Simulation of Motors in EVs

If the last century belonged to internal combustion (IC) engine vehicles and conventional power-train systems, this century can very well belong to electric vehicles (EV) and vehicles that can run on hydrogen / hybrid fuel. It is interesting to note that battery operated electric vehicle senergized by lead-acid batteries and using a DC power system competed with IC engine vehicles way back in the 1890s. EVs did not have the starting problems of the IC engine and had no tailpipe emissions. However, mass manufacturing by the likes of Ford, coupled with extremely high battery prices and long charging period saw the public sway in favour of vehicles that operated on petrol / diesel. Today, the rising price of oil and uncertainty about its supply (due to geo - political tensions) has contributed for a viable alternative to hydrocarbon fuel driven vehicles again. Coupled with this, growing awareness about the environmental repercussions of vehicle emissions has triggered a global effort to develop next generation transportation solutions with increased efficiency. These EVs would reduce greenhouse gas and air pollution emissions. They will even reduce the noise pollution substantially. EVs, depending on their source of electric energy, have the potential to be zero emission vehicles, noise free, and are being looked upon as a future alternative to internal combustion vehicles.

How EVs work
Unlike IC vehicles, EVs are surprisingly uncomplicated.The power system of an electric vehicle consists of just two main components: the motor that provides the power and the controller that controls the application of this power. The electric motor converts electrical energy into mechanical energy (rotation), which in turn transmits power to the wheels, propelling the vehicle.  The EV controller is an electronic gadget that acts as a bridge between the batteries and the electric motor to control the EVs speed and acceleration, much like a carburetor does in a petrol powered vehicle. The advantage of EVs is that they are quiet, emission-free, more comfortable, and save energy. There are four types of EVs in the market today:

• Battery Electric Vehicle (BEV): these run entirely on a battery-powered electric drive-train. The electricity used to drive the vehicle is stored in a large battery pack which can be charged by plugging into the electricity grid.All the two wheelers as well as majority of four wheelers in India are BEVs. Batteries are what determine the EV range to a large extent; we will cover their design in another article.
• Hybrid Electric Vehicle (HEV): Hybrid cars are powered by two engines - fuel and electric. Both work with each other to spin the wheels. The engine gets energy from fuel, and the motor gets electricity from batteries. The transmission is rotated simultaneously by both the engine and the electric motor.
• Plug-in Hybrid Electric Vehicle (PHEV): this is a full hybrid electric vehicle, but with an additional feature that includes the possibility to charge the high voltage battery either by the IC engine, wheel motion, or by simply plugging into a charge point. These EVs have a fuel tank as well as a charging port.
• Fuel Cell Electric Vehicle (FCEV): They employ ‘fuel cell technology’ to generate the electricity required to run the vehicle. The cell generates electricity through an electrochemical reaction of hydrogen and oxygen that occurs within the vehicle itself. This chemical energy is then converted into electric energy.

Working of Electric Motors
Irrespective of the type, all EVs must have an electric motor. There are many types of AC and DC motors that power today’s EVs, but all electric motors have two major parts - a static part called the stator and a rotating part called the rotor. The stator is the non-moving, fixed counterpart in the motor. It is usually a steel cylinder with slots and copper coils that are weaved with a specific geometry. The stator has pairs of poles, each pair of which is activated and made into an electromagnet by a current being passed through the coils wrapped round it. The rotor is the rotating part of the electrical motor. It consists of a group of electro-magnets arranged around a cylinder, with the poles facing toward the stator poles. It is located inside the stator and is mounted on the motor's shaft. When power is applied, an electric current flows through the copper coils, creating an electromagnetic field across the rotor bars. This in turn is converted into rotational movement that is transferred to the wheels.

Importance of Simulation of EV Motors
A quick question for you – if you want to purchase an EV, what is the first thing you look for? Most people would say it is the ‘range’. In other words, how much the EV will run when it is fully charged. The second concern is ‘how much time does it take to fully charge the EV’? These are precisely the kind of questions that affect the designing of electrical motors of EVs. Ultimately, the range is affected by factors like:

• Magnetic eddy currents: these are induced by changing magnetic fields and flow in closed loops, perpendicular to the plane of the magnetic field. The challenge in EV motor design is to minimize these eddies.
• Hysteresis losses in the stator: Hysteresis is a property of ferromagnetic materials in which a coil's magnetic induction lags the magnetic field that charges the coil. They vary with the core material and geometry and with input voltage and need to be minimized in order to increase the efficiency of the EV motor.
• Friction and windage losses: these are caused by friction in the bearings and brushes of the motor and aerodynamic losses associated with the ventilation fan and other rotating armature.
• Weight of the motor: Apart from the above mentioned losses, the weight of the motor is a design concern too. Obviously, the lighter the motor, the better is the range. This in turn involves selection of proper material that is lightweight yet sturdy.
• Regenerative braking: Regenerative braking is a braking method that uses mechanical energy from the motor and converts kinetic energy to electrical energy and gives it back to the battery. The more efficient the motor, the better it can charge the battery. Most of EVs incorporate this mechanism.

The sale of EVs is set to rise in India and other countries.  As people lean towards eco friendly EV vehicles, the R&D departments of almost all automobile are racing to improve motor performance. Since the electric motor is the heart of an EV, all designers rely on simulation software – like Altair SimLab™ and Altair Flux™ to tweak parameters and arrive at the best possible design solution. Such simulation software is a powerful tool that helps engineer optimize the performance of the electric motor, which is the key to gain a competitive edge in the fast growing EV market.