I. What is the difference between a frequency converter and a frequency converter power supply?
Regarding power supplies, everyone may know that frequency converters and variable frequency power supplies are auxiliary devices for charging electrical appliances, but many people don't understand what a variable frequency power supply or frequency converter is. As technology advances, electrical appliances are constantly being updated, and auxiliary devices are also constantly changing. Below, we will explain in detail the differences between frequency converters and variable frequency power supplies. Only by understanding these auxiliary devices can we understand the underlying principles when purchasing them, ensuring a more informed and reliable purchase.
What is a variable frequency power supply (VFD)? A VFD converts the AC power from the mains supply from AC→DC→AC to a pure sine wave. The output frequency and voltage can be adjusted within a specific range. Unlike variable frequency drives used for motor speed control, it also differs from ordinary AC power supplies. An ideal AC power supply is characterized by stable frequency, stable voltage, zero internal resistance, and a pure sine wave voltage waveform (no distortion). VFDs closely approximate an ideal AC power supply, hence their increasing use as a standard power source in advanced cultural and developmental regions. This provides a superior power grid environment for utilities and facilitates objective evaluation of the performance of electrical equipment and products. As you know, VFDs come in two types based on their structure: linear amplifier type and SPWM switching type.
What is a frequency converter? A frequency converter consists of circuits such as AC-DC-AC (modulated wave). The standard name for a frequency converter is a variable frequency speed controller. Its output voltage waveform is a square wave pulse with multiple high-order harmonic components. The voltage and frequency are not adjusted independently but change proportionally, which cannot meet the requirements of AC power supply. Generally, it cannot be used as a power source and is usually only used for speed regulation of three-phase asynchronous motors.
Because the entire circuit of a frequency converter power supply consists of information exchange, DC-AC switching, and filtering components, the output voltage and current signal waveforms are pure sine waves, making it an ideal AC power supply system. It very easily approximates the ideal AC power supply system.
The principle and main functions of a frequency converter: A frequency converter is an electrical energy control device that uses the switching operation of power semiconductor devices to convert the power of an industrial power supply to another frequency. It can be divided into AC-AC frequency converters and AC-DC-AC frequency converters. An AC-AC frequency converter can directly convert alternating current (AC) into AC with variable frequency and voltage. An AC-DC-AC frequency converter first rectifies the AC power into direct current (DC) through a rectifier, and then uses an inverter to convert the DC power into AC with variable frequency and voltage.
II. How to handle overcurrent in frequency converters
Overcurrent or overload faults are common faults of frequency converters. Overcurrent refers to the current flowing through the frequency converter exceeding its rated range.
1. If the power supply of the frequency converter is missing a phase, the output circuit is broken, or there is a short circuit to ground fault between phases of the motor winding, it may cause overcurrent.
2. Sudden changes in motor load may cause a large inrush current to flow through the frequency converter, triggering overcurrent protection. Restarting the frequency converter will resolve the issue. If the frequency converter frequently malfunctions, the load should be checked or a higher-capacity frequency converter should be replaced.
3. Electromagnetic interference can affect the circuitry of motors or frequency converters. During operation, frequency converters generate numerous interfering electromagnetic waves due to rectification and frequency conversion. These high-frequency electromagnetic waves can interfere with nearby instruments and meters. Similarly, if external electromagnetic waves interfere with the motor, it can cause excessive leakage current in the motor, triggering the frequency converter's overcurrent protection. If electromagnetic waves interfere with the frequency converter itself, it may cause errors in the control signals output by the frequency converter, leading to overcurrent.
4. During the operation of an electric motor, a large parasitic capacitance is generated between the windings and the casing, and between the cable and the ground. Current will flow to the ground through the parasitic capacitance (leakage current), which will cause overcurrent.
5. If the inverter capacity is not selected properly or does not match the load capacity, it may cause the inverter to malfunction, resulting in overcurrent or overload faults, or even damage to the inverter.
6. Overload faults include inverter overload and motor overload. Most overload faults are caused by excessively short acceleration time, excessive DC braking force, excessively low grid voltage, or excessive load. Overload means that the selected inverter and motor cannot drive the load.
