Control method of flexible on-load tap changer transformer based on multi-time scale coordination

Abstract

The application discloses a control method of a flexible on-load voltage regulating transformer based on multi-time scale coordination, which comprises a main transformer, a tap switch voltage regulating unit, a power electronic compensation unit, a measurement sampling unit and a control unit. The tap switch voltage regulating unit performs step voltage regulation on the controlled end voltage of the main transformer by changing the gear state of the tap switch, and the power electronic compensation unit outputs a compensation amount to perform stepless compensation on the controlled end voltage of the main transformer. The control unit generates a gear reconstruction instruction or a continuous compensation instruction based on the controlled end voltage collected by the measurement sampling unit, the gear state and the compensation amount output by the power electronic compensation unit, and judges and selects a slow time scale step voltage regulation model or a fast time scale stepless compensation model based on the gear reconstruction instruction or the continuous compensation instruction, so as to perform slow time scale step voltage regulation or fast time scale stepless compensation on the controlled end voltage of the main transformer, and realize multi-time scale coordinated control.

Description

Technical Field

[0001] This invention relates to the field of transformer control technology, and in particular to a control method for flexible on-load tap-changing transformers based on multi-timescale coordination. Background Technology

[0002] Traditional on-load tap-changing transformers primarily rely on tap changers to alter the transformer turns ratio for discrete voltage regulation. While this allows for a wide range of steady-state voltage adjustments, limitations in mechanical action delays, tap position dispersion, and switch lifespan make it difficult to quickly respond to short-term voltage fluctuations caused by factors such as solar cloud shading and sudden load increases. Introducing small-capacity power electronic compensation units into on-load tap-changing transformers can create flexible on-load tap-changing transformers, enabling rapid and continuous stepless compensation. However, the following problems still exist in actual control: First, traditional tap changer voltage regulation is a slow, discrete control method, suitable for handling continuous voltage deviations but insufficient for responding to short-term, rapid disturbances. If relying directly on tap changers to track rapid fluctuations, the unclear division of time scales between stepless compensation operations can easily lead to tap changer malfunctions and frequent trips, increasing mechanical switch losses. Second, while power electronic stepless compensation is a fast and continuous control method suitable for handling local disturbances and small fluctuations, when steady-state voltage deviation persists for a long time, the compensation amount is prone to continuous bias, resulting in long-term occupation of the compensation capacity. If stepless voltage regulation is relied upon for a long time, the compensation amount is likely to operate with a long-term bias and approach the capacity boundary, weakening subsequent dynamic adjustment capabilities. Third, existing control strategies often design stepped voltage regulation and stepless voltage regulation separately, lacking a unified coordination logic for the differences in their time scales. There is a lack of clear engineering criteria for when the tap changer should operate, when power electronic compensation should be prioritized, when the compensation amount should be released, and how to avoid the compensation unit operating close to the capacity boundary for a long time. It is difficult to simultaneously consider voltage regulation effect, the number of mechanical actions, and the operational burden on the compensation unit. Fourth, existing multi-time-scale coordinated control focuses mainly on multi-device coordination at the distribution network level. Research on the coordinated control between the stepped voltage regulation unit and the stepless compensation unit within a single flexible on-load tap-changing transformer is insufficient, making it difficult to directly guide the design of device-level controllers for flexible on-load tap-changing transformers. Summary of the Invention

[0003] Purpose of the invention: In order to overcome the shortcomings of the existing technology, the present invention provides a control method for a flexible on-load tap-changing transformer based on multi-time-scale coordination. The method adopts a designed collaborative criterion strategy to coordinate the control of stepped voltage regulation on the slow time scale and stepless compensation on the fast time scale, thereby achieving multi-time-scale coordinated control of the controlled terminal voltage of the transformer.

[0004] Technical Solution: To achieve the above objectives, the present invention provides a control method for a flexible on-load tap-changing transformer based on multi-timescale coordination, comprising a main transformer, a tap changer voltage regulation unit, a power electronic compensation unit, a measurement and sampling unit, and a control unit. The tap changer voltage regulation unit performs stepped voltage regulation of the controlled terminal voltage of the main transformer by changing the tap position. The power electronic compensation unit outputs compensation to perform stepless compensation of the controlled terminal voltage of the main transformer. The measurement and sampling unit collects the controlled terminal voltage of the main transformer, the tap position of the tap changer voltage regulation unit, and the compensation output of the power electronic compensation unit in real time. The control unit generates tap position reconstruction instructions or continuous compensation instructions based on the data collected by the measurement and sampling unit using a collaborative criterion strategy. Based on the tap position reconstruction instructions or continuous compensation instructions, the control unit determines and selects a slow-timescale stepped voltage regulation model or a fast-timescale stepless compensation model to perform slow-timescale stepped voltage regulation or fast-timescale stepless compensation of the controlled terminal voltage of the main transformer, thereby achieving multi-timescale coordinated control.

[0005] Furthermore, the multi-timescale coordinated control of the control unit includes the following steps:

[0006] Step 1: Construct the equivalent voltage model of the controlled end using the controlled end equivalent modeling method.

[0007] Step 2: Construct a slow-time-scale stepped voltage regulation model based on the tap changer voltage regulation unit, and construct a fast-time-scale stepless compensation model based on the power electronic compensation unit.

[0008] Step 3: Perform time-scale processing on the data collected in real time by the measurement sampling unit, and calculate the current voltage deviation and the average voltage deviation under the current slow time scale window based on the equivalent voltage model of the controlled end.

[0009] Step 4: Based on the current voltage deviation, the average voltage deviation under the current slow time scale window, the compensation amount output by the current power electronic compensation unit, and the time interval between two adjacent gear actions, a collaborative criterion strategy is used to generate gear reconfiguration instructions or continuous compensation instructions respectively.

[0010] Step 5: When the control unit generates a gear reconfiguration command, it uses a slow-time-scale stepped voltage regulation model to perform slow-time-scale stepped voltage regulation on the controlled terminal voltage of the main transformer; when the control unit generates a continuous compensation command, it uses a fast-time-scale stepless compensation model to perform fast-time-scale stepless compensation on the controlled terminal voltage of the main transformer.

[0011] Furthermore, in step 1, the equivalent voltage model of the controlled end is constructed using the controlled end equivalent modeling method, and the calculation process is as follows:

[0012] ;

[0013] ;

[0014] In the formula, The controlled terminal voltage, This is the unregulated natural voltage. This indicates the tap position of the tap changer voltage regulating unit. This refers to the single-stage voltage adjustment step size of the tap changer voltage regulating unit. The compensation amount output by the power electronic compensation unit. The equivalent voltage of the upper-level power grid. and These are the equivalent resistance coefficient and the equivalent reactance coefficient of the line, respectively. The equivalent active power at the controlled end. The equivalent reactive power at the controlled end. This represents the equivalent impact variable of distributed power source fluctuations on the controlled-end voltage.

[0015] Furthermore, in step 2, a slow-time-scale stepped voltage regulation model is constructed based on the tap changer voltage regulation unit. The calculation process is as follows:

[0016] ;

[0017] In the formula, This is the lower limit of the tap position of the tap changer voltage regulating unit. This refers to the upper limit of the tap position of the tap changer voltage regulating unit. For the tap changer voltage regulation unit The gear position of a slow time window. This represents the tap changer adjustment range, with 'sat' indicating the limiting effect.

[0018] A fast-time-scale stepless compensation model is constructed based on power electronic compensation units; the calculation process is shown below:

[0019] ;

[0020] In the formula, The compensation amount output by the power electronic compensation unit (3) For tracking coefficients, This is a continuous compensation instruction.

[0021] Furthermore, in step 3, the current voltage deviation and the average voltage deviation under the current slow time scale window are calculated; the reference voltage of the controlled end is set. The current window controlled-end voltage is calculated based on the controlled-end equivalent voltage model. The current voltage deviation is then calculated based on the current window controlled-end voltage and the controlled-end reference voltage, as shown below:

[0022] ;

[0023] Set the slow time scale window length to Based on the slow time scale window length The average voltage deviation under the current slow time scale window is calculated based on the current voltage deviation; the calculation is shown below:

[0024] ;

[0025] In the formula, Let m be the average voltage deviation under the current m-th slow time scale window, where m is the current m-th slow time scale window.

[0026] Furthermore, in step 4, the current voltage deviation, the average voltage deviation under the current slow time scale window, the compensation amount output by the current power electronic compensation unit, and the time interval between two adjacent gear shifts are respectively compared with the set inner dead zone threshold. Outer trigger threshold Compensation soft threshold ratio and motion delay The comparison is performed to generate a gear reconfiguration command or a continuous compensation command; the calculation process is as follows:

[0027] ;

[0028] In the formula, Instructions generated for the control unit, This represents the current voltage deviation. This is the compensation amount output by the current power electronic compensation unit. This represents the average voltage deviation within the current slow timescale window. The time interval between two consecutive gear shifts. This represents the upper limit of the compensation output by the power electronic compensation unit.

[0029] when Then, a command to maintain the current control state is generated; when Then, a continuous compensation instruction is generated; when Then a gear reconfiguration instruction will be generated.

[0030] Furthermore, in step 5, a persistent deviation counter is defined. The persistent deviation counter The time interval between two adjacent gear shifts and the average voltage deviation under the current slow time scale window Respectively compared with the persistence deviation criterion and action delay and outer trigger threshold Compare and determine the tap changer adjustment amount of the tap changer unit. The value of ; when , and At that time, the tap changer voltage regulating unit is in the upshift position. The value is 1; when , and At that time, the tap changer voltage regulating unit is in downshift mode. The value is -1; otherwise... The value is set to 0; this sets the tap changer voltage regulation unit's range adjustment amount. Substituting the value into the slow-time-scale stepped voltage regulation model yields the stepped voltage regulation range. The tap changer voltage regulation unit is adjusted to the stepped voltage regulation range to perform slow-time-scale stepped voltage regulation on the controlled terminal voltage of the main transformer; the continuous deviation counter The calculation process is as follows:

[0031] ;

[0032] In the formula, The outer trigger threshold, This represents the average voltage deviation within the current slow timescale window.

[0033] Furthermore, in step 5, the continuous compensation command will be... Substituting the values ​​into the fast time-scale stepless compensation model yields the stepless compensation amount. The power electronic compensation unit outputs the stepless compensation amount to perform fast time-scale stepless compensation on the controlled terminal voltage of the main transformer; the continuous compensation command... The calculation process is as follows:

[0034] ;

[0035] ;

[0036] In the formula, This is the proportionality coefficient. The integral coefficient is... This represents the current voltage deviation. This is the reactive current command output by the control unit, and sat is for limiting.

[0037] Beneficial Effects: The control method for flexible on-load tap-changing transformers based on multi-timescale coordination of the present invention, through the coordinated cooperation of slow-timescale stepped voltage regulation and fast-timescale stepless compensation, expands the on-load tap-changing transformer from a discrete voltage regulation method relying solely on tap position switching to a composite voltage regulation method of stepped coarse adjustment and stepless fine adjustment, thereby improving the device's adaptability to voltage fluctuations in complex distribution networks. Based on the characteristics of voltage deviation changes at the controlled end, persistent voltage deviations are handled by slow-timescale stepped voltage regulation, while transient deviations caused by short-term disturbances such as photovoltaic cloud shading and impulsive load connections are preferentially suppressed by fast-timescale stepless compensation, improving the voltage regulation accuracy and dynamic response capability at the controlled end. The designed collaborative judgment strategy can effectively avoid malfunctions of tap changers in response to short-term disturbances, reduce frequent switching of mechanical switches, reduce contact wear and maintenance pressure, and extend the service life of on-load tap changers. By coordinating and controlling multiple time scales, the tap changer voltage regulation unit and the power electronic compensation unit can undertake voltage regulation tasks according to their respective appropriate time scales, thereby improving the overall voltage regulation performance of the flexible on-load tap-changing transformer without significantly increasing the power electronic compensation capacity. Attached Figure Description

[0038] Figure 1 This is a block diagram of a control method for a flexible on-load tap-changing transformer based on multi-timescale coordination. Detailed Implementation

[0039] The invention will now be further described with reference to the accompanying drawings.

[0040] like Figure 1 As shown, a control method for a flexible on-load tap-changing transformer based on multi-timescale coordination includes a main transformer 1, a tap changer voltage regulation unit 2, a power electronic compensation unit 3, a measurement and sampling unit 4, and a control unit 5. The tap changer voltage regulation unit 2 performs stepped voltage regulation of the controlled terminal voltage of the main transformer 1 by changing the tap position. The power electronic compensation unit 3 outputs compensation to perform stepless compensation of the controlled terminal voltage of the main transformer 1. The measurement and sampling unit 4 collects the controlled terminal voltage of the main transformer 1, the tap position of the tap changer voltage regulation unit 2, and the compensation output of the power electronic compensation unit 3 in real time, and inputs them to the control unit 5. The control unit 5 generates tap position reconstruction instructions or continuous compensation instructions based on the data collected by the measurement and sampling unit 4 using a collaborative criterion strategy. Based on the tap position reconstruction instructions or continuous compensation instructions, it determines whether to select a slow-timescale stepped voltage regulation model or a fast-timescale stepless compensation model to perform slow-timescale stepped voltage regulation or fast-timescale stepless compensation of the controlled terminal voltage of the main transformer 1, thereby realizing multi-timescale coordinated control.

[0041] The main transformer 1 performs conventional voltage transformation and power transmission functions; the tap changer unit 2 achieves discrete turns ratio regulation by changing the tap position and thus the tap position; the power electronic compensation unit 3 continuously corrects the controlled-end voltage by injecting compensation voltage in series; the measurement and sampling unit 4 collects the controlled-end voltage of the main transformer 1, the tap position of the tap changer unit 2, and the compensation output of the power electronic compensation unit 3 in real time; the control unit 5 implements unified and coordinated control of the controlled-end voltage, the tap position of the tap changer unit 2, and the compensation output of the power electronic compensation unit 3. From the perspective of operational responsibilities, the tap changer unit 2 is suitable for undertaking large-range, low-frequency steady-state voltage regulation tasks, while the power electronic compensation unit 3 is suitable for undertaking small-amplitude, rapidly changing dynamic regulation tasks; the two are not mutually exclusive, but rather, through the unified coordination of the control unit 5, the flexible on-load tap-changing transformer achieves a better overall effect in terms of steady-state voltage regulation capability, dynamic response speed, and mechanical operation costs.

[0042] Also includes K ck Bypass switch and DC-side energy storage unit; the primary winding of the main transformer 1 includes an Nm main winding, a converter energy extraction winding, and several segmented windings; the Nm main winding, several segmented windings, tap changer voltage regulating unit 2, K ck The bypass switch and the upstream power grid constitute the main circuit; the AC side of the series converter in the power electronic compensation unit 3 is electrically connected to K respectively. ck The two ends of the bypass switch and the AC side of the parallel-side converter in the power electronic compensation unit 3 are electrically connected to the two ends of the converter's energy harvesting winding, respectively; the DC side of the series-side converter, the DC side of the parallel-side converter, and the power supply terminals of the DC-side energy storage unit are all connected in parallel to C. dc The two ends of the bus capacitor. One end of the AC side of the series converter is electrically connected to one end of capacitor C2 and K through inductor L2. ck One end of the bypass switch is electrically connected to the other end of capacitor C2 and K on the AC side of the series converter. ck The other end of the bypass switch; one end of the AC side of the parallel-side converter is electrically connected to one end of the converter's energy extraction winding through the L1 inductor, and the other end of the AC side of the parallel-side converter is electrically connected to the other end of the converter's energy extraction winding.

[0043] One end of the Nm main winding is electrically connected to one end of the upstream power grid, and the other end of the Nm main winding is electrically connected to one end of the first segmented winding among several segmented windings; the other end of any segmented winding among several segmented windings is electrically connected to one end of the next segmented winding; the other end of the Nm main winding and the other ends of the Np1~Npn segmented windings together serve as several taps, which are electrically connected to K through several tap switches K0~Kn in the tap changer voltage regulating unit 2. ckOne end of the bypass switch, K ck The other end of the bypass switch is electrically connected to the other end of the upstream power grid; the two ends of the secondary winding of the main transformer 1 are respectively connected to the positive and negative terminals of the power supply of the downstream load.

[0044] In actual operation, intraday load shifts, long-term power flow deviations, and slow changes in upstream voltage typically manifest as slow-time-scale changes, while photovoltaic cloud shading, impulsive load connections, and local disturbances manifest as fast-time-scale changes. If only the tap changer unit 2 is used for stepped voltage regulation, its ability to track rapid disturbances is insufficient. If only the power electronic compensation unit 3 is used for continuous stepless compensation voltage regulation, the compensation amount will remain under high occupancy for extended periods when steady-state deviation persists. Therefore, a slow-time-scale stepped voltage regulation model and a fast-time-scale stepless compensation model are constructed. The slow-time-scale stepped voltage regulation model is responsible for steady-state voltage reconstruction, with the tap position of the tap changer unit 2 as the control variable. The fast-time-scale stepless compensation model is responsible for dynamic voltage fine-tuning, with the compensation amount output by the power electronic compensation unit 3 as the control variable. A designed collaborative criterion strategy is introduced to connect the two types of voltage regulation models, which can control the frequency of mechanical actions and the burden on the compensation device while ensuring voltage quality.

[0045] The multi-timescale coordinated control of the control unit 5 includes the following steps:

[0046] Step 1: Construct the equivalent voltage model of the controlled end using the controlled end equivalent modeling method.

[0047] Step 2: Construct a slow-time-scale stepped voltage regulation model based on tap changer unit 2, and a fast-time-scale stepless compensation model based on power electronic compensation unit 3. The tap position adjustment of tap changer unit 2 in the flexible on-load tap-changing transformer is defined as a slow-time-scale stepped voltage regulation control task, used to handle large-range, low-frequency, and continuous steady-state voltage reconstruction. The continuous compensation of power electronic compensation unit 3 is defined as a fast-time-scale stepless compensation control task, used to handle small-amplitude, rapidly changing dynamic voltage correction. By dividing the two types of voltage regulation resources into time scales, tap changer unit 2 mainly handles the continuous deviation of slowly changing voltage, while power electronic compensation unit 3 prioritizes suppressing the transient deviation of short-time disturbances, thereby achieving coordinated voltage regulation of mechanical coarse adjustment and power electronic fine adjustment.

[0048] Step 3: Perform time-scale processing on the data collected in real time by the measurement sampling unit 4, and calculate the current voltage deviation and the average voltage deviation under the current slow time scale window based on the equivalent voltage model of the controlled end.

[0049] Step 4: Based on the current voltage deviation, the average voltage deviation under the current slow time scale window, the compensation amount output by the current power electronic compensation unit 3, and the time interval between two adjacent gear actions, a collaborative criterion strategy is used to generate gear reconfiguration instructions or continuous compensation instructions respectively.

[0050] Step 5: When the control unit 5 generates a gear reconfiguration command, it uses a slow time-scale stepped voltage regulation model to perform slow time-scale stepped voltage regulation on the controlled terminal voltage of the main transformer 1; when the control unit 5 generates a continuous compensation command, it uses a fast time-scale stepless compensation model to perform fast time-scale stepless compensation on the controlled terminal voltage of the main transformer 1.

[0051] In step 1, to highlight the collaborative voltage regulation mechanism, the equivalent voltage model of the controlled end is constructed using the controlled end equivalent modeling method. The calculation process is as follows:

[0052] ;

[0053] Under single-branch equivalent and per-unit conditions, the calculation of the unregulated natural voltage is as follows:

[0054] ;

[0055] In the formula, This refers to the controlled terminal voltage, which is the controlled primary side voltage in the main transformer. This is the unregulated natural voltage. This indicates the tap position of tap changer unit 2. The single-stage voltage adjustment step size for tap changer voltage regulating unit 2, The compensation amount output by power electronic compensation unit 3. The equivalent voltage of the upper-level power grid. and These are the equivalent resistance coefficient and the equivalent reactance coefficient of the line, respectively. The equivalent active power at the controlled end. The equivalent reactive power at the controlled end. The variable representing the equivalent impact of distributed power source fluctuations on the controlled-end voltage; This reflects the discrete voltage reconstruction amount generated by stepped voltage regulation. The two parts together determine the final voltage level, reflecting the continuous compensation amount generated by the stepless compensation.

[0056] In step 2, a slow-time-scale stepped voltage regulation model is constructed based on the tap changer voltage regulation unit 2. The calculation process is as follows:

[0057] ;

[0058] In the formula, This is the lower limit of the tap position of tap changer unit 2. This is the upper limit of the tap position of tap changer unit 2. For tap changer voltage regulation unit 2 The gear position of a slow time window. The tap changer voltage regulation unit 2 represents the range adjustment amount, with 'sat' indicating the limiting effect. The discrete voltage regulation mechanism in the slow-time-scale stepped voltage regulation model is used to pull the controlled terminal voltage back to a reasonable operating range at a lower operating frequency, thereby releasing the stepless compensation capacity.

[0059] Considering that the power electronic compensation unit 3 typically uses an average value model to describe the output dynamics, the actual compensation output can be taken as a first-order tracking form; a fast time-scale stepless compensation model is constructed based on the power electronic compensation unit 3; the calculation process is shown below:

[0060] ;

[0061] In the formula, The compensation amount output by the power electronic compensation unit (3) For tracking coefficients, This is a continuous compensation command. In the fast time-scale stepless compensation model, the continuous control quantity, in addition to tracking the voltage deviation, should also take into account control smoothness and equipment operation constraints; therefore, the dynamic process of fast time-scale stepless compensation is constrained by both amplitude limiting operation and first-order tracking.

[0062] In step 3, the current voltage deviation and the average voltage deviation under the current slow time scale window are calculated; the reference voltage of the controlled end is set. The current window controlled-end voltage is calculated based on the controlled-end equivalent voltage model. The current voltage deviation is then calculated based on the current window controlled-end voltage and the controlled-end reference voltage, as shown below:

[0063] ;

[0064] Set the slow timescale window length to Based on the slow time scale window length The average voltage deviation under the current slow time scale window is calculated based on the current voltage deviation; the calculation is shown below:

[0065] ;

[0066] In the formula, Let m be the average voltage deviation under the current m-th slow time scale window, where m is the current m-th slow time scale window.

[0067] In step 4, the current voltage deviation, the average voltage deviation under the current slow time scale window, the compensation amount output by the current power electronic compensation unit 3, and the time interval between two adjacent gear shifts are respectively compared with the set inner dead zone threshold. Outer trigger threshold Compensation soft threshold ratio and motion delay The comparison is performed to generate a gear reconfiguration command or a continuous compensation command; the calculation process is as follows:

[0068] ;

[0069] In the formula, Instructions generated for control unit 5 This represents the current voltage deviation. This is the compensation amount output by the current power electronic compensation unit 3. This represents the average voltage deviation within the current slow timescale window. The time interval between two consecutive gear shifts. The upper limit of the compensation amount output by power electronic compensation unit 3; inner dead zone threshold. The outer trigger threshold is used to suppress control chattering caused by measurement noise and minor fluctuations; its value should not exceed the small disturbance bandwidth within the allowable voltage deviation of the distribution network. The value used to determine whether gear reconfiguration is needed should take into account both the single-gear voltage regulation step size and the compensation unit capacity; compensation soft threshold ratio. This is used to ensure that the continuously variable compensation does not prematurely enter a long-term high-occupancy operating range; action delay. The transient deviation used to distinguish between short-term disturbances and continuous deviations is too small, which will cause the tap changer to operate frequently, while too large a deviation will reduce the steady-state recovery speed.

[0070] when If so, a command to maintain the current control state is generated, ensuring that minor deviations do not trigger voltage regulation; when Then, a continuous compensation command is generated to suppress moderate deviations primarily through stepless compensation; when Then, a gear reconfiguration command is generated. When the voltage deviation continues to exceed the outer trigger threshold or the compensation amount output by the power electronic compensation unit 3 approaches the capacity boundary, the stepped voltage regulation is triggered to complete the steady-state reconfiguration.

[0071] In the collaborative criterion strategy, an inner dead zone threshold is constructed. Outer trigger threshold Compensation soft threshold ratio and motion delay The collaborative control logic with shared constraints ensures that minor deviations do not trigger voltage regulation, moderate deviations are preferentially suppressed by stepless compensation, and only when the voltage deviation continuously exceeds the outer trigger threshold or the compensation output of the power electronic compensation unit 3 approaches the capacity boundary are stepped voltage regulation triggered to complete steady-state reconfiguration. This avoids frequent mechanical switch operation and prevents the power electronic compensation unit 3 from operating at high occupancy for extended periods. Only when the voltage deviation evolves into a continuous deviation or the power electronic compensation unit 3 operates close to its upper limit for an extended period are slow-time-scale stepped voltage regulation models used to trigger the tap changer voltage regulation unit 2 for tap position reconfiguration. This effectively avoids malfunctions of the tap changer in response to short-term disturbances, reduces the number of tap changer operations, and minimizes the cost of mechanical operation.

[0072] The collaborative criterion strategy follows the principle of "fast first, slow second; fine first, coarse third," meaning it first performs fast-timescale stepless compensation followed by slow-timescale stepped voltage regulation, and first performs fine voltage regulation followed by coarse voltage regulation. First, a fast-timescale stepless compensation model is used to quickly suppress real-time deviations, preventing malfunctions of the tap changer in tap changer unit 2 due to instantaneous disturbances. When the voltage deviation evolves into a persistent deviation or the power electronic compensation unit 3 operates close to its upper limit for an extended period, a slow-timescale stepped voltage regulation model is used to adjust the deviation, restoring the circuit system to a new steady-state operating range. After the slow-timescale stepped voltage regulation model completes the switchover, the control unit guides the compensation amount of the power electronic compensation unit back to the intermediate margin zone, preventing the power electronic compensation unit 3 from operating at high occupancy or bias for extended periods, preserving its regulation capability for subsequent disturbances, and improving the operational reliability and continuous regulation capability of the power electronic compensation unit 3. Consistent with the time-domain coordination approach of slow-timescale discrete taps and block-timescale continuous control quantities in multi-feeder scenarios, the collaborative criterion strategy helps to balance stability and response speed.

[0073] In step 5, when the control unit 5 generates a gear reconfiguration command, a slow-time-scale stepped voltage regulation model is used to perform slow-time-scale stepped voltage regulation on the controlled terminal voltage of the main transformer 1; a continuous deviation counter is defined. The persistent deviation counter The time interval between two adjacent gear shifts and the average voltage deviation under the current slow time scale window Respectively compared with the persistence deviation criterion and action delay and outer trigger threshold Compare and determine the tap changer adjustment amount of tap changer unit 2. The value of ; when , and At that time, tap changer unit 2 is in the upshift position. The value is 1; when , and At that time, tap changer unit 2 is in downshift mode. The value is -1; otherwise... The value is set to 0; the tap changer voltage regulating unit 2 adjusts the range. Substituting the value into the slow-time-scale stepped voltage regulation model yields the stepped voltage regulation range. The tap changer voltage regulation unit 2 is adjusted to the stepped voltage regulation range to perform slow-time-scale stepped voltage regulation on the controlled terminal voltage of the main transformer 1. The continuous deviation counter... The calculation process is as follows:

[0074] ;

[0075] In the formula, The outer trigger threshold, This represents the average voltage deviation within the current slow timescale window.

[0076] In step 5, when the control unit 5 generates a continuous compensation command, a fast-time-scale stepless compensation model is used to perform fast-time-scale stepless compensation on the controlled terminal voltage of the main transformer 1; the continuous compensation command is then... Substituting the stepless compensation amount into the fast time-scale stepless compensation model, the power electronic compensation unit 3 outputs the stepless compensation amount to perform fast time-scale stepless compensation on the controlled terminal voltage of the main transformer 1; the continuous compensation command The calculation process is as follows:

[0077] ;

[0078] ;

[0079] In the formula, This is the proportionality coefficient. The integral coefficient is... This represents the current voltage deviation. The reactive current command is output by the control unit (5), and sat is the limiting process.

[0080] When the voltage deviation changes from a transient deviation to a continuous deviation, or when the compensation output of the power electronic compensation unit 3 approaches the capacity boundary, using the power electronic compensation unit 3 for stepless compensation at this time will cause the power electronic compensation unit 3 to maintain a bias state for a long time, weakening the subsequent dynamic adjustment capability; therefore, the control unit 5 generates a tap reconfiguration command and uses a slow-time-scale stepped voltage regulation model to perform slow-time-scale stepped voltage regulation on the controlled terminal voltage of the main transformer 1; after completing the slow-time-scale stepped voltage regulation, the control unit 5 guides the compensation output of the power electronic compensation unit 3 to fall back to the intermediate margin region, so that... ,in It realizes the margin recovery of power electronic compensation unit 3, and retains the regulation capability for subsequent disturbances.

[0081] After completing the slow-time-scale stepped voltage regulation, i.e. after the tap changer voltage regulation unit 2 completes the switch position state, the stepless compensation output of the power electronic compensation unit 3 is guided back to the intermediate margin zone, so that the tap changer voltage regulation unit 2 undertakes the task of reconstructing the new steady-state voltage reference, and the power electronic compensation unit 3 retains sufficient dynamic adjustment margin again. This can reduce the number of tap changer operations in the tap changer voltage regulation unit 2 while ensuring the voltage quality of the controlled end, reduce the long-term operating pressure of the power electronic compensation unit 3, and improve the comprehensive voltage regulation capability of the flexible on-load tap-changing transformer under complex distribution network conditions.

[0082] In this invention, the tap changer voltage regulation unit is responsible for releasing long-term steady-state deviations, ensuring the device has a large voltage regulation range; the power electronic compensation unit is responsible for quickly correcting instantaneous disturbances, improving voltage regulation speed; and the collaborative criterion strategy is used to avoid duplicate actions or improper substitution between the two, thereby improving the overall voltage regulation performance of the flexible on-load tap-changing transformer without significantly increasing the power electronic compensation capacity. Before the tap changer operates in the tap changer voltage regulation unit 2, the power electronic compensation unit 3 quickly corrects the voltage deviation, reducing the voltage fluctuation amplitude caused by short-term disturbances. Then, the steady-state voltage reference is reconstructed through the tap changer in the tap changer voltage regulation unit, avoiding long-term bias of the compensation output of the power electronic compensation unit, thereby improving the voltage regulation accuracy and dynamic response capability under all-day operating conditions.

[0083] This invention is applicable to various distribution network operation scenarios, such as distributed photovoltaic power output fluctuations, intraday load shifts, impulsive load access, and slow voltage changes in the upstream grid. For short-term rapid disturbances, the fast-timescale stepless compensation model can quickly suppress voltage deviations at the controlled end. For persistent low or high voltage deviations, the slow-timescale stepped voltage regulation model can reconstruct a new steady-state operating point. Through the synergy of these two models, the flexible on-load tap-changing transformer can maintain good voltage regulation performance under conditions where steady-state deviations and rapid disturbances coexist, thus improving its adaptability under complex operating conditions.

[0084] In this invention, directly measurable or calculable quantities such as the controlled terminal voltage, the tap position of the tap changer, and the compensation amount output by the power electronic compensation unit are used as control inputs, and an inner dead zone threshold is used. Outer trigger threshold Compensation soft threshold ratio and motion delay The parameters are used to construct the collaborative judgment strategy control logic; the physical meaning of the above parameters is clear, which makes it easy to set them in combination with the allowable deviation of the distribution network voltage, the action characteristics of the tap changer and the capacity of the power electronic compensation unit. This can provide an implementable technical solution for the design, prototype debugging and engineering application of flexible on-load tap-changing transformer controllers, and facilitate engineering implementation and controller parameter setting.

[0085] The above description is merely a preferred embodiment of the present invention. Those skilled in the art can make several modifications and optimizations based on the above disclosure without departing from the basic principles described above. These modifications and optimizations should be considered within the scope of protection as understood by the present invention.

Claims

1. A control method for a flexible on-load tap-changing transformer based on multi-time-scale coordination, characterized in that: The system includes a main transformer (1), a tap changer voltage regulation unit (2), a power electronic compensation unit (3), a measurement and sampling unit (4), and a control unit (5). The tap changer voltage regulation unit (2) adjusts the controlled terminal voltage of the main transformer (1) in stages by changing the tap position. The power electronic compensation unit (3) outputs compensation to perform stepless compensation on the controlled terminal voltage of the main transformer (1). The measurement and sampling unit (4) collects the controlled terminal voltage of the main transformer (1), the tap position of the tap changer voltage regulation unit (2), and the compensation output of the power electronic compensation unit (3) in real time. The control unit (5) generates a tap position reconstruction command or a continuous compensation command based on the data collected by the measurement and sampling unit (4) using a collaborative criterion strategy. Based on the tap position reconstruction command or the continuous compensation command, it selects a slow time scale stepped voltage regulation model or a fast time scale stepless compensation model to perform slow time scale stepped voltage regulation or fast time scale stepless compensation on the controlled terminal voltage of the main transformer (1), thereby realizing multi-time scale coordinated control.

2. The control method for a flexible on-load tap-changing transformer based on multi-time-scale coordination according to claim 1, characterized in that: The multi-timescale coordinated control of the control unit (5) includes the following steps: Step 1: Construct the equivalent voltage model of the controlled end using the controlled end equivalent modeling method; Step 2: Construct a slow-time-scale stepped voltage regulation model based on the tap changer voltage regulation unit (2), and construct a fast-time-scale stepless compensation model based on the power electronic compensation unit (3); Step 3: Perform time-scale processing on the data collected in real time by the measurement sampling unit (4), and calculate the current voltage deviation and the average voltage deviation under the current slow time scale window based on the equivalent voltage model of the controlled end; Step 4: Based on the current voltage deviation, the average voltage deviation under the current slow time scale window, the compensation amount output by the current power electronic compensation unit (3), and the time interval between two adjacent gear actions, a collaborative criterion strategy is used to generate gear reconstruction instructions or continuous compensation instructions respectively. Step 5: When the control unit (5) generates a gear reconfiguration command, it uses a slow time-scale stepped voltage regulation model to perform slow time-scale stepped voltage regulation on the controlled terminal voltage of the main transformer (1); when the control unit (5) generates a continuous compensation command, it uses a fast time-scale stepless compensation model to perform fast time-scale stepless compensation on the controlled terminal voltage of the main transformer (1).

3. The control method for a flexible on-load tap-changing transformer based on multi-time-scale coordination according to claim 2, characterized in that: In step 1, the equivalent voltage model of the controlled end is constructed using the controlled end equivalent modeling method. The calculation process is as follows: ； ； In the formula, The controlled terminal voltage, This is the unregulated natural voltage. The tap position of the tap changer unit (2) is as follows: The single-stage voltage adjustment step size of the tap changer voltage regulating unit (2) is as follows: The compensation amount output by the power electronic compensation unit (3) The equivalent voltage of the upper-level power grid. and These are the equivalent resistance coefficient and the equivalent reactance coefficient of the line, respectively. The equivalent active power at the controlled end. The equivalent reactive power at the controlled end. This represents the equivalent impact variable of distributed power source fluctuations on the controlled-end voltage.

4. The control method for a flexible on-load tap-changing transformer based on multi-time-scale coordination according to claim 2, characterized in that: In step 2, a slow-time-scale stepped voltage regulation model is constructed based on the tap changer voltage regulation unit (2), and the calculation process is as follows: ； In the formula, The lower limit of the tap position of the tap changer unit (2) is the tap position of the tap changer unit (2). This is the upper limit of the tap position of the tap changer unit (2). For the tap changer voltage regulating unit (2) The gear position of a slow time window. The tap position adjustment amount is the tap changer unit (2), and sat is the limiting amount. A fast-time-scale stepless compensation model is constructed based on the power electronic compensation unit (3); the calculation process is shown below: ； In the formula, The compensation amount output by the power electronic compensation unit (3) For tracking coefficients, This is a continuous compensation instruction.

5. The control method for a flexible on-load tap-changing transformer based on multi-time-scale coordination according to claim 2, characterized in that: In step 3, the current voltage deviation and the average voltage deviation under the current slow time scale window are calculated; the reference voltage of the controlled end is set. The current window controlled-end voltage is calculated based on the controlled-end equivalent voltage model. The current voltage deviation is then calculated based on the current window controlled-end voltage and the controlled-end reference voltage, as shown below: ； Set the slow timescale window length to Based on slow time scale window length The average voltage deviation under the current slow time scale window is calculated based on the current voltage deviation; the calculation is shown below: ； In the formula, Let m be the average voltage deviation under the current m-th slow time scale window, where m is the current m-th slow time scale window.

6. The control method for a flexible on-load tap-changing transformer based on multi-time-scale coordination according to claim 2, characterized in that: In step 4, the current voltage deviation, the average voltage deviation under the current slow time scale window, the compensation amount output by the current power electronic compensation unit (3), and the time interval between two adjacent gear shifts are respectively compared with the set inner dead zone threshold. Outer trigger threshold Compensation soft threshold ratio and motion delay The comparison is performed to generate a gear reconfiguration command or a continuous compensation command; the calculation process is as follows: ； In the formula, Instructions generated for the control unit (5), This represents the current voltage deviation. The compensation amount output by the current power electronic compensation unit (3) is... This represents the average voltage deviation within the current slow timescale window. The time interval between two consecutive gear shifts. The upper limit of the compensation amount output by the power electronic compensation unit (3); when Then, a command to maintain the current control state is generated; when Then, a continuous compensation instruction is generated; when Then a gear reconfiguration instruction will be generated.

7. The control method for a flexible on-load tap-changing transformer based on multi-time-scale coordination according to claim 2, characterized in that: In step 5, a persistent deviation counter is defined. The persistent deviation counter The time interval between two adjacent gear shifts and the average voltage deviation under the current slow time scale window Respectively compared with the persistence deviation criterion and action delay and outer trigger threshold Compare and determine the tap changer adjustment amount of the tap changer unit (2). The value of ; when , and At that time, the tap changer regulating unit (2) is in the upshift position. The value is 1; when , and At that time, the tap changer regulating unit (2) is in downshift mode. The value is -1; otherwise... The value is set to 0; the tap changer voltage regulating unit (2) adjusts the range of the tap position. The value of is substituted into the slow-time-scale stepped voltage regulation model to obtain the stepped voltage regulation gear state. The tap changer voltage regulation unit (2) is adjusted to the stepped voltage regulation gear state to perform slow-time-scale stepped voltage regulation on the controlled terminal voltage of the main transformer (1); the continuous deviation counter The calculation process is as follows: ； In the formula, The outer trigger threshold, This represents the average voltage deviation within the current slow timescale window.

8. The control method for a flexible on-load tap-changing transformer based on multi-time-scale coordination according to claim 2, characterized in that: In step 5, the continuous compensation command will be... Substituting the stepless compensation amount into the fast time-scale stepless compensation model, the power electronic compensation unit (3) outputs the stepless compensation amount to perform fast time-scale stepless compensation on the controlled terminal voltage of the main transformer (1); the continuous compensation command The calculation process is as follows: ； ； In the formula, This is the proportionality coefficient. The integral coefficient is... This represents the current voltage deviation. The reactive current command is output by the control unit (5), and sat is the limiting process.

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