Ways to reduce inverter harmonics

Ways to reduce inverter harmonics Insulation, 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 isolation transformer on the input side of the inverter and other electrical equipment. Or put the inverter into the iron box, and the iron box shell is grounded. At the same time, the output power of the inverter should be laid as far as possible from the control cable (not less than 50mm spacing). When it is close to the laying, it should be crossed at an orthogonal angle. When it must be laid in parallel, the length of the parallel section should be shortened (not more than 1mm). Electrically connect the steel pipe and ground it reliably. Install AC reactor and DC reactor: When the inverter is used in a distribution transformer with a capacity greater than 500KVA, and the transformer capacity is greater than 10 times the capacity of the inverter, install an AC reactor on the input side of the inverter. When the output voltage of the distribution transformer is unbalanced in three phases, and the unbalance rate is greater than 3%, the peak value of the inverter input current is very large, which will lead to overheating of the conductor. In this case, an AC reactor needs to be installed. In severe cases, a DC reactor needs to be installed. Install passive filter: install the passive filter on the AC side of the inverter. The passive filter is composed of L, C, R components to form a harmonic resonance circuit. When the harmonic frequency of the LC circuit is When the wave current frequency is the same, high-order harmonics can be prevented from flowing into the power grid. Passive filters are characterized by low investment, high frequency, simple structure, reliable operation and easy maintenance. The disadvantage of passive filters is that filtering is susceptible to system parameters, and it is possible to amplify certain subharmonics, which is costly and bulky. Equipped with a source filter: As early as the early 1970s, Japanese scholars proposed the concept of an active filter. The source filter passes the detection of higher harmonics in the current, and the input is opposite to the higher harmonic components according to the detection result. Phase current to achieve the purpose of real-time compensation of harmonic current. Compared with passive filters, it has a high degree of controllability and fast response, and has the characteristics of one machine with multiple functions. And can eliminate the danger of resonance with the system impedance. It can also automatically track the harmonics of compensation changes. However, it has the characteristics of large capacity and high price. Installation of static reactive power compensation device for reactive power: For large impact loads, static reactive power compensation device for reactive power can be installed to compensate for the rapidly changing reactive power demand of load, improve power factor and filter out System harmonics, reduce the injection of harmonic currents into the system, stabilize the bus voltage, reduce the three-phase voltage imbalance, and improve the ability of the power supply system to withstand harmonics. Among them, the self-saturated reactance type (SR type) has the best effect, its electronic components are few, the reliability is high, the response speed is fast, the maintenance is convenient and economical, and it can be manufactured by ordinary transformer factories in my country. Line separation: The fundamental cause of harmonics is due to the use of non-linear loads. Therefore, the fundamental solution is to separate the power supply lines of loads that generate harmonics from the power supply lines of loads that are sensitive to harmonics. The distortion current caused by the non-linear load produces a distortion voltage drop on the impedance of the cable, and the resulting distortion voltage waveform is applied to other loads connected to the same line, causing harmonic currents to flow on it. Therefore, measures to reduce the harm of harmonics can also be achieved by increasing the cable cross-sectional area and reducing the impedance of the loop. The linear load and the non-linear load can be supplied with separate circuits from the same power interface point (PCC), so that the distortion voltage generated by the non-linear load will not be conducted to the linear load. This is an ideal solution for harmonic problems. Multiplexing and diversification of the circuit: Parallel multiplexing of the inverter units adopts two or more inverter units in parallel, through waveform shift superposition to cancel the harmonic components; the multiplexing of the rectifier circuit adopts 12 pulses, 18 Pulse wave and 24-pulse rectification can reduce the harmonic component; the series multiplexing of power units adopts multi-pulse wave (such as the series connection of 30 pulses), and the multiple circuit of power units can also reduce the harmonic component. In addition, there are new frequency conversion modulation methods, such as the deformation modulation of the voltage vector. Improvement of the control method of the inverter: With the development of power electronics technology, microelectronic technology, computer network and other high-tech development, the control method of the inverter has the following development: digital control of the inverter, the digitalization of the inverter uses a single chip MCS51 or 80C196MC, etc. Use SLE4520 or EPLD liquid crystal display to achieve more perfect control performance; a combination of multiple control methods, a single control method has its own shortcomings, if you combine these single control methods, you can take advantage of the shortcomings, so as to reduce harmonics and improve efficiency efficacy. Use the ideal green frequency converter without harmonic pollution: The quality standard of the green frequency converter is: the input and output currents are sine waves, the input power factor can be controlled, and any load can make the power factor 1 and can be obtained Any controllable output power above and below power frequency. The built-in AC reactor of the inverter can suppress harmonics well and protect the rectifier bridge from the instantaneous spikes of the power supply voltage. Practice shows that the harmonic current without reactor is significantly higher than that produced by the reactor Harmonic current. In order to reduce the interference caused by harmonic pollution, install a noise filter in the output circuit of the inverter. And when the inverter agrees, reduce the carrier frequency of the inverter. In addition, in high-power frequency converters, 12-pulse or 18-pulse rectification is usually used, so that in the power supply, the harmonic content is reduced by eliminating the lowest harmonic.

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