CN110676820A - High-frequency resonance backup protection method for flexible direct-current power transmission system - Google Patents
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
- H02H7/00—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions
- H02H7/26—Sectionalised protection of cable or line systems, e.g. for disconnecting a section on which a short-circuit, earth fault, or arc discharge has occured
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
- H02H3/00—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection
- H02H3/08—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection responsive to excess current
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- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
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Abstract
The invention discloses a high-frequency resonance backup protection method for a flexible direct-current transmission system, which is characterized in that alternating-current network side voltage harmonic out-of-limit protection, connection variable current harmonic out-of-limit protection and converter bridge arm reactor overload protection are arranged by monitoring the alternating-current side voltage distortion rate of flexible direct current and the harmonic tolerance capacity of related equipment (a connection transformer and a bridge arm reactor), and the method is used for protecting the safety of main operation equipment under the condition that a harmonic suppression control strategy is invalid.
Description
Technical Field
The invention belongs to the field of power systems, and is suitable for a modular multilevel flexible direct current transmission control protection system.
Background
Flexible direct current transmission (VSC-HVDC) technology is a hot spot for current grid technology development. The valve arm of the Modular Multilevel Converter (MMC) is composed of a plurality of sub-modules (SM), sine wave signals are output by superposition of output levels of the sub-modules, the modular multilevel converter has the advantages of low switching frequency, low loss, small harmonic wave and the like, is easy to expand to a higher voltage level, and is the main direction of the current flexible direct current transmission research and application.
In the operated flexible direct current engineering and simulation experiment, system resonance can occur when the flexible direct current transmission system operates under the following operating conditions. When the AC side fails, harmonic waves are transmitted to the DC side; high-frequency oscillation occurs in the flexible direct current grid connection process of the wind power plant; oscillation is caused when the networking mode is switched to the island mode; alternating current oscillation can be caused when the network connection side alternating current switch is switched on; high-frequency oscillation can be caused during the earth fault and fault recovery period of the direct-current system; system oscillation caused when the voltage of the sub-module of the converter deviates from a target value; low frequency oscillations can occur during system power up/down; and oscillation phenomena caused by unreasonable strategy setting of the converter controller, wherein the oscillation problems seriously threaten the equipment safety, the system stability and the power utilization quality of the modern power grid.
A resonance suppression strategy is added into the direct current control system, so that the problem of flexible direct current resonance can be effectively solved. However, because a laboratory cannot traverse all the operation conditions of the alternating current system, under the condition that the control strategy is invalid, a backup direct current locking measure is added by equipping with high-frequency resonance backup protection.
Disclosure of Invention
In order to solve the problems in the prior art, the invention provides a high-frequency resonance backup protection method for a flexible direct-current power transmission system, which is researched aiming at the characteristics of flexible direct-current resonance.
The invention specifically adopts the following technical scheme.
A high-frequency resonance backup protection method for a flexible direct-current transmission system is characterized by comprising the following steps: the method comprises the steps of monitoring the alternating current side voltage distortion rate of the flexible direct current and the harmonic tolerance capacity of operating equipment, and providing alternating current network side voltage harmonic out-of-limit protection, connection variable current harmonic out-of-limit protection and overload protection of a bridge arm reactor of a current converter to protect the safety of the operating equipment under the condition that a harmonic suppression control strategy fails; wherein,
the operating device comprises a coupling transformer and a bridge arm reactor.
The present invention further includes the following preferred embodiments.
The detection criterion of the out-of-limit protection of the voltage harmonic at the side of the alternating current network is as follows:
and calculating the harmonic waves and the voltage distortion rate of the voltage of the network side, and when the voltage distortion rate is greater than a set distortion rate fixed value, performing out-of-limit protection action on the voltage harmonic waves of the alternating current side and sending alarm information.
Calculating 2-30 harmonics and voltage distortion rate of the voltage of the grid side:
when the voltage distortion rate is calculated, replacing the harmonic component values of 2, 3, 5 and 7 orders with the harmonic component values in normal operation for the current calculated value;
and when the voltage distortion rate is greater than a fixed value, the protection action sends alarm information, wherein the fixed value corresponding to the voltage distortion rate is 5%.
The detection criterion of the connection variable current harmonic out-of-limit protection is as follows:
and calculating equivalent total heat current of the connection variable current, and when the equivalent total heat current exceeds the limit, connecting variable current harmonic out-of-limit protection action, locking the direct current system, tripping and sending alarm information.
And calculating equivalent total thermal current of 2-30 harmonic components of the connection variable current, and setting a thermal current reference value and a corresponding time fixed value according to the tolerance time and the harmonic heat loss coefficient of the connection transformer equipment.
Preferably, 8 sections of connection variable current harmonic out-of-limit protection are configured according to different thermal current reference values:
configuring 8 protection sections of 0.06p.u., 0.08p.u., 0.10p.u., 0.12p.u., 0.14p.u., 0.16p.u., 0.18p.u., 0.20p.u., wherein 0.06p.u., 0.08p.u., 0.10p.u., 0.12p.u., 0.14p.u., 0.16p.u., 0.18p.u., 0.20p.u. is 8 thermal current reference value, and p.u. is current per unit value;
and when the duration time of the equivalent total heat current which is greater than the reference value of the corresponding section of heat current reaches the corresponding time fixed value, protecting the action, sending alarm information, locking the direct current system and tripping.
The overload protection detection criterion of the bridge arm reactor of the converter is as follows:
calculating equivalent total heat current of 1-30 harmonic components of bridge arm current, wherein 1 harmonic is fundamental wave, and simulating the temperature rise of the reactor by integrating power consumption on the reactor and a thermal time constant of the reactor by using an inverse time-limit characteristic curve; setting according to a thermal time constant of bridge arm reactor equipment, the actual maximum continuous thermal current endured by the equipment and the continuous running current of the equipment to obtain a thermal current fixed value, protecting when the thermal current is greater than the fixed value, sending alarm information, locking a direct current system and tripping.
A high-frequency resonance backup protection method for a flexible direct-current transmission system is characterized by comprising the following steps:
step 1: collecting AC network side voltage harmonic, connection variable AC side harmonic current and harmonic current, and converter bridge arm harmonic current;
step 2: calculating the harmonic wave and the voltage distortion rate of the network side phase voltage, and when the voltage distortion rate is greater than a set distortion rate fixed value, performing out-of-limit protection action on the voltage harmonic wave of the alternating current side and sending alarm information;
and step 3: calculating equivalent total heat current of the connecting variable current, and when the equivalent total heat current exceeds the limit, connecting variable current harmonic out-of-limit protection action, locking the direct current system and tripping, and sending alarm information;
and 4, step 4: calculating equivalent total thermal current of 1-30 harmonic components of bridge arm current, and simulating the temperature rise of the reactor by integrating power consumption on the reactor and a thermal time constant of the reactor by using an inverse time-lag characteristic curve; setting according to a thermal time constant of bridge arm reactor equipment, the actual maximum continuous thermal current endured by the equipment and the continuous running current of the equipment to obtain a thermal current fixed value, protecting when the thermal current is greater than the fixed value, sending alarm information, locking a direct current system and tripping.
In the step 2, 2-30 harmonics and voltage distortion rates of the voltage of the network side are calculated; the distortion rate set value is typically no greater than 5%.
In step 3, 8-segment protection of 0.06p.u., 0.08p.u., 0.10p.u., 0.12p.u., 0.14p.u., 0.16p.u., 0.18p.u., 0.20p.u. is configured, wherein 0.06p.u., 0.08p.u., 0.10p.u., 0.12p.u., 0.14p.u., 0.16p.u., 0.18p.u., 0.20p.u. is 8-segment thermoelectric current reference value, and p.u. is current standard value, and when the duration of the equivalent total thermal current greater than the corresponding segment thermoelectric current reference value is greater than the time standard value, the protection action is sent, alarm information is sent, and the direct current system is locked and tripped; the value range of each protection time fixed value is determined by the tolerance capability of the converter transformer equipment and is provided by a converter transformer manufacturer.
In step 4, the equivalent total thermal current I is obtained according to the following formulaeqCalculating the formula:
wherein τ is a thermal time constant of the reactor, I∞Is the maximum continuous thermal current resistance of the reactor, IeqIs the equivalent total current.
The invention has the following beneficial technical effects:
when the flexible direct-current power transmission system generates high-frequency resonance, under the condition that a control strategy is invalid, a backup direct-current locking measure is added by equipping with high-frequency resonance backup protection, and the safety of equipment is effectively protected.
Drawings
Fig. 1 illustrates a monitoring point configuration diagram of a high-frequency resonance backup protection of a flexible direct-current power transmission system;
FIG. 2 illustrates a logic decision diagram for AC network side voltage harmonic out-of-limit protection;
FIG. 3 illustrates a logic decision diagram for AC single phase harmonic out-of-limit protection;
FIG. 4 illustrates a logic decision diagram for AC three-phase harmonic out-of-limit protection;
fig. 5 illustrates a logic judgment schematic diagram of the high-frequency resonance backup protection of the flexible direct-current power transmission system.
Detailed Description
The technical solution of the present invention is further explained below with reference to the drawings attached to the specification.
As shown in fig. 5, which is a logic judgment schematic diagram of the high-frequency resonance backup protection of the flexible direct-current power transmission system according to the present invention, the high-frequency resonance backup protection method of the flexible direct-current power transmission system disclosed by the present invention is characterized in that: the method is characterized in that the voltage distortion rate of the alternating current side of the flexible direct current and the harmonic tolerance capacity of the operating equipment are monitored, and the voltage harmonic out-of-limit protection of the alternating current side, the variable current harmonic out-of-limit protection and the overload protection of a bridge arm reactor of a current converter are provided to protect the safety of the operating equipment under the condition that a harmonic suppression control strategy fails.
And (3) voltage harmonic out-of-limit protection on the AC network side:
the voltage distortion rate and the voltage distortion rate U of each phase voltage are calculated by adopting three-phase voltage on the AC network side, namely UacD in figure 1, as a calculation measuring pointthdThe calculation formula is as follows:
wherein i is the harmonic order, UiIs a 2-30 th harmonic effective value of the network side phase voltage, UnomThe rated phase voltage of the AC network side.
In the Yu jaw back-to-back networking direct current engineering, U is calculatedthdThe second harmonic is then set at 0.2% UnomSubstitution, third harmonic at 3.6% UnomSubstitution of the fifth harmonic with 1.8% UnomSubstitution, seventh harmonic at 0.8% UnomInstead, the other harmonic components use the current calculation. The protection logic decision principle is shown in fig. 2.
Connection variable current harmonic out-of-limit protection:
the three-phase current of a connected transformer side or a valve side is adopted for calculating a measuring point, the current of a converter side or the current of an alternating current network side can be selected for the measuring point, namely IacD or IacY in figure 1, the measuring point with high measurement precision can be selected, when different sides need to be selected, the reference value of the current is different, and IacY is selected here. Calculating equivalent total heat current of phase current, and connecting with equivalent total heat current I of variable currenteqComputingThe formula is as follows:
wherein I is the harmonic order, IiCalculated value of 2-30 harmonics for connecting phase-change current, KiThe harmonic conversion scaling factor is obtained from the parameters of the coupling transformer in the range of 2-30 times when the coupling transformer is at the harmonic level of 0.02p.u., 0.04p.u., 0.06p.u., 0.08p.u., 0.10p.u., 0.12p.u., 0.14p.u., 0.16p.u., 0.18p.u., 0.20p.u.
Wherein, 0.06p.u., 0.08p.u., 0.10p.u., 0.12p.u., 0.14p.u., 0.16p.u., 0.18p.u., 0.20p.u. is a thermal current reference value of 8 segments, and p.u. is a current per unit value, when the duration that the equivalent total thermal current is greater than the corresponding thermal current reference value is greater than a time set value, the protection action is carried out, alarm information is sent, a direct current system is locked and tripped; the value range of each protection time fixed value is determined by the tolerance capability of the converter transformer equipment and is provided by a converter transformer manufacturer.
The protection logic decision principle is shown in fig. 3 and 4.
Overload protection of a bridge arm reactor of the current converter:
calculating the equivalent total heat current I of 1-30 harmonics of each bridge arm by using 6 bridge arm currents (the bridge arm currents are bridge arm reactor currents, and reactors are connected in series on the bridge arms) of the converter, namely IbP and IbN in figure 1 at calculating measuring pointseqThe formula is as follows:
wherein I is the harmonic order, IiCalculating the value of 1-30 harmonics of the bridge arm current, KiThe skin effect coefficient corresponding to each harmonic of the bridge arm reactor is obtained by reactor equipment parameters.
The protection utilizes an inverse time-lag characteristic curve to simulate the temperature rise of the reactor by integrating the power consumption on the reactor with its thermal time constant. The pass current and run time calculation formula is as follows:
an iterative calculation formula:
wherein τ is a thermal time constant of the reactor, I∞Is the maximum continuous thermal current tolerance, the superscripts (1) and (2) respectively represent the maximum continuous thermal current tolerance before and after iteration, IeqIs the equivalent total current.
The invention discloses a high-frequency resonance backup protection method for a flexible direct-current power transmission system, which comprises the following steps of:
step 1: collecting AC network side voltage harmonic, connection variable AC side harmonic current and harmonic current, and converter bridge arm harmonic current;
step 2: calculating the harmonic wave and the voltage distortion rate of the network side phase voltage, and when the voltage distortion rate is greater than a set distortion rate fixed value, performing out-of-limit protection action on the voltage harmonic wave of the alternating current side and sending alarm information;
calculating 2-30 harmonics and voltage distortion rate of the voltage of the grid side;
the distortion rate set value is typically no greater than 5%.
And step 3: calculating equivalent total heat current of the connecting variable current, and when the equivalent total heat current exceeds the limit, connecting variable current harmonic out-of-limit protection action, locking the direct current system and tripping, and sending alarm information;
in step 3, 8-segment protection of 0.06p.u., 0.08p.u., 0.10p.u., 0.12p.u., 0.14p.u., 0.16p.u., 0.18p.u., 0.20p.u. is configured, wherein 0.06p.u., 0.08p.u., 0.10p.u., 0.12p.u., 0.14p.u., 0.16p.u., 0.18p.u., 0.20p.u. is 8-segment thermoelectric current reference value, and p.u. is current standard value, and when the duration of the equivalent total thermal current greater than the corresponding segment thermoelectric current reference value is greater than the time standard value, the protection action is sent, alarm information is sent, and the direct current system is locked and tripped; the value range of each protection time fixed value is determined by the tolerance capability of the converter transformer equipment and is provided by a converter transformer manufacturer.
And 4, step 4: calculating equivalent total thermal current of 1-30 harmonic components of bridge arm current, and simulating the temperature rise of the reactor by integrating power consumption on the reactor and a thermal time constant of the reactor by using an inverse time-lag characteristic curve; setting according to a thermal time constant of bridge arm reactor equipment, the actual maximum continuous thermal current endured by the equipment and the continuous running current of the equipment to obtain a thermal current fixed value, protecting when the thermal current is greater than the fixed value, sending alarm information, locking a direct current system and tripping.
In step 4, the equivalent total thermal current I is obtained according to the following formulaeqCalculating the formula:
an iterative calculation formula:
wherein τ is a thermal time constant of the reactor, I∞The maximum continuous thermal current tolerance of the reactor is shown as the superscripts (1) and (2) respectively represent the maximum continuous thermal current tolerance before and after iteration, IeqIs the equivalent total current.
In the preferred embodiment of the present application, the high frequency resonance backup protection involves a list of fixed values as shown in table 1, and the classification detection and logic determination of the high frequency resonance backup protection are shown in fig. 5.
TABLE 1 high frequency resonance backup protection constant value List
Finally, it should be noted that: the above embodiments are only for illustrating the technical solutions of the present invention and not for limiting the same, and although the present invention is described in detail with reference to the above embodiments, those of ordinary skill in the art should understand that: modifications and equivalents may be made to the embodiments of the invention without departing from the spirit and scope of the invention, which is to be covered by the claims.
Claims (10)
1. A high-frequency resonance backup protection method for a flexible direct-current transmission system is characterized by comprising the following steps: the method comprises the steps of monitoring the alternating current side voltage distortion rate of the flexible direct current and the harmonic tolerance capacity of operating equipment, and providing alternating current network side voltage harmonic out-of-limit protection, connection variable current harmonic out-of-limit protection and overload protection of a bridge arm reactor of a current converter to protect the safety of the operating equipment under the condition that a harmonic suppression control strategy fails; wherein,
the operating device comprises a coupling transformer and a bridge arm reactor.
2. The method according to claim 1, characterized by comprising the steps of:
the detection criterion of the out-of-limit protection of the voltage harmonic at the side of the alternating current network is as follows:
and calculating the harmonic waves and the voltage distortion rate of the voltage of the network side, and when the voltage distortion rate is greater than a set distortion rate fixed value, performing out-of-limit protection action on the voltage harmonic waves of the alternating current side and sending alarm information.
3. The method for high-frequency resonance backup protection of the flexible direct-current transmission system according to claim 2, characterized by comprising the following steps:
calculating 2-30 harmonics and voltage distortion rate of the voltage of the grid side:
when the voltage distortion rate is calculated, replacing the harmonic component values of 2, 3, 5 and 7 orders with the harmonic component values in normal operation for the current calculated value;
and when the voltage distortion rate is greater than a fixed value, the protection action sends alarm information, wherein the fixed value corresponding to the voltage distortion rate is 5%.
4. The method according to claim 1, characterized by comprising the steps of:
the detection criterion of the connection variable current harmonic out-of-limit protection is as follows:
and calculating equivalent total heat current of the connection variable current, and when the equivalent total heat current exceeds the limit, connecting variable current harmonic out-of-limit protection action, locking the direct current system, tripping and sending alarm information.
5. The method for high-frequency resonance backup protection of the flexible direct current transmission system according to claim 4, characterized by comprising the following steps:
and calculating equivalent total thermal current of 2-30 harmonic components of the connection variable current, and setting a thermal current reference value and a corresponding time fixed value according to the tolerance time and the harmonic heat loss coefficient of the connection transformer equipment.
Preferably, 8 sections of connection variable current harmonic out-of-limit protection are configured according to different thermal current reference values:
configuring 8 protection sections of 0.06p.u., 0.08p.u., 0.10p.u., 0.12p.u., 0.14p.u., 0.16p.u., 0.18p.u., 0.20p.u., wherein 0.06p.u., 0.08p.u., 0.10p.u., 0.12p.u., 0.14p.u., 0.16p.u., 0.18p.u., 0.20p.u. is 8 thermal current reference value, and p.u. is current per unit value;
and when the duration time of the equivalent total heat current which is greater than the reference value of the corresponding section of heat current reaches the corresponding time fixed value, protecting the action, sending alarm information, locking the direct current system and tripping.
6. The method according to claim 1, characterized by comprising the steps of:
the overload protection detection criterion of the bridge arm reactor of the converter is as follows:
calculating equivalent total heat current of 1-30 harmonic components of bridge arm current, wherein 1 harmonic is fundamental wave, and simulating the temperature rise of the reactor by integrating power consumption on the reactor and a thermal time constant of the reactor by using an inverse time-limit characteristic curve; setting according to a thermal time constant of bridge arm reactor equipment, the actual maximum continuous thermal current endured by the equipment and the continuous running current of the equipment to obtain a thermal current fixed value, protecting when the thermal current is greater than the fixed value, sending alarm information, locking a direct current system and tripping.
7. A high-frequency resonance backup protection method for a flexible direct-current transmission system is characterized by comprising the following steps:
step 1: collecting AC network side voltage harmonic, connection variable AC side harmonic current and harmonic current, and converter bridge arm harmonic current;
step 2: calculating the harmonic wave and the voltage distortion rate of the network side phase voltage, and when the voltage distortion rate is greater than a set distortion rate fixed value, performing out-of-limit protection action on the voltage harmonic wave of the alternating current side and sending alarm information;
and step 3: calculating equivalent total heat current of the connecting variable current, and when the equivalent total heat current exceeds the limit, connecting variable current harmonic out-of-limit protection action, locking the direct current system and tripping, and sending alarm information;
and 4, step 4: calculating equivalent total thermal current of 1-30 harmonic components of bridge arm current, and simulating the temperature rise of the reactor by integrating power consumption on the reactor and a thermal time constant of the reactor by using an inverse time-lag characteristic curve; setting according to a thermal time constant of bridge arm reactor equipment, the actual maximum continuous thermal current endured by the equipment and the continuous running current of the equipment to obtain a thermal current fixed value, protecting when the thermal current is greater than the fixed value, sending alarm information, locking a direct current system and tripping.
8. The method according to claim 7, characterized by comprising the following steps: in the step 2, 2-30 harmonics and voltage distortion rates of the voltage of the network side are calculated; the distortion rate set value is typically no greater than 5%.
9. The method according to claim 7, characterized by comprising the following steps:
in step 3, 8-segment protection of 0.06p.u., 0.08p.u., 0.10p.u., 0.12p.u., 0.14p.u., 0.16p.u., 0.18p.u., 0.20p.u. is configured, wherein 0.06p.u., 0.08p.u., 0.10p.u., 0.12p.u., 0.14p.u., 0.16p.u., 0.18p.u., 0.20p.u. is 8-segment thermoelectric current reference value, and p.u. is current standard value, and when the duration of the equivalent total thermal current greater than the corresponding segment thermoelectric current reference value is greater than the time standard value, the protection action is sent, alarm information is sent, and the direct current system is locked and tripped; the value range of each protection time fixed value is determined by the tolerance capability of the converter transformer equipment and is provided by a converter transformer manufacturer.
10. The method according to claim 7, characterized by comprising the following steps:
in step 4, the equivalent total thermal current I is obtained according to the following formulaeqCalculating the formula:
wherein τ is a thermal time constant of the reactor, I∞Is the maximum continuous thermal current resistance of the reactor, IeqIs the equivalent total current.
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| CN111934339A (en) * | 2020-07-31 | 2020-11-13 | 许继集团有限公司 | Direct current protection method |
| CN111952941A (en) * | 2020-08-05 | 2020-11-17 | 北京交通大学 | Self-adaptive pilot protection method for direct-current power grid |
| CN114665496A (en) * | 2022-03-31 | 2022-06-24 | 广东电网有限责任公司广州供电局 | High-frequency harmonic protection method and device for flexible direct current transmission system |
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| CN111934339A (en) * | 2020-07-31 | 2020-11-13 | 许继集团有限公司 | Direct current protection method |
| CN111952941A (en) * | 2020-08-05 | 2020-11-17 | 北京交通大学 | Self-adaptive pilot protection method for direct-current power grid |
| CN114665496A (en) * | 2022-03-31 | 2022-06-24 | 广东电网有限责任公司广州供电局 | High-frequency harmonic protection method and device for flexible direct current transmission system |
| CN114665496B (en) * | 2022-03-31 | 2023-08-15 | 广东电网有限责任公司广州供电局 | High-frequency harmonic protection method and device for flexible direct-current transmission system |
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