In the face of severe power harmonic pollution problems, active filters are the most effective tools for improving power quality. The active filter is a special equipment for the new type of power harmonics control developed using modern power electronics technology and digital signal processing technology based on high-speed DSP processing devices. The active filter is equivalent to a harmonic current generator that tracks the harmonic components in harmonic currents and produces harmonic currents with an amplitude that is antiphase.
The active power filter is composed of two parts: a command current operation circuit and a compensation current generation circuit. The instruction current calculation circuit detects the current in the circuit in real time, converts the analog current signal into a digital signal, and sends it to a high-speed digital processor (DSP) to process the signal, separates the harmonic wave and the fundamental wave current to obtain the command current, and passes The current tracking control circuit and the drive circuit send a drive pulse to the compensation current generation circuit in the form of a pulse width modulation (PWM) signal to drive the IGBT and the IPM power module to generate a compensation current injection with equal amplitude and opposite polarity to the harmonic current. The power grid compensates or cancels harmonic currents and actively eliminates power harmonics, thereby realizing dynamic, rapid, and thorough processing of power harmonics.
Compared with traditional passive filters, active filters have the following outstanding advantages:
1. The harmonic rejection rate is high, and the harmonic impedance performance is not affected by the system impedance.
2. Dynamic compensation can compensate harmonics with varying frequencies and sizes, as well as changing reactive power, and respond quickly to changes in the object of compensation.
3. Harmonic and reactive power can be compensated at the same time. The size of the compensation reactive power can be adjusted continuously. When compensating for reactive power, no energy storage components are required.
4. When the harmonics are compensated, the capacity of the energy storage components required is small. When the current of the compensation object is too large, the active power filter will not be overloaded, and the compensation can be normally performed.
5. The influence of the grid impedance is not significant, and it is not easy to generate series and parallel resonance with the grid impedance. Changes in the system structure will not affect the control effect.
6, can track the grid frequency changes, compensation performance is not affected by the grid frequency changes, you can compensate for a harmonic and reactive power alone, can also be a centralized compensation for multiple harmonics and reactive power sources.
Harmonic source load
Power UPS, switching power supply
SCR dimming system, UPS, central air conditioning
Electronic equipment, UPS, air conditioning elevator
Variable frequency drive, DC speed drive
Water treatment plant
Inverter, soft starter
Computer equipment, central air conditioning, various types of energy-saving lamps, office equipment, large elevators
Important medical equipment: nuclear magnetic resonance equipment, accelerators, CT, X-ray machines, UPS, etc.
Hot rolling mill, cold rolling mill, spot welding machine, intermediate frequency furnace, electric arc furnace, DC motor, frequency converter, electrolyzer, etc.