Battery Charger Controller Board

Nowadays the PHEV vehicles most uses Li-ion batteries. These type of accumulators require special charging (CCCV), so a special battery charger unit is needed. We built an own made electric vehicle, which uses 50V voltage system for safety reasons. In our report we are going to present the development and the research of an 50V/50A Li-ion battery charger.

Step 1: Li-ion on-board charger for electric vehicles

Nowadays the PHEV vehicles most uses Li-ion batteries. These type of accumulators require special charging (CCCV), so a special battery charger unit is needed.  We built an own made electric vehicle, which uses 50V voltage system for safety reasons. The battery charger will be responsible for the charging processes of the  electric vehicles.To reduce the noises from the mains and to eliminate pulsing current, a PFC circuit protect the charger on the input, which largely reduce the reactive power of the whole circuit. After the PFC there is a DC-DC converter, converted the PFC 400V output DC voltage for the batteries (50V). Due to the high power of the DC-DC converter we have to use a Full-Bridge.. The control signal of the DC-DC converter consists of a PWM signal from a microcontroller, of which the duty cycle can be modified.

Step 2: Controller Board

We use a Microcontroller from Texas Instruments as the central unit of the battery charger. The DC-DC converter and the output current are controlled by this microcontroller. We chose this unit because it has Matlab support and this allows to implement the simulation results. Setting up the parameters of Texas specific blocks, we have the possibility to use the same settings as in the simulation model generated in Matlab. The Embedded Coder convert this into an algorithm that can be inserted into a code made by CodeComposerStudio. Thereby, the simulation results greatly reach the parameters of the real circuit.
During the simulation we applied some simplifications for the shorter simulation time like the idealization of switching elements or the replacement of the PFC circuit by a DC supply (400VDC). During the design of the Full-Bridge Converter's control signal we counted with deadtime. The deadtime can be calculated with a simple equation.  After this equation solved, we can set the Falling and the Rising Edge Delay (FED, RED) on the Texas specific Matlab Block. To reach the sufficient amplitude of the control signal, we designed the IGBT driver circuit, which has previously discussed.

For the output current regulation we used the Zero Voltage Switching method, of which we mentioned earlier. This method shifts the control signals in phase from each other until the output current reaches the desired value. In the simulation model we used a digital PID controller provided by Texas Instruments that is the part of the Matlab support tools as a block. We use 32-bit fixed-point architecture, which is a very efficient C/C++ engine that allows to use mathematical algorithms.That’s why we could use the PID controller to generate the algorithm with Embedded Coder. The output regulation method use the same parameters as the results of the simulation. This simulation shows a slight deviation compared to the reality, because the sampling is continuous, while in a real world application it is discrete (ADC Analog-Digital Conversion never use a continuous sample time)



Dec 09,2015
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