Modeling and design of a pulse phase modulated resonant inverter system

Abstract

Resonant converters have been widely used in consumer electronics, telecom power supplies, and electronic ballasts. Compared with the PWM converters, it has many advantages, such as low EMI, low switching loss, and high power density. Depending on applications requirements, the resonant converters use various modulation schemes including asymmetrical pulse width modulation, frequency modulation, and phase shift modulation. The resonant tank can be of various topologies including the commonly used ones such as parallel resonant tank, series resonant tank, LCC, LLC and LC-LC resonant tanks. The circuit modeling and analysis are complicated because the state variables like inductor currents and capacitor voltages are AC dominant. The phasor dynamic modeling method maps the periodical time-varying state variables into stationary frame for each harmonics of interest. Correspondingly, the circuit is decomposed into two DC sub-circuits, the state variables of which are the time-varying Fourier coefficients of the original AC variables. Small signal model can be derived by applying small perturbation and linearization to the Fourier Coefficients. A general phasor dynamic model is presented for the resonant inverters. Such a model closely relates to the power converter topology in time domain, and therefore keeps the physical meaning of the state variables. This model can be easily extended to more complicated resonant topologies, and to include more parasitical components for higher accuracy of modeling. The model can be applied to a number of modulations as well with minor modifications. It can be used for fast simulation, circuit analysis and controller design. A resonant inverter system with 5 energy storage elements are modeled and compared with switch simulation for both steady state and transients. The simulation results match the switch simulation in both steady state and transients, but takes much less time.