Abstract: An electronic device and a variable frequency control system using the electronic device. The electronic device may comprise: a shielding layer, which is inserted between a current outflow terminal of a switching device and a grounding conductor; and a conductive elastomer, which is used for connecting the current outflow terminal to the shielding layer.

Abstract: The invention relates to an island converter overload limit method and device for a bipolar flexible DC transmission system, and belongs to the field of DC transmission. During stable island operation, both bipolar converters adopt a voltage-frequency droop control strategy; and once it is detected that one converter is overloaded, the control mode of the overloaded converter is automatically switched to active-wattless power control from voltage-frequency droop control to fulfill an overload limit function. The method effectively avoids an overload of the bipolar flexible DC transmission system under island operation, effectively maintains the AC voltage and frequency stable, and has important guiding significance for applying island systems to DC power grids.

Abstract: During initiation under an isolated island condition, the amplitude of a voltage reference wave output generated by a flexible DC transmission control and protection system is in a segmented mode, wherein a first segment of the reference wave amplitude begins at zero or a fixed value Ux and rapidly increases to Ua kV at a rate of a kV/s, avoiding a low output voltage reference wave and high error and harmonic content of a sampled voltage and current. A second segment increases to Ub kV at a rate of ? kV/s, a third segment increases to Uc kV at a rate of ? kV/s, and the Nth segment increases to a rated voltage of UN kV at a rate of ? kV/s, thereby achieving non-disturbance and shockless initiation of a flexible DC transmission system under an isolated island condition.

Abstract: Disclosed in the present invention is a voltage and current control method for a direct-current transmission system. The method comprises: calculating a DC voltage reference value of a voltage source converter of a DC voltage control end, on the basis whether a direct-current voltage end of a direct-current pole of a direct-current transmission system substantially controls a direct-current voltage; using ½ of the calculated direct-current voltage reference value of the voltage source converter as a bridge arm voltage direct-current bias, calculating a difference between the direct-current voltage reference value of the voltage source converter and a measured direct-current voltage value, and inputting the difference into a direct-current voltage control outer loop of the voltage source converter to perform closed-loop control, so as to control the direct-current voltage or the direct current of the direct-current pole.

Abstract: A coordinated control method for series voltage source converter valve groups comprises: allocating a total direct-current voltage reference value or a total active power reference value at the end where a direct-current electrode series voltage source converter valve group is located according to the total number of voltage source converter valve groups in series; for a direct-current voltage control end, controlling the direct-current voltage of each valve group according to the assigned direct-current voltage reference value for each valve group; for an active power control end, controlling the active power of each valve group according to the assigned active power reference value for each valve group and based on adding the active power compensation amount of the valve group which has voltage equalization effects on the valve group. Correspondingly, also providing a coordinated control device for series voltage source converter valve groups.

Abstract: The invention relates to an island converter overload limit method and device for a bipolar flexible DC transmission system, and belongs to the field of DC transmission. During stable island operation, both bipolar converters adopt a voltage-frequency droop control strategy; and once it is detected that one converter is overloaded, the control mode of the overloaded converter is automatically switched to active-wattless power control from voltage-frequency droop control to fulfill an overload limit function. The method effectively avoids an overload of the bipolar flexible DC transmission system under island operation, effectively maintains the AC voltage and frequency stable, and has important guiding significance for applying island systems to DC power grids.

Abstract: A coordinated control method for series voltage source converter valve groups comprises: allocating a total direct-current voltage reference value or a total active power reference value at the end where a direct-current electrode series voltage source converter valve group is located according to the total number of voltage source converter valve groups in series; for a direct-current voltage control end, controlling the direct-current voltage of each valve group according to the assigned direct-current voltage reference value for each valve group; for an active power control end, controlling the active power of each valve group according to the assigned active power reference value for each valve group and based on adding the active power compensation amount of the valve group which has voltage equalization effects on the valve group. Correspondingly, also providing a coordinated control device for series voltage source converter valve groups.

Abstract: Provided in the present invention is a direct current power grid voltage control method, dividing control of a direct current power grid voltage into three processes, namely natural voltage regulation, first voltage regulation and second voltage regulation; the converter stations in the direct current power grid are divided into three types, namely power regulation converter stations, auxiliary voltage regulation converter stations, and voltage regulation converter stations, on the basis of whether the converter station has a voltage regulation capacity, the power regulation converter stations operating in a fixed power control mode, the voltage regulation converter stations operating in a fixed voltage control mode or an auxiliary voltage control mode, and the auxiliary voltage control converter stations operating in the auxiliary voltage control mode; all the converter stations in the direct current power grid participate in natural voltage regulation, the auxiliary voltage regulation converter stations and

Abstract: Disclosed in the present invention is a voltage and current control method for a direct-current transmission system. The method comprises: calculating a DC voltage reference value of a voltage source converter of a DC voltage control end, on the basis whether a direct-current voltage end of a direct-current pole of a direct-current transmission system substantially controls a direct-current voltage; using ½ of the calculated direct-current voltage reference value of the voltage source converter as a bridge arm voltage direct-current bias, calculating a difference between the direct-current voltage reference value of the voltage source converter and a measured direct-current voltage value, and inputting the difference into a direct-current voltage control outer loop of the voltage source converter to perform closed-loop control, so as to control the direct-current voltage or the direct current of the direct-current pole.

Abstract: During initiation under an isolated island condition, the amplitude of a voltage reference wave output generated by a flexible DC transmission control and protection system is in a segmented mode, wherein a first segment of the reference wave amplitude begins at zero or a fixed value Ux and rapidly increases to Ua kV at a rate of a kV/s, avoiding a low output voltage reference wave and high error and harmonic content of a sampled voltage and current. A second segment increases to Ub kV at a rate of ? kV/s, a third segment increases to Uc kV at a rate of ? kV/s, and the Nth segment increases to a rated voltage of UN kV at a rate of ? kV/s, thereby achieving non-disturbance and shockless initiation of a flexible DC transmission system under an isolated island condition.

Abstract: A reconfigurable MMC sub-module unit and a control unit thereof are provided, the reconfigurable MMC sub-module unit is mainly formed by an MMC sub-module unit and a reconfigurable mechanism, wherein the reconfigurable mechanism is formed by switches, and the conversion of MMC sub-module unit topology is achieved through switching on and off the switches in the reconfigurable mechanism. According to the reconfigurable MMC sub-module unit and the control unit thereof, the rapid change of a topology structure for a converter can be achieved, which is suitable for the demand of the line connection of the medium-voltage power distribution network and variable topologies, and meets requirements of dynamic simulation experiment for different converter topologies in the dynamic simulation experiment, thereby reducing construction costs and duration, improving experiment efficiency, and having high flexibility and strong versatility.

Abstract: A method for fault positioning and recovery of a voltage source converter includes following steps. Locking a converter station when it is detected that an alternating-current voltage contains a zero sequence voltage or a direct-current voltage contains an unbalanced voltage. Positioning a fault by continuing to detect the zero sequence voltage of an alternating-current side of the converter. Recovering operation of each station after the fault is positioned. The method for fault positioning and recovery is simple, practical, has high reliability, and can effectively detect the problems that each station contains a zero sequence voltage of an alternating-current side and cannot easily position a fault caused due to transmission of the zero sequence voltage of the alternating-current side to an opposite-side alternating-current system via a voltage source converter.

Abstract: Provided in the present invention is a direct current power grid voltage control method, dividing control of a direct current power grid voltage into three processes, namely natural voltage regulation, first voltage regulation and second voltage regulation; the converter stations in the direct current power grid are divided into three types, namely power regulation converter stations, auxiliary voltage regulation converter stations, and voltage regulation converter stations, on the basis of whether the converter station has a voltage regulation capacity, the power regulation converter stations operating in a fixed power control mode, the voltage regulation converter stations operating in a fixed voltage control mode or an auxiliary voltage control mode, and the auxiliary voltage control converter stations operating in the auxiliary voltage control mode; all the converter stations in the direct current power grid participate in natural voltage regulation, the auxiliary voltage regulation converter stations and

Abstract: A fault current limiting control and protection coordination method for a converter of a flexible direct current transmission system operating in an islanding state is provided. The current output command limit Imax is used to limit the current commands of inner loop currents, and in the event of a fault, Imax is set equal to or slightly larger than a value for an AC line overcurrent protection section.

Abstract: The present invention discloses a passive islanding to grid-connection switching method for a VSC HVDC transmission system. When the VSC HVDC transmission system in an island operation state, whether the VSC HVDC transmission system enters an grid-connection state is determined by detecting whether an overcurrent phenomenon has occurred in a converter valve-side three-phase alternating-current or a converter bridge arm current, and detecting a change status of an alternating-current side voltage. The system is controlled to switch from an island operation control mode to a grid-connection control mode. At a moment of switching, the online control mode is smoothly switched to by changing a power instruction and performing phase tracking on a current grid voltage, so that continuous operation of the system is maintained.

Abstract: A series compensation device suitable to double-circuit lines is disclosed. The device includes one series transformer and one converter. One converter and dual-circuit transmission lines are respectively connected to three windings of one series transformer. In the solution provided in the present application, the device can be independently installed in a power transmission system to be used as a static synchronous series compensator, and can also be used as a component of a unified power flow controller, a convertible static compensator, an interline power flow controller and a unified power quality conditioner to be connected to a power transmission system device in series. The device can save the capacity of a converter, improve the application efficiency of the series compensation device, and reduce the cost and area occupation.

Abstract: A fault current limiting control and protection coordination method for a converter of a flexible direct current transmission system operating in an islanding state, wherein the current output command limit Imax is used to limit the current commands I*Ldq of inner loop dq currents, and in the event of the fault of AC system, Imax is set equal to or slightly larger than a value for an AC line overcurrent protection section III. The value for the II section of the converter bridge arm overcurrent protection is smaller than the value for the II section of the AC line overcurrent protection or the value is equal; the set value for AC line overcurrent protection section I is smaller than the set value for converter bridge arm overcurrent protection section I; the value for proximal AC line overcurrent protection section II is less than or equal to the value for converter bridge arm overcurrent protection section II, and under such condition, the delay is longer than the AC line overcurrent protection section II.

Abstract: Provided is a method for controlling a zero sequence voltage of a voltage source converter. When an alternating current system ground fault occurs, a zero sequence voltage at an alternating current (AC) side or a zero sequence voltage at a direct current (DC) side of a converter is detected. If the detected zero sequence voltage is greater than a set value V0ref, a DC side voltage of the converter can be increased to a set value Udc0, thereby generating an appropriate reference wave at the AC side of the converter to match an AC voltage, and accordingly controlling overmodulation of a reference wave at a faulty station to suppress fluctuation of a DC voltage.

Abstract: A reconfigurable MMC sub-module unit and a control unit thereof are provided, the reconfigurable MMC sub-module unit is mainly formed by an MMC sub-module unit and a reconfigurable mechanism, wherein the reconfigurable mechanism is formed by switches, and the conversion of MMC sub-module unit topology is achieved through switching on and off the switches in the reconfigurable mechanism. According to the reconfigurable MMC sub-module unit and the control unit thereof, the rapid change of a topology structure for a converter can be achieved, which is suitable for the demand of the line connection of the medium-voltage power distribution network and variable topologies, and meets requirements of dynamic simulation experiment for different converter topologies in the dynamic simulation experiment, thereby reducing construction costs and duration, improving experiment efficiency, and having high flexibility and strong versatility.

Abstract: A series compensation device suitable to double-circuit lines is disclosed. The device includes one series transformer and one converter. One converter and dual-circuit transmission lines are respectively connected to three windings of one series transformer. In the solution provided in the present application, the device can be independently installed in a power transmission system to be used as a static synchronous series compensator, and can also be used as a component of a unified power flow controller, a convertible static compensator, an interline power flow controller and a unified power quality conditioner to be connected to a power transmission system device in series. The device can save the capacity of a converter, improve the application efficiency of the series compensation device, and reduce the cost and area occupation.