**3.2 Three-phase SMRs**

Detailed surveys for the existing three-phase SMR circuits can be referred to (Hengchun et al, 1997; Shah & Moschopoulos, 2005). The complexities of schematic and control mechanism depend on the control ability and the desired performances. Some commonly used boost-type SMRs are briefly introduced as followed.

### **3.2.1 Three-leg six-switch standard SMR**

The standard three-phase six-switch SMR (Hengchun et al, 1997; Shah & Moschopoulos, 2005) possesses four operation quadrants and high flexibility in power conditioning control. For a motor drive equipped with such SMR, it may possess regenerative braking ability. However, the switch utilization ratio of this SMR is low, and its control is complicated.

### **3.2.2 Four-leg eight-switch SMR**

In the four-leg three-phase SMR (Zhang et al, 2000) with eight switches, the additional fourth leg can be arranged to regulate the imbalance caused by source voltage and switching operation, and it can provide fault tolerant operation.

Some Basic Issues and Applications of

Switch-Mode Rectifiers on Motor Drives and Electric Vehicle Chargers 259

eliminated in each line-current path resulting to increase the efficiency compared to single-

*an v*

*bn v*

1

1φSMR

1φSMR

φSMR

*n*

(a)

*Lb*1

*b*1 *i*

*b*2 *i*

*b*3 *i*

Fig. 3. Two types of SMRs: (a) modular connection of three single-phase SMRs;

*Lb*<sup>2</sup>

*Lb*<sup>3</sup>

(b)

The soft-switching SMRs using auxiliary switching circuit can be generally classified into zero-voltage-transition (ZVT) and zero-current-transition (ZCT). The choice depends on the semiconductor devices to be used. The ZVS approaches are generally recommended for MOSFET. On the other hand, ZCS approaches are effective for IGBT. Some existing soft-

The classical 3P1SW ZCT SMR (Wang et al, 1994) is simple in structure and easy to realize. However, the auxiliary switch is not operated on ZCS at turn-off. The efficiency is limited.

In the modified 3P1SW ZCT SMR presented in (Das & Moschopoulos, 2007). The addition of the transformer in the auxiliary circuit let the circulating energy from the auxiliary circuit be

As to the three-phase bridgeless ZCT SMR (Mahdavi & Farzanehfard, 2009), the auxiliary circuit provides soft-switching condition through ZCT approach for all semiconductor

transferred to the output. Hence it possesses higher efficiency than the classical type.

*cn v*

Control circuit

*SW*

Control circuit

*SW*

Control circuit

*SW*

Load

*Kv*

*ZL*

*Cd*

*ZL*

*<sup>d</sup> v* Load

*Cd <sup>o</sup> v oi*

switch SMR. However, two additional power switches are employed.

*D*1

*SW*

*Lb*<sup>2</sup> *<sup>D</sup>*<sup>2</sup>

*Lf*

*an i*

*bn i*

*ab v*

*cn i*

*an v*

*bn v*

*n*

(b) bridgeless DCM three-phase SMR

*cn v*

**3.3 Three-phase single-switch ZCT SMRs** 

switching SMRs are introduced as follows:

**3.3.1 Classical three-phase single-switch ZCT SMR** 

**3.3.2 Modified three-phase single-switch ZCT SMR** 

**3.3.3 Three-phase three-switch bridgeless ZCT SMR** 

devices without any extra current and voltage stress.

*Lf*

*Cf*

*Lf*

*Cf Cf*

*Lb*1

Single-phase boost SMR power stage

### **3.2.3 Three-switch Vienna SMR**

The Vienna three-phase SMR (Youssef et al, 2008) uses only three switches to achieve good current command tracking control. It can be regarded as a simplified version of three singlephase PFCs connected to the same intermediate bus voltage. The major features of this SMR are: (i) three output voltage levels ( 0.5 *<sup>o</sup> v* , *<sup>o</sup> v* , -0.5 *<sup>o</sup> v* ) providing larger switching control flexibility; (ii) lower switch voltage rating, 0.5 *<sup>o</sup> v* rather than *<sup>o</sup> v* ; and (iii) lower input current distortion. However, it has only unidirectional power flow capability, and needs complicated power switch and two serially connected capacitors. The specific power switch (VUM 25-05) for implementing this SMR is avaiable from IXYS Corporation, USA.
