CN105552916A - UPFC (unified power flow controller) system-level control method with circuit power out-of-limit control function - Google Patents

Abstract

The invention discloses a UPFC system-level control method with a line power over-limit control function, which realizes the UPFC section power flow control function through a section power flow control strategy, and quickly controls the actual power of the controlled section according to the dispatching instruction under the normal operation state of the power grid. The power is controlled below a reasonable power setting value to ensure that the transmission line connected in parallel with the controlled section meets N-1 check; When the power of the transmission line exceeds the limit, a power deviation dP2 generated by the line power over-limit control module that can reflect the line over-limit is superimposed, thereby automatically generating UPFC control instructions that meet the requirements for safe and stable operation of the power grid, and on the premise of ensuring that the line is not overloaded meet the requirements of cross-section power flow control. The invention not only increases the flexibility of dispatching, but also reduces the complexity of power grid operation, and improves the reliability of power grid operation.

Description

A UPFC system-level control method with line power over-limit control function

technical field

The invention belongs to the technical field of flexible power transmission and distribution of power systems, and in particular relates to a UPFC system-level control method with a line power over-limit control function.

Background technique

The development of the power system to a large-scale interconnected grid has become a common trend in the development of modern power systems in all countries in the world, and the formation of the interconnected grid has made the grid structure increasingly complex and the operation increasingly heavy. In order to meet the needs of power system development, flexible AC transmission system (FACTS) technology is developing rapidly. As the latest generation of FACTS device, the unified power flow controller (unified power flow controller, UPFC) can not only realize the precise control of the power flow, improve the transmission power limit of the section, but also provide dynamic voltage support and improve the voltage stability of the system; system dynamics. Therefore, the reasonable installation of unified power flow controller is of great significance to the development of my country's power grid.

As shown in Figure 1, UPFC is composed of two back-to-back voltage source converters. The two back-to-back converters share the DC bus and DC capacitors. Both of them are connected to the system through the converter transformer. The converter 2’s The converter transformers are connected in series. Active power can flow freely in either direction between the two converters, and the AC output of each converter can also generate or absorb reactive power independently. The function of converter 2 in UPFC is to inject a voltage vector with controllable amplitude and phase angle into the line through the series transformer, so that the voltage, impedance and phase angle on the line can be adjusted simultaneously or selectively; converter 1 The function of is to provide or absorb the active power required by the converter 2 on the common DC bus, so as to maintain the active power exchange between the series injection voltage and the line. In UPFC, in addition to the active and reactive power exchange between the converter 2 and the system, if necessary, the converter 1 can also generate or absorb controllable reactive power at the same time, providing independent parallel reactive power compensation for the line .

The principle of setting the control target value of the unified power flow controller in the normal operation state of the power grid and when an N-1 fault occurs is one of the difficulties in its practical engineering. To formulate a set of reasonable system-level control strategy is the work that must be completed before the UPFC device is put into operation. Academically, most of the research on UPFC focuses on UPFC system modeling and power flow control strategies. In terms of engineering, the engineering application of UPFC is still blank in my country. Although 3 sets of UPFC devices have been put into operation in foreign countries, there is still a lack of engineering experience that can be used for reference. The traditional UPFC device is directly installed on the controlled section, and the dispatcher remotely sets the power setting value of the controlled section. Fixed value; under different operating conditions, the power setting value of the controlled section given by the dispatcher cannot guarantee that the power of the line will not exceed the limit. This greatly increases the complexity of power grid operation and also reduces the reliability of power grid operation. At the same time, due to the limitation of the occupied area of the UPFC device project, it may not be possible to install UPFC on the controlled section in actual engineering. At this time, it is necessary to control the UPFC device installed near the controlled section to achieve the section power flow control effect. Therefore, it is very necessary to formulate a set of UPFC system-level control strategies that can be engineered and practical with the function of line power over-limit control.

Contents of the invention

In view of the above-mentioned technical problems existing in the prior art, the present invention provides a UPFC system-level control method with a line power over-limit control function, which satisfies the requirements of cross-section power flow control as much as possible on the premise of ensuring that the line is not overloaded. It not only increases the flexibility of dispatching, but also reduces the complexity of power grid operation and improves the reliability of power grid operation.

A UPFC system-level control method with a line power over-limit control function, which is realized by combining a section power flow control strategy with a line power over-limit control module; the UPFC system-level control method realizes the UPFC section power flow control function through a section power flow control strategy , in the normal operation state of the power grid, quickly control the actual power of the controlled section below a reasonable power setting value according to the dispatching instruction, and ensure that the transmission line parallel to the controlled section meets the N-1 check; When the power of the transmission line on the controlled section or the transmission line in series with the controlled section exceeds the limit due to the change of the situation, a power deviation dP2 generated by the line power over-limit control module that can reflect the line over-limit situation is superimposed, so as to automatically generate satisfying The UPFC control command required by the safe and stable operation of the power grid meets the requirements of section power flow control on the premise of ensuring that the line is not overloaded.

The specific process of the section power flow control strategy is as follows:

1.1 Calculate the power deviation dP1 between the set power and actual power of the controlled section;

1.2 After superimposing the power of the UPFC installation line, the power deviation dP1 and the power deviation dP2, the active power command value of the UPFC is obtained through the limiting link;

1.3 Calculate the reactive power command value of UPFC by using the active power command value according to the set line power factor;

1.4 According to the active power command value and reactive power command value of UPFC, the UPFC is controlled through relevant control algorithms.

The set power of the controlled section in step 1.1 can ensure that the transmission lines connected in parallel with the controlled section meet the N-1 check, that is, when the controlled section operates at the set power, any transmission line connected in parallel with the controlled section After the N-1 fault occurs on the transmission line, the power of other non-faulty parallel transmission lines shall not exceed their respective power limits.

In the described step 1.3, the reactive power command value of UPFC is calculated by the following formula:

The specific process of the power deviation dP2 generated by the line power over-limit control module is as follows:

2.1 Monitor the actual power of the transmission line on the controlled section or the transmission line in series with the controlled section, calculate the power deviation between the power limit value of each monitored line and the actual power, and correspond to the safe operation power of each monitored line Margin, extract the minimum value X of the safe operation power margin of all monitored lines;

2.2 Determine the selection signal Ctrl through logical judgment according to the power deviation dP1 and the minimum power margin X;

2.3 Determine the input of a PI (proportional-integral) controller according to the selection signal Ctrl, and then use the output of the PI controller to generate the power deviation dP2.

The specific logical judgment criteria in the step 2.2 are as follows:

①When the system is in normal operation state, the actual power of each monitored line is lower than the power limit, then the minimum power margin X is greater than 0, and the selection signal Ctrl=0 at this time;

②When N-1 faults occur in the system or the monitored line is overloaded due to changes in working conditions, that is, there is a situation where the actual power of the monitored line is higher than the power limit, the minimum value of the power margin X is less than 0, and at this time select signal Ctrl=1;

③ When the actual power of the controlled section exceeds the set power and the actual power of each monitored line is lower than the power limit, the power deviation dP1 is less than 0 and the minimum value of the power margin X is greater than 0, and the selection signal Ctrl= 0.

When the selection signal Ctrl=0 in the described step 2.3, then the input signal of the PI controller is 0; limit the difference of the power control margin P _m preset by the control module.

When the actual power of the controlled section exceeds the set power and the actual power of each monitored line is lower than the power limit, select the signal Ctrl=0, the input signal of the PI controller becomes 0 again, and at the same time the The integrator is cleared.

In cases ② and ③, the triggering of the selection signal Ctrl has a certain delay, that is, the selection signal Ctrl=0 or 1 at multiple consecutive moments, and the selection signal Ctrl actually triggers the corresponding selection of the input of the PI controller.

In the normal operation state of the power grid, the UPFC system-level control strategy provided by the present invention can quickly control the actual power of the controlled section to the set value of the section power according to the dispatching instruction, ensuring that the transmission line connected in parallel with the UPFC control section satisfies the N-1 calibration requirement. Nuclear; when the system fails or the working condition changes, the UPFC control section or the transmission line connected in series with the UPFC control section is overloaded, and the UPFC control command value that meets the requirements for safe and stable operation of the power grid is automatically generated. Priority is given to ensuring that the line is not overloaded As far as possible to meet the requirements of cross-section power flow control, it can play the role of a safe and stable automatic device. The invention not only increases the flexibility of dispatching, but also can reduce the complexity of power grid operation and improve the reliability of power grid operation, which is of great significance for the engineering practice of UPFC.

Description of drawings

Figure 1 is a schematic diagram of the structure of UPFC.

Figure 2 is a simplified schematic diagram of an actual power grid.

Figure 3 is a schematic diagram of the control principle of the power flow control strategy for the UPFC section.

Fig. 4 is a schematic diagram of the control principle of the UPFC line power over-limit control module.

Fig. 5 is a schematic diagram of the control principle of the UPFC system-level control strategy of the present invention.

Fig. 6(a) is a schematic diagram of the power change curve of section 1 when N-1 fault occurs on the HF double circuit line after adopting the UPFC system-level control strategy of the present invention.

Fig. 6(b) is a schematic diagram of the power change curve of the HF double-circuit line when N-1 fault occurs on the HF double-circuit line after adopting the UPFC system-level control strategy of the present invention.

Fig. 7(a) is a schematic diagram of the power change curve of section 1 when an N-1 fault occurs on section 1 after adopting the UPFC system-level control strategy of the present invention.

Fig. 7(b) is a schematic diagram of the power change curve of the HF double circuit line when an N-1 fault occurs on section 1 after adopting the UPFC system-level control strategy of the present invention.

detailed description

In order to describe the present invention more specifically, the technical solutions of the present invention will be described in detail below in conjunction with the accompanying drawings and specific embodiments.

Figure 2 shows the simplified structure of an actual power grid. The load in the area is mainly supplied by Section 1 and Section 2. The power flow distribution of the two sections is uneven and often encounters transmission bottlenecks. The transmission power of section 1 is about 600MW, and the transmission power of the HF double circuit line in section 2 is about 780MW. Both transmission sections do not meet the N-1 check. That is: after any one of the BD or BC double-circuit lines is out of operation due to a fault, the power of the non-faulty line will exceed its power limit; after any one of the HF double-circuit lines is out of operation due to a fault, the power of the non-faulty line will exceeds its power limit. Due to the limitation of the occupied area of the UPFC system project, it is impossible to directly control the power of section 1 by installing it on the BC and BD lines. After analyzing the site selection of the project, it is selected to install UPFC device on the AB line to control the power of section 1. The specific control methods include:

(1) Cross-section power flow control strategy.

The UPFC system-level control strategy should first ensure that UPFC can realize its power flow control requirements. Therefore, under the normal operation state of the power grid, UPFC should be able to realize its section power flow function first, that is, to control the transmission power of section 1 at the set value. The power flow control strategy of UPFC section is shown in Fig. 3.

In Fig. 3, P _set and P _a are the set value and actual value of the transmission power of section 1 respectively; dP1 is the output of the power control module of the section, which is assigned to signal A; P _L is the transmission power of AB line; P _max and P _min are respectively is the upper limit and lower limit of the allowable operating power of the AB line; P _ref and Q _ref are the control target values of the AB line power, that is, the UPFC active and reactive command values; among them, δ is the power factor.

Under the normal operation state of the power grid, the power flow control strategy formulated can meet the demand of UPFC power flow control, so that the power flow of section 1 is controlled at the set value, and section 2 can meet the N-1 check at this time. However, only using the line section power flow control strategy as the UPFC system-level control strategy requires the dispatcher to remotely change the set value of the section power when the line power on section 1 exceeds the limit due to faults or changes in operating conditions; Under working conditions, the set value given by the dispatcher cannot guarantee that the line power can be controlled below its power limit, which greatly increases the complexity of grid operation and also reduces the reliability of grid operation.

(2) Line power over-limit control strategy.

In order to reduce the complexity of power grid operation and improve the reliability of power grid operation, the UPFC system-level control strategy should be able to automatically generate UPFC command values that meet the requirements for safe and stable operation of the power grid when the line power on section 1 exceeds the limit due to faults or changes in working conditions . Therefore, on the basis of the section power flow control strategy, a line power over-limit control module as shown in Figure 4 is added. The specific control process is as follows:

2.1 Monitor the actual power of the transmission line on section 1, calculate the power deviation between the power limit value and the actual value of each monitored line, and use it as a margin index for the safe operation of each monitored line, and calculate the safe operation margin of each monitored line The minimum value of the indicator is assigned to signal B;

2.2 Signal A and signal B are used as the input of the trigger module to jointly generate the input selection signal Ctrl of the PI controller of the line power over-limit control module. Its control logic is as follows: ①In the normal operation state of the system, the power of the monitored line is lower than its power limit, that is, B>0, at this time Ctrl=0, the input signal of the PI controller is 0; ②When the system occurs N- 1 When a fault or any one of the monitored lines is overloaded due to a change in working conditions, that is, B<0, at this time Ctrl=1, the input signal of the PI controller becomes a power deviation signal that can reflect the line over-limit situation; ③ When the controlled The cross-section power flow exceeds its set value and the power of the monitored line is lower than its power limit, that is, A<0 and B>0. At this time, CTRL=0, the input signal of the PI controller becomes 0 again, and the PI controller The integrator is cleared. In order to prevent frequent actions of the trigger module, the triggering and returning of the Ctrl signal in ② and ③ have a certain time delay. Only when the control logic is continuously satisfied during the set time delay will the triggering or returning of the Ctrl signal be caused.

2.3 In order to ensure that the operating power of the monitored line has a certain margin from its power limit, the P _m signal is added to the input link of the PI controller as the control margin of the line power over-limit control module; the output of the PI controller is the line power The output dP2 of the limit control module.

In Fig. 4, P _limit1 and P _limit2 are the power limits of BC and BD lines respectively; P _line1 and P _line2 are actual powers of BC and BD lines respectively.

(3) UPFC system level control strategy.

Synthesize the section power flow control strategy and the line power over-limit control strategy proposed above. This implementation mode proposes a set of UPFC system-level control strategies that not only meet the system power flow control requirements but also have the ability to control line power over-limits, as shown in Figure 5:

3.1 In the normal operation state of the system, if the monitored line has not been overloaded, the output of the line power limit control module is 0, and the UPFC control target is generated by the section power control module to ensure that the actual power of the section reaches the set value.

3.2 When a certain line is detected to be overloaded, the line power over-limit control module outputs a power deviation signal that can reflect the line over-limit situation. The control instruction value of the UPFC device is jointly generated by the section power control module and the line power over-limit control module. Under the action of the PI controller of the line power over-limit control module, the power deviation signal dP2 will play a leading role. At this time, the control instruction value generated by the UPFC system-level control strategy will give priority to ensuring that the power of the monitored line is lower than its power limit.

3.3 System control strategy The setting value of the section power is given remotely by the dispatcher. If the section power has not reached the set value and the monitored line is overloaded, the priority control target is to monitor the line without overloading, which can increase the dispatching time. flexibility without compromising the reliability of grid operation. When the UPFC installation line is overloaded, the power of the UPFC installation line is preferentially controlled not to exceed its power limit.

The transmission power setting value P _set of section 1 of the system-level control strategy formulated in this embodiment is 750MW, and the power flow of the HF double-circuit line is transferred to section 1 to ensure that the HF double-circuit line meets the N-1 check. The power limits P _limit1 and P _limit2 of the BC and BD lines are both 45MW; the control margin P _m of the line power overrun control module is 2MW; the upper and lower limits P _max and P _min of the allowable operating power of the AB line are 45MW and - 45MW; the initial value of the input selection signal Ctrl of the PI controller of the line power over-limit control module is 0, and the trigger and return delay is 0.5s; the set power factor of the AB line power is 0.98. The gains of the proportional amplifier and the integrator in the PI controller of the line power over-limit control module are 0.4 and 1.0, respectively.

Under the system-level control strategy formulated in this embodiment, the power variation curves of Section 1 and the HF double-circuit line when an N-1 fault occurs on the HF double-circuit line are shown in FIG. 6 . When a three-phase ground fault occurs in one of the HF double-circuit lines, in order to ensure the safety of the UPFC device, the transformer bypass switch is turned on to bypass the series-side converter. After the fault is removed, in order to ensure the safety of the UPFC device, After the set time (1s), the UPFC is put into operation again. The simulation process is as follows: the UPFC system-level control strategy is put into use at 2s; a three-phase ground fault occurs in the HF circuit at 5s, and the UPFC is out of operation; the HF1 circuit is disconnected at 5.1s, and the fault is removed;

Under the system-level control strategy formulated in this embodiment, when an N-1 fault occurs on section 1, the power change curves of section 1 and the HF double circuit line are shown in Figure 7 . The simulation process is as follows: UPFC system-level control strategy is put into use at 2s; a three-phase ground fault occurs on the BD line at 5s, and the UPFC exits operation; at 5.1s, the BD line is disconnected and the fault is removed; UPFC will be re-enabled at 6.1s.

It can be seen from Fig. 6 and Fig. 7 that in the normal operation state of the power grid, the system-level control strategy formulated in this embodiment can quickly control the actual power of section 1 to the set value of section power (750MW); When an N-1 fault occurs on the circuit line, controlling the power of section 1 to 750MW can ensure that the HF double circuit line meets the N-1 check; The strategy can automatically generate new UPFC command values to meet the requirements of section power flow control as much as possible on the premise of ensuring that non-fault lines are not overloaded.

The above description of the embodiments is for those of ordinary skill in the art to understand and apply the present invention. It is obvious that those skilled in the art can easily make various modifications to the above-mentioned embodiments, and apply the general principles described here to other embodiments without creative efforts. Therefore, the present invention is not limited to the above embodiments, and improvements and modifications made by those skilled in the art according to the disclosure of the present invention should fall within the protection scope of the present invention.

Claims (9)

1. A UPFC system-level control method with line power over-limit control function is characterized in that: the UPFC system-level control method is realized by combining a section power flow control strategy and a line power out-of-limit control module; the UPFC section power flow control function is realized through a section power flow control strategy, and under the normal operation state of a power grid, the actual power of a controlled section is quickly controlled below a reasonable power set value according to a scheduling instruction, so that the power transmission line connected with the controlled section in parallel is ensured to meet N-1 checking; when the power of the transmission line on the controlled section or the transmission line connected with the controlled section in series exceeds the limit due to the fault or the change of the working condition, a power deviation dP2 which is generated by the line power out-of-limit control module and can reflect the line out-of-limit condition is superposed, so that a UPFC control instruction which meets the requirement of safe and stable operation of a power grid is automatically generated, and the requirement of the section flow control is met on the premise of preferentially ensuring that the line is not overloaded.

2. The UPFC system-level control method of claim 1, wherein: the specific process of the section flow control strategy is as follows:

1.1, calculating a power deviation dP1 between the set power and the actual power of the controlled section;

1.2, superposing the power of a UPFC installation line, the power deviation dP1 and the power deviation dP2, and obtaining an active power instruction value of the UPFC through an amplitude limiting link;

1.3 calculating a reactive power instruction value of the UPFC by utilizing the active power instruction value according to a set line power factor;

and 1.4, controlling the UPFC through a related control algorithm according to the active power instruction value and the reactive power instruction value of the UPFC.

3. The UPFC system-level control method of claim 2, wherein: the set power of the controlled section in step 1.1 can ensure that the power transmission lines connected in parallel with the controlled section meet N-1 checking, that is, when the controlled section operates at the set power, any power transmission line connected in parallel with the controlled section has an N-1 fault, and then the power of other non-faulty parallel power transmission lines does not exceed respective power limit values.

4. The UPFC system-level control method of claim 2, wherein: in step 1.3, the reactive power instruction value of the UPFC is calculated by the following formula:

5. the UPFC system-level control method of claim 2, wherein: the specific process of the line power out-of-limit control module generating the power deviation dP2 is as follows:

2.1 monitoring the actual power of the power transmission line on the controlled section or the power transmission line connected with the controlled section in series, calculating the power deviation between the power limit value and the actual power of each monitored line, correspondingly taking the power deviation as the power margin of each monitored line for safe operation, and extracting the minimum value X of the power margin of all monitored lines for safe operation;

2.2 determining a selection signal Ctrl through logic judgment according to the power deviation dP1 and the power margin minimum value X;

2.3 determining the input of the PI controller according to the selection signal Ctrl, and generating the power deviation dP2 by using the output of the PI controller.

6. The UPFC system-level control method of claim 5, wherein: the specific logic judgment criteria in step 2.2 are as follows:

firstly, when the system is in a normal operation state, the actual power of each monitored line is lower than a power limit value, the minimum value X of the power margin is greater than 0, and the selection signal Ctrl is 0;

when the system has an N-1 fault or the monitored line is overloaded due to the change of working conditions, namely the actual power of the monitored line is higher than the power limit value, the minimum value X of the power margin is smaller than 0, and the selection signal Ctrl is 1;

and thirdly, when the actual power of the controlled section exceeds the set power and the actual power of each monitored line is lower than the power limit value, the power deviation dP1 is smaller than 0 and the power margin minimum value X is larger than 0, and the selection signal Ctrl is equal to 0 at the moment.

7. The UPFC system-level control method of claim 5, wherein: when the selection signal Ctrl is 0 in step 2.3, the input signal of the PI controller is 0; when selecting the signalWhen Ctrl equals 1, the input signal of PI controller is power control margin P preset by the line power out-of-limit control module and power margin minimum value X_mThe difference of (a).

8. The UPFC system-level control method of claim 6, wherein: when the actual power of the controlled section exceeds the set power and the actual power of each monitored line is lower than the power limit value, the selection signal Ctrl is 0, the input signal of the PI controller is changed into 0 again, and meanwhile the integrator in the PI controller is cleared.

9. The UPFC system-level control method of claim 6, wherein: in the second and third cases, the triggering of the selection signal Ctrl has a certain delay, that is, the selection signal Ctrl at a plurality of consecutive times is 0 or 1, and the selection signal Ctrl is actually performing corresponding selection triggering on the input of the PI controller.