Research And Equipment Development Of Modular Multi-level Power Amplifier

Power amplifiers have a wide range of applications in the fields of industry,aviation,and communications.With the rapid development of power semiconductor devices,the emergence of fully-controlled devices has led people to gradually draw their attention from traditional linear power amplifiers to digital power amplifiers.The traditional power amplifier power devices work in the linear region and have high loss and low efficiency.It is difficult to meet high power applications.The digital power amplifier power devices work in the switching area,and the loss is small,and high power amplification can be realized easily.The research of power digital power amplifiers is of great significance.This dissertation takes digital power amplifier as the research object,and studies the topological structure,working principle,control strategies and equipment development of digital power amplifier.The main research contents are as follows:(1)A modular multi-level power amplifier(MM-PA)topology is proposed,using a modular cascade structure.Each power module consists of a pre-stage diode rectifier and isolated DC converter.The DC/DC converter and the single-phase full-bridge inverter of the rear stage can effectively increase the output voltage level of the power amplifier and have better dynamic performance.The topology structure and working principle of the MM-PA are elaborated,and four advantages of the proposed MM-PA topology are summarized.The system control strategy of MM-PA is analyzed and the overall control block diagram of MM-PA is given.Double frequency fluctuations of the high-frequency rectifier of MM-PA is introduced with the load of single inverter.This paper deduced the formula of double frequency voltage fluctuations,and effectively suppressed voltage fluctuations through power feedforward control,providing a more stable DC source for the rear stages.Voltage and current double closed-loop control strategy is adopted for the rear multilevel inverters and the parameters of the inner-loop and outerloop are designed,and verifies the effectiveness of the control strategy through simulation.(2)A virtual capacitance voltage sequencing model predictive control strategy is proposed for the rear multilevel inverter.The realization of the control strategy is analyzed in detail,including the construction of a finite control set,the establishment of a cost function,and the control method for virtual capacitor voltage sequencing.The proposed control strategy is verified by simulation.The simulation results verify the proposed model predictive control.The output accuracy of the power amplifier can be effectively improved;the output performance of the double closed-loop control and the model-predicted control strategy is compared and analyzed.The simulation results show that the proposed strategy is superior to the traditional dual in terms of steady-state output fidelity and tracking performance.The proposed control strategy is more suitable for applications with high precision requirements.(3)Completed the engineering design of a 25 kW MM-PA prototype.The circuit parameters of the high-frequency rectifier and the post-stage filter are designed.A three-core controller based on STM32+DSP+FPGA is constructed,and the design of the hardware circuit of the control system is completed,mainly including power supply,AD sampling,serial port communication,and optical fiber transceiver.This paper researched the heat dissipation system of MM-PA,including cooling of the chassis and heat dissipation of the power unit.Finally,a 25 kW MM-PA experimental platform was built.The experimental results meet the requirements of the system performance indicators,verifying the effectiveness of the MM-PA topology,control methods and program design.