谐波和无功功率的产生(Generation of harmonic and reactive power)

谐波和无功功率的产生（Generation of harmonic and reactivepower）Reactive power is also called ineffective power and reactive power. Take a simple example: for example, eat steamed stuffed bun, it was originally to eat 3 to eat, the first two buns is equivalent to reactive power, and the third baozi is active power. The common compensation is reactive power compensation in parallel with the power capacitor in the loop.Harmonics: periodic voltage and current signals of any frequency other than the fundamental frequency (50Hz or 60Hz) are called harmonics.In power system, the commonly used method to suppress harmonics is to adopt parallel passive filter or active filterPassive filters generally use capacitors and reactors in series to form a low impedance loop, which is used to absorb harmonics in the system, also known as passive filtersAccording to the harmonic condition of the system, the active filter produces a harmonic source which is the same as the harmonic direction and the current is equal to counteract the harmonic produced in the system. Also known as active filter 1, when the power is connected to inductive or capacitive load, due to inductive or capacitive load is a complex, expression power is a complex, the imaginary part is called reactive power. But the perceptual load vector angle lag, capacitive load vector angle advance. In order to make the reactive power as small as possible under the condition that the apparent powerremains the same, then adding capacitive loads to reactive power is called compensation.2, the load in a large number of utility power electronic devices, the power grid in the AC in Fourier series, found that in addition to containing the fundamental component, there are a lot more than the fundamental component of higher waves, these waves are called harmonics. There are mainly two ways to eliminate harmonics: using different connection methods of transformer to prevent harmonic transmission, or to filter harmonic with capacitor filter. Harmonic generation: nonlinear load, impact load and other large operation factors of power users, such as arc furnace, electric locomotive running on the power quality, the utility grid harmonic interference, produce large disturbance voltage, voltage fluctuation and flicker.The harm of harmonic, harmonic pollution will have an impact on the electric power equipment, power grid and power transmission lines, mainly in: the capacitor harmonic overload which seriously affect the service life; harmonic will cause increase, loss of power grid equipment, shorten the life of equipment caused by unsafe operation, cause the local substation parallel or series resonant voltage transformer, causing light damage to equipment; harmonic pollution increases the loss of transmission lines; harmonic pollution caused by the increase of the neutral line current, neutral drift; harmonics caused by the risk of instability of the cable medium is larger, more prone to failure, use Baidu Search You'll see. ah ~ ~ ~ ~ ~ this is my Baidu know you can drop further searchDefinition: strictly speaking, refers to the amount of power harmonic current in frequency with the integer multiples of the fundamental, generally refers to the periodic non sinusoidal power by means of Fourier series decomposition, other than the fundamental frequency current produces power. Broadly speaking, since the effective component of an AC network is a single frequency of the power frequency, any component that is different from the power frequency can be called harmonic,At this point, the meaning of the word "harmonic" has become somewhat inconsistent with the original intention. It is precisely because of the broad sense of harmonic concept that there is "fractional harmonics", "inter harmonics", "sub harmonic" and so on.The reason is that when the sinusoidal voltage is applied to the nonlinear load, the fundamental current is distorted and the harmonic is generated. The main nonlinear loads are UPS, switching power supply, rectifier, inverter, inverter and so on.Harmonic harm: reduce system capacity, such as transformers, circuit breakers, cables and other equipment to accelerate aging, shorten the service life of equipment, and even damage equipment, endanger the safety and stability of production, waste of electricity and so on. How is the three harmonic generation?AnswerThe word harmonics comes from acoustics. The mathematicalanalysis of harmonics has laid a good foundation in 18th Century and 19th Century. Harmonic analysis proposed by Fu Liye et alMethods are still widely used today. The harmonic problem of power system has attracted people's attention as early as 1920s and 30s. In Germany, distortion of voltage and current waveforms was caused by the use of stationary mercury arc converters. The papers on harmonic converters published by J.C.Read in 1945 are the classical papers on harmonic research in the early years.By 50s and 60s, due to the development of HVDC technology, a large number of papers were published on the harmonic problems caused by converters. Since 70s, due to the rapid development of power electronics technology, all kinds of power electronic devices are widely used in power system, industry, transportation and home, and the harm caused by harmonics is becoming more and more serious. All countries in the world pay full attention to the problem of harmonics. International conferences on harmonics have been held many times, and many countries and international academic organizations have formulated standards and regulations for limiting harmonics in power system harmonics and power equipment.The significance of harmonic research is that the harm of harmonics is very serious. Harmonics reduce the efficiency of the production, transmission and utilization of electric energy, make the electrical equipment overheat, produce vibration and noise, and make the insulation aging, shorten the service life, and even fail or burn down. Harmonics can cause partial parallel resonance or series resonance in power system,and enlarge harmonic content, resulting in the burnout of capacitor and other equipments. Harmonic will cause relay protection and automatic device misoperation, so that energy measurement confusion. For the outside of power system, harmonic will cause serious interference to communication equipment and electronic equipment.2. harmonic suppressionTo solve the problem of harmonic pollution in power electronic devices and other harmonic sources, there are two basic ideas: one is to install the harmonic compensation device to compensate harmonics, which are applicable to all kinds of harmonic sources; the other is to reconstruct the power electronics equipment, the stage does not produce harmonic wave, and the power factor can control the power electronic device is 1, which of course only apply as the main harmonic sources.The traditional method of installing harmonic compensator is to adopt LC tuned filter. This method can not only compensate harmonics but also compensate reactive power, and has simple structure and has been widely used. The main drawback of this method is that the compensation characteristic is affected by the grid impedance and the operation state, and the parallel resonance is easy to occur with the system, resulting in harmonic amplification,Make the LC filter overloaded or even burned. In addition, it can only compensate the harmonic of fixed frequency, and the compensation effect is not ideal.3., reactive compensation is alsoIt is very easy to understand the active power, but it is not easy to deeply understand the reactive power. In sinusoidal circuits, the concept of reactive power is clear, and there is no generally accepted definition of reactive power in the presence of harmonics. However, the importance of reactive power is consistent with the importance of reactive power compensation. Reactive power compensation should include compensation of fundamental reactive power and harmonic reactive power.Reactive power is very important to the operation of power supply system and load. The impedance of the network components of an electric power system is mainly inductive. Therefore, roughly speaking, in order to transmit active power, requires the sending end and receiving end voltage of a phase difference, which can be implemented in a wide range; and in order to transport the reactive power requires a voltage amplitude difference, this can only be achieved in a narrow range. Not only most network components consume reactive power, but most of the loads also require reactive power. Reactive power required for network components and loads must be obtained from somewhere in the network. Obviously, these reactive power, if all provided by the generator and transmitted over long distances, are unreasonable and usually not possible. The reasonable method is to generate reactive power in the place where the reactive power is needed, which is reactive power compensation.The main function of reactive compensation is the following:(1) increase the power factor of the power supply system and load, reduce the equipment capacity and reduce the power loss.(2) stabilize the voltage of the receiving end and the power grid to improve the quality of the power supply. The dynamic reactive power compensation device can also improve the stability of the transmission system and improve the transmission capacity in the appropriate place of long distance transmission lines.(3) the load imbalance in three-phase electric railway and the other occasions, through appropriate verification can balance three-phase active power and reactive power and reactive load.Two, harmonic and reactive power generationIn industrial and living electrical loads, the resistive load occupies a large proportion. Asynchronous motors, transformers, fluorescent lamps and so on are typical resistive loads. The reactive power consumed by induction motors and transformers occupies a high proportion in the reactive power provided by the power system. Reactors and overhead lines in power systems also consume some reactive power. A resistive load must absorb reactive power to work properly, which is determined by its nature.Nonlinear devices such as power electronic devices also consume reactive power, especially various phase control devices. For example, phase controlled rectifier, phase controlled AC power regulating circuit and cycloconverter, at the same time, thefundamental current lags behind the grid voltage and consumes a great deal of reactive power. In addition, these devices also produce a large amount of harmonic currents, and the harmonic sources are designed to consume reactive power. The fundamental current phase of diode rectifier circuit is approximately the same as that of grid voltage, so the fundamental reactive power is not consumed at all. However, it also generates a large amount of harmonic currents, and therefore consumes a certain amount of reactive power.In recent 30 years, the application of power electronic devices is becoming more and more widespread,It also makes the power electronic device become the biggest harmonic source. In all kinds of power electronic devices, rectifier devices account for the largest proportion. At present, the rectifier circuit usually adopts thyristor phase controlled rectifier circuit or diode rectifier circuit, among which three-phase bridge and single-phase bridge rectifier circuit are the most. The harmonic pollution and power factor hysteresis produced by rectifier circuits with resistive loads are well known. The diode rectifier circuit with capacitor filter on the DC side is also a severely punished harmonic pollution source. The fundamental component of the input current in this circuit is approximately the same as the phase of the supply voltage, so the fundamental power factor is close to 1. However, the harmonic component of the input current is very large, which causes serious pollution to the power grid and makes the total power factor very low. In addition, the power electronic devices using phase controlled AC power adjustment circuit and cycloconverter also produce a largeamount of harmonic currents at the input side.。