Controllable energy dissipation device control protection system and control method

Abstract

This invention discloses a control and protection system, including a control unit, a protection unit, a polar control unit, and a valve control and protection unit. All three units are redundantly configured and interconnected for communication. The invention also discloses a control method for this system. When the converter valve experiences overpressure, the valve control and protection unit sends a closing command to the control unit and the polar control unit for the controllable energy dissipation device control switch. The polar control unit forwards this command to the control unit, which then closes the control switch of the controllable energy dissipation device. When the overpressure disappears, the valve control and protection unit sends a tripping command to the polar control unit for the controllable energy dissipation device control switch. The polar control unit forwards this command to the control unit, which then trips the control switch of the controllable energy dissipation device. The redundant channel for the closing command of the controllable energy dissipation device control switch in this invention improves reliability.

Description

Technical Field

[0001] This invention belongs to the field of DC power transmission, and specifically relates to a controllable energy dissipation device control and protection system and control method. Background Technology

[0002] Conventional DC transmission systems based on grid-commutated converters (LCC-HVDC) have advantages such as low losses, low cost, and mature operating technology, but they also have disadvantages such as susceptibility to commutation failure, strong dependence on AC systems, and absorption of large amounts of reactive power. Flexible DC transmission systems based on voltage source converters (VSC-HVDC) have advantages such as no commutation failure, decoupled active and reactive power control, passive operation, and compact structure. Hybrid DC transmission systems combine the advantages of both LCC-HVDC and VSC-HVDC, and have received increasing research and application in recent years.

[0003] Figure 1 In a hybrid cascaded DC system, the rectifier side consists entirely of LCC converters, while the inverter side comprises an LCC converter and a VSC converter connected in series. When a fault occurs in the AC grid connected to the VSC on the inverter side, the active power output of the DC system is limited. However, the LCC, still in rectification mode, continues to supply power to the DC system according to a predetermined power reference value. At this time, the VSC voltage will rapidly increase due to the continuous accumulation of energy, endangering the safety of the DC equipment. To limit VSC overvoltage, a controllable energy dissipation device is connected in parallel between the VSC terminals. This device consists of a fixed component and a controlled component connected in series, with a control switch connected in parallel with the controlled component. When VSC overvoltage occurs, the control switch closes, bypassing the controlled component of the controllable energy dissipation device. The fixed component and the control switch provide an energy discharge circuit, limiting the VSC voltage. Once the system fault is cleared and the voltage between the VSC terminals returns to normal, the control switch is opened, restoring normal operation.

[0004] In DC systems, the polar control unit typically issues control commands to each device according to system requirements to achieve overall system-level control, while the control and protection of each component group achieves device-level control and protection. However, a drawback is the significant communication delay. Hybrid cascaded DC systems employing controllable energy dissipation devices for voltage limiting require the controllable energy dissipation devices to operate rapidly and reliably when the VSC (Voltage Control Controller) experiences overvoltage, placing higher demands on the communication delay and reliability between the control and protection systems. Summary of the Invention

[0005] The purpose of this invention is to provide a controllable energy dissipation device control and protection system and control method, which reduces the overall delay of closing the control switch of the controllable energy dissipation device and improves the reliability of the control and protection system.

[0006] To achieve the above objectives, the solution of the present invention is:

[0007] A controllable energy dissipation device control and protection system includes a control unit, a protection unit, a polar control unit, and a valve control and protection unit. Each control unit, protection unit, polar control unit, and valve control and protection unit is at least one set. Each control unit is connected and communicates with each protection unit, polar control unit, and valve control and protection unit. Each protection unit is connected and communicates with each control unit and polar control unit. Each polar control unit is connected and communicates with each control unit, protection unit, and valve control and protection unit. Each valve control and protection unit is connected and communicates with each control unit and polar control unit.

[0008] Furthermore: the controllable energy dissipation device is connected in parallel with the converter valve. The controllable energy dissipation device includes a fixed element, a controlled element, and a control switch. The fixed element and the controlled element are connected in series, and the control switch is connected in parallel with the controlled element.

[0009] Furthermore: the control unit and protection unit realize the control and protection of the controllable energy dissipation device, the valve control and protection unit realizes the control and protection of the converter valve, and the pole control unit realizes the control and protection of the DC pole.

[0010] Furthermore: the control unit is a dual set, fully redundant; the protection unit is a triple set, fully redundant; the valve control protection unit is a dual set, mutually serving as primary and backup; the extreme control unit is a dual set, mutually serving as primary and backup.

[0011] Furthermore, the control unit and the valve control and protection unit communicate via 5M / 50K modulated signals and fiber optic point-to-point communication.

[0012] Furthermore, the control unit and the extreme control unit communicate via gigabit Ethernet and fiber optic point-to-point communication.

[0013] Furthermore, the control unit and the protection unit communicate via the IEC60044-8 protocol and fiber optic point-to-point communication.

[0014] Furthermore, the extreme control unit and the valve control and protection unit communicate via 100 Mbps Ethernet.

[0015] Furthermore, the polar control unit and the protection unit communicate via the IEC60044-8 protocol and fiber optic point-to-point communication.

[0016] A control method for a controllable energy dissipation device control and protection system, the specific steps of which are as follows:

[0017] When a fault occurs in the power grid system:

[0018] (1) The valve control and protection unit monitors the converter valve voltage. When the converter valve voltage is greater than the preset value for a set time, the valve control and protection unit sends a controllable energy dissipation device switch closing command to the control unit and the pole control unit.

[0019] (2) The polar control unit forwards the controllable energy dissipation device switch closing command of the valve control protection unit to the control unit;

[0020] (3) After receiving the controllable energy dissipation device switch closing command from the valve control protection unit or the polar control unit, the control unit will control the controllable energy dissipation device switch to close.

[0021] After the power grid system fault is cleared:

[0022] (1) The valve control and protection unit monitors the converter valve voltage. When the converter valve voltage is less than or equal to the preset value for a set time, the valve control and protection unit sends a controllable energy dissipation device switch opening command to the pole control unit.

[0023] (2) The polar control unit forwards the controllable energy dissipation device switch opening command of the valve control protection unit to the control unit;

[0024] (3) After receiving the controllable energy dissipation device switch opening command from the polar control unit, the control unit will control the controllable energy dissipation device switch to open.

[0025] By adopting the above solution, the present invention has the following beneficial effects:

[0026] (1) The valve control protection unit communicates directly with the control unit of the controllable energy dissipation device, using 5M / 50K optical modulation wave signal to reduce the overall delay of the control switch closing of the controllable energy dissipation device and reduce the overvoltage stress of the converter valve.

[0027] (2) The control unit, valve control and protection unit and polar control unit of the controllable energy dissipation device are all configured with dual redundancy and are cross-connected for communication. The control switch closing command of the controllable energy dissipation device has redundant channels, which improves reliability. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of a hybrid cascaded DC system;

[0029] Figure 2 This is a schematic diagram of a controllable energy dissipation device, where 1 is a fixed element, 2 is a controlled element, and 3 is a control switch;

[0030] Figure 3 This is a schematic diagram of a control and protection system in one embodiment of this application. Detailed Implementation

[0031] The technical solution and beneficial effects of the present invention will be described in detail below with reference to the accompanying drawings.

[0032] Figure 1It is a hybrid cascaded DC system. Both the high and low ends on the rectifier side are LCC converters (for pole 1, LCC11 and LCC12 are connected in series; for pole 2, LCC13 and LCC14 are connected in series). On the inverter side, a hybrid cascaded structure of an LCC converter and a VSC converter is adopted (for pole 1, LCC21 is connected in series with three parallel VSC converters VSC11, VSC12, and VSC13; for pole 2, LCC22 is connected in series with three parallel VSC converters VSC21, VSC22, and VSC23). When a fault occurs in the AC-DC system on the VSC side and the power output of the DC system is limited, the voltage between the VSC terminals will rise rapidly, which may endanger the equipment safety in severe cases. Therefore, a controllable energy dissipation device is connected in parallel between the VSC terminals. Figure 2 It is a schematic diagram of the structure of a controllable energy dissipation device, including a fixed element 1, a controlled element 2, and a control switch 3. The fixed element 1 and the controlled element 2 are connected in series, and the control switch 3 is connected in parallel with the controlled element 2.

[0033] Figure 3 This is an embodiment of the control and protection system of a controllable energy dissipation device according to the present invention. The control and protection system of the controllable energy dissipation device for a single pole on the inverter side includes two sets of control units, three sets of protection units, two sets of pole control units, and two sets of valve control and protection units supporting each VSC. Among them, the two sets of pole control units are the main and standby for each other to achieve the overall control of the DC pole; the two sets of valve control and protection units supporting each VSC are the main and standby for each other to achieve the control and protection of the VSC converter; the two sets of control units are fully redundant, and the three sets of protection units are fully redundant to achieve the control and protection of the controllable energy dissipation device.

[0034] Each set of control units is connected and communicates with the two sets of valve control and protection units of each VSC. The communication is fiber optic point-to-point, and a 5M / 50K optical modulation wave signal is adopted, which can send the closing command of the controllable energy dissipation device control switch of the valve control and protection unit to the control unit faster, reduce the intermediate transmission link, reduce the closing command delay, and better limit the overvoltage between the VSC terminals.

[0035] Each set of valve control and protection units is connected and communicates with the two sets of pole control units, and a 100M Ethernet is adopted. Each set of pole control units is connected and communicates with the two sets of control units, and a 1G Ethernet is adopted with fiber optic point-to-point communication. The valve control and protection unit sends the opening and closing commands of the controllable energy dissipation device control switch to the pole control unit, and the pole control unit forwards them to the control unit, forming a redundant channel for the closing command of the controllable energy dissipation device control switch, ensuring the reliability of the closing of the controllable energy dissipation device control switch.

[0036] Each set of protection units is connected and communicates with the two sets of control units and the two sets of pole control units, and the communication is fiber optic point-to-point, and the IEC60044-8 protocol is adopted.

[0037] The present invention also discloses a control method for the control and protection system of a controllable energy dissipation device. The steps are as follows:

[0038] When a fault occurs in the AC / DC system on the VSC side:

[0039] (1) The valve control and protection unit monitors the average voltage of the corresponding VSC converter sub-module. When the average voltage of the sub-module is greater than the preset value and the duration is greater than the preset value, the valve control and protection unit sends a controllable energy dissipation device switch closing command to the control unit and the pole control unit.

[0040] (2) The polar control unit forwards the controllable energy dissipation device switch closing command of the valve control protection unit to the control unit;

[0041] (3) After receiving the controllable energy dissipation device switch closing command from any set of valve control protection unit or polar control unit, the control unit will close the control switch.

[0042] After the AC / DC system fault on the VSC side is cleared:

[0043] (1) The valve control and protection unit monitors the average voltage value of the corresponding VSC converter valve sub-module. When the average voltage value of the sub-module is less than the preset value and the duration is greater than the preset value, the valve control and protection unit sends a controllable energy dissipation device switch opening command to the pole control unit.

[0044] (2) After receiving the controllable energy dissipation device switch-off command from all VSC valve control protection units, the polar control unit sends the controllable energy dissipation device switch-off command to the control unit.

[0045] (3) After receiving the controllable energy dissipation device switch opening command from any set of polar control units, the control unit will open the control switch.

[0046] Finally, it should be noted that the above embodiments are merely illustrative of the technical solutions of the present invention and not intended to limit it. Those skilled in the art should understand that modifications or equivalent substitutions can be made to the specific embodiments of the present invention, but such modifications or alterations are all within the scope of protection claimed in the pending patent application.

Claims

1. A control method based on a controllable energy dissipation device control and protection system, characterized in that, The controllable energy dissipation device control and protection system includes a control unit, a protection unit, a polar control unit, and a valve control and protection unit, with at least one set of each unit. Each control unit is connected and communicates with each protection unit, polar control unit, and valve control and protection unit. Each protection unit is connected and communicates with each control unit and polar control unit. Each polar control unit is connected and communicates with each control unit, protection unit, and valve control and protection unit. Each valve control and protection unit is connected and communicates with each control unit and polar control unit. The controllable energy dissipation device is connected in parallel with the converter valve. The controllable energy dissipation device includes a fixed element, a controlled element, and a control switch. The fixed element and the controlled element are connected in series, and the control switch is connected in parallel with the controlled element. The specific steps of the method are as follows: When a fault occurs in the power grid system: (1) The valve control and protection unit monitors the converter valve voltage. When the converter valve voltage is greater than the preset value for a set time, the valve control and protection unit sends a controllable energy dissipation device switch closing command to the control unit and the pole control unit. (2) The polar control unit forwards the controllable energy dissipation device switch closing command of the valve control protection unit to the control unit; (3) After receiving the controllable energy dissipation device switch closing command from the valve control protection unit or the polar control unit, the control unit closes the control switch of the controllable energy dissipation device. After the power grid system fault is cleared: (1) The valve control and protection unit monitors the converter valve voltage. When the converter valve voltage is less than or equal to the preset value for a set time, the valve control and protection unit sends a controllable energy dissipation device switch opening command to the pole control unit. (2) The polar control unit forwards the controllable energy dissipation device switch opening command of the valve control protection unit to the control unit; (3) After receiving the controllable energy dissipation device switch opening command from the polar control unit, the control unit opens the control switch of the controllable energy dissipation device.

2. The control method based on a controllable energy dissipation device control and protection system as described in claim 1, characterized in that, The control unit and protection unit realize the control and protection of the controllable energy dissipation device, the valve control and protection unit realizes the control and protection of the converter valve, and the pole control unit realizes the control and protection of the DC pole.

3. The control method based on a controllable energy dissipation device control and protection system as described in claim 1, characterized in that, The control unit is dual-set and fully redundant; the protection unit is triple-set and fully redundant; the valve control and protection unit is dual-set and mutually primary / backup; the extreme control unit is dual-set and mutually primary / backup.

4. The control method based on a controllable energy dissipation device control and protection system as described in claim 1, characterized in that, The control unit and the valve control and protection unit communicate via 5M / 50K modulated signal and fiber optic point-to-point communication.

5. The control method based on a controllable energy dissipation device control and protection system as described in claim 1, characterized in that, The control unit and the extreme control unit communicate via gigabit Ethernet and fiber optic point-to-point communication.

6. The control method based on a controllable energy dissipation device control and protection system as described in claim 1, characterized in that, The control unit and the protection unit communicate via the IEC60044-8 protocol and fiber optic point-to-point communication.

7. The control method based on a controllable energy dissipation device control and protection system as described in claim 1, characterized in that, The polar control unit and the valve control and protection unit communicate via 100 Mbps Ethernet.

8. The control method based on a controllable energy dissipation device control and protection system as described in claim 1, characterized in that, The polar control unit and the protection unit communicate via the IEC60044-8 protocol and fiber optic point-to-point communication.

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