Research On Energy Feedback AC Electronic Load And Grid Connection Control Strategy

With the continuous development of power electronics and information technology and the increasingly strict requirements of climate change on energy saving and emission reduction,the high-precision and low-power electronic load has become one of the key test equipment for power products before they leave the factory.At present,most AC electronic loads in the market have some problems such as low accuracy of load simulation,slow dynamic response and poor quality of grid-connected current.Therefore,high efficiency and high precision AC electronic load has become a hot research direction.In this paper,the development history and present situation of AC electronic load are analyzed in detail,and the high efficient main power topology,the load simulation strategy with good dynamic response and low steady error,and the grid-connected control strategy of low harmonic current are emphatically studied.And the feed-back AC electronic load prototype is developed for test verification.The main content of this paper is as follows:(1)The main power circuit topology of the feed-type AC electronic load is analyzed.According to the PWM full bridge circuit has the characteristic of energy bidirectional flow under proper control,this circuit is selected as the load simulation and inverter grid-connected power topology,and the working modes of the circuit under different control are analyzed in detail,and the feasibility of the scheme is verified by simulation.(2)The Radial Basis Function Neural Network(RBFNN)self-tuning PI control load simulation strategy based on rotation coordinate transformation is studied.Rotation transformation and RBFNN are used to optimize the traditional PI controller to improve its poor response to AC and weak adaptability.The simulation results show that the load simulation response time is increased from 0.08 s to 0.015 s,and the current harmonic content is reduced from 6.79% to 1.74%,compared with the traditional PI control under the input power of 3kw.(3)The “PI+QPR” double closed-loop grid-connection control strategy with anti-disturbance ability is studied.The three parameters of QPR are calculated in detail,and their influence on the controller is analyzed.The simulation results show that the current harmonics rate is only 2.26% when the frequency of 50 Hz is connected,and 3.16% when the maximum allowable deviation frequency is 50.5Hz,which meets the requirement that the harmonics of the grid-connected current is less than 4%,verifying the effectiveness of the strategy and expanding the grid-connected bandwidth.(4)The LCL filter feedback network is optimized.Active damping feedback scheme of capacitor current is adopted to improve the high frequency performance and avoid the heat loss caused by passive damping feedback.The simulation results show that the harmonic rate of grid-connected current increases from 2.02% to 3.08% when the capacitor current feedback is disconnected at 0.3s,which proves the feasibility of this strategy.(5)A feed-back type AC electronic load prototype is developed to verify the static and dynamic characteristics of the key circuit,the load simulation and the grid-connection performance.The verification results show that the parameter design is reasonable and the key circuit works normally.The load simulation performance is good,the maximum static error is3.27%,the dynamic response time is less than 1ms.With high grid-connection quality and small loss,the maximum efficiency of the whole machine is 94.52%,the power factor is0.998 and the harmonic distortion of current is only 2.812% when the power is connected to the grid at 2000 W.