Publish Time: 2026-01-06 Origin: Site
Frequency converters have unique advantages：
Excellent speed control performance. It offers a wide speed control range and continuous frequency adjustment. The output frequency ranges from 0 to 400 Hz (0 to 120 Hz for general-purpose models). It provides high speed regulation accuracy for pumps and fans, reaching 0.1% (due to a frequency resolution of 0.1% and stepless speed control). When using vector control, the accuracy can reach 0.01%. The system also features excellent speed stability, maintaining a constant set value with fast dynamic response (10 to 30 ms). Since its introduction, it has almost completely replaced all previous speed control methods, such as DC speed control, slip speed control, cascade speed control, and wound-rotor feedback speed control.
High energy-saving efficiency. Generally, the energy-saving rate is at least 10%, and can even reach 40% to 50%. This depends on the type of load, the operating conditions and parameters used, as well as the specific energy-saving methods, measures, and parameter settings implemented.
Precisely because of the above two outstanding advantages, frequency converters are developing at an annual growth rate of 20%. Currently, the penetration rate abroad is as high as 80% to 85%, while in China, it has reached 25% to 30%.
They serve as an effective means to achieve energy conservation, reduced consumption, low-carbon emissions, increased efficiency, cost reduction, improved product quality, and electrical automation. It is estimated that their development will not decline over the next 20 years; they possess strong vitality and a very broad development.
The technical sophistication of frequency converters has evolved gradually over time. It has advanced progressively alongside increasing application requirements, technological developments, improvements in component quality, expanded functionality, and progress in automation technology.
Generally, the primary factor to consider when evaluating product quality is the control method of the frequency converter. The control method is paramount in determining the performance of the converter, and it depends on the software programming technology employed. With the advancement of the times and technology, the control methods of frequency converters (Table 2-1) have evolved to include:
V /f=C，Belongs to open-loop control.
SVPWM Space Vector Voltage Control, which belongs to open-loop control.
Vector Control (VC), which belongs to closed-loop control. It involves four parameters: current (I), flux, torque (T), and speed (n). Generally, for the inner loop, either T or I is selected, while for the outer loop, n (or ω) is used.
Direct Torque Control (DTC), which belongs to closed-loop control, can provide 400% torque when speed (n) is 0.
| Control Method | U/F = C Control | U/F = C Control | SVPWM Space Vector Control | Vector Control (VC) | Vector Control (VC) | Direct Torque Control (DTC) |
| Speed Ratio (i) | <1：40 | 1：60 | 1：100 | 1：100 | 1：100 | 1：100 |
| Starting Torque (at 3 Hz) | 150% | 150% | 150% | 150% | 150% at Zero Speed | 150%-400% at Zero Speed |
| Static Speed Accuracy | ±（0.2-0.3） | ±（0.2-0.3） | ±0.2 | ±0.2 | ±0.2 | ±0.2 |
| Applicable Scenarios | General Fans and Pumps | High-precision speed regulation and control | General Industrial Speed Control | All speed regulatio | Servo Drive、High-precision Transmission、Torque Control | Heavy-duty Start-up、Super Heavy-load Torque Control System、Constant Torque Load with Large Fluctuations、Electric Traction Locomotive、Metro |
Check if there are any issues with the wiring and peripheral devices.
The inverter installation and wiring must be neat and aesthetically pleasing. Improvised or non-standard installations are strictly prohibited, as is the removal of required protective facilities, which violates safety requirements. The use of non-standard wires or substandard crimp terminals during installation is not allowed. Powering on for testing is prohibited before the terminal connection screws are fully tightened. The base of the crimp terminals must be insulated, and the insulation clearance must meet the specified requirements.
When the cable length between the inverter and the motor exceeds approximately 40m, or when the cable is routed inside iron conduit or metal flexible conduit exceeding approximately 20m, especially in cases where a single inverter drives multiple motors, the distributed capacitance to ground on the inverter output lines can become very large. Excessive capacitive current may damage the inverter's inverter module (IGBTs). An AC reactor should be connected to the inverter output terminals first. (The reactor filters out PWM harmonics, significantly reducing the capacitive current in the distributed capacitance.) Then, connect it to the downstream cabling, and finally to the load. Furthermore, the output AC reactor helps extend the insulation life of the motor and reduces heat generation in the output power transistors.
A circuit breaker or fast-acting fuse must be installed on the inverter's input side. This is a safety necessity to prevent major disasters in case the inverter fails and cannot automatically disconnect from the power supply, especially for unattended equipment. Inverters with a power rating exceeding 22kW must be equipped with a DC reactor. The purpose is to mitigate the inverter's waveform impact on the power grid, extend the lifespan of the rectifier bridge, and improve the power factor. Specifically, DC reactors are mandatory for inverters above 45kW. Additionally, an AC reactor should be installed on the input side, and an output reactor on the output side. In applications with high environmental protection requirements, even smaller-rated inverters should be fitted with these three types of reactors. This is beneficial for improving grid waveforms, protecting against power line overvoltage or interference, and extending the life of the rectifier bridge.
Check that the wiring is correct and secure.
Check the inverter's installation space, location, ventilation, and safety conditions to ensure they comply with the requirements specified in the product manual. Check that the main circuit wiring is correct: Ensure the input terminals (R, S, T) and output terminals (U, V, W) are properly connected; under no circumstances should the input and output be reversed. The negative terminal (N) of the inverter's internal DC circuit (used for connecting braking resistors) must not be connected to the AC power neutral line. (Many electricians mistakenly believe that N should be connected to the neutral line because N represents neutral in AC power systems.) Neither should it be connected to ground. Verify that the inverter's grounding terminal (usually marked "G" or with the ground symbol) or the chassis is reliably grounded.
Check that all control wiring is correct and error-free, that the layout is reasonable, and that measures have been taken to avoid interference during installation. For systems with feedback, verify the electrical phase of the feedback signal.
During the inspection, pay special attention to ensure that all terminal screws are fully tightened. Gently pull on the wires to verify the connections; if any screw is found loose, tighten it immediately.
Check the working environment of the inverter connected to the power grid.
An inverter acts as an interference source itself, but it is also susceptible to external interference. If the power grid to which the inverter is connected contains high-frequency impact loads (such as welding machines or electroplating power supplies), the inverter may be disturbed and trigger protective trips. In such cases, anti-interference measures should be implemented.
These measures include installing input/output electromagnetic filters (or adding ferrite cores), replacing signal twisted-pair wires with shielded twisted-pair cables, and reducing the impedance at the signal input end to eliminate the interference.
Daily maintenance and servicing are the foundation for the safe operation of inverters. Proper daily maintenance allows issues to be identified and addressed promptly. This ensures that the inverter operates at its optimal performance for extended periods, reduces the occurrence of downtime, and improves overall operational efficiency.
During daily operation, the inverter's running status can be evaluated through auditory checks, visual inspections, tactile feedback, and olfactory detection. The general patrol/content of inspection includes:
Whether the ambient environment, temperature, and humidity meet the requirements.
Check for dust accumulation on the inverter's air inlets and outlets, and whether they are blocked by dust.
Whether the inverter's noise, vibration, and odor are within normal ranges.
Whether the inverter's operating parameters and panel display are normal.
The above information covers some aspects of inverters. This is only a partial list, and I hope it will be helpful to everyone.