1. Field
The present disclosure relates generally to electric motor systems and, in particular, to controlling electric motor systems. Still more particularly, the present disclosure relates to a method and apparatus for operating an electric motor phase control system for an electric motor in an electric motor system.
2. Background
An electric motor is a device that converts electrical power into mechanical power. Electric motors are used for various applications. These applications include fans, pumps, tools, disk drives, drills, and other types of devices that may be found in these and other types of platforms.
A brushless electric motor is a commonly used type of electric motor. With brushless electric motors, a controller is configured to change the current in windings in the electric motor. The windings may take the form of coils. The current in the coils may be changed by applying a voltage to the coils that causes a desired amount of current to flow through the coils. In particular, the current is switched at a frequency that changes the amplitude of the current flowing through the windings in phases in a manner that causes the motor to turn. The switching of the current is performed using switches in the form of transistors. When direct current is used to operate the brushless electric motor, the motor may take the form of a brushless direct current electric motor.
The switching of the current in the coils may be referred to as a commutation. A commutation occurs when the current from one coil is moved to another. In other words, a commutation occurs when an energized coil is turned off and a non-energized coil is turned on. Turning “on” a coil refers to a state in which current flows through that coil, while turning “off” a coil refers to a state in which current does not flow through the coil. A commutation is used to rotate the magnetic field configuration for operating a brushless electric motor.
The timing of the current in the coils in a brushless electric motor may be described as a phase angle. A phase angle may be a position of the brushless electric motor relative to the coil plane when the current is flowing through one or more of the coils in the brushless electric motor.
The application of the current to the coils is timed such that the brushless electric motor turns at a desired speed. As the speed of the brushless electric motor increases, a phenomena called back electromotive force (EMF) may affect the performance of the brushless electric motor. The back electromotive force is a voltage which opposes a change in magnetic flux.
Often, the back electromotive force is against the direction of the voltage applied to the coils. This back electromotive force may be present when motion occurs between the coils and a magnetic field.
Back electromotive force increases and decreases over time. With this phenomena, the timing of the application of the voltage to the coils becomes more important as the speed of the brushless electric motor increases. The timing of the current flow to one or more coils may be referred to as commutation time or current start time. In other words, commutation time is the time at which a signal is sent to change the current from one coil to another coil.
As the speed of the brushless electric motor increases, the magnitude of the back electromotive force also increases. As a result, reduced efficiency, current spikes, a reduction in performance, increased noise, and other undesirable effects may occur. Consequently, the brushless electric motor may not perform as desired. Therefore, it would be desirable to have a method and apparatus that take into account at least some of the issues discussed above, as well as other possible issues.