Battery Charger for Electric Vehicle Traction Battery Switch Station with PV System

This paper presents the functionality of a commercialized fast charger for a lithium-ion electric vehicle propulsion battery. The device is intended to operate in a battery switch station, allowing an up-to 1-h recharge of a 25-kWh depleted battery, removed from a vehicle. The charger is designed as a dual-stage-controlled ac/dc converter. The input stage consists of a three-phase full-bridge diode rectifier combined with a reduced rating shunt active power filter. The input stage creates an uncontrolled pulsating dc bus while complying with the grid codes by regulating the total harmonic distortion and power factor according to the predetermined permissible limits. The output stage is formed by six interleaved groups of two parallel dc–dc converters, fed by the uncontrolled dc bus and performing the battery charging process. The charger is capable of operating in any of the three typical charging modes: constant current, constant voltage, and constant power. Simulation results are shown to demonstrate the functionality of the device with including of Photovoltaic system. I.INTRODUCTION The traction battery is undoubtedly the most critical component of an electric vehicle (EV), since the cost and weight as well as the reliability and driving range of the vehicle are strongly influenced by the battery characteristics. Modern rechargeable lithium batteries, which are, by far, the most power or energy dense among modern batteries, are commonly used in traction applications. The high energy/power content requires appropriate battery management to ensure safety and optimal performance. In particular, proper recharging is essential in order to utilize the full capacity of the battery pack and preserve its nominal lifetime there are two common types of vehicle battery chargers. The onboard (often referred to as slow or low power) charger is located on board. The propulsion battery is recharged via the slow charger, plugged into a charging spot, while the vehicle is at parking lot . The off board (so-called fast or high power) charger is located at the battery switch station (BSS). The battery must be removed from the vehicle to be recharged via the fast charger (FC). The slow charger usually operates at 0.15–0.25-C rates, while the FC rate may typically reach 2-C rates, i.e., while charging a 25-kWh battery; the slow charger supplies 3–4 kW, while the FC peak power is typically 30–50 kW. The typical concept of EV includes urban driving only, where the full battery charge is sufficient for mediumrange routes of 50–100 miles. Recharging is accomplished by plugging the car into charge spots placed at different city locations throughout the day and at driver’s home during the night. Recently, a paradigm shift toward closing the gap between EV and conventional vehicles has occurred, forcing the infrastructure to support EV intercity driving as well. The following concept of BSS was developed: When out of charge, the EV battery can be replaced at a BSS, allowing nearly uninterrupted long range driving. The replacement process takes 2–4 min, similar to the duration of conventional refuelling process . The near empty battery, removed from a vehicle at the BSS, is recharged by an FC to be available as quickly as possible for the next customer. The charging time is obviously crucial, affecting the battery stock. For example, assuming 4-min battery replacement time, 15 vehicles per hour may be processed by each service lane. If battery charging time is 1 h, the minimum stock of 15 batteries per lane should be present at the station. Reducing the charging time obviously reduces the stock as well. It is worth noting that, since there is no human involvement in the fast charging process, galvanic isolation is usually not required to be present in an FC. M.Deepthi et. al. / International Journal of New Technologies in Science and Engineering Vol. 2, Issue 6,Dec 2015, ISSN 2349-0780 Available online @ www.ijntse.com 225 The FC is basically a controlled ac/dc power supply, drawing the power from the three-phase ac utility grid, converting it to dc and injecting it into the traction battery. In order to create a feasible solution, the FC must both satisfy the grid code in terms of power factor (PF) and harmonic content from the utility side and support lithium-ion charging modes from the battery side. Since the BSS usually contains multiple FCs, its impact on the distribution grid is very significant, as shown by previous research. Therefore, the input stage of the FC usually performs PF correction (PFC) according to the regulation requirements in addition to rectification. It can be accomplished by employing either an active rectifier , or a diode rectifier combined with a PFC circuit. The wellknown single-phase PFC approach, utilizing an uncontrolled rectifier followed by a full-rating boost dc–dc converter, is unsuitable for the three-phase diode rectifier case. However, it can be modified by splitting the three-phase rectifier into either two single-phase legs followed by two independent PFC converters or three single-phase Δor Y-connected stages. Alternatively, a more elegant approach employs a shunt connected active power filter (APF) at the uncontrolled rectifier input, supplying the reactive current to the diode rectifier, thus achieving both near-unity PF and near-zero total harmonic distortion (THD) by letting the utility to supply the active current only, which is in phase with the utility voltage and of the same shape. The use of either one three-phase or three single-phase APF configurations is potentially feasible for implementing a three-phase PFC stage. The additional advantage of the approach is the fact that, because of the shunt connection, the APF rating is less than onethird of the bridge rectifier rating, since the APF supplies the reactive and harmonic power only, while the series-connected PFC converter rating is equal to the load kilo volt ampere rating. The resulting loss reduction is an extremely desirable feature for an FC since the dissipated heat must be removed from the BSS by means of a cumbersome ventilation system, whose complexity is proportional to the amount of the heat to be removed. From the battery side, a conventional lithium-ion battery charging is characterized by two main phases: constant current (CC) and constant voltage (CV). Recently, constant power (CP) charging became popular in large vehicle battery packs. Hence, the charger output stage (typically consisting of dc–dc converters) must be capable of operating as either a current or voltage source. Alternatively, it can be operated as a voltage supply with dynamic current limitation. CP mode is usually achieved by operating as a current source, constantly varying according to the power profile. Moreover, the charger output current ripple should be kept as low as possible in order to prevent undesired influence on the battery chemistry. The wellknown solution, allowing splitting the load power between multiple modules in order to reduce both the conduction losses and current ripple, is interleaving. Interleaving employs parallel operation of converters, whose output current is equally shifted with respect to others such that, when summed, the current ripples partially cancel each other, creating a low ripple total output current. In addition, interleaving also reduces the implementation challenge of designing a single fullrating converter by using several lower rating converters instead at the expense of somewhat increased hardware cost, volume/weight, and more complex control circuitry. M.Deepthi et. al. / International Journal of New Technologies in Science and Engineering Vol. 2, Issue 6,Dec 2015, ISSN 2349-0780 Available online @ www.ijntse.com 226 II.POWER QUALITY Electric power quality may be defined as a measure of how well electric power service can be utilized by customers. Power Quality problem is an occurrence manifested as a nonstandard voltage, current or frequency that results in a failure or a mis operation of end user equipment. To compensate harmonics conventional Passive Filters are used for specific number of harmonics. To compress total harmonic content Active Power Filters are used. For all types of power quality solutions at the distribution system voltage level DFACTS also called as Custom Power Devices are introduced to improve Power Quality. Power quality is certainly a major concern in the present era; it becomes of especially important with the introduction sophisticated devices, whose performance is very sensitive to the quality of power supply. Modern industrial processes are based on a large amount of electronic devices such as programmable logic controllers and adjustable speed drives. Electronic devices are very sensitive to disturbances and thus industrial loads become less tolerant to power quality problems. Power Quality has become an important issue since many loads at various distribution ends like adjustable speed drives, process industries, printers, domestic utilities; computers, microprocessor based equipments etc. have become intolerant to voltage fluctuations, harmonic content and interruptions. Power Quality mainly deals with issues like maintaining a fixed voltage at the Point of Common Coupling for various distribution voltage levels irrespective of voltage fluctuations, maintaining near unity power factor power drawn from the supply, blocking of voltage and current unbalance from passing upwards from various distribution levels, reduction of voltage and current harmonics in the system and suppression of excessive supply neutral current. Recently, the importance of power quality issues has increased due to various reasons. First of all, there have been changes in the nature of electrical loads. On one hand, the characteristics of load have become more complex due to the increased use of power electronic equipment, which results in a deviation of voltage and current from its sinusoidal wavefor