How to Deal with Frequency Inverter Interference?

Introduction

Frequency inverters, also known as variable frequency drives (VFD) or variable speed drives, are crucial components in modern industrial applications. They enable precise control over motor speed and torque, improving efficiency and performance. The working principle of frequency inverters inherently generates strong electromagnetic interference. This article discusses the working principles of frequency inverters and outlines effective methods for mitigating interference.

Desembalaje de las interferencias armónicas

Frequency inverters convert a fixed frequency AC input into a variable frequency output to control motor speed. This process generates harmonics, which are multiples of the fundamental frequency. Harmonic interference can distort voltage and current waveforms, leading to reduced efficiency and potential damage to sensitive equipment.

1. Herramientas de detección y vigilancia:

Las herramientas tradicionales, como amperímetros y voltímetros, cumplen su función, pero la integración de pantallas digitales, como los tacómetros, mejora la capacidad de supervisión al convertir las magnitudes analógicas en valores digitales. Esto ayuda a identificar y cuantificar las frecuencias armónicas.

2. Dispositivos de control para una gestión precisa:

Para garantizar un control preciso frente a las interferencias armónicas, entran en juego los módulos analógico-digitales (AD) y los controladores lógicos programables (PLC). Estos dispositivos convierten eficazmente las magnitudes analógicas en realimentación digital, lo que permite matizar las estrategias de control y mitigación.

3. VFD Ajustes:

Fine-tuning the inverter settings proves crucial in mitigating harmonic interference. Users can choose output parameters like voltage or current signals, providing adaptability to specific operational needs. This flexibility is essential for tailoring the frequency converter’s output to meet diverse requirements.

Interferencias por emisiones conducidas de radiofrecuencia

Conducted emissions occur when high-frequency noise generated by the inverter propagates along power lines and other conductors. This type of interference can affect the operation of nearby equipment connected to the same power supply, causing malfunctions or even damage.

1. Protocolos de comunicación:

El aprovechamiento de métodos de comunicación avanzados como MODBUS, PROFIBUS o PROFINET proporciona una solución integral a las interferencias por emisiones conducidas de radiofrecuencia. Estos protocolos permiten recopilar y controlar datos en tiempo real, minimizando el impacto de las interferencias en los equipos que comparten la misma red eléctrica.

2. Prácticas de cableado:

Para minimizar las interferencias, es esencial seguir unas prácticas de cableado meticulosas. Garantizar una separación clara entre las líneas de alimentación y señal y mantenerlas alejadas de las líneas de entrada y salida del inversor minimiza el potencial de interferencias, independientemente de la distancia entre el equipo y el convertidor de frecuencia.

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Addressing Radio Frequency Radiation Interference

Radiated interference happens when the high-frequency signals generated by the frequency inverter are emitted into the surrounding environment as electromagnetic waves. These waves can interfere with the operation of nearby electronic devices, particularly those with sensitive radio frequency components.

1. Medidas eficaces de blindaje:

While convertidores de frecuencia typically feature iron shells for shielding, additional measures are necessary for preventing radiation interference. Shielding the output lines with steel pipes fortifies the electromagnetic interference prevention, ensuring minimal impact on nearby electronic equipment.

2. Consideraciones de distancia:

Maintaining a considerable distance between signal lines and main circuit lines, along with control lines, is pivotal. This separation minimizes cross-interference, creating a more controlled environment for electronic equipment operating in proximity to the frequency converter.

3. Puesta a tierra para mejorar el apantallamiento:

La eficacia de las capas de apantallamiento para prevenir las interferencias de radiación depende de una conexión a tierra fiable. Garantizar la conexión a tierra de las capas de blindaje mejora su capacidad para neutralizar la radiación electromagnética, lo que hace que las medidas de blindaje sean más sólidas.

What Are the Main Steps to Solve On-Site Interference?

1. Adopting Software Anti-Interference Measures

Implementing software solutions such as adaptive filtering, error correction algorithms, and noise suppression techniques can significantly reduce the impact of interference. These measures can help in differentiating between actual signals and noise, improving the reliability of the system.

2.Perform Correct Grounding

Proper grounding is essential to mitigate interference from frequency inverters. Ensure that all components are correctly grounded to provide a path for unwanted noise to dissipate safely. Grounding also helps to reduce potential differences that can cause interference.

• The main circuit terminal PE (E, G) of the inverter must be grounded.
• The grounding wire of the inverter should have a cross-sectional area of at least 4mm² and be kept within 20 meters in length.
• Other electrical equipment’s protective and operational grounding should have separate grounding poles and ultimately converge at the electrical grounding point of the distribution cabinet.
• Shielded grounds for control signals and main circuit wires should also have separate grounding poles and ultimately converge at the electrical grounding point of the distribution cabinet.

3.Block Interference Sources

Shielding the inverter and its components can prevent interference from spreading. Use metal enclosures and shielding materials to block electromagnetic waves from escaping and affecting other devices. Properly shielded cables and components can also minimize conducted and radiated emissions.

4.Reasonable Wiring

Organize wiring layouts to minimize the risk of interference. Keep power and signal cables separate, and avoid running them parallel to each other. Use twisted pair cables for signal lines to reduce the impact of electromagnetic fields. Proper wiring practices can significantly reduce both conducted and radiated interference.

5.Isolation of Interference

Using isolation transformers or optocouplers can help in breaking the path of interference. These devices ensure that signals can be transmitted without direct electrical connection, reducing the potential for noise to propagate.

6. Set Filters in the System Circuit

Filters are used to suppress interference signals conducted through power lines:

• Input Filters: Reduce conducted interference from the power supply. They include line filters (composed of inductors to increase impedance at high frequencies) and radiation filters (composed of high-frequency capacitors to absorb high-frequency harmonic components).
• Output Filters: Reduce high-order harmonic components in the output current. They also mitigate additional torque caused by harmonic currents in motors.

7.Using Reactors

Reactors, or inductors, can be added to the input and output of frequency inverters to limit the rate of voltage change and reduce harmonic distortion. Reactors help in smoothing the current waveform, thus minimizing harmonic interference and improving the overall power quality.

Conclusión

Managing interference from frequency inverters is essential for maintaining the performance and reliability of industrial systems. By implementing appropriate measures such as software adjustments, proper grounding, shielding, reasonable wiring, isolation, filtering, and using reactors, the impact of electromagnetic interference can be significantly reduced, ensuring the smooth operation of frequency inverters and nearby electronic equipment.