Nr Electric Co., Ltd

Nr Engineering Co., Ltd

Nr Electric Engineering Co., Ltd.

Yunlong Dong

Yu Lu

Jie Tian

Haiying Li

Zhaoqing Hu

Gang Li

Dongming Cao

Nannan Wang

Jiudong Ding

Ke Wang

Jiang Lu

Lei Pan

Haibin Liu

Chongxue Jiang

Tiangui Jiang

Defeng Qiu

Chao Liu

Yongping Wang

Quanrong Shen

Shunke Sui

Ruhai Huang

Jiacheng Wang

Hui Wang

Wenqiang Zhao

Jianyang Lian

Xinbao Wang

Baoli Chang

Minglian Zhu

Fengfeng Ding

Yadong Feng

Qiwen Zhou

Xianlai Hu

Guorong Shen

Xiuda Ma

Baoshun Zhang

Hua Xie

Jianchun Li

Jianmin Xiao

Yizhe Lin

Tieqiang Ren

Feixiang Wu

Changjiang Zhan

Zhenxia Shao

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.

Converter control method and device

Disclosed are a control method and system for a parallel converter system, including a common AC voltage controller and a separate current controller for each converter; the AC voltage controller generates an active current, a wattless current, and a system voltage phase reference value and, by means of communication, sends same to the current controller of each converter in island control mode to be a converter control signal; the active and wattless current outputted by each converter, along with the corresponding current reference value, accomplish the objective of the parallel converter system collectively controlling the amplitude and frequency of an AC bus voltage. The method and system are highly reliable and effectively ensure the synchronization of a plurality of converters.

Control system and control method for parallel converter system

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 Uand rapidly increases to UkV 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 UkV at a rate of &#x3b2; kV/s, a third segment increases to UkV at a rate of &#x3b3; kV/s, and the Nsegment increases to a rated voltage of UkV at a rate of &#x3b5; kV/s, thereby achieving non-disturbance and shockless initiation of a flexible DC transmission system under an isolated island condition.

Method for initiating flexible DC transmission system under isolated island condition

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 &#xbd; 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. Correspondingly, also provided is a voltage and current control device for the direct-current transmission system. By the means of the present invention, the direct-current voltage and the direct current of the direct-current transmission system provided with the voltage source converter can be effectively controlled.

Voltage and current control method and device for direct-current power transmission system

The present invention provides a series compensator and a control method. The series compensator includes a series transformer, a series transformer bypass device, a voltage source converter, a high-speed converter bypass device, a high-speed switch, and a reactor. The reactor and the high-speed switch are connected in parallel to form a current limiting module; one winding of the series transformer has two ends connected in series to a line, and the other winding thereof is sequentially connected to the current limiting module and the high-speed converter bypass device; the voltage source converter and the high-speed converter bypass device are connected in parallel; and at least one winding of the series transformer are connected in parallel to at least one series transformer bypass device. The series compensator of the present invention indirectly provides the current limiting module, so as to effectively limit the short-circuit current of a system, reduce the fault current to which the compensator is subjected, and improve the reliability of an alternating current system and the series compensator. Moreover, the current limiting module has a low voltage level, and the high-speed switch has a small breaking current, thereby providing good industrial applicability.

Series compensator and control method

A DC voltage coordination control method is applied to a multi-terminal VSC-HVDC power transmission system or a VSC-HVDC power grid system. When a lower-level control is used in the active power control mode, the active power reference value of the converter is generated according to the converter DC voltage and the converter DC voltage active power curve; it also includes an upper-level control to adjust the control mode and active power setting value of the lower-level control to ensure the steady-state performance of the system. This method has low dependence on communication, avoids the problem that the fixed slope and margin cannot meet all operating conditions, and is suitable for large-scale VSC-HVDC systems, and has scalability.

Direct current voltage coordination control method

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. The direct-current voltage equalization of each valve group in operation of the direct-current voltage control end or the active power control end of the series voltage source converter valve group is achieved.

Coordinated control method and device for series voltage source converter valve group

A method and apparatus for suppressing the impact of a compensator on line distance protection is provided, wherein the method comprises: obtaining a first current of a line connected to a compensator or series converters in the compensator, and a first voltage of a bus connected to the compensator or the line connected to the compensator; exiting the series converters and series transformers if the first current is greater than a preset current threshold and a duration is greater than a first preset time threshold; exiting the series converters and the series transformers if the first voltage is less than or equal to a preset voltage threshold and duration is greater than a second preset time threshold set the output voltage of the series converters to zero, and if a second current of an element corresponding to the first current meets conditions which the first current needs to meet; and otherwise, canceling the setting of the output voltage of the series converters to zero and obtaining a first current if a second voltage of the line corresponding to the first voltage is greater than the preset voltage threshold and the duration is greater than a third preset time threshold.

Method and apparatus for suppressing impact of compensator on line distance protection

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 the voltage regulation converter stations participate in first voltage regulation, and the voltage regulation converter stations participate in second voltage regulation; by means of a combination of the three voltage regulation processes, accurate control of the direct current voltage can be implemented in a steady state, and direct current voltage change can be suppressed in a transient state.

Direct current power grid voltage control method

Provided is an on-line input and quit control method for a voltage-source converter unit. The method achieves the on-line input of a voltage-source converter unit by means of performing steps, such as charging control, deblocking transfer control and operation adjustment control, on a voltage-source converter to be input, and achieves the on-line quitting of the voltage-source converter unit by means of performing steps, such as direct-current voltage reduction control, bypass transfer control and converter blocking control, on a voltage-source converter to be quit. Correspondingly, provided is an on-line input and quit control device for a voltage-source converter unit, which can achieve the on-line steady input and quitting of a voltage-source converter in a series-type hybrid direct-current power transmission system or a series-type flexible direct-current power transmission system, without affecting the normal and stable operation of other already running converters.

On-line input control method, on-line input and quit device for voltage-source converter unit

A sub-module based hybrid converter is provided. By setting a half-controlled charging link of changing full bridge sub-modules from a blocked state to a half-blocked state one by one in a charging process, and raising the voltages of half bridge sub-modules to reach the starting point of a half bridge sub-module based self-powered supply in an uncontrolled stage of the half bridge sub-modules, the starting point of the sub-module based self-powered supply is increased, and the design difficulty of the sub-module based self- powered supply is reduced. The present invention also includes another charging method for a sub-module based hybrid converter.

Charging method for sub-module based hybrid converter

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.

Reconfigurable MMC sub-module unit and control unit thereof

The present invention discloses a charging method for a sub-module based hybrid converter. By setting a half-controlled charging link of half-blocking all full bridge sub-modules in a charging process, and raising the voltages of half bridge sub-modules to reach the starting point of a half bridge sub-module based self-powered supply in an uncontrolled stage of the half bridge sub-modules, the starting point of the sub-module based self-powered supply is increased, and the design difficulty of the sub-module based self-powered supply is reduced. The present invention also discloses another charging method for a sub-module based hybrid converter. The above objective can also be achieved by setting a half-controlled charging link of bypassing all full bridge sub-modules in the charging process.

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.

Method and system for fault positioning and recovery of voltage source converter

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.

Fault current limiting control and protection coordination method for converter of flexible direct current power transmission system operating in islanding state

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Jiangsu, China

Yunlong Dong