H Henk Huisman

A DC to 3-Phase Series-Resonant Converter with Low Harmonic Distortion

A type of dc to 3-phase series-resonant converter (s.r.converter) or potentially submegawatt industrial applications is presented. The converter provides variable-frequency sine-wave currents, with low harmonic distortion at the output terminals, and with the frequency ranging from -200 through dc to +200 Hz. The converter can transfer power in both forward and reverse power-flow directions to almost any type of load circuit. The methods of control are formulated such that they can be implemented easily with high-speed logical circuits. Test results for a 1-kW demonstration converter are supplied.

A 80-kW Isolated DC–DC Converter for Railway Applications

This paper provides an analysis of a three-phase dual active bridge (DAB) topology used as high-power-density dc-dc converter for railway applications. The three-phase DAB is analyzed concerning the current intervals, the output power, and softswitching region, including the impact of zero-voltage switching capacitors. Furthermore, two measures are proposed to achieve soft-switching in the entire operating range, being auxiliary inductors and a straightforward switching strategy called the burst mode. Optimal component values are calculated to minimize losses in the complete operating range and to assess which measure is best suited. A prototype with the specifications acquired from the application has been built, yielding an efficiency of 95.6% at a nominal output power of 80 kW.

Novel operation and control modes for series-resonant converters

A series-resonant converter (SRC) able to generate an output voltage either lower or higher than the source voltage is described. Moreover, a novel control scheme is presented which renders two degrees of freedom for control and which guarantees symmetrical steady-state waveforms in all operation modes. Both the average resonant current as well as the peak voltage of the resonant capacitor can be controlled independently. Special attention is given to an operation mode which facilitates converter operation when the output voltages approximately equal the source voltage (q approx equal to 1). Test results are presented of both controller and converter.

Generalized harmonic elimination method for interleaved power amplifiers

This paper examines interleaved converters in which tolerances of the cell inductors are taken into account. Normally, an equally distributed phase-shift is applied to the PWM of an interleaved converter, which results in optimal ripple-cancellation for the output current. This is true for the ideal case in which cell inductors are identical. However, in practice, cell inductors are not equal, leading to the return of fundamental switching-frequency subharmonic components in the spectrum of the output current. In this paper it is shown that for this situation an optimal phase-shift exists. A generalized method is proposed to calculate the phase-shift in such a way that harmonics, such as the fundamental switching frequency harmonic component, are removed from the spectrum. For three parallel cells an analytic and a geometric method, supported by simulation results, to calculate the phase-shift is presented. Finally, results from an experimental setup are shown to verify the proposed ideas.

A multiphase series-resonant converter with a new topology and a reduced number of thyristors

Multiphase series resonant (SR) power converters provide a flexible way to transform power between a utility grid and a multiphase load or source. The current implementations all suffer from a high component count, which makes the use of these power converters unattractive from an economical point of view. A new topology for multiphase SR power converters has been proposed in the literature in a simulation context. This topology uses half the number of power semiconductors compared to the existing multiphase SR power converters. The present paper addresses the implementation of the new topology in a prototype power converter. The old and new topologies are presented. The operation of the new topology is explained. In the new topology the resonant circuit is grounded at one side, which compared to the old topology imposes a restriction on the operation. The paper shows both simulation data and measured waveforms. It is explained that the economical gain due to the reduction in component count is offset by a lower power rating. The paper finishes with conclusions and acknowledgments. >

A three-phase to three-phase series-resonant power converter with optimal input current waveforms. I. Control strategy

A control strategy for multiphase-input multiphase-output AC to AC series-resonant (SR) power converters is presented. After reviewing some basics in SR power converters, a hierarchy of control mechanisms is presented, together with their respective theoretical backgrounds and practical limitations. The respective controllers are then presented in a simulation context. The control scheme fully exploits the capabilities of high-frequency power converters and facilitates the extraction of currents at a unity power factor from the supply side, even under transient conditions. The control scheme takes into account losses and inaccuracies in the control electronics without deteriorating the intended waveforms. Through computer simulation, it has been shown that, in particular, the input current wave-shapes are greatly improved compared to the best-available operating data. >

Elimination of zero-crossing distortion for high-precision amplifiers

Switch blanking time, also referred to as dead-time, is one of the dominant sources of output current and voltage distortion in pulse width modulated amplifiers. Extensive studies are known on elimination, minimization, and compensation of the effect. Most techniques achieve a reduction but are not capable of completely removing it. This paper demonstrates that it is possible to fully eliminate dead-time effects by applying the socalled opposed current converter topology in combination with advanced feedforward techniques. The zero-crossing behavior of the opposed current converter is analyzed and compared to a conventional full-bridge converter with equivalently filtered output. Simulations and measurements on a full-bridge and an opposed current converter of 1.5 kW are included to demonstrate the effectiveness of the proposed ideas for high-precision applications.

Harmonic elimination by adaptive phase-shift optimization in interleaved converters

Interleaving is a commonly used technique to reduce the output current ripple in parallel connected buck-stages. Harmonic cancellation is achieved by applying a phase-shift to the carrier waves of the pulse width modulator, resulting in a reduced output current ripple at a higher effective frequency. However, optimal interleaving is only achieved when switching cells are identical. When variations between switching cells are taken into account, subharmonic switching-frequency components will appear in the output current, resulting in a higher voltage ripple than designed for. In this paper an adaptive phase-shift control method is proposed which can solve the optimal phase-shift problem. Additionally, it will be shown that the phase-shift values can be determined by only measuring the output current. The proposed algorithm has also been verified on a experimental setup.

Harmonics in opposed current converters

Practical switching devices have finite turn-on and turn-off times. Normally a blanking time is added between the turn-off and turn-on of switches to avoid a short circuit during switching. This blanking time results in a current dependent voltage error of the pulse width modulated output of a converter. Topologies based on only one active device in series with a freewheeling diode, like the opposed current converter, do not need blanking time, and the output voltage distortion is greatly improved but not absent. This paper focuses on the harmonic distortion due to nonideal components in the opposed current converter switching leg and compares different modulation strategies. It is shown that the opposed current converter switching leg can be linearized by proper selection of its components. Furthermore, by applying the right modulation strategy it is possible to achieve a double effective switching frequency, as with unipolar switching, while maintaining constant common mode voltage at the output, as for bipolar switching.

Fast-Shared Current Transient Response in High-Precision Interleaved Inverters

A robust self-interleaving mechanism for paralleled hysteresis-current-controlled inverters is proposed, featuring sustained switching under all load conditions. A fast interleaving technique that can be applied when no clamping of the output voltage occurs is combined with a self-interleaving mechanism that ensures correct switching during output-voltage-clamping conditions. The self-interleaving mechanism was analyzed using the state-plane method, extended to multiple modules in parallel. A minimum switching frequency and maximum duty cycle are guaranteed under all load conditions, enabling the use of low-cost bootstrap circuits to drive the high-side switches. The interleaving approach results in reduced volume of the passive components and improved dynamic response. Simulations were conducted to verify the combined operation of both methods, and measurements were performed on a 2.8-kW prototype zero-voltage-switching inverter with a discrete hysteresis current controller.