2.7 Variable Frequency Drive Selection Guide
The inverter can provide three control modes: general V/F, SVC, and VC.
When selecting an inverter, it is necessary to first clarify the technical requirements for variable frequency speed regulation of the system, the specific application scenarios of the inverter, and the characteristics of the load. Comprehensive considerations should be made from factors such as matching motors, output voltage, rated output current, etc., to choose a model that meets the requirements and determine the operating mode.
The basic principle is that the motor’s rated load current should not exceed the inverter’s rated current. Generally, select the motor capacity specified in the inverter manual, and compare the rated currents of the motor and the inverter. The overload capacity of the inverter is only meaningful during startup and braking. Short-term overloads during operation will cause changes in the load speed. If high speed accuracy is required, consider selecting a model with higher overload capacity.
For fan and pump types: Low overload capacity is required because the load torque is proportional to the square of the speed. When running at low speeds, the load is lighter (except for Roots blowers). Since this type of load does not have special requirements for speed accuracy, select the square torque V/F mode.
Constant torque load: Most loads have constant torque characteristics, but generally do not have high requirements for speed accuracy and dynamic performance. For example, extruders, mixers, conveyors, in-plant transport carts, and crane translation mechanisms. For selection, you can choose the multi-section V/F operating mode.
The controlled object has certain dynamic and static index requirements: Such loads generally require relatively stiff mechanical characteristics at low speeds to meet the dynamic and static index requirements of the control system for production processes. For selection, you can choose the SVC control mode.
The controlled object has higher dynamic and static index requirements: For occasions with high requirements for speed accuracy and dynamic performance, and for high-precision synchronous control, you can choose the VC control mode. For example, elevators, papermaking, and plastic film processing production lines.
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