**3.2.4 Single-switch SMR**

The three-phase single-switch SMR (3P1SW) possesses the simplest schematic and control scheme. By operating it in DCM, the PFC is naturally preserved without applying current PWM control. However, it possesses the limits: (i) Having higher input peak current and switch stress; (ii) The input line current contains significant lower-frequency harmonics with the orders of 6n ± 1, n=1, 2, …, and the dominant ones are the 5th and 7th harmonics. Thus suitably designed AC-side low-pass filter is required to yield satisfactory power quality; (iii) The line drawn power quality is limited, typically the power factor is slightly higher than 0.95; (iv) Similarly, this 3P1SW SMR possesses only one-quadrant capability.

To improve the input power quality of this three-phase single-switch SMR, many existing researches have been conducted, see for example: (i) Fifth-order harmonic band-stop filtering; (ii) Harmonic-injection approach; (iii) Variable switching frequency controls; (iv) Passive filtering and input current steering; (v) Optimum PWM pattern; and (vi) Injected PWM robust compensation control. In (Chai et al, 2010), the robust current harmonic cancellation scheme is developed to yield improved line drawn power quality. The robust cancellation weighting factor is automatically tuned according to load level.

### **3.2.5 Two-switch SMR**

This SMR (Badin & Barbi, 2008) is constructed by two serially connected DC/DC boost converter cells behind the rectifier. It possesses only unidirectional power flow capability. The boost converters are applied to shape the input currents, and the current injection device is used to inject the third-harmonic currents in front of the diode bridge to improve the line drawn power quality. This converter uses fewer switches but possesses higher input current harmonics.

### **3.2.6 Modular connection using single-phase SMRs**

Similar to three-phase transformers, three-phase SMRs can also be formed by suitable connection of multiple single-phase modules (Hahn et al, 2002; Li & Liaw, 2004c). Fig. 3(a) shows a Y-connected three-phase boost-type SMR. For Δ − connected three-phase SMR, when one module is faulted, the remaining two modules can continuously provide DC power output subject to the reduction of rating.

#### **3.2.7 Bridgeless SMR**

As shown in Fig. 3(b) (Reis et al, 2008; Oliverira et al, 2009), the SMR uses three diodes and three switches rather than using diode bridge rectifier. Obviously, one diode drop is

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

The three-phase single-switch SMR (3P1SW) possesses the simplest schematic and control scheme. By operating it in DCM, the PFC is naturally preserved without applying current PWM control. However, it possesses the limits: (i) Having higher input peak current and switch stress; (ii) The input line current contains significant lower-frequency harmonics with the orders of 6n ± 1, n=1, 2, …, and the dominant ones are the 5th and 7th harmonics. Thus suitably designed AC-side low-pass filter is required to yield satisfactory power quality; (iii) The line drawn power quality is limited, typically the power factor is slightly higher than

To improve the input power quality of this three-phase single-switch SMR, many existing researches have been conducted, see for example: (i) Fifth-order harmonic band-stop filtering; (ii) Harmonic-injection approach; (iii) Variable switching frequency controls; (iv) Passive filtering and input current steering; (v) Optimum PWM pattern; and (vi) Injected PWM robust compensation control. In (Chai et al, 2010), the robust current harmonic cancellation scheme is developed to yield improved line drawn power quality. The robust

This SMR (Badin & Barbi, 2008) is constructed by two serially connected DC/DC boost converter cells behind the rectifier. It possesses only unidirectional power flow capability. The boost converters are applied to shape the input currents, and the current injection device is used to inject the third-harmonic currents in front of the diode bridge to improve the line drawn power quality. This converter uses fewer switches but possesses higher input

Similar to three-phase transformers, three-phase SMRs can also be formed by suitable connection of multiple single-phase modules (Hahn et al, 2002; Li & Liaw, 2004c). Fig. 3(a) shows a Y-connected three-phase boost-type SMR. For Δ − connected three-phase SMR, when one module is faulted, the remaining two modules can continuously provide DC

As shown in Fig. 3(b) (Reis et al, 2008; Oliverira et al, 2009), the SMR uses three diodes and three switches rather than using diode bridge rectifier. Obviously, one diode drop is

(VUM 25-05) for implementing this SMR is avaiable from IXYS Corporation, USA.

0.95; (iv) Similarly, this 3P1SW SMR possesses only one-quadrant capability.

cancellation weighting factor is automatically tuned according to load level.

**3.2.6 Modular connection using single-phase SMRs** 

power output subject to the reduction of rating.

**3.2.3 Three-switch Vienna SMR** 

**3.2.4 Single-switch SMR** 

**3.2.5 Two-switch SMR** 

current harmonics.

**3.2.7 Bridgeless SMR** 

eliminated in each line-current path resulting to increase the efficiency compared to singleswitch SMR. However, two additional power switches are employed.

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