CN105576708A - Reactive power equilibrium distribution control method during parallel operation of inverters in microgrid - Google Patents

Abstract

The invention relates to a reactive power equilibrium distribution control method during parallel operation of inverters in a microgrid. The method comprises the steps as follows: (1) a central controller collects reactive powers output by various DGs, and obtains total reactive power Q<a>; (2) given reactive powers of various DGs are calculated according to the total reactive power Q<a> and the capacities of various DGs; (3) an integral controller adjusts virtual impedance values according to difference values between the given reactive powers and corresponding output reactive powers of the DGs to obtain adaptive virtual impedances of the DGs; and (4) a reference voltage of voltage-current double loop control is obtained according to droop control and the adaptive virtual impedances, and reactive power output of the corresponding DG is adjusted. Compared with the prior art, the adaptive virtual impedances are added under a traditional droop control strategy, so that a voltage drop fall caused by a line difference is compensated; the influence on reactive power distribution caused by an impedance difference is eliminated; reasonable distribution of the reactive power can also be achieved when a load power factor changes; and the impedance values of lines do not need to be measured.

Description

Idle equilibrium assignment control method during inverter parallel in a kind of micro-capacitance sensor

Technical field

The present invention relates to the micro-capacitance sensor technical field in electric power system, the control method of reactive power reasonable distribution when especially relating to inverter parallel in a kind of micro-capacitance sensor.

Background technology

Micro-capacitance sensor is made up of equipment such as distributed power source (distributedgeneration, DG), energy storage device, energy conversion device, protective device and loads, can run on grid-connected and isolated island two kinds of patterns.When micro-grid connection is run, voltage and frequency are determined by system, more easily can reach power-sharing.

Traditional droop control of micro-capacitance sensor regulates each inverter output voltage amplitude and frequency according to each the meritorious and idle of DG unit output, and droop control equation can be expressed as:

$\left\{\begin{array}{c}{\mathrm{\&omega;}}_i={\mathrm{\&omega;}}_0-m_i{P}_i\\ U_i=U_0-n_i{Q}_i\end{array}\right.---\left(1\right)$

In formula: ω ₀, U ₀the voltage angle frequency exported when being respectively each DG zero load and amplitude; P _i, Q _ibe respectively i-th DG active power of output and reactive power; m _i, n _ibe respectively the meritorious sagging coefficient of i-th DG and idle sagging coefficient; ω _i, U _ibe respectively voltage angle frequency and the amplitude of i-th DG output.

Fig. 1 gives traditional droop control block diagram that formula (1) represents, i in figure _ofor inverter output inductor electric current; u _ofor inverter output filter capacitor voltage; ω, U are respectively droop control device and regulate the voltage angle frequency and amplitude that obtain, in order to the reference voltage of resultant voltage double current loop modulation.

Tradition droop control proposes under inverter output impedance and line impedance sum are the condition of perception.Micro-capacitance sensor adopts low-voltage transmission circuit usually, and in low pressure micro-capacitance sensor, line impedance is mainly in resistive, and according to traditional droop control, the adjustment of voltage magnitude can have influence on active power, and the adjustment of frequency also will have influence on idle, meritorious and reactive power coupling.Usually by adding virtual impedance, meritorious and idle decoupling zero is realized.

Because frequency is the global variable of micro-grid system, phase angle and frequency proportional, therefore active power can carry out reasonable distribution by the meritorious sagging coefficient of traditional droop control method.And voltage is local variable, if the line length that each DG is connected to points of common connection is inconsistent, then there are differences between the line impedance of DG, cause reactive power not divide equally.

The DG parallel running that two capacity are identical is load supplying jointly, and capacity is all identical with idle sagging coefficient.If DG ₁connection line inductance be less than DG ₂, represent that droop control can obtain idle distribution condition as shown in Figure 2 according to formula (1).Because line inductance is inconsistent, the load curve of output slope of two DG is different, and output end voltage is also different.DG ₂line inductance comparatively DG ₁greatly, load curve of output slope is comparatively large, and the terminal voltage of output is comparatively large, and that thus distributes is idle less, idlely can not divide equally.

Fig. 3 is the isolated island type micro-capacitance sensor equivalent electric circuit of two DG parallel runnings, and DG is connected to points of common connection by different line impedance.

In Fig. 3: R, Χ are DG ₁with DG ₂the line impedance of formed objects; Δ R, Δ Χ are DG ₁with DG ₂the difference of line impedance; Δ U ₁, Δ U ₂be respectively DG ₁and DG ₂output voltage is to the voltage-drop of PCC point.If DG ₂line impedance be greater than DG ₁, can release according to Fig. 3:

${\mathrm{\&Delta;U}}_1\&ap;\frac{{\mathrm{XQ}}_1+{\mathrm{RP}}_1}{U_0}---\left(2\right)$

${\mathrm{\&Delta;U}}_2\&ap;\frac{{\mathrm{XQ}}_2+{\mathrm{RP}}_2}{U_0}+\frac{{\mathrm{\&Delta;XQ}}_2+{\mathrm{\&Delta;RP}}_2}{U_0}={{\mathrm{\&Delta;U}}_2}^{-}+{{\mathrm{\&Delta;U}}_2}^{\&prime;}---\left(3\right)$

In formula, Δ U ₂ ^-, Δ U ₂' be respectively DG ₂power output is passed through and DG ₁the voltage-drop that same line impedance and different line impedance produce.The voltage drop drop that line impedance difference causes causes reactive power can not according to sagging coefficient reasonable distribution.

The reasonable distribution problem of reactive power is one of focus of micro-capacitance sensor research.Find a kind of microgrid inverter parallel Operation Control strategy, most important for the reactive power between reasonable distribution inverter.

The problem that the shortcoming of prior art and the application's motion will solve:

Micro-capacitance sensor adopts traditional droop control strategy, during inverter parallel, when the line impedance of each DG is inconsistent, reactive power will be caused can not to carry out idle dividing equally according to sagging coefficient, produce reactive circular power flow, affect the electrical network quality of power supply between inverter.

Many Chinese scholars attempt traditional droop control to improve.By injecting the very little harmonic wave of amplitude in DG output voltage, utilize harmonic voltage frequency feature all identical in whole microgrid to realize pro rate reactive power, but the injection of harmonic voltage makes DG output voltage electric current produce distortion, particularly in the circuit of output impedance in perception, harmonic wave is easily exaggerated, and affects the quality of power supply of electrical network.Reactive power can be improved by the droop control coefficient adjusting inverter and distribute offset issue, but excessive sagging coefficient can cause inverter output point voltage and points of common connection (pointofcommoncoupling, PCC) voltage-drop, even affects the operation stability of micro-capacitance sensor.By adding virtual impedance, inverter output impedance being designed to perception, with the application conditions of satisfied traditional droop control method, realizing rational power division, but need know line impedance value, in Practical Project, line impedance value is difficult to accurately record.And the virtual impedance value that the method adds immobilizes, when load power factor changes, can not accurately distribute idle between DG.

Summary of the invention

Object of the present invention is exactly idle equilibrium assignment control method when providing inverter parallel in the micro-capacitance sensor that a kind of convenience of calculation, control precision are high to overcome defect that above-mentioned prior art exists.

Object of the present invention can be achieved through the following technical solutions:

Idle equilibrium assignment control method during inverter parallel in a kind of micro-capacitance sensor, comprises the following steps:

1) central controller gathers the reactive power that each DG exports, and draws total reactive power Q _a:

$Q_a=\underset{i=1}{\overset{n}{\&Sigma;}}{Q}_i$

Wherein, Q _ibe the reactive power that i-th DG exports, i=1,2 ..., n, n are total number of DG;

2) according to total reactive power Q _awith the given reactive power of each DG of each DG calculation of capacity;

3) integral controller regulates virtual impedance value according to the difference of the given reactive power of each DG and corresponding actual output reactive power, obtains the self adaptation virtual impedance of each DG;

4) according to droop control and described self adaptation virtual impedance, obtain the reference voltage of electric current and voltage double-loop control, regulate the idle output of corresponding DG.

When multiple DG capacity of parallel connection are identical, described step 2) in, the given reactive power of each DG is by following formulae discovery:

Q _i0＝Q _a/n。

When multiple DG capacity of parallel connection are different, described step 2) in, the given reactive power of each DG carries out pro rate according to the capacity of each DG:

Q _i0＝r _iQ _a

Wherein, r _ibe the capacity ratio of i-th DG, r _i=C _i/ C _a, C _ibe the capacity of i-th DG, C _afor the total capacity of each DG.

Described step 3) in, the expression formula of self adaptation virtual impedance is:

$L_{iv}=\frac{K}{s}(Q_i-Q_{i0})$

Wherein, L _ivbe the self adaptation virtual impedance of i-th DG, Q _ibe the actual output reactive power of i-th DG, Q _i0be the given reactive power of i-th DG, K is integral coefficient.

Described step 4) be specially:

401) first voltage reference value of a DG and corresponding phase angle θ is obtained by droop control device;

402) according to the filter inductance current i that corresponding inverter exports by voltage phase angle θ _ocarry out dp conversion, obtain i _dand i _q;

403) according to step 402) i that obtains _dand i _qand step 3) obtain the self adaptation virtual impedance of corresponding DG, obtain the second voltage reference value;

404) by the first voltage reference value and the second voltage reference value superimposed, obtain the reference voltage of electric current and voltage double-loop control.

Compared with prior art, the present invention has the following advantages:

(1) the present invention carries out the adjustment of virtual impedance by load power, does not need the resistance value of measurement circuitry, and control method realizes simple;

(2) the present invention can conveniently realize DG line impedance inconsistent time the dividing equally of DG reactive power, namely idle in inverter capacity ratio reasonable distribution.

(3) when load power factor changes, the present invention also can facilitate, accurately realize idle reasonable distribution.

Accompanying drawing explanation

Fig. 1 is traditional droop control block diagram;

Two DG idle distribution condition when Fig. 2 is line inductance difference;

Fig. 3 is two DG parallel equivalent circuit;

Fig. 4 is self adaptation virtual impedance control block diagram of the present invention;

Fig. 5 be DG capacity identical time tradition droop control method under active power and reactive power simulation result figure;

Fig. 6 be DG capacity identical time control method of the present invention under active power and reactive power simulation result figure;

Fig. 7 be DG capacity different time control method of the present invention under active power and reactive power simulation result.

Embodiment

Below in conjunction with the drawings and specific embodiments, the present invention is described in detail.The present embodiment is implemented premised on technical solution of the present invention, give detailed execution mode and concrete operating process, but protection scope of the present invention is not limited to following embodiment.

Idle equilibrium assignment control method when the present embodiment provides inverter parallel in a kind of micro-capacitance sensor, central controller exports gross power and each inverter capacity according to inverter, calculate each inverter give constant volume, then be sent to inverter this locality to control, for adjusting virtual impedance size, the voltage drop drop that compensated line resistance difference causes, the high precision realizing load power is distributed.This control method specifically comprises the following steps:

1) central controller gathers the reactive power that each DG exports, and draws total reactive power Q _a:

Q _a＝Q ₁+Q ₂+…+Q _n(4)

Wherein, Q _ibe the reactive power that i-th DG exports, i=1,2 ..., n, n are total number of DG.

2) according to total reactive power Q _awith the given reactive power of each DG of each DG calculation of capacity.When multiple DG capacity of parallel connection are identical, load power allows each inverter divide equally, and the given reactive power of each DG is by following formulae discovery:

Q _i0＝Q _a/n。

When multiple DG capacity of parallel connection are different, the given reactive power of each DG carries out pro rate according to the capacity of each DG:

Q _i0＝r _iQ _a

Wherein, r _ibe the capacity ratio of i-th DG, r _i=C _i/ C _a, C _ibe the capacity of i-th DG, C _afor the total capacity of each DG.

3) integral controller regulates virtual impedance value according to the difference of the given reactive power of each DG and corresponding actual output reactive power, obtains the self adaptation virtual impedance of each DG:

$L_{iv}=\frac{K}{s}(Q_i-Q_{i0})$

Wherein, L _ivbe the self adaptation virtual impedance of i-th DG, Q _ibe the actual output reactive power of i-th DG, Q _i0be the given reactive power of i-th DG, K is integral coefficient.

4) according to droop control and described self adaptation virtual impedance, obtain the reference voltage of electric current and voltage double-loop control, regulate the idle output of corresponding DG, concrete control block diagram as shown in Figure 4:

401) obtain first voltage reference value of a DG and corresponding phase angle θ by droop control device, U can be obtained by the first Voltage Reference value transform _dand U _q;

402) according to the filter inductance current i that corresponding inverter exports by voltage phase angle θ _ocarry out dp conversion, obtain i _dand i _q;

403) according to step 402) i that obtains _dand i _qand step 3) obtain the self adaptation virtual impedance of corresponding DG, obtain the second voltage reference value;

404) by the first voltage reference value and the second voltage reference value superimposed, obtain the reference voltage of electric current and voltage double-loop control.

Matlab/Simulink software emulation platform is built microgrid inverter parallel running simulation model, in order to verify the validity of put forward the methods of the present invention.Simulation model is made up of two DG, in parallel powers for linear load.Load parameter is: P ₁=2.5kW, Q ₁=1kvar; P ₂=4.5kW, Q ₂=1kvar.When operating mode 1 simulation analysis two DG capacity are identical, the impact of power division when comparative analysis inverter adopts Traditional control strategy and control method of the present invention to change micro-grid load respectively; Operating mode 2 simulating, verifying inverter adopts the accuracy of control method of the present invention when DG capacity is different to sharing of load.Simulation parameter is as shown in table 1.

Table 1 simulation parameter

Operating mode 1

The DG parallel running that two capacity are identical, only load 1 is dropped into before 1s, active power and reactive power are respectively 2.5kW, 1kvar, during 1s, load 2 also puts into operation, systematic steady state runs afterload active power and reactive power becomes 7kW and 2kvar respectively, during 2s, load 2 is out of service, and systematic steady state runs afterload active power and reactive power becomes 2.5kW and 1var again, and simulation time is 3s.When two DG adopt traditional droop control, DG power output as shown in Figure 5.

Due to DG ₁with DG ₂capacity identical, reach reactive power reasonable distribution, when system cloud gray model is in stable state, each DG should be equal to the distribution of load or burden without work.Can be drawn by Fig. 5, when the DG of two identical capacity adopts traditional droop control method parallel running, before and after load change, DG can divide equally active power according to meritorious sagging coefficient, but due to the existence of connection line resistance difference, DG ₂line impedance is DG comparatively ₁be assigned with less load or burden without work greatly, reactive power can not realize dividing equally by sagging coefficient.

When two DG adopt control method of the present invention, DG ₁and DG ₂power output as shown in Figure 6.

As seen from Figure 6, when the DG of two identical capacity adopts control method parallel running of the present invention, before and after load change, DG can divide equally meritorious according to meritorious sagging coefficient, and add the voltage drop drop that self adaptation virtual impedance compensated line resistance difference causes in droop control, when line impedance is different, idlely also can realizes high precision by sagging coefficient and distribute.

Operating mode 2

DG ₁with DG ₂parallel running, rated capacity is than being 1:2.All adopt control method of the present invention, simulation process is identical with operating mode 1, and inverter exports meritorious and reactive power simulation waveform as shown in Figure 7.

Realize the reasonable distribution of power, DG ₁with DG ₂distribute power ratio and should be 1:2.As seen from Figure 7, the active power that inverter exports can according to DG capacity ratio distribution load before and after load power factor change, DG ₁with DG ₂the ratio distributing power is 1:2.Adopt control method of the present invention, inverter output reactive power meets the requirement of 1:2.When 1s and 2s, load increases respectively and reduces, and the reactive power before inverter still can by DG capacity pro rate, and transitional processes is level and smooth and the time is short.

The present embodiment well demonstrates the validity of the present invention to reasonable distribution DG reactive power.

Claims (5)

1. idle equilibrium assignment control method during inverter parallel in micro-capacitance sensor, is characterized in that, comprise the following steps:

1) central controller gathers the reactive power that each DG exports, and draws total reactive power Q _a:

Wherein, Q _ibe the reactive power that i-th DG exports, i=1,2 ..., n, n are total number of DG;

2) according to total reactive power Q _awith the given reactive power of each DG of each DG calculation of capacity;

3) integral controller regulates virtual impedance value according to the difference of the given reactive power of each DG and corresponding actual output reactive power, obtains the self adaptation virtual impedance of each DG;

4) according to droop control and described self adaptation virtual impedance, obtain the reference voltage of electric current and voltage double-loop control, regulate the idle output of corresponding DG.

2. idle equilibrium assignment control method during inverter parallel in micro-capacitance sensor according to claim 1, is characterized in that, when multiple DG capacity of parallel connection are identical, and described step 2) in, the given reactive power of each DG is by following formulae discovery:

Q _i0＝Q _a/n。

3. idle equilibrium assignment control method during inverter parallel in micro-capacitance sensor according to claim 1, it is characterized in that, when multiple DG capacity of parallel connection are different, described step 2) in, the given reactive power of each DG carries out pro rate according to the capacity of each DG:

Q _i0＝r _iQ _a

Wherein, r _ibe the capacity ratio of i-th DG, r _i=C _i/ C _a, C _ibe the capacity of i-th DG, C _afor the total capacity of each DG.

4. idle equilibrium assignment control method during inverter parallel in micro-capacitance sensor according to claim 1, is characterized in that, described step 3) in, the expression formula of self adaptation virtual impedance is:

Wherein, L _ivbe the self adaptation virtual impedance of i-th DG, Q _ibe the actual output reactive power of i-th DG, Q _i0be the given reactive power of i-th DG, K is integral coefficient.

5. idle equilibrium assignment control method during inverter parallel in micro-capacitance sensor according to claim 1, is characterized in that, described step 4) be specially:

401) first voltage reference value of a DG and corresponding phase angle θ is obtained by droop control device;

402) according to the filter inductance current i that corresponding inverter exports by voltage phase angle θ _ocarry out dp conversion, obtain i _dand i _q;

403) according to step 402) i that obtains _dand i _qand step 3) obtain the self adaptation virtual impedance of corresponding DG, obtain the second voltage reference value;

404) by the first voltage reference value and the second voltage reference value superimposed, obtain the reference voltage of electric current and voltage double-loop control.