Frequency converter harmonics management method - Database & Sql Blog Articles

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(1) Isolation, shielding and grounding of the inverter: The power supply of the inverter system is independent of the power supply of other equipment. Or install an isolating transformer on the input side of the frequency converter and other electrical equipment. Or put the inverter into the iron box and ground the iron box. At the same time, the output power of the inverter should be as far as possible from the control cable laying (not less than 50mm spacing). It must be crossed at an orthogonal angle when laying close to the ground. When parallel laying, the parallel section length should be shortened (not more than 1mm), and the output cable should be worn through the steel pipe. The steel pipe is electrically connected and grounded reliably.
(2) Adding AC reactor and DC reactor: When the inverter is used in the distribution transformer capacity is greater than 500KVA, and the transformer capacity is more than 10 times of the inverter capacity, an AC reactor is installed on the input side of the inverter. When the output voltage of the distribution transformer is unbalanced and the unbalance ratio is greater than 3%, the peak value of the input current of the inverter is large, which will cause the conductor to overheat. At this time, an AC reactor is required. In severe cases, a DC reactor is required. )
(3) Adding a passive filter: the passive filter is installed on the AC side of the inverter, and the passive filter is composed of L, C, and R components to form a harmonic resonance circuit. When the harmonic frequency of the LC circuit is once and some time When the higher harmonic currents have the same frequency, high harmonics can be prevented from flowing into the grid. Passive filters are characterized by low investment, high frequency, simple structure, reliable operation and easy maintenance. The disadvantage of the passive filter is that the filter is susceptible to system parameters, and it is possible to amplify certain subharmonics, and it is expensive and bulky.
(4) Adding a source filter: As early as the early 1970s, Japanese scholars proposed the concept of an active filter. The source filter detects high-order harmonics in the current and inputs and higher harmonics based on the detection results. The components have opposite phase currents for real-time compensation of harmonic currents. Compared with passive filters, it has high controllability and fast response, and has a multi-function. It also eliminates the danger of resonance with the system impedance. It also automatically tracks the harmonics that compensate for the changes. However, it has the characteristics of large capacity and high price.
(5) Adding reactive power static type reactive power compensation device: For large impact load, static reactive power compensation device with reactive power can be installed to obtain the reactive power demand for quick compensation of load and improve power factor. Filter system harmonics, reduce harmonic current injection into the system, stabilize bus voltage, reduce three-phase voltage imbalance, and improve the harmonics of the power supply system. Among them, the self-saturated reactance type (SR type) has the best effect, and its electronic components are few, the reliability is high, the reaction speed is fast, the maintenance is convenient and economical, and the general transformer factory in China can manufacture.
(6) Separation of lines: Due to the impedance in the power supply system, the harmonic load current will cause the harmonic voltage of the voltage waveform to be deformed. The power supply line that generates the harmonic load is separated from the harmonic-sensitive load supply line. The linear load and the non-linear load are fed by different circuits from the same power interface point PCC, so that the distortion voltage generated by the nonlinear load does not Conducted to a linear load.
(7) Multiplexing and diversification of the circuit: Parallel diversification of the inverter unit is to use two or more inverter units in parallel, and the harmonic components are cancelled by waveform shift superposition; the multiplexing of the rectifier circuit is 12 pulses. Wave, 18-pulse, and 24-pulse rectification can reduce harmonic components; multi-pulse (such as 30-pulse series) is used for series doubling of power cells, and power unit multiplexed lines can also reduce harmonic components. There are also new variable frequency modulation methods, such as deformation modulation of voltage vectors.
(8) Improvement of control mode of frequency converter: With the development of high-tech such as power electronics technology, microelectronic technology and computer network, the inverter control mode has the following development: digital control inverter, digital inverter adopts single chip MCS51 or 80C196MC In addition, the SLE4520 or EPLD liquid crystal display can be used to achieve more perfect control performance; a variety of control methods are combined, and a single control method has its own shortcomings. If these single control methods are combined, the length can be complemented, thereby reducing harmonics. Improve efficiency.
(9) Green frequency converter using idealized harmonic pollution-free: The quality standard of green frequency converter is: the input and output currents are both sinusoidal, the input power factor is controllable, and the power factor can be made with any load. The output power of any controllable power frequency can be obtained.