**1. Introduction**

Switch-mode rectifier (SMR) or called power factor corrected (PFC) rectifier (Erickson & Maksimovic, 2001; Mohan et al, 2003; Dawande & Dubey, 1996) has been increasingly utilized to replace the conventional rectifiers as the front-end converter for many power equipments. Through proper control, the input line drawn current of a SMR can be controlled to have satisfactory power quality and provide adjustable and well-regulated DC output voltage. Hence, the operation performance of the followed power electronic equipment can be enhanced. Taking the permanent-magnet synchronous motor (PMSM) drive as an example, field-weakening and voltage boosting are two effective approaches to enhance its high-speed driving performance. The latter is more effective and can avoid the risk of magnet demagnetization. This task can naturally be preserved for a PMSM drive being equipped with SMR.

Generally speaking, a SMR can be formed by inserting a suitable DC-DC converter cell between diode rectifier and output capacitive filter. During the past decades, there already have a lot of SMRs, the survey for single-phase SMRs can be referred to the related literatures. Since the AC input current is directly related to the pulse-width modulated (PWM) inductor current, the boost-type SMR possesses the best PFC control capability subject to having high DC output voltage limitation. In a standard multiplier based highfrequency controlled SMR, its PFC control performance is greatly affected by the sensed double-frequency voltage ripple. In (Wolfs & Thomas, 2007), the use of a capacitor reference model that produces a ripple free indication of the DC bus voltage allows the trade off regulatory response time and line current wave shape to be avoided. A simple robust ripple compensation controller is developed in (Chen et al, 2004), such that the effect of double frequency ripple contaminated in the output voltage feedback signal can be cancelled as far as possible. In (Li & Liaw, 2003), the quantitative digital voltage regulation control for a zero-voltage transition (ZVT) soft-switching boost SMR was presented. As to (Li & Liaw, 2004b), the robust varying-band hysteresis current-controlled (HCC) PWM schemes with fixed and varying switching frequencies for SMR have been presented. In (Chai & Liaw, 2007), the robust control of boost SMR considering nonlinear behavior was presented. The adaptation of voltage robust compensation control is made according to the observed nonlinear phenomena. The development and control for a SRM drive with front-end boost SMR were presented in (Chai & Liaw, 2009). In (Chai et al, 2008), the novel random

Some Basic Issues and Applications of

the SMR operating performance.

Switch-Mode Rectifiers on Motor Drives and Electric Vehicle Chargers 253

2000), average current control, charge control and its modifications (Tang et al, 1993). In the peak current controlled flyback converter presented in (Backman & Wolpert, 2000), the proper choice of magnetizing inductance is suggested to reduce the distortion of input current. In (Tang et al, 1993; Larouci et al, 2002), after turning on the switch at clock, the switch is turned off as the integration of switch current is equal to the control voltage. As to (Buso et al, 2000), a modified nonlinear carrier control approach is developed to avoid the sense of AC input voltage. For easily treating the dynamic control of a single-stage PFC converter, its general dynamic modeling and controller design approaches have been conducted in (Uan-Zo-li et al, 2005). In addition, there were also some special control methods for flyback SMR. See for example, a simplified current control scheme using sensed inductor voltage is developed in (Tanitteerapan & Mori, 2001). In (Y.C. Chang & Liaw,

2009a), a flyback SMR in DCM with a charge-regulated PWM scheme is developed.

scheme with fixed turn-on period and varying turn-off period is presented.

For a SMR, the nonlinear behavior and the double-frequency voltage ripple may let the closed-loop controlled SMR encounter undesired nonlinear phenomena (Orabi & Ninomiya, 2003). The key parameters to be observed in nonlinear behavior of a SMR will be the loading condition, the value of output filtering capacitor and the voltage feedback controller parameters. In the flyback SMR developed in (Y.C. Chang & Liaw, 2009a), the simple robust control is proposed to avoid the occurrence of nonlinear phenomena, and also to improve

Random PWM switching is an effective means to let the harmonic spectrum of a power converter be uniformly distributed. Some typical existing studies concerning this topic include the ones for motor drives (Liaw et al, 2000), DC-DC converters (Tse et al, 2000), SMRs (Li & Liaw, 2004b; Chai et al, 2008), etc. In the flyback SMR developed by (Y.C. Chang & Liaw, 2011), to let the harmonic spectrum be dispersdly distributed, a random switching

Although flyback SMR possesses many merits, it suffers from the major limitation of having limited power rating. To enlarge the rating, the parallel of whole isolated converter of flyback SMR was made in (Sangsun & Enjeti, 2002). In the existing interleaved flyback converters, the researches made in (Forest et al, 2007, 2009) are emphasized on the use of intercell transformers. However, the typical interleaving of flyback SMR requires multiple switches and diodes, which increases the cost and complexity of power circuit. For a singlephase flyback SMR, the major DC output voltage ripple is double line frequency component. Hence PWM interleaving control is not beneficial in its ripple reduction. Moreover, the power limitation of flyback transformer is more critical than the other system active components. It follows that sole parallel of transformer (Manh & Guldner, 2006; Inoue et al, 2008) will be the convenient way to enlarge the rating of whole flyback SMR. In (Y.C. Chang & Liaw, 2009b), the rating enlargement is made by parallel connection of transformer. For the power equipments with higher ratings, the three-phase SMR is a natural choice for higher rated plants. The systematic surveys for the existing three-phase SMRs can be found in (Hengchun et al, 1997; Shah et al, 2005). Similar to transformers, three-phase SMRs can also be formed using multiple single-phase SMR modules via proper connection (Hahn et al, 2002; Li & Liaw, 2004c). For simplicity and less stringent performance, the three-phase single-switch (3P1SW) SMR will be a good choice. In the 3P1SW SMR presented in (Chai et al, 2010), a robust current harmonic cancellation scheme and a robust voltage control scheme are developed. The undesired line current and output voltage ripples are regarded as disturbances and they are reduced via robust controls. In voltage control, a feedback controller is augmented with a simple robust error canceller. The robust cancellation

switching approach was developed for effectively reducing the acoustic noise of a lowfrequency switching employed in a PMSM drive. In the bridgeless SMRs developed in (Huber et al, 2008), the higher efficiency is achieved by reducing loop diode voltage drops.

In some occasions, the galvanic isolation of power equipment from AC source is required. In (Hsieh, 2010), a single-phase isolated current-fed push pull (CFPP) boost SMR is developed, and the comparative evaluation for the PMSM drive equipped with standard, bridgeless and CFPP isolated boost SMRs is made.

From input-output voltage magnitude relationship, the buck-boost SMR is perfect in performing power factor correction control (Erickson & Maksimovic, 2001; Matsui et al, 2002). And it is free from inrush current problem owing to its indirect energy transfer feature. However, the traditional non-isolated buck-boost SMR possesses some limitations: (i) without isolation; (ii) having reverse output voltage polarity; (iii) discontinuous input and output currents; and (iv) having relatively high voltage and current stresses due to zero direct power transfer. As generally recognized, the use of high-frequency transformer isolated buck-boost SMR can avoid some of these limitations. The performance comparison study among Cuk, single ended primary inductor converter (SEPIC), ZETA and flyback SMRs in (Singh et al, 2006) concludes that the flyback SMR is the best one in the control performance and the required number of constituted component. In (Lamar et al, 2007), in addition to the power rating limits, the limitations of flyback SMR in PFC characteristics and output voltage dynamic response are discussed.

In (Papanikolaou et al, 2005), the design of flyback converter in CCM for low voltage application is presented. In the power circuit developed in (Lu et al, 2003), a dual output flyback converter is employed to reduce the storage capacitor voltage fluctuation against input voltage and load changes of flyback SMR in DCM. Similarly, two flyback converters are also used in the flyback SMRs developed in (Zheng & Moschopoulos, 2006) and (Mishra et al, 2004) to achieve direct power transfer and improved voltage regulation control characteristics. As to the single-stage SMR developed in (Lu et al, 2008), it combines a boost SMR front-end and a two-switch clamped flyback converter. Similarly, an intermediate energy storage circuit is also employed. In (Rikos & Tatakis, 2005), a new flyback SMR with non-dissipative clamping is presented to obtain high power factor and efficiency in DCM. The proposed clamping circuit utilizes the transformer leakage inductance to improve input current waveform. In (Jang et al, 2006), an integrated boost-flyback PFC converter is developed. The soft switching of all its constituted switches is preserved to yield high efficiency. On the other hand, the improved efficiency of the flyback converter presented in (Lee et al, 2008) is obtained via the use of synchronous rectifier.

It is known that digital control for power converter is a trend to promote its miniaturization. In (Newsom et al, 2002), the control scheme realization is made using off-the-shelf digital logic components. And recently, the VLSI design of system on chip application specific integrated circuit (SoC-ASIC) controller for a double stage SMR has also been studied in (Langeslag et al, 2007). It consists of a boost SMR and a flyback DC-DC converter. The latter is controlled using valley-switching approach operating in quasi-resonant DCM, which has fixed on-time and varying off-time according to load.

As far as the switching control strategies are concerned, they can be broadly categorized into voltage-follower control (Erickson & Madigan, 1990) and current-mode control (Backman & Wolpert, 2000). The former belongs to open-loop operation under DCM, and thus the current feedback control is not needed. As to the latter, the multiplier-based current control loop is necessary to achieve PFC control. Basically, the commonly used PWM switching control approaches for a flyback SMR include peak current control (Backman & Wolpert,

switching approach was developed for effectively reducing the acoustic noise of a lowfrequency switching employed in a PMSM drive. In the bridgeless SMRs developed in (Huber et al, 2008), the higher efficiency is achieved by reducing loop diode voltage drops. In some occasions, the galvanic isolation of power equipment from AC source is required. In (Hsieh, 2010), a single-phase isolated current-fed push pull (CFPP) boost SMR is developed, and the comparative evaluation for the PMSM drive equipped with standard, bridgeless

From input-output voltage magnitude relationship, the buck-boost SMR is perfect in performing power factor correction control (Erickson & Maksimovic, 2001; Matsui et al, 2002). And it is free from inrush current problem owing to its indirect energy transfer feature. However, the traditional non-isolated buck-boost SMR possesses some limitations: (i) without isolation; (ii) having reverse output voltage polarity; (iii) discontinuous input and output currents; and (iv) having relatively high voltage and current stresses due to zero direct power transfer. As generally recognized, the use of high-frequency transformer isolated buck-boost SMR can avoid some of these limitations. The performance comparison study among Cuk, single ended primary inductor converter (SEPIC), ZETA and flyback SMRs in (Singh et al, 2006) concludes that the flyback SMR is the best one in the control performance and the required number of constituted component. In (Lamar et al, 2007), in addition to the power rating limits, the limitations of flyback SMR in PFC characteristics and

In (Papanikolaou et al, 2005), the design of flyback converter in CCM for low voltage application is presented. In the power circuit developed in (Lu et al, 2003), a dual output flyback converter is employed to reduce the storage capacitor voltage fluctuation against input voltage and load changes of flyback SMR in DCM. Similarly, two flyback converters are also used in the flyback SMRs developed in (Zheng & Moschopoulos, 2006) and (Mishra et al, 2004) to achieve direct power transfer and improved voltage regulation control characteristics. As to the single-stage SMR developed in (Lu et al, 2008), it combines a boost SMR front-end and a two-switch clamped flyback converter. Similarly, an intermediate energy storage circuit is also employed. In (Rikos & Tatakis, 2005), a new flyback SMR with non-dissipative clamping is presented to obtain high power factor and efficiency in DCM. The proposed clamping circuit utilizes the transformer leakage inductance to improve input current waveform. In (Jang et al, 2006), an integrated boost-flyback PFC converter is developed. The soft switching of all its constituted switches is preserved to yield high efficiency. On the other hand, the improved efficiency of the flyback converter presented in

It is known that digital control for power converter is a trend to promote its miniaturization. In (Newsom et al, 2002), the control scheme realization is made using off-the-shelf digital logic components. And recently, the VLSI design of system on chip application specific integrated circuit (SoC-ASIC) controller for a double stage SMR has also been studied in (Langeslag et al, 2007). It consists of a boost SMR and a flyback DC-DC converter. The latter is controlled using valley-switching approach operating in quasi-resonant DCM, which has

As far as the switching control strategies are concerned, they can be broadly categorized into voltage-follower control (Erickson & Madigan, 1990) and current-mode control (Backman & Wolpert, 2000). The former belongs to open-loop operation under DCM, and thus the current feedback control is not needed. As to the latter, the multiplier-based current control loop is necessary to achieve PFC control. Basically, the commonly used PWM switching control approaches for a flyback SMR include peak current control (Backman & Wolpert,

and CFPP isolated boost SMRs is made.

output voltage dynamic response are discussed.

(Lee et al, 2008) is obtained via the use of synchronous rectifier.

fixed on-time and varying off-time according to load.

2000), average current control, charge control and its modifications (Tang et al, 1993). In the peak current controlled flyback converter presented in (Backman & Wolpert, 2000), the proper choice of magnetizing inductance is suggested to reduce the distortion of input current. In (Tang et al, 1993; Larouci et al, 2002), after turning on the switch at clock, the switch is turned off as the integration of switch current is equal to the control voltage. As to (Buso et al, 2000), a modified nonlinear carrier control approach is developed to avoid the sense of AC input voltage. For easily treating the dynamic control of a single-stage PFC converter, its general dynamic modeling and controller design approaches have been conducted in (Uan-Zo-li et al, 2005). In addition, there were also some special control methods for flyback SMR. See for example, a simplified current control scheme using sensed inductor voltage is developed in (Tanitteerapan & Mori, 2001). In (Y.C. Chang & Liaw, 2009a), a flyback SMR in DCM with a charge-regulated PWM scheme is developed.

For a SMR, the nonlinear behavior and the double-frequency voltage ripple may let the closed-loop controlled SMR encounter undesired nonlinear phenomena (Orabi & Ninomiya, 2003). The key parameters to be observed in nonlinear behavior of a SMR will be the loading condition, the value of output filtering capacitor and the voltage feedback controller parameters. In the flyback SMR developed in (Y.C. Chang & Liaw, 2009a), the simple robust control is proposed to avoid the occurrence of nonlinear phenomena, and also to improve the SMR operating performance.

Random PWM switching is an effective means to let the harmonic spectrum of a power converter be uniformly distributed. Some typical existing studies concerning this topic include the ones for motor drives (Liaw et al, 2000), DC-DC converters (Tse et al, 2000), SMRs (Li & Liaw, 2004b; Chai et al, 2008), etc. In the flyback SMR developed by (Y.C. Chang & Liaw, 2011), to let the harmonic spectrum be dispersdly distributed, a random switching scheme with fixed turn-on period and varying turn-off period is presented.

Although flyback SMR possesses many merits, it suffers from the major limitation of having limited power rating. To enlarge the rating, the parallel of whole isolated converter of flyback SMR was made in (Sangsun & Enjeti, 2002). In the existing interleaved flyback converters, the researches made in (Forest et al, 2007, 2009) are emphasized on the use of intercell transformers. However, the typical interleaving of flyback SMR requires multiple switches and diodes, which increases the cost and complexity of power circuit. For a singlephase flyback SMR, the major DC output voltage ripple is double line frequency component. Hence PWM interleaving control is not beneficial in its ripple reduction. Moreover, the power limitation of flyback transformer is more critical than the other system active components. It follows that sole parallel of transformer (Manh & Guldner, 2006; Inoue et al, 2008) will be the convenient way to enlarge the rating of whole flyback SMR. In (Y.C. Chang & Liaw, 2009b), the rating enlargement is made by parallel connection of transformer.

For the power equipments with higher ratings, the three-phase SMR is a natural choice for higher rated plants. The systematic surveys for the existing three-phase SMRs can be found in (Hengchun et al, 1997; Shah et al, 2005). Similar to transformers, three-phase SMRs can also be formed using multiple single-phase SMR modules via proper connection (Hahn et al, 2002; Li & Liaw, 2004c). For simplicity and less stringent performance, the three-phase single-switch (3P1SW) SMR will be a good choice. In the 3P1SW SMR presented in (Chai et al, 2010), a robust current harmonic cancellation scheme and a robust voltage control scheme are developed. The undesired line current and output voltage ripples are regarded as disturbances and they are reduced via robust controls. In voltage control, a feedback controller is augmented with a simple robust error canceller. The robust cancellation

Some Basic Issues and Applications of

**2.2.2 Active power filter** 

current as far as possible.

*vac*

*vac*

valley-fill filter

*ac i*

*ac i*

**2.2.3 Passive PFC circuits** 

is needed the redesign adapted to load changes.

Switch-Mode Rectifiers on Motor Drives and Electric Vehicle Chargers 255

reducing EMI. However, it is bulky and cannot completely regulate nonlinear loads, and it

Compared with passive filter, active power filter (APF) has the higher control ability to compensate load reactive and harmonic current components. According to the types of connections, active power filters can be categorized into series, shunt and hybrid types (Erickson & Maksimovic, 2001; Mohan et al, 2003). Taking the shunt type active power filter as an example, a controlled current is generated from the APF to compensate the load ripple

Fig. 1(a) shows the sketched key waveforms of a full-bridge rectifier with large and small filtering capacitors. One can be aware that if a very small filtering capacitor is employed, the line drawn power quality is improved, and thus the Class A rather than the Class D is applied. However, the effects of DC-link voltage ripple should be considered in making the control of the followed power stage. Recently, to reduce the rectified DC voltage ripple,

> θ*c*

*Cdc* Large

*Cdc* Small

*vac*

*ac i*

*ac i*

 filter Valley − fill

*vac*

*vac ac i vdc*

*vdc*

*vdc*

*t*

*t*

*t*

some plants employ the valley-fill filter as shown in Fig. 1(b) (Farcas et al, 2006).

Load

*vdc*

*Cdc*

*vdc*

Load

(a)

(h)

Fig. 1. Some passive PFC circuits: (a) rectifier with small filtering capacitor; (b) rectifier using

weighting factor is automatically tuned according to load level to yield compromised voltage and power quality control performances.

Similar to single-phase bridgeless SMRs (Zhang et al, 2000; Youssef et al, 2008), there were also some researches being emphasized on the development of three phase bridgeless SMRs (Reis et al, 2008; Oliverira et al, 2009). In (Wang, 2010), a bridgeless DCM three phase SMR is developed and used as a front-end AC-DC converter for the SRM drive.

As generally recognized, soft-switching can be applied for various converters to reduce their switching lossess, voltage stresses and electromagnetic interference. The applications of softswitching in 3P1SW SMRs have also been conducted in (Gataric et al, 1994; Ueda et al, 2002). For the 3P1SW SMR operating under DCM, only the zero-current switching (ZCS) at turnoff is effective in reducing its switching losses. In (Wang, 2010), the zero-current transition (ZCT) (Gataric et al, 1994) is utilized to the developed 3P1SW to achieve the ZCS of the main switch at turn-off. In realization, an auxiliary resonant branch is added, and the proper switching signals are generated for the main and auxiliary switches. The soft-switching can be achieved without adding extra sensors. And also in (Wang, 2010), the comparative performance evaluation is made for the SRM drive powered using standard 3P1SW SMR, ZCT 3P1SW SMR and bridgeless DCM three phase SMR.

### **2. Power factor correction approaches**

For facilitating the research made concerning power quality, the commonly referred harmonic standard is first introduced. Then the possible power factor correction approaches are described to comprehend their comparative features.

#### **2.1 Harmonic ccurrent emission standard**

IEC 61000-3-2 (previously, IEC-555) is the worldwide applied harmonic current emission standard. This standard specifically limits harmonics for equipments with an input current up to 16A, connected to 50Hz or 60Hz, 220V to 240V single phase circuit (two or three wires). The IEC 61000-3-2 standard distinguishes the loads into four classes with different harmonic limits (Erickson & Maksimovic, 2001; Mohan et al, 2003). From the contents one can find that for the equipments below 600W, the harmonic limits of Class A are larger than those of Class D. This advantage will be more significant for lower power level. Taking the third harmonic under 100W as an example, the limit in Class A is 2.3A compared to 0.34A in Class D. Power converter can apply Class D or Class A regulation depending on its input current wave shape. The peaky line drawn current of a diode rectifier with larger filtering capacitor definitely belongs to Class D. However, if the simple low-frequency switching SMR (Chai et al, 2008) is employed, the modified line drawn current may fall into Class A and thus possesses the advantage mentioned above.

#### **2.2 Possible power factor correction methods**

Depending on rating, schematic and control complexities, control performance and cost, there are many possible power factor correction approaches. The suited and cost effective one can be chosen according to the desired performance for specific application.

#### **2.2.1 Passive filter**

Various series L-C resonant trap filters are connected across the line terminal to attenuate the specific order harmonics. This approach is simple, rugged, reliable and helpful in reducing EMI. However, it is bulky and cannot completely regulate nonlinear loads, and it is needed the redesign adapted to load changes.

## **2.2.2 Active power filter**

254 Electrical Generation and Distribution Systems and Power Quality Disturbances

weighting factor is automatically tuned according to load level to yield compromised

Similar to single-phase bridgeless SMRs (Zhang et al, 2000; Youssef et al, 2008), there were also some researches being emphasized on the development of three phase bridgeless SMRs (Reis et al, 2008; Oliverira et al, 2009). In (Wang, 2010), a bridgeless DCM three phase SMR is

As generally recognized, soft-switching can be applied for various converters to reduce their switching lossess, voltage stresses and electromagnetic interference. The applications of softswitching in 3P1SW SMRs have also been conducted in (Gataric et al, 1994; Ueda et al, 2002). For the 3P1SW SMR operating under DCM, only the zero-current switching (ZCS) at turnoff is effective in reducing its switching losses. In (Wang, 2010), the zero-current transition (ZCT) (Gataric et al, 1994) is utilized to the developed 3P1SW to achieve the ZCS of the main switch at turn-off. In realization, an auxiliary resonant branch is added, and the proper switching signals are generated for the main and auxiliary switches. The soft-switching can be achieved without adding extra sensors. And also in (Wang, 2010), the comparative performance evaluation is made for the SRM drive powered using standard 3P1SW SMR,

For facilitating the research made concerning power quality, the commonly referred harmonic standard is first introduced. Then the possible power factor correction approaches

IEC 61000-3-2 (previously, IEC-555) is the worldwide applied harmonic current emission standard. This standard specifically limits harmonics for equipments with an input current up to 16A, connected to 50Hz or 60Hz, 220V to 240V single phase circuit (two or three wires). The IEC 61000-3-2 standard distinguishes the loads into four classes with different harmonic limits (Erickson & Maksimovic, 2001; Mohan et al, 2003). From the contents one can find that for the equipments below 600W, the harmonic limits of Class A are larger than those of Class D. This advantage will be more significant for lower power level. Taking the third harmonic under 100W as an example, the limit in Class A is 2.3A compared to 0.34A in Class D. Power converter can apply Class D or Class A regulation depending on its input current wave shape. The peaky line drawn current of a diode rectifier with larger filtering capacitor definitely belongs to Class D. However, if the simple low-frequency switching SMR (Chai et al, 2008) is employed, the modified line drawn current may fall into Class A

Depending on rating, schematic and control complexities, control performance and cost, there are many possible power factor correction approaches. The suited and cost effective

Various series L-C resonant trap filters are connected across the line terminal to attenuate the specific order harmonics. This approach is simple, rugged, reliable and helpful in

one can be chosen according to the desired performance for specific application.

developed and used as a front-end AC-DC converter for the SRM drive.

voltage and power quality control performances.

ZCT 3P1SW SMR and bridgeless DCM three phase SMR.

are described to comprehend their comparative features.

and thus possesses the advantage mentioned above.

**2.2 Possible power factor correction methods** 

**2.2.1 Passive filter** 

**2. Power factor correction approaches** 

**2.1 Harmonic ccurrent emission standard** 

Compared with passive filter, active power filter (APF) has the higher control ability to compensate load reactive and harmonic current components. According to the types of connections, active power filters can be categorized into series, shunt and hybrid types (Erickson & Maksimovic, 2001; Mohan et al, 2003). Taking the shunt type active power filter as an example, a controlled current is generated from the APF to compensate the load ripple current as far as possible.

### **2.2.3 Passive PFC circuits**

Fig. 1(a) shows the sketched key waveforms of a full-bridge rectifier with large and small filtering capacitors. One can be aware that if a very small filtering capacitor is employed, the line drawn power quality is improved, and thus the Class A rather than the Class D is applied. However, the effects of DC-link voltage ripple should be considered in making the control of the followed power stage. Recently, to reduce the rectified DC voltage ripple, some plants employ the valley-fill filter as shown in Fig. 1(b) (Farcas et al, 2006).

Fig. 1. Some passive PFC circuits: (a) rectifier with small filtering capacitor; (b) rectifier using valley-fill filter

Some Basic Issues and Applications of

2003; Wang, 2010).

SMR and flyback SMR.

**3.1 Single-phase SMRs** 

**3.2 Three-phase SMRs** 

**2. Control methods** 

Switch-Mode Rectifiers on Motor Drives and Electric Vehicle Chargers 257

e. One-quadrant or multi-quadrant: multiple quadrant SMR may possess reverse power flow from DC side to AC source, such as the regenerative braking of a SMR-fed AC motor drive can be performed by sending braking energy back to the utility grid. f. Hard-switching or soft-switching: Similarly, suited soft switching technique can also be applied to reduce the switching loss, switching stress and EMI of a SMR (Li & Liaw,

a. Low-frequency control: only v-loop is needed and only one switching per half AC cycle

b. High-frequency control- voltage-follower control: without current control loop, only some specific SMRs operating in DCM possess this feature, see for example, buck-boost

c. High-frequency control- standard control: it belongs to multiplier-based current-mode

The typical existing single-phase SMR circuits include: (a) boost SMR; (b) buck SMR; (c) buck- boost SMR; (d) Ćuk SMR; (e) SEPIC SMR with coupled inductors; (f) SEPIC SMR; (g) ZETA SMR; (h) buck-boost cascade SMR; (i) boost-buck hybrid SMR; (j) flyback SMR; (k) isolated Ćuk SMR; and (l) isolated ZETA SMR. Some comments are given for these circuits: (i) The SMRs of (a) to (i) belong to non-isolated types, whereas (j) to (l) are isolated ones; (ii) Among the non-isolated SMRs, the boost-type SMR possesses the best PFC control performance, since its AC input current is directly related to the switched inductor current; (iii) The circuits of (d), (i) and (k) possess the common features of having both continuous input and output currents, and hence needing less stringent filter design requirement. In addition to the SMRs of (j) to (l) mentioned above, some isolated SMRs specifically for PMSM drives (Singh B. & Singh S., 2010) include: (a) push-pull buck; (b) push-pull boost; (c) half-bridge buck; (d) half-bridge boost; (e) full-bridge buck; (f) full-bridge boost. The push-

pull boost SMR possesses excellent PFC control ability and high voltage boost ratio.

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

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.

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

is applied. It is simple but has limited power quality characteristics.

control approach with both v- and i- control loops.

used boost-type SMRs are briefly introduced as followed.

operation, and it can provide fault tolerant operation.

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

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