The basic principle of voltage transmitter

Basic structure of active power filter

The figure above is the basic block diagram of the active power filter, where RS and LS are the grid impedance, and the active power filter adopts the voltage source inverter structure.

In the application of active power filter, a group of five LEM sensors are shared, in which LEM1 is used to detect the harmonic current of the load and provides a reference for the output of the active power filter; LEM2 is a voltage detection of the grid; LEM3 is used to detect the presence of The three-phase output current of the source power filter, the voltage transmitter provides a feedback signal for the control of the active power filter; the LEM4 is used to detect the DC side voltage of the active power filter and provide a feedback signal for the stability control of the DC side voltage; The LEM5 is used to detect the DC side output current, prevent the DC output current from being too high, and provide fast protection when the active inverter phase-to-phase short circuit or the upper and lower arm power switches are turned on at the same time.

The development foreword "harmonic pollution" is recognized as a major public power system. In order to suppress the influence of harmonics in the power system, the active power filter uses power electronics to output harmonic currents with harmonic amplitudes equal in magnitude and opposite in phase to the loads, so that the harmonic energy is between the voltage transmitter and the load. Flow without affecting the grid. The voltage transmitter has the characteristics of flexible control, dynamic tracking and compensation for various harmonics, and suppression of resonance with the grid impedance, which plays a very important role in maintaining the “green” environment of the power grid.

With the rapid development of power electronics technology, a large number of power electronic devices are connected to the power grid, which brings huge economic benefits to the national economy and also brings harmonics to the power grid. Power system harmonics will not only increase the loss of the power grid, but also cause the malfunction of the protection system and affect the power system communication, which seriously threatens the safe and stable operation of the power grid.

In the application of voltage transmitters, its control accuracy and dynamic tracking performance play a key role. Under normal circumstances, harmonic detection accuracy and dynamic response speed are contradictory, and the improvement of detection accuracy often requires more historical data, which causes the dynamic response speed to decrease. At this time, the current transmitter will output harmonic current. It is difficult to obtain a good filtering effect with the time delay between the ideal compensation of the harmonic current, and the improvement of the dynamic response is often because the amount of data information extracted is not enough, which affects the detection accuracy. This makes APF often over-compensate or under-compensate for harmonic compensation, which also affects the performance of current transducers in Shaoxing Zhongyi Electronics. In order to ensure the high accuracy and high real-time performance of current transducers, high-performance sensors play a key role.

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