EPE Journal Volume 22-2 
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EPE Journal Volume 22-2 - Editorial
EPE Journal Volume 22-2 - Papers
EPE Journal Volume 22-2: Other



 EPE Journal Volume 22-2 - Editorial 

Editorial: EPE-PEMC 2012 ECCE Europe, a summary  [Details]
By V. Katic
Editorial: EPE-PEMC 2012 ECCE Europe, a summary, written by Vladimir Katiç, University of Novi Sad, General Chairman


 EPE Journal Volume 22-2 - Papers 

New Junction Temperature Balancing Method for a Three Level Active NPC Converter  [Details]
By E. Hauk; R. Álvarez; J. Weber; St. Bernet; D. Andler; J. Rodríguez
The three-level Neutral Point Clamped Voltage Source Converter (3L-NPC VSC, 3L-ANPC VSC) has many attractive features like its high reliability and availability. Nowadays, this technology is mature and can be found in several industrial applications [1], [2]. Some common applications are pumps, fans, compressors, mixers, extruders, crushers, rolling mills, mine hoist drives and excavators.

The three-level Active NPC VSC (3L-ANPC VSC) was introduced in 2001 to overcome the drawbacks of the conventional 3L-NPC VSC [3]. The 3L-ANPC VSC includes additionally active switches parallel to the NPC diodes for clamping the neutral tap of the converter. It features 3 extra switch states in contrast to the conventional 3L-NPC VSC, which enable the possibility to reduce the temperature imbalance and/or to increase the output frequency or the converter power. In order to use the potential of the 3L-ANPC VSC and to balance the losses among the semiconductors, the implementation of a temperature balancing strategy is necessary [4] and [5].

The medium voltage 3L-ANPC VSC is especially advantageous in the following applications:

– High power applications, where the required output power cannot be archived without a serial/parallel connection of devices.
– Medium voltage converters, where the switching frequency should be increased without decreasing the converter power (e.g. applications which require a sine filter or high speed applications).
– Applications where the nominal converter current is required at low modulation index and low fundamental frequencies (e.g. zero speed operating points, hot and cold rolling mill applications, converters for doubly fed induction generators, etc.).

The starting point for the derivation of the new balancing algorithm was the Active Loss Balancing (ALB) system, which is reported in [4] and [5]. The new temperature balancing scheme profits from the features of Predictive Control [6] in order to precalculate the conduction and the switching losses and finally the temperature of each semiconductor up to the future commutation to the zero state, i.e. over the next period of the switching frequency. The precalculated maximal junction temperature will be used for the control strategy in order to determine the optimal switch state to be applied.

Some additional features of the new balancing algorithm with respect to the ALB algorithm are: consideration of the conduction losses fed into the balancing algorithm, regard of the temperature ripple between two consecutive commutations and the use of a control criteria (cost function) in the selection of the zero state [6]. The algorithm is implemented in Matlab and compared with the 3L-NPC VSC using experimental data of a 4.5 kV Press-pack IGBT and Diode for the calculation of the losses. The comparison shows a potential to increase the output power of the 3L-ANPC VSC.

Straightforward Current Control - One Step Controller based on Current Slope Detection  [Details]
By Fr. Becker; H. Ennadifi; M. Braun
In order to control the speed or the position of an electrical drive, the torque of the machine has to be set accordingly. The torque is a function of the machine current which is set commonly by means of a voltage source power converter. Because of the simplification of the set-up procedure, cascaded control structures are used. For a stable operation it is important that the speed of the inner control loop is much higher than the outer ones. Hence the speed of the current control limits the dynamics of the drive control.

This means that the speed and the accuracy of the current control is decisive for the overall performance of the drive control. In this paper a new control method will be presented which is capable to reach the setpoint value in the shortest possible time of only one control period (comp. fig. 7) but without the knowledge of the machine parameters. This is the fastest possible response for digital controls which can be obtained theoretically by deadbeat controllers. However, high dynamics can hardly be achieved by deadbeat controls in practice because they are very sensitive against variations of the control parameters. Therefore the machine parameters like the inductance and the resistance as well as the course of the induced voltage have to be determined by a measurement for a proper operation. Furthermore the control has to be adjusted manually by the user. This leads to an high effort for the set-up procedure. In addition these parameters may vary during operation because of warming for instance, which can lead to a maladjustment of the control.

The new control will adapt onto the load automatically which leads to a significant simplification of the set-up procedure. The identification of the control path is based on the detection of the current slopes of the load current ripple, caused by the alternating of the switching states of the power converter. Hence no additional test pulse are necessary for the identification of the system behaviour. This permanent adaptation leads to an optimal dynamic behaviour of the drive system. In contrast to many model predictive control methods, the new control has a low computation effort and no extensive model of the control path is necessary. The principle function of this new control approach will be explained and verified for an armature current control of a d.c.-drive system. However the principles of this control can also be applied on three-phase application which will be demonstrated by experimental results.

Thermal Modeling of a High-Speed Switched Reluctance Machine with Axial Air-gap Flow for Vacuum Cleaners  [Details]
By H. J. Brauer; R. W. De Doncker
Knowing the precise thermal behavior of switched reluctance machines (SRM) is important to increase the power density of such machines. Up to now, literature is lacking about how to model in detail switched reluctance machines at high speed with axial air-gap flow. The aim of this paper is to present a model showing the effects of varied air-gap flow on temperature distribution in vacuum cleaner machines with a power of 1kW and 60.000 rpm. First, a simulation model was set up, illustrating various operating points of the drive. Then the results of this model were verified on a test bench. Hereby, a simulation was found for high-speed switched reluctance machines that ideally reflects the temperature distribution within the machine and also depicts the effects of changing axial air-gap flow. In conclusion, this presented model indicates that even at high speed and with reduced air-gap flow, these switched reluctance machines can be operated within established temperature limits. Ultimately, this model is very good for predicting the thermal behavior of similar switched reluctance machines with air-gap flow.

Fault Ride Through Capability for Solar Inverters  [Details]
By K. Fujii; N. Kanao; N. T. Yamada; Y. Okuma
A solar inverter for utility scale has been developed in this paper, and the inverter has fault ride through (FRT) capability, which is now discussed in Japan and similar to requirement in U.S.A and Europe. This solar inverter consists of a boost chopper and a three-phase 2-level inverter, and the capacity covers from 20 kW to 600 kW. This paper first describes the FRT capability. Second, how to control the boost chopper and the inverter is shown. Especially, a new inverter current control to achieve FRT capability and dynamic voltage support (DVS) during a grid fault is proposed. After that, several results using an experimental model (5-kW solar inverter) are shown. Finally, results of a prototype model (20 kW), which has been installed in an actual grid, are presented.


 EPE Journal Volume 22-2: Other 

In Memoriam: Alfio Consoli  [Details]
By F. Profumo
In memoriam: Alfio Consoli

Brief report from EPE Joint Wind Energy and T&D Chapters Seminar 2012  [Details]
By C. Oates; R. Teodorescu; P.C. Kjaer
Brief report from EPE Joint Wind Energy and T&D Chapters Seminar, held at the Utzon Centre & Aalborg University in Aalborg, Denmark.
Thursday-Friday 28th-29th June 2012