CN103560547A - Method for processing alternating current system failures in alternating current and direct current electric transmission line - Google Patents

Abstract

The invention discloses a method for processing alternating current system failures in an alternating current and direct current electric transmission line. The method comprises the steps of obtaining actual operation data of a power grid; according to overload capacity designed for direct currents, confirming power value, capable of being instantly increased or reduced, of a direct current system, and designing the transmission function controlled by direct current emergency power; obtaining the generator tripping value needed when the direct current emergency power is adopted to control conditions under failures of an alternating current system through an offline computing mode, pushing out action effect of the direct current emergency power control on the alternating current system failures, and making an offline control strategy; when the alternating current system failures occur, judging whether to adopt the direct current emergency power control according to the strategy, and safely and stably controlling the device to adopt generator tripping or load tripping measures according to the strategy. According to the method, the direct current emergency power control and the safe and stable control strategy are combined, a direct current emergency power control method is adopted to reduce total generator tripping value after the alternating current system failures occur, and overall economic benefits of power grid operation is improved.

Description

A processing method for AC system faults in AC-DC transmission lines

technical field

The invention belongs to the field of power system operation control, and in particular relates to the coordination problem of safety and stability control of power transmission of an AC/DC hybrid system and DC emergency power control.

Background technique

High-voltage, long-distance DC transmission technology is an effective way to solve the contradiction between primary energy and load distribution in my country. In the next few years, my country will build a series of ultra-high voltage and ultra-high voltage DC transmission projects on a large scale to alleviate the contradiction between power supply and demand. The AC/DC hybrid transmission system will exist in the grid structure of many provinces and regions in my country.

Under the adjustment of the control system, the direct current transmission system has the ability to quickly adjust the active power. Making full use of this function can improve the transient stability level of large disturbances and improve the dynamic recovery characteristics after being disturbed. In power grids where multiple DCs are centrally sent or fed in, in addition to considering factors such as safety and reliability in the main grid planning, it is also necessary to further consider the emergency power support capability for flexible transfer of power flows between multiple DC circuits and between AC and DC.

The conventional HVDC transmission system has a long-term overload capacity of 1.1 times and a short-term overload capacity of 1.5 times for 3s, which can support a large DC capacity. When the AC system suffers from a serious fault, the short-term overload capacity of HVDC can be used to compensate During the transient process, the power imbalance between the sending end and the receiving end improves the transient power angle stability of the system, and correspondingly improves the phenomenon of voltage fluctuations and low voltage durations caused by power imbalances.

China Invention Application No. 201210088791.9 "An AC-DC Coordinated Control Method Based on DC Power Emergency Control", this method mainly involves the power optimization distribution control principle of AC-DC transmission lines, and does not propose the use of DC emergency power control and safety and stability control matching scheme.

China Invention Application No. 201210444402.1 "Grid Optimization Method Adapting to DC Emergency Power Support", this method mainly analyzes the problem of grid structure optimization from the perspective of using multiple DC emergency power supports, and the impact of DC emergency power control on AC system failures Issues of impact were not addressed.

In view of the above analysis, through the research on the simultaneous operation of AC and DC in the power grid, a method of cooperating with DC emergency power control and safety and stability control strategy is proposed, so as to realize the effective handling of AC system faults.

Contents of the invention

The object of the present invention is to provide a processing method for AC system faults in AC-DC transmission lines, which combines DC emergency power control with a safety and stability control strategy, and uses DC emergency power control to reduce the The total cut-off capacity of the system improves the overall economic benefits of power grid operation.

In order to achieve the above object, the solution of the present invention is:

A method for processing an AC system fault in an AC-DC transmission line, comprising the following steps:

(1) Obtain the actual operation data of the power grid;

(2) Obtain the real-time transmission power value of the DC line, and according to the overload capacity of the DC design, determine the power value that the DC system can instantly increase or decrease, and design the transfer function of the DC emergency power control;

(3) Obtain the cut-off amount required for DC emergency power control under AC system faults through offline calculation, deduce the effect of DC emergency power control on AC system faults from the offline calculation results, and formulate offline control strategies;

(4) When an AC system failure occurs, judge whether DC emergency power control is required according to the off-line control strategy. If not, no signal is sent to the DC power control device. The power value that needs to be increased is transmitted to the DC power modulation controller, and the safety and stability control device takes machine or load shedding measures according to the off-line control strategy.

In the above step (2), when designing the transfer function of DC emergency power control, the input power of the line is selected as the line of the transmission section, and then passes through the inertial link, filter link, DC blocking link, lead-lag link and limiting link in turn, and then outputs Modulated active power.

The above step (3) specifically includes the following contents:

(31) Scan important AC transmission sections, N-2 faults or combined faults of important AC lines, and determine which AC system faults DC emergency power control has a more obvious effect on;

(32) To determine the impact of DC emergency power control on the amount of machine cut-off after the failure of the safety and stability control under the fault of the AC system, and whether it can reduce the amount of machine cut-off after the system failure;

(33) Calculate which AC system faults can be controlled by DC emergency power through offline simulation, and write into the offline control strategy.

After adopting the above scheme, the present invention cooperates the DC emergency power control with the safety and stability control strategy, and when the AC and DC systems are running at the same time, after a serious fault occurs in the AC system, the emergency power control is enabled through the DC, thereby reducing the safety and stability control after the failure. The cut-off capacity of the device can instantly increase or decrease the transmission power, maintain the stability of the system, and improve the overall economic benefits of the power grid operation.

Description of drawings

Fig. 1 is a flow chart of the present invention;

Fig. 2 is the flow chart of cooperation of DC emergency power control and safety and stability control in the present invention;

Fig. 3 is a schematic diagram of the transfer function of DC emergency power control in the present invention;

in:

S: complex frequency;

P _LINE : Active power input, which can be the power of a certain line, or the sum of the total transmission power of a certain section;

T _mesR : frequency measurement time constant (seconds);

T _W : Time constant of the DC link (seconds);

K _p : power modulation gain;

T ₀ : filter parameters (seconds);

T ₁ : first lead time function (seconds);

T ₂ : first lag time function (seconds);

T ₃ : the second leading time function (seconds);

T ₄ : second lag time function (seconds);

P _max : DC power modulation upper limit (pu, based on DC rated power);

P _min : lower limit value of DC power modulation (pu, based on DC rated power);

ΔP _mod : the change in output power of the DC line (pu, based on the rated DC power);

Fig. 4 is a schematic diagram of formulating an off-line control strategy in the present invention.

Detailed ways

The technical solutions of the present invention will be described in detail below in conjunction with the accompanying drawings.

As shown in Figure 1, the present invention provides a method for processing faults in AC systems in AC-DC transmission lines, including the following steps:

(1) Obtain the actual operation data of the power grid, including the data of the stability control station, load shedding execution station, machine cut execution station, etc.;

(2) Obtain the real-time transmission power value of the DC line, and determine the power value that the DC system can instantaneously increase or decrease according to the overload capacity of the DC system, and design the transfer function of the DC emergency power control; as shown in Figure 3, the line input The power can choose the line of the transmission section as the input, and then output the modulated active power after passing through the inertial link, filtering link, DC blocking link, lead-lag link, and limiting link in sequence, as shown in Figure 3.

For example, according to the 1.1 times overload capacity of the DC system, the active power increase rate is controlled at 500MW/s, then the limiting link of the DC active power transfer function must be limited within the active power range of 1.1 times, that is, the final limiting link is limited, and the power increase rate is controlled Below 500MW/s.

(3) Obtain the cut-off capacity required for DC emergency power control under serious AC system faults through off-line calculation, such as a double-line trip fault on a double-circuit 500kV line in a transmission section. Calculate the simultaneous action of the emergency power control and the safety device of the DC system, and the cut-off and load shedding of the safety device. The effect of DC emergency power control on AC system faults is deduced from the offline calculation results, and the offline control strategy can be formulated, as shown in Figure 4; the effect of DC emergency power control on AC system faults is deduced from the offline calculation results, and the offline control strategy is formulated ; Specifically include the following:

(31) Scan important AC transmission sections, N-2 faults or combined faults of important AC lines, and determine which AC system faults DC emergency power control has a more obvious effect on;

(32) To determine the impact of DC emergency power control on the amount of machine cut-off after the failure of the safety and stability control under the fault of the AC system, and whether it can reduce the amount of machine cut-off after the system failure;

(33) Calculate which AC system faults can be controlled by DC emergency power through offline simulation, and write into the offline control strategy;

(4) Establish communication between the DC power modulation controller and the safety and stability control device, and write the offline control strategy formulated in step (3) into the device program; when an AC system failure occurs, judge whether it is necessary to take the offline control strategy DC emergency power control, if not needed, no signal will be sent to the DC power control device, if emergency power boost is needed, then the power value to be boosted will be transmitted to the DC power modulation controller according to the established offline control strategy, and at the same time, it will be safely and stably controlled The device takes machine or load shedding measures according to the off-line control strategy.

The above embodiments are only to illustrate the technical ideas of the present invention, and can not limit the protection scope of the present invention with this. All technical ideas proposed in accordance with the present invention, any changes made on the basis of technical solutions, all fall within the protection scope of the present invention. Inside.

Claims (3)

1. a processing method for fault in ac transmission system in AC/DC transmission line, is characterized in that comprising the steps:

(1) obtain electrical network actual operating data;

(2) obtain the performance number that DC line is carried in real time, and according to the capability of overload of direct current design, determine that direct current system can instantaneous lifting or the performance number of reduction, the transfer function that the urgent power of design direct current is controlled;

(3) mode by calculated off-line obtains taking the machine of cutting amount required in the urgent power control of direct current situation under fault in ac transmission system, releases the urgent power of direct current control the action effect to fault in ac transmission system by calculated off-line result, formulates Off-line control strategy;

(4) when there is fault in ac transmission system, according to Off-line control strategy, judge whether to take the urgent power of direct current to control, if do not need, do not signal to direct current power control device, if desired urgent power ascension, the magnitude of power according to the Off-line control strategy of formulating, needs being promoted is passed to DC power modulation controller, and safety and stability control device takes to cut machine or cutting load measure according to Off-line control strategy simultaneously.

2. the processing method of fault in ac transmission system in a kind of AC/DC transmission line as claimed in claim 1, it is characterized in that in described step (2), while designing the transfer function of the urgent power control of direct current, circuit input power selects the circuit of transmission cross-section as input, pass through successively inertial element, filtering link, every straight link, lead-lag link and amplitude limit link, then the active power of output modulation.

3. the processing method of fault in ac transmission system in a kind of AC/DC transmission line as claimed in claim 1 or 2, is characterized in that: described step (3) specifically comprises following content:

(31) scan N-2 fault or the combined fault of important ac transmission section, important alternating current circuit, determine the urgent power control of direct current to which fault in ac transmission system plays a role clearly;

(32) determine that under fault in ac transmission system, the urgent power of direct current is controlled the impact of safety and stability control after fault being cut to machine amount, whether can reduce the machine of the cutting amount after the system failure;

(33) by off-line simulation, calculate which fault in ac transmission system and can adopt the urgent power of direct current to control, write Off-line control strategy.

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