CN104377735A - Droop control algorithm for grid-connected inverters of distributed power sources - Google Patents

Abstract

The invention relates to methods for controlling inverters in the field of grid connection of distributed power sources with electric power technologies, in particular to a droop control algorithm for grid-connected inverters of distributed power sources. The droop control algorithm has the advantages that active circular currents between the inverters can be reduced by the aid of additional (1+m<p>P) factors; the purpose of performing complete decoupling control on P-omega can be achieved by the aid of additional -n<1>Q items; the response speeds of the inverters can be increased by the aid of additional differential items; reactive circular currents between the inverters can be prevented by the aid of additional (1+n<q>Q) factors; influence of P-V positive correlation can be reduced by the aid of additional +m<2>P items; the dynamic performance of the inverters can be improved by the aid of the additional differential items; the response speeds of the DG (distributed generation) inverters can be increased, the reactive circular currents between the DG inverters can be reduced, overload of the inverters can be effectively prevented, and the droop control algorithm for the grid-connected inverters of the distributed power sources has an excellent prospect.

Description

A kind of droop control algorithm of distributed electrical source grid-connected inverter

Technical field

The present invention relates to the method for the control of the inverter in the grid-connected field of power technology distributed power source, be specially a kind of droop control algorithm of distributed electrical source grid-connected inverter.

Background technology

Along with the fast development of Chinese national economy, electricity needs increases rapidly, and power grid construction paces are accelerated day by day.But along with electrical network scale constantly expands, the drawback of ultra-large electric power system also manifests day by day: cost is high, loss is large, runs difficulty large, is difficult to meet user's requirement more and more higher to the aspect such as Supply Security, reliability.In addition, traditional electrical network consumes the energy based on coal in large quantities, and along with the constant tension of energy supply and the continuous lifting of conservation culture consciousness, distributed power source (DG) starts the generating that is connected to the grid.The DG such as wind energy, solar energy inverter, and the amplitude of these DG inverter terminal voltages such as miniature gas turbine, fuel cell and frequency different, be difficult to direct grid-connected run, need to be connected with electrical network by Technics of Power Electronic Conversion device, the amplitude of DG inverter terminal voltage and frequency are by Technics of Power Electronic Conversion device regulable control.

The control method of common DG interface inverter can be divided into according to power division control strategy: power limitation control, droop control and constant voltage constant frequency control.Power limitation control, controls also referred to as PQ, and the control objectives of this DG interface inverter is that active power that DG interface inverter is exported and reactive power are equal to reference power; Droop control be simulation synchronous generator export active power, reactive power and electric voltage frequency and amplitude relation property, people is that active power that DG interface inverter is exported and frequency, reactive power and voltage magnitude are linear, and the equity realizing each component units of micro-capacitance sensor controls; Constant voltage constant frequency controls (V/f control) no matter be then how DG interface inverter output power changes, and the amplitude and the frequency that maintain DG interface inverter terminal voltage are all the time constant.

Droop control is the one that equity controls, because it does not need complexity, expensive communication system, reliability is high, is easy to the plug and play realizing DG interface inverter and load, the requirement of micro-capacitance sensor plurality of operating modes can be met, obtain the extensive concern of Chinese scholars.

The implementation of droop control can be divided into: the reference signal producing DG power output according to the frequency of micro-capacitance sensor and the terminal voltage amplitude of DG interface inverter, frequency and the amplitude of DG interface inverter terminal voltage is regulated with the active power exported according to DG and reactive power, wherein the former is called f-P and V-Q droop control, and the latter is called P-f and Q-V droop control.These two kinds of control strategies have use at present, also have used in combination.

Distributed electrical source inventer adopts droop control to be amplitude and the frequency of its output voltage of size adjustment by detecting self power output.But, due to the difference of connecting line length between the difference of device property and DG, may circulation be there is between traditional droop control DG inverter, inverter overload can be caused even to damage.Method that Yu Wei etc. propose " the uninterrupted power supply parallel system sharing control based on virtual impedance ", the method adopts and regulates the method for inverter virtual impedance that circulation is limited within desirable scope, but there is the shortcoming regulating frequent and computing complexity.Method that Wang Wenjun etc. propose " the circulation FEEDBACK CONTROL of inverter parallel ", the method increases feedback compensation control loop on the basis in original droop control loop, this improves the dynamic current equalizing ability of system to a certain extent, but the control of complexity reduces the reliability of control loop, too increase the difficulty of selection of control parameter.

Summary of the invention

There is the dynamic property such as circulation and low-response problem in order to the droop control method solving inverter employing in the present invention, provides a kind of droop control algorithm of distributed electrical source grid-connected inverter.

The present invention adopts following technical scheme to realize: a kind of droop control algorithm of distributed electrical source grid-connected inverter, comprises the following steps:

S1: measure the voltage V that inverter exports ₀, frequencies omega ₀, active-power P and reactive power Q;

S2: the rate of change calculating active-power P and node reactive power Q, obtains with

S3: the parameter recorded according to S1 and S2 calculate with by formula $\left\{\begin{array}{c}\mathrm{\&omega;}={\mathrm{\&omega;}}_0-m_1(1+m_{p}P)P-n_{1}Q-j\frac{\mathrm{dP}}{\mathrm{dt}}\\ V=V_0+m_{2}P-n_2(1+n_{q}Q)Q-k\frac{\mathrm{dQ}}{\mathrm{dt}}\end{array}\right.$ Calculate target voltage V and target frequency ω, wherein 1+m _pp and 1+n _qq is respectively the sagging factor of P-ω sagging Summing Factor Q-V, m ₁and n ₂represent the sagging coefficient of P-ω and the sagging coefficient of Q-V respectively, m ₂, n ₁represent the sagging coefficient of Q-ω and the sagging coefficient of P-V respectively, j, k are ω, V and meritorious, idle rate of change coefficient correlation;

S4: carry out inverter control according to target voltage V and target frequency ω.

Frequency comparatively phase angle difference Ф is more easily monitored, general monitoring frequency replaces phase angle difference Ф to control inverter, again because inverter terminal impedance Z is approximate in pure perception, can be similar to the uneoupled control realizing P, Q and Ф, V, therefore inverter adopts traditional droop control to be often expressed as formula $\left\{\begin{array}{c}\mathrm{\&omega;}={\mathrm{\&omega;}}_0-m_{1}P\\ V=V_0-n_{2}Q\end{array}\right.,$ Droop control after optimization provided by the invention is expressed as formula $\left\{\begin{array}{c}\mathrm{\&omega;}={\mathrm{\&omega;}}_0-m_1(1+m_{p}P)P-n_{1}Q-j\frac{\mathrm{dP}}{\mathrm{dt}}\\ V=V_0+m_{2}P-n_2(1+n_{q}Q)Q-k\frac{\mathrm{dQ}}{\mathrm{dt}}\end{array}\right.,$ When the active-power P that inverter exports is larger, because add the sagging factor 1+m of P-ω in droop control mode _pp, increases the sagging Coefficient m of P-ω ₁can reach the object reducing the active-power P that inverter exports, vice versa, thus reach the object of active-power P current-sharing, reduces the meritorious circulation between inverter; Simultaneously due to phase angle difference Ф and reactive power Q negative correlation, when the reactive power Q that inverter exports increases, phase angle difference Ф can reduce, and frequencies omega is increased ,-the n in formula ₁q can reduce or eliminate the impact of reactive power Q increase on frequency, and reduce the frequencies omega that inverter exports, offset with the frequency of the increase in actual motion, thus reach the object of the full decoupled control of P-ω, vice versa;

When the reactive power Q that inverter exports is larger, because add the sagging factor 1+n of Q-V in droop control mode _qq, increases the sagging coefficient n of Q-V ₂can reach the object reducing the reactive power Q that inverter exports, vice versa, thus can prevent from occurring reactive circular power flow between inverter; Simultaneously due to voltage and active-power P positive correlation, when the reactive power Q that inverter exports increases, voltage can reduce, and active-power P is reduced ,+the m added in droop control mode ₂p can reduce or eliminate the impact of reactive power Q increase on frequency, and increase the voltage V that inverter exports, offset with the voltage of the reduction in actual motion, vice versa, and the differential term in droop control mode can improve the response speed of inverter.

The invention provides a kind of droop control algorithm of distributed electrical source grid-connected inverter, this algorithm can effectively eliminate the circulation occurred between inverter, and there is the feature of fast response time, be the droop control algorithm of very promising a kind of distributed electrical source grid-connected inverter.

Accompanying drawing explanation

Fig. 1 is configuration of power network.

Embodiment

A droop control algorithm for distributed electrical source grid-connected inverter, comprises the following steps:

S1: measure the voltage V that inverter exports ₀, frequencies omega ₀, active-power P and reactive power Q;

S2: the rate of change calculating active-power P and node reactive power Q, obtains with

S3: the parameter recorded according to S1 and S2 calculate with by formula $\left\{\begin{array}{c}\mathrm{\&omega;}={\mathrm{\&omega;}}_0-m_1(1+m_{p}P)P-n_{1}Q-j\frac{\mathrm{dP}}{\mathrm{dt}}\\ V=V_0+m_{2}P-n_2(1+n_{q}Q)Q-k\frac{\mathrm{dQ}}{\mathrm{dt}}\end{array}\right.$ Calculate target voltage V and target frequency ω, wherein 1+m _pp and 1+n _qq is respectively the sagging factor of P-ω sagging Summing Factor Q-V, m ₁and n ₂represent the sagging coefficient of P-ω and the sagging coefficient of Q-V respectively, m ₂, n ₁represent the sagging coefficient of Q-ω and the sagging coefficient of P-V respectively, j, k are ω, V and meritorious, idle rate of change coefficient correlation;

S4: carry out inverter control according to target voltage V and target frequency ω.

During concrete enforcement, for Fig. 1, electrical network is made up of three nodes, three DG inverters and three loads, DG inverter parameters m _p=1 × 10 ^-4, n _q=1.5 × 10 ^-4, load parameter is: R _load1=25 Ω, X _load1=0 Ω, R _load2=30 Ω, X _load2=0 Ω, R _load3=20 Ω, X _load3=0 Ω; Line parameter circuit value is: R _line1=0.23 Ω, X _line1=0.1 Ω, R _line2=0.35 Ω, X _line2=0.58 Ω.Initial condition load 2 disconnects, and as t=1s, load 2 is grid-connected.

DG inverter adopts traditional droop control, and after load 2 is grid-connected, through the transient process of 0.5s, each DG inverter tends towards stability; The peak value of the active-power P 2 of DG2 inverter is maximum, is 5.22kW, and maximum overshoot is 2.4%, after 1.5s is stable, the reactive power Q 2 of DG2 inverter is maximum, is 1.85kVA, the reactive power Q 3 of DG3 inverter is minimum, is 0.95kVA, minimax value difference 0.9kVA.

The improvement droop control that DG inverter adopts the present invention to propose, after load 2 is grid-connected, through the transient process of 0.3s, each DG inverter tends towards stability; The peak value of the active-power P 1 of DG inverter is maximum, is 5.09kW, and maximum overshoot is 1.1%, after 1.3s is stable, the reactive power Q 2 of DG2 inverter is maximum, is 1.32kVA, the reactive power Q 3 of DG3 inverter is minimum, is 1.08kVA, minimax value difference 0.24kVA.

Improve the response speed that droop control improves DG inverter, reduce the maximum overshoot of DG inverter active power of output, obviously reduce the reactive circular power flow between DG inverter.If the reactive power of DG inverter output is simultaneously large, then its active power of output is little, and the apparent power that each DG inverter is exported is similar to identical, can effectively prevent inverter from occurring overload.

Claims (1)

1. a droop control algorithm for distributed electrical source grid-connected inverter, is characterized in that comprising the following steps:

S1: measure the voltage V that inverter exports ₀, frequencies omega ₀, active-power P and reactive power Q;

S2: the rate of change calculating active-power P and node reactive power Q, obtains with

S3: the parameter recorded according to S1 and S2 calculate with by formula $\left\{\begin{array}{c}\mathrm{\&omega;}={\mathrm{\&omega;}}_0-m_1(1+m_{p}P)P-n_{1}Q-j\frac{\mathrm{dP}}{\mathrm{dt}}\\ V=V_0+m_{2}P-n_2(1+n_{q}Q)Q-k\frac{\mathrm{dQ}}{\mathrm{dt}}\end{array}\right.$ Calculate target voltage V and target frequency ω, wherein 1+m _pp and 1+n _qq is respectively the sagging factor of P-ω sagging Summing Factor Q-V, m ₁and n ₂represent the sagging coefficient of P-ω and the sagging coefficient of Q-V respectively, m ₂, n ₁represent the sagging coefficient of Q-ω and the sagging coefficient of P-V respectively, j, k are ω, V and meritorious, idle rate of change coefficient correlation;

S4: carry out inverter control according to target voltage V and target frequency ω.