Transition Mode Analysis And Seamless Control Of High-voltage Energy-recycling SiC DC Electronic Load

In energy Internet era,the global installed capacity of Battery Energy Storage System(BESS)is growing up rapidly and a large number of energy storage batteries are put into use.On the other hand,power electronic converters are widely applied in human life.Load plays an important role in the test of batteries and electronic devices.Compared with conventional energy-dissipation load,the energy-recycling electronic load has the advantages of energy recycling,high power density with small volume for heat dissipation and low testing cost.There have been rarely universal solutions of energy recycler with a wide input voltage range reported yet.According to the design specifications of the dc electronic load including wide input voltage range,high efficiency and high power density,a 5-k W three-stage energy-recycling DC electronic load with a wide input voltage range of 150 V-750 V is proposed.The system is composed of a interleaved boost DC-DC converter with an input current loop and an input voltage loop,a LLC resonant converter(DC-DC transformer,DCX)and a single-phase grid-connected T-type inverter with the double loop control including the outer voltage loop and the inner current loop.Three stages of the electronic load have separate control loops,achieving control decoupling,and operate simultaneously to achieve complex load testing function.The hardware circuit parameters and control loops of the T-type inverter are designed in this paper.The logic sequence of the inverter soft start is given.In the progress,the inverter acts as a rectifier to complete bus voltage buildup.Based on four basic load operation modes:Constant Current(CC),Constant Voltage(CV),Constant Resistance(CR)and Constant Power(CP),seamless transition mode control of the energy-recycling load is proposed to meet the different property of the power source as voltage source,current source and the battery pack.A control method with the voltage loop and current loop following mutually based on digital control is applied to solve the problem of current and voltage spike caused by the duty cycle mutation during transition between the input current loop and voltage loop.A three-stage energy-recycling DC electronic load prototype is built to verify the feasibility of the load topology and control strategy.The secondary harmonic of the load input current is within 8%,and the secondary harmonic of the input voltage is within 1%.The grid-connect current has a good quality(THDi=1.42%at 5 k W).The prototype of the proposed energy-recycling load achieves the peak full-load efficiency of 95%and high power density of 12.5 W/in~3.The proposed load composite transition mode realizes seamless transition without voltage or current spike.