CN111600326A - Power conversion method of parallel three-terminal direct-current power transmission system - Google Patents

Abstract

The invention discloses a power transfer method of a parallel three-terminal direct-current transmission system, which comprises three converter stations, wherein under the working condition that the two poles of the three stations are all operated, if a certain converter station is subjected to unipolar locking, the power transfer method calculates and resets the power/current reference value of each pole of each station according to the power level, the minimum and maximum transmission power capability and the control mode of each pole of the three stations before locking, so that the inter-pole transfer and/or the inter-station transfer of power are realized, the loss of direct-current power is reduced to the maximum extent, meanwhile, the balance of the ground pole current of a non-fault converter station can be ensured to the greatest extent, and the stability and the flexibility of the parallel three-terminal direct-current transmission system are improved.

Description

Power conversion method of parallel three-terminal direct-current power transmission system

Technical Field

The invention belongs to the field of direct current transmission, and discloses a power conversion method of a parallel three-terminal direct current transmission system.

Background

The multi-terminal direct current transmission system is formed by connecting at least three converter stations through a high-voltage direct current transmission line, can realize interconnection of a plurality of alternating current power grids with different delivery and absorption capacities, realizes multi-power supply and multi-drop power receiving, saves transmission line corridors, and is a more flexible transmission mode. The common types of the multi-terminal direct-current transmission system include a parallel type, a series type, a mixed type and the like, wherein the parallel type multi-terminal direct-current transmission system is formed by connecting direct-current sides of all converter stations in parallel through transmission lines and bus bars, is the most common type of the multi-terminal direct-current transmission system, has several engineering applications internationally at present, and has a plurality of engineering constructions domestically.

Multi-terminal dc transmission systems can be divided into three types: conventional direct current transmission systems employing thyristor technology (LCC-HVDC), flexible direct current transmission systems based on fully controlled voltage source converters (VSC-HVDC) and hybrid direct current transmission systems combining the two. The conventional direct current transmission system (LCC-HVDC) has the advantages of low cost, low loss and mature operation technology, and has the disadvantages of easy occurrence of commutation failure on an inversion side, strong dependence on an alternating current system, large reactive power absorption and large occupied area of a converter station. The flexible direct-current power transmission system has the advantages of capability of realizing active power and reactive power decoupling control, capability of supplying power to a passive network, compact structure, small occupied area, no problem of inversion side commutation failure and the like, but has the defects of high cost, large loss and the like. In recent years, a hybrid direct-current transmission technology integrating LCC-HVDC and VSC-HVDC technologies has a good engineering application prospect, the problem of commutation failure on an inversion side can be avoided by adopting LCC-HVDC on the rectification side and VSC-HVDC on the inversion side, and meanwhile, the advantages of engineering cost are guaranteed to a certain extent.

The parallel three-terminal direct-current transmission system is used as a common topology in a multi-terminal direct-current transmission system, power conversion after locking of a single pole is a key technology, loss of direct-current power is reduced to the greatest extent, current balance of a grounding electrode of a non-fault station can be considered to the greatest extent, and the scheme is still researched.

Disclosure of Invention

The invention aims to provide a power conversion method of a parallel three-terminal direct-current transmission system, which aims to solve the problem of power conversion after locking of a single pole, reduce the loss of direct-current power and simultaneously consider the current balance of a grounding electrode of a non-fault station.

In order to achieve the purpose, the invention adopts the technical scheme that:

a power transfer method of a parallel three-terminal direct-current transmission system comprises three converter stations, under the working condition that the bipolar of the three stations are all operated, if a certain converter station is subjected to unipolar locking, the power transfer method calculates and resets power/current reference values of poles of the three stations according to the power levels, the minimum and maximum power transmission capacities and the control mode of the poles of the three stations before locking, and inter-pole transfer and/or inter-station transfer of power are/is achieved.

In a preferred technical scheme, the three converter stations comprise two rectifying stations and one inverter station, or comprise one rectifying station and two inverter stations; two converter stations which are in rectification mode or inversion mode are called a first converter station and a second converter station, and the rest converter stations are called a third converter station; of the first converter station and the second converter station, the converter station in which unipolar blocking occurs is referred to as a first converter station, the converter station in which unipolar blocking does not occur is referred to as a second converter station, the pole in which unipolar blocking occurs is referred to as a first pole, and the pole in which unipolar blocking does not occur is referred to as a second pole.

In a preferred technical solution, if the second pole is in a unipolar current control mode, after a unipolar lockup occurs at the first pole of the first converter station, the lost power is transferred to the first pole of the second converter station until the power is at an upper limit; the second pole power of the first converter station, the second converter station and the third converter station are kept unchanged; if the second pole is in bipolar power control mode, the lost power is preferentially transferred to the second pole of the first converter station up to its upper power limit, and if the second pole of the first converter station reaches its upper limit, the insufficient power is continuously transferred to the second converter station.

In a preferred technical scheme, if the first pole and the second pole are both in a unipolar current control mode, after unipolar locking occurs to the first pole of the first converter station, the lost power is transferred to the first pole of the second converter station until the power reaches the upper limit; the second pole powers of the first, second and third converter stations are kept constant.

In a preferred technical solution, if the first pole is in a bipolar power control mode and the second pole is in a unipolar power control mode, after the first pole of the first converter station is subjected to unipolar blocking, the first pole is switched to the unipolar power control mode, and the lost power is transferred to the first pole of the second converter station until the power is limited; the second pole powers of the first, second and third converter stations are kept constant.

In a preferred embodiment, if the first pole is in the unipolar current control mode and the second pole is in the bipolar power control mode, after the unipolar shutdown of the first pole of the first converter station, the power of the first pole of the second converter station remains unchanged, and the power of the first pole of the third converter station decreases to the same power level as the power of the first pole of the second converter station; the lost power is preferentially transferred to the second pole of the first converter station up to its upper power limit, and if the second pole of the first converter station reaches its upper limit, the insufficient part is continuously transferred to the second pole of the second converter station up to its upper power limit.

In a preferred embodiment, if the first pole and the second pole are both in bipolar power control mode, after the first pole of the first converter station has unipolar shutdown, the first pole is switched to unipolar power control mode, the lost power is preferentially transferred to the second pole of the first converter station until the power upper limit, and if the second pole of the first converter station reaches the power upper limit, the insufficient power is continuously transferred to the second converter station.

In an embodiment, if the second pole of the first converter station reaches its upper limit, the excess power is transferred to the second converter station, and specifically, the first and second pole power distribution of the second converter station is divided into four cases: let P_TransferFor switching from a first converter station to a second converter stationPower of the converter station, P_21maxIs the first maximum power limit, P, of the second converter station_22maxIs the second pole power upper limit, P 'of the second converter station'₂₁Power of the first pole of the second converter station, P 'before single-pole blocking'₂₂For the power of the second pole of the second converter station before unipolar blocking, U₁Is a DC voltage of a first pole, U₂A DC voltage of a second polarity; order to

Case 1) if P ″)₂₁＜P_21maxAnd P ″)₂₂＜P_22maxThe power is distributed according to the bipolar voltage proportion, and the first pole power of the second converter station is P ″)₂₁The power of the second pole is P₂₂″；

Case 2) if P ″)₂₁＜P_21max,P″₂₂＞P_22maxAnd P ″)₂₁+P″₂₂＜P_21max+P_22maxThe first pole power of the second converter station is P₂₁″+P₂₂″-P_22maxThe power of the second pole is P_22max；

Case 3) if P₂₁″＞P_21max,P″₂₂＜P_22maxAnd P ″)₂₁+P″₂₂＜P_21max+P_22maxThe first pole power of the second converter station is P_21maxThe power of the second pole is P₂₁+P″₂₂-P_21max；

Case 4) if P ″)₂₁+P″₂₂≥P_21max+P_22maxThe first pole power of the second converter station is P_21maxThe power of the second pole is P_22max。

In the preferred technical scheme, when the second pole is in a bipolar power control mode, if the minimum power of the non-locked station is 0, the power lost by the station where the locked pole is located is preferentially transferred between poles of the station, and the insufficient power is transferred between the stations; if the minimum power of the non-locked station is larger than 0, forced inter-station power transfer exists, and the power of forced inter-station transfer needs to be deducted when the inter-electrode transfer power is calculated.

In the preferred technical scheme, if the minimum power of the non-locking station is greater than 0, when P'₂₁+P’₂₂＜P_31min+P_22minOf which is P'₂₁Power, P 'of the first pole of the second converter station before being single-pole latched'₂₂Power, P, of the second pole of the second converter station before unipolar blocking_31minFor the first pole minimum power, P, of the third converter station_22minThe minimum power of the second pole of the second converter station exists, when the first pole of the first converter station is locked, the power between the stations is forced to transfer, and the power between the stations is forced to transfer is P_{Transfer_forced＝}P_31min+P_22min-P’₂₁+P’₂₂。

In a preferred embodiment, if the first pole is in the unipolar current control mode and the second pole is in the bipolar power control mode, after the first pole of the first converter station is subjected to unipolar shutdown, if the forced inter-station power transfer occurs, the lost power is transferred to the second pole of the first converter station after the power transferred between the forced inter-station is subtracted, and the two cases are:

1) if the second pole of the first converter station does not reach the upper power limit, the second pole power of the first converter station is P₁₂＝P’_3BP-(P_31min+P_22min) The first pole power of the second converter station is P_31minThe second pole power of the second converter station is P_22minOf which is P'_3BPIs the sum of the bipolar powers of the third converter station before the lock-out;

2) if the second pole of the first converter station reaches the upper power limit, the second pole power of the first converter station is P_12maxThe first pole power of the second converter station is P_31minThe second pole power of the second converter station is P₂₂＝min[P_22max,P’_3BP-P_12max-P_31min]In which P is_12maxFor the second power limit, P, of the first converter station_22maxIs the second power limit of the second converter station.

In a preferred technical solution, if the first pole and the second pole are both in a bipolar power control mode, after the first pole of the first converter station is locked in a unipolar mode, if the power transfer between the forced stations occurs, the lost power is preferentially transferred to the second pole of the first converter station after the power transferred between the forced stations is subtracted, and the two situations are divided into two situations:

1) if the second pole of the first converter station does not reach the upper power limit, the second pole power of the first converter station is P₁₂＝P’_3BP-(P_31min+P_22min) The first pole power of the second converter station is P_31minThe second pole power of the second converter station is P_22minOf which is P'_3BPIs the sum of the bipolar powers of the third converter station before the lock-out;

2) if the second pole of the first converter station reaches the upper power limit, the second pole power of the first converter station is P_12maxPower P of the first pole of the second converter station₂₁＝max[P_31min,P_{21_cal}]，

The power of the second pole of the second converter station is P₂₂＝min[P_22max,P’_3BP-P_12max-P₂₁]；

Wherein P is_22maxFor the second power limit of the second converter station, P_12maxAn upper power limit of a second pole of the first converter station;

the P is_{21_cal}Calculating the power for the first pole of the second converter station comprises the following four cases:

P_Transferfor transferring power from a first converter station to a second converter station, P_21maxIs the first pole power upper limit, P 'of the second converter station'₂₁Power of the first pole of the second converter station, P 'before single-pole blocking'₂₂For the power of the second pole of the second converter station before unipolar blocking, U₁Is a DC voltage of a first pole, U₂A DC voltage of a second polarity; order to

Case 1) if P ″)₂₁＜P_21maxAnd P ″)₂₂＜P_22maxThen divided by the voltage proportion of the bipole, then P_{21_cal}＝P″₂₁；

Case 2) if P ″)₂₁＜P_21max,P″₂₂＞P_22maxAnd P ″)₂₁+P″₂₂＜P_21max+P_22maxThen P is_{21_cal}＝P₂₁″+P₂₂″-P_22max；

Case 3) if P₂₁″＞P_21max,P″₂₂＜P_22maxAnd P ″)₂₁+P″₂₂＜P_21max+P_22maxThen P is_{21_cal}＝P_21max；

Case 4) if P ″)₂₁+P″₂₂≥P_21max+P_22maxThen P is_{21_cal}＝P_21max。

The invention has the beneficial effects that: according to the method, the control mode and the power/current reference value of each pole of each station are calculated and reset according to the power level, the minimum and maximum transmission power capability and the control mode of each pole of the three stations before locking, the inter-pole transfer and the inter-station transfer of power are realized, the loss of direct current power is reduced to the maximum extent, and meanwhile, the ground electrode current balance of a non-fault converter station can be ensured to the greatest extent, so that the stability and the flexibility of the parallel three-terminal direct current transmission system are improved.

Drawings

In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings needed to be used in the description of the embodiments will be briefly introduced below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings based on these drawings without creative efforts.

Fig. 1 is a schematic flow chart of a power conversion method of a parallel three-terminal direct-current power transmission system according to the present invention;

fig. 2 is a schematic diagram of a topology structure of a parallel three-terminal dc power transmission system according to the present invention.

Detailed Description

The present invention will be better understood and implemented by those skilled in the art by the following detailed description of the technical solution of the present invention with reference to the accompanying drawings and specific examples, which are not intended to limit the present invention. Wherein like components are given like reference numerals.

Fig. 1 shows an embodiment 1 of a power conversion method of a parallel three-terminal dc transmission system according to the present invention. The method comprises the following steps: under the working condition that all three stations and double poles operate, if a certain converter station has single-pole locking, the power/current reference value of each pole of each station is calculated and reset according to the power level, the minimum and maximum power transmission capacity and the control mode of each pole of the three stations before locking, and inter-pole transfer and/or inter-station transfer of power are/is realized.

The parallel three-terminal direct-current transmission system comprises three converter stations. The three converter stations comprise two rectifying stations and one inverter station, or comprise one rectifying station and two inverter stations; two converter stations which are in rectification mode or inversion mode are called a first converter station and a second converter station, and the rest converter stations are called a third converter station; of the first converter station and the second converter station, the converter station in which unipolar blocking occurs is referred to as a first converter station, the converter station in which unipolar blocking does not occur is referred to as a second converter station, the pole in which unipolar blocking occurs is referred to as a first pole, and the pole in which unipolar blocking does not occur is referred to as a second pole.

In a preferred embodiment 2, if the second pole is in unipolar current control mode, the lost power is transferred to the first pole of the second converter station up to its upper power limit after unipolar blocking of the first pole of the first converter station; the second pole power of the first converter station, the second converter station and the third converter station are kept unchanged; if the second pole is in bipolar power control mode, the lost power is preferentially transferred to the second pole of the first converter station up to its upper power limit, and if the second pole of the first converter station reaches its upper limit, the insufficient power is continuously transferred to the second converter station.

In a preferred embodiment 3, if the first pole and the second pole are both in the unipolar current control mode, after the unipolar blocking of the first pole of the first converter station, the lost power is transferred to the first pole of the second converter station until the upper power limit thereof; the second pole powers of the first, second and third converter stations are kept constant.

In a preferred embodiment 4, if the first pole is in bipolar power control mode and the second pole is in unipolar control mode, after unipolar blocking of the first pole of the first converter station, the first pole is switched to unipolar control mode, and the lost power is transferred to the first pole of the second converter station until its upper power limit; the second pole powers of the first, second and third converter stations are kept constant.

In a preferred embodiment 5, if the first pole is in the unipolar current control mode and the second pole is in the bipolar power control mode, after the unipolar shutdown of the first pole of the first converter station, the power of the first pole of the second converter station remains unchanged, and the power of the first pole of the third converter station decreases to the same power level as the power of the first pole of the second converter station; the lost power is preferentially transferred to the second pole of the first converter station up to its upper power limit, and if the second pole of the first converter station reaches its upper limit, the insufficient part is continuously transferred to the second pole of the second converter station up to its upper power limit.

In a preferred embodiment 6, when the first pole and the second pole are both in bipolar power control mode, after the first pole of the first station has unipolar shutdown, the first pole is switched to unipolar power control mode, the lost power is preferentially transferred to the second pole of the first station up to its upper power limit, and when the second pole of the first station reaches its upper limit, the insufficient power is transferred to the second station.

In a preferred embodiment 7, based on embodiment 6, if the second pole of the first converter station reaches its upper limit, the excess power is transferred to the second converter station, specifically, the first and second pole power distribution of the second converter station are divided into four cases: let P_TransferFor transferring power from a first converter station to a second converter station, P_21maxIs the first maximum power limit, P, of the second converter station_22maxIs the second pole power upper limit, P 'of the second converter station'₂₁Power of the first pole of the second converter station, P 'before single-pole blocking'₂₂For the power of the second pole of the second converter station before unipolar blocking, U₁Is a DC voltage of a first pole, U₂A DC voltage of a second polarity; order to

Case 1) if P ″)₂₁＜P_21maxAnd P ″)₂₂＜P_22maxThe power is distributed according to the bipolar voltage proportion, and the first pole power of the second converter station is P ″)₂₁The power of the second pole is P₂₂″；

Case 2) if P ″)₂₁＜P_21max,P″₂₂＞P_22maxAnd P ″)₂₁+P″₂₂＜P_21max+P_22maxThe first pole power of the second converter station is P₂₁″+P₂₂″-P_22maxThe power of the second pole is P_22max；

Case 3) if P₂₁″＞P_21max,P″₂₂＜P_22maxAnd P ″)₂₁+P″₂₂＜P_21max+P_22maxThe first pole power of the second converter station is P_21maxThe power of the second pole is P₂₁+P″₂₂-P_21max；

Case 4) if P ″)₂₁+P″₂₂≥P_21max+P_22maxThe first pole power of the second converter station is P_21maxThe power of the second pole is P_22max。

In a preferred embodiment 8, in addition to embodiments 1, 2, 5, 6 and 7, when the second pole is in the bipolar power control mode, if the minimum power of the non-locked station is 0, the power lost by the locked pole in the station is preferentially transferred between the stations, and the insufficient power is transferred between the stations; if the minimum power of the non-locked station is larger than 0, forced inter-station power transfer exists, and the power of forced inter-station transfer needs to be deducted when the inter-electrode transfer power is calculated.

In a preferred embodiment 9, based on embodiment 8, if the minimum power of the non-locking station is greater than 0, when P'₂₁+P’₂₂＜P_31min+P_22minWhen it is used, itMiddle P'₂₁Power, P 'of the first pole of the second converter station before being single-pole latched'₂₂Power, P, of the second pole of the second converter station before unipolar blocking_31minFor the first pole minimum power, P, of the third converter station_22minThe minimum power of the second pole of the second converter station exists, when the first pole of the first converter station is locked, the power between the stations is forced to transfer, and the power between the stations is forced to transfer is P_{Transfer_forced}＝P_31min+P_22min-P’₂₁+P’₂₂。

In a preferred embodiment 10, in addition to embodiment 9, when the first pole is in the unipolar current control mode and the second pole is in the bipolar power control mode, and when the forced inter-station power transfer occurs after the unipolar shutdown of the first pole of the first converter station, the lost power is transferred to the second pole of the first converter station after the power transferred between the forced stations is subtracted, and the two cases are divided into two cases:

1) if the second pole of the first converter station does not reach the upper power limit, the second pole power of the first converter station is P₁₂＝P’_3BP-(P_31min+P_22min) The first pole power of the second converter station is P_31minThe second pole power of the second converter station is P_22minOf which is P'_3BPIs the sum of the bipolar powers of the third converter station before the lock-out;

2) if the second pole of the first converter station reaches the upper power limit, the second pole power of the first converter station is P_12maxThe first pole power of the second converter station is P_31minThe second pole power of the second converter station is P₂₂＝min[P_22max,P’_3BP-P_12max-P_31min]In which P is_12maxFor the second power limit, P, of the first converter station_22maxIs the second power limit of the second converter station.

In a preferred embodiment 11, based on embodiment 9, if the first pole and the second pole are both in the bipolar power control mode, and after the first pole of the first converter station is subjected to unipolar shutdown, and then forced inter-station power transfer occurs, the lost power is preferentially transferred to the second pole of the first converter station after the power transferred between the forced inter-station is subtracted, and the two cases are:

1) if the second pole of the first converter station does not reach the upper power limit, the second pole power of the first converter station is P₁₂＝P’_3BP-(P_31min+P_22min) The first pole power of the second converter station is P_31minThe second pole power of the second converter station is P_22minOf which is P'_3BPIs the sum of the bipolar powers of the third converter station before the lock-out;

2) if the second pole of the first converter station reaches the upper power limit, the second pole power of the first converter station is P_12maxPower P of the first pole of the second converter station₂₁＝max[P_31min,P_{21_cal}]，

The power of the second pole of the second converter station is P₂₂＝min[P_22max,P’_3BP-P_12max-P₂₁]；

Wherein P is_22maxFor the second power limit of the second converter station, P_12maxAn upper power limit of a second pole of the first converter station;

the P is_{21_cal}Calculating the power for the first pole of the second converter station comprises the following four cases:

P_Transferfor transferring power from a first converter station to a second converter station, P_21maxIs the first pole power upper limit, P 'of the second converter station'₂₁Power of the first pole of the second converter station, P 'before single-pole blocking'₂₂For the power of the second pole of the second converter station before unipolar blocking, U₁Is a DC voltage of a first pole, U₂A DC voltage of a second polarity; order to

Case 1) if P ″)₂₁＜P_21maxAnd P ″)₂₂＜P_22maxThen divided by the voltage proportion of the bipole, then P_{21_cal}＝P″₂₁；

Case 2) if P ″)₂₁＜P_21max,P″₂₂＞P_22maxAnd P ″)₂₁+P″₂₂＜P_21max+P_22maxThen, thenP_{21_cal}＝P₂₁″+P₂₂″-P_22max；

Case 3) if P₂₁″＞P_21max,P″₂₂＜P_22maxAnd P ″)₂₁+P″₂₂＜P_21max+P_22maxThen P is_{21_cal}＝P_21max；

Case 4) if P ″)₂₁+P″₂₂≥P_21max+P_22maxThen P is_{21_cal}＝P_21max。

Embodiments 12 to 20 are described below with reference to a schematic topology of a parallel three-terminal dc power transmission system shown in fig. 2. Wherein include a rectifier station and two contravariant stations, be respectively: the system comprises an inversion station 1, an inversion station 2, a rectification station 3, a power transmission line 4, a power transmission line 6 and a bus bar 5. The rectifier station 3 is an LCC converter station, the inverter stations 1 and 2 are VSC converter stations, one of the 2 inverter stations is a fixed direct-current voltage station, and the other station is a fixed direct-current power station. The rectifying station 3 is connected to a bus bar 5 through a power transmission line 4, the inverter station 2 is directly connected to the bus bar 5, and the inverter station 1 is connected to the bus bar 5 through a power transmission line 6, so that a parallel three-terminal direct-current power transmission system is formed.

Example 12: the operating power boundary conditions are that the minimum power of the single pole of the rectifying station 3 is 400MW, and the maximum power is 4000 MW. The minimum power of the inversion station 1 monopole is 150MW, and the maximum power is 1500 MW. The minimum power of the single pole of the inverter station 2 is 250MW, and the maximum power is 2500 MW. The rated dc voltage of the pole 1 is 800kV, and the rated dc voltage of the pole 2 is-800 kV.

Utmost point 1 and utmost point 2 all adopt the unipolar current control mode, and 3 utmost point 1 and 2 operating power of rectifier station are 800MW, and 1 utmost point 1 and 2 operating power of inverter station are 300MW, and 2 utmost point 1 and 2 operating power of inverter station are 500 MW. The inverter station 1, pole 1, is shut down with a single pole latch. Then it is determined that,

the remaining sound system (the pole 1 is composed of a rectification station 3 and an inversion station 2, the pole 2 is composed of the rectification station 3, the inversion station 1 and the inversion station 2) continues to operate, and the lost power is transferred to the pole 1 of the inversion station 2, and the power of the three stations of the pole 2 is kept unchanged. The rectifier station 3 has a pole 1 power of 800MW and a pole 2 power of 800 MW. The power of the 1 pole of the inverter station is 0MW, and the power of the 2 pole is 300 MW. The power of the pole 1 of the inverter station 2 is 800MW, and the power of the pole 2 is 500 MW.

Example 13: the power boundary conditions of each station operation were the same as in example 12.

Utmost point 1 adopts the bipolar power control mode, and utmost point 2 adopts the unipolar current control mode, and 3 utmost point 1 and 2 operating power of rectifier station are 800MW, and 1 utmost point 1 and 2 operating power of contravariant station are 300MW, and 2 utmost point 1 and 2 operating power of contravariant station are 500 MW. The inverter station 1, pole 1, is shut down with a single pole latch. Then it is determined that,

and the remaining sound system (the pole 1 is a system consisting of the rectifying station 3 and the inverter station 2, and the pole 2 is a system consisting of the rectifying station 3, the inverter station 1 and the inverter station 2) continues to operate, the pole 1 is switched into a single-pole current control mode, the lost power is converted into the pole 1 of the inverter station 2, and the power of the three stations of the pole 2 is kept unchanged. The rectifier station 3 has a pole 1 power of 800MW and a pole 2 power of 800 MW. The power of the 1 pole of the inverter station is 0MW, and the power of the 2 pole is 300 MW. The power of the pole 1 of the inverter station 2 is 800MW, and the power of the pole 2 is 500 MW.

Example 14: the power boundary conditions of each station operation were the same as in example 12.

Utmost point 1 adopts unipolar current control mode, and utmost point 2 adopts bipolar power control mode, and 3 utmost point 1 and 2 operating power of rectifier station are 800MW, and 1 utmost point 1 and 2 operating power of contravariant station are 300MW, and 2 utmost point 1 and 2 operating power of contravariant station are 500 MW. The inverter station 1, pole 1, is shut down with a single pole latch. Then it is determined that,

the remaining sound system (the system of the pole 1 composed of the rectification station 3 and the inversion station 2, the pole 2 composed of the rectification station 3, the inversion station 1 and the inversion station 2) continues to operate, and the lost power is transferred to the pole 2 of the inversion station 1. The rectifier station 3 has a pole 1 power of 500MW and a pole 2 power of 1100 MW. The power of the 1 pole of the inverter station is 0MW, and the power of the 2 pole is 600 MW. The power of the pole 1 of the inverter station 2 is 500MW, and the power of the pole 2 is 500 MW.

Example 15: the maximum power of the inverter station 1, pole 2 is limited to 500MW for some reasons, and other boundary conditions are the same as those of the embodiment 12

Utmost point 1 adopts unipolar current control mode, and utmost point 2 adopts bipolar power control mode, and 3 utmost point 1 and 2 operating power of rectifier station are 800MW, and 1 utmost point 1 and 2 operating power of contravariant station are 300MW, and 2 utmost point 1 and 2 operating power of contravariant station are 500 MW. The inverter station 1, pole 1, is shut down with a single pole latch. Then it is determined that,

the remaining sound system (the pole 1 is composed of a rectification station 3 and an inversion station 2, the pole 2 is composed of the rectification station 3, the inversion station 1 and the inversion station 2) continues to operate, the lost power is preferentially transferred to the pole 2 of the inversion station 1, and the excessive part is transferred to the pole 2 of the inversion station 2. The rectifier station 3 has a pole 1 power of 500MW and a pole 2 power of 1100 MW. The power of the pole 1 of the inversion station is 0MW, and the power of the pole 2 is 500MW (reaching the upper limit). The power of the pole 1 of the inverter station 2 is 500MW, and the power of the pole 2 is 600 MW.

Example 16: the power boundary conditions of each station operation were the same as in example 12.

Utmost point 1 adopts unipolar current control mode, and utmost point 2 adopts bipolar power control mode, and 3 utmost point 1 and 2 operating power of rectifier station are 400MW, and 1 utmost point 1 and 2 operating power of contravariant station are 150MW, and 2 utmost point 1 and 2 operating power of contravariant station are 250 MW. The inverter station 1, pole 1, is shut down with a single pole latch. Then it is determined that,

the remaining sound system (the system that utmost point 1 is become by rectifier station 3 and contravariant station 2, utmost point 2 is become by rectifier station 3, contravariant station 1 and contravariant station 2) continues to operate, because of the power of shutting loss is 150MW, and in order to guarantee rectifier station 3 utmost point 1's minimum power requirement (400MW), force the interstation power to change into 150MW, consequently the power is all changed into the utmost point 1 of contravariant station 2, then 3 utmost point 1 powers of rectifier station are 400MW, and utmost point 2 power is 400 MW. The power of the pole 1 of the inverter station is 0MW, and the power of the pole 2 of the inverter station is 150 MW. The power of the pole 1 of the inverter station 2 is 400MW, and the power of the pole 2 is 250 MW.

Example 17: the power boundary conditions of each station operation were the same as in example 12.

The pole 1 and the pole 2 both adopt a bipolar power control mode, the 3 poles of the rectifier station 1 and the 2 poles of the rectifier station are both 800MW, the 1 poles of the inverter station 1 and the 2 poles of the inverter station are both 300MW, and the 2 poles of the inverter station 2 and the 2 poles of the inverter station are both 500 MW. The inverter station 1, pole 1, is shut down with a single pole latch. Then it is determined that,

and the remaining sound system (the pole 1 is a system consisting of the rectifying station 3 and the inverter station 2, and the pole 2 is a system consisting of the rectifying station 3, the inverter station 1 and the inverter station 2) continues to operate, the pole 1 is switched into a single-pole current control mode, and the lost power is transferred to the pole 2 of the inverter station 1. The rectifier station 3 has a pole 1 power of 500MW and a pole 2 power of 1100 MW. The power of the 1 pole of the inverter station is 0MW, and the power of the 2 pole is 600 MW. The power of the pole 1 of the inverter station 2 is 500MW, and the power of the pole 2 is 500 MW.

Example 18: the maximum power of the inverter station 1, pole 2 is limited to 500MW for some reasons, and other boundary conditions are the same as those of the embodiment 12

The pole 1 and the pole 2 both adopt a bipolar power control mode, the 3 poles of the rectifier station 1 and the 2 poles of the rectifier station are both 800MW, the 1 poles of the inverter station 1 and the 2 poles of the inverter station are both 300MW, and the 2 poles of the inverter station 2 and the 2 poles of the inverter station are both 500 MW. The inverter station 1, pole 1, is shut down with a single pole latch. Then it is determined that,

the remaining sound system (the pole 1 is composed of a rectification station 3 and an inversion station 2, the pole 2 is composed of the rectification station 3, the inversion station 1 and the inversion station 2) continues to operate, the pole 1 is switched to a single-pole current control mode, the lost power (300MW) is preferentially transferred to the pole 2 of the inversion station 1, and the pole 2 of the inversion station 1 receives 200MW from the pole to reach the upper limit (500 MW). The excess (100MW) is transferred to the inversion station 2 and distributed according to the proportion of the direct current voltage of the two poles, namely, each pole is increased by 50 MW. The final rectifier station 3 has a pole 1 power of 550MW and a pole 2 power of 1050 MW. The power of the pole 1 of the inversion station is 0MW, and the power of the pole 2 is 500MW (reaching the upper limit). The power of the pole 1 of the inverter station 2 is 550MW, and the power of the pole 2 is 550 MW.

Example 19: the maximum power of the pole 2 of the inverter station 1 is limited to 500MW for some reasons, the maximum power of the pole 1 of the inverter station 2 is limited to 500MW for some reasons, and other boundary conditions are the same as those in the embodiment 12

The pole 1 and the pole 2 both adopt a bipolar power control mode, the 3 poles of the rectifier station 1 and the 2 poles of the rectifier station are both 800MW, the 1 poles of the inverter station 1 and the 2 poles of the inverter station are both 300MW, and the 2 poles of the inverter station 2 and the 2 poles of the inverter station are both 500 MW. The inverter station 1, pole 1, is shut down with a single pole latch. Then it is determined that,

the remaining sound system (the pole 1 is composed of a rectification station 3 and an inversion station 2, the pole 2 is composed of the rectification station 3, the inversion station 1 and the inversion station 2) continues to operate, the pole 1 is switched to a single-pole current control mode, the lost power (300MW) is preferentially transferred to the pole 2 of the inversion station 1, and the pole 2 of the inversion station 1 receives 200MW from the pole to reach the upper limit (500 MW). The excess (100MW) is transferred to the inverter station 2, and because the pole 1 of the inverter station 2 has reached the upper limit, all the excess is transferred to the pole 2 of the inverter station 2. The rectifier station 3 has a pole 1 power of 500MW and a pole 2 power of 1100 MW. The power of the pole 1 of the inversion station is 0MW, and the power of the pole 2 is 500MW (reaching the upper limit). The power of the pole 1 of the inverter station 2 is 500MW (reaching the upper limit), and the power of the pole 2 is 600 MW.

Example 20: the power boundary conditions of each station operation were the same as in example 12.

The pole 1 and the pole 2 both adopt a bipolar power control mode, the 3 poles of the rectifier station and the 1 poles of the rectifier station and the 2 poles of the rectifier station both have the operating power of 400MW, the 1 poles of the inverter station and the 2 poles of the inverter station both have the operating power of 150MW, and the 2 poles of the inverter station both have the operating power of 250 MW. The inverter station 1, pole 1, is shut down with a single pole latch. Then it is determined that,

the remaining sound system (the pole 1 is by rectification station 3 and inverter station 2, the pole 2 is by rectification station 3, the system that inverter station 1 and inverter station 2 constitute) continues the operation, the pole 1 switches into unipolar current control mode, because of the power of shutting down the loss is 150MW, and in order to guarantee the minimum power requirement (400MW) of rectification station 3 utmost point 1, force the power of station to change into 150MW, equal with the power of loss, therefore the power of loss is all changed into to the utmost point 1 of inverter station 2, the 3 utmost point 1 power of final rectification station is 400MW, utmost point 2 power is 400 MW. The power of the pole 1 of the inverter station is 0MW, and the power of the pole 2 of the inverter station is 150 MW. The power of the pole 1 of the inverter station 2 is 400MW, and the power of the pole 2 is 250 MW.

The above embodiments are only for illustrating the technical idea of the present invention, and the protection scope of the present invention is not limited thereby, and any modifications made on the basis of the technical scheme according to the technical idea of the present invention fall within the protection scope of the present invention.

Claims (12)

1. A power transfer method of a parallel three-terminal direct-current transmission system comprises three converter stations and is characterized in that under the working condition that the bipolar of the three stations are all operated, if a certain converter station is subjected to unipolar locking, the power transfer method calculates and resets power/current reference values of poles of the stations according to power levels, minimum and maximum transmission power capacities and a control mode of the poles of the three stations before locking, and realizes inter-pole transfer of power and/or inter-station transfer of power.

2. The power conversion method of the parallel three-terminal DC transmission system according to claim 1, wherein the three converter stations comprise two rectifying stations and one inverter station, or comprise one rectifying station and two inverter stations; two converter stations which are in rectification mode or inversion mode are called a first converter station and a second converter station, and the rest converter stations are called a third converter station; of the first converter station and the second converter station, the converter station in which unipolar blocking occurs is referred to as a first converter station, the converter station in which unipolar blocking does not occur is referred to as a second converter station, the pole in which unipolar blocking occurs is referred to as a first pole, and the pole in which unipolar blocking does not occur is referred to as a second pole.

3. The power conversion method of the parallel three-terminal direct-current transmission system according to claim 2, characterized in that: if the second pole is in the unipolar current control mode, after the first pole of the first converter station is subjected to unipolar blocking, the lost power is transferred to the first pole of the second converter station until the upper power limit of the first pole is reached; the second pole power of the first converter station, the second converter station and the third converter station are kept unchanged; if the second pole is in bipolar power control mode, the lost power is preferentially transferred to the second pole of the first converter station up to its upper power limit, and if the second pole of the first converter station reaches its upper limit, the insufficient power is continuously transferred to the second converter station.

4. A method for power transfer in a parallel three terminal dc transmission system according to claim 3, wherein if the first and second poles are both in a unipolar current control mode, when the first pole of the first converter station has unipolar blocking, the lost power is transferred to the first pole of the second converter station up to its upper power limit; the second pole powers of the first, second and third converter stations are kept constant.

5. A method according to claim 3, wherein if the first pole is in bipolar power control mode and the second pole is in unipolar power control mode, after unipolar blocking occurs at the first pole of the first converter station, the first pole is switched to unipolar power control mode, and the lost power is transferred to the first pole of the second converter station up to the upper power limit; the second pole powers of the first, second and third converter stations are kept constant.

6. A power transfer method for a parallel three terminal dc transmission system according to claim 3, wherein if the first pole is in unipolar current control mode and the second pole is in bipolar power control mode, after unipolar blocking of the first pole of the first converter station, the power of the first pole of the second converter station remains unchanged and the power of the first pole of the third converter station decreases to the same power level as the first pole of the second converter station; the lost power is preferentially transferred to the second pole of the first converter station up to its upper power limit, and if the second pole of the first converter station reaches its upper limit, the insufficient part is continuously transferred to the second pole of the second converter station up to its upper power limit.

7. A method for power transfer in a parallel three terminal dc transmission system according to claim 3, wherein if the first and second poles are both in bipolar power control mode, after unipolar blocking of the first pole of the first converter station, the first pole is switched to unipolar power control mode, the lost power is transferred preferentially to the second pole of the first converter station up to its upper power limit, and if the second pole of the first converter station reaches its upper limit, the insufficient power is transferred continuously to the second converter station.

8. The power transfer method of the parallel three-terminal dc transmission system according to claim 7, wherein if the second pole of the first converter station reaches its upper limit, the excess power is transferred to the second converter station, and specifically, the first and second pole power distribution of the second converter station are divided into four cases: let P_TransferFor transferring power from a first converter station to a second converter station, P_21maxIs the first maximum power limit, P, of the second converter station_22maxIs the second pole power upper limit, P 'of the second converter station'₂₁Power of the first pole of the second converter station, P 'before single-pole blocking'₂₂For the power of the second pole of the second converter station before unipolar blocking, U₁Is a DC voltage of a first pole, U₂A DC voltage of a second polarity; order to

Case 1) if P ″)₂₁＜P_21maxAnd P ″)₂₂＜P_22maxThe power is distributed according to the bipolar voltage proportion, and the first pole power of the second converter station is P ″)₂₁The power of the second pole is P₂₂″；

Case 2) if P ″)₂₁＜P_21max,P″₂₂＞P_22maxAnd P ″)₂₁+P″₂₂＜P_21max+P_22maxThe first pole power of the second converter station is P₂₁″+P₂₂″-P_22maxThe power of the second pole is P_22max；

Case 3) if P₂₁″＞P_21max,P″₂₂＜P_22maxAnd P ″)₂₁+P″₂₂＜P_21max+P_22maxThe first pole power of the second converter station is P_21maxThe power of the second pole is P₂₁+P″₂₂-P_21max；

Case 4) if P ″)₂₁+P″₂₂≥P_21max+P_22maxThe first pole power of the second converter station is P_21maxThe power of the second pole is P_22max。

9. The power transfer method of the parallel three-terminal dc transmission system according to any of claims 2, 3, and 6 to 8, wherein when the second pole is in the bipolar power control mode, if the minimum power of the non-locked stations is 0, the power lost by the locked pole is transferred between the stations preferentially, and the insufficient power is transferred between the stations; if the minimum power of the non-locked station is larger than 0, forced inter-station power transfer exists, and the power of forced inter-station transfer needs to be deducted when the inter-electrode transfer power is calculated.

10. The power generation method of the parallel three-terminal direct-current transmission system according to claim 9, wherein if the minimum power of the non-locking station is greater than 0, when P'₂₁+P′₂₂＜P_31min+P_22minOf which is P'₂₁Power, P 'of the first pole of the second converter station before being single-pole latched'₂₂Power, P, of the second pole of the second converter station before unipolar blocking_31minFor the first pole minimum power, P, of the third converter station_22minThe minimum power of the second pole of the second converter station exists, when the first pole of the first converter station is locked, the power between the stations is forced to transfer, and the power between the stations is forced to transfer is P_{Transfer_forced}＝P_31min+P_22min-P′₂₁+P′₂₂。

11. The power transfer method of the parallel three-terminal dc transmission system according to claim 10, wherein if the first pole is in the unipolar current control mode and the second pole is in the bipolar power control mode, after the unipolar shutdown of the first pole of the first converter station occurs, if the forced inter-station power transfer occurs, the lost power is transferred to the second pole of the first converter station after the power transferred between the forced inter-station is subtracted, which is divided into two cases:

1) if the second pole of the first converter station does not reach the upper power limit, the second pole power of the first converter station is P₁₂＝P′_3BP-(P_31min+P_22min) The first pole power of the second converter station is P_31minThe second pole power of the second converter station is P_22minOf which is P'_3BPIs the sum of the bipolar powers of the third converter station before the lock-out;

2) if the second pole of the first converter station reaches the upper power limit, the second pole power of the first converter station is P_12maxThe first pole power of the second converter station is P_31minThe second pole power of the second converter station is P₂₂＝min[P_22max,P′_3BP-P_12max-P_31min]In which P is_12maxFor the second power limit, P, of the first converter station_22maxIs the second power limit of the second converter station.

12. The power transfer method of the parallel three-terminal dc transmission system according to claim 10, wherein if the first pole and the second pole are both in the bipolar power control mode, after the first pole of the first converter station is locked by a single pole, if the power transfer between the forced stations occurs, the lost power is transferred to the second pole of the first converter station preferentially after the power transferred between the forced stations is subtracted, which is divided into two cases:

1) if the second pole of the first converter station does not reach the upper power limit, the second pole power of the first converter station is P₁₂＝P′_3BP-(P_31min+P_22min) The first pole power of the second converter station is P_31minThe second pole power of the second converter station is P_22minOf which is P'_3BPIs the sum of the bipolar powers of the third converter station before the lock-out;

2) if the second pole of the first converter station reaches the upper power limit, the second pole power of the first converter station is P_12maxPower P of the first pole of the second converter station₂₁＝max[P_31min,P_{21_cal}]，

The power of the second pole of the second converter station is P₂₂＝min[P_22max,P′_3BP-P_12max-P₂₁]；

Wherein P is_22maxFor the second power limit of the second converter station, P_12maxAn upper power limit of a second pole of the first converter station;

the P is_{21_cal}Calculating the power for the first pole of the second converter station comprises the following four cases:

P_Transferfor transferring power from a first converter station to a second converter station, P_21maxIs the first pole power upper limit, P 'of the second converter station'₂₁Power of the first pole of the second converter station, P 'before single-pole blocking'₂₂For the power of the second pole of the second converter station before unipolar blocking, U₁Is a DC voltage of a first pole, U₂Is a second pole of direct currentPressing; order to

Case 1) if P ″)₂₁＜P_21maxAnd P ″)₂₂＜P_22maxThen divided by the voltage proportion of the bipole, then P_{21_cal}＝P″₂₁；

Case 2) if P ″)₂₁＜P_21max,P″₂₂＞P_22maxAnd P ″)₂₁+P″₂₂＜P_21max+P_22maxThen P is_{21_cal}＝P₂₁″+P₂₂″-P_22max；

Case 3) if P₂₁″＞P_21max,P″₂₂＜P_22maxAnd P ″)₂₁+P″₂₂＜P_21max+P_22maxThen P is_{21_cal}＝P_21max；

Case 4) if P ″)₂₁+P″₂₂≥P_21max+P_22maxThen P is_{21_cal}＝P_21max。

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