Evaluation of a High Power ARCP Voltage Source Inverter with IGCTs S. Bernet, R. Teichmann, J. Weber, P. K. Steimer IAS, October 1999, Phoenix, USA
Copyright © [1999] IEEE. Reprinted from the Industry Applications Society.
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High Power ARCP Source Voltage Source Inverter
Evaluation of a High Power ARCP Voltage Source Inverter with IGCTs S. Bernet
R. Teichmann, J. Weber
P. K. Steimer
ABB Corporate Research P.O. Box 101332 69003 Heidelberg Germany
Dept. of Electrical Engineering Dresden University 01062 Dresden Germany
ABB Industrie AG R&D Drives and Power Electronics CH-5300 Turgi Switzerland
[email protected] AbstractAn evaluation and comparison of a two-level conventional Voltage Source Inverter (VSI) and an Auxiliary Resonant Commutated Pole Voltage Source Inverter (ARCPVSI) featuring IGCTs for a 3MVA application is presented. Design issues of both topologies are addressed. The IGCT loss approximations are based on extensive measurements of the devices under hard and soft switching conditions. The results show that the ARCPVSI with IGCTs is a highly competitive alternative to conventional VSIs in this power range.
I.
INTRODUCTION
Gate Turn Off Thyristors (GTO), Integrated Gate Commutated Thyristors (IGCT) and Insulated Gate Bipolar Transistors (IGBT) are the high power semiconductors currently available on the market which can be turned off actively. Conventional GTOs are the gate-controlled semiconductors still used mostly at high voltages (VBR>3300V) and high power (i.e. S≥0.5 MVA) in traction and industrial inverters. Several manufacturers offer commercial GTOs up to a rated switch power of 36MVA (6000V, 6000A). The bulky and expensive snubber circuits, which limit the turn-off dv/dt to about 500-1000V/µs, the complex gate drive as well as the relatively high power required to control the GTO will lead to an increasing replacement of GTOs by IGCTs and IGBTs. Declining prices for GTOs (by a factor two to three over the past five years [1]) will only marginally influence this trend. Substantial improvements of the conventional GTO structure, the gate drive, the packaging, and the inverse diode as well as the modification of the turn-off process resulted in a drastically improved GTO which is considered to be a new device - the IGCT. Both 4.5kV (1.9kV/2.7kV dc-link) and 5.5kV (3.3kV dc-link) IGCTs with current ratings of 275A≤Itgqm≤3120A have been developed [2]. The nearly ideal plasma distribution inside the IGCT [3] leads to lower total losses at 1.5-2.9 times higher current densities than in state-of-the-art high voltage IGBT modules. The low total losses, the low part count of the Gate Commutated Thyristor (GCT), and the reliable press pack in a compact mechanical arrangement which can easily be assembled enable the design of low cost, compact, reliable, highly efficient, and 100% explosion free IGCT converters [4], [5]. 3.3kV and 4.5kV High Voltage IGBTs (HVIGBT) are currently available on the market as module and as press pack (e.g. [6], [7]). HVIGBTs offer advantageous features like active control of dv/dt and di/dt, active clamping, short circuit current limitation, a low gate drive power, and active protection. However the higher onstate losses, a smaller utilization of the active silicon area, reliability concerns and higher costs are disadvantages of state-of-the-art HVIGBTs in comparison to IGCTs [8]. The introduction of IGCTs and HVIGBTs has substantially pushed the development of high power hard switching Pulse Width Modulated (PWM) Voltage Source Inverters (VSI) for industrial and traction applications. The switching frequencies are typically
IAS
limited to about fS=500Hz-1kHz by the switching losses at snubberless operation. An output filter is generally used to protect the insulation of the electric machine against overvoltages and the stress caused by steep dv/dts at the terminals of the VSI. While IGCT based hard switching snubberless three-level NPCVSI are already offered for medium voltage drives, IGCT based soft switching topologies for variable speed drives have not yet been investigated. An extensive comparison of various soft switching topologies has shown, that the Auxiliary Resonant Commutated Pole Voltage Source Inverter (ARCPVSI) is one of the best suited soft switching topologies for high power applications. Compared to snubberless VSIs, the ARCPVSI permits a substantial increase of the switching frequency and yields a higher total converter efficiency. The output filter can be removed if the operation of the converter and the design of the resonant elements limit the dv/dts at the inverter terminals to about dv/dt=500V/µs-1000V/µs. Conversely, the additional components required to achieve soft switching increase the number of components and the complexity of the converter control. First the behavior of IGCTs at hard and soft switching is described to evaluate the potential and risks of an ARCPVSI with IGCTs. A test circuit for an experimental investigation of 51mm (4.5kV, 628A) IGCTs in ARCP VSIs and comparable snubberless conventional topologies is derived. Both design and simulation of a 3MVA two-level PWM inverter applying 91mm (4.5kV, 2190A) Reverse Conducting IGCTs (RCIGCT) provide the basis for a detailed comparison of the ARCPVSI and a conventional VSI topology. II.
REVIEW OF ARCP PRINCIPLE
The operation principles of an ARCPVSI have been discussed extensively in the literature, e. g. [9], [10]. For simplicity the commutations are discussed in a concise manner. The equivalent circuit of an ARCPVSI commutation cell for two-level converters is shown in Fig. 1. Ideal switches and negligibly small stray inductances (Lσ≈0) are assumed. The main switches S1 and S2 operate as Zero Voltage Switches (ZVSs) (active turn-off transient relieved by Cr (Cr=CS1+CS2), passive turn-on at zero voltage) and the auxiliary switch SAS operates as Zero Current Switch (ZCS) (active turn-on relieved by Lr, passive turn-off at reverse recovery current). Three types of commutations can be distinguished: 1) the capacitive commutation, 2) the ARCP commutation, and 3) the ARCP supported capacitive commutation. 1) Capacitive commutation: This commutation is a conventional forced commutation with snubber capacitors in parallel to the commutating switches taking over the current after the active turn-off, thus relieving the switch stress of the device that turns off. The commutation is completed by a passive zero voltage turn-on transient. Capacitive commutations are characterized by a negative gradient of the output power during a commutation (S1àS2 [io>0]
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Phoenix , 1999
ABB Switzerland Ltd.
High Power ARCP Source Voltage Source Inverter
and S2àS1 [io0] and S1àS2 [io0) in a hard switching converter. However, the ARCP commutation transforms an inductive commutation into a relieved (in terms of switching losses) capacitive commutation (active turn-off and passive turn-on at zero voltage) of the main switches, and two inductive (ZCS) switching transients (active turn-on, passive turn-off during reverse recovery process) of the auxiliary switch SAS by changing the polarity of the switch current in the main switch being turned off. 3) ARCP supported capacitive commutation: To accelerate the capacitive commutation in (1), the auxiliary switch S AS will be turned on at low currents iload, causing an increased current through the main switch that is going to turn off which accelerates the capacitive commutation. The threshold current iload=Ith, below which the ARCP supported capacitive commutation kicks in, is mainly dependent on the maximum commutation time (Tcap)max to be defined.
resonant circuit during the ARCP commutation. Thus an additional boost current established by a delayed turn-off of the IGCT in S2 was not required. 2) Data of Test Circuit: The test setup is depicted in Fig. 5. The test circuit was constituted of 51mm IGCTs 5SGX0845F0001 (VDRM=4500V, Vdc-link=2700V, ITGQM=628A) as switches S1, S2 and SAS1, the 38mm diode 5SDF0345D0006 (VRRM=4500V, Vdclink=2700V, IF=628A) as series diode of the switch SAS1 and low inductive (Lstray
