Abstract
A simulation model of a converter with soft switching of transistors has been created. New calculation methods and means of measuring the equivalent frequency characteristics of converting devices with negative feedback to the problems of stability analysis have been applied. A comparative analysis of the calculated frequency characteristics of the converter in the normal operation mode with the characteristics of its linear model is presented. The features of calculating the equivalent frequency characteristics of the loop amplification of key devices are considered. It is noted that it is the equivalent frequency characteristics of the loop amplification that describe the relationship of frequency properties with the dynamics of voltage converters with pulse-width modulation and make it possible to reliably determine the real stability margins, predict the generation modes and open up the possibility of obtaining maximum negative feedback in a given frequency band of key devices. The non-minimal phase properties of the converter significantly complicate the achievement of high-quality stabilization of the output current (stabilization coefficient) of pulse stabilizers using only the deflection control principle. A successful solution to the problem is provided by the use of the principle of combined control. Compensation of the disturbance effect (changes in the supply voltage) gives a much better result than countering it through the feedback loop. It is quite realistic to exclude the influence of the input voltage u ( t ) on the output current i 2 in a static mode ( u =const) and in the absence of a negative feedback loop, which provides for u =const in a steady state, and to provide better dynamic properties of the converter. The influence of the nonlinear properties of pulse width modulation on stability is manifested in the considered characteristics in the form of an additional phase shift and resonant bursts in the vicinity of the clock frequency subharmonics. Additional feedbacks introduced into the control loop make it possible to solve synthesis problems using the most simple technical means
Highlights
Analysis of information materials [1,2,3,4,5,6,7,8] showed that at present high-frequency voltage converters (HVС) implementing the technology of “soft” switching, known as Zero Voltage Switch (ZVS), seem to be the most promising for the implementation of highly reliable medium-power power supplies for modern electrical technologies [2]
Oscillograms of the transient and steady-state modes: a – for the current in the load when working out the jump of the reference action Uref=1 V from zero initial conditions; b, c – frequency dependence for the exact pulse model of the converter with control only by the output The output of an object excited by such an action will change according to the law y(t) = Aс (ω)sin ωt + φс (ω), where the function Aс (ω) is the amplitude-frequency characteristic of the closed-loop system
The equivalent frequency response (EFR) of the loop amplification really more successfully describes the relationship of frequency properties with the dynamics of voltage converters with pulse width modulation (PWM) and makes it possible to reliably estimate the real stability margins in amplitude and phase, predict the generation modes and open up the possibility of obtaining a simpler way of maximum NFB in a given frequency band of the converting devices
Summary
Analysis of information materials [1,2,3,4,5,6,7,8] showed that at present high-frequency voltage converters (HVС) implementing the technology of “soft” switching, known as Zero Voltage Switch (ZVS), seem to be the most promising for the implementation of highly reliable medium-power power supplies for modern electrical technologies (plasma – cutting, welding, surfacing and spraying) [2]. Pulse DC voltage converters using the technology of “soft” switching based on pulse width modulation (PWM) provide high efficiency (at least 90–95 %), corresponding to the world standards “80 PLUS, GOLD”, acceptable weight and dimensions (up to 1.5 kW/kg) and reliability [3, 4]. They are nonlinear closed-loop automatic control systems prone to chaotic dynamics. With a certain combination of parameters, low-frequency periodic oscillations with large amplitude, as well as quasiperiodic and chaotic oscillations [11], which are dangerous for the power section of the converter, can occur. Achieving high-quality stabilization of the output current remains an important direction in the construction of power supplies for modern electrical technologies
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