Dual Inverter Control Strategy for High Speed Operation of E

Dual Inverter Control Strategy for High Speed Operation of EV

Dual Inverter Control Strategy for High Speed Operation of EV Induction MotorsJunha Kim and Kwanghee NamDepartment of Electrical Engineering, POSTECH University, Hyoja San-31, Pohang, 790-784 Rcpublic of Korea. Tel:(82)54-279-2218, Fax: (82)54-279-5629, E-mail:kwnam@postech.ac.kr .Abstract- ISA (integrated starter/alternator) will be used for cars soon with 42 volt system. ISA is a multi-functional integrated device t h a t functions as starting motor, generator, flywheel, or torque assist t o combustion engine. But, other than thermal and cost problem, there is an inherent difficulty in t h e design of motor-inverter system. Specifically, it should produce 150 N m starting torque and also generate electricity while engine is running 6000 rpm. To produce t h e required torque, ISA has normally as many as 12 poles. A great problem is t h a t t h e generated voltage must be limited t o under 42 volt even when 12 pole ISA is running 6000 rpm. Hence, t h e recent ISA design shows t h a t it has as much as 1O:l speed range, i.e., t h e field weakening operation should be extended t o 10 times higher than t h e rated speed. In this work, we are considering t h e use of induction machine instead of permanent synchronous machine. As an idea for solving t h e voltage limit problem, we a r e utilizing two inverters. Sharing t h e voltage requirements by dual inverters is t h e main idea. But, t h e secondary inverter only takes care of t h e reactive voltage component which grows very large in high speed operation. Therefore, t h e secondary inverter does not require t h e use of extra voltage source. Capacitor bank suffices the purpose of t h e secondary inverter. Finally, both simulation and experiment for confirmation are presented.Inverter

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Fig. 1. Dual Inverter System for ISA.

tem integrated starter/altcrnator (ISA). According to the performance specification devcloped by several automotive manufacturcrs, ISA needs to supply 150 N . m of starting torque and to deliver 42 V powcr to the automotive accessories over a 1 O: l speed range extending 4 IW at 600 rpm C to 6 kW at 6000 rpm. Thc interior permanent magnet (IPM) machine is an attractive candidate for this application[3][4][5][6]. However, the IPM machine must havc a special structure so that a large rcluctance contribution plays a role in high speed range[6]. Further, due to the use of permanent magnets, cost of IPM is higher than that of induction machine. Another disadvantage of IPM is that back-emf voltage does not disappcar as far as the rotor is running, which is sometimes fatal to the inverter in the case of unexpcctcd shut down at high spccd. Induction machine is an alternative for ISA[7]. Though the cost is cheaper, it requires more volume. Further, since the magnetizing current has to be supplied from the stator side, its constant power range is not wide if thc source voltage is low such as 42V.

NOMENCLATURE stator voltagc(currcnt) vector. rotor flux vector. ang

lc of A,. angular (rated angular) frequency of A,. actual rotor spccd. angular frcquency at which thc ficld weakening control is activatcd. d-axis rotor flux in the rotor flux reference frame (RFRF). d(q)-axis voltage in the RFRF. d(q)-axis stator current in thc RFRF. stator (rotor) rcsistancc. stator(rotor, mutual) inductance. total leakage coefficient (A 1- L;/(L,L,)). rotor time constant (A L~/ R~ ) . gcnerated torque. numbcr of pole.

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I. INTRODUCTIONDue to the increase in electrical cquipments in a car, the powcr demand grows steadily. Today, the clcctrical power dcmand is around betwecn 750 W and 1 k W . However, in luxury cars in 2005 to 2010, the auxiliary electric power requirement is cxpccted to increase to 4 to 6 kW[2]. This turns out to bc one motivation to adopt 42 V sys-

s In this work, induction machine was considered a a candidate of ISA. With an objectivc of the enlarging constant powcr region up to 1 O: l under 42 V source, a dual inverter system is considered here. Dual inverter system is shown in Fig. 1 in which thc other ends of phase windings, instead of being shorted, are connccted t o the secondary inverter. Pulse width modulation (PWM) stratcgy for dual inverter system was studied in[8][9]. Howevcr, it should be emphasized that the sccondary inverter docs not requirc any powcr source in the DC-link. It just have a capacitor bank which makes a great difference from the previous dual inverter[8][9]. Thc dual invcrtcr systcm also enhances an redundancy provision in emergency cases if wc add somc by-pass switches.

0-7803-7474-6/02/$17.00 02002 IEEE

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Dual Inverter Control Strategy for High Speed Operation of EV

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Fig. 4. Two phase equivalent circuit of dual inverter system in stator reference frame. Fig. 2. Basic idea.

B. Motivation for the Dual InverterWe call dual inverter system the induction motor control system shown in Fig.1. In the dual inverter, two inverters are connected a t both ends of stator phase windings. This connection topology appears in the previous work[8][9]. But, this dual inverter system is different from the previous onc in that the second inverter does not have any voltage source other than capacitor bank. The basic rationalc is that only the reactive power is handled in the second inverter. In the high speed region, the reactive voltage develops a lot so that it takes a significant portion of thc: limited source voltage, making hard to produce torque. If the reactive voltage part is covered by the second inverter, the primary inverter reserves more voltagc t o extend operating speed. Thus, the objective of this topology is to increase the operation speed range where source voltage it; limited at the expense of utilizing two inverter. In the following, we describe in detail how big the reactive vol …… 此处隐藏：20061字，全部文档内容请下载后查看。喜欢就下载吧 ……