CS should have multiple charging systems with bidirectional power flow functionality that facilitates EVs of different battery ratings to charge or discharge. This bidirectional power flow functionality of CS are referred as G2V and V2G technology [1, 40]. The G2V and V2G process can be achieved when the CS is situated near the DN in a parking lot with a charging bay [66]. The parking lot can be a residential complex or office complex or shopping complex, where EVs tends to stay for longer duration and thereby this concept can be easily achieved [74]. Thus it is possible to exchange active as well as reactive power between the grid and the EVs batteries using bidirectional converters in the charging systems [76]. Therefore, it is required to develop a CS which can handle multiple EVs of different ratings mainly in terms for voltage regulation at the distribution node (DN).
Many studies on EVs and battery models have been published in recent years [28,77–79] and many other studies have focussed on battery charging systems [2, 62–64]. Concerning the power converters involved in charging systems, a two stage structure composed of three-phase rectifier followed with dc- dc converter is the simplest and most economical form of circuit [1,2]. Few traditional charging systems have used two-stage structure with an isolated transformer [62,64]. Non-isolation type battery charging systems are more preferable when considering the efficiency, volume and cost [1,2,63]. Very few studies have reported non-isolation type battery charging systems because of the difficulty in handling batteries of different ratings during its two way power transfer [1, 2]. Another set of studies have focussed on optimization models to represent EV charging systems [57,58,80–82]. Among those, few of which have paid more attention to prove the validity of EVs in terms of frequency regulation [80–83]. In [57, 58], a control algorithm is developed for scheduling the charging and discharging of EVs’ batteries for autonomous distributed V2G systems. All of these studies have pointed the need to coordinate the charging or discharging in some way to accommodate a large number of EVs. However, a very few works have addressed on voltage regulation issue using EV charging system. In [73], authors have studied the V2G existence using load flow techniques for voltage regulation at the DN. They have considered the aggregated EVs’ energy in a particular area and analyzed the impact on the distribution network. In [65,66], a real-time coordination of plug-in EVs charging have been explained to minimize the power losses and to improve the voltage profile. These system level control approaches aims at the effective utilization of EVs for grid support. However, it has been observed from the literature; so far these studies have dealt only with active power transfer to realize the CS for DN voltage regulation.
Nevertheless, there has not been much technical analysis done in both active and reactive power
2.1 Introduction
transfer with component level contact based EV charging system model to regulate the DN voltage.
While, the benefits of active and reactive power transfer have been widely studied in wind, photovoltaic and other grid integrated converter applications [84–86]. In similar manner, if EVs’ batteries exchange active as well as reactive power to the distribution network, a better coordination and control can be achieved. Moreover, the multiple charging systems of the CS also needs an additional control mechanism to coordinate the sudden arrival and departure of EVs, yet to be reported. Based on the above discussions, the following are the main objectives of the present chapter.
• Design and simulation of EV charging systems with its associated controllers to enable successful integration of EVs during its bidirectional power transfer.
• Design of grid connected three-phase ac-dc and dc-dc converter with enhanced PLL based PWM control and CC-CV charging strategy; to improve the quality of grid waveform and to increase the performance of the battery during charge/discharge operation.
• Design of master controller and an aggregator to control and coordinate multiple EVs arrived at the CS.
• Investigating the behavior of CS with different power transfer approaches such as active, reactive and combined active and reactive power.
The CS designed in this chapter has multiple charging systems which facilitates EVs of different ratings to charge or discharge their batteries. To control and coordinate the sudden arrival and depar- ture of EVs and to regulate the specified voltage limit (1±0.13), the CS is externally controlled using a fuzzy logic controller (FLC) and an aggregator. Here, the usage of other traditional control meth- ods; often results in computational burdens due to large number of operations such as trigonometric functions, parametric identifications, filtering and so forth. An FLC indeed, does not require neither detailed knowledge of the system under control nor its precise description in terms of mathematical model. FLC here acts as a master control, which decides the total power to be injected or drawn from the DN. Aggregator distributes the power among multiple EVs arrived in the CS. EVs in the CS exchange active power or reactive power or both through charging systems from/to the DN. A CS has been modeled in simulation environment and has been tested with 35 EVs of different ratings connected to a realistic radial distribution system of Guwahati city (shown in Appendix A.1) [87].
TH-1345_TPERJOY
This chapter is organized as follows: Section 2.2 explains the voltage regulation concept at the distribution node. Section 2.3 describes the framework of the simulation model. Problem definition is detailed in Section 2.4. Simulation results are discussed in Section 2.5 and the conclusions are given in Section 2.6.