- By Arya Admin
- Posted January 21, 2021
How Mechanical Engineers design Electric Vehicle Charger?
Electric Vehicle Charger
The popularity of electric vehicles is rapidly increasing in India. The EV market in India is estimated to increase from 3 million units in 2019 to 29 million units by 2027 with a CAGR of 21.1 per cent. As a result, demand for AC/DC chargers increases the smart chargers for EVs.
In order to charge the batteries efficiently, and to ensure their long life, students of Mechanical Engineering Colleges in Jaipur need a smart battery management or charging system. To realise such an EV charging system, experts has come up with smart EV charger solutions based on their low-cost ASSP flash micro controller (MCU) HT45F5Q-X for charging EV batteries. Today, three Electric Vehicle charger designs are suitable for Indian market. With specifications of 48V/4A, 48V/12A and 48V/15Aare available for rapid development of the product. This semiconductor-based smart charging system can support both lithium-ion along with the lead-acid battery types.
The battery charger ASSP flash MCU HT45F5Q-X is the heart of Electric Vehicle charger circuitry. With in-built operational amplifiers (OPAs) and digital-to-analogue converters (DACs). That are necessary to the students of Top Engineering Colleges in Rajasthan for battery charging function. Specifications of the battery charger flash MCU HT45F5Q-X help designers to choose an appropriate MCU from HT45F5Q-X series as per the application requirement.
Working of EV charger
Input power to the EV charger is an AC voltage ranges from 170V to 300V. The Electric Vehicle charger uses a half-bridge LLC resonant converter design and influence high-power and high-efficiency characteristics, to obtain DC power for charging the battery. The design uses a rectifier circuit for converting input AC voltage to high-voltage DC output with an electromagnetic interference (EMI) filter to eliminate high-frequency noise from input power source. A pulse-width modulation (PWM) controller IC can be used by the students of top mechanical engineering colleges for driving the MOSFETs of half-bridge LLC converter.
The battery charging process is supervised by the MCU HT45F5Q-2. And monitors the battery voltage and charging current levels and provides feedback to the PWM controller IC. Based on the feedback, the PWM controller differs the duty cycle of its PWM signal and drives the MOSFET circuit to obtain variable output voltage and current for charging the battery. For better protection, HT45F5Q-2 is isolated from other circuit and uses a photo-coupler. Battery-level LED indicators are given for knowing the charging status.
Battery charging process
There is a constant change in charging voltage and current during the charging process. If the battery voltage is too low when connected for charging, low charging current will be set initially and charging process will start.
When the battery voltage increases to a pre-defined level (Vu), constant voltage (CV) and constant current (CC) is applied for charging and fully charge the battery. Battery is considered to be fully charged when voltage reaches to the OFF option. When charging current drops to Iu, final voltage (FV) becomes permanent. The voltage, current and temperature control process in this Electric Vehicle charger are as follows:
The charging voltage is based on the initial voltage of battery when it is connected for charging. As the charging progresses, charging voltage accordingly changes and set the voltage when the battery is fully charged. The charging-voltage decision levels for 48V/12A battery charger includes the following:
- If Battery Voltage <36V, TC (0.6A) Charging, Voltage Setting FV (56V)
- If Battery Voltage <40V, TC (0.6A) Charging, Voltage Setting CV (58V)
- If Battery Voltage >40V, CC (12.0A) Charging, Voltage Setting CV (58V)
During the full charge, voltage fits to FV (56V). If battery voltage is lower than FV, the charging current will direct reset to CC (12.0A).
Charging current is set as per the battery voltage. During the initial stages, if the battery voltage is too less, trickle-charge current would be set for charging the battery. Once battery voltage reaches some level, constant current is supplied for charging, until fully charge the battery. The charging-current decision levels for 48V/12A battery charger includes Recharging Current <1.2A, determine the end of charging and Recharging Current >0.2A, determine the start of charging.
The EV charger has a negative temperature coefficient (NTC) thermistor which helps the students of private engineering colleges in Jaipur to monitor the temperature and a fan to regulate the heat. During the increase in temperature, the fan is automatically switched on to dissipate the heat; it gets switched off when the temperature is reduced to the lower set threshold. Besides, the fan turns on when charging current is high and turns off when charging current is low.
When NTC temperature is greater than 110°C, the charging current will be reduced to 50 per cent of charging current and will be monitored periodically.
LED indications for charging status
Some of the important indications of LED includes TC charge, red light flashes slowly (0.3 sec on, 0.3 sec off), CC, CV charge, red light flashes quickly (0.1 sec on, 0.1 sec off), When not charging, green light is on, and When charging time exceeds eight hours, red and green lights are bright.
When charging duration exceeded, the voltage drops to FV, the current reduced to TC, and charger repeatedly monitors the battery voltage.
Schematic and PCB assembly
The ASSP flash MCU HT45F5Q-2 can be used by the students of BTech mechanical engineering for designing higher-wattage solutions. It offers a programmable option for setting parameter thresholds, and makes it convenient for EV charger designs. They provide technical resources like block diagram, application circuits, source code, PCB files, etc to help designers in rapid product development and speed up time-to-market.
EV charger development platform for HT45F5Q-X series will be available to the students of Engg colleges soon. Using this software tool, users can easily select the charging voltage/current and other parameters to create a program. This application will generate a program containing a standard charging process, thereby significantly simplifying the development process.
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