Single-core independent phase-shifting transformer and control method thereof

Abstract

The application discloses a single-core independent phase-shifting transformer and a control method thereof. The single-core independent phase-shifting transformer comprises an excitation winding, a source-side voltage regulation winding, a load-side voltage regulation winding and an on-load voltage regulation switch. The excitation winding is a primary side of the single-core independent phase-shifting transformer and is connected in a triangle mode. The source-side voltage regulation winding and the load-side voltage regulation winding are secondary sides of the single-core independent phase-shifting transformer and are directly connected in series in a circuit. The source-side voltage regulation winding and the load-side voltage regulation winding are both provided with the on-load voltage regulation switch. The source-side voltage regulation winding and the load-side voltage regulation winding are divided into several sections according to phase-shifting angles, that is, the phase-shifting angle of each section is changed by the same value, and the voltage of each section is changed by different values. The application can independently adjust the phase and effective value of the circuit voltage, independently adjust the active power flow and the reactive power flow of the circuit, and further optimizes the adjustment performance of the phase-shifting transformer.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of power grid, in particular to a single-core independent phase-shifting transformer and a control method thereof. BACKGROUND

[0002] With the continuous development of power systems, the power grid is becoming more and more complex, facing problems such as uneven power flow distribution and circulating current. And with the continuous access of new energy, the flow direction and randomness of power flow in the power system are enhanced, which is easy to cause transmission congestion in local area, affecting the stability of the power system and the consumption of new energy. Therefore, the power system urgently needs to use power flow control devices to increase the controllability of power flow in the power grid.

[0003] The single-core symmetric phase-shifting transformer is a traditional power flow control device, which is used in 110kV and below power systems. By switching the tap of the voltage regulating winding through the on-load tap changer, it injects adjustable series compensation voltage into the line, changes the effective value and phase of the line voltage, and thus controls the system power flow.

[0004] The existing single-core phase-shifting transformer can only adjust the phase of the line voltage while keeping the effective value of the line voltage unchanged, or adjust the phase of the line voltage while increasing the effective value of the line voltage. It cannot independently adjust the phase and effective value of the line voltage, nor can it independently adjust the active power flow and the reactive power flow. It has some deficiencies in function, low adjustment precision, and cannot meet the demand of new power system for power flow control. Therefore, it is urgent to improve the function of the single-core phase-shifting transformer, so that the single-core symmetric phase-shifting transformer can meet the demand of future power system for power flow control. SUMMARY

[0005] In view of the problems raised in the background art, the present application proposes a single-core independent phase-shifting transformer, which can independently adjust the effective value and phase of the line voltage, and improve the adjustment performance and precision.

[0006] To solve the above technical problems, the technical solution adopted by the present application is as follows:

[0007] A single-core independent phase-shifting transformer, characterized in that it comprises an excitation winding, a source-side voltage regulating winding, a load-side voltage regulating winding and an on-load tap changer; the excitation winding is the primary side of the single-core independent phase-shifting transformer and is connected in a delta configuration; the source-side voltage regulating winding and the load-side voltage regulating winding are the secondary side of the single-core independent phase-shifting transformer and are directly connected in series in the line, and the source-side voltage regulating winding and the load-side voltage regulating winding are each provided with an on-load tap changer; the source-side voltage regulating winding and the load-side voltage regulating winding are divided into several steps according to the phase-shifting angle, that is, the phase-shifting angle changes the same in each step, and the voltage changes differently in each step.

[0008] In the single-core independent phase-shifting transformer, the working characteristics of the source-side voltage regulating winding and the load-side voltage regulating winding are analyzed, and the influence of the two sides of the voltage regulating winding on the phase-shifting line voltage is determined in the lead adjustment and the lag adjustment. The lead adjustment is that the phase of the adjusted line voltage is ahead of the phase of the unadjusted line voltage. The lag adjustment is that the phase of the adjusted line voltage lags behind the phase of the unadjusted line voltage.

[0009] In the single-core independent phase-shifting transformer, when only the source-side voltage regulating winding works, that is, the gear position of the source-side voltage regulating winding is not zero and the gear position of the load-side voltage regulating winding is zero, the effective value of the line voltage after adjustment is smaller than the effective value of the line voltage before adjustment, and the working of the source-side voltage regulating winding will reduce the effective value of the line voltage.

[0010] When only the load-side voltage regulating winding works, that is, the gear position of the load-side voltage regulating winding is not zero and the gear position of the source-side voltage regulating winding is zero, the effective value of the line voltage after adjustment is larger than the effective value of the line voltage before adjustment, and the working of the load-side voltage regulating winding will increase the effective value of the line voltage.

[0011] In the single-core independent phase-shifting transformer, the working principle of the single-core independent phase-shifting transformer is to independently adjust the gear positions of the source-side voltage regulating winding and the load-side voltage regulating winding during adjustment, so that the gear positions of the two sides of the voltage regulating winding are inconsistent, and a plurality of compensation voltage combinations are obtained.

[0012] In the single-core independent phase-shifting transformer, k S , k L are respectively defined as the gear positions of the source-side voltage regulating winding and the load-side voltage regulating winding, k S , k L ∈[0, ±n], n is the maximum gear position of the source-side voltage regulating winding and the load-side voltage regulating winding, and δ is the phase-shifting angle changed by each gear position. The phase-shifting angle α of the single-core independent phase-shifting transformer is:

[0013] (1)

[0014] Wherein αS and αL are respectively the phase-shifting angles of the source-side voltage regulating winding and the load-side voltage regulating winding, and k is the sum of the gear positions of the two sides of the voltage regulating winding. According to formula 1, when the phase-shifting angle α is a fixed value, k is also a fixed value. At this time, the independent adjustment of kS and kL can obtain a plurality of gear position combinations.

[0015] In the single-core independent phase-shifting transformer,

[0016] When |kS|=|kL|, the effective value of the voltage after phase-shifting is unchanged.

[0017] When |kS|<|kL|, the effective value of the voltage after phase-shifting is increased.

[0018] When |kS|>|kL|, the effective value of the phase-shifted voltage is reduced.

[0019] In the single-core independent phase-shifting transformer, the voltage parameters of each gear level are designed as follows: assuming that the total number of gears of the voltage regulating winding is ±n, the effective value of the voltage change of each gear of the source-side voltage regulating winding is ΔU Sk :

[0020] (2)

[0021] ΔU Sk , ΔU Lk are the effective values of the voltage change of each gear of the source-side and load-side voltage regulating windings respectively,

[0022] From the above analysis, it can be seen that the compensation voltage on the source-side voltage regulating winding has a voltage reducing effect on the line voltage after phase shifting, and the compensation voltage on the load-side winding has a voltage increasing effect on the line voltage after phase shifting,

[0023] Let k S , k L be the gears of the source-side voltage regulating winding and the load-side voltage regulating winding respectively, k S , k L ∈[0, ±n], then the total phase-shifting angle α is:

[0024] (3)

[0025] The phase-shifting angles of the source-side and load-side voltage regulating windings are α S , α L :

[0026] (4)

[0027] (5)

[0028] The amplitude of the primary-side input voltage U 10 is:

[0029] (6)

[0030] The amplitude of the phase-shifted voltage U LA is:

[0031] (7)

[0032] The amplitude change ΔU of the phase-shifted voltage is:

[0033] (8).

[0034] In the single-core independent phase-shifting transformer, when the required phase-shifting angle is kδ, k is selected according to the working characteristics of the voltage regulating winding S , k L , the effective value of the line voltage can be flexibly changed, so as to independently adjust the effective value and phase of the line voltage,

[0035] When the phase-shifting range of the single-core independent phase-shifting transformer is ±θ, the line voltage regulating range ΔU is:

[0036] (9)

[0037] As can be seen from formula 9, the larger the phase-shifting range of the single-core independent phase-shifting transformer, the larger the voltage regulating range,

[0038] When the adjustable gear position of the voltage regulating winding is ±n, the number m of the compensation voltages that can be output by the single-core independent phase-shifting transformer is:

[0039] (10)

[0040] As can be seen from formula 10, the more the gear positions of the voltage regulating winding, the more the compensation voltages that can be output, which greatly increases the adjustment accuracy of the single-core independent phase-shifting transformer.

[0041] A control method of a single-core independent phase-shifting transformer, characterized in that:

[0042] The target values of the input active power, the line voltage and the phase-shifting angle are measured, and the phase difference between the voltage U L after phase-shifting and the line voltage U R of the receiving end is obtained, the target phase difference and the measured phase difference are subtracted to obtain the required phase-shifting angle Δα, if Δα is less than or equal to 50% of the phase-shifting angle changed by each gear position, at this time the target value is located in the adjustment dead zone, only the amplitude of the line voltage after phase-shifting is adjusted,

[0043] The target phase difference δ ref can be calculated by the following formula:

[0044] (11)

[0045] Wherein, P ref is the target value of the active power, R and X are the line resistance and reactance,

[0046] The target line voltage U ref and the measured line voltage are subtracted to obtain the required voltage ΔU ref ,

[0047] The data is sent to the tap control unit, the gear of the two sides voltage regulating winding is adjusted according to delta alpha and delta U, and the error after adjustment is judged, if it is greater than the allowed error value, the adjustment is continued.

[0048] In the above control method, the optimal switching position is determined:

[0049] (1) input target active P ref , target voltage U ref , calculate target phase difference delta ref according to formula (10)

[0050] (2) measure the phase difference delta of the voltage U L after phase shifting and the voltage U R of the receiving end line, calculate whether the required change of phase shifting angle delta alpha is in the dead zone, if yes, select the switching position of the phase shifting angle change of 0 as the candidate switching position, go to step 4; if not, go to step 3,

[0051] (3) according to the difference between delta alpha and delta alpha k in table 1, select the minimum difference as the candidate switching position,

[0052] (4) calculate the change amount delta U k of the line voltage of the candidate switching position according to formula (8), and compare it with delta U ref , select the switching position with the minimum difference to switch,

[0053] (5) after the switching is finished, judge whether the active and voltage are in the error range, if not, go to step 2.

[0054] Compared with the prior art, the beneficial effects of the present application are:

[0055] 1. The existing single-core symmetric phase-shifting transformer can only adjust the line voltage phase while keeping the line voltage effective value unchanged, and the adjustment function is single and the adjustment precision is insufficient. The single-core independent phase-shifting transformer can adjust the line voltage phase while keeping the line voltage effective value unchanged, and can also adjust the line voltage effective value while keeping the line voltage phase unchanged, the adjustment function is diverse, and the adjustment precision is improved;

[0056] 2. The existing single-core asymmetric phase-shifting transformer can change the line voltage effective value while adjusting the line voltage phase, and cannot be independently adjusted. The single-core independent phase-shifting transformer can independently adjust the phase and effective value of the line voltage, greatly improving the adjustment performance and adjustment precision of the traditional single-core phase-shifting transformer;

[0057] 3. The single-core independent phase-shifting transformer can independently adjust the active power and reactive power of the line by independently adjusting the phase and effective value of the line voltage, further optimizing the adjustment performance of the phase-shifting transformer.

[0058] 4. Compared with the existing single-core Sen transformer, the single-core independent phase-shifting transformer has fewer windings, a simple structure, a small footprint, and low cost, and is highly implementable in actual engineering applications. BRIEF DESCRIPTION OF DRAWINGS

[0059] Figure 1 Fig. 1 is a topological structure diagram of the single-core independent phase-shifting transformer;

[0060] Figure 2 Fig. 3 is a voltage phase diagram of the single-core independent phase-shifting transformer;

[0061] Figure 3 Fig. 5 is a structure diagram of the voltage regulation winding of the single-core independent phase-shifting transformer;

[0062] Figure 4 Fig. 7 is a voltage phase diagram when the source-side voltage regulation winding works alone;

[0063] Figure 5 Fig. 9 is a voltage phase diagram when the load-side voltage regulation winding works alone;

[0064] Figure 6 Fig. 11 is a voltage phase diagram when the source-side voltage regulation winding gear k S = 3 and the load-side voltage regulation winding gear k L = 1;

[0065] Figure 7 Fig. 13 is a voltage phase diagram when the source-side voltage regulation winding gear k S = 1 and the load-side voltage regulation winding gear k L = 3;

[0066] Figure 8 Fig. 15 is a voltage phase diagram when the source-side voltage regulation winding gear k S = 2 and the load-side voltage regulation winding gear k L = 0;

[0067] Figure 9 Fig. 17 is a voltage phase diagram when the source-side voltage regulation winding gear k S = 0 and the load-side voltage regulation winding gear k L = 2;

[0068] Figure 10 Fig. 19 is a voltage phase diagram when the source-side voltage regulation winding gear k S = 3 and the load-side voltage regulation winding gear k L = -1;

[0069] Figure 11k is the gear position of the source side voltage regulating winding S k is the gear position of the load side voltage regulating winding L the voltage phase diagram when k = 3;

[0070] Figure 12 is a simulation result diagram. DETAILED DESCRIPTION

[0071] The technical solutions of the present application are further specifically described below by examples in combination with the drawings.

[0072] The topological structure of the single-core independent phase-shifting transformer is shown in Figure 1 The primary side is an excitation winding, which is connected in a triangle, and the secondary side is a voltage regulating winding, which is directly connected in the circuit to inject compensation voltage into the circuit. The voltage regulating winding is divided into a source side voltage regulating winding and a load side voltage regulating winding, both of which are installed with on-load voltage regulating switches with polarity switching devices, so as to adjust the size of the compensation voltage and change the polarity of the output voltage. The input end of the excitation winding is connected to the middle of the two voltage regulating windings for power taking.

[0073] wherein U SA , U LA respectively represent the phase voltages of the A-phase circuit before and after adjustment, U 10 , U 20 , U 30 are the single-core independent phase-shifting transformer primary side three-phase input voltages, ΔU SA , ΔU LA respectively represent the compensation voltages on the source side voltage regulating winding and the load side voltage regulating winding in the A-phase circuit, ΔU SB , ΔU LB respectively represent the compensation voltages on the source side voltage regulating winding and the load side voltage regulating winding in the B-phase circuit, ΔU SC , ΔU LC respectively represent the compensation voltages on the source side voltage regulating winding and the load side voltage regulating winding in the C-phase circuit.

[0074] The compensation voltage of the A-phase circuit is provided by U 23 ; the compensation voltage of the B-phase circuit is provided by U 31 ; and the compensation voltage of the C-phase circuit is provided by U 12 .

[0075] In order to enable the single-core independent phase-shifting transformer to independently adjust the line voltage amplitude and phase, the voltage regulating winding needs to be improved first. The gears on the conventional voltage regulating winding are evenly distributed according to the voltage, and the compensation voltage changed by each gear is the same. After improvement, the gears on the voltage regulating winding are evenly distributed according to the phase-shifting angle, i.e. the phase-shifting angle changed by each gear is the same, and the voltage phase diagram is shown in Figure 2 wherein δ represents the phase-shifting angle changed by each gear, ΔU S1, ΔU S2 , ΔU S3 These represent the voltage amplitude change of the source-side regulating winding at each step, ΔU L1 , ΔU L2 , ΔU L3 These represent the voltage amplitude changes for each step of the load-side regulating winding. The structural diagram of the regulating winding of a single-core independent phase-shifting transformer is shown below. Figure 3 As shown, the voltage change for each gear decreases as the gear level increases.

[0076] The operating characteristics of the source-side voltage regulating winding and the load-side voltage regulating winding are analyzed separately.

[0077] When only the source-side regulating winding is working, the voltage phase diagram is as follows: Figure 4 As shown, the phase-shifting transformer is a single-core asymmetrical type at this time, ΔU SA U represents the voltage on the source-side regulating winding and the primary input voltage of the phase-shifting transformer. 10 Equal to the phase-shifted voltage U LA Since the primary input voltage and the compensation voltage are orthogonal, the voltage after phase shift is less than the voltage before phase shift, regardless of whether it is a leading or lagging regulation.

[0078] When only the load-side winding is working, the voltage phase diagram is as follows: Figure 5 As shown, the primary input voltage U of the phase-shifting transformer at this time 10 Equal to the voltage U before phase shift SA Similarly, U SA With ΔU LA Because they are orthogonal, whether it is leading or lagging regulation, the voltage after phase shift is greater than the voltage before phase shift.

[0079] The voltage parameters for each level are designed as follows. Assuming the regulating winding has ±n levels, the effective voltage change ΔU of the source-side regulating winding for each level is as follows. Sk for:

[0080] (2)

[0081] ΔU Sk , ΔU Lk These represent the effective voltage values ​​that change for each step of the voltage regulating winding on the source and load sides, respectively.

[0082] The above analysis shows that the compensation voltage on the source-side voltage regulating winding reduces the line voltage after phase shift, while the compensation voltage on the load-side winding increases the line voltage after phase shift.

[0083] Let k S k L These are the tap positions for the source-side voltage regulating winding and the load-side voltage regulating winding, respectively, k S kL ∈[0, ±n], the total phase shift angle a is:

[0084] (3)

[0085] Phase shift angle a of voltage regulating winding on source side and load side S , a L is:

[0086] (4)

[0087] (5)

[0088] Amplitude of input voltage U on primary side 10 is:

[0089] (6)

[0090] Amplitude of voltage U after phase shift LA is:

[0091] (7)

[0092] Voltage amplitude change ΔU after phase shift is:

[0093] (8)

[0094] From the above analysis, the voltage regulating characteristics of single-core independent PST are as follows:

[0095] |k S |=|k L , the compensation voltage amplitude of voltage regulating winding on source side is equal to that of load side winding, and the amplitude of line voltage after phase shift is unchanged;

[0096] |k S |<|k L , the compensation voltage amplitude of voltage regulating winding on source side is smaller than that of load side winding, and the amplitude of line voltage after phase shift is increased;

[0097] |k S |>|k L , the compensation voltage amplitude of voltage regulating winding on source side is greater than that of load side winding, and the amplitude of line voltage after phase shift is decreased.

[0098] When the required phase shift angle is kδ, k S and k L are selected according to the working characteristics of the above voltage regulating winding, and the effective value of line voltage can be flexibly changed, so as to independently regulate the effective value and phase of line voltage.

[0099] The phase-shifting range of the single-core independent phase-shifting transformer is ±θ, and the line voltage regulating range ΔU is:

[0100] (9)

[0101] As shown in equation 9, the larger the phase-shifting range of the single-core independent phase-shifting transformer, the larger the voltage regulating range.

[0102] When the adjustable gear position of the voltage regulating winding is ±n, the number of compensation voltages m that can be output by the single-core independent phase-shifting transformer is:

[0103] (10)

[0104] As shown in equation 10, the more the number of gear positions of the voltage regulating winding, the more the number of compensation voltages that can be output, greatly increasing the regulating accuracy of the single-core independent phase-shifting transformer.

[0105] The gear position control strategy of the single-core independent PST is as follows.

[0106] The target values of the input active power, line voltage and phase-shifting angle are input, the phase difference between the measured voltage U L and the receiving end line voltage U R is measured, the target phase difference and the measured phase difference are subtracted to obtain the required change in the phase-shifting angle Δα, and if Δα is less than or equal to 50% of the change in the phase-shifting angle per gear position, the target value is located in the regulating dead zone, and only the amplitude of the line voltage after phase-shifting is regulated.

[0107] The target phase difference δ ref can be calculated by the following equation:

[0108] (11)

[0109] Where P ref is the target value of the active power, and R and X are the line resistance and reactance.

[0110] The target line voltage U ref and the measured line voltage are subtracted to obtain the required change in the voltage ΔU ref .

[0111] The data is sent to the tap control unit, and the gear positions of the two voltage regulating windings are adjusted according to Δα and ΔU, respectively, and the error after adjustment is judged, and if it is greater than the allowed error value, the adjustment is continued.

[0112] Suppose the gear positions of the two voltage regulating windings are k1 and k2, respectively, then there are 9 choices for the next step, as shown in Table 1, where Δα k and ΔU k represent the relative phase-shifting angle change and the relative voltage change of the switching position, respectively.

[0113]

[0114] If the current gear is at the highest or lowest gear, the increase or decrease operation of the regulating winding is locked, and only the remaining switching operation can be performed.

[0115] The following steps are used to determine the optimal switching position:

[0116] (1) input target active power P ref , target voltage U ref , and calculate the target phase difference δ ref according to formula (10).

[0117] (2) measure the phase difference δ between the voltage U L after phase shifting and the voltage U R of the receiving end line, and calculate whether the required change in phase shifting angle Δα is within the dead zone. If it is, select the switching position with a phase shifting angle change of 0 as the candidate switching position, and go to step 4; if not, go to step 3.

[0118] (3) according to the difference between Δα and Δα k in table 1, select the one with the smallest difference as the candidate switching position.

[0119] (4) calculate the change ΔU k in line voltage of the candidate switching position according to formula (8), and compare it with ΔU ref , and select the switching position with the smallest difference for switching.

[0120] (5) after the switching is completed, determine whether the active power and voltage are within the error range. If not, go to step 2.

[0121] Example 1

[0122] In this embodiment, the maximum adjustable gear of the single-core independent phase shifter regulating winding is ±3, and the phase shifting angle is 4δ.

[0123] When the line voltage effective value does not need to be adjusted, the gear of both sides of the regulating winding is adjusted to 2, i.e. k S =k L =2, at this time the compensation voltage ΔU SA of the source side regulating winding is equal to the compensation voltage ΔU LA of the load side regulating winding, the phase shifting angle is 4δ, and the line voltage effective value U LA after adjustment is equal to the line voltage effective value U SA before adjustment, as shown in Figure 6 .

[0124] When the line voltage effective value needs to be reduced, k S =3, kL =1, the compensation voltage ΔU of the source side voltage regulating winding SA is greater than the compensation voltage ΔU of the load side voltage regulating winding LA , the phase shift angle is 4φ, and the effective value of the regulated line voltage U is LA less than the effective value of the unregulated line voltage U SA , as shown in Fig. 2. Figure 7

[0125] When the effective value of the line voltage needs to be increased, k S =1, k L =3, the compensation voltage ΔU of the load side voltage regulating winding LA is greater than the compensation voltage ΔU of the source side voltage regulating winding SA , the phase shift angle is 4φ, and the effective value of the regulated line voltage U is LA greater than the effective value of the unregulated line voltage U SA , as shown in Fig. 3. Figure 8

[0126] Embodiment Two

[0127] In this embodiment, the maximum adjustable gear of the single-core independent phase shifter voltage regulating winding is ±3, and the phase shift angle is 2δ.

[0128] When the effective value of the line voltage does not need to be regulated, the gears of the voltage regulating windings on both sides are adjusted to 1 gear, i.e. k S =k L =1, the phase shift angle is 2δ, and the effective value of the regulated line voltage is unchanged;

[0129] When the effective value of the line voltage needs to be decreased, k S =2, k L =0, the phase shift angle is 2δ, and the effective value of the regulated line voltage is decreased;

[0130] When the effective value of the line voltage needs to be increased, k S =0, k L =2, the phase shift angle is 2δ, and the effective value of the regulated line voltage is increased;

[0131] In addition, the on-load voltage regulating switches of the single-core independent phase shifter transformer are all equipped with polarity switching switches, which can make the compensation voltages output by the source side voltage regulating winding and the load side voltage regulating winding have opposite polarities, can further increase the number of compensation voltages, and improve the regulation accuracy.

[0132] When the effective value of the line voltage needs to be decreased, k S =3, k L =-1, the phase shift angle is 2δ, and the effective value of the regulated line voltage is decreased, as shown in Fig. 4. Figure 9

[0133] When the effective value of the line voltage needs to be increased, k​​​S = -1, k L = 3, the phase shift angle is 2δ, and the effective value of the line voltage after adjustment is increased, as shown in Figure 10

[0134] The beneficial effects of the present application are further illustrated below by computer simulation.

[0135] A simulation model of a single-core independent phase-shifting transformer applied to a 110kV system is established using Matlab / Simulink, and the power flow regulation effect is simulated and verified.

[0136] A simulation model as shown in Figure 11 is established, the voltage phase of substation B is set to lag behind that of substation A, the initial phase difference between the two ends of the line is 5°, the line transmission active power is 46.37MW, and the reactive power is 14.54MVar. The maximum adjustable gear of the single-core independent phase-shifting transformer is ±4, and each gear changes the phase shift angle by 4°

[0137] The single-core independent phase-shifting transformer is adjusted, and the active and reactive power of the line after adjustment of each gear is recorded. The steady-state regulation performance of the single-core independent phase-shifting transformer is shown in Figure 12 , where each point in the figure represents the line active and reactive power corresponding to one gear combination.

[0138] Under the same parameter settings, the single-core symmetric phase-shifting transformer has only 9 adjustment points, as can be seen from Figure 12 , the single-core independent phase-shifting transformer has 73 adjustment points, and the adjustment accuracy is greatly improved. When the phase shift angle is kept unchanged and only the line voltage is adjusted, the change rate of active power is much smaller than that of reactive power. The strong correlation between voltage and reactive power can be utilized to adjust the line active and reactive power relatively independently, thereby improving the regulation performance.

[0139] In the initial state, the line phase voltage is 67.5kV; k S = 0, k L = 4, the effective value of the line phase voltage after adjustment is 70.0kV; k S = 4, k L = 0, the effective value of the line phase voltage after adjustment is 65.1kV, and the overall voltage regulation range is about 3.7%.

[0140] The specific embodiments described herein are merely illustrative of the spirit of the present application. Those skilled in the art of the present application can make various modifications or supplements to the described specific embodiments or replace them with similar ways, without deviating from the spirit of the present application or exceeding the scope defined by the appended claims.​

Claims

1. A control method of a single-core independent phase-shifting transformer, characterized by: The single-core independent phase-shifting transformer comprises an excitation winding, a source-side voltage regulation winding, a load-side voltage regulation winding and an on-load voltage regulation switch; the excitation winding is a primary side of the single-core independent phase-shifting transformer and is connected in a delta connection; the source-side voltage regulation winding and the load-side voltage regulation winding are secondary sides of the single-core independent phase-shifting transformer and are directly connected in series in a circuit, and the source-side voltage regulation winding and the load-side voltage regulation winding are each provided with an on-load voltage regulation switch; the source-side voltage regulation winding and the load-side voltage regulation winding are divided into different gears according to phase-shifting angles, i.e., the phase-shifting angle changed by each gear is the same, and the voltage changed by each gear is different; and the control method comprises: Input active power target value P ref , line voltage target value U ref , measured line voltage U L after phase shifting, and the phase difference of the receiving end line voltage U R , i.e. the measured phase difference δ, the target phase difference δ ref is subtracted from the measured phase difference δ to obtain the required change in phase shift angle Δα. If the required change in phase shift angle Δα is less than or equal to 50% of the phase shift angle changed per gear, the required change in phase shift angle Δα is located in the adjustment dead zone at this time, and only the line voltage amplitude after phase shifting is adjusted, Target phase difference δ ref may be calculated by the following equation: （1） where P ref is the active power target value, R, X are the line resistance and reactance, Subtracting the measured line voltage from the line voltage target value U ref gives the voltage ΔU required for change ref , The phase shift angle Δα and the voltage ΔU to be changed are calculated ref The phase shift angle Δα and the voltage ΔU to be changed are calculated ref The gear positions of the two voltage regulating windings are adjusted respectively, and the error after adjustment is judged. If the error is greater than the allowed error value, the adjustment is continued.

2. The control method of a single-core independent phase-shifting transformer according to claim 1, characterized by: The working characteristics of the source-side voltage regulation winding and the load-side voltage regulation winding are analyzed, and the influence effects of the two voltage regulation windings on the line voltage after phase-shifting are determined when the two voltage regulation windings are in lead regulation and lag regulation respectively; the lead regulation refers to that the phase of the line voltage after regulation is ahead of the phase of the line voltage before regulation; and the lag regulation refers to that the phase of the line voltage after regulation lags behind the phase of the line voltage before regulation.

3. The control method of a single-core independent phase-shifting transformer according to claim 1, characterized by: When only the source-side voltage regulation winding works, i.e., the gear position of the source-side voltage regulation winding is not zero and the gear position of the load-side voltage regulation winding is zero, the effective value of the line voltage after regulation is smaller than the effective value of the line voltage before regulation no matter the lead regulation or the lag regulation, and the working of the source-side voltage regulation winding will reduce the effective value of the line voltage; When only the load-side voltage regulation winding works, i.e., the gear position of the load-side voltage regulation winding is not zero and the gear position of the source-side voltage regulation winding is zero, the effective value of the line voltage after regulation is larger than the effective value of the line voltage before regulation no matter the lead regulation or the lag regulation, and the working of the load-side voltage regulation winding will increase the effective value of the line voltage.

4. The control method of a single-core independent phase-shifting transformer according to claim 1, characterized by: The working principle of the single-core independent phase-shifting transformer is to independently adjust the gear positions of the source-side voltage regulation winding and the load-side voltage regulation winding during regulation, so that the gear positions of the two voltage regulation windings are inconsistent, thereby obtaining a plurality of compensation voltage combinations.

5. The control method of a single-core independent phase-shifting transformer according to claim 1, characterized by: Definition k S , k L are gear positions of the source side and load side voltage regulating windings, respectively, k S , k L ∈[0, ±n], n is the maximum gear position of the source side and load side voltage regulating windings, is the phase shift angle changed for each gear position, and the total phase shift angle α of the single-core independent type phase shift transformer is: （2） wherein α S , α L are the phase shift angles of the source-side and load-side voltage regulating windings, respectively, and k is the sum of the number of steps of the two voltage regulating windings.

6. The control method of the single-core independent phase-shifting transformer according to claim 5, characterized in that: When |k S |=|k L |, the effective value of the phase-shifted line voltage remains unchanged. When |k S |<|k L |, the effective value of the phase-shifted line voltage increases; When |k S |>|k L | the effective value of the phase-shifted line voltage decreases.

7. The control method of a single-core independent phase-shifting transformer according to claim 5, characterized by: If the voltage regulating winding has ±n steps, the voltage effective value ΔU of the source side voltage regulating winding changes every step Sk is: （3） ΔU Sk , ΔU Lk are the effective values of the voltage per step change of the source-side and load-side voltage regulating windings, respectively SA Ua represents the phase voltage of the A-phase line Phase shift angle α of source side and load side voltage regulating winding S , α L are respectively: （5） （6） where ΔU SA represents the source side compensation voltage injected into the A-phase line, ΔU LA represents the load side compensation voltage injected into the A-phase line, U LA represents the phase voltage of the A-phase line after phase shifting; Primary input voltage U 10 has a magnitude of: （7） the phase voltage U of the a-phase line after phase shifting LA is: （8） The voltage amplitude change amount ΔU after phase-shifting is: （9）。 8. The control method of a single-core independent phase-shifting transformer according to claim 5, characterized by: When the required phase-shifting angle is k is selected according to the operating characteristics of the voltage-regulating winding S , k L , the effective value of the line voltage can be flexibly changed, so that the effective value and phase of the line voltage can be independently regulated. Supposing that the phase-shifting range of the single-core independent phase-shifting transformer is ±θ, the line voltage regulation range ±U% is: （10） Supposing that the adjustable gear position of the voltage regulation winding is ±n, the number m of compensation voltages that can be output by the single-core independent phase-shifting transformer is: （11）。 9. The control method of a single-core independent phase-shifting transformer according to claim 1, characterized by: The optimal switching position is determined, comprising the following steps: (1) input an active power target value P ref , a target line voltage U ref , calculates a target phase difference δ ref , (2) Measure the line voltage U after phase shifting L and the phase difference of the receiving end line voltage U R , i.e. the measured phase difference δ, to calculate whether the required change in phase shifting angle Δα is within the dead zone. If yes, select the switching position with a phase shifting angle change of 0 as the candidate switching position and go to step (4); if not, go to step (3), (3) According to the difference between the phase shift angle Δα to be changed and the relative phase shift angle change amount Δα of the switching position, the candidate switching position with the smallest difference is selected, k the difference between the phase shift angle Δα to be changed and the relative phase shift angle change amount Δα of the switching position, the candidate switching position with the smallest difference is selected, (4) Calculate the relative voltage amplitude change ΔU of the candidate switching position according to formula (9) k Compare with the required voltage change ΔU ref Select the switching position with the smallest gap for switching. (5) After the switching is completed, the measured phase difference δ after phase shifting is compared with the target phase difference δ ref The measured line voltage after phase shifting is compared with the target line voltage U ref The comparison is made to determine whether it is within the error range. If not, go to step (2).

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