| The ocean is an outpost of national defense,an importan t barrier to maintain national security,and an important carrier of China’s "One Belt,One Road" strategy.The establishment of underwater long-range target detection system is the inevitable demand of national defense at sea,and is also an effective mea ns to detect underwater resources.Power amplifier is the core of electric energy supply of underwater long-range target detection system.In the field of underwater remote detection,the power amplifier has experienced the development and iteration from a nalog power amplifier to digital power amplifier,and the digital power amplifier has been widely used because of its higher operating efficiency and smaller size.With the development of underwater remote target detection system towards high power,ultra-low frequency,distributed and miniaturization,the system also puts higher requirements on the operation efficiency and power density of digital power amplifier.To this end,this dissertation systematically and thoroughly studies the basic theories and key technologies for reducing the operating losses and device volume of digital power amplifiers,and provides scientific theoretical guidance and engineering design reference for the engineering application of high-efficiency and high-power density digital power amplifiers.This dissertation has been funded by the National Natural Science Foundation of China under the Major Research Instrument Development Project –‘Multi-frequency and multi-directional cooperative sonar measurement instrument for marine underwater moving targets’ [52127901],the Key Project of the National Natural Science Foundation of China – ‘Research on the mechanism and control method of high-power electro-acoustic high-efficiency transducer’ [51837005],the Surface Project of the National Natural Science Foundation of China – ‘Research on the key problem of very low frequency switching power amplifier with integrated super capacitor energy storage’ [52177178] and the Youth Fund Project of the National Natural Science Foundation o f China – ‘Research on key issues of very low frequency switching power amplifier for ocean sonar detection system’ [52207198].The research is supported by the National Electric Power Conversion and Control Engineering Technology Research Center.It focuses on the loss-volume integrated model of digital power amplifier,DC-link voltage optimization control,power decoupling control method,soft-switching modulation method and wide-band power amplifier topology,with the following five main areas of work an d innovation:(1)A DC-link voltage optimization control method is proposed to reduce the DC-link voltage and improve the operating efficiency without affecting the output waveform quality and power density of the digital power amplifier.Based on the full-bridge digital power amplifier topology,the loss of each component of the digital power amplifier is analyzed and a loss model is established.The causes of DC-link double-frequency voltage and current ripple generation in digital power amplifiers are analyzed,and the influencing factors of the double-frequency ripple are deduced.The quantitative relationship among the double-frequency ripple and the output power,output frequency and load impedance angle of the digital power amplifier is analyzed.The change law of loss and volume of each component under different conditions is studied,and the main factors affecting the operation efficiency and power density of digital power amplifier are clarified.The optimized control method of DC-link voltage is proposed,and the calculation method of the minimum value of DC-link average voltage is derived.Experimental results show that the proposed DC-link voltage optimization control method can flexibly adjust the average DC-link voltage according to the operating conditions without affecting the output waveform quality and power density of the digital power amplifier.Compared to the operation mode operating at the rated DC-link voltage,the proposed control method can improve the modulation index,reduce the ind uctor current ripple and reduce the switching losses of power switches by 11.68%.(2)The adaptive active power decoupling control method is proposed,and the effects of factors such as equivalent series resistance of electrolytic capacitors,the front DC source and delay of control system on the power decoupling control at different ripple frequencies are analyzed and corrected.The operating principle and operating characteristics of the Buck power decoupling circuit are analyzed,and the corresponding circuit model is established.The effects of equivalent series resistance of electrolytic capacitor,the front DC power source and control system delay on the calculated value of capacitor current are revealed,and based on this,an adaptive active power d ecoupling control method is proposed to correct the calculated value of capacitor current.The stability of the proposed power decoupling control method is analyzed,and the design principles of controller parameters and passive parameters are described.T he experimental results show that the proposed power decoupling control method achieves effective suppression of the DC-link voltage ripple of the digital power amplifier without ripple frequency limitation.After using the active power decoupling control,the DC-link voltage ripple rate decreases from the original 6.35% to 0.70%;the volume of the prototype based on the active power decoupling method is 32.6% of the volume of the prototype based on the passive decoupling method with the same voltage rippl e rate.The use of the active power decoupling method significantly reduces the DC-link capacitance capacity and effectively increases the power density of the device.(3)A fixed switching frequency zero voltage switching hybrid modulation method is proposed,which provides a new modulation method reference for the zero voltage switching operation of the full-bridge digital power amplifier.Based on the full-bridge topology,an auxiliary resonant circuit is added,and the impedance difference between the resonant circuit and the filter circuit is used to decouple the low-frequency current and the high-frequency current,and the effect of the auxiliary resonant circuit on the efficiency and volume of the digital power amplifier is analyzed.To address the pr oblems of conventional BCM modulation with a wide range of switching frequency variation,high turn-off loss and output capacitor loss,a fixed switching frequency zero voltage switching hybrid modulation method is proposed,and the sequencing method and mode calculation method of different operating modes are studied.The mode state machine is summarized to simplify the control complexity.The experimental results show that,compared with BCM modulation,the proposed modulation method can reduce the power switch current peak and improve the operating efficiency of the digital power amplifier with the full-load efficiency of 98.17% while the power switch switching frequency remains unchanged.(4)A BCM modulation switching frequency optimization method and a power decoupling control method based on energy conservation are proposed.Both operating efficiency and power density of the digital power amplifier are improved.The operating principle of the differential digital power amplifier is analyzed,the current loops for different frequency currents after adding the auxiliary resonant circuit are derived,the equivalent circuit model is established,and the modal analysis of the circuit is performed.In terms of modulation,a general switching frequency optimization method is proposed according to the loss model of power switches and BCM modulation,which regulates the conduction loss and switching loss of power switches and achieves the purpose of minimizing the total loss of power switches.In terms of power decoupling control,a fast calculation of the fluctuating power of the digital power amplifier is achieved by calculating the energy of each energy storage element in the circuit according to the law of energy conservation,and a corresponding power decoupling control method is proposed,which can also be applied to other coupled power decoupling topologies.The experimental results show that the differential digital power amplifier can achieve both soft switching and power decoupling control without increasing the power switches.Compared with BCM modulation,the proposed switching frequency optimization method can result in a significant reduction in the switching frequency range of power devices and a 40%reduction in power switch losses;the DC-link voltage ripple rate decreases from 3.65%to 0.30% after the proposed active power decoupling control is activated.The proposed active power decoupling method reduces the demand for DC-link capacitance of the device and improves the power density of the device.(5)An asymmetrical multi-bridge arm interleaved parallel digital power amplifier topology is proposed to improve the output band and peak efficiency of the digital power amplifier through bridge arm multiplexing and mode switching.The asymmetrical multi-bridge arm interleaved parallel digital power amplifier topology is proposed,and the operating mode and bridge arm combination mode of this topology are analyzed,and the equivalent circuit with different frequency currents is established.The effect of decoupling capacitance on the bridge arm impedance is analyzed,and the difference in current stress between the proposed topology and the conventional interleaved parallel topology is quantitatively compared.Based on this,a fundamental frequency current control method based on thermal stress equalization is proposed for the different power switch parameters,and the effect of this method on the high frequency harmonics of the output current is derived.The experimental results show that the proposed current control method reduces the temperature difference between power switches,achieves thermal stress equalization of power switches and improves the reliability of the device compared with the traditional equal-current control;compared with the existing active power decoupling and multilevel topology.The proposed topology reduces the number of power switches and improves the utilization of power switches through bridge arm multiplexing,and the output voltage total harmonic distortion of the device can be less than 1% in the 50-2000 Hz band.This dissertation takes the underwater long-range target detection system as the research background,takes the key scientific and technical problems of high-efficiency and high-power density digital power amplifier as the research target,and deeply studies the theories and methods related to the soft-switching modulation and power decoupling control of digital power amplifier around two aspects of power density and working efficiency.The research covers the working mechanism,circuit topology,modulation method,control method and loss optimization of digital power amplifier,and forms a more complete theoretical analysis method and technical scheme. |
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