Ilya Zeltser

The dynamics of a PWM boost converter with resistive input

This paper investigates the large- and small-signal response issues and, in particular, the inner loop gain and outer loop response of an indirect control method for active power-factor correction. The control scheme is based on sensing the average inductor current and generating a D/sub OFF/ (the complement of the switch duty cycle) which is proportional to the current. The method is demonstrated by considering the performance of a boost-type active power-factor corrector (APFC) that does not need to sense the input voltage. Theoretical and experimental results confirm the validity of the approach and demonstrate that the proposed method can be useful in the design of robust APFC with low total harmonic distortion. The indirect control method investigated in this paper is also compared to the classical direct APFC control method, pointing to the differences between the two.

The dynamics a PWM boost converter with resistive input

An average modeling methodology is proposed for deriving PWM programming rules that cause DC-DC power converters to look resistive at the input terminals. The proposed approach was verified by average and cycle-by-cycle simulation. The study investigated the large and small signal response issues and, in particular, the inner loop gain and outer loop response. It is demonstrated that the proposed method can be useful in the design of robust active power factor correctors with low total harmonic distortion (THD).

Reducing IGBT losses in ZCS series resonant converters

The fundamental operational parameter that controls the losses in series resonant power converters was found to be the reflected DC voltage transfer ratio. Losses which are a function of the average current (such as conduction losses of insulated gate bipolar transistors and diodes) are independent of the switching frequency. Losses which are associated with the RMS current are a function of both the reflected DC voltage ratio and the switching frequency ratio. Universal and normalized graphs, derived in this paper, can be conveniently used to assess the expected RMS and average current conduction losses under any given operational conditions. The residual switching losses in zero-current-switching series resonant power converters operating in continuous current mode can be reduced by simple current snubbers placed in the commutation circuits. The experimental results of this paper confirm the theoretical predictions and demonstrate that the turn-on snubbers can reduce switching losses by about 1.5% at a switching frequency of 65 kHz.

Transformer's capacitance effect on the operation of triangular-current shaped soft-switched converters

This paper addresses the effect of the isolating transformer parasitic capacitor in soft switched converter topologies that apply triangular inductor current. When a transformer is included in the circuit, it will not only add (leakage) inductance to the converter but will also add capacitance. This capacitance will cause a partial resonance behavior and therefore may alter the voltage transfer ratio of the converter. The objective of this study was to analyze the effect of this capacitance on the behavior of Triangular Current Shaped (TCS) soft-switched converters. The isolated TCS converter was analyzed and the theoretical results were verified by simulations and experimentally at a 1kW power level. The analysis show that the transformers capacitance boosts the voltage gain of the converter, changes the shape of the inductor current and hence modifies the RMS value of the current. It was found though, that by proper design the RMS current (for same power level) may in fact be reduced and consequently, will result in lower conduction losses as compared to the case with no capacitor.

New snubbers with energy recovery into a local power supply

The general attributes governing the design of local power supplies (LPS) circuits that are piggybacked on a lossless turn off snubbers are highlighted and analyzed. Based on the proposed general principles, new LPS circuits are presented. They are incorporated as part of a lossless turn-on/turn-off snubber. The proposed snubber/LPS topologies serve two important functions: they help to achieve soft switching of the main switch and main diode at turn-on and turn-off and provide low voltage power source for the auxiliary circuitry such as IC controllers. Since all the switching processes are soft and the reactive energy is recycled (or outputted by the LPS), the losses of the main switch and main diode are significantly reduced. The theoretical analysis of the proposed circuits was verified by simulation and experimental results.

ZCS resonant converter based parallel balancing of serially connected batteries string

This paper introduces a new topology for parallel balancing of serially connected batteries string. The main advantage of the balancing concept is that energy is transferred only when the cells are unbalanced. As a result, the power losses are significantly reduced since no current circulates through the system when balanced. This has been enabled by a modification of an isolated series-resonant converter operating in DCM and features zero current switching (ZCS). Another attractive feature is that one transformer for two cells is used, as opposed to conventional isolated topologies that require a transformer per cell. The realization is simple and requires simple current polarity detector. Experimental results have been obtained by a prototype of two series connected batteries, which demonstrates the balancing capabilities of the system.

Current sourcing ZCS magnetron driver for low input voltage applications

The use of topologies that have an output current sourcing behavior could be advantageous when driving constant voltage loads that call for the stabilization of the output current rather than output voltage. The load characteristic of the magnetron considered in this study can be modeled as a voltage source of about 3.9kV with a relatively small internal resistance of about 1.5kOhm that needs to be driven by a current of about 300mA. This study proposes a one-stage, zero current switched, high voltage gain, and current sourcing converter, to drive such a load. The topology is based on the parallel resonant converter but includes blocking diodes at the input bridge to assist the soft switching operation. The theoretical analyses were verified by simulations and experimentally on a 1.3kW magnetron driver which was fed from a low voltage source in the range of 20V to 32V. The circuit was controlled by dsPIC30F2020 (Microchip, USA) in closed loop.

A resonant local power supply with turn off snubbing features

A local power supply circuit which is driven by the main switch of a PWM power converter is described and analyzed. The operation of the circuit is based on the charge pump principle with a resonant reset of the charge pump capacitor. The charge pump capacitor also serves as a turn off snubber of the main switch. The analytical derivations are verified by experimental results.

Fast transition high voltage modulator using SiC MOSFETs connected in parallel

This study investigates the applicability of parallelly connected SiC MOSFETs to high voltage, high input current, and fast transient modulator. The behavior of the proposed approach was tested experimentally on a 650W prototype. The SiC MOSFET transistors were operated at nominal voltage of 840V and current of 800A. The modulator was loaded by a 30kV magnetron. Rise and fall times obtained at the magnetron were below 200nsec. The results of the present study show that the proposed approach can be a good engineering choice for high voltage and high current applications where very fast transition times are required.

An “AC inductor” based grid connected inverter

This study proposes a soft switched Output Current Sourcing (OCS) grid connected inverter that applies a high frequency isolation transformer. Current sourcing at the output implies that, ideally, the injected current will be independent on the load voltage. The current injected to the line is controlled by varying the switching frequency and dithering at low currents. The system does not require the sensing of the output current or even the line voltage - except for synchronization. This is in contrast to the conventional voltage sourcing inverters where the small disturbance at the line voltage may lead to current run away and consequently a tight current feedback loop must be applied. The proposed topology and several proposed control approaches were analyzed and verified by simulations and by experiments. The simulation and experimental results confirm the theoretical analysis and show that the proposed inverter can be operated with no sensing of the line current or voltage.