NR Electrical Co.

Nanjing, China

NR Electrical Co.

Nanjing, China
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Patent
NR Electrical Co. and NR Engineering Co. | Date: 2017-08-30

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 a 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.


Patent
NR Electrical Co. and NR Engineering Co. | Date: 2017-08-30

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.


Patent
NR Electrical Co. and NR Electrical Engineering Co. | Date: 2017-03-01

The invention discloses a high voltage/ultrahigh voltage direct current transmission inverter side frequency control implementing method, comprising the following steps: transmitting a deviation between the inverter side power grid frequency and rated frequency to the inverter side frequency controller, wherein the frequency controller regulates and outputs a modulation quantity by adopting self-adaptive parameters according to different operation conditions; when the interstation communication is normal, the modulation quantity output of the inverter side frequency controller causes the rectifier side and the inverter side to form a new power/current order through the interstation communication, thus realizing the inverter side frequency control by changing the size of the transmission power; when the interstation communication is abnormal, converting the inverter side to current control from voltage control and converting the rectifier side to voltage control from current control; superposing the modulation quantity output of the inverter side frequency controller to the power/current order of the inverter side, changing the size of the transmission power to realizing the inverter side frequency control. The method realizes the fast efficient regulation function on the inverter side frequency, and effectively solves the problem of the inverter side frequency control for the interstation communication failure.


Patent
NR Electrical Co. and NR Electrical Engineering Co. | Date: 2017-03-08

A relay protection method against LC parallel circuit detuning faults comprises the steps of: a relay protection device samples a current of a parallel LC, that is, a reactor and a capacitor, and samples a total current flowing through the whole LC; convert the current of the reactor into a current of an equivalent capacitor; calculate amplitudes of the current of the equivalent capacitor and a current of a realistic capacitor and calculate an amplitude of the total current flowing through the LC; calculate a current amplitude ratio of the equivalent capacitor to the realistic capacitor; and when the amplitude of the total current flowing through the LC is large enough, send an alarm signal or a trip after a setting time delay if the current ratio exceeds a preset upper and lower limit range. Also provided is a corresponding relay protection device. The relay protection method and device against LC parallel circuit detuning faults can improve stability of calculation results of a current ratio and raise sensitivity and rapidity of protection.


Patent
NR Electrical Co. and NR Electrical Engineering Co. | Date: 2017-01-04

The present invention discloses a direct-current power transmission protection device, including a resistor unit and a bidirectional circulation current switch unit, and the resistor unit and the bidirectional circulation current switch unit being connected in parallel to form the protection device, where at least one resistor is cascaded to form the resistor unit, and at least one bidirectional circulation current switch is cascaded to form the bidirectional circulation current switch unit. In addition, the present invention also provides a converter including the protection device, and at least one protection device is connected in series in each phase unit. The present invention provides the protection device, the converter and a protection method for flexible direct-current power transmission, which can rapidly and effectively suppress direct-current short circuit current and damp current oscillation, and not only can better protect equipment safety, but also can greatly shorten fault current attenuation time, thus shortening direct-current shutdown time and further decreasing economic loss and system destabilization risk caused by shutdown to the max. Moreover, the protection device is structurally simple and low in cost, and has good implementability and economic efficiency.


A voltage-source multi-level converter, including a phase unit (0). The phase unit (0) includes a first bridge arm (100) and a second bridge arm (200), where a first terminal of the first bridge arm (100) is a first DC terminal (P) of the phase unit (0), and a first terminal of the second bridge arm (200) is a second DC terminal (N) of the phase unit (0); a second terminal of the first bridge arm (100) and a second terminal of the second bridge arm (200) are shorted together, as an alternating-current terminal (A) of the phase unit (0); the first bridge arm (100) includes first modules (101) and one first reactor (102) connected in series, where a first terminal of the first reactor (102) is connected to the alternating-current terminal (A), a second terminal (X1) thereof is connected to a first terminal of the first modules (101), and a second terminal of the first modules (101) is connected to the first DC terminal (P); the second bridge arm (200) includes second modules (201) and one second reactor (202) connected in series, where a first terminal of the second reactor (202) is connected to the alternating-current terminal (A), a second terminal (X2) thereof is connected to a first terminal of the second modules (201), and a second terminal of the second modules (201) is connected to the second DC terminal (N); and a parallel fault shunt circuit (300) is connected between the second terminals (X1, X2) of the first reactor (102) and the second reactor (202). Also disclosed are a DC power transmission system and a fault processing method and device.


Patent
NR Electrical Co. and NR Electrical Engineering Co. | Date: 2017-02-01

An unified power flow controller for a double-circuit transmission line comprises at least one parallel-connection transformer (1), three current converters (4), at least two series-connection transformers (8), a parallel-connection side switching circuit (3), a series-connection side switching circuit (6) and a direct current common bus (5). At least one side of the series-connection transformers is connected with at least one group of by-pass switches (9, 10) in parallel. The alternating current sides of the three current converters are connected to each loop line in series after being connected with at least one series-connection transformer through the series-connection side switching circuit (6). The alternating current sides of the three current converters are connected to an alternating current system after connected with at least one parallel-connection transformer (1) through a parallel-connection side switching circuit starting circuit (2). The direct current sides of the three current converters are connected to the direct current common bus (5) through a transfer switch. With the unified power flow controller, various operating modes can be realized, and when one current converter is in fault, power flow control of the double-circuit transmission line can still be achieved. The unified power flow controller is small in occupied space, low in cost, and excellent in economy, flexibility and reliability.


Patent
NR Electrical Co. and NR Electrical Engineering Co. | Date: 2017-04-19

The present invention provides a line power control method and system for a unified power flow controller. The line power control method 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 I_(sedref) and I_(seqref) are calculated by means of the outer loop line power control according to line power instructions P and Q that are input, a measured line power U_(L), and measured line power P and Q; a converter output voltage reference value U 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. The control method is simple and practical, has high reliability, can rapidly and accurately control the line power, and can implement independent decoupling control of active power and reactive power of a line.


Patent
NR Electrical Co. and NR Engineering Co. | Date: 2017-09-27

A starting and stopping method for a static synchronous series compensator (SSSC) is provided. A starting process includes: first, connecting a converter (4) to a shunt transformer (2), and closing an incoming line switch (1) of the shunt transformer to charge the current converter until a direct-current voltage is stable; then, opening the incoming line switch of the shunt transformer, and connecting the converter to a series transformer (5) through a change-over switch (3); deblocking the converter, and controlling a current of a bypass switch (6) of the series transformer to approach zero; further, opening the bypass switch of the series transformer, and enabling the converter to enter a normal operation mode after a line is stable; and in stopping the SSSC, first, switching a control mode of the converter to make the current of the bypass switch approaches zero when closed the bypass switch, then controlling a current of the series transformer to be gradually reduced to zero to make the series transformer out of service, and then blocking the converter. By means of the method, an overvoltage and an overcurrent of a converter when a series transformer is put into use and exits can be effectively suppressed, and current oscillation of an line and impact on the series transformer can be reduced, thereby achieving stable starting and stopping of an SSSC


Patent
Zhejiang Electrical Power Test, Research Institute, State Grid Corporation of China and NR Electrical Co. | Date: 2016-04-13

A low-frequency band suppression enhanced anti-reversal power system stabilizer is presented by the invention. Currently the widely used PSS2B power system stabilizer needs lead elements above Order 2 to meet the phase compensation requirement of DC blocking signal of active power, thus quickly increasing high-frequency band gain, restricting allowable total setting gain of PSS, limiting low-band gain and reducing low-frequency band suppression ability of power system stabilizer. The invention will add generator speed signal (which is treated by DC blocking element and corrected by parallel proportional differential PD) and active power signal P_(e )(which is treated by DC blocking element and gained by gain factor K_(s3)) to get equivalent synthetic mechanical power of power system stabilizer. The actual active power signal gained by gain factor K_(S1 )can meet the requirement of phase compensation through Order 1 lead and lag elements, thus increasing allowable total setting gain of PSS and improving the ability of low-frequency band oscillation suppression.

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