Active Power Flow Transfer Method and Device for Dual-Power Three-Channel Power System
The dual-source, three-channel power system actively reroutes flow using capacitors to manage impedance, addressing the challenge of fault-induced overload and ensuring stable power transfer.
Patent Information
- Application Number
- CN202310171564.0
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Filing Date
- 2023-02-27
- Publication Date
- 2025-07-15
- Estimated Expiration
- 2043-02-27
AI Technical Summary
In the prior art, there is a lack of effective active current transfer method after the transmission channel fails, resulting in frequent line overload conditions, affecting the reliability and safety of the power system.
A dual-power three-channel power system is adopted. By selecting a transmission channel with a larger upper power limit as the transfer channel, and switching the series capacitor on the transfer channel to reduce the reactance, actively transfer the current, and adjustable capacitance value to adjust the current transfer ratio to ensure that the current is within the redundant amount.
It realizes the rapid and effective avoidance of line overload after a fault, improves the operating reliability of the power system and the ability to deal with transmission channel failures, and ensures the continuous power supply of the power grid.
Smart Images
Figure CN116073383B_ABST
Abstract
Description
Technical Field
[0001] The present invention belongs to the technical field of power system fault protection, and particularly relates to an active power flow transfer method and device for a dual-power three-channel power system. Background Art
[0002] With the rapid growth of the national economic level, people's demand for electric energy is increasing day by day, and the requirements for power systems are also constantly improving. The power transmission system plays the role of economically and safely transporting the electric energy generated by power plants to the power load center, and has an important position in the power system. Whether it is perfect or not will directly affect the power supply reliability and power quality of the majority of users. Faults in the power system may not only lead to the interruption of power supply, resulting in the stagnation of social production and economic losses, but also may damage the safety performance of the power grid, cause damage to power equipment, and even threaten personal safety.
[0003] After the fault line is removed, the power flow on the original fault line will naturally transfer to other lines, resulting in overload conditions on other lines. Faults in the power system are inevitable due to various factors, but currently there are few effective methods for actively transferring power flow after a transmission channel fault. Summary of the Invention
[0004] The purpose of the present invention is to solve the problems existing in the above-mentioned prior art, and provide an active power flow transfer method for a dual-power three-channel power system, which can actively transfer the power flow after a fault occurs to avoid line overload.
[0005] The present invention is realized through the following technical solutions: An active power flow transfer method for a dual-power three-channel power system. When a line on a transmission channel fails, select the one with the larger power upper limit among the other two transmission channels as the transfer-in channel, and the one with the smaller power upper limit as the transfer-out channel; switch on and off a series capacitor on the line corresponding to the transfer-in channel to reduce the reactance of the transfer-in channel, so that after the fault line is removed, the power flow on the transfer-out channel actively transfers towards the transfer-in channel.
[0006] Further, adjust the power flow transfer ratio η by adjusting the capacitive reactance of the capacitor. The power flow transfer ratio η refers to the ratio of the increased active power of the transfer-in channel after the series capacitor is switched on to the active power transmitted by the transfer-out channel before the series capacitor is switched on.
[0007] Further, the series capacitor is a controllable capacitor with adjustable capacitance value, and the capacitive reactance is adjusted by adjusting the capacitance value.
[0008] Further, after the fault line is removed, control the total transmitted active power to recover to the initial power value P0 before the fault occurs. After switching on and off the series capacitor, the power flow distribution between the transfer-in channel and the transfer-out channel is as follows:
[0009]
[0010] Wherein, X I represents the reactance of the incoming channel before switching the series capacitor; X II represents the reactance of the outgoing channel before switching the series capacitor; X C represents the capacitive reactance of the switched series capacitor; X″ ∑ represents the total parallel reactance of the incoming and outgoing channels after switching the series capacitor.
[0011] Furthermore, the calculation formula of the power flow transfer ratio η is as follows:
[0012]
[0013] Wherein, X I represents the reactance of the incoming channel before switching the series capacitor; X II represents the reactance of the outgoing channel before switching the series capacitor; X C represents the capacitive reactance of the switched series capacitor.
[0014] Furthermore, after the faulty line is removed, the electromotive forces of the two sending - end power sources are kept constant. After switching the series capacitor, the power flow is distributed between the incoming and outgoing channels as follows:
[0015]
[0016] Wherein, P0 represents the initial power value of the total transmitted active power before the fault occurs; P0″ represents the power value of the total transmitted active power after the faulty line is removed; P″ I0 represents the transmitted active power of the incoming channel after switching the series capacitor; P″ II0 represents the transmitted active power of the outgoing channel after switching the series capacitor; E S and E R are the electromotive forces of the two sending - end power sources respectively, X S and X R represent the sending - end line reactances of the two sending - end power sources to the transmission channel respectively; X I represents the reactance of the incoming channel before switching the series capacitor; X II represents the reactance of the outgoing channel before switching the series capacitor; X C represents the capacitive reactance of the switched series capacitor; X″ ∑ represents the total reactance of the incoming and outgoing channels after switching the series capacitor; δ represents the phase - angle difference between the electromotive forces of the two sending - end power sources; X ∑ represents the total parallel reactance of the three transmission channels before the fault occurs.
[0017] Furthermore, the series capacitor is switched before the circuit protection action.
[0018] The present invention also provides an active power flow transfer device for a dual - power three - channel power system, which includes two capacitors respectively used to be connected in series to the lines corresponding to two transmission channels with larger power upper limits among the three transmission channels; each capacitor is connected in parallel with a capacitor switching switch; and a controller is also included, which is used to, after a fault occurs in one transmission channel, select a transmission channel with a larger power upper limit from the remaining two transmission channels as the transfer - in channel and control the action of the capacitor switching switch on the transfer - in channel.
[0019] Further, the capacitor is a controllable capacitor with adjustable capacitance value.
[0020] Further, the controller is used to adjust the capacitance value of the controllable capacitor according to the redundancy of the input channel, so as to adjust the power flow transfer ratio η to control the power flow transfer amount within the redundancy; the power flow transfer ratio η refers to the ratio of the increased active power of the transfer - in channel after the series capacitor is put into operation to the active power transmitted by the transfer - out channel before the series capacitor is put into operation; the redundancy refers to the difference between the active power currently transmitted by the transmission channel and its power upper limit.
[0021] Compared with the prior art, the beneficial effects of the present invention include:
[0022] 1. After some transmission channels in the power system fail, the present invention can achieve active and rapid power flow transfer of the power system by selecting the transfer - in channel to switch the series capacitor. The power upper limit of the transfer - in channel is relatively high, and it is not easy to exceed the limit. After the series capacitor is connected, the reactance becomes smaller, and the power flow will actively transfer towards the transfer - in channel, avoiding the overload of other lines that are relatively easy to exceed the limit.
[0023] 2. By adjusting the reactance of the series capacitor, the power flow transfer amount can be quantitatively controlled, and the power flow transfer amount is controlled within the redundancy to avoid the transfer - in channel from exceeding the limit.
[0024] 3. The series capacitor is switched before the circuit protection action. There is a certain time delay for the circuit protection action to cut off the faulty line. By switching the series capacitor before the circuit protection action, the active transfer of the power flow can be achieved immediately after the fault is removed, avoiding exceeding the limit from beginning to end.
[0025] 4. The present invention can effectively improve the operation reliability of the power system, enhance the ability of the transmission network to cope with transmission channel faults, ensure the continuous power supply of the power grid, and avoid the collapse of the transmission system caused by transmission channel faults. BRIEF DESCRIPTION OF THE DRAWINGS
[0026] Figure 1 It is a flowchart of the active power flow transfer method after a fault occurs.
[0027] Figure 2 It is an equivalent model of a dual - power three - channel power system;
[0028] Figure 3 The equivalent model of the power system after a line fault exits;
[0029] Figure 4 The equivalent model of the power system after series capacitors are added;
[0030] Figure 5 The curve of the active power transmitted by the line changing with the series capacitor when the total transmitted power is constant;
[0031] Figure 6 The curve of the active power transmitted by the line changing with the series capacitor when the power supply potential is constant. Specific implementation manners
[0032] The present invention will be further described in detail below with reference to the accompanying drawings.
[0033] An active power flow transfer method for a dual - power - supply three - channel power system. When a line on a transmission channel fails, select one of the other two transmission channels with a larger power upper limit as the transfer - in channel and the one with a smaller power upper limit as the transfer - out channel; switch the series capacitor on the line corresponding to the transfer - in channel to reduce the reactance of the transfer - in channel, so that after the faulty line is removed, the power flow on the transfer - out channel actively transfers towards the transfer - in channel.
[0034] Refer to Figure 1 As shown in the flowchart of the active power flow transfer method, where Δt IC is the time required for switching the capacitor, Δt is the circuit protection action delay. To switch the capacitor before the circuit protection action, Δt IC <Δt. Once the faulty line is disconnected, the power flow on the transfer - out channel can actively transfer to the transfer - in channel.
[0035] To avoid over - limit after the transfer - in channel receives the transferred power flow, adjust the power flow transfer ratio η by adjusting the capacitive reactance of the capacitor. The power flow transfer ratio η refers to the ratio of the increased active power of the transfer - in channel after the series capacitor is switched in to the active power transmitted by the transfer - out channel before the series capacitor is switched in. The series capacitor is a controllable capacitor with an adjustable capacitance value, and the capacitive reactance is adjusted by adjusting the capacitance value.
[0036] To implement the active power flow transfer method of the present invention, the present invention also provides an active power flow transfer device for a dual - power - supply three - channel power system, including two capacitors, which are respectively used to be connected in series to the lines corresponding to the two transmission channels with larger power upper limits among the three transmission channels; each capacitor is shunted with a capacitor switching switch; and a controller is further included, which is used to select a channel with a larger power upper limit as the transfer - in channel from the remaining two transmission channels after a transmission channel fails and control the action of the capacitor switching switch on the transfer - in channel.
[0037] The controller is used to adjust the capacitance value of the controllable capacitor according to the redundancy of the input channel, so as to adjust the power flow transfer ratio η to control the power flow input within the redundancy; the power flow transfer ratio η refers to the ratio of the increased active power of the incoming channel after the series capacitor is put into operation to the active power transmitted by the outgoing channel before the series capacitor is put into operation; the redundancy refers to the difference between the active power currently transmitted by the transmission channel and its power upper limit.
[0038] The present invention can effectively improve the operation reliability of the power system, enhance the ability of the transmission grid to cope with transmission channel faults, ensure the continuous power supply of the power grid, and avoid the situation of the transmission system collapse caused by transmission channel faults. The following provides two embodiments to further illustrate the beneficial effects of the present invention.
[0039] Embodiment 1
[0040] This embodiment aims at the situation where the total transmitted active power is restored to the initial power P0 after the fault.
[0041] As Figure 2 shown, the equivalent model of the dual-power three-channel power system, P0 is the total transmitted active power of the line, E S is the electromotive force of the first sending-end power supply, X S is the reactance of the first sending-end line, δ S is the phase angle of the electromotive force of the first sending-end power supply. E R is the electromotive force of the second sending-end power supply, X R is the reactance of the second sending-end line, δ R is the phase angle of the electromotive force of the second sending-end power supply. X I 、X II and X III are the reactances of the three transmission channels respectively.
[0042] When the dual-power three-channel system operates normally, the equivalent model is as Figure 1 shown, the total power transmitted by the line is,
[0043]
[0044] In the formula, δ is the phase angle difference between δ S and δ R , X ∑ is the total parallel reactance of the three transmission channels, that is,
[0045]
[0046] When the transmission channel III is removed due to a fault, it causes power flow transfer, resulting in possible overload of other normal lines. To avoid cascading failures, the overload situation should be eliminated as soon as possible.
[0047] Refer to Figure 3As shown, an equivalent model of the power system after a line fails and exits is established, and the power flow transfer effect of the series capacitor in the non-faulty channel on the double power sources is derived:
[0048] After transmission channel III is removed due to a fault, the reactance between the equivalent nodes of the power grids at both ends increases, and the total power transmitted by the line decreases. To maintain power balance and meet the power grid load demand, the sending-end power source is controlled to restore the total power transmitted by the line to the initial power value P0. Then, the equivalent electromotive force of the sending-end power source satisfies:
[0049]
[0050] In the formula, X' ∑ is the total parallel reactance of the two transmission channels after transmission channel III fails and is removed, that is,
[0051]
[0052] From formula (1), it can be seen that the active power transmitted by the line is related to the voltages at both ends of the line and the line reactance. Since the voltages at both ends of line I and line II are equal, the power transmitted by the two lines is inversely proportional to their reactances, that is:
[0053]
[0054] During the active power flow transfer process, the total power transmitted by the line is always kept unchanged at the initial power value P0. Then, the power flow of line I and line II is distributed according to the inverse ratio of their reactances, which are respectively:
[0055]
[0056] Use a thyristor-controlled series capacitor (TCSC) for fast power flow transfer after a fault occurs:
[0057] Due to the removal of the faulty line, the power flow on the original faulty line will be transferred to other lines, which may cause overloading of other lines.
[0058] From formula (6), it can be seen that by connecting a series capacitor on a normal line where the transmitted power is not exceeding the limit, the power flow distribution can be changed by changing the line reactance to achieve active power flow transfer. Refer to Figure 4 as shown.
[0059] Since the voltages at both ends of the two lines are equal and the transmitted power is inversely proportional to the line reactance, adjusting the sending-end power source to keep the total transmitted power always at P0, then there is:
[0060]
[0061] Then, after the capacitor is put into operation, the reactance of line I changes, thus changing the distribution of the power transmitted by the line. The powers transmitted by the two lines are respectively:
[0062]
[0063] Wherein, X I represents the reactance of the incoming channel before switching the series capacitor; X II represents the reactance of the outgoing channel before switching the series capacitor; X C represents the capacitive reactance of the switched series capacitor; X″ ∑ represents the total parallel reactance of the incoming and outgoing channels after switching the series capacitor.
[0064] The curves of the active power transmitted by the two lines varying with the series capacitor are as Figure 5 shown. It can be seen from the curves that as the value of the series capacitor of Line I increases, the active power transmitted by Line II decreases, and the active power transmitted by Line I increases, that is, the series capacitor can realize the power flow transfer from Line II to Line I. When the value of the series capacitor is exactly equal to the original reactance value of Line I, the active power transmitted by Line II decreases to 0. Since the total power transmitted by the two lines remains unchanged all the time, at this time, all the line power flow is transferred to Line I.
[0065] After the series capacitor is installed, the change amount of the power flow of Line I, that is, the power flow transferred from Line II to Line I, is:
[0066]
[0067] Define the power flow transfer ratio η as the ratio of the power flow transferred from Line II to Line I to the power transmitted by Line II before the capacitor is put in, and we can get:
[0068]
[0069] Therefore, by adjusting the capacitance value of the thyristor controlled series capacitor (TCSC), the power flow transfer ratio η can be adjusted, so as to change the power flow transfer amount.
[0070] Embodiment 2
[0071] This embodiment is for the case where the potential of the control power supply is kept constant after a fault.
[0072] After the transmission channel XIII is removed due to a fault, the reactance between the equivalent nodes of the two-terminal power grids increases, and the total power transmitted by the line decreases. At this time, if the two-terminal power supplies are not adjusted and the equivalent potential of the power supply remains constant, then the total active power transmitted by the line at this time is:
[0073]
[0074] The active power transmitted by Line I and Line II is distributed in inverse proportion to the line reactance, and they are respectively:
[0075]
[0076] After the capacitor is put in, the total active power transmitted by the line and the active power transmitted by Line I and Line II are:
[0077]
[0078] The curves of the active power transmitted by the two lines varying with the series capacitor are as Figure 6 shown. From the curves, it can be obtained that when the electromotive forces of the double-end power supplies remain unchanged, the variation trend of the active power transmitted by the two lines with the series capacitor is the same as that in the case of keeping the total power transmitted by the control line unchanged. However, it can be seen from Equation (11) that when the electromotive forces of the two-end power supplies remain unchanged, the active power transmitted by the line is inversely proportional to the reactance value. When the line reactance decreases, the total power transmitted by the line will increase. That is, if the electromotive forces of the double-end power supplies are kept constant, at the same series capacitor compensation level, the total power transmitted by the line will increase. At this time, when the series capacitor is inserted into Line I, more attention should be paid to whether the power redundancy of Line I is sufficient.
[0079] The above technical solution is only one implementation manner of the present invention. For those skilled in the art, based on the disclosed principle of the present invention, it is very easy to make various types of improvements or deformations, not limited to the technical solution described in the above specific embodiments of the present invention. Therefore, the foregoing description is only preferred and does not have a limiting meaning.
Claims
1. An active power flow transfer method for a dual-power three-channel power system, characterized in that: When a fault occurs on a line of a transmission channel, select the one with the larger power upper limit among the other two transmission channels as the transfer-in channel, and the one with the smaller power upper limit as the transfer-out channel; Switch the series capacitor on and off on the line corresponding to the transfer-in channel to reduce the reactance of the transfer-in channel, so that the power flow on the transfer-out channel actively transfers towards the transfer-in channel after the faulty line is removed; where Adjust the power flow transfer ratio η by adjusting the capacitive reactance of the capacitor. The power flow transfer ratio η refers to the ratio of the increased active power of the transfer-in channel after the series capacitor is put in to the active power transmitted by the transfer-out channel before the series capacitor is put in; After the faulty line is removed, control the total transmitted active power to recover to the initial power value P0 before the fault occurs. After switching the series capacitor on and off, the power flow is distributed between the transfer-in channel and the transfer-out channel as follows: Wherein, P″ Ⅰ represents the transmission power of line I after switching the series capacitor, P″ Ⅱ represents the transmission power of line II after switching the series capacitor, X I represents the reactance of the incoming channel before switching the series capacitor; X II represents the reactance of the outgoing channel before switching the series capacitor; X C represents the capacitive reactance of the switched series capacitor; X′ ∑ ′ represents the total parallel reactance of the incoming channel and the outgoing channel after switching the series capacitor.
2. The active power flow transfer method of the dual-power three-channel power system according to claim 1, wherein: The series capacitor is a controllable capacitor with adjustable capacitance value, and the capacitive reactance is adjusted by adjusting the capacitance value.
3. The active power flow transfer method of the dual-power three-channel power system according to claim 1, characterized in that: The calculation formula of the power flow transfer ratio η is as follows: Wherein, X I represents the reactance of the incoming channel before switching the series capacitor; X II represents the reactance of the outgoing channel before switching the series capacitor; X C represents the capacitive reactance of the switched series capacitor.
4. The active power flow transfer method for a dual-power three-channel power system according to claim 1, characterized in that: After the faulty line is removed, control the electromotive forces of the two sending-end power supplies to be constant. After switching the series capacitor on and off, the power flow is distributed between the transfer-in channel and the transfer-out channel as follows: In the formula, P0 represents the initial power value of the total transmitted active power before the fault occurs; P0″ represents the power value of the total transmitted active power after the faulty line is removed; P″ I0 Indicates the transmitted active power of the channel after switching in the series capacitor; P″ II0 represents the active power transmitted through the transfer-out channel after switching the series capacitor; E S and E R are the electromotive forces of the two sending-end power sources respectively, and X S and X R represent the sending-end line reactances from the two sending-end power sources to the transmission channel respectively; X I represents the reactance of the transfer-in channel before switching the series capacitor; X II represents the reactance of the transfer-out channel before switching the series capacitor; X C represents the capacitive reactance of the switched series capacitor; X″ ∑ represents the total reactance of the transfer-in and transfer-out channels after switching the series capacitor; δ represents the phase angle difference between the electromotive forces of the two sending-end power sources; X ∑ represents the total parallel reactance of the three transmission channels before the fault occurs.
5. The active power flow transfer method of the dual-power three-channel power system according to claim 1, characterized in that: Switch the series capacitor on and off before the circuit protection action.
6. An active power flow transfer device for a dual - power three - channel power system, characterized in that: It includes two capacitors, which are respectively used to be connected in series to the lines corresponding to the two transmission channels with larger power upper limits among the three transmission channels; each capacitor is shunted with a capacitor switching switch; It further includes a controller, which is used to select a channel with a larger power upper limit from the remaining two transmission channels as the transfer-in channel after a fault occurs in one transmission channel, and control the action of the capacitor switching switch on the transfer-in channel.
7. The active power flow transfer device of the dual-power three-channel power system according to claim 6, characterized in that: The capacitor is a controllable capacitor with adjustable capacitance value.
8. The active power flow transfer device for a dual-power three-channel power system according to claim 7, characterized in that: The controller is used to adjust the capacitance value of the controllable capacitor according to the redundancy of the input channel, so as to adjust the power flow transfer ratio η to control the power flow transfer amount within the redundancy; the power flow transfer ratio η refers to the ratio of the increased active power of the transfer-in channel after the series capacitor is put in to the active power transmitted by the transfer-out channel before the series capacitor is put in; the redundancy refers to the difference between the current transmitted active power of the transmission channel and its power upper limit.