Michael Bierhoff

Semiconductor losses in voltage source and current source IGBT converters based on analytical derivation

A crucial criterion for the dimensioning of three phase PWM converters is the cooling of the power semiconductors and thus determination of power dissipation in the semiconductors at certain operating points and its maximum. Methods for the calculation and simulation of semiconductor losses in the most common voltage source and current source three phase PWM converters are well known. Here a complete analytical calculation of the power semiconductor losses for both converter types is presented, most parts are already known, some parts are developed here, as far as the authors know. Conduction losses as well as switching losses are included in the calculation using a simplified model, based on power semiconductor data sheet information. This approach should benefit the prediction and further investigations of the performance of power semiconductor losses for both kinds of converters. Results of the calculation are shown. Dependencies of the semiconductor power losses on the type of converter, the operating point and the pulse width modulation are pointed out, showing the general behaviour of power losses for both converter types.

Active Damping for Three-Phase PWM Rectifiers With High-Order Line-Side Filters

Active rectifiers interfacing the grid have gained much attention in recent years due to their current control capability that enables the application to exchange a certain range of power at the benefit of low harmonic distortion compared to line commutated converters. Moreover, the amount of active and reactive powers can be arbitrarily chosen within certain limits. These limits as well as the degree of harmonic attenuation is determined by the line-side filter. This paper basically focuses on the current control of active rectifiers incorporating a line-side filter of first- up to third-order degree. Thus, it treats both the current-source converter (CSC) as well as the voltage-source converter (VSC). The basic models of the plant are derived for each case, and important dualities are pointed out. As a conclusion, a recipe for the controller design of particularly CSCs with LC filters and VSCs with LCL filters is proposed.

DC-Link Harmonics of Three-Phase Voltage-Source Converters Influenced by the Pulsewidth-Modulation Strategy—An Analysis

DC-link current harmonics are the predominant factor to be considered for dimensioning dc capacitors in three-phase pulsewidth-modulation (PWM) voltage-source converters. In this paper, an analysis of the dc-link current harmonics applying a double Fourier series is derived. The analytical results for the dc-link current spectra of continuous and discontinuous PWMs are presented and compared with measurement results taken from a converter test setup. A good match between theoretically expected and actually obtained experimental results can be stated. Moreover, characteristic differences between the investigated modulation strategies regarding their dc-link current spectra become evident.

Loss Minimized Pulse Width Modulation of IGBT Current Source Converters

The current source converter represents the dual counter part to the better known and more frequently used voltage source converter. As such due to duality rules many off-the-shelf solutions concerning the VSC can be used in a modified manner to handle the CSC. This work gives a comprehensive overview of IGBT CSC PWM methods and shows how they are to be distinguished. Then based on duality considerations a complete recipe is given on how to utilize usual micro controller peripherals along with some logic elements to achieve the most significant PWM methods with little effort

An Analysis on Switching Loss Optimized PWM Strategies for Three Phase PWM Voltage Source Converters

The pulse width modulation of power converters is an operation parameter that exhibits a great influence on occurring semiconductor losses. Especially the switching losses can be reduced significantly by applying the appropriate PWM method maintaining the value of pulse frequency. To achieve such effect usually a so called discontinuous PWM is applied. But there is still a certain degree of freedom in using such PWM strategy. Thus the question for the optimal adjustment to the corresponding operation point arises. This work derives the basic rules for adjusting the discontinuous PWM appropriately with special focus on the semiconductor switching losses. The theoretical results are validated by experimental evidence that was gained at a calorimetric test set up.

DC link harmonics of three phase voltage source converters influenced by the pulse width modulation strategy-an analysis

DC link current harmonics are the predominant factor to be considered for dimensioning DC capacitors in three phase PWM voltage source converters. In this article an analysis of the DC link current harmonics applying double Fourier series is derived. The analytical results for the DC link current spectra of continuous and discontinuous PWM are presented and compared with measurement results taken from a converter test setup. A good match between theoretically expected and actually obtained experimental results can be stated. Moreover significant differences between the investigated modulation strategies regarding their DC link current spectra can be found.

Analytical evaluation of the total harmonic current in three phase voltage and current source converters

To facilitate the design of ac side filters, this work gives analytical expressions for the root mean square value of the total harmonic phase currents in voltage and current source converters depending on the modulation schemes and passive filter components. Novel equations were found for the calculation of total harmonic phase currents regarding the CSC with LC filter. The results are verified by appropriate measurements for selected PWM schemes and are valid for most common applications

Theoretical output current spectra of three phase current source converters

The geometric-wall-model by Black has successfully been applied to calculate the harmonic spectra of voltage source converters. This paper derives the application of the geometric-wall-model on the output currents of a current source converter, CSC, by utilizing duality considerations to voltage source converters to determine the spectra of the pulsed output currents occurring in a CSC

A current sensor less speed control algorithm for induction motors

Most speed control algorithms for induction motors (IM) require at least two current sensors. Due to the fact that especially the speed sensor can be related to an increased fault probability and maintenance effort, speed-sensor-less control algorithms are applied for drive applications where corresponding dynamical deficiencies can be tolerated. In any case the current sensors are required to employ field oriented control (FOC) algorithms. Alternative old fashioned slip control techniques which do not necessarily rely on current sensors, are considered to be inferior compared to field oriented control methods in terms of dynamical performance and efficiency. A new simple speed control algorithm without any need for other sensor signals than the speed is presented here. Based on the steady state model of the IM and employing the stator voltage magnitude (scalar control) instead of the slip as control variable, it proves to achieve a with FOC comparably dynamical performance thereby exhibiting superior drive efficiencies.

A General PLL-Type Algorithm for Speed Sensorless Control of Electrical Drives

Speed control of electrical drives without additional speed sensors is preferable in terms of cost and maintenance effort. Common approaches are either simple but inaccurate with deteriorated drive performance in the low-speed range, or they offer full torque even at zero speed at the cost of high implementation effort and parameter sensitivity. Moreover, most of the suggested solutions are tailor made for specific machine types. The proposed method constitutes a simple phase-locked-loop-type sensorless algorithm that can be related to the former category. The outstanding feature of the presented method is its effectiveness and simplicity at the same time. This paper presents corresponding design guidelines for an easy to implement and robust speed sensorless control algorithm for all kinds of electrical machines that includes induction machines as well as synchronous reluctance machines with and without extra/permanent excitation.