Flexible interconnection device and control method thereof

Abstract

The application discloses a flexible interconnection device and a control method thereof. The device comprises three power electronic conversion units with the same structure, which are connected between the same phases of AC power grids U1 and U2 respectively. One end of a filter inductor L1 in the power electronic conversion unit is connected to the neutral point of the power grid U1, and the other end is connected to a rectifier bridge. One end of a filter inductor L2 is connected between a switching device S6 and an AC interconnection capacitor C3, and the other end is connected to an inverter bridge. DC side capacitors C1 and C2 are connected in series in the forward direction and then connected in parallel between the rectifier bridge and the inverter bridge. The series connection point of the DC side capacitors C1 and C2 is connected to the series connection point of the switching device S5 and the AC interconnection capacitor C3. The AC interconnection capacitor C3 is connected in series between the switching devices S5 and S6, and the other ends of the switching devices S5 and S6 are connected to the same phase of the AC power grids U1 and U2. The technical scheme of the application realizes flexible interconnection between different AC regions, and can reduce the equipment cost and improve the power transmission efficiency.

Description

Technical Field

[0001] This invention belongs to the field of power distribution network optimization operation control, and specifically relates to a flexible interconnection device and its control method. Background Technology

[0002] In recent years, the global new energy industry has continued to grow and expand, with distributed power sources, represented by solar and wind power, receiving increasing attention and widespread application. The vigorous promotion of renewable energy, rapid load growth, and diversified access are changing the structure and operating characteristics of traditional power distribution networks. Existing power distribution systems face problems such as insufficient power supply capacity, difficulty in guaranteeing power quality, and reduced power supply reliability. Based on this, key equipment and technologies for flexible interconnection of power distribution networks have gradually gained favor among scholars both domestically and internationally, and flexible interconnected power distribution networks have gradually become a research hotspot in the field of power distribution network development.

[0003] Flexible interconnection devices are a new type of flexible primary equipment that can replace traditional tie switches at several key nodes in a power distribution network. Compared with traditional tie switches, they not only have both on and off states, but also do not have the limitation of the number of operations of traditional mechanical switches, increasing the state of continuous power control, and also have the characteristics of flexible switching of operating modes and flexible and diverse control methods.

[0004] Existing flexible interconnection devices mostly adopt a back-to-back configuration, with two converters connected to a common DC bus and their AC sides connected to distribution transformers. However, this approach has significant drawbacks: first, both converters need to carry the full power, placing high demands on the performance of the power electronic equipment, resulting in large equipment capacity and size, and high equipment costs; second, the operating efficiency of the device is relatively low. If the average operating efficiency of a single power electronic converter is calculated at 98%, the transfer loss between different AC zones is around 4%. Therefore, traditional back-to-back flexible interconnection devices are difficult to promote in the distribution network field. Summary of the Invention

[0005] Objectives of the Invention: One objective of this invention is to provide a flexible interconnection device that enables flexible interconnection between different AC zones while reducing equipment costs and improving power transmission efficiency. Another objective of this invention is to provide a control method for the flexible interconnection device that achieves power transfer by controlling capacitor voltage alone, without the need for an isolation transformer.

[0006] Technical Solution: A flexible interconnection device includes three identical power electronic conversion units, which are respectively connected between the same phases of AC power grids U1 and U2. Each power electronic conversion unit includes filter inductors L1 and L2, a rectifier bridge, an inverter bridge, reverse-connected switching devices S5 and S6, DC-side capacitors C1 and C2, and an AC interconnection capacitor C3. One end of the filter inductor L1 is connected to the neutral point of power grid U1, and the other end is connected to the rectifier bridge. One end of the filter inductor L2 is connected between the switching device S6 and the AC interconnection capacitor C3, and the other end is connected to the inverter bridge. The DC-side capacitors C1 and C2 are connected in series in the forward direction and then in parallel across the rectifier bridge and the inverter bridge. The series connection point of the DC-side capacitors C1 and C2 is connected to the series connection point of the switching device S5 and the AC interconnection capacitor C3. The AC interconnection capacitor C3 is connected in series between the switching devices S5 and S6, and the other ends of the switching devices S5 and S6 are connected to the same phase of AC power grids U1 and U2.

[0007] The rectifier bridge includes two forward-connected switching devices S1 and S2, and the inverter bridge includes two forward-connected switching devices S3 and S4.

[0008] The other end of the filter inductor L1 is connected to the series connection point of the forward-connected switching devices S1 and S2, and the other end of the filter inductor L2 is connected to the series connection point of the switching device S6 and the AC interconnecting capacitor C3.

[0009] By controlling the on and off of each switching device, the power flow direction of AC power grids U1 and U2 can be controlled.

[0010] When the switching device S5 is in the on state, the DC side voltage Ud is controlled to the set value by pulse width adjustment.

[0011] When the switching device S6 is in the on state, the voltage across the AC interconnect capacitor C3 is controlled by the pulse width adjustment method, thereby causing a phase difference between the AC power grids U1 and U2.

[0012] The present invention also includes a control method for a flexible interconnect device, the control method being applied to the flexible interconnect device, comprising the following steps:

[0013] (a) Drive switching devices S5 and S6 to conduct, connecting the flexible interconnection device to power grids U1 and U2;

[0014] (b) Set the reference voltage values ​​for DC-side capacitors C1 and C2 to [values ​​to be filled in]. The actual voltage v of DC-side capacitors C1 and C2 is controlled by adjusting the pulse width to turn the rectifier bridge on and off. d Make it equal to the voltage reference value.

[0015] (c) Set the active power P that the flexible interconnect device needs to transmit. * and reactive power Q * The voltage reference value of AC interconnect capacitor C3 was calculated. The actual voltage u of the AC interconnect capacitor C3 is controlled by adjusting the pulse width to turn the inverter bridge on and off. c Make it equal to the voltage reference value. This enables power transfer.

[0016] If a fault occurs in the AC power grid during power transfer, switching devices S5 and S6 are disconnected, and the rectifier bridge and inverter bridge are locked out.

[0017] The present invention also includes an apparatus comprising a memory and a processor, wherein:

[0018] Memory is used to store computer programs that can run on a processor;

[0019] A processor for executing steps of a control method for the flexible interconnect device while running the computer program.

[0020] The present invention also includes a computer-readable storage medium storing a computer program that, when executed by at least one processor, implements the steps of the control method for the flexible interconnect device.

[0021] Beneficial effects: Compared with the prior art, the technical solution of the present invention has the following beneficial effects: (1) The device of the present invention can realize flexible interconnection between different AC areas, and since the capacity flowing through the converter is small, there is no need to use a large capacity power electronic conversion device, which greatly reduces the equipment cost and improves the equipment efficiency; (2) The control method of the present invention can achieve the power transfer effect by controlling the capacitor voltage, without the need to use an isolation transformer, which reduces the size of the equipment and has high promotion value and significance in the field of power distribution network. Attached Figure Description

[0022] Figure 1 This is a topology diagram of the flexible interconnection device described in this invention;

[0023] Figure 2 This is a topology diagram of the rectifier circuit;

[0024] Figure 3 This is the topology diagram of the inverter circuit;

[0025] Figure 4 This is the control principle diagram of the rectifier circuit;

[0026] Figure 5 This is the control principle diagram of the inverter circuit. Detailed Implementation

[0027] The technical solution of the present invention will now be described in detail with reference to specific embodiments and accompanying drawings.

[0028] Example 1

[0029] like Figure 1 As shown, the flexible interconnection device of the present invention includes three identical power electronic conversion units M1, M2, and M3, which are respectively connected between the same phases of AC power grids U1 and U2. Taking unit M1 as an example, the power electronic conversion unit includes filter inductors L1 and L2, a rectifier bridge composed of two forward-connected series switching devices S1 and S2, an inverter bridge composed of two forward-connected series switching devices S3 and S4, reverse-connected series switching devices S5 and S6, DC-side capacitors C1 and C2, and AC interconnection capacitor C3. The specific connection relationship is as follows: one end of filter inductor L1 is connected to the neutral point of power grid U1, and the other end is connected to the series connection point of forward-connected series switching devices S1 and S2. One end of filter inductor L2 is connected to the circuit between switching device S6 and AC interconnection capacitor C3, and the other end is connected to the series connection point of forward-connected series switching devices S3 and S4. DC-side capacitors C1 and C2 are connected in series in the forward direction and then in parallel across the rectifier bridge and inverter bridge. The series connection point of DC-side capacitors C1 and C2 is connected to the series connection point of switching device S5 and AC interconnect capacitor C3. AC interconnect capacitor C3 is connected in series between switching devices S5 and S6. The other end of switching devices S5 and S6 is connected to the same phase of AC power grid U1 and U2.

[0030] By controlling the on and off states of switches S1 to S6, the power flow direction of AC power grids U1 and U2 can be controlled. S1, S2, S5, C1, C2, and L1 constitute a rectifier circuit, as shown below. Figure 2 As shown. S5 is in the on state, and the DC side voltage Ud is controlled to the set value by pulse width modulation. C1, C2, C3, S3, S4, S6, and L2 constitute an inverter circuit, as shown. Figure 3 As shown, S6 is in the conducting state, and the voltage across capacitor C3 is controlled by pulse width modulation, thereby creating a phase difference between AC grids U1 and U2, and achieving efficient power transmission.

[0031] Example 2

[0032] This invention provides a control method based on the flexible interconnection device in Embodiment 1, comprising the following steps:

[0033] (a) Drive switching devices S5 and S6 to conduct, connecting the flexible interconnection device to grid U1 and grid U2; monitor the operating status of grid U1 and U2, and when no loop closure is required, switch devices S5 and S6 are in the open state;

[0034] (b) Set the reference voltage values ​​for DC-side capacitors C1 and C2 to [values ​​to be filled in]. The actual voltage v of DC-side capacitors C1 and C2 is controlled by adjusting the pulse width of switching devices S1 and S2 in the rectifier bridge to control their on / off states. d Make it equal to the voltage reference value. like Figure 4 As shown.

[0035] (c) Set the active power P that the flexible interconnect device needs to transmit. * and reactive power Q * The line impedance is X line The voltages of grids U1 and U2 are respectively and The voltage reference value of AC interconnect capacitor C3 is calculated based on Kirchhoff's voltage law and current law. As shown in the following formula:

[0036]

[0037] The actual voltage u of the AC interconnect capacitor C3 is controlled by adjusting the pulse width of the inverter bridge to control the on / off state of S3 and S4. c Make it equal to the voltage reference value. This enables power transfer, such as Figure 5 As shown.

[0038] If a fault occurs on one side of the AC grid during power transfer, the switching devices S5 and S6 are disconnected, and the rectifier bridge and inverter are locked out.

[0039] The present invention also includes an apparatus comprising a memory and a processor, wherein:

[0040] Memory is used to store computer programs that can run on a processor;

[0041] A processor for executing steps of a control method for a flexible interconnect device while running the computer program.

[0042] The present invention also includes a computer-readable storage medium storing a computer program that, when executed by at least one processor, implements the steps of a control method for a flexible interconnect device.

Claims

1. A flexible interconnection device, characterized in that: It includes three identical power electronic conversion units, which are respectively connected between the same phases of AC power grids U1 and U2; The power electronic conversion unit includes filter inductors L1 and L2, a rectifier bridge, an inverter bridge, reverse-connected switching devices S5 and S6, DC-side capacitors C1 and C2, and AC interconnection capacitor C3. One end of the filter inductor L1 is connected to the neutral point of the AC power grid U1, and the other end is connected to the rectifier bridge; one end of the filter inductor L2 is connected between the switching device S6 and the AC interconnecting capacitor C3, and the other end is connected to the inverter bridge. The DC-side capacitors C1 and C2 are connected in series in the forward direction and then connected in parallel across the rectifier bridge and inverter bridge. The series connection point of the DC-side capacitors C1 and C2 is connected to the series connection point of the switching device S5 and the AC interconnection capacitor C3. The AC interconnecting capacitor C3 is connected in series between the switching devices S5 and S6, and the other end of the switching devices S5 and S6 is connected to the same phase of the AC power grid U1 and U2. The rectifier bridge includes two forward-connected switching devices S1 and S2, and the inverter bridge includes two forward-connected switching devices S3 and S4. The other end of the filter inductor L1 is connected to the series connection point of the forward-connected switching devices S1 and S2, and the other end of the filter inductor L2 is connected to the series connection point of the switching device S6 and the AC interconnecting capacitor C3.

2. The flexible interconnection device according to claim 1, characterized in that: By controlling the on and off of each switching device, the power flow direction of AC power grids U1 and U2 can be controlled.

3. The flexible interconnection device according to claim 2, characterized in that: When the switching device S5 is in the on state, the DC side voltage Ud is controlled to the set value by pulse width adjustment.

4. The flexible interconnection device according to claim 2, characterized in that: When the switching device S6 is in the on state, the voltage across the AC interconnect capacitor C3 is controlled by the pulse width adjustment method, thereby causing a phase difference between the AC power grids U1 and U2.

5. A control method for a flexible interconnected device, characterized in that, The control method, when applied to the flexible interconnect device of claim 1, includes the following steps: (a) Drive switching devices S5 and S6 to conduct, connecting the flexible interconnection device to power grids U1 and U2; (b) Set the reference voltage values ​​for DC-side capacitors C1 and C2 to be... The actual voltage of DC-side capacitors C1 and C2 is controlled by adjusting the pulse width to turn the rectifier bridge on and off. Make it equal to the voltage reference value. ; (c) Set the active power that the flexible interconnect device needs to transmit. and reactive power The voltage reference value of AC interconnect capacitor C3 was calculated. The actual voltage of the AC interconnect capacitor C3 is controlled by adjusting the pulse width to turn the inverter bridge on and off. Make it equal to the voltage reference value. This enables power transfer.

6. The control method for the flexible interconnection device according to claim 5, characterized in that: If a fault occurs in the AC power grid during power transfer, switching devices S5 and S6 are disconnected, and the rectifier bridge and inverter bridge are locked out.

7. A device, characterized in that, Includes memory and processor, wherein: Memory is used to store computer programs that can run on a processor; A processor, configured to, while running the computer program, perform the steps of the control method for the flexible interconnect device as described in any one of claims 5-6.

8. A computer-readable storage medium, characterized in that, The storage medium stores a computer program that, when executed by at least one processor, implements the steps of the control method for the flexible interconnect device as described in any one of claims 5-6.

Images