A conventional direct current online power flow inversion reactive power optimization method for a new power system

Abstract

The application discloses a conventional DC online power flow inversion reactive power optimization method for a new power system, and is applied to the technical field of DC power transmission and comprises the following steps: based on the state transition diagram under the reactive power-voltage variation, the reactive power curve variation of the reactive power balance of the converter bus and the total reactive power variation of the conventional DC absorption in the online power flow inversion process, the reactive power-voltage variation before and after inversion is determined, and the state voltage is limited; according to the voltage offset absolute value size relationship of the reactive power-voltage variation in the first three stages under different conditions of the total active power entering the power cycle mode, the limitation of the state voltage under general conditions is determined, the total active power is limited through the minimum frequency modulation capacity and the maximum voltage offset, and the total active power entering the monopole operation mode is determined according to the total active power. The application effectively realizes the reactive power-voltage stability of the online power flow process, and solves the problem that the system voltage out-of-limit phenomenon caused by the reactive power balance state transition is serious.

Description

Technical Field

[0001] The present invention relates to the technical field of direct current (DC) transmission, and in particular to a conventional DC online power flow reversal reactive power optimization method for a new 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 shift from traditional electromechanical processes to the coupled coordination of electromechanical processes and power electronic equipment switching control characteristics. Large-scale synchronous power grid control will face challenges such as complex stability mechanisms, randomized power flow distribution, and a surge in controlled objects.

[0003] The "asynchronous partitioning and flexible interconnection" of large power grids uses conventional direct current (DC) (line-commutated converter-based high-voltage direct current; LCC-HVDC) as the primary carrier. In the context of new power systems, higher requirements are placed on the bidirectional controllable power flow capabilities of conventional DC. These capabilities can decouple the highly complex stability issues of large synchronous power grids from different regions, reducing the impact of these issues and improving stability support capabilities. Furthermore, they can maintain the scale advantages of large synchronous power grids through flexible bidirectional power flow control. Furthermore, they can form a cross-regional DC interconnection network, leveraging the supporting power sources and flexible system resources of each regional power grid to further improve resource optimization and system security and stability.

[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 optimized 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 reactive balance state transfer that seriously damages the stable operation of the system, and maximize the guarantee of the 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 type of power system.

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

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

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

[0009] Step 2: Based on the premise, according to the voltage offset absolute value size relationship 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 cycle mode, the state voltage is determined in the general case, and the total active power is limited by the minimum frequency modulation capacity and the maximum voltage offset, and the total active power entering the monopolar operation mode is determined according to the total active power.

[0010] Optionally, in step 1, based on the reactive-voltage change in the online power flow reversal process, the analysis is as follows:

[0011] First stage, positive bipolar + monopolar operation: the total active power decreases from the rated value to P2, the total reactive power decreases, and according to the commutation bus reactive power balance principle, the AC voltage rises;

[0012] Second stage, unlock pole 2: pole 2 is unlocked, the total active power remains unchanged, the total reactive power increases, and according to the commutation bus reactive power balance principle, the AC voltage decreases;

[0013] Third stage, positive power cycle mode: the total active power decreases from P2 to 0, the total reactive power decreases, and according to the commutation bus reactive power balance principle, the AC voltage rises;

[0014] Fourth stage, reverse power cycle mode: the total active power rises from 0 to P2, the total reactive power increases, and according to the commutation bus reactive power balance principle, the AC voltage decreases;

[0015] Fifth stage, lock pole 1: pole 1 is locked, the total active power remains unchanged, the total reactive power decreases, and according to the commutation bus reactive power balance principle, the AC voltage rises;

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

[0017] Optionally, in step 1, based on the reactive-voltage change in the online power flow reversal process, the analysis is as follows:

[0018] The reactive power curve includes: the incoming AC / 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; considering the situation of reducing DC power, including: operating state B and operating state C;

[0019] When the state transitions 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 balance of operating state B, Q ac Need to increase more to meet Q fc The increase of Δv2 and the AC voltage change need to be larger;

[0020] When the state transitions 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 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 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, an analysis is performed based on a state transition diagram of total reactive power changes of conventional DC absorption during the online power flow reversal process, 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; B->C corresponds to the second stage of reactive power-voltage change during the online power flow reversal; C->D corresponds to the third stage of reactive power-voltage change during the online power flow reversal; D->E corresponds to the fourth stage of reactive power-voltage change during the online power flow reversal; E->F corresponds to the fifth stage of reactive power-voltage change during the online power flow reversal; F->A corresponds to the sixth stage of reactive power-voltage change during the online power flow reversal.

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

[0028] max{v B ,V D}<1.05v 额 ;

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

[0030] Optionally, in step 2, the precondition is specifically:

[0031] The minimum operating power P min of the conventional DC is 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 size relationship of the voltage offset in the first three stages of the reactive power-voltage change in the online power flow reversal process under different conditions of the total active power entering the power cycle mode, the state voltage is limited in the general case, specifically:

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

[0035] The absolute values of the voltage offset in the first stage, the second stage, and the third stage of the reactive power-voltage change in 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 under the operating state B is less than 1.05 times the rated value;

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

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

[0038] Case three: 0.5PN

[0039] The absolute values of voltage deviation of the first stage, the second stage and the third stage of reactive power-voltage change in the online power flow reversal process satisfy |Δvac,3|>|Δvac,2|>|Δvac,1|, the maximum voltage deviation occurs in the operating state B, and it is required that the AC voltage in the operating state B is less than 1.05 times the rated value;

[0040] Case four: 0.8PN

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

[0042] Case one needs to check the voltage of the operating state B, and the voltage of the operating state D needs to be checked in other cases. Since the P2 value of case one does not have sufficient frequency modulation capacity, it is concluded that case one is not suitable for general cases. In general cases, the voltage peak of the operating state D occurs at the power zero point, and only the AC voltage of the operating state D needs to be checked to be 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

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

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

[0047] P1, min

[0048] Wherein, P1 is the total active power entering the single-pole 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 single-pole 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] Through the technical solution, compared with the prior art, the application provides a conventional DC online power flow reversal reactive power optimization method for a new power system. An inter-pole coordinated method under an optimal reactive power cycle operation mode is proposed, realizing zero-switching reactive-voltage stability considering online power flow reversal; a multi-mode flexible continuous interaction method based on bipolar-single-pole-optimal reactive power cycle is proposed, forming an online power flow reversal system with adaptive reactive power regulation; the interaction mechanism of AC-DC reactive power change and AC voltage is explored, and an online power reversal technology system suitable for multiple operation conditions is established according to complex system operation conditions and requirements. BRIEF DESCRIPTION OF DRAWINGS

[0050] In order to more clearly illustrate the technical solutions in the embodiments of the application or the prior art, the drawings needed in the embodiments or the prior art description will be briefly introduced below. Obviously, the drawings in the following description are only embodiments of the application, and those skilled in the art can obtain other drawings according to the provided drawings without creative labor.

[0051] Figure 1 The method flowchart of the application.

[0052] Figure 2 The bipolar operation mode schematic diagram in the conventional DC online power flow reversal process of the application.

[0053] Figure 3 The single-pole operation mode schematic diagram in the conventional DC online power flow reversal process of the application.

[0054] Figure 4 The power cycle mode schematic diagram in the conventional DC online power flow reversal process of the application.

[0055] Figure 5 The realization scheme schematic diagram of each stage of the conventional DC online power flow reversal specific process of the application.

[0056] Figure 6 The reactive-voltage change schematic diagram in the online power flow reversal process of the application.

[0057] Figure 7 The converter bus reactive power balance schematic diagram of the application.

[0058] Figure 8 Fig. 1 is a schematic diagram of the reactive power curve variation of the present application.

[0059] Figure 9 Fig. 2 is a schematic diagram of the state transition under the total reactive power variation of the conventional DC absorption of the present application.

[0060] Figure 10 Fig. 3 is a schematic diagram of the comparison between the reactive power optimization method of the present application and the power cycle operation of the existing minimum line loss mode. DETAILED DESCRIPTION

[0061] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the protection scope of the present application.

[0062] Embodiment 1

[0063] Embodiment 1 of the present application discloses a conventional DC online power flow inversion reactive power optimization method for a new power system, as shown in Fig. 1, which comprises the following steps. Figure 1

[0064] Step 1: Based on the reactive power-voltage variation in the online power flow inversion process, the reactive power curve variation of the reactive power balance of the converter bus and the state transition diagram under the total reactive power variation of the conventional DC absorption, the reactive power-voltage variation before and after the power flow inversion is determined, and the state voltage in the state transition diagram is limited; wherein the reactive power-voltage variation in the online power flow inversion process is divided into six stages.

[0065] The conventional DC online power flow inversion method involves the switching of different operation modes of the DC system. During the entire power flow inversion process, there are the following three operation modes in total:

[0066] The bipolar operation mode, as shown in Fig. 2: in this operation mode, both poles of the DC system work normally, and the power transmission directions of the two poles are always the same, and the sizes are equal. Figure 2 The monopole operation mode, as shown in Fig. 3: in this operation mode, only one pole of the DC system works normally, and the other pole is in the DC blocking state, and the transmission power is zero.

[0067] Figure 3 The power cycle mode, as shown in Fig. 4: in this operation mode, the power transmission direction of the DC system is opposite to the power transmission direction of the AC system.

[0068] The power cycle mode, as shown in Fig. 4: in this operation mode, the power transmission direction of the DC system is opposite to the power transmission direction of the AC system. Figure 4 ​​As shown: in this mode of operation, both poles of the DC system are working normally, and the power direction transmitted by the two poles is always opposite, one pole transmits constant power, and the other pole transmits variable and opposite power.

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

[0070] When transmitting large power, the DC system operates in the bipolar operation mode.

[0071] When transmitting medium power, the DC system operates in the monopolar operation mode.

[0072] When transmitting small power, the DC system operates in the power cycle mode.

[0073] The implementation scheme of each stage of the specific process of the conventional DC online power flow reversal is as shown in the table: Figure 5 Specifically:

[0074] Stage 1: In this stage, the DC system operates in the bipolar mode, and the two poles transmit equal and positive-direction power. In this stage, the rectifier side of the two poles is used to control power, and the inverter side is used to control voltage, and 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 stage is P1, and when the total power reaches P1, stage 2 is entered.

[0075] Stage 2: In this stage, the DC system operates in the monopolar mode, pole 1 bears all the transmission power, and pole 2 is in DC lockout, with zero transmission power. The minimum value of the total transmission power in this stage is P2, and when the total power reaches P2, stage 3 is entered.

[0076] Stage 3: In this stage, the DC system operates in the cycle power mode. In this stage, the total transmission power in this stage ranges from -P2 to P2, where the negative sign represents the reverse direction of the power. In this mode of operation, the total transmission power needs to undergo a change in direction. In the time when the total power decreases from P2 to 0, pole 2 bears a constant reverse power, and only the power transmitted by pole 1 decreases in the positive direction. In the time when the total power reverses from 0 to P2, pole 1 bears a constant positive power, and only the power transmitted by pole 2 reverses and increases. When the total power reverses to P2, stage 4 is entered.

[0077] Stage 4: In this stage, the DC system operates in the monopolar mode, pole 2 bears all the transmission power and reverses and increases, and pole 1 is in DC lockout with zero transmission power. The maximum value of the total transmission power in this stage is P1, and when the total power reverses to P1, stage 5 is entered.

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

[0079] Based on the analysis of the reactive power-voltage change in the online power flow reversal process, as shown in FIG. 2, the specific process is as follows: Figure 6

[0080] First phase, forward bipolar + monopole operation (t1-t3): the total active power decreases from the rated value to P2, the total reactive power decreases, and according to the principle of reactive power balance of the converter bus, the AC voltage rises;

[0081] Second phase, unblocking pole 2 (t3): pole 2 is unblocked, the total active power remains unchanged, the total reactive power increases, and according to the principle of reactive power balance of the converter bus, the AC voltage decreases;

[0082] Third phase, forward power cycle mode (t3-t4): the total active power decreases from P2 to 0, the total reactive power decreases, and according to the principle of reactive power balance of the converter bus, the AC voltage rises;

[0083] Fourth phase, reverse power cycle mode (t4-t5): the total active power increases from 0 to P2, the total reactive power increases, and according to the principle of reactive power balance of the converter bus, the AC voltage decreases;

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

[0085] Sixth phase, reverse bipolar + monopole operation (t5-t7): the total active power increases from P2 to the rated value, the total reactive power increases, and according to the principle of reactive power balance of the converter bus, the AC voltage decreases.

[0086] Blocking pole 2 (t2), unblocking pole 1 process (t6) can be ignored, and the reasons are as follows:

[0087] When pole 2 is blocked, 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 of the whole DC system and the net absorbed reactive power are both 0, and the blocking of pole 2 only takes tens of milliseconds, which is very short. Therefore, the blocking of pole 2 stage can be ignored, and the forward bipolar + monopole operation can be regarded as a continuous process.

[0088] ​When the pole 1 is unlocked, the pole 1 power rises, the reactive power absorption increases, the pole 2 power decreases, the reactive power absorption decreases, the net power change of the whole DC system and the net reactive power absorption are both 0, and the unlocking of the pole 1 only needs tens of milliseconds, which is very short, so the unlocking of the pole 1 stage can be ignored, and thus the reverse bipolar + monopole operation can be regarded as a continuous process.

[0089] Based on the analysis of the reactive power curve change of the converter bus reactive power balance in the online power flow reversal process, specifically:

[0090] The converter bus reactive power balance is as shown in Figure 7 , and the reactive power curve change is as shown in Figure 8 .

[0091] The reactive power curve includes: the incoming AC-DC reactive power exchange Q ac , the filter provided reactive power Q fc , and the total reactive power Qd c absorbed by the conventional DC; wherein, point A is the rated operation state; considering the case of reducing the DC power, including: operation state B and operation state C;

[0092] When the state is converted to A→B, Q fc and Q alc both increase, and the change rate also increases, Q dc decreases due to the decrease of the DC power, and the change rate also decreases; in order to meet the reactive power balance of the operation state B, Q ac needs to increase more to meet the increase of Q fc , and the AC voltage change Δv2 needs to be larger;

[0093] When the state is converted to A→C, Q fc and Q ac both decrease, and the change rate also decreases, Q dc decreases due to the decrease of the DC power, but the change rate increases, and the decrease of Q dc can quickly match the decrease of Q fc and Q ac , and the AC voltage change Δv1 does not need to be large to meet the reactive power balance of the operation state C;

[0094] From the same voltage state, if it changes in the direction of high voltage, a larger voltage offset is needed to meet the reactive power balance, and if it changes in the direction of low voltage, only a smaller voltage offset is needed to meet the reactive power balance; the first stage of the reactive power-voltage change in the online power flow reversal process corresponds to A→B, the fifth stage corresponds to C→A, and the reactive power and voltage change of the fifth stage are weaker than those of the first stage, and the reactive power and voltage change of the fourth stage are weaker than those of the second stage.

[0095] Based on the total reactive power Qdc The state transition diagram under the change is analyzed, as shown in the following table, specifically: Figure 9

[0096] The state transition diagram under the change is analyzed, as shown in the following table, specifically:

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

[0098] The strength of the 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.

[0099] The state voltage in the state transition diagram is limited, specifically:

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

[0101] max{v B ,v D}<1.05v 额 ;

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

[0103] Step 2: Based on the premise condition, according to the absolute value size relationship of voltage offset in the first three stages of reactive power-voltage change in the online power flow reversal process under different conditions of total active power entering the power cycle mode, the limitation of state voltage under general conditions is determined, and the total active power is limited by the minimum frequency modulation capacity and the maximum voltage offset, and the total active power entering the single-pole operation mode is determined according to the total active power.

[0104] The premise condition is specifically:

[0105] The minimum operating power P min of the conventional DC is equal to 0.1 times the rated power 0.1PN;

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

[0107] ​According to the absolute value size relationship of voltage deviation of the first stage, the second stage and the third stage of the reactive power-voltage change in the online power flow inversion process under different conditions of the total active power entering the power cycle mode, the limit of the state voltage under the general condition is determined, specifically:

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

[0109] The absolute values of voltage deviation of the first stage, the second stage and the third stage of the reactive power-voltage change in the online power flow inversion process satisfy |Δvac,1| > |Δvac,2| > |Δvac,3|, the maximum voltage deviation occurs in the operating state B, and it is required to satisfy that the AC voltage under the operating state B is less than 1.05 times the rated value;

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

[0111] The absolute values of voltage deviation of the first stage, the second stage and the third stage of the reactive power-voltage change in the online power flow inversion process satisfy |Δvac,1| > |Δvac,3| > |Δvac,2|, the maximum voltage deviation occurs in the operating state D, and it is required to satisfy that the AC voltage under the operating state D is less than 1.05 times the rated value;

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

[0113] The absolute values of voltage deviation of the first stage, the second stage and the third stage of the reactive power-voltage change in the online power flow inversion process satisfy |Δvac,3| > |Δvac,1| > |Δvac,2|, the maximum voltage deviation occurs in the operating state D, and it is required to satisfy that the AC voltage under the operating state D is less than 1.05 times the rated value;

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

[0115] The absolute values of voltage deviation of the first stage, the second stage and the third stage of the reactive power-voltage change in the online power flow inversion process satisfy |Δvac,3| > |Δvac,2| > |Δvac,1|, the maximum voltage deviation occurs in the operating state B, and it is required to satisfy that the AC voltage under the operating state B is less than 1.05 times the rated value;

[0116] Case one needs to check the voltage of the operating state B, and the voltage of the operating state D needs to be checked in other cases. Since the P2 value of case one does not have sufficient frequency modulation capacity, it is concluded that case one is not applicable to the general case; in the general case, the voltage peak of the operating state D appears at the power zero point, and only the AC voltage of the operating state D needs to be checked to be less than 1.05 times the rated value.

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

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

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

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

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

[0122] wherein P1 is the total active power entering the monopole 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 monopole operation time; tmp = 2tv + tr; tv is the DC blocking or unblocking time, generally 200 ms; tr is the line recovery time, which is related to the line type, and the overhead line takes 200 ms and the cable line takes 2 min; and P1,max takes the minimum frequency modulation capacity. At this time, PN-P1,max is the minimum frequency modulation capacity (such as FLC, etc.) in the bipolar operation.

[0123] Embodiment 2

[0124] Embodiment 2 of the present application discloses a comparison between a conventional DC online power flow reversal reactive power optimization method for a new type of power system and an existing minimum line loss mode for power cycle operation, as shown in Figure 10 , specifically:

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

[0126] Since P q > P min , the active power change in the optimized reactive power operation mode is smaller, and the reactive power-voltage change is smaller. The blue area in the figure is the power cycle operation stage, and it can be found that in the minimum line loss mode (loss-opt), the AC-DC exchange reactive power Q ac will appear "spikes", resulting in "spikes" in the AC voltage. In the optimized reactive power operation mode (Q-opt), the peak value of Q ac is reduced, and therefore the peak value of the voltage is reduced. In summary, the purpose of Q-opt is to prevent the voltage from exceeding the boundary at the power zero point.

[0127] The embodiment of the application discloses a conventional DC online power flow inversion reactive power optimization method for a new power system. An inter-pole coordination method under an optimal reactive power cycle operation mode is proposed, zero switching reactive-voltage stability considering online power flow inversion is realized; a bipolar-monopole-optimal reactive power cycle multi-mode flexible continuous interaction method is proposed, an online power flow inversion system with adaptive reactive power regulation is formed; and an AC-DC reactive power change and AC voltage interaction mechanism is explored, and an online power inversion technology system adapting to multiple operation conditions is established according to complex system operation conditions and demands.

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

[0129] The above description of the disclosed embodiments enables a person skilled in the art to implement or use the application. Various modifications of the embodiments will be apparent to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the application. Therefore, the application will not be limited to the embodiments shown herein, but will conform 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 new power systems, characterized in that: include: Step 1: Analyze the reactive-voltage variation during the online power flow reversal process, the reactive curve variation of the commutation bus reactive balance, and the state transition diagram under the total reactive power variation of conventional DC absorption to determine the strength of the reactive-voltage variation before and after the power flow reversal, and define the state voltage in the state transition diagram; wherein the reactive-voltage variation during the online power flow reversal process is divided into six stages; Step 2: Based on the prerequisites, determine the general limit of the state voltage according to the absolute value relationship of the voltage offset in the first three stages of the reactive power-voltage change during the online power flow reversal process under different conditions of the total active power entering the power circulation mode, and limit the total active power by the minimum frequency modulation capacity and the maximum voltage offset. Determine the total active power for entering the monopole operation mode based on the total active power; In step 1, the reactive power-voltage change during the online power flow reversal process is divided into six stages, specifically: In the first stage, forward bipolar + unipolar operation; The second stage is to unlock the latch pole 2; The third stage is the forward power cycle mode; The fourth stage is the reverse power cycle mode; The fifth stage, blocking pole 1; The sixth stage is reverse bipolar + unipolar operation; In step 1, the state transition diagram of 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; B->C corresponds to the second stage; C->D corresponds to the third stage; D->E corresponds to the fourth stage; E->F corresponds to the fifth stage; F->A corresponds to the sixth stage; In step 2, the limit of the state voltage under general circumstances is determined based on 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 circumstances of the total active power entering the power circulation mode, specifically: Case 1: 0.1PN< <0.2PN; where PN is the rated power; 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 variation during the online power flow reversal process satisfy |Δvac,1|>|Δvac,2|>|Δvac,3|, and the maximum voltage offset occurs in operating state B. The AC voltage in operating state B must be less than 1.05 times the rated value. Case 2: 0.2PN< <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|, the maximum voltage offset occurs in operating state D, and the AC voltage in operating state D must be less than 1.05 times the rated value; Case 3: 0.5PN< <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|, the maximum voltage offset occurs in operating state D, and the AC voltage in operating state D must be less than 1.05 times the rated value; Case 4: 0.8PN< <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 operating state B. The AC voltage in operating state B must be less than 1.05 times the rated value. In case 1, the voltage of operating state B needs to be verified, and in other cases, the voltage of operating state D needs to be verified. The value does not have sufficient frequency regulation capacity, so situation 1 is not applicable to general situations. Under general circumstances, the voltage peak of operating state D occurs 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.

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: The first stage, forward bipolar + unipolar operation: the total active power decreases from the rated value to , the total reactive power decreases, and according to the reactive power balance principle of the commutation bus, the AC voltage rises; The second stage is to release the blocking of pole 2: pole 2 is unblocked, 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; The third stage, forward power circulation mode: the total active power is from When it drops to 0, the total reactive power decreases, and according to the reactive power balance principle of the commutation bus, the AC voltage rises; The fourth stage, reverse power cycle mode: the total active power increases from 0 to , the total reactive power increases, and according to the reactive power balance principle of the commutation bus, the AC voltage decreases; The fifth stage, blocking pole 1: Pole 1 is blocked, the total active power remains unchanged, the total reactive power decreases, and according to the reactive power balance principle of the commutation bus, the AC voltage rises; Phase 6, reverse bipolar + unipolar operation: total active power from When it rises 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 , the filter provides reactive power and the total reactive power absorbed by conventional DC ; Among them, point A is the rated operating state; consider the case of reducing DC power, including: operating state B and operating state C; When the state transitions to A→B, 、 Both increase, and the rate of change also increases. As the DC power decreases, the rate of change also decreases; in order to meet the reactive balance of operating state B, Need to increase more to meet increases, and the AC voltage changes Needs to be bigger; When the state transitions to A→C, 、 Both decrease, and the rate of change also decreases. It decreases due to the decrease of DC power, but the rate of change increases. The reduction can quickly match and The decrease in AC voltage It does not need to be very large to satisfy 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 strength of the 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.

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 state voltage in the state transition diagram is limited, specifically: The voltages of the operating states B and D are and The maximum value in satisfies the following: in, is the rated AC voltage.

6. 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 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.

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 total active power is limited by the minimum frequency modulation capacity and the maximum voltage offset, specifically: in, is the total active power; Take the minimum frequency modulation capacity; Take the maximum voltage offset.

8. 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: in, is the total active power entering the unipolar operation mode; ; is the total active power entering the power cycle mode; is the power reduction rate; is the total duration of monopolar operation; It is the DC blocking or releasing time; Line recovery time; Take the minimum frequency modulation capacity.

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