The power factor automatic compensator is a fully automated electronic device designed to enhance the efficiency of electrical systems by improving the power factor within the grid. By intelligently managing reactive power, it helps reduce energy waste and optimize electricity usage. The GBK4-1C type controller used in our facility continuously monitors the system's power factor and adjusts the compensation capacitors accordingly, ensuring that the power factor remains within the desired range.
The core principle behind the control method involves detecting when the power factor drops below or exceeds predefined thresholds. When the power factor falls below the lower limit, the system automatically connects a capacitor to compensate for the reactive power. Conversely, if the power factor rises above the upper limit, the capacitor is disconnected. This approach ensures stable and efficient operation of the electrical system. A visual representation of this control mechanism is shown in Figure 1, which illustrates how the system dynamically adjusts the capacitor banks based on load changes.
In the diagram, OA represents the lower limit setting for the power factor (cosφ), while OB represents the upper limit. As the load increases along the OD line, the power factor decreases. At the critical point M1, the first capacitor (C1) is engaged, providing reactive power compensation (M1K1), which raises the apparent power to OK1, thus bringing the power factor back within the acceptable range defined by OA and OB. If the load continues to increase to M2, the second capacitor (C2) is activated, and at M3, the third capacitor (C3) is added. When the load decreases, the capacitors are sequentially removed: C1 at N1, C2 at N2, and all capacitors are disconnected once the load falls below the critical adjustment line. The exact position of this line depends on factors such as the minimum capacitor bank size, load characteristics, and the allowable power factor range.
Figure 2 provides an overview of the automatic compensation controller’s internal structure, which consists of four main parts: the measuring section, DC amplification stage, execution unit, and power supply. The process begins with converting the phase difference between the AC voltage and current into a DC signal. This signal is then amplified to trigger the execution unit, which controls the connection or disconnection of the capacitors.
The measuring part takes input from the AC voltage (uAC) of phases A and C, as well as the current (iB) of phase B. In a three-phase system, the phase relationship between the current and voltage determines the power factor. For example, when iB is in phase with uB, the power factor is 1. If there is a phase shift of π/2, the power factor is purely reactive. To measure these changes, a half-wave phase-sensitive differential amplifier is used. The signals u1 and u2 reflect the AC voltages across the respective phases.
As shown in Figures 4, 5, and 6, the conduction behavior of transistors T1 and T2 varies depending on the phase relationship between u1 and u2. When the two signals are in phase, only T1 conducts, producing a maximum positive DC output. When u1 leads u2 by π/2, both transistors conduct for part of the cycle, resulting in a zero output. If the phase difference is less than π/2, T1 conducts longer, leading to a positive output, while a larger phase difference results in a negative output.
This DC voltage is then used to drive either relay J1 or J2, depending on whether the output is negative or positive. If Uab is negative, relays J1 and J3 are activated after a delay, connecting the first capacitor group. If the power factor still needs improvement, the second capacitor group is connected after another delay. On the other hand, if Uab is positive, the system disconnects the capacitors in a similar manner, ensuring the power factor stays within the desired range. This intelligent control mechanism allows the system to operate efficiently under varying load conditions.
Low Frequency Power Supply
The category introduction of Low Frequency UPS Power Supply can be explained from its definition, characteristics, applications and development trends. The following is a detailed introduction to the low-frequency UPS power supply:
I. Definition
Low-frequency UPS power supply, as the name suggests, refers to the use of low-frequency switching power supply technology UPS system. This UPS has a lower switching frequency than a high-frequency UPS during the conversion process. While the specific "low frequency" range may vary by product and standard, in general, low frequency UPS switch at a much lower frequency than high frequency UPS.
Ii. Characteristics
High reliability:
Low-frequency UPS usually use more mature technologies and components, with high reliability and stability. The design is often more focused on system redundancy and backup to ensure continuous power supply at critical times.
Strong anti-interference ability:
Because the switching frequency of low-frequency UPS is low, its electromagnetic interference to the outside world is also relatively low. This makes low-frequency UPS more advantageous in some occasions with higher requirements for electromagnetic environments.
Large size and weight:
Compared with high-frequency UPS, the components and circuits of low-frequency UPS may be larger and more complex, so its overall volume and weight are also larger. This limits the application of low-frequency UPS in space-limited environments to a certain extent.
The conversion efficiency is relatively low:
Low-frequency UPS may generate more energy loss during the conversion process, so its conversion efficiency is relatively low. However, with the advancement of technology, some new low-frequency UPS are also trying to improve the conversion efficiency.
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