As can be seen from the name, the active filter needs to provide power. In practical applications, it can overcome the shortcomings of harmonic suppression and reactive power compensation methods of traditional filters such as LC filters (traditional only fixed numerical compensation ), but it realizes dynamic tracking compensation, and at the same time it can compensate harmonics and reactive power; three-phase circuit instantaneous reactive power theory is the main basic theory for the development of APF; APF can be divided into two types: parallel type and series type , The former is mostly used; the main purpose of the parallel active filter is to control current harmonics, and the series active filter mainly focuses on the problems caused by voltage harmonics. The active filter device has a better treatment effect, and can filter out multiple and high-order harmonics at the same time without causing resonance.
1. Energy saving 5%～8%
2. Derating reduces the investment in transformers, circuit breakers, and cables
3. Improve productivity and maintain continuous power supply
4. It can dynamically filter out various harmonics, and can completely absorb the harmonics in the system
5. No resonance
Disadvantages of active filters1. The cost is too high
2. Due to hardware limitations, it cannot be used in large-capacity occasions: a single set of active filter capacity does not exceed 100 kVA, and the current maximum applicable grid voltage does not exceed 690 volts
Advantages of active filtering over passive filtering1. Analysis from a design perspective: Compared with passive filter devices, active filter devices only need to estimate the maximum value of harmonic current without considering factors such as grid impedance, characteristic harmonics, and simulation verification. It may cause resonance accidents due to improper design of passive filter devices. The design is simple, can realize the standardized design, make the scheme unified.
2. Analysis from the perspective of installation: Passive filter devices are only suitable for in-situ treatment and installation at the harmonic source. Centralized compensation will not avoid resonance. The use of active filter devices can be installed at the harmonic source or at the time of change. Centralized management of power stations to reduce management costs.
3. From the analysis of the control effect: the active filter device specifically detects harmonics, controls the harmonics, and can simultaneously filter for multiple harmonics at the same time. The theoretical filter rate is greater than 90%, and the passive filter device must consider the grid resonance, LC The loop must generally deviate from the resonance point, resulting in a theoretical filtering rate of less than 70%.
4. From an economic point of view: it is more economical to use active filter devices than passive filter devices for power grids with the same harmonic content. This is mainly reflected in the smaller device capacity and higher filter rate. If centralized governance is used instead of decentralized governance, the device capacity will be more economical than passive filtering. The passive filter device for decentralized management is smaller. From an economic point of view, active filter devices have a higher cost performance.
5. Analyze from the treatment method: Active filter device can realize dynamic automatic real-time treatment, while passive filter device can only perform static treatment, and must be manually operated. The switching is determined according to the working state of the harmonic source.
6. Analysis from the perspective of energy saving: Since the capacity of the active filter device is much smaller than that of the passive filter device, the loss is less than that of the passive filter device. The use of active filter device is more energy-saving.
Active filter technical parameters1. Rated working voltage: 380V/220V, 50 Hz
2. Rated harmonic compensation capacity: 50A/100A/150A/200A
3. Power consumption of the whole machine: less than 3% of capacity
4. Harmonic suppression effect: meet the requirements of national standard, steady state THD can be reduced to below 5%
5. Rated insulation voltage: 3000V AC, 2500V DC.
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