一种高效、轻便、高效的电动自行车充电电池充电器的设计、施工及实施07421480.doc

Design, Construction and Implementation of aHighly Efficient, Lightweight and Cost EffectiveBattery Charger for Electric Easy BikesKhosru M. Salim, Md. Jasim Uddin, M. Ishtiaque Rahman, Mohammad Rejwan UddinDepartment of Electrical and Electronic Engineering Independent University, Bangladesh Dhaka, Bishtiaque_Abstract Electric three-wheeler auto rickshaws known as easy rickshaws known as easy bikes are becoming more and more bikes are becoming quite common in Bangladesh. Due to obvious popular. The charging stations all employ the conventional advantages offered by these vehicles such as zero carbonemission and no requirement of gas encourages people totransition from traditional fuel-operated vehicle to electricimproving the efficiency of easy bike battery chargers. Using vehicles. The battery charging stations for these vehicles employbulky chargers containing iron core transformers with maximumiron core charger which is only about 80% efficient. Hence, there exists an excellent opportunity to save energy by the proposed charger, it is possible to achieve efficiencies of the order of 90%. efficiency around 80%. As a country which suffers from powershortages, it is highly desirable to have a charger that is moreefficient. In this paper, a new type of charger is proposed whichA considerable amount of research has been done over the uses a ferrite core transformer. A prototype of this charger is years regarding the various aspects of electric vehicle built and compared with a conventional charger. It is found from charging. Pellitteri et al 2 proposed an efficient wireless the experiments that the proposed charger exhibits efficiencymore than 90%. In addition, the proposed charger weighs onlyabout 2 kilograms, whereas the conventional charger weighscharging on the power distribution system. Wang et al 4 about 10 kilograms.charging scheme for electric pedal bikes. Bass and Zimmerman 3 explored the effects of electric vehicle highlighted the various design aspects related to inductive power transfer system necessary for constructing a contactless charger for electric vehicles. Zhou et al 5 proposed a multi function bi directional charger for plug-in hybrid electric Keywords Easy bikes, iron core transformer, ferrite coretransformer, efficiency, charging current.vehicles, which can accomplish three functions namely, charging, vehicle to grid, and vehicle to home. I. INTRODUCTIONGlobal population increase has led to an exponential rise in the amount of transportation vehicles. Almost all of these vehicles are run on fossil fuels, which causes environmental problems. The rapid decrease of fossil fuel reserves is an equally alarming issue. As a green solution, electric vehicles are gradually becoming more and more popular. Electric vehicles have several advantages 1 over regular vehicle; they do not require any gas, they emit no harmful substances into the atmosphere, they are subsidized by the government, and they require less maintenance. However, there are a few disadvantages of these vehicles as well. For instance, electric vehicles are not suitable for countries facing major shortage of power. Electric vehicles contain a battery bank which needs to be charged at regular intervals. The chargers used to charge these vehicles contain iron core transformers, which gives rise to power losses, and hence, inefficient charging operation. If these chargers are replaced with more efficient ones, it will save a substantial amount of energy and in the process, encourage countries with power shortages to use more electric vehicles. In Bangladesh, the use of electric three wheeler auto II. THE CONVENTIONAL EASY BIKE CHARGERElectric easy bikes contain a 60V battery bank. The chargers used at present for charging these bikes typically consist of two major components, namely, an iron core toroidal transformer and a full bridge diode rectifier. The complete charging scheme of such a battery is represented in the form of a block diagram in the figure below. The iron core transformer of the charger primarily receives power from the grid, and steps down the voltage to an appropriate level that matches the battery bank voltage. This ac voltage is then fed to a full bridge rectifier, which provides a dc voltage that charges the battery bank. In order to identify the problems associated with this charging system, the practical aspects concerning the iron core transformer of the conventional charger have been explored. Keeping these points in mind, an actual charger has been examined in the lab with the aim of determining the system efficiency at a range of charging currents. Fig. 1 Conventional easy bike charging schemeA. The Iron Core Transformer and Its Associated Drawbacks The main function of the iron core toroidal transformer in conventional easy bike charger is to step down the mains AC voltage to 60V, which matches the battery bank voltage. The typical charging power for a 60V battery bank is 600W. However, during the step-down operation, the transformer incurs power losses such as magnetizing loss in the core, eddy current loss, hysteresis loss, and resistive losses in the copper coil 6. Depending on the efficiency of the transformer, these losses will vary. If an efficiency of 70% is assumed, a power loss of about 200W must be taken into account. Hence, the total input power of conventional charger should be about 800W to 900W. As a result, an iron core transformer with a high VA rating is required. This makes the charger quite bulky, which affects its portability significantly. The figure below shows a typical charger that weighs about 10 kilograms. About 95% of the total weight is attributed to the transformer. Fig. 3 Experimental setup of conventional chargerThe setup consists of the following: 1.2.3.A variable transformer to control the charging current A wattmeter to monitor the input power A conventional 60V easy bike charger to convert the AC input into DC power 4.A 60V battery bank The charging current was varied using the variac, and the corresponding input power was recorded using a wattmeter. The output power was measured by calculating the product of the charging current and the voltage that appeared across the battery bank. Finally, using the ratio of output to input power, the efficiency of the charging system was calculated. Table 1 below shows the experimental data obtained from the system. TABLE IEXPERIMENTAL DATA OF CONVENTIONAL CHARGERVbattery (V) Ichar (A) Pin (W)(%) 61 1 117 170 240 305 370 445 520 595 650 720 800 900 965 52.13 72 61.2 61.8 62.3 62.8 63.2 63.7 64.1 64.8 65.2 65.6 65.9 66.3 2 3 77.25 81.70 84.86 85.21 85.75 86.18 89.72 90.55 90.2 4 5 6 7 8 Fig. 2 Typical iron core easy bike charger9 10 11 12 13 B. Experimentation with an Actual Charger One of the primary activities of this research study was to examine an actual conventional electric easy bike charger. Parameters such as battery voltage, charging current and input power were monitored during the experiment. The following figure shows the experimental setup of conventional easy bike charger. 87.86 89.31 III. THE PROPOSED HIGH FREQUENCY CHARGER OVERVIEWOF SYSTEM DESIGN AND CONSTRUCTIONA. Design Procedure in Brief Creating a functional prototype of the proposed charger involved a few strategic steps. The abstract idea was implemented using PSIM software, where the preliminary testing and parameter adjustments were made. Then, once a stable model was created in PSIM, the next step was to design the hardware and improve it through necessary adjustments of component values, until the desired outcome was obtained. 1) Design Issues Regarding Ferrite Core Transformer: A high frequency ferrite core transformer was used in the prototype. The transformer is designed to ensure that the flux density in the core of the transformer is maintained at a considerably high level which minimizes the eddy current loss of the transformer. To make the prototype more cost effective, the inductance of the transformer is also used by the LC filter circuit. Furthermore, ferrite shield has been used B. Working Principle of the Proposed Charger The fundamental difference between a conventional charger and the proposed charger is that the proposed charger uses a high frequency ferrite core transformer. This drastically above the surface of the transformer to maximize the magnetic field strength and minimize eddy current loss. All manipulated in several stages in order to achieve the desired these factors contribute in making the transformer very reduces the weight of the charger. The power from the grid is charging condition for the battery bank. The figure below is a block representation of the system containing the proposed charger. highly efficient (around 98%).2) LC Filter Design: In order to prevent short circuits, a very small dead time between complementary PWM signals was provided. During this short period, both MOSFETs are turned off. For this reason, the output current and voltage contain some ripple. So, in order to reduce this ripple in current a small inductor must be used. Similarly, to reduce the ripple in voltage a small capacitor bank should be used in parallel with the load. The inductance and capacitance of the filter was determined using the equation 7 below. The higher the frequency of ripple, the smaller the size of the filter. In this study, since the switching frequency of half bridge inverter was 20kHz, a small filter worked quite well to reduce the ripple in the output.f = 2 1(1) LCFig. 4 Block diagram describing the charging system containing theproposed chargerThe figure below shows the completed prototype of the proposed charger. The ac voltage from the grid is first converted to dc using a full wave diode rectifier. The rectified output is fed to a half bridge inverter constructed using MOSFETs. A microcontroller is used to provide the gate signals to the MOSFETs. The output of the inverter is high frequency ac voltage which is applied across the ferrite core transformer in order to step down the voltage as required for charging operation. However, voltage is ac and therefore must be converted to dc using a center tap rectifier. Finally, an LC filter is used to remove any ripple from the dc voltage before it is applied across the battery bank for charging. The figure below shows the entire arrangement of the proposed charger in PSIM. Fig. 6 Prototype of proposed chargerC. Experimental Setup of the Proposed Charger A similar experiment to the conventional charger was conducted for the purpose of comparing the two charging systems. In the proposed system, the same parameters such as battery voltage, charging current and input power were monitored during the experiment. The following figure shows the experimental setup of the proposed easy bike charger. Fig. 5 PSIM schematic consisting of proposed charger Fig. 7 Experimental setup of Conventional Charger Fig. 8 Graph of efficiency against charging current for both systemsJust as with the conventional setup, in the proposed setup D. Comparison of Efficiencies the charging current was varied using the variac, and the It is quite apparent from the figure above that the efficiency corresponding input power was recorded using a wattmeter. The output power was measured by calculating the product of the charging current and the voltage that appeared across the battery bank. Finally, using the ratio of output to input power, the efficiency of the charging system was calculated. Table 2 below shows the experimental data obtained from the charging system containing the proposed charger. of the proposed charging system is significantly higher than that of the conventional system. The average efficiency of the conventional charging system is 82%, whereas that of the proposed system is 93%. Therefore, the proposed charger is roughly 11% more efficient than the conventional one. E. Comparison of Size The use of the ferrite core transformer in the proposed charging system has resulted in a much lighter charger than the conventional iron core charger, which weighs about five times as much as ferrite core charger. This makes the proposed charger much more compact, portable and easier to handle. TABLE IIEXPERIMENTAL DATA OF PROPOSED CHARGERVbattery (V)Ichar (A)Pin (W) (%) 61 1 95 64.21 81.6 F. Comparison of Price 61.2 61.8 62.3 62.8 63.2 63.7 64.1 64.8 65.2 65.6 65.9 66.3 2 150 210 260 325 385 455 525 600 665 750 830 890 Although at present, the price of the proposed charger is not too less than the conventional charger, as time progresses the proposed charger is expected to become only cheaper. The reason is that it is mainly comprised of silicon, which exhibits a decline in price with the passage of time. On the other hand, the contrary is true for the iron core charger, since the price of iron is rising with time. 3 88.28 95.84 96.61 98.49 98 4 5 6 7 8 97.67 97.2 V. CONCLUSIONS9 In this paper, a detailed description of the design and construction of a more efficient, lightweight and cost-effective charger for electric easy bikes has been presented. A direct comparison of the proposed charger has been made with a typical conventional charger by creating the same charging conditions in the lab. The use of the ferrite core transformer in the proposed charger not only makes it much lighter, but also more efficient. Furthermore, the cost of such a charger is expected to fall with time, whereas iron core chargers are 10 11 12 13 98.04 96.21 95.27 96.84 IV.RESULTS AND DISCUSSIONSFrom the data obtained in Tables 1 and 2, a curve of likely to become more expensive. The experimental findings efficiency, , against charging current, I char, can be plotted for suggest that if the proposed charger is produced in a large scale, it has the potential to completely replace the conventional iron core chargers. Considering the fact that there are about one million easy bikes in Bangladesh at present, implementing the proposed charging scheme can boost energy savings by a huge amount. both systems using the same axes. As a result, since the same charging current is applied in both cases, a direct comparison of efficiency can be made. The figure below shows