The three-phase distribution transformer is composed of an input stage, isolation stage, and output stage: the input stage is a cascaded modular converter, and the input of the cascaded modular converter is directly connected to the three-phase AC power grid. The output of the combined modular converter is connected to the primary side of the dual winding intermediate frequency or high-frequency transformer of the isolation stage; the secondary side of the dual winding intermediate frequency or high-frequency transformer of the isolation stage is connected to the fully controlled H bridge; the output stage is shared One or more single-phase or three-phase inverters of the DC bus.
The three-phase distribution transformer can overcome the shortcomings of the existing power electronic transformers for power distribution, reduce the volume and weight of the device, and improve the efficiency of power conversion. It can not only realize the functions of traditional distribution transformers such as voltage transformation, isolation, and energy transmission, but also provide reactive power compensation for the power grid as required to ensure a constant secondary output voltage, isolate the high-voltage side power grid and the low-voltage side user faults, and have voltage The continuous regulation and comprehensive control capabilities of current can realize the uninterrupted power supply on the user side when interconnected with new energy power generation equipment, and realize many advantages such as interaction with other equipment of the power grid.
The three-phase power electronic transformer for power distribution adopts fully-controlled devices, which can realize the bidirectional flow of energy(three phase voltage regulator). Another structure of the isolation stage is to connect a resonant capacitor in series between the dual-winding intermediate frequency or high-frequency transformer and the fully-controlled H-bridge to form an isolation stage that can achieve series resonance.
Compared with the isolation stage without series resonance, the use of series resonance can realize the zero-current resonance soft switching of the primary and secondary circuits of the intermediate frequency or high-frequency transformer, which can greatly reduce the loss of the device and improve the operating efficiency.
Three-phase power electronic transformers for power distribution have the following characteristics:
Three-phase distribution transformers can easily realize online monitoring of operating status, communicate with other electrical equipment and coordinate control, and provide more flexibility for the construction and improvement of digital power stations and smart grids.
It can realize the basic functions of traditional power distribution transformers such as voltage transformation, isolation, and energy transfer; it can also realize the isolation of the load and the power supply system and can provide reactive power compensation for the grid side as required.
The input stage adopts a cascaded modular converter, as long as enough modules are cascaded, it can withstand very high voltage. At the same time, when a three-phase isolation transformer is used in a three-phase system, only a dual-winding intermediate frequency or high-frequency transformer is needed, which can greatly reduce the volume and weight of the transformer compared to the existing topology.
three phase ei laminated power transformer
When a three-phase power electronic transformer is composed of an existing single-phase power electronic transformer, in practical applications, the AC-DC module DC bus of each phase input stage generally needs an additional passive filter to eliminate the voltage fluctuation of the double frequency of the grid voltage. Since the three-phase isolation transformer is directly connected to the three-phase power grid, the instantaneous active power of the three-phase system is a constant amount, and there is no fluctuation in the DC bus voltage, so there is no need for a passive filter. This also further reduces the volume and weight of the system.
The three-phase distribution transformer can realize the isolation between the load and the power supply system and can provide reactive power compensation or active filtering functions for the grid side as required, which improves the power quality and operation reliability of the power supply system.
The three-phase distribution transformer can automatically adjust the power supply voltage of the output stage to ensure that the power supply voltage at the user end does not change with the load. When the power supply grid fails or the equipment is repaired, the DC bus of the present invention can be connected to power generation equipment such as new energy sources to ensure uninterrupted power supply at the user end, and can greatly improve the stability and reliability of the user and the electrical equipment.