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 line power control method and system for a unified power flow controller includes outer loop line power control, inner loop valve side current control, and converter valve control. Series-side converter valve side current reference values Isedref and Iseqref are calculated by means of the outer loop line power control according to line power instructions Pref and Qref that are input, a measured line power UL, and measured line power Pline and Qline; a converter output voltage reference value Ucref is calculated by means of the inner valve side current control according to the valve side current reference values that are output by means of the outer loop power control, a measured valve side current, and a measured valve side voltage; and finally, a converter outputs, according to the voltage reference value, a corresponding voltage to control line power to achieve a reference value.

Abstract: According to the overload current limiting method for a voltage source converter, when a pole control system receives a water-cooling overload current limiting instruction, an active and reactive instruction are changed at the same time according to a specified slope, so that an absolute value of an arm current of the converter decreases in a fixed slope, and can be ensured that active power and reactive power fall to zero at the same time, and a water-cooling load limiting aim of the converter can be achieved by reducing the arm current. After a water-cooling overload power limiting instruction received by the pole control system is cancelled, a current value of the active power and the inactive power remain unchanged. When a water-cooling overload power limiting instruction is received again, decrease continues on the basis of current power values until the power falls to zero.

Abstract: The present invention provides a method for inhibiting multiple inverter stations from entering a passive control mode in an island state. The method includes dividing inverter stations into groups in advance; a principle for group division is dividing inverter stations whose alternating-current sides are connected to each other through an alternating-current line in a normal running condition into a group; priorities of the inverter stations are preset in each group to tune relevant fixed values of the inverter stations for island detection; a tuning principle is that an inverter station with a higher priority has a more sensitive relevant fixed value, and an island state is more easily detected for the corresponding inverter station; an inverter station for which an island state is detected can enter a passive control mode only when all the other inverter stations with priorities higher than the priority of the inverter station in the group send enabling signals.

Abstract: The disclosure is related to a voltage-source multi-level converter including a phase unit. The phase unit includes first and second bridge arms, each includes modules and reactor connected in series. In the first bridge arm, a first terminal of first reactor is connected to alternating-current terminal of the phrase unit, a second terminal thereof is connected to a first terminal of the first modules, and second terminal of the first modules is connected to first DC terminal of the phrase unit. In the second bridge arm, a first terminal of the second reactor is connected to the alternating-current terminal, a second terminal thereof is connected to a first terminal of the second modules, and a second terminal of the second modules is connected to second DC terminal of the phrase unit. Then, a parallel fault shunt circuit is connected between the second terminals of the first and second reactors.

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 unified power flow controller for a double-circuit transmission line comprises at least one parallel-connection transformer, three current converters, at least two series-connection transformers, a parallel-connection side switching circuit, a series-connection side switching circuit and a direct current common bus. The series-connection transformers connected with at least one group of by-pass switches in parallel. The three current converters connected to each loop line in series after being connected with at least one series-connection transformer through the series-connection side switching circuit. The three current converters connected to an alternating current system after connected with at least one parallel-connection transformer through a parallel-connection side switching circuit starting circuit. The three current converters are connected to the direct current common bus through a transfer switch.

Abstract: A submodule distributed control method, device and system are provided. Submodules of each bridge arm are grouped. Each group corresponds to one valve based controller. An upper-level control device calculates a weight of each group according to a bridge arm current, an average voltage of normal submodules in each group, and the number of the normal submodules in each group; calculates, according to the number of submodules to be input in a corresponding bridge arm, the number of submodules being input in each group and delivers the number to the valve based controller. The valve based controller operates according to a voltage balancing policy and a gating method that are provided in the prior art.

Abstract: The present invention discloses a direct current (DC) voltage control method. The present invention further discloses an apparatus for implementing the method. With the present invention, DC voltage oscillation of a system, which is caused when a DC voltage primary control station stops running, may be reduced.

Abstract: The present invention provides a method for inhibiting multiple inverter stations from entering a passive control mode in an island state. The method includes dividing inverter stations into groups in advance; a principle for group division is dividing inverter stations whose alternating-current sides are connected to each other through an alternating-current line in a normal running condition into a group; priorities of the inverter stations are preset in each group to tune relevant fixed values of the inverter stations for island detection; a tuning principle is that an inverter station with a higher priority has a more sensitive relevant fixed value, and an island state is more easily detected for the corresponding inverter station; an inverter station for which an island state is detected can enter a passive control mode only when all the other inverter stations with priorities higher than the priority of the inverter station in the group send enabling signals.

Abstract: A submodule distributed control method, device and system are provided. Submodules of each bridge arm are grouped. Each group corresponds to one valve based controller. An upper-level control device calculates a weight of each group according to a bridge arm current, an average voltage of normal submodules in each group, and the number of the normal submodules in each group; calculates, according to the number of submodules to be input in a corresponding bridge arm, the number of submodules being input in each group and delivers the number to the valve based controller. The valve based controller operates according to a voltage balancing policy and a gating method that are provided in the prior art.

Abstract: A starting and stopping method for a static synchronous series compensator (SSSC) is provided.

Abstract: A method for incorporating a non-operating station into an operating system in a multi-terminal flexible DC transmission system. The method includes selecting a STATCOM operation mode for the non-operating station; opening a bypass switch at an AC side and connecting a charging resistor to an AC line; closing the AC incoming-line breaker, and pre-charging a converter valve of the non-operating station through the resistor; closing the bypass switch after the pre-charging; selecting a constant-DC voltage control mode for the non-operating station to perform deblocking; controlling the difference between a non-operating station DC voltage value and an operating system direct voltage value to be within an allowable range; closing the pole-connection device at the DC side of a converter of the non-operating station; and switching the non-operating station from the STATCOM operation mode to a DC operation mode, and incorporating the non-operating station into the operating system.

Abstract: A line power control method and system for a unified power flow controller includes outer loop line power control, inner loop valve side current control, and converter valve control. Series-side converter valve side current reference values Isedref and Iseqref are calculated by means of the outer loop line power control according to line power instructions Pref and Qref that are input, a measured line power UL, and measured line power Pline and Qline; a converter output voltage reference value Ucref is calculated by means of the inner valve side current control according to the valve side current reference values that are output by means of the outer loop power control, a measured valve side current, and a measured valve side voltage; and finally, a converter outputs, according to the voltage reference value, a corresponding voltage to control line power to achieve a reference value.

Abstract: A unified power flow controller for a double-circuit transmission line comprises at least one parallel-connection transformer, three current converters, at least two series-connection transformers, a parallel-connection side switching circuit, a series-connection side switching circuit and a direct current common bus. The series-connection transformers connected with at least one group of by-pass switches in parallel. The three current converters connected to each loop line in series after being connected with at least one series-connection transformer through the series-connection side switching circuit. The three current converters connected to an alternating current system after connected with at least one parallel-connection transformer through a parallel-connection side switching circuit starting circuit. The three current converters are connected to the direct current common bus through a transfer switch.

Abstract: A method for charging a modular multilevel converter includes: firstly, electrifying DC side of a converter; after voltages of submodules are stabilized, deblocking the converter, turning on all the submodules, then reducing the number of turned on submodules in phase unit; when over-current occurs on a bridge arm, temporarily increasing the number of turned on submodules to suppress the over-current; after the voltages of the sub-modules are stabilized, continuously reducing the number of the turned on submodules until the number of the turned on submodules in the phase unit is finally equal to the number of working submodules of the bridge arm, so as to smoothly transit to a normal operation state. The DC side is charged, such that the voltages of the submodules reach a working voltage before the converter normally operates, and an impacting current is avoided in the charging process by using a proper control strategy.

Abstract: A voltage-source multi-level converter, including a phase unit (0).

Abstract: A method for charging a modular multilevel converter includes: firstly, electrifying DC side of a converter; after voltages of submodules are stabilized, deblocking the converter, turning on all the submodules, then reducing the number of turned on submodules in phase unit; when over-current occurs on a bridge arm, temporarily increasing the number of turned on submodules to suppress the over-current; after the voltages of the sub-modules are stabilized, continuously reducing the number of the turned on submodules until the number of the turned on submodules in the phase unit is finally equal to the number of working submodules of the bridge arm, so as to smoothly transit to a normal operation state. The DC side is charged, such that the voltages of the submodules reach a working voltage before the converter normally operates, and an impacting current is avoided in the charging process by using a proper control strategy.

Abstract: The present invention discloses a coordination control method of a multi-terminal VSC-HVDC transmission system. If a direct current voltage master control station shuts down, a direct current voltage control slave station takes over direct current voltage control, and remaining convertor stations keep original control modes. The takeover steps comprise that under the condition that inter-station communications are effective, the master control station sends a shutdown message to the slave station through the inter-station communications, and when the slave station monitors that the direct current voltage master control station shuts down, the slave station switches a current control mode into a direct current voltage control mode; and under the condition that inter-station communications fail or inter-station communications are absent, the slave station monitors changes of the direct current voltage of a system.

Abstract: The present invention discloses a direct current (DC) voltage control method. The present invention further discloses an apparatus for implementing, the method. With the present invention DC voltage oscillation of a system, which is caused when a DC voltage primary control station stops running, may be reduced.