Research And Equipment Development Of High Power Cascaded Digital Power Amplifier

One of the key technologies to realize China’s maritime power strategy is the long distance underwater acoustic communication.High quality and efficient electroacoustic energy conversion system is an important guarantee for marine military confrontation and the development of marine industry.As the power part of the electroacoustic energy conversion system,the operation performance of the power amplifier is very important to the whole system.The high power cascaded digital power amplifier can not only break through the capacity limitation of power devices and improve the power rating of the system,but also improve the waveform quality of output voltage with the cascaded multilevel characteristics.The two-stage submodule of the high power cascaded digital power amplifier increases the degree of freedom of control and realizes the sharing of input dc source.This thesis focuses on the working principle,control strategy,performance optimization and prototype manufacturing of digital power amplifier and mainly studies the suppression method of DC/DC stage secondary ripple current and the improvement strategy of DC/AC stage broadband high fidelity output performance.The main work and achievements in this thesis are as follows:1)Focusing on the problem of secondary ripple current in DC/DC stage of the high power cascaded digital power amplifier,a secondary ripple current suppression method is proposed,which forces the dc bus filter capacitor to bear almost all the second-frequency pulsating power.The generating mechanism and the harm of the secondary ripple current are clarified.The mathematical expression of the secondary ripple current of the DC input source under the closed-loop control is derived.The influence of the capacitance of the bus filter on the secondary ripple current is revealed.The small signal model of phase shifted full bridge DC/DC converter is established,the mathematical expressions of current reverse gain and secondary ripple current ratio related with outer loop voltage compensator gain under the conventional double loop control are derived,and the limitation of improving the suppression ability by adjusting the compensator parameters is revealed.On this basis,a method of secondary ripple current suppression based on dc bus voltage feedback and output current feedforward is proposed.The suppression ability is analyzed based on the current reverse gain and the equivalent branch impedance and the effectiveness of the proposed method is verified theoretically.The sensitivity of the suppression ability to the circuit parameters is analyzed,and the zero error of the steady-state tracking is verified.The parameter design principle of the proposed method is given,which ensures the high stability margin of the system.The simulation results show that the proposed method can effectively restrain the secondary ripple current from entering the DC/DC converter,and improve the dynamic performance and conversion efficiency of the system.2)In order to realize the satisfactory output performanc of the high power cascaded digital power amplifier,a wide-band and high-fidelity control strategy with inner and outer control loop based on different coordinate system is proposed,which breaks through the limitation of conventional control methods in steady-state tracking precision and bandwith.The mathematical model of cascaded digital amplifier DC/AC in dq frame is established,and the characteristic expression of LC filter in dq frame is derived,which reveals αβ/dq transformation will cause coupling,increase system order and worsen resonance.The expression of dq decoupling term that is complex to design and implement for single voltage loop PI control is given.Combining the rapidity of model predictive control and zero state-error of PI control in dq frame,a wide-band highfidelity control method of output voltage based on different coordinate system is proposed.The realization of fast predictive control method of inner current is described,including the elimination of switching state redundancy,the construction of voltage evaluation subset,the design of bi-level linear combination and the distribution of switching action.The outer voltage is controlled by PI in dq fram with the prediction of orthogonal component whose influence on loop is analysed.The design principles for PI parameters is given,which is simple and reliable.Finally,the simulation results show that the fast predictive current control can effectively reduce the current tracking error and evenly distribute the power and switching.The simulation results also show that the proposed double-loop control strategy realizes zero-error tracking in wide band and improves the fidelity of output voltage.3)A high power cascaded digital power amplifier with input of 600 VDC,output of 2k VAC/ 200-1200Hz/30 k VA was built,and its hardware circuit and software system design method is specifically described.The design method and selection principle of the main circuit parameters are deeply discussed,which include election of power devices,calculation of transformation ratio of high frequency transformer,design of filter parameters and resonance inductance.According to the modular structure features and real-time control requirements of the cascaded digital power amplifier,the control system is designed into three layers,namely human-computer interaction layer,general controller layer and power submodule control layer.These three layers are oriented to different objects and coordinate to complete their respective functions.On this basis,the control chips of each layer are selected reasonably,and the circuit of control board is constructed orderly,including sampling and conditioning circuit,driving circuit,protection circuit,optical fiber transmission and reception circuit,etc.Finally,the experimental results show that the prototype design is rational and feasible.