Franc Mihalic

Reduced Conductive EMI in Switched-Mode DC–DC Power Converters Without EMI Filters: PWM Versus Randomized PWM

This paper addresses improved electromagnetic compatibility (EMC) in switched-mode power converters (SMPCs), without using electromagnetic interference (EMI) filters. A practical solution is proposed for minimizing conductive EMI in a pulsewidth modulated (PWM), and random PWM dc-dc power converters. A comparative investigation is performed into the use of different random modulation schemes (driven by the DSP-2 board with the TMS320C32) as against the normal PWM. The effectiveness of randomization on spreading those dominating frequencies that normally exist in constant frequency PWM schemes is evaluated by power spectral density (PSD) estimations in the low-frequency range. Some parasitical- and topology-based EMI sources in devices are presented and frequency analysis is shown by using the discrete Fourier transform (DFT). SPICE simulations are also used to verify practical solutions for eliminating negative EMI sources and achieving EMC improvements. Finally, levels of conductive EMI are estimated with DFT, and experimentally verified to comply with the CISPR 25 (or EN 55025) regulations. Moreover, it is clearly shown, that limited speed PWM driving of the power switches with appropriate snubber circuits guarantees reduced conductive EMI. When considering the price and high EMC, in the final solution the power converter is driven by the mu-controller PIC16F876 with limited numerical and peripheral capabilities, where only normal PWM and randomized PWM can be implemented

Safe start-up procedures of isolated bi-directional DC-DC converter

This paper presents a safe start-up procedures of an isolated bi-directional DC-DC converter in buck and boost modes. This converter has been developed as a part of multifunctional up to 4 kW power supply system that uses a high voltage (450 V) DC-link. The isolated bi-directional DC-DC converter can charge 28 V batteries and supply auxiliary low voltage DC loads. Additionally, the isolated bidirectional converter can also draw power from the batteries or from trucks engine driven alternator to keep maintain the high voltage DC-link. Modulation strategies, start-up procedures and control of this converter have been validated by using the Matlab SymPowerSystems Toolboxes and finally, they have been also experimentally verified.

Digitally controlled buck converter

Digitally controlled step down converter with different control law algorithms is studied in this paper. The state controller is designed to eliminate the start-up overshoot and reduce maximal dynamic error of load change response, but the state controller is not capable of eliminating the steady-state error under the load change condition. By using an additional discrete PID controller the steady state error could be eliminated. For the next consideration, the decomposed discrete fuzzy PID controller has been analyzed. All control algorithms are performed at a continuous current mode of operation. The experimental results are presented in the paper. The control algorithms were implemented on 16-bit microcomputer.

Improved frequency characteristics of the randomized PWM boost rectifier

A randomized pulse width modulation (RPWM) algorithm is applied in the control unit of the boost rectifier to achieve improved frequency characteristics in the wide band. First, the introduction of the RPWM switching is reflected in a smaller increase of the total harmonic distortion (THD) factor in the input current. Nevertheless, decrease of the power factor is negligibly small. Second, the power spectrum density (PSD) of the input current is estimated and measured to evaluate the influence of randomization in the high-frequency range. This approach offers an effective and credible prediction method for reduction of conductive electromagnetic interference (EMI) by using the RPWM switching.

Snubbers in the Three-phase AC to DC Buck Converter

In this paper, investigation of effective snubber circuits in the three-phase AC to DC buck converter is presented. Based on the theoretical analysis and from the conventional matrix converters theory approach, the mathematical proof for an AC to DC power converter with unity input displacement factor (IDF) operation without current sensing, is provided. For the DC output current bulky inductance in the output filter is needed and appropriate modulation strategy without open circuit terminals must be assured. High inductance and very short switching times of the power switches are main source of the high and destroying dv/dt in the power converter. This problem can be overcome by proper driving circuits and by appropriate design of the effective snubber circuits not only at the switching power transistors but also at the series diodes as well. And finally, all theoretical considerations are verified by digital simulations and measurements on a low-power prototype of a three-phase buck rectifier.

COMPONENT MINIMIZED TOPOLOGY OF DC TO THREE-PHASE INVERTER

A DC to three-phase converter based on using a two-phase to three-phase transformation has been developed. To provide a better understanding of the operation principle, the transformer, which is the main element of the system, has been supplied by two single-phase inverters. According to this, the theoretical analysis of the proposed system is shown. This analysis is based on two-phase to three-phase transformation. The theoretical analysis and the experimental verification of the proposed principle are presented. In this paper the component minimized inverter topology is also proposed.

Improved EMC of Switched-Mode Power Converters with Randomized Modulation

This paper surveys some analytical and experimental results concerning different randomized modulation strategies in switched-mode power converters (SMPCs). After a short review of practical experiences within the literature it presents the benefits of several randomized schemes for power converters (i.e. reduced electromagnetic interference—EMI, and lower acoustic noise). It also introduces the mathematical background for dealing with randomized modulation within the medium-frequency range: power spectrum density (PSD). Finally, the EMI measurements confirm the improved EMC performances of the randomized boost rectifier, as also in the DC-DC buck converter.

AN EXPERIMENTAL ANALYSIS OF THE RANDOMIZED PWM IN THE BOOST RECTIFIER

Several recommendations and standards have increased the interest in power factor correction circuits. There are multiple solutions in which line current is sinusoidal and boost rectifier is one of them. In this paper an experimental analysis of the randomized pulse width modulation (RPWM) algorithm in the boost rectifier is performed. The influence of randomization is followed: first, introduction of the RPWM switching is reflected in smaller increase of the total harmonic distortion (THD) factor in the input current. Nevertheless, decrease of the power factor is negligibly small. Second, power spectrum density (PSD) of the input current is estimated and measured to evaluate the influence of the randomization in the high frequency range. Based on this approach, lower conductive electromagnetic interference (EMI) is expected and also experimentally verified.

PWM algorithm for three-phase three-level AC to DC boost rectifier

This paper considers the connection between switching matrix function and pulse width modulation algorithm with emphasis on the unity power factor correction requirements for three-phase three-level AC to DC converter. Based on the switching matrix converter theory, the switching sequences for PWM of the three-phase three-level AC to DC converter (rectifier) have been developed. Such an approach enables the input displacement factor correction without an input current sensor. The necessary control variable is only the measured displacement angle between the input voltage and the input current.