CN103401467A - Bidirectional ac power controller of ac-dc mixing mini electrical network - Google Patents

Abstract

The invention relates to a bidirectional converter power controller for an AC-DC hybrid micro-grid, comprising a bidirectional converter module, the DC side of the bidirectional converter module is connected to the DC bus of the AC-DC hybrid micro-grid through a step-down module, and the bidirectional converter module The AC side of the module is connected to the AC busbar of the AC-DC hybrid micro-grid through a filter. The beneficial effects of the present invention are: by disposing the bidirectional converter power controller of the present invention between the AC node and the DC node of the AC-DC hybrid micro-grid, the interconnection between the AC part and the DC part is realized, and the micro-grid is enhanced. Stability, making the power distribution of the microgrid more balanced.

Description

A Bidirectional Converter Power Controller for AC-DC Hybrid Microgrid

technical field

The invention relates to a bidirectional variable current power controller of an AC-DC hybrid micro-grid, which belongs to the field of automatic control of the micro-grid.

Background technique

Microgrid is an important means of stably and efficiently coupling distributed power and large power grid, and it is the best way to utilize distributed energy. The development of micro-grid will inevitably promote the transformation and upgrading of the traditional grid structure. The micro-grid unifies the one-way energy flow distributed power supply, the two-way energy flow distributed power supply, load, power control and other devices into an organic system to realize the efficient utilization and intelligent control of electric energy. The close relationship between microgrid and power consumption terminals can greatly improve power energy efficiency and improve customer experience.

Micro-grids can generally be divided into three types according to the form of power: AC micro-grids, DC micro-grids, and AC-DC hybrid micro-grids. Single power form micro-grids have their own advantages and disadvantages: AC micro-grids are easier to match with large power grids; DC micro-grids can reduce system costs and effectively suppress the circulation between distributed power sources. Considering the characteristics of distributed power sources, the power supply demand of loads and the best application expectations of micro-grid systems, the research on AC-DC hybrid micro-grids has become the most cutting-edge field in the intelligent construction of power grids. At present, domestic micro-grid construction is mostly an exploratory project, and most of the research is based on computer simulation, and the engineering application of AC-DC hybrid micro-grid is still in a blank stage. The core device in the AC/DC hybrid microgrid is the bidirectional converter power controller. In the AC-DC hybrid microgrid, the voltage range of the DC bus is between 200V and 400V. The bi-directional converter power control equipment is located at the DC-AC node of the AC-DC hybrid micro-grid, as a primary coupling device between the 240V DC bus and the 400V AC bus in the micro-grid, and is used for the two-way connection between the DC bus and the AC bus in the AC-DC hybrid micro-grid Current conversion, power regulation, power distribution, DC side voltage stabilization, AC side voltage frequency control.

Theoretically, the system protection and control strategy of the microgrid is an integrated structure of control and protection, which requires its key power electronic equipment to meet the requirements of system control and protection in the case of complex energy flow paths in the microgrid.

Contents of the invention

The object of the present invention is to provide a bidirectional converter power controller for an AC/DC hybrid micro-grid, which is used to solve the problem that the power in the AC part and the DC part of the AC-DC hybrid micro-grid cannot flow bidirectionally.

In order to achieve the above object, the solution of the present invention is: a bidirectional converter power controller for an AC-DC hybrid micro-grid, including a bidirectional converter module, the DC side of the bidirectional converter module is connected to the AC-DC hybrid micro-grid through a buck-boost module. The DC bus of the power grid, and the AC side of the bidirectional converter module are connected to the AC bus of the AC-DC hybrid micro-grid through a filter.

The bidirectional converter module is a three-level full bridge bidirectional converter module.

The filter is an LCL filter.

The buck-boost module is a bidirectional DC/DC module.

The beneficial effects of the present invention are: by disposing the bidirectional converter power controller of the present invention between the AC node and the DC node of the AC-DC hybrid micro-grid, the interconnection between the AC part and the DC part is realized, and the micro-grid is enhanced. Stability, making the power distribution of the microgrid more balanced.

Description of drawings

Fig. 1 is a kind of bidirectional variable current power controller hardware structure of the present invention;

Figure 2 is an equivalent model of a three-phase full-bridge converter circuit;

Fig. 3 is the vector diagram of the three-phase full-bridge converter circuit;

Fig. 4 is a kind of circuit topological structure that can realize direct current bidirectional step-down and step-down of the present invention;

Fig. 5 is a kind of three-level bridge circuit topological structure that can realize bidirectional current conversion of the present invention;

Fig. 6 is the modularized two-way inverter structure of the present invention;

Fig. 7 is the control circuit of the bidirectional converter power conversion of the present invention.

Detailed ways

The present invention will be described in further detail below in conjunction with the accompanying drawings.

As shown in Figure 1, it is a bidirectional converter power controller hardware structure suitable for AC-DC hybrid microgrid. flow, power regulation, power distribution, DC side voltage stabilization, and AC side voltage frequency control.

The present invention designs a circuit topology capable of realizing DC bidirectional buck-boosting, which is used to complete the boosting function when the DC bus transmits power to the AC side and the voltage-down function when the AC side transmits power to the DC bus. The bidirectional DC buck-boost topology is shown in Figure 4. Two separate IGBTs and a DC side inductor form a T-shaped structure. The DC side capacitor is an energy storage filter capacitor, which is used to keep the input DC bus voltage stable and also has a filter function. The DC side inductor is mainly used for periodic storage and release of electric energy to maintain continuous and stable DC current. The capacity and operating frequency of the separate IGBT determine the size of the rated power capacity and DC ripple coefficient.

。保留2-3倍的裕量，选用直流耐压为1200V的模块，设计转换功率为10kW。另外，图5右侧为本发明设计的LCL滤波器，通过参数设计，使LCL滤波器与三电平桥电路完全匹配，滤除设备输出的高次谐波，保证纯净的正弦波输出。The present invention designs a three-level full-bridge bidirectional converter module capable of bidirectional conversion, as shown in Figure 5, the left side of Figure 5 is used to realize the interconnection between the DC side and the AC side and bidirectional power conversion. The topology is realized by using a power electronics module integrating twelve IGBTs with gate drive control, fault detection and protection circuits inside the integrated component. The system requires the realization of three-phase full-bridge conversion, and the DC side voltage requirement is

. Reserve a margin of 2-3 times, select a module with a DC withstand voltage of 1200V, and design a conversion power of 10kW. In addition, the right side of Figure 5 shows the LCL filter designed by the present invention. Through parameter design, the LCL filter is completely matched with the three-level bridge circuit, and the high-order harmonics output by the equipment are filtered out to ensure pure sine wave output.

Fig. 6 shows the schematic diagram of multi-channel connection of the bidirectional converter power controller of the present invention, the minimum modularization unit of the bidirectional converter power controller designed by the present invention is a 10kW unit, and the unit consists of a DC bidirectional step-up and down step The circuit is composed of a bidirectional variable current three-level bridge circuit. When the power capacity between the DC bus and the AC bus increases, multiple units can be connected in parallel to achieve the required capacity. The advantage of this design is: the power between the busbars can be varied within a large range. The bidirectional converter power controller can improve the utilization efficiency of power electronic components, reduce the average working time of components, and prolong the life of the system through the coordinated control of each unit.

The invention designs a control circuit for bidirectional variable current power conversion. The control circuit is designed around the microcontroller, which is the control core of the whole system. It outputs PWM pulse signals, processes AC and DC sampling signals, and controls relay switching and communication. The specific hardware connections are shown in Figure 7.

Taking the smallest modular unit with a power of 10kW as an example, the hardware design of a bidirectional converter power controller is illustrated. The device is located at the DC-AC node of the AC-DC hybrid micro-grid. It is used as a primary coupling device for the 240V DC bus and the 400V AC bus in the micro-grid to complete bidirectional conversion, power regulation, power distribution, DC side voltage stabilization, and AC side voltage frequency. control functions. The bidirectional converter power controller is composed of four parts: power electronic main circuit, control circuit, power supply circuit and drive circuit. The bidirectional DC buck-boost topology is used to complete the boost function when the DC bus transmits power to the AC side and the step-down function when the AC side transmits power to the DC bus. This topology is mainly realized by two fully controllable separate IGBTs . The conversion part of the main circuit is implemented by a three-level bridge bidirectional power topology, which is implemented by a power electronic module integrated with twelve IGBTs. The design of the LCL filter is fully matched with the three-level bridge circuit to filter out the high-order harmonics output by the device and ensure a pure sine wave output. The control circuit is the core of the whole system, which outputs PWM pulse signal, processes AC and DC sampling signal, controls relay switch and communication. According to the situation of the micro-grid: the DC bus voltage is 240V, and the AC bus voltage is 400V. The parameters of the above-mentioned equipment are designed as follows: the DC side voltage stabilizing capacitor is a multi-capacitor parallel connection type, the size of the ripple inductor is 20-30mH, the working switching frequency of the two separate IGBTs is 30-40kHz, and the total amount of 400V voltage stabilizing capacitors is 7000 ~8000uF, the highest operating frequency of the IGBT in the three-level full-bridge circuit is 10kHz.

The bidirectional variable current power controller proposed by the present invention can realize the inverter and rectification functions, and the specific principle is analyzed as follows:

The realization of DC-AC bidirectional conversion in the bidirectional converter power controller depends on the power electronic circuit. Its topology is a three-phase full-bridge circuit including LCL filter design. When the DC bus transmits power to the AC bus, the three-phase full-bridge circuit works in the inverter state; when the AC bus transmits power to the DC bus, the three-phase full-bridge circuit works in the rectification state. Suppose the AC side input voltage is v, the current is i, the DC side input voltage is v _dc , and the current is i _dc , and according to the nature of the power grid, the AC side power grid presents an inductive impedance, and the DC side power grid presents a resistive impedance, then the three-phase The equivalent model of the full-bridge converter circuit is shown in Figure 2:

According to the voltage relationship on the AC side, the formula v=ev _L can be obtained, so it can be known that the four-quadrant operation of the three-phase full-bridge circuit can be realized by controlling the AC voltage vector v. As shown in Figure 3, the trajectory of the end point of the current vector i on the AC side forms a circle with i as the radius.

When the current i runs in the first and fourth quadrants, the power flow is directed from the AC side to the DC side, and the power electronic main circuit realizes the rectification function; when the current i runs in the second and third quadrants, the power flow is directed from the DC side to the AC side, The power electronic main circuit realizes the inverter function.

Claims (4)

1. A bidirectional converter power controller of an AC-DC hybrid microgrid, characterized in that it comprises a bidirectional converter module, and the DC side of the bidirectional converter module is connected to the DC busbar of the AC-DC hybrid microgrid through a buck-boost module, The AC side of the bidirectional converter module is connected to the AC busbar of the AC-DC hybrid micro-grid through a filter. 2. A bidirectional converter power controller for an AC/DC hybrid micro-grid according to claim 1, wherein the bidirectional converter module is a three-level full-bridge bidirectional converter module. 3 . The bidirectional converter power controller for an AC/DC hybrid micro-grid according to claim 1 , wherein the filter is an LCL filter. 4 . 4. A bidirectional converter power controller for an AC/DC hybrid micro-grid according to claim 1, wherein the buck-boost module is a bidirectional DC/DC module.

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