The last part focused entirely on the operation or commutation logic for Motor Controller or Motor Control Unit (MCU) integrated in both Battery Electric Vehicles (BEVs) and Hybrid Electric Vehicles (HEVs). This part will emphasize on the features and protection control embedded in the Motor Controllers for smooth operation of Electric Vehicles.

Motor Controller features and protection controls are highly dynamic and depends entirely on Vehicle functionalities, essentially transforming into input and output on the controller ports. Apart from this, such features and control are also subjected to the voltage class, motor characteristics, position sensor feedback, control logic & control mode.

FEATURES

The table below summarizes some of the features for EV Motor Controllers

1. Motor Type:

Electric Vehicles utilize primarily three categories of Motor subjected to vehicle class:

a) Brushless DC (BLDC)

b) Induction Motor (IM)

c) Permanent Magnet Synchronous Motor (PMSM)

Though the operational concept remains similar for motor controller, control/commutation logic differs subjected to motor type. For example: BLDC motors use three Hall Effect sensors where commutation is achieved in six-steps resulting in commutation breaking and thereby, resulting in torque ripples at the end of every step. While in PMS motor, only one Hall Effect Sensor/Encoder is used as commutation is continuous, thereby, resulting in absence of torque ripples. As operation differs for both the motor types, switching on Motor Phase current at right time is determined differently via commutation logic.

2. Regeneration:

Motor Controllers, at its core is purely a power conversion unit. The unit acts as an interface between Battery and Motor. Battery being a DC Power source supplies DC current which is converted to AC Current and being fed to motor. This is the normal operation for controller during vehicle start & cruising. But during braking, the entire sequence is reversed. Motor instead of propelling the vehicle acts as a generator while Motor Controller inverses the torque generated from motor to that of its rotation. During this operation, back-emf generated in the motor is higher than the DC supply voltage to Motor Controller. This potential difference between back-emf and supply voltage results current being flown from Motor to Battery via Motor Controller.

3. Input & Output Pins:

A Motor Controller is embedded with several analog and digital inputs/outputs (I/Os) for wide control on Electric Vehicle System. Such I/Os can be classified under following categories:

a) Digital Inputs

Such inputs are reserved & utilized for control of vehicle’s digital features. Some of these include Park, Low Speed & High-Speed Modes, Anti-Theft, Charger & Side-Stand.  Such features increase as application class goes up from Electric 2-Wheelers (e-2W) to Electric Commercial Vehicles.

b) Analog Inputs

Few pins are reserved for analog inputs with prominent utilization for interfacing throttle, brake & motor temperature sensor.

c) Power Outputs

Such outputs are used to drive various loads including inductive, resistive, electromagnetic, and low current loads that are connected with +12V external supply.

d) Power Supply Outputs

Usually, these ports are used as an auxiliary output power to drive low power circuits – LED indicators, electronic throttles, position encoders and remote I/O pins.

e) Position Sensor Interface

Subjected to Position Sensor type, specific ports are utilized as inputs to capture rotor position and activate a feedback control mechanism.

f) Communication Interface

CAN being the default industry standard is used extensively for flashing, monitoring and programming the Motor Control Units (MCUs).

4. Multi-Function Features:

To curtail the space occupied by auxiliary power electronics components in heavy-duty applications, Motor Controllers/Traction Inverters are embedded with such auxiliary units, viz; DC/DC Converter, DC/AC Converters & Power Distribution Units (PDUs). Additionally, validation for EMI/EMC compliance is also eased to certain extent due to such multi-function controllers.

5. Programmable Parameters:

The operation of Motor Controller involves an extensive of list of parameters that are being monitored for smooth and dynamic response. Some of these parameters are categorized separately and made available for customers to customize as per vehicle requirements. Availability of these parameters for customization are highly subjected to design and manufacturer’s choice. A separate programming unit or debug tool is furnished to customers for monitoring and customization of controller parameters.

PROTECTION

Motor Controllers integrated in Electric Vehicles are subjected to varied form the operating and ambient environment. Any extreme stress on the vehicle enhances the probability of component failure which in turn can be a major cause for human fatality. Protection measures are adopted in various forms in all the EV components and Motor Controllers are no exception. Some of these measures include:

1. Overvoltage:

Overvoltage refers to increase in the input battery voltage for a very short duration, exceeding the limits of a controller voltage range. Such undue stress can result in damage of controller components which in turn can prove to be fatal for vehicle & human safety. Therefore, once the voltage exceeds the limits, controller either shuts off or get damaged, thereby, making it imperative to eliminate all the sources for abnormal voltage levels.

2. Undervoltage:

Undervoltage is opposite to Overvoltage in terms of protection measures. The voltage range are pre-determined by the chemistry utilized in the Li-Ion battery. If Motor Control Unit (MCU) operates below lower voltage limit, it will draw higher currents from battery which can result in thermal runaway in battery either degrading its cycles or permanent damage to cells. Therefore, the controller will cutoff the battery supply once the voltage below its operational limit.

3. Overcurrent:

It refers to the state where controller starts drawing current beyond its design limits. In such a scenario, there is a huge risk to MOSFETs in the controller being damaged permanently. Therefore, current is being continuously monitored and in case of overcurrent, discharge MOSFETs turn off, thereby, suspending the battery supply.

4. Overtemperature:

It is a protection system that shuts down the battery supply when the internal temperature of motor controller exceeded a safe value. A circuit is used to monitor and generate a trigger signal that starts the shutdown process at high temperatures. High temperatures may be a result of faulty components, overloading, overvoltage, or insufficient cooling. To prevent such condition, controllers are designed for operation till a specific temperature beyond which current derating kick-in and once the extreme temperature is reached, controller cuts-off the supply.

5. Phase-to-Phase Protection:

In an MCU-Motor operation, six sequences are possible as far as phase connections are concerned. Out of these six sequences, one sequence is applicable for forward direction while one to the reverse. In case two phase are short-circuited, the impedance of the system is infinite resulting in dropping of current rapidly. As there is no current in motor phases, the rotor is locked preventing the system form failure. But in case, if any of the phase is connected to the Ground, circuit becomes a close loop resulting in an infinite current flow and damaging the entire system as a consequence.