376
Alternative Fuels for Transportation
fed doubly salient, SDFDS machine) can be derived from the DSPM machine
(Chau, Cheng, and Chan 2002). This arrangement can solve the problem of
uncontrollable PM flux, and can offer the possibility to on-line optimize efficiency. However, it seriously deteriorates an important merit of PM excitation, namely high-energy density. Consequently, by incorporating PMs into
the BDFDS machine, the BDF-DSPM machine is created that can offer a very
wide constant-power speed range for ISG application (Chau et al. 2006b).
The power converter functions to regulate bidirectional power flow within
the ISG system. Conventionally, it is a low-voltage high-current inverter that
generally suffers from high-power losses (Liu, Hu, and Xu 2004). By incorporating an additional DC-DC stage, the DC-DC-AC converter can provide
a flexible DC-link voltage, hence improving the torque–speed characteristics
and system efficiency (Xu and Liu 2004). However, these converters have the
drawbacks of high-switching stress and electromagnetic interference (EMI).
To alleviate these drawbacks, both the resonant inverter and multilevel
inverter are proposed. The resonant inverter can offer the merit of soft switching, but needs a complicated operation of an additional resonant circuitry
(Alan and Lipo 2000; Chau, Yao, and Chan 1999). The multilevel inverter can
be classified as a high-frequency pulse-width-modulation (PWM) multilevel inverter type, and a fundamental-frequency, multilevel inverter type
(Loh, Holmes, and Lipo 2005; Rodriguez, Lai, and Peng 2002). Particularly,
the latter type generates staircase AC output that takes advantage of low
switching loss and minimum EMI. This includes the diode-clamped, multilevel inverter, capacitor-clamped multilevel inverter, cascaded multilevel
inverter, and switched capacitor converter multilevel inverter (Axelrod,
Berkovich, and Ioinovici 2005). However, they have the drawbacks that many
switches and capacitors are necessary to generate a sufficient level of staircase AC voltage waveform, whereas the maximum number of capacitors is
governed by the stipulated output voltage. Recently, these drawbacks have
been alleviated by using partial charging; namely, multiple voltage steps per
capacitor (Chan and Chau 2007).
12.4.6 eCVT System Operation
The turning point of HEV development was the advent of the Toyota Prius
in 1997, which first adopted the ECVT propulsion system. Subsequently, the
development of HEVs is one of the major strategic plans for all giant automakers. After the introduction of ECVT that was marketed under the Toyota
hybrid system, there have been many derivatives. Those viable ones are the
Ford hybrid system input split ECVT, the GM–Allison compound split ECVT,
the Timken compound split ECVT, and the Renault compound split ECVT
(Miller 2006; Miller and Everett 2005).
As shown in Figure 12.12, a basic ECVT propulsion system is mainly composed of a planetary gear, a motor, and a generator. Figure 12.13 shows this
planetary gear that consists of a sun gear, a planet carrier that holds several
Alternative Fuels for Transportation
fed doubly salient, SDFDS machine) can be derived from the DSPM machine
(Chau, Cheng, and Chan 2002). This arrangement can solve the problem of
uncontrollable PM flux, and can offer the possibility to on-line optimize efficiency. However, it seriously deteriorates an important merit of PM excitation, namely high-energy density. Consequently, by incorporating PMs into
the BDFDS machine, the BDF-DSPM machine is created that can offer a very
wide constant-power speed range for ISG application (Chau et al. 2006b).
The power converter functions to regulate bidirectional power flow within
the ISG system. Conventionally, it is a low-voltage high-current inverter that
generally suffers from high-power losses (Liu, Hu, and Xu 2004). By incorporating an additional DC-DC stage, the DC-DC-AC converter can provide
a flexible DC-link voltage, hence improving the torque–speed characteristics
and system efficiency (Xu and Liu 2004). However, these converters have the
drawbacks of high-switching stress and electromagnetic interference (EMI).
To alleviate these drawbacks, both the resonant inverter and multilevel
inverter are proposed. The resonant inverter can offer the merit of soft switching, but needs a complicated operation of an additional resonant circuitry
(Alan and Lipo 2000; Chau, Yao, and Chan 1999). The multilevel inverter can
be classified as a high-frequency pulse-width-modulation (PWM) multilevel inverter type, and a fundamental-frequency, multilevel inverter type
(Loh, Holmes, and Lipo 2005; Rodriguez, Lai, and Peng 2002). Particularly,
the latter type generates staircase AC output that takes advantage of low
switching loss and minimum EMI. This includes the diode-clamped, multilevel inverter, capacitor-clamped multilevel inverter, cascaded multilevel
inverter, and switched capacitor converter multilevel inverter (Axelrod,
Berkovich, and Ioinovici 2005). However, they have the drawbacks that many
switches and capacitors are necessary to generate a sufficient level of staircase AC voltage waveform, whereas the maximum number of capacitors is
governed by the stipulated output voltage. Recently, these drawbacks have
been alleviated by using partial charging; namely, multiple voltage steps per
capacitor (Chan and Chau 2007).
12.4.6 eCVT System Operation
The turning point of HEV development was the advent of the Toyota Prius
in 1997, which first adopted the ECVT propulsion system. Subsequently, the
development of HEVs is one of the major strategic plans for all giant automakers. After the introduction of ECVT that was marketed under the Toyota
hybrid system, there have been many derivatives. Those viable ones are the
Ford hybrid system input split ECVT, the GM–Allison compound split ECVT,
the Timken compound split ECVT, and the Renault compound split ECVT
(Miller 2006; Miller and Everett 2005).
As shown in Figure 12.12, a basic ECVT propulsion system is mainly composed of a planetary gear, a motor, and a generator. Figure 12.13 shows this
planetary gear that consists of a sun gear, a planet carrier that holds several