Electrical machine commutation methods are techniques used to switch the direction of current in the coils of an electrical machine, such as a motor or generator. Commutation is crucial for the operation of these machines as it determines the direction of torque or voltage output. There are several types of commutation methods, each suited for different types of electrical machines. The main commutation methods are:
Brush Commutation: This method is commonly used in direct current (DC) motors and generators. It involves the use of brushes and a commutator, which is a rotary switch that reverses the current direction in the coils at specific positions. The brushes maintain electrical contact with the rotating commutator, ensuring the appropriate connection to the coils.
Electronic Commutation (Brushless DC): Also known as electronic commutators or sensorless commutation, this method is used in brushless DC motors (BLDC) and certain types of AC motors. Instead of brushes and commutators, electronic commutation relies on sensors (e.g., Hall effect sensors) to detect the rotor position. The electronic controller then switches the current in the coils accordingly to achieve smooth rotation.
AC Commutation: AC machines, such as AC induction motors and synchronous motors, do not use traditional commutation methods like those in DC machines. Instead, the direction of the rotating magnetic field in the stator is synchronized with the rotor's position. This is typically achieved using slip rings and brushes or electronic methods, depending on the type of AC machine.
Phase Advancement Commutation: This method is used in some types of AC synchronous machines. By advancing or retarding the phase angle of the rotor's excitation current, the rotor can be made to run in synchronization with the rotating magnetic field in the stator.
Hysteresis Commutation: This method is specific to hysteresis motors, which are a type of synchronous motor. Hysteresis motors use a rotor with a high hysteresis loss material. The rotating magnetic field in the stator causes the rotor to follow and align with it due to hysteresis effects, achieving commutation.
Each commutation method has its advantages and disadvantages, and the choice of the appropriate method depends on the specific application and requirements of the electrical machine.