Research And Equipment Development Of Multi-level Power Amplifier

Power amplifiers are widely used in underwater acoustic communication and ocean exploration.The traditional analog power amplifier operates in linear amplifier region,the high loss results in low efficiency,which limits the improvement of its power level.With the development of power electronic devices and application technologies,digital power amplifiers with fully-controlled switching devices have gradually replaced analog power amplifiers.The digital power amplifier works in the cut-off and saturation regions,which has high efficiency and can meet the application of high power.The development of this technology is of great significance to China's marine strategy.This paper takes high fidelity,broadband,high voltage and high power multi-level power amplifier as the research object,and studies the topology,working principle,control strategy and device development of multi-level power amplifie.The main research contents are as follows:(1)A DC-DC-AC two-stage multi-level digital power amplifier topology is proposed,which is composed of a two-winding phase-shifted full-bridge converter with forward-output inductor and a diode-clamped five-level inverter.The clamped multi-level structure can effectively reduce the output harmonics,and the full-bridge converter with positive and negative equal voltage output solves the unbalanced DC capacitor voltage problem of the inverter.Starting from the two-part structure,the working principle is analyzed in detail.The small-signal model of the full-bridge converter is derived by the principle of power conservation,and the voltage singleclosed-loop PI control strategy is designed.Then,the single-phase control model of the clamped multi-level inverter is established by using the state space method.The unipolar frequency doubling modulation strategy is designed,so the equivalent switching frequency is improved,and the amplitude and frequency are continuously adjustable.The effectiveness of the proposed topology and control strategy is verified by simulation.(2)A cascaded digital power amplifier topology with multiple sub-modules output in series is proposed,which can effectively realize the boost and capacitance of the digital power amplifier.It has the advantages of modularization,easy redundancy and high waveform quality.The principle of forward cascade and reverse cascade carrier modulation is expounded,and the unbalanced output power of cascaded modules under carrier cascade modulation is revealed.On this basis,the mathematical expressions of half-cycle and full-cycle carrier phase-shifted modulation series output voltage are deduced,and the fundamental wave amplification factor,harmonic frequency and equivalent switching frequency are quantitatively compared and analyzed.Thus the half-cycle carrier phase-shifted modulation is selected,whose modulation effect is not affected by the number of series.Then,the steady-state error in traditional doubleclosed-loop control is analyzed,and a load current feedforward control strategy based on proportional differential feedforward is designed.The influence of load current disturbance on output voltage is restrained consequently,and the steady-state error is eliminated.In addition,the control system parameters are designed in detail.The correctness and effectiveness of the proposed control strategy are verified by simulation.(3)For the engineering design of 1kV/10 kW high-power multi-level power amplifier,the selection principle of main circuit parameters is elaborated in detail,and the hardware circuit of the control system is designed.According to the parameters,an experimental platform with four modules output in series is built.The proposed topology,control strategy and parameter design are verified by experiments.