Abstract: In the actual operation of active power filters, there are numerous instances of real-world noise interference. These interferences significantly impair the effectiveness of the filters. An analysis of the current sampling loop in the active power filter is provided, along with an examination of potential interference phenomena that could arise under high-frequency conditions. The differences between the source power filter for a common grid-connected inverter are discussed, and the importance and uniqueness of designing a low-pass filter in the sampling loop are emphasized. Based on these analyses, a practical solution to mitigate interference in the current sampling loop is presented, leading to notable improvements in practical applications.
As the variety of electrical equipment continues to grow, many non-linear loads have emerged. During their operation, these loads produce a significant amount of high-order harmonics, which pose considerable harm to the power equipment within the grid. Regulatory bodies impose strict limitations on the amount of harmonic injection. The design of the active filter involves injecting a current other than the fundamental current into the circuit, effectively canceling out the original harmonic current in the system. This ensures that the system current contains only the necessary fundamental current. Unlike grid-connected inverters, active power filters themselves emit a non-sinusoidal waveform. Consequently, the application of traditional digital signal processing algorithms to eliminate noise is not entirely effective in this context. The interference from external sources in practical applications greatly affects the system's performance. Here, the focus is on selecting the appropriate current sensor and designing the sampling conditioning circuit. Due to the non-ideal nature of both, the impact on the system is minimized.
1. Introduction to Active Power Working Principle
High Gain panel antenna,outdoor high gain antenna,high gain indoor antenna Mianyang Ouxun Information Industry Co., Ltd , https://www.ouxunantenna.com
Keywords: active power filter; signal transmission; noise suppression; current sensor; MAX275
The active filter circuit is illustrated in Figure 1. Two sets of current sensors are employed to measure the load current (Iload) and the actual compensation current (Icom) produced by the filter. The signal transformer transmits the three-phase system AC voltage (Usys), while 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 of the three-phase load current can be calculated, and the aim is to ensure that the system-side current consists solely of the positive-sequence active current. Once the positive-sequence active fundamental current of the load current is obtained, the difference between the load current and the fundamental active positive-sequence current is treated as the output of the active filter. This enables the active filter to output a current that results in the system current being composed only of the positive-sequence active current.
[3]