A different type of motor is recommended according to the actual application:
- Stepper motors
Stepper motors are synchronous machines. They have at least two phases that are controlled by PWM via half-bridges. Two half-bridges are required for bipolar control of a two-phase stepper motor.
Since the number of poles of stepper motors is high, each rotor revolution can be divided into a discrete number of steps. The rotor angle and the position of the load can be determined with the aid of a reference point.
Stepper motors are, e.g., recommended for self-leveling headlamp systems, adaptive headlamp actuators, and various flap control units.
- DC motors with brushes
DC motors with brushes are easy to control and supply a torque that is proportional to the armature current if the stator field is constant - or in other words: The armature current can be used to easily deduce the load torque. At the same time, the speed is largely proportional to the armature voltage.
A transistor controlled by PWM (pulse width modulation) as the power output stage is sufficient for unidirectional operation, while a half-bridge is suitable for clockwise/counterclockwise rotation. Actuators with comparatively short duty cycles can thus be achieved with reduced switching and computation complexity, e.g. for seat or mirror adjustment or for the windshield wiper system pump.
Disadvantages: Contact of the armature windings via commutator and brushes is, however, subject to wear and tends to create conductive fine dust. Moreover, mechanical commutation also generates electromagnetic disturbances.
- Brushless DC motors (BLDC motors)
BLDC motors have high endurance qualities as they do not require wear-prone electro-mechanical commutation via brushes or commutator. They are therefore ideal for use in pumps, fans, and other actuators operating at higher duty cycles.
Which phase currents for controlling a BLDC motor?
BLDC motor control is rather more complex than with standard DC motors since the controller must usually generate three alternating voltages whose frequency and voltage can be adjusted and always need to be correctly in phase. Sinusoidal phase currents are desired to ensure the BLDC motor rotates quietly and smoothly. This is achieved, e.g., through pulse width modulated phase voltages with sinewave oscillation (sinusoidal commutation).
Determining and controlling the torque of the BLDC motor at dynamic load
BLDC motors are classed as synchronous machines. This means, the motor's speed is based on the frequency of the phase currents and the number of poles. A field-oriented control (FOC) can be used to determine and control the torque with dynamic load. Based on this mathematical model, the user can access a calculated armature current and stator flow, similar to the DC motor. This requires information about the position of the rotor, the phase currents, and a bit of computation capacity. The hardware output stage of the inverter for a BLDC motor with three phases requires six switching transistors more than for the half-bridge of a DC motor.
DC motor with or without brushes?
Although implementation of the hardware and determination of the control variables are more complex than with a comparable DC motor, the BLDC motor offers various advantages: Minimum wear and thus longer lifetime, less weight or smaller motor dimensions with greater efficiency. It will, therefore, eventually force the traditional DC motor into niche applications.
Motor controller: One for all
A motor controller that enables control of all three motor types at low power paves the way for step-by-step migration of traditional DC motors to state-of-the-art BLDC motors. The HVC4223F from Micronas can be operated in the following motor configurations:
- independent operation of two or three DC motors
- operation of a BLDC motor or other permanent magnet synchronous motors (PMSM)
- operation with a bipolar stepper motor
In this case, the motor controller features integrated output transistors that are connected to three half-bridges or two 6-pulse bridges along with a corresponding PWM timer.
Furthermore, it offers high performance for smart actuators with reduced CO2 emissions.
As a one-chip solution in a small QFN package (6mm x 6mm), the HVC4223F motor controller contains
- a 32-bit ARM® Cortex®-M3 microcontroller with 32KB flash memory and 2KB SRAM
- low dropout voltage regulator for direct connection to the 12V battery
- LIN-2.x transceiver
- watchdog timer
- output transistors for direct connection of the motor.
As a result, the motor controller requires less space and can - thanks to its wide temperature range up to 150°C - also be installed directly in the motor.
The computation capacity of the CPU core supports complex motor control algorithms such as the field-oriented control of BLDC motors with space vector modulation (SVC), block commutation (six-step modulation) with and without sensors, as well as various configurations for controlling stepper motors.
For the simple creation of LIN clusters, the motor controller has an integrated LIN transceiver with additional pin for auto-addressing (Micronas easyLin®). The ability to automatically identify various homogeneous applications enables the simple creation of LIN clusters.
The TDK-Micronas HVC4223F motor controller is ideal for numerous automotive applications, e.g.:
- mirror adjustment systems
- self-leveling headlamp systems
- adaptive headlamp actuators
- exhaust flaps
- lens caps for cameras
- automotive grille adjustment
- seat temperature control
- fans and pumps
- HVAC flap control
- retractable interior
Find the demo-kit here: www.rutronik24.com.