Current sensor noise suppression circuit in an active filter - Power Circuit - Circuit Diagram

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Abstract: There are a lot of actual noise interferences in the actual operation of active power filters. These interferences seriously affect the working effect of the filters. The analysis of the current sampling loop of the active power filter is given, and the interference phenomenon that may occur under the high frequency interference is analyzed. The difference of the source power filter for the common grid-connected inverter is analyzed, and the low-pass filter in the sampling loop is proposed. The importance and particularity of the design. And for these analyses, a practical solution to reduce the interference of current sampling loops is provided, and significant improvement in practical applications has been achieved.
Keywords: active power filter; signal transmission; noise suppression; current sensor; MAX275

With the increasing types of electrical equipment, there are many non-linear loads. During the operation, such loads generate a large number of high-order harmonics, which are very harmful to the power equipment in the power grid. The department has strict limits on the amount of harmonic injection. The design of the active filter is to inject a current other than the fundamental current into the circuit, thereby canceling the original harmonic current in the system, so that only the required fundamental current is needed in the system current. Unlike grid-connected inverters, the active power filter itself emits a non-sinusoidal waveform. This means that the method of applying traditional digital signal processing algorithms to eliminate noise is not fully applicable here, and the interference from the outside in practical applications greatly affects the operation of the system. The focus here is on the selection of the current sensor and the design of the sampling conditioning circuit. Because of the non-ideality of the two, the impact on the system is minimal.

1 Active power working principle Introduction The active filter circuit is shown in Figure 1. Two sets of current sensors are used to detect the load current Iload. And the actual compensation current Icom of the filter. The signal transformer transmits the three-phase system AC voltage Usys, and the DC voltage sensor is responsible for transmitting the DC terminal capacitor voltage Udc.
After the load current is read by the DSP, the positive sequence active current among the three-phase load current can be obtained through calculation, and the purpose of the compensation is to make the system-side current only contain the positive-sequence active current. After obtaining the positive sequence active fundamental current of the load current, the difference between the load current and the fundamental active positive sequence current is regarded as the output of the active filter, so that the active filter outputs the current, and the system current is Positive sequence active current.

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