Design And Implementation Of 400kW Energy Feedback Electronic Load

With the development of power electronics technology,Power Electronic Load(PEL)gradually replaces the traditional energy-consuming load for factory testing.In order to meet the needs of DC power supply testing,this thesis develops a 400 kW energy-feeding DC power electronic load.The power electronic load consists of six single-phase 70 kW power electronic loads in parallel.Each 70 kW power electronic load adopts a two-stage structure.The front stage is the load simulation unit,which is composed of a cascade of LC filters and Phase-Shifted Full-Bridge(PSFB)circuits.The latter stage is the energy feedback unit,which is composed of passively damped LCL grid-connected inverters.The load simulation unit realizes the function of load simulation by controlling the input current.The energy feedback unit not only feeds energy back to the power grid,but also needs to control the stability of the intermediate bus voltage.This paper establishes the small-signal model of the load simulation unit based on the small-signal model of the phase-shifted full-bridge circuit.According to the characteristics of the load simulation unit,the incomplete derivative PID controller is used as the current controller.Multiple sets of PID parameters were selected and their performance impact on the load simulation unit was compared.Finally,the most suitable PID parameter was selected.In order to improve the reliability of the phase-shifted full-bridge circuit,a method for suppressing the voltage oscillation of the secondary side of the transformer was discussed and the RCD buffer circuit was adopted.The energy feedback unit adopts the control method of the bus voltage outer loop and the grid-connected current inner loop.The current inner loop adopts a PI controller,according to the constraint relationship between the amplitude error and phase margin on the integral coefficient,the relationship between the integral coefficient and the crossing frequency was derived.According to the requirements of amplitude error and phase margin index,the required integral coefficient can be designed.Then according that the gain at the crossing frequency is 1,the proportional coefficient can be obtained.The voltage outer loop also uses a PI controller and is designed according to a typical type II system.In order to improve the reliability of the grid connection,this thesis uses the digital phase-locked loop technology based on the Discrete Fourier Transform,and briefly explains its principle and implementation method.At last,the simulation and experimental research are carried out.The simulation and experimental results showed that the proposed design of power electronic load is feasible.The electronic load has good dynamic performance and steady state performance under full load,half load,overload,sudden load increase,sudden load reduction and other conditions.