Research And Design Of 50kW AC Electronic Load With DC Energy Feedback

With the continuous rapid development of electrical and information technology and people's increasing awareness of energy conservation,for the problem of the huge energy consumption caused by the analog load used in conventional power supply factory testing,an AC electronic load with DC energy feedback that feed back the test energy to the input of the power source to be tested is developed to test the inverter power supply.Combining with the basic structure of common AC electronic loads and the input and output characteristics of the inverter power supply to be tested,the form of DC energy feedback is used in this thesis.The energy is directly fed back to the power input to be tested,instead of being fed back to the grid.This method eliminates inverters,rectification,and other conversion circuits,avoiding the losses caused by multiple conversions.So it is more energy-efficient.The topology uses a single-phase PWM rectifier and a phase-shifted full-bridge DC/DC converter cascade.After the two-stage circuits were analyzed separately,their respective mathematical models were established.Since the former stage should realize the function of load simulation,the main target is to control the input current of the AC electronic load,so the former stage uses the control strategy of a single current loop.The PI controller was designed first,but the PI controller could not track the sinusoidal current signal without static error.Considering that to eliminate static error of AC current,synchronous reference rotating frame is usually used in three-phase PWM rectifier.Therefore,the equivalent rotation coordinate transformation can achieve the same effect in single-phase PWM rectifier.A control method: passivity-base control based on synchronous reference rotating frame is present in this thesis.The passive-based controller is designed based on it.For the control strategy of latter stage,the double-closed-loop control system of the DC bus voltage outer loop and the grid-connected current inner loop was adopted.In this thesis,the PI controller of the current loop and voltage loop were designed using the pole configuration method.The simulation model of the main circuit and the control part of the whole system were built on MATLAB/Simulink.Firstly,the waveforms of the load simulation unit using PI control and passive-based control are verified through simulation.The results proved that the passive-based control can effectively solve the problem of the current static error.Then the function of the AC electronic load with DC energy feedback was simulated to verify the feasibility of the main circuit structure and control strategy.According to the characteristics of the inverter power source to be tested,the technical specifications of the AC electronic load with DC energy feedback are determined,and then the key devices in the main circuit are designed and selected.For the software,a DSP and CPLD control system was used.Then DSP and CPLD software parts were analyzed and designed.Finally,a small power prototype experiment was performed.By observing the waveforms of the input voltage and input current of the load simulation unit,The results proved that under low power condition,each power supply test can be completed: the simulation function of resistive load,resistive inductive load and capacitive and capacitive load can be realized.In the sudden increase of load and load abrupt decrease experiment,it can also achieve better dynamic performance.