Research On Compounded High-frequency Link Inverter For Soft-switching

On the basis of the research on the phase-shift-controlled technology and the high-frequency (HF)link inverting technology, and the key technical problems of the novel single-phase and three-phase compounded HF link inverter for soft-switching are studied and discussed in detail .From the viewpoint of the direction of power flow, a single-phase HF link inverter circuit topology on the basis of LCC-type resonant circuit with constant-frequency phase-shifted control is proposed. Under the condition of 0. 1 m 0.5 , the phase-shifted angle 6 is controlled in term of sine law which makes the magnitude of resonant voltage track a reference sine voltage , and the resonant voltage is rectified , filtered, inverted and then the better sine-voltage output is obtained , Theoretical analysis and experimental results show that for the resistive load and inductive load, the switches of leading leg of the phase-shift-controlled circuit are always turned on at ZVS, and ones of lagging leg are turned on at ZVS( < 0 ) or turned off at ZCS( ( > 0 ), moreover, all switches in the low-frequency inverter are always turned on and off at ZVS , the measured circuit efficiency for rated load reaches up to 88% .Based on the study of transferring characteristics of the LCC-type resonant voltage, the parameter combinations, which make widths and magnitudes of voltage pulses of resonant network adjustable, arededucedo When the following requirements are met: fn>3, K>3 or Cp/Cs>8, the above circuit is of natural voltage-stabilized characteristics, thus open-loopcontrol method for bucking voltage is presented and the experimental results verify that the method is feasible., For the purpose of boosting voltage, because of the effect of the load R on Q, the proposed close-loop control method is the best choice to ensure the stable output voltage .A novel cycloconverter-rype three-phase HF link inverter topology for soft-switching based on phase-shifted full-bridge mode is proposed, whose main advantages are as follows: under the conditions of d < i < and overlap - d, the switches of the leading leg are turned on at ZVS and the switches of the lagging leg are turned off at ZCS and all switches of the cycloconverter circuit are commutated in the overlapping mode in the interval of zero voltage, which makes the circuit realize soft switching to the utmost extent and reliably solve the problem of peak voltage caused by the storing energy of leakage inductance of HF transformer. Theoretical analysis and experimental results prove that the HF link inverter for soft-switching is prospective and it can be used in driving specific three-phase motors isolated from power supply .Due to the complexity of the structure and control of cycloconverter-type three-phase HF link inverter for soft-switching based on phase-shift-controlled full-bridge mode, a simple and optimized VVVF control strategy is proposed . This control strategy includes: produced PWM by space voltage vector ( SVM ) and equivalent carrier frequency fe =1/Te are introduced into the PDM Control of the cycloconverter; softened equivalent PWM wave is generated at the notches of HF voltage pulses; the harmonious control between regulating pulse width by phase-shifted angle and regulating voltage of equivalent PWM is to minimize the harmonics content of output voltage of the inverter. Digital control system based on DSP is designed and it realizes the above control strategy, the feasibility and validity of the control are verified by experiments .The optimal relationships among switch frequency fs of the phase-shifted full-bridge circuit , equivalent carrier frequency fe of the cycloconverter and output frequency fo are also studied, and under the conditions of fs 3.5 feand fe 12 fo, the output voltageof the HF link inverter has the good sinusoidal characteristics.