CN105186906A - Improved three-phase LCL photovoltaic grid-connected inverter control method - Google Patents

Abstract

The invention mainly provides an improved three-phase LCL photovoltaic grid-connected inverter control method, which is characterized in that current and voltage three-closed-loop control is adopted. The method specifically comprises the steps of S1, acquiring grid current signals ia, ib, ic, acquiring synchronous current signals through a phase-locked loop, and then acquiring current signals i<salpha>, i<sbeta> in a static coordinate system through abc/alpha beta coordinate transformation; S2, sending a difference value between DC bus voltage Udc and a reference value Uref to a proportional resonant (PR) controller, increasing second-order generalized integral Hi(s) on the basis of a transfer function Gpr=Kp+Kis/(s<2>+omega<0><2>) so as to acquire a new transfer function Gpr=Kp+ Kp+Kis/(s<2>+omega<0><2>)+Hi(s); S3, carrying out addition-subtraction operations on current signals i<salpha><*>, i<sbeta><*> outputted by a PR regulator and the current signals i<salpha>, i<sbeta> respectively so as to acquire current signals, and carrying out alpha beta/abc coordinate transformation on the sum of the current signals and inner ring capacitive current signals of a proportional controller (P) so as to generate a corresponding SVPWM signal control power tube. Simulation and experimental results show that the method provided by the invention effectively improves the grid-connected current waveform of the system, and high-quality grid-connected current is acquired.

Description

Improved three-phase LCL type photovoltaic combining inverter control method

The present invention relates to a kind of improved three-phase LCL type photovoltaic combining inverter control method.

Background technology

Photovoltaic generation has many advantages, and technology also reaches its maturity.Combining inverter, as the core link of photovoltaic generating system, can bear the effects such as the maximal power tracing of photovoltaic battery array, DC boosting inversion, anti-island protect in grid-connection control system.LCL type photovoltaic combining inverter adds LCL type filter relative to traditional combining inverter.Although it has the ability suppressing high order harmonic component, add the difficulty of its control strategy.At present, more existing documents propose concrete control method for LCL type photovoltaic combining inverter." in LCL type combining inverter repetitive control research " in 30th phase " Proceedings of the CSEE " in 2010 one literary composition use Repetitive controller and PI to control the composite control method combined, because of PI control cannot ensure to obtain while the stability of a system enough for line voltage in industrial frequency harmonic rejection ability thus Repetitive controller need be adopted to be a kind of reasonable supplementary in the ability suppressing Voltage Harmonic as the LCL type combining inverter controlled PI, for LCL combining inverter, it is a kind of composite control method that can improve system and suppress low-frequency harmonics ability that Repetitive controller and PI control to combine." the combining inverter control strategy research of band LCL output filter " in 12nd phase " Proceedings of the CSEE " in 2011 proposes a kind of combining inverter control strategy feedovered based on inverter side current closed-loop and capacitance current, by inverter side Current Indirect Control grid-connected current.This control strategy can ensure that system stability and unity power factor run, and whole control procedure is without the need to increasing extra transducer, reduces system cost, enhances system reliability.Grid side inductive current and inverter side inductive current double-loop control strategy is adopted directly to control grid-connected current in " control strategy of LCL filtering combining inverter " literary composition in 27th phase " Proceedings of the CSEE " in 2012, grid side inductive current more easily suppresses the harmonic wave factor of grid-connected current as outer shroud, and directly can control the unity power factor of networking electric current, adopt inverter side inductive current can increase system damping as inner ring, thus can system oscillation be suppressed, increase the stability of a system.A kind of complete voltage feed-forward control control strategy being applicable to inverter side current feedback LCL combining inverter is adopted in " the LCL combining inverter voltage feed-forward control control strategy of inverter side current feedback " literary composition in 6th phase " Proceedings of the CSEE " in 2013, this strategy can eliminate the impact of line voltage on power network current completely, and grid-connected power factor obtains and promotes greatly.

Summary of the invention

The present invention mainly proposes a kind of improved three-phase LCL type photovoltaic combining inverter control method, it is characterized in that adopting current/voltage Three-loop control, and concrete steps are as follows:

Concrete implementation step is as follows:

The first step, obtains current signal i from grid side _a, i _b, i _c, obtain synchronizing current signal through phase-locked loop (PLL), then through abc/ α β coordinate transform, obtain the current signal i in rest frame _{s α}, i _{s β};

Second step, sampling calculates DC bus-bar voltage U _dcand with reference value U _refcompare, errors through proportional control (PR) device, in order to solve PR to control in the gain of fundamental frequency place be infinitely great and being attenuation trend problem in the gain at other frequency places, in original transfer function (K _pfor the coefficient of proportional component, K _ifor the coefficient of integral element, ω ₀for resonance angular frequency) basis on increase second order improper integral H _is () obtains new transfer function G _pr+ H _is (), has without the need to coordinate transform, just can reach the feature of zero steady-state error under rest frame;

3rd step, the current signal that PR adjuster exports respectively with i _{s α}, i _{s β}carry out plus-minus and calculate current signal, for improving the ability introducing Repetitive controller that PR controller suppresses grid-connected harmonic current and follows the tracks of various disturbance, for the resonance peak that stable three-phase LCL type inverter control system damping exists, the inner ring capacitance current signal of above-mentioned output signal and ratio (P) controller is sued for peace, then produces corresponding space vector pulse width modulation signal (SVPWM) after carrying out α β/abc coordinate transform and control power tube switch.

Accompanying drawing explanation

The control structure figure of Fig. 1 three-phase LCL grid-connected inverter system

Fig. 2 grid-connected current oscillogram

Fig. 3 modified model complex controll experimental waveform figure

Simulation and experiment interpretation of result

Utilize Matlab/Simulink simulation software to build system simulation model, simulation parameter is as follows: line voltage 220V/50Hz, DC side busbar voltage 380V, and setting IGBT is full-bridge inverting form, DC bus capacitor C ₁be 7500 μ F, pusher side filter inductance L ₁for 1.2mH, net side filter inductance L ₂for 0.4mH, filter capacitor C is 10 μ F, and DC voltage reference value is 700V, switching frequency f _sfor 10kHz.In emulation, assuming that voltage on line side has larger fluctuation, its total harmonic distortion (TotalHarmonicDistortion, THD) is 4.6%.Fig. 2 (a) is the grid-connected current waveform under conventional composite control, and (b) is the grid-connected current waveform under modified model controls.Can find out from simulation result and ratio resonance (PR) controller is introduced the grid-connected current waveform that can effectively improve system complex controll.

In order to verify the effect of above-mentioned control method, build the LCL type photovoltaic combining inverter experimental prototype of a 10kW.Experiment porch mainly comprises main circuit structure and accessory power supply, sample circuit structure and controller.Experiment parameter is with reference to simulation parameter, and wherein controller hardware part adopts (DSP) TMS320F28027.This experiment porch carries out experimental verification to the controller of Three phase LCL type photovoltaic combining inverter of the present invention.

Fig. 3 (a) is shown as the experimental waveform adopting the grid-connected output voltage electric current of three-phase LCL type photovoltaic combining inverter under new controller.Adopt HDGC3510 power quality analyzer to carry out analysis to the output current in Fig. 3 (a) and Fig. 3 (b) grid-connected current harmonic analysis figure can be obtained, as can be seen from the figure each harmonic content of steady-state current is all below 0.5%, adopt modified model complex controll to have obvious inhibitory action to harmonic wave, make grid-connected current waveform meet the requirement of GB.The validity of the results show the method and feasibility.

Claims (1)

1. the present invention mainly proposes a kind of improved three-phase LCL photovoltaic combining inverter control method, it is characterized in that adopting current/voltage Three-loop control, and concrete steps are as follows:

The first step, obtains current signal i from grid side _a, i _b, i _c, obtain synchronizing current signal through phase-locked loop (PLL), then through abc/ α β coordinate transform, obtain the current signal i in rest frame _{s α}, i _{s β};

Second step, sampling calculates DC bus-bar voltage U _dcand with reference value U _refcompare, errors through proportional control (PR) device, in order to solve PR to control in the gain of fundamental frequency place be infinitely great and being attenuation trend problem in the gain at other frequency places, in original transfer function (K _pfor the coefficient of proportional component, K _ifor the coefficient of integral element, ω ₀for resonance angular frequency) basis on increase second order improper integral H _is () obtains new transfer function G _pr+ H _is (), has without the need to coordinate transform, just can reach the feature of zero steady-state error under rest frame;

3rd step, the current signal that PR adjuster exports respectively with i _{s α}, i _{s β}carry out plus-minus and calculate current signal, for improving the ability introducing Repetitive controller that PR controller suppresses grid-connected harmonic current and follows the tracks of various disturbance, for the resonance peak that stable three-phase LCL type inverter control system damping exists, the inner ring capacitance current signal of above-mentioned output signal and ratio (P) controller is sued for peace, then produces corresponding space vector pulse width modulation signal (SVPWM) after carrying out α β/abc coordinate transform and control power tube switch.