Research And Design Of Controlling Inrush Current In TSC Reactive Power Compensation With Asynchronous Switching

Currently in the low-voltage network, TSC is still widely used as low-voltage reactive power compensator because of its low price, convenient maintenance and expansion, as well as small size and so on. However, in order to save costs, there are many manufacturers use mechanical switches such as vacuum contactor or magnetic latching relays as the switching capacitance of the implementing agencies. Firstly, compared with using the thyristors, one of this mechanical switch’s fatal defect is that it cannot master the mechanic action time and will vary from the temperature, humidity and using times, so there’s no real "zero-cross switching" unless its mechanical characteristics’fully grasped. And some manufacturers even use small inductor in series to lower the impact of inaccurate flow so as to avoid the quality inspection. Second, even use thyristor switched capacitors as the implementing agency, there are also many manufacturers do not consider the safety and reliability of TSC, but simply apply optocoupler MOC3061 or MOC3083 as a trigger of thyristor driving circuit. In application, such optocoupler does trigger thyristors, especially zero-cross trigger, but such application ought to be applied in household appliance whose voltage should be 220V, which means, due to that devices can be easily burned up while the optpcoupler is applied to thytistor-switched reactor, for thyristor voltage on both ends and residual voltage from capacitance can add up to over 1 kV.Therefore, taking reactive compensation to power system and improve the power factor safely and reliably, this thesis discuss the basic principle of reactive compensation, and finds out that there are small sudden changes and oscillation in capacitance current even with accurate zero-crossing switch in TSC’s actual use, and studies the throw-switch oscillation under processing in different line parameter. Then, this thesis develops a set of TSC low-voltage reactive power compensator, whose master controller takes ARM chip ADμC7026 as its main control chip to collect data and realize control algorithm, and STC chip to realize the data’s real-time display and keys operating. In addition, this thesis designs both a low voltage reactive compensation adjuster responsible for thyristor switched capacitor, and zero-crossing capture circuit, as well as thyristor drives circuit, to ensure reliable triggering of thyristor. Moreover, this thesis describes and analyzes each hardware circuit, especially the characteristic of optocoupler, and captures the circuit of zero-cross point of voltage. Also, it uses electromagnetic drive circuit to trigger the thyristor, insulates the control curcuit’s low-voltage and thyristor’s high-voltage by driver transformer, so as to ensure the safety and reliability. In the end, this thesis takes actual test on sample driver, marks down the experimental waveforms and has it analysed.