| Distributed sound systems have been widely used in public broadcasting and background music occasions,where a single audio power amplifier is required to directly drive multiple constant-loudspeakers over long distances.However,an isolated DC/DC converter is utilized to provide a stable DC voltage for the latter Class D power amplifier,thus the system configuration is two power conversion.Meanwhile,the output side of the DC-DC converter uses DC LC filter,where the volume of the filter inductor and the electrolytic capacitor is relatively large.In addition,the larger system power level leads to the higher power supply voltage of audio power amplifier.Accordingly,the higher drain-source breakdown voltage of the switches is required for the class D amplifier.The switching frequency of all switches is high(hundreds of kHZ)as well.High voltage high switching-frequency switches work in hard switching operation,which will lead to high switching loss,reduce the system efficiency and affect the thermal design.This thesis is focused on the single stage audio power amplifier by seamlessly integrating the front isolated DC/DC converter and the latter class D amplifier into single power conversion.Besides,all switching switches can achieve zero voltage switching(ZVS),which significantly reduces switching losses of the device and increases system efficiency and power density.The research objective is the cycloconverter-type high frequency link(CHFL)DC-AC converter based on the Uni-polarity(UP)modulation strategy.The low frequency decoupling method and high-frequency decoupling algorithm of cycloconverter are proposed and studied.The problem of resonance between leakage inductance and parasitic capacitance is analyzed in detatil and the realization methods of wide-range soft switching of switches are investigated as well.The main research contents and innovations of this thesis are as follows:(1)Topology classification and evolution of CHFL DC-AC converters based on three-level(3L)UP modulation strategy are introduced.The low-frequency decoupling principle and implementation methods of the cycloconverter are analyzed in detail.A low-frequency decoupling modulation strategy without current sensor is proposed to solve the problem where the converter needs to sample the output current under non-resistive load.At the same time,a low-frequency decoupled CHFL DC-AC converter is proposed and analyzed as well.(2)The resonance between the leakage inductance and the parasitic capacitance is analyzed,resulting in overvoltage and EMI problems.The limitations of employing the snubber circuit and clamping circuit to solve the resonance problem are described.The CHFL DC-AC converter with primary clamping diode is proposed to solve the resonance problem and the operation principles are analyzed in detail.In addition,the active clamping circuit applied for CHFL DC-AC converter is investigated,and an active clamping phase-shifted modulation strategy with a fixed duty cycle is proposed as well.(3)The CHFL DC-AC converter based on two level(2L)UP modulation strategy is presented.The operation principles of high-frequency decoupling 2L-UP modulation strategy are analyzed in detail.The high-frequency decoupling algorithms based on frequency-doubling unipolar and unipolar SPWM are proposed.The implementation methods,operating principle,commutation process and soft switching characteristics of the two modulation strategies are analyzed in detail.(4)The soft-switching characteristics and conditions of CHFL DC-AC converters are introduced.According to passive loseless soft-switching technology,two wide-range soft-switching methods with fixed auxiliary current amplitude and adaptive amplitude are proposed and studied in detail.The operation mechanism,soft switching conditions and circuit parameter design guidelines are presented.In addition,the experimental design process of the single-stage constant-voltage power amplifier is given by adopting the CHFL DC-AC converter with phase-shifted active clamping circuit.The experimental results verify the theoretical analysis and performance of single stage power amplifier. |
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