Simplified analysis of PWM converters using model of PWM switch.II. Discontinuous conduction mode

For pt.I see ibid., vol.26, no.3, p.490-6 (1990). According to the method of state-space averaging, when a pulsewidth modulation (PWM) converter enters discontinuous conduction mode (DCM), the inductor current state is lost from the average model of the converter. It is shown that there is neither theoretical nor experimental justification for the disappearance of the inductor state as claimed by the method of state-space averaging. For example, when the model of the PWM switch in DCM is substituted in the buck, boost, or buck-boost converter while the inductor is left intact, the average model has two poles: the first pole f_p1 agrees with the single pole of state-space averaging, while the second pole f_p2 occurs in the range f_p2⩾F_s/π. It is shown that the right-half plane zeros present in the control-to-output transfer functions of the boost, buck-boost, and Cuk converters in continuous conduction mode are also present in discontinuous conduction mode     

The effect of the magnetizing inductance on the small-signaldynamics of the isolated Cuk converter

The magnetizing inductance of the isolated Cuk converter introduces an undesirable pair of closely spaced complex zeros and poles, or a glitch, in the control-to-output transfer function. Limited analysis and experimentation in the past have shown that sufficient increase in the magnetizing inductance or manipulation of the ratio of the capacitances of the energy transfer capacitors can reduce the glitch. In this work, the isolated Cuk converter with coupled input and output inductors has been studied and the dependence of the glitch on various circuit parameters has been determined analytically. A condition has been derived for the ratio of the capacitances of the two energy transfer capacitors which completely eliminates the glitch at a given operating point. With this condition satisfied, it is shown that the energy transfer capacitors can be easily damped by a simple RC network to eliminate the glitch from a wide range of operation about an operating point     

Analysis of a PWM-resonant converter

When a parallel resonant tank is excited by a bipolar current pulse train a sinusoidal voltage develops across the tank whose amplitude depends on the duty cycle of the pulse train. An isolated secondary can be derived by applying the tank voltage to an isolation transformer whose magnetizing inductance acts as the resonant inductor of the tank circuit. A dc output voltage is obtained after rectification and filtering of the sinusoidal secondary voltage and regulation is achieved by controlling the duty cycle of the pulse train. The sinusoidal nature of the voltage across the isolation transformer alleviates some of the noise problem associated with parasitic capacitances of an isolation transformer when operated with square voltage waveform. In this work the dc and small-signal analysis of the converter is given and an equivalent small-signal circuit model is derived. Experimental results which confirm the validity of the model are presented.     

Generation and classification of PWM DC-to-DC converters

A method is presented by which generation and classification of pulsewidth-modulated (PWM) DC-to-DC converters can be effected. Fundamental blocks known as converter cells can be used to generate a plethora of converters leading to a number of useful new converter topologies. A classification of basic converters is proposed in terms of converter-cell generated families     

Simplified analysis of PWM converters using model of PWM switch.Continuous conduction mode

A circuit-oriented approach to the analysis of pulsewidth modulation (PWM) converters is presented. This method relies on the identification of a three-terminal nonlinear device, called the PWM switch, which consists of only the active and passive switches in a PWM converter. Once the invariant properties of the PWM switch are determined, its average equivalent circuit model can be derived. This model is versatile enough to easily account for storage-time modulation of bipolar junction transistor(s) (BJTs); the DC- and small-signal characteristics of a large class of PWM converters can then be contained by a simply replacing the PWM switch with its equivalent circuit model. The methodology is very similar to linear amplifier circuit analysis, whereby the transistor is replaced by its equivalent circuit model