EPE Journal Volume 15-1 
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EPE Journal Volume 15-1 - Editorial
EPE Journal Volume 15-1 - Papers



 EPE Journal Volume 15-1 - Editorial 

Invitation to EPE 2005 in Dresden (Germany)  [Details]
By Dr. L. Lorenz

Editorial of EPE Journal Volume 15-1 - Invitation to EPE 2005 in Dresden (Germany), written by Dr. Leo Lorenz


 EPE Journal Volume 15-1 - Papers 

A Sampled-Data Reduced Order Dynamic Model for a Self-Sustained Series-Parallel Resonant Converter  [Details]
By M. Z. Youssef; H. Pinheiro; P. K. Jain

Resonant converters are well known in many industrial applications due to their high operating frequency and lossless switching. The series parallel hybrid type converter has been known as the most promising resonant topology, as it provides a considerably wide operating range with optimized ratings of components. Unfortunately, it has a wide range of operating frequency under the conventional variable frequency control (VF). The self-sustained oscillation control (SSOC) technique was proposed in 1997 in order to further reduce the range of regulating frequency necessary for zero voltage switching (ZVS) and consequently optimize the converter design to achieve a more compact size and consequently lower cost. However, optimizing the converter design at such high frequencies is not an easy task. The first step for achieving this objective is to have a sound and accurate mathematical model for the converter. This paper describes a simple fifth-order dynamic model with a more systematic approach based on the sampled data technique; it has the advantages of being more accurate, easily computed, and has a lower order than its continuous time predecessor found in [1], which was of a seventh order model. In this paper, the complete analysis, modeling, and design of the seriesparallel resonant converter with an inductive output filter under the SSOC is investigated and verified.

The Use of Power Sums to Solve the Harmonic Elimination Equations for Multilevel Converters  [Details]
By J. N. Chiasson; L. M. Tolbert; Z. Du; K. J. McKenzie

A method is presented to compute the switching angles in a multilevel converter so as to produce the required fundamental voltage while at the same time not generate higher order harmonics. Previous work has shown that the transcendental equations characterizing the harmonic content can be converted to polynomial equations which are then solved using the method of resultants from elimination theory. However, when there are several DC sources, the degree of the polynomials are quite large making the computational burden of their resultant polynomials via elimination theory quite high. Here, it is shown that by reformulating the problem in terms of power sums, the degree of the polynomial equations that must be solved are reduced significantly which in turn reduces the computational burden. In contrast to numerical techniques, the approach here produces all possible solutions.

Non-Equilibrium State Capacitor-Voltage Stabilization in a Hybrid Asymmetric Nine-level Inverter: Nonlinear Model-Predictive Control  [Details]
By M. Veenstra; A. Rufer

In symmetric multilevel inverters, there is a tradeoff between the output quality and the reliability and efficiency of the converter. New asymmetric and hybrid solutions, using different voltages and devices in various parts of the inverter, promise significant improvements for medium-voltage applications. This paper investigates such a hybrid asymmetric nine-level inverter. It consists of a three-phase three-level main inverter, with a two-leg two-level sub inverter in series with each phase (Fig. 1). To keep the power part simple and the efficiency high, the sub inverters have no feeding from the net and can only supply reactive power. But the nonsupplied intermediate-circuit capacitors form an unstable system. This paper proposes a control method to stabilize their voltages. Power balancing is guaranteed by varying the common-mode voltage, using an on-line nonlinear model-predictive controller. The controller predicts the system evolution as a function of the control inputs. A cost function of system and control quantities is iteratively minimized in real time, to find the optimal control to apply to the system. Simulations and measurements demonstrate stable behaviour in steady state and during transients. The originality of this paper is the application of nonlinear model-predictive control in power electronics.

A Space Phasor Based Current Hysteresis Controller Using Adjacent Inverter Voltage Vectors with Smooth Transition to Six Step Operation for a Three Phase VSI  [Details]
By M. R. Baiju; K. K. Mohapatra; R. S. Kanchan; P. N. Tekwani; K. Gopakumar

In this paper, a space phasor based current hysteresis controller for a three-phase voltage source inverter is proposed. The current errors are determined along three axes, which are orthogonal to the A, B, C phases, and the current error space phasor is held within a hexagonal boundary. The proposed controller does not require any computation of machine voltage vector and uses only those inverter voltage vectors, which are adjacent to the machine voltage vector for the entire range of operation. The region detection logic employed in the proposed controller ensures that, the vector (among the three adjacent vectors), which has the largest deviation in the opposite direction, is selected, for all the regions of the hexagonal boundary. A simple self-adapting logic is used to effect sector changes and smooth transition to six-step mode of operation is achieved. The proposed controller is implemented for a 5hp induction motor drive.

Comparative Study of Starting Methods for a Single-Phase Permanent Magnet Synchronous Motor  [Details]
By M. Popescu; T.J.E. Miller; C. Cossar; M. McGilp; G. Strappazzon; N. Trivillin; R. Santarossa

This paper compares three starting methods for a single-phase interior permanent magnet synchronous motor. One is a line-start capacitor motor with a starting cage. The second is the same cage motor with an open-loop variable-voltage fixed-frequency inverter. The third uses the same motor without its starting cage, fed from a closed-loop current-regulated inverter with shaft position feedback. The computed starting performance is compared with test data for all three cases.

Compact ASD Topologies for Single-Phase Integrated Motor Drives with Sinusoidal Input Current  [Details]
By C. Klumpner; F. Blaabjerg; P. Thogersen

A standard configuration of an Adjustable Speed Drive (ASD) consists of two separate units: an AC motor, which runs with fixed speed when it is supplied from a constant frequency grid voltage and a frequency converter, which is used to provide the motor with variable voltage-variable frequency needed to adjust the speed of the motor. The integrated motor drive concept is a result of merging the two units in order to achieve the following benefits [1-3]: reducing the design and the commissioning time in complex industrial equipments, no need for a cabinet to host the frequency converter, no need for shielded cables to reduce EMI (Electro Magnetic Interference), no need for cables for the speed transducers or for other sensors for industrial process control (e.g. pressure). This solution is currently available up to 7.5 kW being not used in the medium and high power range due to a low-density integration of the converter caused by the large size of the passive components (electrolytic capacitors and iron chokes) and vibration of the converter enclosure. This paper analyzes the implementation aspects for obtaining a compact and cost effective single-phase ASD with sinusoidal input current, investigating the physical removal of power inductors from the converter enclosure in conjunction with reducing the number of semiconductor active devices. There are two ways to do that: to integrate the inductors in the unused area of the stator yoke of the motor or to use the leakage inductance of the induction motor as a boost inductor for a PFC (Power Factor Correction) stage controlled by the inverter zero-sequence voltage component. By determining how much energy is possible to store in a corner inductor, it is proven that integrating the magnetics into the stator yoke is a feasible solution. Topologies of single-phase converters that take advantage of the motor leakage inductance are analyzed. The installed power in silicon active devices of these topologies is compared with a standard situation, showing that this will involve higher cost. As the iron core of the inductors is not suitable for high frequency operation, higher core losses will occur, but outside the converter enclosure. The advantages are: the reduction of the number of active semiconductor devices, the reduction of the ASD size and the better integration potential.