Energy storage type flexible on-load tap changing transformer based on power control and model prediction control method thereof

Abstract

The invention discloses an energy storage type flexible on-load tap-changing transformer based on power control and a model prediction control method thereof, and belongs to the technical field of transformer topology and control. The transformer comprises a multi-winding transformer, a plurality of on-load tap-changers, a power electronic converter and an energy storage module; a primary side winding of the energy storage type flexible on-load tap changing transformer based on power control comprises a main winding, a plurality of segmented windings and an isolation winding. Wherein the main winding and the plurality of segmented windings are respectively connected with the on-load tap-changer, the on-load tap-changer acts to cut off or access a primary side winding of the energy storage type flexible on-load tap-changing transformer, and the isolation winding provides energy for the power electronic converter and is connected with the input side of the power electronic converter; the power electronic converter is a back-to-back power electronic converter; according to the invention, the energy storage module is connected to the direct current side of the power electronic converter, so that the problem of insufficient power quality control capability of the flexible on-load tap-changing transformer is solved.

Description

Technical Field

[0001] This invention belongs to the field of transformer topology and control technology, specifically relating to a power control-based energy storage flexible on-load tap-changing transformer and its model predictive control method. Background Technology

[0002] In existing technologies, after photovoltaic power generation is connected to the DC side of a power electronic converter, the electrical energy generated by the photovoltaic must be output in real time through a parallel-side converter. The photovoltaic power generation unit must generate electricity during the sunshine period, and without a buffer energy storage unit, power control is limited.

[0003] Existing flexible on-load tap-changing transformers can control the output voltage of the power electronic converter to achieve a compensated voltage with a specific phase angle and amplitude. This, combined with coordinated control of the power electronic converter and the on-load tap changer, enables continuous voltage regulation, solving the problem of traditional on-load tap-changing transformers only allowing for discrete voltage regulation. However, to increase the voltage output range of the series-side converter or even the inductor current range of the parallel-side converter in a flexible on-load tap-changing transformer, the only solution is to increase the overall power rating of the power electronic converter.

[0004] Given that series-side converters struggle to quickly calculate and control output voltage under various conditions, and that strong power coupling exists between parallel-side and series-side converters, making direct control of the parallel-side converter based on instantaneous power difficult, there is an urgent need to address the problem of improving power quality without increasing the input voltage of the power electronic converter. The technical objective of this invention is to expand the voltage output range of the series-side converter or the inductor current range of the parallel-side converter in a flexible on-load tap-changing transformer without increasing the overall power rating of the power electronic converter. Summary of the Invention

[0005] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0006] A power-controlled energy storage flexible on-load tap-changing transformer includes: a multi-winding transformer T1 and multiple on-load tap changers K0~K n Power electronic converters and energy storage modules;

[0007] The primary winding of a power-controlled energy storage flexible on-load tap-changing transformer includes the main winding N. 1m Multiple segmented windings N 11 ~N 1n 1. Isolation winding N3, where n represents the number of segmented windings; 2. Main winding N 1m Multiple segmented windings N 11 ~N 1n Connected to on-load tap changers K0~K respectivelyn On-load tap changers K0~K n The action enables the disconnection or connection of the primary winding of the energy storage type flexible on-load tap-changing transformer. The isolation winding N3 provides energy to the power electronic converter and is connected to the input side of the power electronic converter.

[0008] The power electronic converter is a back-to-back power electronic converter; the output of the power electronic converter is coupled in series to the main circuit of the primary winding of the energy storage type flexible on-load tap-changing transformer based on power control through the isolation transformer T2, and the energy storage module is connected to the DC side of the power electronic converter.

[0009] The power electronic converter consists of parallel-side and series-side converters. The parallel-side converter is filtered by the grid-connected inductor L1, and the series-side converter is filtered by a low-pass filter composed of the filter inductor L2 and the filter capacitor C2. The output of the power electronic converter is coupled in series to the main circuit of the primary winding of the energy storage flexible on-load tap-changing transformer based on power control through the isolation transformer T2.

[0010] A model predictive control method for a power-controlled energy storage flexible on-load tap-changing transformer is provided, comprising: predictive control of the parallel-side converter model and model predictive control of the series-side converter.

[0011] Predictive control of the parallel-side converter model includes: real-time acquisition of the parallel-side converter input voltage. With input current and will , After being transformed into α-axis and β-axis components, the real-time active power of the parallel-side converter is obtained through instantaneous power calculation. With reactive power DC bus voltage reference value The actual value of DC bus voltage u dc After the difference calculation, the voltage is passed through a PI controller, and the output of the PI controller is compared with the actual value u of the DC bus voltage. dc Multiply the values ​​and then add them to the SOC feedforward value of the energy storage module to obtain the active reference power P of the parallel-side converter. ref The modulation function is optimized using a model-predictive instantaneous power control scheme. Then, the switching signal of the parallel-side converter is generated by SPWM control;

[0012] Model predictive control of the series-side converter includes: acquiring the output voltage u of the series-side converter. c2 In the The value of the sampling interval and the first sampling interval The values ​​of each sampling interval are used to obtain u. c2 In the The values ​​of each sampling interval are then used to optimize the modulation function using a model-predicted instantaneous power control scheme. Finally, the switching signal for the series-side converter is generated through SPWM control.

[0013] The present invention has the following beneficial effects:

[0014] This invention solves the problem of insufficient power quality management capability of flexible on-load tap-changing transformers by connecting the energy storage module to the DC side of the power electronic converter;

[0015] This invention reconstructs the power flow mechanism inside the energy storage flexible on-load tap-changing transformer and constructs a multi-path power transmission topology, solving the problems of single power flow direction and limited operational flexibility in traditional structures.

[0016] This invention achieves inductor current control of the parallel-side converter by employing model predictive control based on direct power control;

[0017] This invention achieves capacitor voltage control of the series-side converter by adjusting the compensation voltage across the filter capacitor using a model predictive control method. Attached Figure Description

[0018] Figure 1 This is a single-phase circuit topology for an energy storage type FOVRT;

[0019] Figure 2 Power flow diagram for energy storage FOVRT;

[0020] Figure 3 Predictive control block diagram for the parallel-side converter model;

[0021] Figure 4 The predictive control block diagram for the series-side converter model. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0023] This invention provides a model predictive control method for an energy storage flexible on-load tap-changing transformer based on power control.

[0024] The system topology of the present invention is described in detail below:

[0025] The single-phase circuit topology of the power-controlled energy storage flexible on-load voltage regulating transformer (FOVRT) of this invention is as follows: Figure 1 As shown, it includes a multi-winding transformer T1 and multiple on-load tap changers K0~K n Power electronic converters and energy storage modules; the primary side of the energy storage-type FOVRT is connected to renewable energy or the external power grid, and the secondary side is connected to various loads of the distribution network.

[0026] The primary winding of an energy storage FOVRT consists of the main winding N 1m Segmented winding N 11 ~N 1n (n represents the number of segmented windings), consisting of isolation winding N3, where the main winding N 1m Multiple segmented windings N 11 ~N 1n Connected to on-load tap changers K0~K respectively n On-load tap changers K0~K n The operation can disconnect or connect the primary winding of the energy storage FOVRT. N2 is the secondary winding of the energy storage FOVRT. The isolation winding N3 provides energy to the power electronic converter and is connected to the input side of the power electronic converter. N4 and N5 are the primary and secondary sides of the isolation transformer T2, respectively, and are connected to the output side of the power electronic converter and the primary main circuit of T1.

[0027] The power electronic converter is a back-to-back power electronic converter, consisting of parallel and series converters. The parallel converter is filtered by a grid-connected inductor L1, and the series converter is filtered by a low-pass filter composed of a filter inductor L2 and a filter capacitor C2. The output of the power electronic converter ( Figure 1 The power electronic converter includes parallel and series converters (N3 winding is the input and N4 winding is the output). The main circuit is coupled in series to the primary winding of the energy storage type FOVRT through the isolation transformer T2. The energy storage module is connected to the DC side of the power electronic converter.

[0028] like Figure 1 As shown, both the parallel-side converter and the series-side converter are single-phase full-bridge circuits. S1~S4 are parallel-side devices, and S5~S8 are series-side devices, all of which are IGBTs (Insulated Gate Bipolar Transistors) with reverse recovery diodes. The positive and negative output terminals of the parallel-side converter are connected to the positive and negative terminals of N3, respectively, and the two positive terminals are directly connected to L1. The positive and negative output terminals of the series-side converter are connected to L2 and C2, respectively, and then connected to the positive and negative terminals of the primary side of T2 (N4 winding).

[0029] Figure 1 in,u S i S These represent the input voltage and current on the primary side of the energy storage FOVRT, u L i L These represent the voltage and current on the secondary side (load side) of the energy storage FOVRT, respectively. gw For N 11 ~N 1n The winding voltage, u in i L1 These are the input voltage and input current of the parallel-side converter, u. pa u se These are the grid-side voltages of the parallel-side converter and the series-side converter, respectively, u dc The DC bus voltage, u c2 u cm This refers to the output voltage of the series-side converter and the secondary voltage of the isolation transformer T2. es i dp i ds These represent the DC port currents of the energy storage unit, the parallel-side converter, and the series-side converter, respectively. L2 For the current flowing through inductor L2, i so i is the output current of the series-side converter. dc For the DC-side capacitor C of the power electronic converter dc The current. The circuit equations for the parallel and series sides of the energy storage FOVRT converter are obtained through Kirchhoff's laws, as shown in equation (2).

[0030] (2)

[0031] For ease of explanation, the switching functions of the parallel and series converters are defined. and As shown in equation (3), the circuit equations of the DC side of the parallel and series converters in the energy storage FOVRT are obtained, as shown in equation (4).

[0032] (3)

[0033] (4)

[0034] in, For time, , Switching devices for parallel-side converters , Open, , Switching devices for series-side converters , Open.

[0035] The following is a power flow analysis:

[0036] In the proposed energy storage-type FOVRT, the parallel-side converter achieves reactive power compensation by controlling the grid-connected current, thereby improving the power factor. The series-side converter compensates for voltage fluctuations and regulates reactive power by adjusting the amplitude and phase angle of the output voltage. The energy storage module can enhance the compensation capability of the corresponding converters (parallel-side and series-side converters). Since the energy storage module is connected to both the parallel-side and series-side converters, there are power interaction and distribution issues between the energy storage module and both the parallel-side and series-side converters.

[0037] The power flow diagram of the energy storage FOVRT is as follows: Figure 2 As shown, the arrows indicate the flow of active and reactive power, respectively. The arrow direction is the reference direction, and the active and reactive power losses of the multi-winding transformer T1 and the isolation transformer T2 are ignored.

[0038] The active and reactive power balance equations for an energy storage-type FOVRT can be derived as equations (5) and (6), where, It is the ratio of the fluctuating grid voltage to the rated voltage.

[0039] (5)

[0040] (6)

[0041] in, , These represent the active and reactive power flowing from the primary side to the secondary side of the multi-winding transformer T1. , These represent the active and reactive power on the load side, respectively. , These represent the active and reactive power flowing from the primary side to the secondary side of the multi-winding transformer T1, respectively. , These represent the active and reactive power flowing from isolation transformer T2 to the secondary side, respectively. , These represent the active and reactive power flowing from the parallel-side converter to the DC side of the power electronic converter, respectively. , These represent the active and reactive power flowing from the series-side converter to the isolation transformer T2, respectively. , These represent the active power flowing from the energy storage unit to the parallel-side converter and the series-side converter, respectively. This represents the ratio of the voltage drop to the rated voltage of the power grid.

[0042] Equation (7) is the power expression for the DC side of the power electronic converter. Substituting equation (4) into equation (7) yields the power relationship for the DC side of the power electronic converter, as shown in equation (8), where, This refers to the power on the DC side of the power electronic converter.

[0043] (7)

[0044] (8)

[0045] Substituting equation (2) into equation (8) yields equation (9) for the DC-side power of the power electronic converter, where... This indicates the active power output of the energy storage module.

[0046] (9)

[0047] Ignoring the high-frequency current component on C2, since L1 and L2 are both purely inductive, we can obtain equation (10). Substituting equation (10) into equation (9) yields equation (11).

[0048] (10)

[0049] (11)

[0050] Then, substituting equation (5) into equation (11) yields the DC-side power of the power electronic converter. Grid power (active power flowing from the primary side to the secondary side of multi-winding transformer T1) ) and active power on the load side The relationship between them.

[0051] (12)

[0052] in, The active power output by the energy storage module. .

[0053] The following section introduces model predictive control methods for parallel and series converters.

[0054] Predictive control method for parallel-side converter model:

[0055] The parallel-side converter controls the grid-connected inductor current. To achieve power control, this invention employs model prediction based on instantaneous power theory. (Input voltage of the parallel-side converter) With input current The fundamental component in the αβ coordinate system can be expressed as equation (13).

[0056] (13)

[0057] in, For the input voltage of the parallel-side converter Axial components, This is the rated peak value of the input voltage of the parallel-side converter. Angular frequency, For time, For the input voltage of the parallel-side converter Axial components, For the input current of the parallel-side converter Axial components, This is the rated peak value of the input current of the parallel-side converter. The phase angle between the input current and the input voltage of the parallel-side converter. For the input current of the parallel-side converter Axial components.

[0058] Based on instantaneous power theory, the real-time active power of the parallel-side converter With reactive power It can be expressed as equation (14), and by differentiating equation (14), we can obtain , Over time The relationship between the changes is shown in equation (15).

[0059] (14)

[0060] (15)

[0061] Combining equations (2) and (13) Differentiating the αβ axis components yields equation (16). Substituting equations (13) and (16) into equation (15) yields equation (17):

[0062] (16)

[0063] (17)

[0064] in, For the grid-side voltage of the parallel-side converter Axial components, For the grid-side voltage of the parallel-side converter Axial components.

[0065] Based on equation (17), the parallel-side converter can be obtained at the first... Active power in each sampling interval and reactive power As shown in equation (18).

[0066] (18)

[0067] In this invention, a variable is added after it. Indicates the first This variable, for each sampling interval, is added Indicates the first This variable, for each sampling interval, is added Indicates the first The variable is taken at sampling intervals, where, For the time variable in the modulation function, The sampling time is the time interval between the current sampled signal and the next sampled signal.

[0068] According to model prediction theory, the cost function must be related to active power and reactive power; the cost function of model predictive control for parallel-side converters... Defined as equation (19), where, and They represent the first Active and reactive reference power of the parallel-side converter in each sampling interval.

[0069] (19)

[0070] Cost function of model predictive control for parallel-side converter Perform differential calculations with respect to the modulated signal, so that Minimize. The β-axis component is used to estimate the virtual quantity of instantaneous power, hence equation (20) is achieved. right Taking the partial derivative and setting it equal to zero, we can derive the following: The value is as shown in equation (21).

[0071] (20)

[0072] (twenty one)

[0073] in, This is the real-time active power reference value for the parallel-side converter.

[0074] Optimized control variables As the input to the parallel-side converter, the model predictive control of the parallel-side converter can be realized, which can be expressed as equation (22), where, Let (22) represent the modulation function. Substituting equation (22) into equation (23) yields the optimized modulation function. As shown in equation (23).

[0075] (twenty two)

[0076] (twenty three)

[0077] This is the DC side voltage.

[0078] Figure 3 The predictive control block diagram for the parallel-side converter model.

[0079] Model predictive control of the parallel-side converter includes: real-time acquisition of the input voltage of the parallel-side converter. With input current and will , After being transformed into α-axis and β-axis components, the real-time active power of the parallel-side converter is obtained through instantaneous power calculation. With reactive power .

[0080] DC bus voltage reference value The actual value of DC bus voltage u dc After the difference calculation, the voltage is passed through a PI controller, and the output of the PI controller is compared with the actual value u of the DC bus voltage. dc Multiply the values ​​and then add them to the SOC (State of Charge) feedforward value of the energy storage module to obtain the active reference power P of the parallel-side converter. ref The SOC feedforward value is the sum of the current SOC value and the reference value. The value obtained after subtraction and proportional adjustment. To achieve unity power factor, the reactive power reference power Q... ref It is set to zero.

[0081] As shown in equation (23), the modulation function is optimized using a model-predictive instantaneous power control scheme. Subsequently, the switching signal of the parallel-side converter is generated by SPWM (Sinusoidal Pulse Width Modulation).

[0082] The model predictive control method for the series-side converter is as follows:

[0083] The series-side converter achieves a series compensation voltage with controllable output amplitude and phase angle by controlling the voltage across capacitor C2. This invention uses a model predictive control method for the series-side converter to optimize the modulation function.

[0084] Using the backward difference method to apply the current formula for inductor L2 in equation (2), we can obtain the first... Predicted value of inductor current for each sampling interval By applying the forward difference method to the voltage formula of capacitor C2 in equation (2), we can obtain the first... Predicted value of capacitor voltage at each sampling interval ,in, It is the switching cycle.

[0085] (twenty four)

[0086] (25)

[0087] Transforming equation (25) yields the result in the first... The output current of the series-side converter at each sampling interval With the filter inductor current The relationship is shown in equation (26), and it is assumed that the output current of the series-side converter is within one switching cycle. The values ​​within remain unchanged, as shown in equation (27).

[0088] (26)

[0089] (27)

[0090] Combining equations (24) to (27), we can obtain the first... Predicted output voltage of the series-side converter at each sampling interval As shown in (28).

[0091] (28)

[0092] Cost function of model predictive control for series-side converter The definition is as shown in equation (29), where, Indicates the first Reference value of the output voltage of the series-side converter for each sampling interval.

[0093] (29)

[0094] Similarly, for the cost function Perform differential calculations with respect to the modulated signal to make the cost function To achieve minimization. Equation (30) is obtained through the cost function. right Taking the partial derivative and setting it equal to zero, we can derive the following: value As in equation (31):

[0095] (30)

[0096] (31)

[0097] Optimized control variables As the input to the series-side converter, model predictive control can be achieved, as shown in equation (32), where, This represents the modulation function. Substituting equation (32) into equation (31), we can obtain the optimized modulation function. As shown in (33).

[0098] (32)

[0099] (33)

[0100] Figure 4 Here is the predictive control block diagram for the series-side converter model, where u S_m It is the amplitude of grid voltage fluctuation, U S_m It is the rated mains voltage amplitude, SOC min SOC max These are the minimum and maximum values ​​under normal operating conditions of the energy storage battery cell. It is the output voltage u of the series-side converter. c2 The maximum value of θ; uL θ iL The phase angles of the secondary voltage and current on the secondary side of the multi-winding transformer T1 are θ. Δ It is the impedance angle θ on the secondary side of the multi-winding transformer T1. pa_max It is the maximum phase angle that the series-side converter can compensate for.

[0101] In this scheme, the voltage reference value u output by the series-side converter c2ref From the reference amplitude and reference phase angle It consists of two parts. Reference phase angle Based on the impedance angle θ of the secondary side of the multi-winding transformer T1 Δ Determine, when θ Δ <θ pa_max At this time, there is no need for a series-side converter to change the output voltage phase angle. =0; when θ Δ ≥θ pa_max At that time, Set to (θ) pa_max -θ Δ Reference amplitude According to the voltage fluctuation amplitude u S_m There are two cases related to the SOC state:

[0102] When the grid voltage drops, u S_m S_m The maximum amplitude of the output voltage of the series-side converter is determined by judging the SOC state. ​When SOC <SOC min hour, Unchanged; when SOC ≥ SOC min hour, It can be expanded to k times the original size.

[0103] When the grid voltage rises, u S_m >U S_m The maximum amplitude of the output voltage of the series-side converter is determined by judging the SOC state. When SOC <SOC max hour, It can be expanded to k times the original value; when SOC ≥ SOC max hour, constant.

[0104] The above steps can be used to synthesize the reference value of the output voltage of the series-side converter. The output voltage u of the series-side converter is then acquired. c2 The The sampling interval and the first Substituting the values ​​of each sampling interval into equation (28) yields u. c2 In the The values ​​of each sampling interval are then used to optimize the modulation function by using the model to predict the instantaneous power control scheme through equation (33). Finally, the switching signal for the series-side converter is generated through SPWM control.

[0105] The energy storage module of this invention can be directly connected to the power distribution network near the FOVRT equipment via a grid-connected inverter. This solution can realize all the functions of the parallel-side converter of the energy storage FOVRT of this invention. However, it cannot change the internal power flow path of the existing FOVRT, cannot increase the compensation capability of the circuits on both sides of the converter, and will increase the cost of a grid-connected inverter.

[0106] The above description is merely an embodiment of the present invention and does not limit the scope of the present invention. Any equivalent structural or procedural transformations made based on the content of the present invention specification and drawings, or direct or indirect applications in other related system fields, are similarly included within the protection scope of the present invention.

[0107] The contents not described in detail in this specification are existing technologies known to those skilled in the art.

Claims

1. A power control-based energy storage flexible on-load tap-changing transformer, characterized in that, include: Multi-winding transformer T1, multiple on-load tap changers K0~K n Power electronic converters and energy storage modules; The primary winding of a power-controlled energy storage flexible on-load tap-changing transformer includes the main winding N. 1m Multiple segmented windings N 11 ~N 1n 1. Isolation winding N3, where n represents the number of segmented windings; 2. Main winding N 1m Multiple segmented windings N 11 ~N 1n Connected to on-load tap changers K0~K respectively n On-load tap changers K0~K n The action enables the disconnection or connection of the primary winding of the energy storage type flexible on-load tap-changing transformer. The isolation winding N3 provides energy to the power electronic converter and is connected to the input side of the power electronic converter. The power electronic converter is a back-to-back power electronic converter; the output of the power electronic converter is coupled in series to the main circuit of the primary winding of the energy storage type flexible on-load tap-changing transformer based on power control through the isolation transformer T2, and the energy storage module is connected to the DC side of the power electronic converter. The power electronic converter consists of parallel-side and series-side converters. The parallel-side converter is filtered by the grid-connected inductor L1, and the series-side converter is filtered by a low-pass filter composed of the filter inductor L2 and the filter capacitor C2. The output of the power electronic converter is coupled in series to the main circuit of the primary winding of the energy storage flexible on-load tap-changing transformer based on power control through the isolation transformer T2.

2. The energy storage flexible on-load tap-changing transformer based on power control according to claim 1, characterized in that, Both the parallel-side converter and the series-side converter are single-phase full-bridge circuits.

3. The energy storage flexible on-load tap-changing transformer based on power control according to claim 2, characterized in that, The circuit equations for the parallel-side converter and the series-side converter are as follows: （2） in, For time, , These are the grid-side voltages of the parallel-side converter and the series-side converter, respectively. This is the output voltage of the series-side converter. This refers to the output current of the series-side converter. The input voltage of the parallel-side converter. This is the input current of the parallel-side converter. This is the current flowing through inductor L2.

4. The energy storage flexible on-load tap-changing transformer based on power control according to claim 3, characterized in that, The relationship between the power on the DC side of the power electronic converter, the active power flowing from the primary side to the secondary side of the multi-winding transformer T1, and the active power on the load side is as follows: （12） in, This refers to the power on the DC side of the power electronic converter. The active power output by the energy storage module. This refers to the active power on the load side. The ratio of the voltage drop to the rated voltage of the power grid. This refers to the active power flowing from the primary side to the secondary side of the multi-winding transformer T1.

5. A model predictive control method for a power-controlled energy storage flexible on-load tap-changing transformer, used in any one of claims 1 to 4, characterized in that, include: Model predictive control for parallel-side converters and model predictive control for series-side converters; Predictive control of the parallel-side converter model includes: real-time acquisition of the parallel-side converter input voltage. With input current and will , After being transformed into α-axis and β-axis components, the real-time active power of the parallel-side converter is obtained through instantaneous power calculation. With reactive power DC bus voltage reference value The actual value of DC bus voltage u dc After the difference calculation, the voltage is passed through a PI controller, and the output of the PI controller is compared with the actual value u of the DC bus voltage. dc Multiply the values ​​and then add them to the SOC feedforward value of the energy storage module to obtain the active reference power P of the parallel-side converter. ref The modulation function is optimized using a model-predictive instantaneous power control scheme. Then, the switching signal of the parallel-side converter is generated by SPWM control; Model predictive control of the series-side converter includes: acquiring the output voltage u of the series-side converter. c2 In the The value of the sampling interval and the first sampling interval The values ​​of each sampling interval are used to obtain u. c2 In the The values ​​of each sampling interval are then used to optimize the modulation function using a model-predicted instantaneous power control scheme. Finally, the switching signal for the series-side converter is generated through SPWM control.

6. The model predictive control method for energy storage flexible on-load tap-changing transformers based on power control according to claim 5, characterized in that, In the predictive control of the parallel-side converter model, the real-time active power of the parallel-side converter is obtained through instantaneous power calculation. With reactive power : （14） in, For the input voltage of the parallel-side converter Axial components, For the input voltage of the parallel-side converter Axial components This is the rated peak value of the input current of the parallel-side converter. For the input current of the parallel-side converter Axial components, For the input current of the parallel-side converter Axial components.

7. The model predictive control method for energy storage flexible on-load tap-changing transformers based on power control according to claim 6, characterized in that, In predictive control of the parallel-side converter model, the parallel-side converter in the first... Active power in each sampling interval and reactive power for: （18） Add after the variable Indicates the first This variable, for each sampling interval, is added Indicates the first The variable is taken at sampling intervals, where, For time variables in the modulation function; Cost function of model predictive control for parallel-side converter for: （19） in, and The first Active and reactive reference power of the parallel-side converter at each sampling interval, Sampling time, Angular frequency, This is the rated peak value of the input voltage of the parallel-side converter. For the grid-side voltage of the parallel-side converter Axial components, For the grid-side voltage of the parallel-side converter Axial components.

8. The model predictive control method for energy storage flexible on-load tap-changing transformers based on power control according to claim 7, characterized in that, In predictive control of the parallel-side converter model, the optimized modulation function for: （23） in, This is the DC side voltage.

9. The model predictive control method for energy storage flexible on-load tap-changing transformers based on power control according to claim 5, characterized in that, In model predictive control of a series-side converter, the output voltage of the series-side converter is acquired. No. The value of the sampling interval and the first sampling interval Substituting the values ​​of each sampling interval into equation (28) yields... In the The value of each sampling interval Then, the modulation function is optimized by using model prediction instantaneous power control scheme through equation (33). ; （28） for In the The value of each sampling interval, for In the The value of each sampling interval, Sampling time, For the series-side converter The grid-side voltage at each sampling interval; Cost function of model predictive control for series-side converter Defined as: （29） in, For the first The reference value of the output voltage of the series-side converter at each sampling interval. for In the The value of each sampling interval.

10. The model predictive control method for energy storage flexible on-load tap-changing transformers based on power control according to claim 9, characterized in that, In the model predictive control of a series-side converter, the optimized modulation function for: （33） in, This is the DC side voltage.

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