**6.3 Flyback Switch-Mode Rectifier based auxiliary plug-in charger**

#### **6.3.1 System configuration**

Fig. 25 shows a switched-reluctance generator (SRG) based DC microgrid distributed power system (Y.C. Chang & Liaw, 2011). The SRG establishes a 48V DC-link voltage, and a common 400V DC-grid is formed through a current-fed push-pull (CFPP) DC-DC converter. To preserve the microgrid power quality, a lead-acid battery energy storage system is equipped. The battery bank (48V) is interfaced to the common 400V DC-grid via a bidirectional buck-boost converter. The battery bank can also be charged from the utility grid by a flyback SMR based auxiliary plug-in charger. For the flyback converter employed in the SMR, three paralleled transformers are used to enlarge its power rating. The The specifications of the developed flyback SMR are given as: (i) AC input: 110V/60Hz; (ii) DC output: *V V o b* = = 48V/300W; and (iii) power factor: PF > 0.97. The flyback SMR is operated under discontinuous current mode using the charge-regulated PWM scheme developed in (Y.C. Chang & Liaw, 2009a). The turn-on time in is set as 9.2 *on s t dT s* = = μ , which is constant for the employed PWM switching scheme.

#### **6.3.2 Performance evaluation for the flyback SMR based auxiliary plug-in charger**

For the battery bank shown in Fig. 25, the constant charging current *Ib* = 6A (i.e., ˆ *Sc* 6 / 6 /1.107 5.42A *ic I K* == = ) is set. The measured ( *ac v* , *ac i* ) and ( *<sup>b</sup> v* , *bi* ) at steady state of *Ib* = 6A during charging process are plotted in Figs. 26(a) and 26(b). The measured static characteristics under two charging currents ( *Ib* = 6A and 5A) are listed in Table 10. The results show that good charging characteristics with satisfactory line drawn power quality are obtained by the developed flyback SMR based auxiliary plug-in charger.

Fig. 25. System configuration of a switched-reluctance generator based DC micro-grid system with flyback SMR auxiliary plug-in charger

Fig. 26. Measured results of the developed flyback SMR based auxiliary plug-in charger under steady-state charging current of *Ib* = 6A : (a) ( *ac v* , *ac i* ); (b) ( *<sup>b</sup> v* , *bi* )


Table 10. Measured results of the developed flyback SMR based auxiliary plug-in charger at two charging current levels

### **7. Conclusions**

284 Electrical Generation and Distribution Systems and Power Quality Disturbances

Fig. 25 shows a switched-reluctance generator (SRG) based DC microgrid distributed power system (Y.C. Chang & Liaw, 2011). The SRG establishes a 48V DC-link voltage, and a common 400V DC-grid is formed through a current-fed push-pull (CFPP) DC-DC converter. To preserve the microgrid power quality, a lead-acid battery energy storage system is equipped. The battery bank (48V) is interfaced to the common 400V DC-grid via a bidirectional buck-boost converter. The battery bank can also be charged from the utility grid by a flyback SMR based auxiliary plug-in charger. For the flyback converter employed in the SMR, three paralleled transformers are used to enlarge its power rating. The The specifications of the developed flyback SMR are given as: (i) AC input: 110V/60Hz; (ii) DC output: *V V o b* = = 48V/300W; and (iii) power factor: PF > 0.97. The flyback SMR is operated under discontinuous current mode using the charge-regulated PWM scheme developed in

μ

, which is constant

**6.3 Flyback Switch-Mode Rectifier based auxiliary plug-in charger** 

(Y.C. Chang & Liaw, 2009a). The turn-on time in is set as 9.2 *on s t dT s* = =

are obtained by the developed flyback SMR based auxiliary plug-in charger.

*ve* + −

*Lmk*

*iN*11

*Lk i*

*N k i* 1

*L*1 *i*

:

: *N*1 *N*2

*N*<sup>1</sup> *N*2

+ − *<sup>d</sup> Cd v*

*N k i* 2

*iN*21

Fig. 25. System configuration of a switched-reluctance generator based DC micro-grid

*vb Lm*<sup>1</sup>

*D Co*

*iD*

Current-fed push-pull DC/DC boost converter

DC 48V DC 400V

+ − *dc Cdc v*

Battery bank (48V)

Common

DC bus AC outputs

inverter 1φ3W

110V/220V 1φ3W

A

B N

Bidirectional DC/DC converter

Energy storage system

Wind powered switchedreluctance generator system Converter

*S*

system with flyback SMR auxiliary plug-in charger

−

*vdi*

*iS*

**6.3.2 Performance evaluation for the flyback SMR based auxiliary plug-in charger**  For the battery bank shown in Fig. 25, the constant charging current *Ib* = 6A (i.e.,

*Sc* 6 / 6 /1.107 5.42A *ic I K* == = ) is set. The measured ( *ac v* , *ac i* ) and ( *<sup>b</sup> v* , *bi* ) at steady state of *Ib* = 6A during charging process are plotted in Figs. 26(a) and 26(b). The measured static characteristics under two charging currents ( *Ib* = 6A and 5A) are listed in Table 10. The results show that good charging characteristics with satisfactory line drawn power quality

**6.3.1 System configuration** 

for the employed PWM switching scheme.

IM SRG

*e* ω*<sup>r</sup> T*

*ac i*′

<sup>+</sup> *Lf*

*<sup>C</sup> <sup>f</sup> vac*

Flyback SMR auxiliary plug-in charger

> *ac i Pac*

+ −

AC source

ˆ

This article has presented the basic issues of switch-mode rectifiers for achieving batter performance. The schematic type and control scheme should be properly chosen according to the specific application and the desired operation characteristics. The considering issues include input-output relative voltage levels, operation quadrant, galvanic isoltation, phase number, DCM or CCM operation, voltage mode or current mode control, dynamic control requirement, etc. In power circuit establishment, the ratings of circuit components and the ripples of energy storage components should be analytically derived, and accordingly, the constituted components are designed and implemented.

As to the control affairs, the sensed inductor current and output voltage should be filtered with suited low-pass cut-off frequencies. Then the basic feedack controllers are designed considring the desired perfromance and the effects of comtaiminated system noises. If more stringent control requirements are desired. The simple advanced control, such as the robust tracking error cancellation controls (Chai & Liaw, 2007; Y.C. Chang & Liaw, 2009a), can further be applied. Other possible affairs lie in the digital control with properly chosen sampling intervals, random switching, the considrations of DC-link ripple effects on the followed power stage, parallel opeartion to enlarge SMR ratings, etc.

In this article, the applications of various SMRs to PMSM drive, SRM drive, electric vehicle plug-in battery charger and microgrid plug-in battery charger were presented. The

Some Basic Issues and Applications of

ISBN 0-7803-2795-0

3

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#### **8. References**


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**0**

**12**

Dylan Dah-Chuan Lu

*The University of Sydney*

*Australia*

*School of Electrical and Information Engineering*

**Battery Charger with Power Quality Improvement**

Battery storage has long been used in many applications such as portable multimedia player, mobile phone, portable tool, laptop computer, emergency exit sign, uninterruptible power supply and transportation auxiliary supply. Owing to the advancement of material science and packaging technologies, newer batteries with higher energy density and reliability have been produced. Batteries are now being used in higher power applications such as electric vehicles (EV), renewable energy systems and microgrid. Examples of high power batteries are Lithium-ion and Zinc-Bromine which are rated at kilo-watt range and mega-watt range respectively (Roberts, 2009). At such high power level, these batteries will have significant

Power quality is one of major impacts to the grid when these high power batteries are charging. Since the battery is working at DC level, rectification (i.e., AC to DC conversion) is required. For the traditional design of rectifiers, for example diode-capacitor rectifier and phase-controlled thyristor rectifier, the current drawn by these battery chargers causes high total harmonic distortion (THD) and poor power factor (PF). This results in heating of transformer and cables and tripping of circuit breakers (Bass et al., 2001; Gomez & Morcos, 2003). Switching AC/DC converters with active power factor correction (PFC) is able to reduce THD and improve PF effectively. This technique has been applied to battery charger

Power electronics enables intelligent control of battery charger such that the power quality of the grid can be improved. One example is the vehicle-to-grid (V2G) reactive power compensation. A mathematical analysis of an electric vehicle charger based on a full-bridge inverter/rectifier and a half-bridge bi-directional dc/dc converter is presented (Kisacikoglu, et al. (2001)). The charger is able to handle different PQ conditions at different operation modes. A relationship between dc link ripple and reactive power flow direction is also derived. The analysis shows that while the charger can achieve reactive power compensation, one has to set a limit on the four-quadrant power transfer of the charger due

Active power filters (APF) have been developed primarily to compensate the harmonic and reactive power components of line current generated by the nonlinear loads and to improve the power quality of the grid (El-Haborouk et al., 2000; Singh et. al., 1999). Current-fed type APF uses an inductor for reactive power compensation while voltage-fed type APF uses a

**1. Introduction**

impact on the grid.

for electric vehicles (Mi, et al., 2003).

to the stresses on the components.

capacitor.

