Active power filter
Definition of harmonic
Due to the existence of nonlinear load, the current and voltage waveforms in the power grid will be distorted to non-sinusoidal wave. Through the decomposition of the non-sinusoidal wave by fourier series, the component whose frequency is the same as the power frequency is called fundamental wave, The component whose frequency is greater than the power frequency is called harmonics.
Harm of harmonics
①The harmonic loss can reduce the efficiency of the power transmission and distribution of the power grid;
②The zero-sequence component current of the triple harmonics and their integer ones can cause severe heating of the neutral wire.
③The additional heat effect intensifies the insulation aging of the electric equipment and shortens the service life;
④Series resonance or parallel resonance may easily occur between harmonic and compensation condenser, causing the damage to the components or even tripping accidents;
⑤Cause faulty operations to some protective equipment, and may cause the inaccurate measurement of electrical measuring instruments;
⑥Disturb the communication system and even block the communication signal.
2、Introduction of APF
The active power filter (APF) is connected with the power grid in parallel, adopting the PWM conversion technology to produce the current equal but opposite to the harmonics by conducting the real-time detection of the laden harmonics and reactive component, which will be distilled into the power supply and distribution system, thus realizing the function of restraining the harmonics and reactive dynamic compensation.
1） Real-time tracking and dynamic compensation
It adopts the inspection technology based on the instantaneous reactive power theory, conducts the real-time detection of the harmonic current, and automatically tracks the change in the harmonics of the power grid by tracking and controlling the instantaneous current. It features high controllability and fast responsiveness.
2） Excellent filtering characteristic
The filtering performance is free from the impact of system impedance and risk of resonance.
3） Flexible compensation mode
One machine serves several purposes, it can not only filter the harmonic current, but also compensate the reactive power, thus improving the power factor.
4） DSP intelligent monitoring
The high-speed DSP inspection and calculation can ensure accurate and effective inspection and compensation control of the harmonic, having the functions of intelligent monitoring and automatic fault diagnosis at the same time; it has the remote communication interface and can conduct the real-time monitoring via the PC.
5） Advanced power conversion design
It adopts the latest IGBT high frequency switching elements, and the main circuit adopts the three-phase, bridge-type, full-controlled PWM current conversion technology, with such characteristics as small size, high efficiency and high reliability. The advanced multiplex technology realizes the expansion of the machine’s capacity.
6） Standard modular design
The power circuit and control circuit adopt the module or component structures, which enhance the reliability and maintainability during the use while realizing the standardized production.
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