How to Improve the Speed Regulation Accuracy of V/F Control?

I. Core Optimization Measures

1. Incorporate Speed Feedback (Closed-Loop V/F Control)
   Install an encoder or Hall sensor on the motor shaft to real-time detect the actual speed, compare it with the target speed, and dynamically correct the output frequency via PID regulation. This reduces the speed error from ±2%–5% (in open-loop mode) to ±0.5%–1%.
   Suitable for scenarios with moderate accuracy requirements (e.g., conveyor synchronization), and its cost is lower than that of vector control.
2. Optimize V/F Curve Design
   • Segmented V/F Curve: Set different V/F ratios for distinct frequency ranges based on motor characteristics (e.g., increase voltage compensation in the low-frequency range and moderately reduce it in the high-frequency range) to minimize nonlinear errors.
   • Custom Curve Calibration: Manually correct the voltage value at specific frequency points through no-load or load tests to offset individual motor differences (e.g., deviations caused by varying winding resistance or iron core losses).
3. Dynamic Parameter Compensation
   • Temperature Compensation: Detect the temperature of the motor windings and real-time adjust the resistance voltage drop model (copper loss increases as temperature rises) to prevent insufficient torque at low frequencies or magnetic flux saturation at high frequencies.
   • Load Compensation: Estimate the impact of load fluctuations on speed by detecting changes in output current, and automatically fine-tune the frequency (e.g., slightly increase the frequency when the load increases to maintain stable speed).
4. Suppress Grid and Load Interference
   • Install an input filter to reduce the impact of grid voltage fluctuations on the output voltage, avoiding deviations in the V/F ratio caused by unstable voltage.
   • For shock loads (e.g., mixers), extend the acceleration or deceleration time setting, or enable the “slip compensation” function (estimate the slip rate based on load current and compensate the frequency accordingly).

II. Advanced Technical Methods

1. Adopt Sensorless Vector Control (Open-Loop Vector Control)
   Although it does not belong to pure V/F control, it retains the simplicity of V/F control. It estimates motor speed and torque through mathematical models, achieving an accuracy of ±0.5% (without feedback) and balancing cost-effectiveness and performance.
2. Motor Parameter Self-Learning
   Utilize the inverter’s “static self-learning” function to automatically identify motor parameters (such as resistance and inductance), optimize the V/F curve and compensation algorithm, and reduce errors caused by parameter mismatches.

III. Applicable Scenarios and Limitations