What Is the Principle of V/F Control for Inverters?
V/F control (Voltage/Frequency Control) is the most fundamental speed regulation method for inverters. Its core principle involves maintaining a constant ratio between the motor’s stator voltage (V) and supply frequency (F), which ensures the motor’s air-gap magnetic flux remains essentially stable—ultimately enabling smooth speed regulation.
The specific principle can be broken down into the following key points:
- Core of Constant Magnetic Flux: According to motor theory, the motor’s air-gap magnetic flux is proportional to the stator voltage and inversely proportional to the frequency (Φ ∝ V/F). Maintaining a constant V/F ratio prevents magnetic flux saturation (during overvoltage) or insufficient magnetic flux (during undervoltage), thus ensuring stable motor output performance.
- Low-Frequency Compensation: In practical applications, additional voltage compensation (commonly referred to as “torque boost”) is necessary in the low-frequency range (e.g., below 5Hz). This compensates for magnetic flux attenuation caused by voltage drops across the motor’s stator resistance, ensuring the motor still delivers sufficient torque at low speeds.
- Implementation of Speed Regulation: Motor speed is adjusted by modifying the output frequency (F), as speed is directly proportional to frequency (n ∝ F). Simultaneously, the output voltage (V) is adjusted proportionally to maintain the preset V/F ratio, allowing for smooth speed regulation across a wide range.
This control method boasts a simple structure and low cost, making it ideal for scenarios like fan and pump systems where high dynamic response is not required. However, it has relatively limited performance in terms of speed regulation accuracy and low-speed torque.