The core working principle of the three-phase ac flow control load box is based on power electronics technology and load simulation theory. It realizes precise control and simulation of the power system flow by dynamically adjusting the parameters such as voltage, current, and power factor in the three-phase ac circuit. Its essence is to combine power electronic devices with programmable control units to build a simulation platform that can flexibly adjust load characteristics to meet the needs of power system testing, simulation, and operation regulation.
The working basis of the three-phase ac flow control load box starts from the input link of the three-phase power supply. When the three-phase ac power supply is connected to the load box, it first passes through the voltage and current detection module to collect the voltage amplitude, frequency, phase and other parameters of the power grid in real time. These real-time data are transmitted to the core control unit, which is usually a control system based on a digital signal processor (DSP) or a field programmable gate array (FPGA). The system analyzes the collected parameters through a preset control algorithm and compares them with the set target values (such as the expected load power, power factor, etc.) to generate corresponding control instructions.
The load regulation unit is the key actuator to achieve flow control. It is usually composed of resistive, inductive, and capacitive load modules, which are dynamically switched or continuously adjusted through power electronic switches (such as IGBT, MOSFET, etc.). For example, resistive loads are used to simulate active power consumption, and inductive and capacitive loads are used to adjust reactive power. The combination of the three can simulate a variety of load characteristics from pure resistance to inductive and capacitive. The control unit drives the power electronic switch to adjust the input ratio of each type of load based on the real-time calculation results, thereby changing the equivalent impedance of the load box and realizing accurate control of the power flow distribution (such as active power, reactive power, and current phase) in the three-phase AC circuit.
In the adjustment process, the feedback control mechanism plays a vital role. By real-time monitoring of the output current, power and other parameters of the load box, the control system forms a closed-loop feedback loop and continuously corrects the control instructions to eliminate errors. For example, when the power factor needs to be adjusted from a lagging state to a leading state, the control system calculates the required capacitive load input amount and gradually switches the capacitor module while monitoring the change of the power factor until the target value is reached. This dynamic adjustment process is usually completed within milliseconds to ensure rapid response and stable control of load characteristics.
Another core function of the three-phase AC flow control load box. Since the unbalanced three-phase load in the actual power system will lead to problems such as neutral point offset and increased line loss, the load box achieves accurate matching of the three-phase power by independently controlling the load impedance of each phase. For example, when the system requires the simulation of a three-phase unbalanced load, the control system can adjust the resistive, inductive, and capacitive load ratios of the three phases A, B, and C respectively, so that the power of each phase presents the set difference, and at the same time, the zero-sequence current suppression technology is used to reduce the impact of the unbalanced current on the power grid, thereby truly simulating the complex load conditions in actual operation.
In order to meet different test requirements, the load box usually has programmable characteristics. Users can set multiple working modes through the host computer software, such as constant power mode, constant current mode, dynamic load mode, etc. In constant power mode, the load box automatically adjusts the impedance to keep the active power and reactive power constant, even if the grid voltage fluctuates; the dynamic load mode can change the load characteristics in real time according to the preset waveform (such as step wave, sine wave, random wave, etc.), which is used to simulate the intermittent power output of impact loads or new energy generation in the power grid, and provide a real scenario for the stability test of the power system.
In practical applications, the working principle of the three-phase ac flow control load box also involves electromagnetic compatibility design and thermal management technology. Power electronic switches may generate electromagnetic interference when operating at high frequencies, so it is necessary to suppress interference through filtering circuits, shielding structures, etc. to ensure the stable operation of the load box itself and friendly access to the power grid. At the same time, the load module will generate a lot of heat when working, especially high-power resistive loads. It is necessary to dissipate the heat in time through cooling fans, heat pipes or liquid cooling systems to avoid excessive temperature causing component performance degradation or shortened life. This is also a key link to ensure long-term stable operation of the load box.
The three-phase ac flow control load box realizes precise control and flexible simulation of the power flow parameters in the three-phase ac circuit through the closed-loop control process of "detection-calculation-regulation-feedback" and the dynamic combination of power electronic switches for multiple types of loads. Its core lies in the combination of digital control technology and physical load regulation, which can not only meet the precise requirements for load characteristics in static testing of power systems, but also adapt to the simulation requirements of complex working conditions in dynamic simulation, providing reliable technical support for power equipment research and development, power grid operation and commissioning, and new energy grid connection testing.
