega;}}---\left(12\right)$

In formula: Q _hfor h subharmonic reactive power.By above formula, can be tried to achieve:

$m_h={\mathrm{<figure-callout\; id="1"\; label="m"\; filenames="HDA00003171139400021.png"\; state="\{\{state\}\}">m</figure-callout>}}_1\frac{\mathrm{hQ}}{Q_h}---\left(13\right)$

From formula (13), can find out m _hshould be much larger than m ₁, because Q _hmuch smaller than hQ.

Conventional power droop control is relevant with inverter equivalent output impedance, and by table 1, when inverter output impedance is resistive, active power is relevant with voltage, and reactive power is relevant with frequency.The unloaded output reference voltage amplitude of inverter E ^*, unloaded reference angle frequencies omega ^*, fundamental active power average value P, reactive power mean value Q carry out power droop control, can calculate first-harmonic reference voltage u _r1, be expressed as

$u_{r1}=\sqrt{2}(E^{*}-n_{1}P)\sin \left(({\mathrm{\&omega;}}^{*}+m_{1}Q)t\right)---\left(14\right)$

H subharmonic reference voltage u _rhwith first-harmonic reference voltage u _r1after superposeing, obtain inverter output reference voltage u _rsend into the many ring controllers of inverter output voltage.

Fig. 3 is that inverter output voltage encircles control block diagram more.Generally, the micro-power network line impedance comparison of low-voltage is high, for inverter equivalent output impedance is well mated with micro-power network line impedance, in outer voltage, adopt virtual impedance method to introduce output current feedback, make inverter equivalent output impedance be resistive.The expression formula of introducing output current feedback is

u _r ^*=u _r-R _Vi _o （15）

R wherein _vfor current feedback coefficient, obviously, R _vvalue is larger, and inverter equivalent output impedance is larger.But when design harmonic wave droop control device, Z _o(hj ω) is less, and voltage distortion rate is less, therefore, and R _vshould not choose excessive.

Double closed-loop of voltage and current is mainly controlled in outer shroud, capacitance current ratio and is encircled and form by voltage quasi-resonance QPR.Voltage reference signal u wherein _rharmonic wave droop control device in Fig. 3 produces.Consider filter capacitor reference voltage u _r ^*with filter capacitor actual voltage value u _othe voltage error signal obtaining is AC signal, adopts traditional PI to control and is difficult to eliminate steady-state error, affects the harmonic suppression effect of harmonic wave droop control device.And quasi-resonance is controlled at the gain of fundamental frequency place greatly, at harmonic frequency place, gain very little, both can eliminate steady-state error completely, can reduce again the impact of electric voltage frequency skew, can well reduce inverter output voltage aberration rate.

The transfer function of accurate ratio resonant controller is:

$G\left(s\right)=k_p+\frac{2k_r{\mathrm{\&omega;}}_{c}s}{{\mathrm{<figure-callout\; id="2"\; label="s"\; filenames="HDA00003171139400022.png"\; state="\{\{state\}\}">s</figure-callout>}}^2+2{\mathrm{\&omega;}}_{c}s+{{\mathrm{\&omega;}}_o}^2}---\left(16\right)$

Wherein: k<sub TranNum="369">p</sub>and k<sub TranNum="370">r</sub>be as the criterion respectively proportionality coefficient and the resonance gain of PR controller, 3<k<sub TranNum="371">p</sub><5,100<k<sub TranNum="372">r</sub><150, ω<sub TranNum="373">c</sub>for cut-off frequency.

The accurate ratio resonance of voltage is controlled outer shroud and is obtained capacitance current reference signal i _c ^*with capacitor current feedback signal i _cin regulating through ratio, ring obtains SPWM modulation signal.SPWM modulation signal and triangular carrier carry out bipolarity modulation, draw the duty cycle signals of full-control type power device.

Figure 4 shows that two inverter parallel simulation waveform figure of the inverter parallel harmonic circulating current inhibition method that adopts harmonic wave droop control.Suppose that inverter capacity is 2kVA, load as uncontrollable rectifier bridge nonlinear-load.Wherein, 4 (a) are circulation waveform between ac bus voltage waveform and inverter, and 4 (b) are the spectrum analysis of ac bus output voltage waveforms.From simulation waveform, can find out, a kind of micro-electrical network multi-inverter parallel harmonic wave droop control method proposed by the invention can effectively be improved inverter output voltage waveform, reduces output voltage aberration rate, suppress circulation between inverter, realizes power between inverter and accurately distributes.

Claims (4)

1. the inverter parallel harmonic circulating current inhibition method of a harmonic wave droop control, comprise the multi-inverter parallel system with nonlinear-load, described multi-inverter parallel system comprises the inverter that several are in parallel, and described inverter comprises DC power supply, inverter circuit, LC filter circuit, line impedance, processor, Drive Protecting Circuit; Described DC power supply, inverter circuit, LC filter circuit connect successively, and described LC filter circuit is by line impedance incoming transport bus; Described processor input is connected with described LC filter circuit; Described processor output is connected with described Drive Protecting Circuit input; Described inverter circuit comprises two brachium pontis in parallel, and described brachium pontis is composed in series by two full-control type power devices, and described Drive Protecting Circuit drives the full-control type power device in described inverter circuit, it is characterized in that, the method is:

1) in the starting point in each sampling period, processor is by LC filter circuit filter capacitor voltage u _owith filter capacitor current i _c, line current i _osample respectively and process;

2) by LC filtering circuit capacitor voltage u _oafter 90 ° of phase shifts, with line current i _omultiply each other and obtain virtual instantaneous reactive power q, LC filtering circuit capacitor voltage u _owith line current i _omultiply each other and obtain instantaneous active power p;

3) instantaneous active power p obtains inverter fundamental active power average value P through digital low-pass filtering, and virtual instantaneous reactive power q obtains inverter First Harmonic Reactive Power mean value Q through digital band pass filtering;

4) to the unloaded output reference voltage amplitude of inverter E ^*, unloaded reference angle frequencies omega ^*, fundamental active power average value P, First Harmonic Reactive Power mean value Q carry out power droop control, calculates first-harmonic reference voltage u _r1;

5) instantaneous active power p and virtual instantaneous reactive power q are carried out to fast Fourier transform FFT, obtain the active power average value P of the h subharmonic of inverter output _hwith reactive power mean value Q _h;

6) to the unloaded reference angle frequencies omega of inverter ^*active power average value P with h subharmonic _h, reactive power mean value Q _hcarry out the computing of h subharmonic droop control, obtain the effective value E of inverter output h subharmonic reference voltage _hand angular frequency _h;

7) by the effective value E of h subharmonic reference voltage _hand angular frequency _hthe synthetic h subharmonic reference voltage u that obtains _rh;

8) by h subharmonic reference voltage u _rhwith first-harmonic reference voltage u _r1superpose, obtain inverter output reference voltage u _r;

9) introduce virtual resistance R _v, by inverter output reference voltage u _rdeduct line current i _owith virtual resistance R _vproduct, obtain LC filtering circuit capacitor voltage reference value u ^* _r;

10) LC filtering circuit capacitor voltage reference value u ^* _rwith LC filter circuit filter capacitor voltage u _othrough quasi-resonance, control, obtain the reference value i of LC filtering circuit capacitor electric current _c ^*;

11) the reference value i of LC filtering circuit capacitor electric current _c ^*with filter capacitor current i _cthrough ratio, regulate and obtain SPWM modulating wave d, SPWM modulating wave and triangular carrier carry out bipolarity modulation, obtain the duty cycle signals of full-control type power device, through Drive Protecting Circuit, control opening and turn-offing of full-control type power device;

In described step 4), first-harmonic reference voltage u _r1computing formula is:

$u_{r1}=\sqrt{2}(E^{*}-n_{1}P)\sin \left(({\mathrm{\&omega;}}^{*}+m_{1}Q)t\right)$

Wherein, m ₁and n ₁sagging coefficient for power droop control;

In described step 6), the effective value E of h reference harmonic voltage of inverter output _hand angular frequency _hcomputing formula be:

$\left\{\begin{array}{c}{\mathrm{\&omega;}}_h={\mathrm{h\&omega;}}^{*}-m_h{Q}_h\\ E_h=-n_h{P}_h\end{array}\right.,$

Wherein, m _hand n _hsagging coefficient for h subharmonic;

In described step 7), h subharmonic reference voltage u _rhcomputing formula is:

$u_{\mathrm{rh}}=\sqrt{2}{E}_h\sin (\mathrm{h\&omega;t}+{\mathrm{\&phi;}}_h)$

Wherein, h is harmonic number, and ω is first-harmonic angular frequency, φ _hstarting phase angle for h reference harmonic voltage.

2. the inverter parallel harmonic circulating current inhibition method of harmonic wave droop control according to claim 1, is characterized in that, in described step 3), the expression formula of inverter fundamental active power average value P, First Harmonic Reactive Power mean value Q is:

$\left\{\begin{array}{c}P=\frac{{\mathrm{\&omega;}}_o}{s+{\mathrm{\&omega;}}_o}p\\ Q={\mathrm{\&omega;}}_o\frac{s}{(s+{\mathrm{\&tau;}}^{-1})(s+{\mathrm{\&omega;}}_o)}q\end{array},\right.$

Wherein, ω<sub TranNum="456">o</sub>for the cut-off frequency of wave digital lowpass filter, τ is the sagging time constant of transient state, 0.95<τ<1.05, and s is complex frequency.

3. the inverter parallel harmonic circulating current inhibition method of harmonic wave droop control according to claim 1, is characterized in that, in described step 10), the transfer function that quasi-resonance is controlled is:

$G\left(s\right)=k_p+\frac{2k_r{\mathrm{\&omega;}}_{c}s}{s^2+2{\mathrm{\&omega;}}_{c}s+{{\mathrm{\&omega;}}_o}^2}$

Wherein, k<sub TranNum="462">p</sub>and k<sub TranNum="463">r</sub>be respectively proportionality coefficient and the resonance gain of quasi-resonance controller, 3<k<sub TranNum="464">p</sub><5,100<k<sub TranNum="465">r</sub><150, ω<sub TranNum="466">c</sub>for cut-off frequency, s is complex frequency, ω<sub TranNum="467">o</sub>cut-off frequency for wave digital lowpass filter.

4. the inverter parallel harmonic circulating current inhibition method of harmonic wave droop control according to claim 1, is characterized in that, the sagging Coefficient m of described h subharmonic _hand n _hcomputing formula be respectively:

$m_h=m_1\frac{\mathrm{hQ}}{Q_h},U_o\left(\mathrm{THD}\right)=\frac{\left|Z_{\mathrm{oh}}\left(\mathrm{hj\&omega;}\right)\right|I_{\mathrm{oh}}}{(1+n_h{I}_{\mathrm{oh}})E^{*}},$

Wherein, h is harmonic number, m ₁and n ₁for the sagging coefficient of power droop control, U _o(THD) be the aberration rate of inverter output voltage, Z _o(hj ω) is the impedance of h subharmonic, I _oheffective value for h subharmonic current.

Images