Algorithms that Make Electric Vehicle Motor Control System Highly Efficient
Electric vehicles have been around for decades (world’s first EV was developed in 1890). However, EVs could not make a major impact on the automotive industry and buyers continued to opt for diesel or petrol cars.
Things started to change when OEMs, governments and other stakeholders came together to make electric vehicles more efficient, less costly and something that is worthy of replacing the IC engine vehicles.
In EVs, internal combustion engines are replaced by a motor control system. Similar to how an engine drives the powertrain of regular vehicles, it is the motor controller that does this job in an electric vehicle. A motor controller can be seen as a system comprising a BLDC, PMSM or an AC induction motor and an electronic component driving it. The electronic component is made up of an automotive-grade microcontroller and a set of algorithms that enable the motor to work at the utmost efficiency.
Let us examine two of the algorithms mostly used in advanced motor controllers for electric vehicles:
Field-Oriented Control Algorithm: Known as FOC in popular automotive jargon, this algorithm provides precise control over the motor by factoring in speed and torque. Inside the FOC algorithm, multiple calculations take place.
FOC takes speed and flux components as input and calculates the corresponding current component which is dependent on the drive’s speed control. The proportional-integral algorithm then takes charge and converts the output current to voltage signals. These voltage signals, after going through some more transformations, are fed to the Pulse Width Modulator (PWM). The PWM signals at the end of this process drive the motor.
The FOC algorithm determines the exact rotor position so that it can generate optimum magnetic force in the stator. This results in maximum torque and also reduced fluctuation in the torque which leads to smooth motor operation. For an EV, smoother motor operation translates into reduced noise, one of the key parameters of optimum operation of a vehicle. It has other advantages too that includes reduced wear and tear of the bearings, resulting in durability and reliability of the motor.
Regenerative Braking: The electric motor in an electric vehicle acts as a generator and redirects the current flow into the supply battery. Kinetic or potential energy of the vehicle mass is converted into electric energy that can be stored.
Regenerative Braking is the process of regaining the energy during braking. But for a complete stop, the mechanical brakes are required.
Regenerative braking can be achieved by the reversal of current in the motor-battery circuit, redirecting the current flow into the supply battery. To store the voltage in the battery, the bus voltage should be higher than the battery terminal voltage. We must boost the voltage developed from motor higher than the battery using software algorithm with the help of Inverter and motor setup.
A boost to the back EMF is required so that even at lower speeds, the motor can work as brake. Hence, if the DC Bus voltage is less, we can boost the voltage which is required to charge the battery. A Boost Converter circuit helps in boosting the voltage. A 3Phase motor circuit acts as the Boost converter circuit.
The motor windings act as the step-up converter inductor and top MOSFETs serve as diodes, while the bottom MOSFETS act as switch.
Conclusion
With these algorithms getting more advanced, electric vehicles are likely to have higher range, better optimization of battery, safety and much more. In addition to the motor control system, advancements can be observed in the charging of EVs and the vehicle’s interaction with an external charging system. All of these are gradually translating into higher acceptance of electric vehicles among buyers across the globe. EV startups are also lapping up this scenario to build EVs at lower cost with advanced features.
