Contents I. Introduction
One of the methods which is used in class D resonant converters is an integration control (Fig. 1) [4]. In the integration control, the changes of switch control signals may occur only at zero current. Therefore, it is very important to follow the resonance frequency because it allows to fulfill zero-current-switching (ZCS) conditions. The principle of the circuit operation is based on utilization energy stored in passive elements of the resonant circuit. It allows to keep the current continuous when the switches are turned-off [Fig. 1(b)], although a total disappearance of a current flow is possible as well [Fig. 2(a)]. Generally, a current magnitude in the resonant circuit is a subject of constant changes, but these changes are periodic, whereas the voltage changes on series resonant circuit (SRC) are nonperiodic. The voltage at the diagonal of the bridge can be in opposite phase to resonant current, in phase, or can be equal to zero as well (Fig. 2). Therefore, the definition, measurement, and regulation of current and voltage phase shift in the integration control are more complicated than in methods with periodic current and voltage waveforms.
Class D series-resonant bridge converter with integration control and phase shift controller: (a) Basic configuration of the circuit. (b) Time waveforms of resonant current , diagonal voltage , and control signals in phase controller for . (c) Characteristic of phase controller tuning. CT—current transformer; BS—bidirectional switch.
Simulated waveforms of resonant current , diagonal voltage in bridge converter with phase controller that operates with (a) PDM (—bidirectional switch control signal), (b) SWIPDM, and (c) SIC method (step change of SRC parameters).
