The interference of the inverter in the application mainly includes: high harmonics, noise and vibration, load matching, and heat generation. These disturbances are unavoidable because the input part of the inverter is a rectifier circuit and the output part is an inverter circuit. They are all composed of nonlinear components that function as switches, and in the process of breaking the circuit, Generates higher harmonics that distort the voltage and current waveforms of its input supply and output. The following is an analysis of harmonic problems and proposes corresponding measures.
For inverters with smaller capacities, the influence of higher harmonics is smaller. However, when the capacity is large or large, it is necessary to deal with high-order harmonic interference caused by high-order harmonic currents, otherwise it will affect the equipment and the detection components, and in serious cases, these devices may malfunction. According to the British ACE report, the sensitivity of various objects to higher harmonics is as follows: the motor has no effect below 10%~20%; the instrument voltage distortion is 10%, the current distortion is 10%, the error is below 1%; the electronic switch exceeds 10% will cause a malfunction; more than 5% of the computer will go wrong. In view of the above, in the industrial field, measures must be taken to reduce the interference and to suppress the interference within the allowable range.
1. Disconnect the interference propagation path (1) The propagation of interference is often propagated through a common ground line. Separating the grounding of the power line from the grounding of the control line is the fundamental way to cut this path by connecting the ground terminal of the power unit to the ground line and the ground terminal of the control unit to the metal housing of the unit disk.
(2) When the signal line is close to the wire with the interference source, the interference will be induced to the signal line, causing the signal to be interfered. The wiring separation is effective for eliminating such interference. In actual engineering, high-voltage cables, power cables, and control cables are often separately routed from instrument cables and computer cables, and different bridges are separated. The control line of the frequency converter is also preferably routed perpendicularly to its main circuit line.
2. Suppressing higher harmonics (1) Install line reactors on the front side of the inverter to suppress overvoltage on the power supply side and reduce the current distortion generated by the inverter to avoid serious interference to the main power supply.
The solution is inexpensive, but the efficiency of limiting harmonics is limited, and an unacceptable voltage drop loss occurs when the reactance is too large.
(2) Install an LC passive filter in front of the inverter to filter out the higher harmonics. Usually, the 5th and 7th harmonics are filtered out, but the method is completely dependent on the power supply and load, and the flexibility is small.
(3) Set a special filter to detect the inverter and phase, and generate a current with the same amplitude and opposite phase of the harmonic current, which is passed to the inverter, so that the harmonic current can be effectively absorbed.
(4) When the environment near the equipment is subject to electromagnetic interference, an anti-radio frequency interference filter should be installed to reduce the conducted emission of the main power supply, and measures must be taken to shield the motor cable.
(5) When the motor cable length is greater than 50m or 80m (unshielded), in order to prevent the instantaneous overvoltage when the motor starts, reduce the leakage current and noise of the motor to the ground, protect the motor, and install a reactor between the inverter and the motor. .
(6) Increase the internal impedance of the inverter power supply. Usually, the internal impedance of the power supply device can buffer the reactive power of the DC filter capacitor of the inverter. The larger the internal impedance, the smaller the harmonic content. This internal impedance is the short-circuit impedance of the transformer. Therefore, when selecting the inverter power supply, it is best to choose a transformer with a short circuit impedance.
(7) Multi-phase operation with transformers. The general-purpose inverter is a six-pulse rectifier, so the harmonics generated are large. If multi-phase operation of the transformer is used, the phase angles are different by 30°. For example, the combination of Y-Δ and Δ-Δ constitutes a 12-pulse effect, which can reduce the low-order harmonic current and suppress the harmonics well.
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Capacitor For Electric Furnace, commonly referred to as capacitors, are capacitors, expressed in the letter C.Definition 1: a capacitor, as the name implies, is a "charging vessel", a device that holds charge.Capacitor.Capacitors are one of the most widely used electronic components in electronic equipment. They are widely used in the fields of interleaving, coupling, bypass, filtering, tuning circuit, energy conversion and control.Definition 2: a capacitor consisting of any two conductors (including wires) that are insulated from each other and are very close together.
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