The major components of an electric vehicle system are the motor, controller, power source, charger for electric vehicle although other promising battery technologies are emerging in the horizon.
The controller is needed for controlling the parameters of the vehicle, taking into consideration the overall performance of the vehicle. A DC shunt motor is used, in which the field windings and the armature may be connected in parallel across a constant voltage supply. In adjustable speed application as it is used in electric vehicle the field is connected across an independent adjustable voltage supply. Since the motor is of primary importance to the electric vehicle system, the determination of the speed of the motor for the various terrains is considered here.
FIELD PROGRAMMABLE GATE ARRAY (FPGA)
A Field Programmable Gate Array is a digital integrated circuit that can be programmed to do any type of digital function. There are two main advantages of an FPGA over a microprocessor chip for controller:’) An FPGA has the ability to operate faster than a microprocessor chip. 2) The new FPGAs that are on the market will support hardware that is upwards of one million gates. FPGAs are programmed using support software and a download cable connected to a host computer. Once they are programmed, they can be disconnected from the computer and will retain their functionality until the power is removed from the chip. The FPGAs can be programmed while they run, because they can be reprogrammable in the order of microseconds. This short time means that the system will not even sense that the chip was reprogrammed and there may be a small waiting period, but the system will not have to be shut down. The FPGA consists of three major configurable elements:
1. Configurable Logic Blocks (CLBs) arranged in an array that provides the functional elements and implements most of the logic in an FPGA.
2. Input-output blocks (IOBs) that provide the interface between the package pins and internal signal lines.
3. Programmable interconnect resources that provide routing path to connect inputs and outputs of CLBs and IOBs onto the appropriate network.
HARDWARE DESCRIPTION LANGUAGES (HDL)
HDL describes how hardware behaves. There are two main differences between traditional programming languages and HDL:
1. Traditional languages are a sequential process whereas HDL is a parallel process.
2. HDL runs forever whereas traditional programming languages will only run if directed.
A digital design can be created using schematic digital design editor that uses graphic symbols of the circuit or by using hardware description languages such as Verilog, Very High Speed Integrated Circuit hardware description language (VHDL). One of the key features of using VHDL is that it can be used to achieve all the goals for documentation, simulation, verification and synthesis of digital designs, thus saving a lot of effort and time. VHDL can be used to model a digital system at many levels of abstraction, ranging from the algorithmic level to the gate level. The VHDL language can be regarded as an integrated amalgamation of the following factors, such as, Sequential language + Concurrent language + Net-list language + timing-specifications + waveform generation language = VHDL. Therefore, the language has constructs that enable one to express the concurrent or sequential behavior of a digital system with or without timing. In this paper, the implementation of the controller on a FPGA using VHDL is presented.