By enpmsm
PREVIEW
A Brief Introduction of Field-Oriented Control (FOC)
Field-Oriented Control (FOC) is a motor control technique that involves aligning the stator current vector within a rotating reference frame of the machine. It is a specific type of vector control that represents currents, voltages, and magnetic fluxes of the machine as space vectors within this rotating reference frame. In the case of a synchronous machine, the stator and rotor fluxes are synchronous, making it ideal to align the rotating reference frame’s d-axis with the rotor flux. To achieve this alignment, the position of the rotor needs to be determined either through measurement using an encoder or through estimation using a sensorless technique.
Field-oriented control (FOC) is a significant control method used for Brushless DC motors. It bears similarity to sinusoidal commutation but introduces a significant mathematical modification. One noteworthy aspect of FOC is that as the motor rotation frequency rises, maintaining the desired current becomes more challenging. This is because the rotation frequency affects the current loop. When operating at lower rotation speeds, any delay in the current loop is relatively unimportant, but as the rotation speed increases, this delay leads to the generation of undesirable D torque, reducing the available torque.
A Brief Introduction of Direct Flux Control (DFC)
The advanced control method known as direct flux control (sometimes referred to as direct torque control, or DTC), is utilized in electric motors, particularly induction motors. The motor’s torque and speed may be precisely and effectively controlled thanks to this digital control approach.Direct flux control’s core idea is to directly regulate the motor’s flux and torque components without the use of intricate transformation algorithms or coordinate systems. It enables a quicker and more precise control response, which enhances motor performance and effectiveness.
In traditional motor control methods, such as field-oriented control (FOC), a transformation of motor variables from the stator reference frame to the rotor reference frame is required within the control algorithm. This modification introduces complexity and increases computing time. However, direct flux control eliminates the need for coordinate transformations by directly adjusting the stator flux and torque components in the stationary reference frame. In doing so, it simplifies the control structure and reduces computational complexity through a combination of hysteresis comparators and lookup tables.
A Brief Introduction of Scalar Control (Volts per Hertz Control)
Scalar control is a widely adopted and simpler method for controlling Permanent Magnet Synchronous Motors (PMSM). It involves adjusting the motor by manipulating the voltage and frequency provided to it while maintaining a consistent volts per hertz ratio. This control method is relatively easy to execute and is suitable for applications with moderate performance requirements.
Scalar control modifies the motor’s voltage in direct proportion to the power supply’s frequency. This method’s fundamental idea is to maintain a steady volts-per-hertz ratio to make sure the motor runs securely and within a stable range. The basic idea is to maintain the correct volts-per-hertz ratio by increasing the voltage provided to the motor correspondingly as the power source frequency rises. This method assists in regulating the magnetic flux and supplying sufficient torque to reach the desired speed.
Scalar control is relatively uncomplicated to implement and does not necessitate intricate control algorithms. It is commonly employed in situations where speed variations are infrequent or where load fluctuations are minimal. Examples of such applications include fans and pumps.
These are just a few of the commonly used control methods for Permanent Magnet Synchronous Motors. The appropriate control method depends on the specific application, performance requirements, and desired level of control precision.
