With the advancement of inverter technology, AC motor frequency converters are becoming increasingly popular for speed control. These devices offer enhanced precision, efficiency, and product quality in industrial applications, contributing significantly to automation. The performance of the drive system ensures better control and substantial energy savings across various production scenarios.
1. Application of Inverters
In China, electric motors account for 60%–70% of national electricity consumption. Fans and pumps alone consume about one-third of the total power. Traditional methods like adjusting valves or dampers lead to high energy waste. Since fans and pumps are torque loads, reducing their speed can dramatically cut energy use. Using frequency converters to regulate flow is an effective way to save energy, often reducing power consumption by 20%–50%, making it a highly beneficial solution.
Many machines require precise motor speed control. While DC systems were once used due to their superior control, they are complex and hard to maintain. As inverter technology matures, AC speed control is now replacing DC systems, offering better performance and flexibility for various process needs.
By using inverters, motors can start smoothly with reduced current, allowing for stepless speed control and easy acceleration/deceleration. This not only improves performance but also saves energy, leading to wider adoption in both industrial and daily applications.
2. Existing Problems and Solutions
As inverters become more widely used, issues such as harmonics, noise, vibration, load mismatch, and heat generation have become more common. This section discusses these problems and provides practical solutions to improve system performance and reliability.
3. Harmonic Issues and Mitigation Strategies
Most general-purpose inverters consist of rectification, filtering, and inverter stages. The output voltage contains harmonic components that can affect motor performance. Lower-order harmonics may cause torque ripple, while higher-order harmonics increase leakage currents. To reduce these effects, several strategies can be employed:
(1) Increase Internal Impedance – Using a transformer with high short-circuit impedance can help suppress harmonics by limiting reactive power from the DC filter capacitor.
(2) Install Reactors or Filters – Adding reactors or LC filters at the inverter output can absorb harmonics and reduce their impact on the system.
(3) Multi-Phase Operation with Transformers – Using transformers in multi-phase configurations (e.g., 12-pulse) helps reduce low-order harmonics effectively.
(4) Dedicated Harmonic Filters – Special filters can detect and cancel out harmonic currents, improving power quality and system stability.
4. Noise and Vibration Challenges
Inverter-driven motors may produce noise and vibration due to high harmonic content in the output waveform. These harmonics can resonate with mechanical components, causing unwanted noise and vibrations. Common mitigation techniques include adding AC reactors, adjusting U/f ratios, and ensuring proper resonance checks between the motor and load system.
5. Load Matching and Solutions
Understanding the type of load is crucial when selecting an inverter. Loads can be categorized into constant torque, fan/pump, and constant power types. Each requires specific inverter settings to ensure optimal performance and longevity. For example, constant torque loads need inverters with strong overload capabilities, while fan/pump loads benefit from U/f control modes.
6. Heat Dissipation and Cooling Methods
Heat is primarily generated in the main circuit of the inverter, accounting for about 98% of losses. Proper cooling is essential for reliable operation. Common methods include built-in fans, maintaining ambient temperatures within safe limits, and ensuring adequate ventilation to extend the life of the inverter and maintain stable performance.
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