Novel power system-oriented conventional direct current online power flow reversal reactive power optimization method

Abstract

The invention discloses a novel power system-oriented conventional direct-current online power flow reversal reactive power optimization method, which is applied to the technical field of direct-current power transmission. Comprising the following steps: determining the reactive power-voltage change strength before and after inversion based on reactive power-voltage change in an online power flow inversion process, reactive power curve change of reactive power balance of a current conversion bus and a state conversion diagram under total reactive power change of conventional direct current absorption, and limiting state voltage; the method comprises the following steps: determining the limitation of a state voltage under a general condition according to the magnitude relationship of the absolute values of voltage excursion of the total active power entering a power circulation mode in the first three stages of reactive-voltage change under different conditions, and limiting the total active power through the minimum frequency modulation capacity and the maximum voltage excursion; and determining the total active power entering the single-pole operation mode according to the total active power. According to the invention, reactive power-voltage stabilization in the online power flow process is effectively realized, and the problem of serious system voltage border crossing phenomenon caused by reactive power balance state transition is solved.

Description

Technical Field

[0001] The invention relates to the technical field of direct current transmission, and in particular to a conventional direct current online power flow reversal reactive power optimization method for a new type of power system. Background Art

[0002] In the context of new power systems, the proportion of uncertain and highly random new energy sources is increasing, a high proportion of power electronic equipment is widely connected, and system control needs to coordinate massive converters / distributed generation / controllable load clusters. The system stability characteristics will change from traditional electromechanical processes to the coupled coordination of electromechanical processes and switching control characteristics of power electronic equipment. Large-scale synchronous power grid control will face challenges such as complex stability mechanisms, randomized power flow distribution, and a surge in control objects.

[0003] The "asynchronous partitioning and flexible interconnection" of large power grids uses conventional direct current (line-commutated converter-based high-voltage direct current; LCC-HVDC) as the main carrier. Under the background of the new power system, higher requirements are placed on the bidirectional controllable power flow capability of conventional direct current: it can decouple the highly complex stability problems of large synchronous power grids by partition, reduce the impact range of stability problems, and improve the stability support capability; it can also flexibly control the bidirectional power flow to retain the scale advantage of large synchronous power grids; it can also form a cross-regional direct current interconnection network, relying on the supporting power supply and flexible system resources of each partition power grid, to further improve the resource optimization allocation capability and the safety and stability level of the system.

[0004] To this end, how to provide a conventional DC online power flow reversal reactive power optimization method for new power systems that can be based on the optimal power circulation mode, reasonably design the switching power levels of each mode, effectively achieve reactive power-voltage stability in the online power flow process, and solve the system voltage crossing phenomenon caused by the transfer of reactive balance state, which seriously damages the stable operation of the system, and maximize the guarantee of safe and stable operation of the system is an urgent problem that technicians in this field need to solve. Summary of the invention

[0005] In view of this, the present invention proposes a conventional DC online power flow reversal reactive power optimization method for a new power system.

[0006] In order to achieve the above object, the present invention adopts the following technical solution:

[0007] A conventional DC online power flow reversal reactive power optimization method for a new power system, comprising:

[0008] Step 1: Based on the reactive power-voltage change during the online power flow reversal process, the reactive power curve change of the commutation bus reactive balance, and the state transition diagram under the total reactive power change of conventional DC absorption, the strength of the reactive power-voltage change before and after the power flow reversal is determined, and the state voltage in the state transition diagram is limited; wherein, the reactive power-voltage change during the online power flow reversal process is divided into six stages;

[0009] Step 2: Based on the prerequisites, according to the absolute value relationship of the voltage offset in the first three stages of the reactive-voltage change during the online power flow reversal process under different conditions of the total active power entering the power circulation mode, determine the limit of the state voltage under general conditions, and limit the total active power by the minimum frequency regulation capacity and the maximum voltage offset, and determine the total active power entering the monopole operation mode based on the total active power.

[0010] Optionally, in step 1, an analysis is performed based on reactive power-voltage changes during the online power flow reversal process, specifically:

[0011] In the first stage, forward bipolar + unipolar operation: the total active power drops from the rated value to P2, the total reactive power decreases, and the AC voltage rises according to the reactive power balance principle of the commutation bus;

[0012] The second stage, unlocking pole 2: pole 2 is unlocked, the total active power remains unchanged, the total reactive power increases, and according to the reactive power balance principle of the commutation bus, the AC voltage drops;

[0013] The third stage is the forward power circulation mode: the total active power decreases from P2 to 0, the total reactive power decreases, and the AC voltage increases according to the reactive power balance principle of the commutation bus.

[0014] The fourth stage is the reverse power cycle mode: the total active power increases from 0 to P2, the total reactive power increases, and the AC voltage decreases according to the reactive power balance principle of the commutation bus.

[0015] The fifth stage, blocking pole 1: Pole 1 is blocked, the total active power remains unchanged, the total reactive power decreases, and the AC voltage rises according to the reactive power balance principle of the commutation bus;

[0016] The sixth stage, reverse bipolar + unipolar operation: the total active power increases from P2 to the rated value, the total reactive power increases, and according to the reactive power balance principle of the commutation bus, the AC voltage decreases.

[0017] Optionally, in step 1, the reactive power curve change of the commutation bus reactive power balance during the online power flow reversal process is analyzed, specifically:

[0018] Reactive power curve, including: incoming AC and DC reactive power exchange Q ac , the filter provides reactive power Q fcAnd the total reactive power Qd absorbed by conventional DC c ; Among them, point A is the rated operating state; the situation of reducing DC power is considered, including: operating state B and operating state C;

[0019] When the state changes to A→B, Q fc , Q ac Both increase, and the rate of change also increases, Q dc As the DC power decreases, the rate of change also decreases; in order to meet the reactive power balance of operating state B, Q ac Need to increase more to meet Q fc increases, and the AC voltage change Δv2 needs to be larger;

[0020] When the state changes to A→C, Q fc , Q ac Both decrease, and the rate of change also decreases, Q dc It decreases due to the decrease of DC power, but the rate of change increases, Q dc The reduction in Q can quickly match fc and Q ac The reduction in AC voltage Δv1 does not need to be very large to meet the reactive balance of operating state C;

[0021] Starting from the same voltage state, if the voltage changes in the direction of higher voltage, a larger voltage offset is required to meet the reactive balance. If the voltage changes in the direction of lower voltage, only a smaller voltage offset is required to meet the reactive balance. The first stage of the reactive-voltage change during the online power flow reversal process corresponds to A→B, and the fifth stage corresponds to C→A. The reactive and voltage changes in the fifth stage are weaker than those in the first stage, and the reactive and voltage changes in the fourth stage are weaker than those in the second stage.

[0022] Optionally, in step 1, the state transition diagram under the total reactive power change of conventional DC absorption during the online power flow reversal process is analyzed, specifically:

[0023] Including: rated operating state A, operating state B, operating state C, operating state D, operating state E, operating state F;

[0024] A->B corresponds to the first stage of reactive power-voltage change during the online power flow reversal process; B->C corresponds to the second stage of reactive power-voltage change during the online power flow reversal process; C->D corresponds to the third stage of reactive power-voltage change during the online power flow reversal process; D->E corresponds to the fourth stage of reactive power-voltage change during the online power flow reversal process; E->F corresponds to the fifth stage of reactive power-voltage change during the online power flow reversal process; F->A corresponds to the sixth stage of reactive power-voltage change during the online power flow reversal process.

[0025] Optionally, in step 1, the strength of reactive power-voltage change before and after the power flow reversal is determined, specifically: the reactive power-voltage change after the power flow reversal is weaker than that before the power flow reversal.

[0026] Optionally, in step 1, the state voltage in the state transition diagram is limited, specifically:

[0027] The voltage v of the operating state B and the operating state D B and v D The maximum value in satisfies the following:

[0028] max{v B ,V D}<1.05v 额 ;

[0029] Among them, v 额 is the rated AC voltage.

[0030] Optionally, in step 2, the prerequisites are:

[0031] Conventional DC minimum operating power P min Equal to 0.1 times the rated power 0.1PN;

[0032] The absolute value of the DC active power change |Δpdc| and the absolute value of the AC voltage change |Δvac| are positively correlated.

[0033] Optionally, in step 2, according to the absolute value relationship of the voltage offset in the first three stages of the reactive-voltage change in the online power flow reversal process of the total active power entering the power circulation mode under different conditions, the limitation of the state voltage under general conditions is determined, specifically:

[0034] Case 1: 0.1PN<P2<0.2PN; where PN is the rated power; P2 is the total active power entering the power cycle mode;

[0035] The absolute values ​​of voltage deviations in the first, second and third stages of reactive power-voltage changes during the online power flow reversal process satisfy |Δvac,1|>|Δvac,2|>|Δvac,3|. The maximum voltage deviation occurs in operating state B. The AC voltage in operating state B must be less than 1.05 times the rated value.

[0036] Case 2: 0.2PN<P2<0.5PN;

[0037] The absolute values ​​of voltage deviations in the first, second and third stages of reactive power-voltage changes during the online power flow reversal process satisfy |Δvac, 1|>|Δvac, 3|>|Δvac, 2|. The maximum voltage deviation occurs in the operating state D. It is required that the AC voltage in the operating state D is less than 1.05 times the rated value.

[0038] Case 3: 0.5PN <P2<0.8PN;

[0039] The absolute values ​​of voltage deviations in the first, second and third stages of reactive power-voltage changes during the online power flow reversal process satisfy |Δvac, 3|>|Δvac, 1|>|Δvac, 2|. The maximum voltage deviation occurs in the operating state D. It is required that the AC voltage in the operating state D is less than 1.05 times the rated value.

[0040] Case 4: 0.8PN <P2<PN;

[0041] The absolute values ​​of voltage deviations in the first, second and third stages of reactive power-voltage changes during the online power flow reversal process satisfy |Δvac, 3|>|Δvac, 2|>|Δvac, 1|. The maximum voltage deviation occurs in the operating state B. It is required that the AC voltage in the operating state B is less than 1.05 times the rated value.

[0042] Case 1 needs to verify the voltage of operating state B, and other cases need to verify the voltage of operating state D. Because the P2 value of case 1 does not have sufficient frequency regulation capacity, case 1 is not applicable to general situations. Under general circumstances, the voltage peak of operating state D appears at the power zero crossing point, and it is only necessary to verify that the AC voltage of operating state D is less than 1.05 times the rated value.

[0043] Optionally, in step 2, the total active power is limited by the minimum frequency modulation capacity and the maximum voltage deviation, specifically:

[0044] P2, min <P2<P2,max;

[0045] Among them, P2 is the total active power; P2,min is the minimum frequency modulation capacity; P2,max is the maximum voltage deviation.

[0046] Optionally, in step 2, the total active power for entering the unipolar operation mode is determined according to the total active power, specifically:

[0047] P1, min <P1<P1,max;

[0048] Among them, P1 is the total active power entering the unipolar operation mode; P1,min=P2+kP·tmp; P2 is the total active power entering the power cycle mode; kP is the power reduction rate; tmp is the total duration of unipolar operation; tmp=2tv+tr; tv is the DC blocking or unblocking time; tv is the line recovery time; P1,max takes the minimum frequency modulation capacity.

[0049] It can be seen from the above technical solutions that, compared with the prior art, the present invention proposes a conventional DC online power flow reversal reactive power optimization method for new power systems. A pole-to-pole coordination method under the optimal reactive power cycle operation mode is proposed, which realizes zero-switching reactive power-voltage stability while taking into account online power flow reversal; a multi-mode flexible continuous interaction method based on bipolar-monopolar-optimal reactive power cycle is proposed, forming an online power flow reversal system with adaptive reactive power regulation; the interaction mechanism between AC-DC reactive power changes and AC voltage is explored, and an online power reversal technology system that adapts to multiple operating conditions is established for complex system operating conditions and requirements. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying creative work.

[0051] Figure 1 It is a schematic diagram of the method flow of the present invention.

[0052] Figure 2 It is a schematic diagram of the bipolar operation mode during the conventional DC online power flow reversal process of the present invention.

[0053] Figure 3 It is a schematic diagram of the monopole operation mode during the conventional DC online power flow reversal process of the present invention.

[0054] Figure 4 It is a schematic diagram of the power circulation mode during the conventional DC online power flow reversal process of the present invention.

[0055] Figure 5 It is a schematic diagram of the implementation scheme of each stage of the specific process of conventional DC online power flow reversal of the present invention.

[0056] Figure 6 It is a schematic diagram of reactive power-voltage changes during the online power flow reversal process of the present invention.

[0057] Figure 7 It is a schematic diagram of reactive power balance of the commutation busbar of the present invention.

[0058] Figure 8 It is a schematic diagram of the changes of each reactive power curve of the present invention.

[0059] Fig. 9 It is a schematic diagram of state transition under the change of total reactive power of conventional DC absorption of the present invention.

[0060] Fig.10 It is a schematic diagram comparing the power cycle operation of the reactive power optimization method of the present invention and the existing minimum line loss mode. DETAILED DESCRIPTION

[0061] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0062] Embodiment 1:

[0063] Embodiment 1 of the present invention discloses a conventional DC online power flow reversal reactive power optimization method for a new power system, such as Figure 1 As shown, including:

[0064] Step 1: Based on the reactive power-voltage changes during the online power flow reversal process, the reactive power curve changes of the commutation bus reactive balance, and the state transition diagram under the total reactive power changes of conventional DC absorption, the strength of the reactive power-voltage changes before and after the power flow reversal is determined, and the state voltage in the state transition diagram is limited; among them, the reactive power-voltage changes during the online power flow reversal process are divided into six stages.

[0065] Conventional DC online power flow reversal methods involve switching between different operating modes of the DC system. During the entire power flow reversal process, there are three operating modes:

[0066] Bipolar operation mode, such as Figure 2 As shown: In this operating mode, both poles of the DC system work normally, and the power transmitted by the two poles is always in the same direction and equal in magnitude.

[0067] Unipolar operation mode, such as Figure 3 As shown: In this operating mode, only one pole of the DC system works normally, the other pole is in a DC blocking state, and the transmission power is zero.

[0068] Power cycling mode, such as Figure 4As shown: In this type of operation mode, both poles of the DC system work normally, and the power transmitted by the two poles is always in opposite directions, one pole transmits constant power, and the other pole transmits variable, reverse power.

[0069] The specific process of conventional DC online power flow reversal with mode switching characteristics is as follows:

[0070] When transmitting higher powers, the DC system operates in bipolar operation mode.

[0071] When transmitting medium powers, the DC system operates in unipolar operation mode.

[0072] When transmitting low power, the DC system operates in power cycling mode.

[0073] The implementation scheme of each stage of the specific process of conventional DC online power flow reversal, such as Figure 5 As shown, specifically:

[0074] Phase 1: In this phase, the DC system operates in bipolar mode, and the two poles transmit equal power in the positive direction. In this phase, the rectifier side of the two poles is used to control the power, and the inverter side is used to control the voltage. Each pole only needs to reduce the power command value to complete the reduction of the transmission power. The minimum value of the total transmission power in this phase is P1. When the total power reaches P1, it enters Phase 2.

[0075] Phase 2: In this phase, the DC system operates in unipolar mode, with pole 1 bearing all the transmission power, pole 2 in DC blocking, and the transmission power is zero. The minimum value of the total transmission power in this phase is P2, and when the total power reaches P2, it enters phase 3.

[0076] Phase 3: In this phase, the DC system operates in a circulating power mode. In this phase, the total transmission power ranges from -P2 to P2, where the negative sign represents the reverse direction of the power. In this operating mode, the total transmission power needs to undergo a change in direction. During the time when the total power drops from P2 to 0, pole 2 bears a constant reverse power, and only the power transmitted by pole 1 decreases in the positive direction. During the time when the total power rises from 0 to P2 in the reverse direction, pole 1 bears a constant forward power, and only the power transmitted by pole 2 increases in the reverse direction. When the total power reaches P2 in the reverse direction, it enters phase 4.

[0077] Phase 4: In this phase, the DC system operates in unipolar mode, with pole 2 bearing all the transmission power and increasing in the reverse direction, and pole 1 in DC blocking with zero transmission power. The maximum value of the total transmission power in this phase is P1, and when the total power reaches P1 in the reverse direction, phase 5 is entered.

[0078] Phase 5: In this phase, the DC system operates in bipolar mode, and both poles transmit power of equal magnitude and opposite direction. Under the power control of the rectifier side, the total transmission power in this phase can eventually reach the rated power, and the entire power flow reversal process is completed.

[0079] Analysis is performed based on the reactive power-voltage changes during the online power flow reversal process, such as Figure 6 As shown, specifically:

[0080] The first stage, forward bipolar + unipolar operation (t1-t3): the total active power drops from the rated value to P2, the total reactive power decreases, and the AC voltage rises according to the reactive power balance principle of the commutation bus;

[0081] The second stage, unlocking pole 2 (t3): pole 2 is unlocked, the total active power remains unchanged, the total reactive power increases, and according to the reactive power balance principle of the commutation bus, the AC voltage decreases;

[0082] The third stage, forward power circulation mode (t3-t4): the total active power decreases from P2 to 0, the total reactive power decreases, and the AC voltage increases according to the reactive power balance principle of the commutation bus.

[0083] The fourth stage, reverse power circulation mode (t4-t5): the total active power increases from 0 to P2, the total reactive power increases, and the AC voltage decreases according to the reactive power balance principle of the commutation bus;

[0084] The fifth stage, blocking pole 1 (t5): pole 1 is blocked, the total active power remains unchanged, the total reactive power decreases, and the AC voltage rises according to the reactive power balance principle of the commutation bus;

[0085] The sixth stage, reverse bipolar + unipolar operation (t5-t7): the total active power increases from P2 to the rated value, the total reactive power increases, and according to the reactive power balance principle of the commutation bus, the AC voltage decreases.

[0086] The process of locking pole 2 (t2) and releasing pole 1 (t6) can be ignored for the following reasons:

[0087] When pole 2 is locked, the power of pole 1 increases, the absorbed reactive power increases, the power of pole 2 decreases, the absorbed reactive power decreases, the net power change and net absorbed reactive power of the entire DC system are both 0, and locking pole 2 only takes tens of milliseconds, which is an extremely short time. Therefore, the locked pole 2 stage can be ignored, and the forward bipolar + unipolar operation can be regarded as a continuous process.

[0088] When pole 1 is unlocked, the power of pole 1 increases, the absorbed reactive power increases, the power of pole 2 decreases, the absorbed reactive power decreases, the net power change and net absorbed reactive power of the entire DC system are both 0, and unlocking pole 1 only takes tens of milliseconds, which is an extremely short time. Therefore, the unlocking pole 1 stage can be ignored, and the reverse bipolar + unipolar operation can be regarded as a continuous process.

[0089] The reactive power curve change of the commutation bus reactive power balance during the online power flow reversal process is analyzed as follows:

[0090] The reactive power balance of the commutation busbar is as follows: Figure 7 As shown; each reactive power curve changes, such as Figure 8 shown.

[0091] Reactive power curve, including: incoming AC and DC reactive power exchange Q ac , the filter provides reactive power Q fc And the total reactive power Qd absorbed by conventional DC c ; Among them, point A is the rated operating state; the situation of reducing DC power is considered, including: operating state B and operating state C;

[0092] When the state changes to A→B, Q fc , Q alc Both increase, and the rate of change also increases, Q dc As the DC power decreases, the rate of change also decreases; in order to meet the reactive power balance of operating state B, Q ac Need to increase more to meet Q fc increases, and the AC voltage change Δv2 needs to be larger;

[0093] When the state changes to A→C, Q fc , Q ac Both decrease, and the rate of change also decreases, Q dc It decreases due to the decrease of DC power, but the rate of change increases, Q dc The reduction in Q can quickly match fc and Q ac The reduction in AC voltage Δv1 does not need to be very large to meet the reactive balance of operating state C;

[0094] Starting from the same voltage state, if the voltage changes in the direction of higher voltage, a larger voltage offset is required to meet the reactive balance. If the voltage changes in the direction of lower voltage, only a smaller voltage offset is required to meet the reactive balance. The first stage of the reactive-voltage change during the online power flow reversal process corresponds to A→B, and the fifth stage corresponds to C→A. The reactive and voltage changes in the fifth stage are weaker than those in the first stage, and the reactive and voltage changes in the fourth stage are weaker than those in the second stage.

[0095] Total reactive power Qd based on conventional DC absorption during online power flow reversalc The state transition diagram under changes is analyzed, such as Fig. 9 As shown, specifically:

[0096] Including: rated operating state A, operating state B, operating state C, operating state D, operating state E, operating state F;

[0097] A->B corresponds to the first stage of reactive power-voltage change during the online power flow reversal process; B->C corresponds to the second stage of reactive power-voltage change during the online power flow reversal process; C->D corresponds to the third stage of reactive power-voltage change during the online power flow reversal process; D->E corresponds to the fourth stage of reactive power-voltage change during the online power flow reversal process; E->F corresponds to the fifth stage of reactive power-voltage change during the online power flow reversal process; F->A corresponds to the sixth stage of reactive power-voltage change during the online power flow reversal process.

[0098] Determine the strength of reactive power-voltage changes before and after the power flow reversal. Specifically, the reactive power-voltage change after the power flow reversal is weaker than that before the power flow reversal.

[0099] The state voltage in the state transition diagram is limited as follows:

[0100] The voltage v of the operating state B and the operating state D B and v D The maximum value in satisfies the following:

[0101] max{v B ,v D}<1.05v 额 ;

[0102] Among them, v 额 is the rated AC voltage.

[0103] Step 2: Based on the prerequisites, according to the absolute value relationship of the voltage offset in the first three stages of the reactive-voltage change during the online power flow reversal process under different conditions of the total active power entering the power circulation mode, determine the limit of the state voltage under general conditions, and limit the total active power by the minimum frequency regulation capacity and the maximum voltage offset, and determine the total active power entering the monopole operation mode based on the total active power.

[0104] Prerequisites, specifically:

[0105] Conventional DC minimum operating power P min Equal to 0.1 times the rated power 0.1PN;

[0106] The absolute value of the DC active power change |Δpdc| and the absolute value of the AC voltage change |Δvac| are positively correlated.

[0107] According to the absolute value relationship of the voltage offset in the first three stages of the reactive-voltage change in the online power flow reversal process of the total active power entering the power circulation mode under different conditions, the limitation of the state voltage under general conditions is determined, specifically:

[0108] Case 1: 0.1PN<P2<0.2PN; where PN is the rated power; P2 is the total active power entering the power cycle mode;

[0109] The absolute values ​​of voltage deviations in the first, second and third stages of reactive power-voltage changes during the online power flow reversal process satisfy |Δvac,1|>|Δvac,2|>|Δvac,3|. The maximum voltage deviation occurs in operating state B. The AC voltage in operating state B must be less than 1.05 times the rated value.

[0110] Case 2: 0.2PN<P2<0.5PN;

[0111] The absolute values ​​of voltage deviations in the first, second and third stages of reactive power-voltage changes during the online power flow reversal process satisfy |Δvac, 1|>|Δvac, 3|>|Δvac, 2|. The maximum voltage deviation occurs in the operating state D. It is required that the AC voltage in the operating state D is less than 1.05 times the rated value.

[0112] Case 3: 0.5PN <P2<0.8PN;

[0113] The absolute values ​​of voltage deviations in the first, second and third stages of reactive power-voltage changes during the online power flow reversal process satisfy |Δvac, 3|>|Δvac, 1|>|Δvac, 2|. The maximum voltage deviation occurs in the operating state D. It is required that the AC voltage in the operating state D is less than 1.05 times the rated value.

[0114] Case 4: 0.8PN <P2<PN;

[0115] The absolute values ​​of voltage deviations in the first, second and third stages of reactive power-voltage changes during the online power flow reversal process satisfy |Δvac, 3|>|Δvac, 2|>|Δvac, 1|. The maximum voltage deviation occurs in the operating state B. It is required that the AC voltage in the operating state B is less than 1.05 times the rated value.

[0116] Case 1 needs to verify the voltage of operating state B, and other cases need to verify the voltage of operating state D. Because the P2 value of case 1 does not have sufficient frequency regulation capacity, case 1 is not applicable to general situations. Under general circumstances, the voltage peak of operating state D appears at the power zero crossing point, and it is only necessary to verify that the AC voltage of operating state D is less than 1.05 times the rated value.

[0117] The total active power is limited by the minimum frequency regulation capacity and the maximum voltage deviation, specifically:

[0118] P2, min <P2<P2,max;

[0119] Among them, P2 is the total active power; P2,min is the minimum frequency modulation capacity; P2,max is the maximum voltage deviation.

[0120] The total active power to enter the unipolar operation mode is determined according to the total active power, specifically:

[0121] P1, min <P1<P1,max;

[0122] Among them, P1 is the total active power entering the unipolar operation mode; P1,min=P2+kP·tmp; P2 is the total active power entering the power cycle mode; kP is the power reduction rate; tmp is the total duration of unipolar operation; tmp=2tv+tr; tv is the DC blocking or unlocking time, generally 200ms; tv is the line recovery time, which is related to the line type, 200ms for overhead lines and 2min for cable lines; P1,max takes the minimum frequency modulation capacity. At this time, PN-P1,max is the minimum frequency modulation capacity (such as FLC, etc.) during bipolar operation.

[0123] Embodiment 2:

[0124] Embodiment 2 of the present invention discloses a comparison of power cycle operation using a conventional DC online power flow reversal reactive power optimization method for a new power system and an existing minimum line loss mode, such as Fig.10 As shown, specifically:

[0125] The solid line part is the minimum line loss mode, in which case the line loss is the smallest. The dotted line part is the reactive power optimization operation mode, in which case the reactive power absorbed by the DC system will be reduced.

[0126] Because P q >P min Therefore, the active power changes are smaller under the optimized reactive power operation mode, and the reactive power-voltage changes are smaller. The blue area in the figure is the power cycle operation stage. It can be found that in the minimum line loss mode (loss-opt), the AC / DC exchange reactive power Q ac There will be a "spike", which will cause the AC voltage to also have a "spike". In the reactive power optimization operation mode (Q-opt) Q ac The peak value of the power is reduced, so the peak value of the voltage is also reduced. In summary, the purpose of Q-opt is to prevent the voltage from crossing the limit at the power zero point.

[0127] The embodiment of the present invention discloses a conventional DC online power flow reversal reactive power optimization method for a new power system. A pole coordination method under the optimal reactive power cycle operation mode is proposed, and zero-cut reactive power-voltage stability is achieved while taking into account online power flow reversal; a multi-mode flexible continuous interaction method based on bipolar-monopolar-optimal reactive power cycle is proposed, forming an online power flow reversal system with adaptive reactive power regulation; the interaction mechanism between AC-DC reactive power changes and AC voltage is explored, and an online power reversal technology system that adapts to multiple operating conditions is established for complex system operating conditions and requirements.

[0128] In this specification, each embodiment is described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the embodiments can be referred to each other. For the device disclosed in the embodiment, since it corresponds to the method disclosed in the embodiment, the description is relatively simple, and the relevant parts can be referred to the method part.

[0129] The above description of the disclosed embodiments enables one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A conventional DC online power flow reversal reactive power optimization method for a new power system, characterized in that: include: Step 1: Analyze the reactive-voltage change during the online power flow reversal process, the reactive curve change of the commutation bus reactive balance, and the state transition diagram under the total reactive change of conventional DC absorption, determine the strength of the reactive-voltage change before and after the power flow reversal, and limit the state voltage in the state transition diagram; wherein the reactive-voltage change during the online power flow reversal process is divided into six stages; Step 2: Based on the prerequisites, according to the absolute value relationship of the voltage offset in the first three stages of the reactive-voltage change in the online power flow reversal process under different conditions of the total active power entering the power circulation mode, determine the limit of the state voltage under general conditions, and limit the total active power by the minimum frequency regulation capacity and the maximum voltage offset, and determine the total active power entering the monopole operation mode based on the total active power.

2. A conventional DC online power flow reversal reactive power optimization method for a new power system according to claim 1, characterized in that: In step 1, the reactive power-voltage change during the online power flow reversal process is analyzed as follows: In the first stage, forward bipolar + unipolar operation: the total active power drops from the rated value to P2, the total reactive power decreases, and the AC voltage rises according to the reactive power balance principle of the commutation bus; The second stage, unlocking pole 2: pole 2 is unlocked, the total active power remains unchanged, the total reactive power increases, and according to the reactive power balance principle of the commutation bus, the AC voltage drops; The third stage is the forward power circulation mode: the total active power decreases from P2 to 0, the total reactive power decreases, and the AC voltage increases according to the reactive power balance principle of the commutation bus. The fourth stage is the reverse power cycle mode: the total active power increases from 0 to P2, the total reactive power increases, and the AC voltage decreases according to the reactive power balance principle of the commutation bus. The fifth stage, blocking pole 1: Pole 1 is blocked, the total active power remains unchanged, the total reactive power decreases, and the AC voltage rises according to the reactive power balance principle of the commutation bus; The sixth stage, reverse bipolar + unipolar operation: the total active power increases from P2 to the rated value, the total reactive power increases, and according to the reactive power balance principle of the commutation bus, the AC voltage decreases.

3. A conventional DC online power flow reversal reactive power optimization method for a new power system according to claim 1, characterized in that: In step 1, the reactive power curve change of the commutation bus reactive power balance during the online power flow reversal process is analyzed, specifically: The reactive power curve includes: incoming AC and DC reactive power exchange Q ac , the filter provides reactive power Q fc And the total reactive power Q absorbed by conventional DC dc ; Among them, point A is the rated operating state; the situation of reducing DC power is considered, including: operating state B and operating state C; When the state changes to A→B, Q fc , Q ac Both increase, and the rate of change also increases, Q dc As the DC power decreases, the rate of change also decreases; in order to meet the reactive power balance of operating state B, Q ac Need to increase more to meet Q fc increases, and the AC voltage change Δv2 needs to be larger; When the state changes to A→C, Q fc , Q ac Both decrease, and the rate of change also decreases, Q dc It decreases due to the decrease of DC power, but the rate of change increases, Q dc The reduction in Q can quickly match fc and Q ac The reduction in AC voltage Δv1 does not need to be very large to meet the reactive balance of operating state C; Starting from the same voltage state, if the voltage changes in the direction of a higher voltage, a larger voltage offset is required to meet the reactive balance. If the voltage changes in the direction of a lower voltage, only a smaller voltage offset is required to meet the reactive balance. The first stage of the reactive-voltage change in the online power flow reversal process corresponds to A→B, and the fifth stage corresponds to C→A. The reactive and voltage changes in the fifth stage are weaker than those in the first stage, and the reactive and voltage changes in the fourth stage are weaker than those in the second stage.

4. A conventional DC online power flow reversal reactive power optimization method for a new power system according to claim 1, characterized in that: In step 1, the state transition diagram under the total reactive power change of conventional DC absorption during the online power flow reversal process is analyzed, specifically: Including: rated operating state A, operating state B, operating state C, operating state D, operating state E, operating state F; A->B corresponds to the first stage of reactive-voltage changes during the online power flow reversal process; B->C corresponds to the second stage of reactive-voltage changes during the online power flow reversal process; C->D corresponds to the third stage of reactive-voltage changes during the online power flow reversal process; D->E corresponds to the fourth stage of reactive-voltage changes during the online power flow reversal process; E->F corresponds to the fifth stage of reactive-voltage changes during the online power flow reversal process; F->A corresponds to the sixth stage of reactive-voltage changes during the online power flow reversal process.

5. A conventional DC online power flow reversal reactive power optimization method for a new power system according to claim 1, characterized in that: In step 1, the strength of reactive power-voltage change before and after the power flow reversal is determined, specifically: the reactive power-voltage change after the power flow reversal is weaker than that before the power flow reversal.

6. A conventional DC online power flow reversal reactive power optimization method for a new power system according to claim 4, characterized in that: In step 1, the state voltage in the state transition diagram is limited, specifically: The voltage v of the operating state B and the operating state D is B and v D The maximum value in satisfies the following: max{v B ,v D }<1.05v 额 ; Among them, v 额 is the rated AC voltage.

7. A conventional DC online power flow reversal reactive power optimization method for a new power system according to claim 1, characterized in that: In step 2, the prerequisites are specifically: Conventional DC minimum operating power P min Equal to 0.1 times the rated power 0.1PN; The absolute value of the DC active power change |Δpdc| and the absolute value of the AC voltage change |Δvac| are positively correlated.

8. A conventional DC online power flow reversal reactive power optimization method for a new power system according to claim 4, characterized in that: In step 2, according to the absolute value relationship of the voltage offset in the first three stages of the reactive-voltage change in the online power flow reversal process under different conditions of the total active power entering the power circulation mode, the limitation of the state voltage under general conditions is determined, specifically: Case 1: 0.1PN<P2<0.2PN; where PN is the rated power; P2 is the total active power entering the power cycle mode; The absolute values ​​of the voltage offsets in the first, second and third stages of the reactive-voltage change during the online power flow reversal process satisfy |Δvac,1|>|Δvac,2|>|Δvac,3|, and the maximum voltage offset occurs in the operating state B, which needs to satisfy that the AC voltage in the operating state B is less than 1.05 times the rated value; Case 2: 0.2PN<P2<0.5PN; The absolute values ​​of the voltage offsets in the first, second and third stages of the reactive-voltage change during the online power flow reversal process satisfy |Δvac,1|>|Δvac,3|>|Δvac,2|, and the maximum voltage offset occurs in the operating state D, which needs to satisfy that the AC voltage in the operating state D is less than 1.05 times the rated value; Case 3: 0.5PN<P2<0.8PN; The absolute values ​​of the voltage offsets in the first, second and third stages of the reactive-voltage change during the online power flow reversal process satisfy |Δvac,3|>|Δvac,1|>|Δvac,2|, and the maximum voltage offset occurs in the operating state D, which needs to satisfy that the AC voltage in the operating state D is less than 1.05 times the rated value; Case 4: 0.8PN<P2<PN; The absolute values ​​of the voltage offsets in the first, second and third stages of the reactive-voltage change during the online power flow reversal process satisfy |Δvac,3|>|Δvac,2|>|Δvac,1|, and the maximum voltage offset occurs in the operating state B, which needs to satisfy that the AC voltage in the operating state B is less than 1.05 times the rated value; Case 1 needs to verify the voltage of operating state B, and other cases need to verify the voltage of operating state D. Because the P2 value of case 1 does not have sufficient frequency regulation capacity, case 1 is not applicable to general situations. Under general circumstances, the voltage peak of operating state D appears at the power zero crossing point, and it is only necessary to verify that the AC voltage of operating state D is less than 1.05 times the rated value.

9. A conventional DC online power flow reversal reactive power optimization method for a new power system according to claim 1, characterized in that: In step 2, the total active power is limited by the minimum frequency modulation capacity and the maximum voltage deviation, specifically: P2,min <P2<P2,max; Among them, P2 is the total active power; P2,min is the minimum frequency modulation capacity; P2,max is the maximum voltage deviation.

10. A conventional DC online power flow reversal reactive power optimization method for a new power system according to claim 1, characterized in that: In step 2, the total active power for entering the unipolar operation mode is determined according to the total active power, specifically: P1,min <P1<P1,max; Among them, P1 is the total active power entering the unipolar operation mode; P1,min=P2+kP·tmp; P2 is the total active power entering the power cycle mode; kP is the power reduction rate; tmp is the total duration of unipolar operation; tmp=2tv+tr; tv is the DC blocking or unblocking time; tv is the line recovery time; P1,max takes the minimum frequency modulation capacity.

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