Variable frequency power supplies are very close to ideal AC power supplies, boasting stable frequency and voltage, zero internal resistance, and a pure sinusoidal voltage waveform (no distortion). Therefore, many developed countries use variable frequency power supplies as standard power sources, providing the best power supply environment for electrical appliances.
How a variable frequency power supply works
The entire circuit of a variable frequency power supply consists of AC → DC → AC → filtering (i.e., AC → DC → AC → filtering). Specifically, a 220V AC power supply is first converted to DC using a rectifier bridge, and then converted back to AC using an inverter bridge. The frequency of the resulting AC power can be controlled during the inversion process, resulting in pure sinusoidal voltage and current waveforms, very close to ideal AC power supply. It can output the voltage and frequency of any power grid in the world. This is different from a frequency converter.
A frequency converter is an energy control device that uses the switching action of power semiconductor devices to convert a commercial frequency power supply to another frequency. It can be categorized as an AC→AC converter or an AC→DC→AC converter. An AC-to-AC inverter directly converts AC power into variable-frequency and voltage AC power. An AC-to-DC-to-AC inverter first rectifies AC power into DC power through a rectifier, then converts this DC power into variable-frequency and voltage AC power through an inverter.
Variable-Frequency Power Supply Classification Principles
Variable-frequency power supplies are primarily divided into two types: transistor-amplified and PWM-switched. The DP series variable-frequency power supply, with a microprocessor as its core and utilizing PWM technology and sinusoidal pulse-width modulation, offers a single-unit capacity of up to 1000 kVA. Its output utilizes an isolation transformer for enhanced overall stability. It features strong load adaptability, high-quality output waveforms, smooth operating waveforms, simple operation, compact size, and light weight. It also incorporates short-circuit, overcurrent, overvoltage, and overheating protections to ensure reliable operation.
Variable Frequency Power Supply Repair
Electronic devices rely on reliable variable frequency power supplies. AC variable frequency power supplies are widely used in almost all electronic devices due to their compactness, lightness, and high efficiency. Let's learn about several common variable frequency power supply faults, analyze their causes, and provide some repair tips.
Variable Frequency Power Supply Fault 1: Fuse Blowing
Generally, a blown fuse indicates a problem with the power supply's internal wiring or excessive load (inrush current). Because variable frequency power supplies operate at high voltage and high current, grid voltage fluctuations and surges can cause a transient increase in current within the power supply, potentially blowing the fuse. Focus on inspecting the rectifier diodes, high-voltage filter electrolytic capacitors, and inverter power switching transistors (IGBTs) at the power supply input to check for breakdown, open circuits, or damage. If the fuse is indeed blown, first check the components on the circuit board to see if they are burnt or if there is any electrolyte leakage. If none of these conditions are found, use a multimeter to test the switching transistors for breakdown and short circuits. Importantly, do not replace a damaged component and immediately turn it on. This could damage the replaced component if other high-voltage components remain faulty. A thorough inspection and measurement of all high-voltage components in the circuits mentioned above is essential to completely rule out a blown fuse.
Inverter Power Supply Fault 2: No AC Voltage Output or Unstable Voltage Output
If the fuse is intact, there will be no AC voltage output at any level under load. This condition is primarily caused by the following: an open or short circuit in the power supply, a malfunction in the overvoltage or overcurrent protection circuit, a faulty auxiliary power supply, a non-functioning oscillator circuit, excessive power load, a breakdown of the rectifier diode in the high-frequency rectifier and filter circuit, or leakage in the filter capacitor. After using a multimeter to measure the secondary components and ruling out high-frequency rectifier diode breakdown or a load short circuit, if the output is zero, the power supply's control circuit is definitely faulty. If there is some voltage output, the upstream circuitry is functioning normally, and the fault lies in the high-frequency rectifier and filter circuits. The high-frequency filter circuit primarily consists of a rectifier diode and a low-voltage filter capacitor, creating a DC voltage output. A breakdown in the rectifier diode will result in no voltage output, while leakage in the filter capacitor can cause unstable output voltage. Using a multimeter to statically measure the corresponding components can identify damaged components.
Inverter Power Supply Fault #3: Poor Power Supply Load Capacity
Poor power supply load capacity is a common fault, often found in older or older power supplies. The main causes are aging components, unstable switching transistors, and inadequate heat dissipation. Check for heat and leakage from the voltage regulator diode, damage to the rectifier diode, and damage to the high-voltage filter capacitor.
Inverter Power Supply Maintenance
Whether you're using a single-phase or high-power three-phase inverter power supply, minor faults are inevitable during operation. After all, inverter power supplies are machines, and machines can malfunction. To prevent these minor faults from recurring, regular maintenance is essential. Therefore, after extended use, inverter power supplies require regular maintenance.
1. Regularly clean the air filter, cooling ducts, and internal dust.
2. Regularly check screws, bolts, and other components for looseness.
3. Clean conductors and insulators promptly with alcohol.
4. Verify that the UV/W phase waveforms are sinusoidal.
5. Measure the square wave of each driver circuit waveform for distortion.
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