Motor types
Electric motors could be divided into several groups. ESC controllers can drive motor types, that are marked with green color. Each motor consists of two main parts:
- Stator: stationary part, the part that is not moving. Winding is located here in synchronous and induction motor. Magnets are usually located here for the DC motors.
- Rotor: rotating part of the motor. Magnets are located here in synchronous motors (except reluctance motors). Winding is located here in the DC motor and induction motor. The winding of the induction motor is called a squirrel cage.
Supported motor types
BLDC motor
BLDC stands for brushless DC motor. 3-phase winding is in the stator, magnets are in the rotor. This construction is very same as the BLAC motor but characteristics and motor driving are different. Driving and characteristics is similar to DC motor. In each moment only two of three phases are connected, last one is left
disconnected. Phases are reconnected by the controller as the rotor rotates to create a magnetic field that drags magnets of the rotor in the direction of rotation to create torque. The controller is working here as an electronic commutator. That is why a BLDC motor is also called an electronically commutated motor. Relations between voltage, RPM, current, and torque are the same as for DC motors. Voltage is proportional to RPM and motor current is proportional to generated torque.
Induced voltage (Back-EMF) has a trapezoidal shape (as shown in the picture). The induced voltage is the phase voltage of the motor measured when the motor is rotating and no current is owing through the winding. If these three trapezoidal curves were rectified, it would create smooth DC voltage without ripple. This rectification is done by the controller that works as an electronic commutator (an electronic commutator is the same as a rectifier) That is why the BLDC motor with the controller has the same characteristics as the DC motor.
BLAC motor
BLAC stands for brushless AC motor. This motor is sometimes inaccurately called PMSM (permanent magnet synchronous motor). The construction of the motor is similar to the construction of the BLDC motor. Three-phase winding is located in the stator and magnets are located in the rotor. Characteristics and driving are different for BLAC and BLDC motor. For the BLAC motor, all three phases are connected by the controller all the time. By switching transistors in the power stage of the controller sinusoidal current is created in the phases. These three currents create a rotating magnetic field in the stator. Created magnetic field drags magnets in the rotor and produces torque.
Induced voltage (Back-EMF) has a sinusoidal shape. The induced voltage is the phase voltage of the motor measured when the motor is rotating and no current is
owing through the winding. The amplitude of the induced voltage is proportional to the RPM of the motor. The frequency of the induced voltage is also proportional to the RPM of the motor. Phase currents have two compounds magnetizing current and torque-generating current. When measuring phase current, only the geometric sum of these two compounds can be measured. Additional information is needed to distinguish these two parts from each other
Induction motor
Motor identification (identrun) is not working for induction motors. If you want to use this motor, contact siliXcon support.
An induction motor is sometimes called an asynchronous motor because the rotor of the motor is spinning at a slightly different speed than the rotating magnetic field of the stator. The stator of the induction motor is similar to synchronous motors, three phase winding is located here. The rotor is different, usually short-circuited aluminum winding is located here. This type of winding is called a squirrel cage. As the rotor has a different speed than the stator, the current is induced by the rotor winding. This induced current interacts with the magnetic field of the stator and motor generates torque. The induction motor is cheap and very durable, but its efficiency is lower and it is heavier and bigger than a synchronous motor with the same parameters. Control of the induction motor is a little bit more complicated than control of the BLAC motor. Frequency and voltage are approximately proportional to motor RPM. Phase currents have two compounds magnetizing current and torque-generating current. When measuring phase current, only geometric sum of these two compounds can be measured. Additional information is needed to distinguish these two parts from each other.
DC (or series) motor
DC motor is the oldest and simplest electric motor. Magnets or excitation winding is located in the stator, and working winding is located in the rotor. The rotor winding is connected to commutator mechanical contacts that conduct current into the rotating rotor. The commutator also works as a mechanical rectifier that allows current in the rotor to ow in the desired direction independently of the rotor position. The commutator is the weakest part of the DC motor because it is a mechanical part and it wears out quickly. DC motor is very easy to control. Motor current is exactly proportional to the generated torque on the shaft. Motor revolutions are proportional to the motor-induced voltage.
The main purpose of ESC controllers is not to drive DC motors, but it is possible. Check this guide, on how to configure controller for DC motor
Unsupported motor types
Stepper motor
A Stepper motor is a type of synchronous motor specialized for position control in an open loop (without feedback). It has usually two phases wound in the stator and magnets in the stator.
Each time, the current in phases is switched, the rotor is dragged to a new position, aligned with currently operating winding. This means that the rotor does one step. Steps exactly correspond to a change of rotor position. Steps are counted by the controller, so the change of rotor position is known without the need to measure it. The Stepper motor is optimized for positioning, not for power performance, relationships between voltage, current RPM and torque are not usually important.
Reluctance motor
Construction of the reluctance motor is similar to BLAC and BLD motors. Stator also has three-phase winding but the rotor is different. The rotor is made of steel with good magnetic properties, no magnets are in the rotor nor in the stator. Rotor has different magnetic reluctance in different directions. When the magnetic field is applied to the rotor, it rotates until is aligned with the direction of the applied magnetic field in respect with different magnetic reluctances. If the applied magnetic field is rotating, the rotor is following it continuously. Reluctance motor is very hard to control, relations between current, voltage, frequency, RPM, and torque are complicated. When the reluctance motor is controlled properly, it has very good efficiency.
Synchronous reluctance motors (magnetless) are officially not supported, because the configuration requires extensive assistance from our side. The platform is generally suited for driving this type of motor.