Introduction:

There are four primary motor control methods used to regulate induction motors connected to variable frequency drives (VFDs). These methods are: Voltage/Frequency (V/F), V/F with Encoder, Open-Loop Vector, and Closed-Loop Vector. This article will delve into these four control methods, aiding in your comprehension of the attributes of each method, and thereby facilitating your selection of the appropriate CHRH brand VFDs.

V/F

V/F Control can be regarded as the simplest motor control method. This mode of control is often the preferred choice due to its plug-and-play nature and straightforward operation. A series of electrical pulses is generated as the motor shaft completes each revolution; these pulses are conveyed back to the VFD and employed as speed feedback. The V/F control method typically does not employ encoders. The absence of encoders can reduce customer costs and simplify wiring, endowing V/F-controlled VFDs with the advantage of lower procurement expenses. Moreover, because V/F control allows for facile high-frequency operation, it finds extensive application in machinery such as machine tools. Additionally, the V/F control method permits multiple motors to operate through a single VFD. When multiple motors are operated, all motors start and stop simultaneously, following the same rotational speed. Due to the diverse characteristics of V/F VFDs, most fans and pumps employ V/F control mode.

The distinction of V/F control from other control methods lies in how the output voltage sent to the motor is determined. V/F control establishes the ratio of voltage to frequency that the motor must adhere to. Under a given reference speed, the corresponding variable voltage will be outputted to the motor.

V/F with Encoder 

While V/F control typically excludes encoders, V/F control mode with encoder feedback can achieve enhanced speed regulation and higher frequency operation. Building upon the general features of standard V/F control, V/F control with an encoder allows for preset frequency and voltage. Compared to standard V/F VFDs, those integrated with encoders entail a slightly higher purchase cost.

Open-Loop Vector And Closed-Loop Vector

Open-Loop Vector control, often termed sensorless vector control, implies the absence of encoders. This method determines the optimal output voltage required for the motor to run through vector algorithms, achieved by employing current feedback from the motor. Open-Loop Vector control realizes more flexible motor regulation and boasts independent control over motor speed and torque. In the case of CHRH F-series High-Performance Vector Inverters, under Open-Loop Vector control, the startup torque is 150% at 0.25 Hz.

Similarly, Closed-Loop Vector control utilizes vector algorithms to ascertain output voltage, yet it incorporates encoders. Encoder feedback is paired with vector control methodology, granting the motor a certain starting torque even at 0 Hz. For instance, with CHRH F-series High-Performance Vector Inverters, the startup torque at 0 Hz is 180%. This feature is advantageous for applications that necessitate maintaining load without running, providing the application with 180% startup torque at 0 Hz.

Conclusion:

The above provides a concise elucidation of the four VFD control methods: V/F Control, V/F with Encoder Control, Open-Loop Vector Control, and Closed-Loop Vector Control. All four of these control modes are supported by CHRH series products. Feel free to reach out to our global sales personnel anytime, anywhere, to obtain further information.