Research On Active Disturbance Rejection Control Of Three Level Photovoltaic Inverter

Photovoltaic power generation is developed to cope with fossil energy shortages and environmental pollution.For the same time,three level inverters suitable for fileds of high voltage and large capacity are widely used.It is worthy of studying on how to improve waveform quality and operation efficiency of the three level inverter.In this paper,optimized modulation and inverter-oriented active disturbance rejection control strategy were concerned.Discontinuous space vector modulation attracts attention due to its characteristics of low switching loss.However,problem that the neutral point potential fluctuation of the three-level inverter is even more serious under the discontinuous modulation.In this paper,an adaptive dc voltage disturbance modulation called dynamic space vector strategy was proposed.This strategy realized real-time detection of capacitor voltage to generate dynamic space vector,and then accurately synthesizes reference vector.Furthermore,gh coordinate system and a parity sector conversion method were used in the optimization process to reduce the complexity of the dynamics algorithm.In order to eliminate the neutral point potential offset,this paper proposed a method of switching vector sequence with reverse effect on the neutral point potential in real time.A method of evaluating the modulation strategy based on the error current vector was given,which verifies the advantages of the dynamic space vector modulation.Simulation and experimental results further show the effectiveness of the proposed method.The typical proportional integral control of LCL-type photovoltaic inverters suffers from current coupling,poor perturbation rejection capability and other issues.To this end,active disturbance rejection control(ADRC)was introduced.Based on synchronous rotating d-q coordinate,the state space average model for three-phase LCL photovoltaic inverters was built.The closed-loop transfer function matrix,which is helpful for analysis of current coupling,was deduced with the control of proportional integral controller.Furthermore,this paper designed a second-order LADRC and then analyzed how observation bandwidth and control bandwidth of the LADRC have effects on current decoupling and disturbance rejection.Besides,the parameter tuning method was given.Through simulation,it is verified that LADRC play better performance on decoupling the dq axis current compared with PI controller and enhanced disturbance rejection capability as well as robustness of the system.As for the inverter control of island mode,similarly,the second order linear active disturbance rejection controller was designed in the dq rotating coordinate system,taking output voltage and its differential as state variables.Considering that the extended state observer(ESO)is the core of LADRC,the output error derivative term,which could be achieved by measuring the filter capacitance current,was introduced to improve the observation capability of ESO.Further,a first-order inertial link was embedded in the total perturbation channel to avoid increasing observation noise.Analysis of the frequency response characteristics of LADRC and typical double loop control system shows that the improved LADRC has better disturbance rejection performance.Simulation and experimental results further proved the effectiveness of the proposed strategy.The experiment platform based on TMS320F28335 was built in this paper.A prototype of three-level photovoltaic inverters was developed.The experiments further proved the accuracy and the effectiveness of the dynamic space vector modulation algorithm and the proposed ADRC control algorithm.