A T-type non-isolated transformer medium-voltage flexible power flow transfer device and power control method

Abstract

This invention proposes a transformerless medium-voltage power flow transfer device composed of a capacitor switching circuit and a series active circuit. This effectively solves the problems of high cost, large size, and significant operating losses associated with traditional Unified Power Controllers (UPFCs) and back-to-back converters due to the inclusion of isolation transformers. Furthermore, if only a series active circuit is used for active power transmission, reactive power control is difficult, resulting in a low system power factor when there is a large difference in voltage amplitude between the sending and receiving ends. The proposed device, through the coordinated control of a floating module on the sending end and the passive capacitor switching, brings the voltage amplitudes on both sides closer together, significantly suppressing reactive power deviations during active power transmission and improving power quality during power flow control. Finally, the device can perform power flow transfer control regardless of whether the sending-end voltage amplitude is higher or lower than the receiving-end voltage amplitude, offering high flexibility.

Description

Technical Field

[0001] This invention relates to a low-cost, transformerless medium-voltage power flow transfer device that combines passive capacitor circuitry and series active circuitry, applicable to flexible power flow transfer in medium-voltage distribution networks within power systems. The proposed device can complete power flow transfer without a transformer, and it can perform power flow transfer control regardless of whether the sending-end voltage amplitude is higher or lower than the receiving-end voltage amplitude. Its low-cost, miniaturized, and low-loss design fully meets the economic, efficient, and flexible requirements of medium-voltage distribution networks in flexible power flow control. Background Technology

[0002] With the large-scale grid connection and application of distributed new energy sources such as wind power and photovoltaics, the power flow characteristics of distribution networks have undergone fundamental changes, completely breaking the inherent unidirectional power flow pattern of traditional distribution networks and transforming into a bidirectional power flow network. This significantly increases the complexity of power flow regulation. At the same time, the increasing prevalence of new power loads such as electric vehicle charging stations and data centers has led to higher and more stringent requirements from users regarding power supply reliability and power quality. As a core link connecting upper and lower levels in the power system, the operational efficiency, regulation flexibility, power supply reliability, and economic rationality of the medium-voltage distribution network directly determine the overall operational performance of the entire power system.

[0003] Traditional power flow transfer schemes primarily rely on power equipment such as UPFCs and back-to-back converters to achieve reasonable power flow transfer. However, these devices generally require transformers to achieve voltage level adaptation, electrical isolation, and stable power transmission between the sending and receiving ends. This approach not only suffers from high equipment purchase costs and large space requirements, but the transformer connection also increases system energy losses, affecting operational efficiency. Furthermore, when there is a significant voltage difference between the sending and receiving ends, using series active circuits for power flow transfer cannot achieve independent control of active and reactive power; they are coupled together. While active power is being delivered to the receiving end, a large amount of reactive power is also transmitted. Therefore, developing a partial-capacity medium-voltage power flow transfer device that does not require transformer support and balances adjustment flexibility and operational economy has become an urgent need to solve the current power flow control dilemma in distribution networks, achieving low-cost, high-efficiency, and flexible power flow control goals.

[0004] This invention proposes a transformerless medium-voltage power flow transfer device composed of a capacitor switching circuit and a series active circuit. This effectively solves the problems of high cost, large size, and significant operating losses associated with traditional Unified Power Controllers (UPFCs) and back-to-back converters due to the inclusion of isolation transformers. Furthermore, if only a series active circuit is used for active power transmission, reactive power control is difficult, resulting in a low system power factor when there is a large difference in voltage amplitude between the sending and receiving ends. The proposed device, through the coordinated control of a floating module on the sending end and the passive capacitor switching, brings the voltage amplitudes on both sides closer together, significantly suppressing reactive power deviations during active power transmission and improving power quality during power flow control. Finally, the device can perform power flow transfer control regardless of whether the sending-end voltage amplitude is higher or lower than the receiving-end voltage amplitude, offering high flexibility. Summary of the Invention

[0005] This invention proposes a transformerless medium-voltage power flow transfer device composed of a capacitor switching circuit and a series active circuit. This effectively solves the problems of high cost, large size, and significant operating losses associated with traditional Unified Power Controllers (UPFCs) and back-to-back converters due to the inclusion of isolation transformers. Furthermore, if only a series active circuit is used for active power transmission, reactive power control is difficult, resulting in a low system power factor when there is a large difference in voltage amplitude between the sending and receiving ends. The proposed device, through the coordinated control of a floating module on the sending end and the passive capacitor switching, brings the voltage amplitudes on both sides closer together, significantly suppressing reactive power deviations during active power transmission and improving power quality during power flow control. Finally, the device can perform power flow transfer control regardless of whether the sending-end voltage amplitude is higher or lower than the receiving-end voltage amplitude, offering high flexibility.

[0006] The objective of this invention is achieved through the following technical solution: An electrical connection structure for a T-type non-isolation transformer medium-voltage flexible power transfer device and power control method is characterized by comprising: taking phase A as an example, measuring the voltage on the g1 side of the power grid using the voltage sensor according to claim 1. v g1(a) Voltage at point POC1 between the two floating modules v poc1(a) Floating module capacitor voltage v N,dc,1(a) ~ v N,dc,n(a) , v M,dc,1(a) ~ v M,dc,m(a) Device output port voltage v N(a) and v M(a) ,poc2 voltagev poc1(a) The current sensor according to claim 1 measures the line transmission current. i N(a) and i M(a) ; The device receives the voltage on the g1 side of the power grid measured by the voltage sensor. v g1(a) ,poc1 voltage v poc1(a) ,poc2 voltage v poc1(a) and device output port voltage v N(a) and v M(a) and the line transmission current measured by the current sensor. i N(a) and i M(a) The voltage amplitude of POC1 is obtained through the amplitude calculation process. E poc1(a) POC2 voltage amplitude E poc2(a) and line current amplitude I N(a) and I M(a) The phase of voltage POC1 is obtained through a phase-locked loop. i poc1(a) voltage phase of poc2 i poc2(a) Output voltage i N(a) and i M(a) ; The capacitor switching control obtains the POC1 voltage amplitude through a voltage sensor and amplitude calculation. E poc1(a) With POC2 voltage amplitude E poc2(a) Without the capacitor engaged, if the voltage amplitude at point POC1 is higher than that at point POC2, and the difference between the two voltage amplitudes reaches a certain level, the capacitor is engaged based on the deviation value. This causes the capacitor and the floating module 1 to divide the voltage, reducing the voltage amplitude at point POC1 to approach that at point POC2. If the voltage amplitude at point POC1 is lower than that at point POC2, and the difference between the two voltage amplitudes reaches a certain level, the deviation is controlled by the controller. G Q(s) is adjusted, and the required number of capacitors is obtained through reactive power calculation. In conjunction with the floating module 1, the voltage at point POC1 is raised to approach the voltage at point POC2. The corresponding number of capacitors are connected when the voltage across the thyristor module is zero. If the voltage amplitude at POC1... E poc1(a) With POC2 voltage amplitude E poc2(a) If the amplitudes are close, power flow transfer control will be implemented directly.

[0007] At the voltage amplitude of poc1 E poc1(a) Approximately the voltage amplitude of POC2 E poc2(a) Then, the power transfer controller determines the active power flow reference that needs to be transferred. P ref(a) For the g1-side floating module, the current reference amplitude under this reference is obtained through the power control circuit. After obtaining the current reference amplitude, multiply the current reference amplitude by the desired impedance value to obtain the reactive component of the reference voltage. The active component of the reference voltage This is achieved through voltage regulation control of the DC side of the g1-side suspended module. After obtaining the active and reactive components of the reference voltage, the instantaneous value of the reference voltage of the g1-side suspended module is obtained through inverse transformation. v N,ref The reference angular frequency is obtained through the relative relationship between the voltage amplitudes of grid g1 and grid g2. If the voltage amplitude of g1 is higher than that of g2, the reference angular frequency lags behind the phase of the line current. i N(a) A 90-degree angle makes the levitation module capacitive; if the voltage amplitude of g1 is lower than the voltage amplitude of g2, then the reference angular frequency leads the phase of the line current. i N(a) The 90-degree angle gives the floating module a sensual feel.

[0008] In addition to controlling the entire suspension module, voltage equalization control is also required for each individual suspension module. By comparing the DC-side voltage of a single suspension capacitor on the g1 side with the DC-side equalization voltage value of the suspension module on the g1 side, a reference voltage for voltage equalization control of the suspension module is obtained. By superimposing the instantaneous value of the reference voltage, the modulation voltage of the suspension module on the g1 side is finally obtained. .

[0009] During the power flow conversion control process, the DC-side voltage regulation of the suspended module is based on the phase difference between points poc1 and poc2. i M Using this as a reference, the phase deviation value is obtained by controlling the DC side voltage of the levitation module to stabilize. α Phase deviation affects the phase of the reference current. (The last part, "90°-", appears to be an error and is left untranslated.)α Then with one-half i M By superimposing these values, the phase information of the reference current can be obtained. i M,ref Through the active reference that needs to be transferred P ref With actual power transferred P poc2 The amplitude information of the reference current is obtained, and the reference current is obtained by combining the obtained amplitude and phase information. The reference current is then used to obtain the reference voltage through a current controller.

[0010] In addition to controlling the entire suspension module, voltage equalization control is also required for each individual suspension module. By comparing the DC-side voltage of a single suspension capacitor on the g2 side with the DC-side equalization voltage value of the suspension module on the g2 side, a reference voltage for voltage equalization control of the suspension module is obtained. By superimposing the instantaneous value of the aforementioned reference voltage, the modulation voltage of the suspension module on the g2 side is finally obtained. .

[0011] Compared with the prior art, the beneficial effects of the technical solution of the present invention are: 1. Using the circuit structure proposed in this invention, the voltage at point POC1 is controlled by switching the inverter circuit at the sending end with the passive capacitor. If the voltage amplitude at the sending end is higher than that at the receiving end, the voltage at point POC1 is reduced; if the voltage amplitude at the sending end is lower than that at the receiving end, the voltage at point POC1 is increased. This device has good flexibility.

[0012] 2. It does not require the use of a transformer and has normal power flow transfer capability, overcoming the disadvantages of traditional UPQC which requires the use of a transformer to stabilize DC bus voltage, resulting in high cost and further increased losses. It is suitable for low-cost, high-efficiency, and flexible power flow control in medium-voltage distribution networks. Attached Figure Description

[0013] Figure 1 A three-phase electrical connection structure diagram of a T-type non-isolation transformer medium-voltage flexible power transfer device provided in an embodiment of the present invention; Figure 2 This is a single-phase topology diagram of a T-type non-isolation transformer medium-voltage flexible power flow transfer device provided in an embodiment of the present invention; Figure 3 This is an algorithm diagram of a T-type non-isolation transformer medium-voltage flexible power transfer device system provided in an embodiment of the present invention; Figure 4 This is a block diagram of the controller components of a T-type non-isolation transformer medium-voltage flexible power transfer device provided in an embodiment of the present invention; Figure 5 This is a schematic diagram of the voltage and current vectors of the system under different voltage amplitudes on the g1 side, provided in an embodiment of the present invention. Figure 6 This document describes the operation of the medium-voltage flexible power transfer device provided in the embodiments of the present invention under different working conditions. Figure 7 The system power flow conversion response curve provided in the embodiment of the present invention; Figure 8 This is a graph showing the active power, reactive power, voltage, and line current response at point POC2 provided in this embodiment of the invention. Figure 9 This is a circuit current flowing through the g1 side suspension module and the phase angle response curve of the voltage vector across the suspension module provided in an embodiment of the present invention; Figure 10 This is the DC-side voltage response curve of the g1-side floating module provided in this embodiment of the invention; Figure 11 This is the DC-side voltage response curve of the g2-side floating module provided in this embodiment of the invention; Figure 12 This is a schematic diagram of the power conversion device and power system structure provided in the embodiments of the present invention. Detailed Implementation

[0014] To make the objectives, technical solutions, and advantages of this application clearer, the application will be further described in detail below with reference to the accompanying drawings. The specific operational methods in the method embodiments can also be applied to the device embodiments or system embodiments. It should be noted that in the description of this application, "at least one" refers to one or more, where "multiple" refers to two or more. Therefore, in the embodiments of this application, "multiple" can also be understood as "at least two". "And / or" describes the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone. Additionally, the character " / ", unless otherwise specified, generally indicates that the preceding and following related objects have an "or" relationship. Furthermore, it should be understood that in the description of this application, terms such as "first" and "second" are only used for distinguishing the descriptive purpose and should not be construed as indicating or implying relative importance or order. The invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0015] The present invention proposes a T-type non-isolation transformer medium-voltage flexible power transfer device and control strategy, which includes the following steps: Please refer to Figure 1 An electrical connection structure for a T-type non-isolation transformer medium-voltage flexible power transfer device is characterized by comprising: a suspension module, a suspension capacitor, a capacitor bank, a thyristor module, a current sensor, a voltage sensor, and controllers for each module. There are two suspended modules. One end of suspended module 1 is connected to the medium-voltage power grid 1 via a first current sensor, and the other end is connected to suspended module 2. A capacitor bank is connected to the middle of the two suspended modules via a thyristor module. A first voltage sensor is installed at both ends of the thyristor module, and a second voltage sensor measures the potential of the midpoint between the two suspended modules and ground, i.e., the potential at point POC1. The DC side of each suspended module is connected to a suspended capacitor. A third voltage sensor is installed on each suspended capacitor. The other end of suspended module 2 is connected to the output port of the medium-voltage flexible power transfer device via a second current sensor. A fourth voltage sensor measures the potential of the output port of the medium-voltage flexible power transfer device and ground, i.e., the potential at point POC2. The output port of the medium-voltage flexible power transfer device is connected to the medium-voltage line. The medium-voltage flexible power transfer device relies on the switching of the suspended modules and capacitors to boost the voltage and transfer power.

[0016] Please refer to Figure 2 A T-type non-isolation transformer medium-voltage flexible power transfer device and its control strategy, comprising: Step S201: Taking phase A as an example, the voltage on the g1 side of the power grid is measured using the voltage sensor according to claim 1. v g1(a) Voltage at point POC1 between the two floating modules v poc1(a) Floating module capacitor voltage v N,dc,1(a) ~ v N,dc,n(a) , v M,dc,1(a) ~ v M,dc,m(a) Device output port voltage v N(a) and v M(a) ,poc2 voltage v poc1(a) The current sensor according to claim 1 measures the line transmission current. i N(a) and i M(a) .

[0017] Please refer to Figure 3 The controller is used to receive voltage and current information measured by the aforementioned sensors and to receive power flow regulation commands issued by the power grid dispatch center. The device receives the grid g1-side voltage measured by the voltage sensor. v g1(a) ,poc1 voltage v poc1(a) ,poc2 voltage v poc1(a) and device output port voltage vN(a) and v M(a) and the line transmission current measured by the current sensor. i N(a) and i M(a) The voltage amplitude of POC1 is obtained through the amplitude calculation process. E poc1(a) POC2 voltage amplitude E poc2(a) and line current amplitude I N(a) and I M(a) The phase of voltage POC1 is obtained through a phase-locked loop. i poc1(a) voltage phase of poc2 i poc2(a) Output voltage i N(a) and i M(a) .

[0018] Step S202: The capacitor switching control obtains the voltage amplitude of poc1 through a voltage sensor and amplitude calculation. E poc1 With POC2 voltage amplitude E poc2 Without capacitors connected, if the voltage amplitude at point POC1 is higher than that at point POC2, and the difference between the two voltage amplitudes reaches a certain level, capacitors are connected based on the deviation value. This causes the capacitors and the floating module 1 to divide the voltage, reducing the voltage amplitude at point POC1 to approach that at point POC2. If the voltage amplitude at point POC1 is lower than that at point POC2, and the difference between the two voltage amplitudes reaches a certain level, the required number of capacitors is calculated based on the deviation and reactive power. These capacitors, in conjunction with the floating module 1, raise the voltage at point POC1 to approach that at point POC2. The corresponding number of capacitors are connected when the voltage across the thyristor module is zero.

[0019] Step S203: The g2-side power transfer regulating controller determines the active power reference to be transferred. P ref The line current reference is obtained through the power control. d Axis component, then with POC1 voltage phase i poc1 Phase with POC2 voltage i poc2 deviation i M Based on the reference value of the floating module voltage v ref Control it to match the line current.i M Keep it vertical. During this process, the phase deviation value is... α The voltage vector of the floating module fluctuates around the line current. i M It swings left and right from a vertical position. Since phase deviation affects the phase of the reference current, it is possible to achieve this by swinging 90°... α and i M The reference current phase is obtained by superimposing 1 / 2 of the phases. f Then, by performing a coordinate transformation on the dq-axis current reference, the instantaneous current reference value can be obtained, which is then controlled by the current controller. G i,M ( s The line current is adjusted in a closed loop to obtain the reference voltage. v M,ref .

[0020] Step S204: The proposed control must ensure the stability of the DC side voltage of a single floating module, and the average DC side voltage of the floating module on side g2 is... V M,dc,ave , and the actual DC side voltage V M,dc,i The difference is calculated, and further processing is performed to obtain the phase-to-phase voltage equalization regulation voltage. v M,i,ref .

[0021] Please refer to Figure 4 The present invention provides a block diagram of the controller components of a T-type non-isolation transformer medium-voltage flexible power transfer device, comprising: 3. The capacitor switching control of a T-type non-isolation transformer medium-voltage flexible power transfer device according to claim 2, characterized in that: The capacitor switching control obtains the POC1 voltage amplitude through a voltage sensor and amplitude calculation. E poc1 With POC2 voltage amplitude E poc2 If the voltage amplitude at point POC1 is higher than that at point POC2 and the difference between the two voltage amplitudes is significant enough without the capacitor being engaged, the capacitor is engaged based on the deviation value. This causes the capacitor to divide the voltage with the floating module 1, reducing the voltage amplitude at point POC1 to be closer to that at point POC2. (1) In the formula, Z ref This represents the equivalent impedance value of the floating module on the g1 side. If the voltage amplitude at point POC1 is lower than that at point POC2, and the difference between the two voltage amplitudes reaches a certain level, the deviation is controlled by the controller.G Q (s) is adjusted, and the required number of capacitors is obtained through reactive power calculation. In conjunction with the floating module 1, the voltage at point POC1 is raised to be close to the voltage at point POC2. The corresponding number of capacitors are connected when the voltage across the thyristor module is zero. (2) (3) (4) (5) In the formula, k p,Q , k i,Q These are the proportional and integral coefficients of the reactive power closed-loop controller, respectively. L The inductance value is the value of the filter inductor. X For line reactance, X L For filtering inductive reactance, X C For filter capacitive reactance, C For the required capacitor size, N c represents the number of capacitors connected. C 0 represents the size of a single capacitor, and Ceil indicates rounding up.

[0022] 4. The capacitor switching control of a T-type non-isolation transformer medium-voltage flexible power transfer device according to claim 2, characterized in that: The number of capacitors to be switched is calculated, and the corresponding capacitor switch flag is set. After the flag is set, if the voltage sensor preset at both ends of the thyristor measures that the voltage across the thyristor is zero after the flag is set, then the capacitor is switched into the system.

[0023] For the floating module on the g1 side of the power grid, the power transfer regulator determines the required power transfer. P ref The DC component of the line current on the g1 side of the power grid is obtained through power control, as shown in the following formula: (6) In the formula, k p,pN , k i,pN These are the proportional and integral coefficients of the power closed-loop controller on the g1 side, respectively. This represents the DC component of the line current on the g1 side of the power grid. With the expected impedance value of the levitation module Z ref Multiplying, we get the g1 side suspension module.d Shaft reference voltage .

[0024] 5. The power flow transfer control method for a T-type non-isolation transformer medium-voltage flexible power flow transfer device according to claim 2, characterized in that: The DC-side voltage stabilization controller on the g1 side receives the DC-side voltage amplitude of the floating capacitor on the g1 side. V N,dc,ref The g1-side suspension module is obtained through DC voltage control. q Shaft reference voltage As shown in the following formula: (7) In the formula, k p,VN , k i,N These are the proportional and integral coefficients of the DC voltage regulator on the g1 side, respectively. V N,dc,ave This represents the average voltage value of the DC bus voltage of the floating module on the g1 side.

[0025] 6. The power flow transfer control method for a T-type non-isolation transformer medium-voltage flexible power flow transfer device according to claim 2, characterized in that: The reference voltage phase generation controller on the g1 side generates the line current on the g1 side based on the relationship between the voltage amplitude on the g1 side and the voltage amplitude on the g2 side. i N The phase is processed to generate the reference voltage phase for the floating module on side g1. If the voltage amplitude on side g1 is lower than that on side g2, it is desirable for floating module 1 to be inductive. Therefore, the reference phase is as shown in the following formula: (8) In the formula, i N For the phase of the line current on the g1 side, i N,ref The reference voltage phase for the floating module; If the voltage amplitude on side g1 is higher than that on side g2, then it is desirable for the floating module 1 to be capacitive. Therefore, the reference phase is as shown in the following formula: (9) , , i N,ref The three factors generate the reference voltage for the g1-side suspension module. v N,ref .

[0026] 7. The method for phase-to-phase voltage equalization regulation and control of a T-type non-isolation transformer medium-voltage flexible power transfer device according to claim 2, characterized in that: The proposed control needs to ensure the stability of the DC-side voltage of a single floating module, and the average DC-side voltage of the floating module on side g1 should be calculated. V N,dc,ave , and the actual DC side voltage V N,dc,i The difference is calculated, and further processing is performed to obtain the phase-to-phase voltage equalization regulation voltage. v N,i,ref : (10) v N,ref and v N,i,ref The final reference voltage of the levitation module is generated by superposition. .

[0027] 8. The method for regulating and controlling the power transfer on the g2 side of a T-type non-isolation transformer medium-voltage flexible power transfer device according to claim 2, characterized in that: The g2-side power transfer regulator controller determines the active power reference that needs to be transferred. P ref The line current reference is obtained through the power control. d The axial components are shown in the following formula: (11) In the formula, k p,Mp , k i,Mp These are the proportional and integral coefficients of the power closed-loop controller on the g2 side, respectively. Transmit current to the g2 side line d Axis reference, E * indicates the system's rated voltage; With the voltage phase of poc1 i poc1 Phase with POC2 voltage i poc2 deviation i M Based on the reference value of the floating module voltage v ref Control it to match the line current. i M Keep it vertical. During this process, the phase deviation value is... α The voltage vector of the floating module fluctuates around the line current. i MIt swings left and right from a vertical position. Since phase deviation affects the phase of the reference current, it is possible to achieve this by swinging 90°... α and i M The reference current phase is obtained by superimposing 1 / 2 of the phases. f Then, by performing a coordinate transformation on the dq-axis current reference, the instantaneous current reference value can be obtained: (12) (13) Then, through the current controller G i,M ( s The line current is adjusted in a closed loop to obtain the reference voltage. v M,ref； (14) In the formula, k p,Mi and k r,Mi These are the proportional coefficient and resonant coefficient of the current controller, respectively. oh b For controller bandwidth, oh 0 is the reference frequency.

[0028] 9. The DC-side voltage stabilization control method for a single suspended module of a T-type non-isolation transformer medium-voltage flexible power transfer device according to claim 2, characterized in that: The proposed control needs to ensure the stability of the DC-side voltage of a single floating module, and the average DC-side voltage of the floating module on side g2 should be calculated. V M,dc,ave , and the actual DC side voltage V M,dc,i The difference is calculated, and further processing is performed to obtain the phase-to-phase voltage equalization regulation voltage. v M,i,ref : (15) In the formula, i M This refers to the phase of the line current on the g2 side.

[0029] 10. The control method for a T-type non-isolation transformer medium-voltage flexible power transfer device according to claim 2, characterized in that: The g2-side suspension module controller obtains the feedforward compensation voltage by measuring the difference between the instantaneous voltage at point POC1 and point POC2, and then superimposes the aforementioned reference voltage. v M,ref and phase equalization voltage regulation v M,i,refObtain the converter modulation voltage : (16) Figure 5 The diagrams below illustrate the voltage and current vectors under the control strategy of the medium-voltage flexible power flow transfer device provided in this embodiment of the invention. (a) is a diagram of the voltage and current vectors for power flow transfer without boosting the voltage of POC1. At this time, the angle between the line current and the voltage vector of POC2 is large, and a large amount of reactive power is transmitted while transmitting active power. (b)(c)(d) are diagrams of power flow transfer after boosting the voltage of POC1 by connecting capacitors. At this time, the power factor is high, and the angle between the line current vector and the device voltage vector fluctuates around 90°, maintaining the stability of the average voltage fluctuation of the DC side of the suspended module.

[0030] Figure 6 The following describes the different operating conditions of the T-type non-isolation transformer medium-voltage flexible power transfer device provided in the embodiments of the present invention: Operating condition 1: grid g1 is 1.05pu∠10°, grid g2 is 1.0pu∠0°, and the power transfer command is 0.5MW; Operating condition 2: grid g1 amplitude is 0.95pu∠10°, grid g2 is 1.0pu∠0°, and the power transfer command is 0.5MW.

[0031] in Figure 7 The power flow response curve during system operation shows that the system transmits 0.5MW of active power within 0.5s to 1.0s. At 1.0s, the grid voltage on the g1 side jumps from 1.05pu to 0.95pu. However, within 100ms of the jump, the active power transmitted by the system returns to stability, and the average active power transmitted by the floating modules on both sides is 0 throughout the entire process.

[0032] Figure 8 The simulation diagram shows the active power, reactive power, voltage amplitude, and line current amplitude at point POC2 during system operation. During this process, the power factor is high.

[0033] Figure 9 This is a simulation diagram showing the phase angle of the DC bus voltage of the floating module on the G1 side and the phase angle of the line current flowing through the floating module. It is easy to see that during the period of 0.5s to 1.0s, the voltage amplitude of the grid on the G1 side is higher than that of the grid on the G2 side. The floating module on the G1 side is capacitive, and it divides the voltage with the switching capacitor, reducing the voltage amplitude at point POC1. During the period of 1.0s to 1.5s, the voltage amplitude of the grid on the G1 side is lower than that of the grid on the G2 side. The floating module on the G1 side is inductive, and it works with the switching capacitor to increase the voltage amplitude at point POC1, verifying the feasibility of the control strategy.

[0034] Figure 10 and Figure 11The simulation operation diagrams show the DC side voltages of the g1-side floating module and the g2-side floating module during system operation. Both remain stable, verifying the feasibility of the control strategy.

[0035] Labels such as Figure 12 As shown, the labels are as follows.

[0036] 1: Sending-end power grid g1; 2: Power conversion device; 21a~21i are all voltage sensors; 22a~22b are all current sensors; 23: Sending-end power conversion device on the g1 side; 24: Capacitor switching circuit; 25: Receiving-end power conversion device on the g2 side; 26: Control device; 261: Voltage stabilization and equalization estimation unit for the floating module on the g1 side; 262: Inverter circuit control unit on the g1 side; 263: Reference voltage estimation unit for the floating module on the g1 side; 264: Capacitor switching control unit; 265: Inverter circuit control unit on the g2 side; 266: Voltage stabilization and equalization estimation unit for the floating module on the g2 side; 267: Reference current estimation unit for the receiving-end line; 3: Line impedance; 4: Receiving-end power grid g2.

[0037] This invention is not limited to the embodiments described above. The above description of specific embodiments is intended to illustrate and explain the technical solutions of this invention. The specific embodiments described above are merely illustrative and not restrictive. Without departing from the spirit and scope of the claims, those skilled in the art can make many specific modifications based on the teachings of this invention, and these modifications all fall within the scope of protection of this invention.

[0038] It should be understood that the sequence number of each step in the above embodiments does not imply the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present invention.

[0039] Example module Figure 12 As shown, a T-type non-isolation transformer medium-voltage flexible power transfer device and its control strategy include: The controller receives voltage and current information measured by the aforementioned sensors and accepts power flow regulation commands issued by the power grid dispatch center. The device receives the grid g1-side voltage measured by the voltage sensor. v g1(a) ,poc1 voltage v poc1(a) ,poc2 voltage v poc1(a) and device output port voltage v N(a) and v M(a) and the line transmission current measured by the current sensor. i N(a) andi M(a) The voltage amplitude of POC1 is obtained through the amplitude calculation process. E poc1(a) POC2 voltage amplitude E poc2(a) and line current amplitude I N(a) and I M(a) The phase of voltage POC1 is obtained through a phase-locked loop. i poc1(a) voltage phase of poc2 i poc2(a) Output voltage i N(a) and i M(a) .

[0040] The power transfer regulation section of the suspended module 1 controller receives power flow transfer instructions issued by the power grid dispatch center and determines the active power reference power that needs to be transferred. P ref The dual-loop controller for power and voltage enables the conversion of power supply. P g1 Precise control is achieved to obtain the voltage reference DC active component of the device on the g1 side. .

[0041] The DC-side voltage regulation section of the floating module 1 controller obtains the voltage reference DC reactive component of the g1-side device through DC voltage control loop switching control based on the DC-side reference voltage command. .

[0042] The voltage reference phase generation part of the levitation module 1 controller generates the voltage reference phase based on the voltage amplitude of the power grid g1. E g1 With POC2 voltage amplitude E poc2 The magnitude of the voltage relative to the line current determines whether the voltage phase of the levitation module leads or lags the line current, ultimately generating a voltage reference phase. i N,ref .

[0043] The phase-to-phase voltage equalization controller of the suspension module 1 controller controls a single suspension module and calculates the average DC-side voltage of the suspension module on side g1. V N,dc,ave , and the actual DC side voltage V N,dc,ave,i The comparison and processing yielded the phase-to-phase voltage equalization regulation voltage. v N,dc,ave .

[0044] The capacitor switching control obtains the POC1 voltage amplitude through a voltage sensor and amplitude calculation. E poc1 With POC2 voltage amplitude E poc2 Without capacitors connected, if the voltage amplitude at point POC1 is higher than that at point POC2, and the difference between the two voltage amplitudes reaches a certain level, capacitors are connected based on the deviation value. This causes the capacitors and the floating module 1 to divide the voltage, reducing the voltage amplitude at point POC1 to approach that at point POC2. If the voltage amplitude at point POC1 is lower than that at point POC2, and the difference between the two voltage amplitudes reaches a certain level, the required number of capacitors is calculated based on the deviation and reactive power. These capacitors, in conjunction with the floating module 1, raise the voltage at point POC1 to approach that at point POC2. The corresponding number of capacitors are connected when the voltage across the thyristor module is zero.

[0045] The power transfer regulation section of the suspended module 2 controller receives power flow transfer instructions issued by the power grid dispatch center and determines the active power reference that needs to be transferred. P ref The dual-loop controller for power and current achieves the conversion of power supply. P poc2 Precise control is achieved. The power transfer regulation section of the levitation module 2 controller works in conjunction with the DC-side voltage regulation of the levitation module to generate a reference current.

[0046] The DC-side voltage regulation of the suspension module is based on the phase difference between points poc1 and poc2. i M Using this as a reference, the phase deviation value is obtained by controlling the DC side voltage of the levitation module to stabilize. α Phase deviation affects the phase of the reference current. (The last part, "90°-", appears to be an error and is left untranslated.) α Then with one-half i M By superimposing these values, the phase information of the reference current can be obtained. i M,ref Through the active reference that needs to be transferred P ref With actual power transferred P poc2 The amplitude information of the reference current is obtained, and the reference current is obtained by combining the obtained amplitude and phase information. The reference current is then used to obtain the reference voltage through a current controller.

[0047] The phase-to-phase voltage equalization controller of the suspension module 2 controller controls a single suspension module and calculates the average DC-side voltage of the suspension module on side g2. V M,dc,ave , and the actual DC side voltage V M,dc,ave,i The comparison and processing yielded the phase-to-phase voltage equalization regulation voltage.v M,dc,ave .

[0048] Those skilled in the art will clearly understand that, for the sake of convenience and brevity, the above-described division of functional units and modules is merely an example. In practical applications, the above functions can be assigned to different functional units and modules as needed, that is, the internal structure of the device can be divided into different functional units or modules to complete all or part of the functions described above. The functional units and modules in the embodiments can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit. The integrated unit can be implemented in hardware or as a software functional unit. Furthermore, the specific names of the functional units and modules are only for easy differentiation and are not intended to limit the scope of protection of this application. The specific working process of the units and modules in the above system can be referred to the corresponding process in the foregoing method embodiments, and will not be repeated here.

[0049] In the above embodiments, the descriptions of each embodiment have different focuses. For parts that are not described in detail or recorded in a certain embodiment, please refer to the relevant descriptions of other embodiments.

[0050] Those skilled in the art will recognize that the units and algorithm steps of the various examples described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementations should not be considered beyond the scope of this invention.

[0051] In the embodiments provided by this invention, it should be understood that the disclosed apparatus / terminal devices and methods can be implemented in other ways. For example, the apparatus / terminal device embodiments described above are merely illustrative. For instance, the division of modules or units is only a logical functional division, and in actual implementation, there may be other division methods. For example, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed. Furthermore, the coupling or direct coupling or communication connection shown or discussed may be through some interfaces; the indirect coupling or communication connection between devices or units may be electrical, mechanical, or other forms.

[0052] The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some units can be selected to achieve the purpose of this embodiment according to actual needs.

[0053] Furthermore, the functional units in the various embodiments of the present invention can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit. The integrated unit can be implemented in hardware or as a software functional unit.

[0054] If the integrated module / unit is implemented as a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, all or part of the processes in the methods of the above embodiments can also be implemented by a computer program instructing related hardware. The computer program can be stored in a computer-readable storage medium, and when executed by a processor, it can implement the steps of the various method embodiments described above. The computer program includes computer program code, which can be in the form of source code, object code, executable files, or certain intermediate forms. The computer-readable medium can include: any entity or device capable of carrying the computer program code, recording media, USB flash drives, portable hard drives, magnetic disks, optical disks, computer memory, read-only memory (ROM), random access memory (RAM), electrical carrier signals, telecommunication signals, and software distribution media, etc. It should be noted that the content included in the computer-readable medium can be appropriately added or removed according to the requirements of legislation and patent practice in the jurisdiction. For example, in some jurisdictions, according to legislation and patent practice, computer-readable media do not include electrical carrier signals and telecommunication signals.

[0055] The above-described embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention, and should all be included within the protection scope of the present invention.

Claims

1. An electrical connection structure for a T-type non-isolation transformer medium-voltage flexible power transfer device and power control method, characterized in that, include: Floating module, floating capacitor, capacitor bank, thyristor module, current sensor, voltage sensor and controller for each module; There are two suspended modules. One end of suspended module 1 is connected to the medium-voltage power grid 1 via a first current sensor, and the other end is connected to suspended module 2. A capacitor bank is connected to the middle of the two suspended modules via a thyristor module. A first voltage sensor is installed at both ends of the thyristor module, and a second voltage sensor measures the potential of the midpoint between the two suspended modules and ground, i.e., the potential at point POC1. The DC side of each suspended module is connected to a suspended capacitor. A third voltage sensor is installed on each suspended capacitor. The other end of suspended module 2 is connected to the output port of the medium-voltage flexible power transfer device via a second current sensor. A fourth voltage sensor measures the potential of the output port of the medium-voltage flexible power transfer device and ground, i.e., the potential at point POC2. The output port of the medium-voltage flexible power transfer device is connected to the medium-voltage line. The medium-voltage flexible power transfer device relies on the switching of the suspended modules and capacitors to boost the voltage and transfer power.

2. An electrical connection structure for a T-type non-isolation transformer medium-voltage flexible power transfer device and power control method, characterized in that: include: Taking phase A as an example, According to claim 1, the voltage sensor measures the voltage on the g1 side of the power grid. v g1(a) Voltage at point POC1 between the two floating modules v poc1(a) Floating module capacitor voltage v N,dc,1(a) ~ v N,dc,n(a) , v M,dc,1(a) ~ v M,dc,m(a) Device output port voltage v N(a) and v M(a) ,poc2 voltage v poc1(a) The current sensor according to claim 1 measures the line transmission current. i N(a) and i M(a) ; The device receives the voltage on the g1 side of the power grid measured by the voltage sensor. v g1(a) ,poc1 voltage v poc1(a) ,poc2 voltage v poc1(a) and device output port voltage v N(a) and v M(a) and the line transmission current measured by the current sensor. i N(a) and i M(a) The voltage amplitude of POC1 is obtained through the amplitude calculation process. E poc1(a) POC2 voltage amplitude E poc2(a) and line current amplitude I N(a) and I M(a) The phase of voltage POC1 is obtained through a phase-locked loop. θ poc1(a) voltage phase of poc2 θ poc2(a) Output voltage θ N(a) and θ M(a) ; The simplified single-phase structure and control strategy of the proposed hybrid medium-pressure flexible power flow regulator are shown in the previous figure. v g1 , v g2 These are the voltages of the sending-end power grid 1 and the receiving-end power grid 2, respectively. i N This represents the current in the left-side circuit. i M It transmits current to the right-side line. v dc,n The DC-side voltage of the floating module n v dc,m The DC-side voltage of the floating module m; The device control strategy is shown in the lower half of the figure, and is broadly divided into two parts: capacitor switching control and floating module control. As a direct participant in power flow regulation, the floating module controller can be further divided into a g1-side floating module 1 controller and a g2-side floating module 2 controller. The floating module 1 controller includes four parts: power transfer regulation, floating module voltage regulation, floating module voltage equalization regulation, and voltage reference phase generation. The floating module 2 controller is divided into three parts: power transfer regulation, floating module voltage regulation, and floating module voltage equalization regulation. The specific control strategy is shown in Figure 4. The power transfer regulation section of the suspended module 1 controller receives power flow transfer instructions issued by the power grid dispatch center and determines the active power reference power that needs to be transferred. P ref The dual-loop controller for power and voltage enables the conversion of power supply. P g1 Precise control is achieved to obtain the voltage reference DC active component of the device on the g1 side. ; The DC-side voltage regulation section of the floating module 1 controller obtains the voltage reference DC reactive component of the g1-side device through DC voltage control loop switching control based on the DC-side reference voltage command. ; The voltage reference phase generation part of the levitation module 1 controller generates the voltage reference phase based on the voltage amplitude of the power grid g1. E g1 With POC2 voltage amplitude E poc2 The magnitude of the voltage relative to the line current determines whether the voltage phase of the levitation module leads or lags the line current, ultimately generating a voltage reference phase. θ N,ref ; The phase-to-phase voltage equalization controller of the suspension module 1 controller controls a single suspension module and calculates the average DC-side voltage of the suspension module on side g1. V N,dc,ave , and the actual DC side voltage V N,dc,ave,i The comparison and processing yielded the phase-to-phase voltage equalization regulation voltage. v N,dc,ave ; The capacitor switching control obtains the POC1 voltage amplitude through a voltage sensor and amplitude calculation. E poc1 With POC2 voltage amplitude E poc2 Without capacitors, if the voltage amplitude at point POC1 is higher than that at point POC2, and the difference between the two voltage amplitudes reaches a certain level, capacitors are added based on the deviation value. This causes the capacitors and the floating module 1 to divide the voltage, reducing the voltage amplitude at point POC1 to approach that at point POC2. If the voltage amplitude at point POC1 is lower than that at point POC2, and the difference between the two voltage amplitudes reaches a certain level, the required number of capacitors is calculated based on the deviation and reactive power. These capacitors are then used in conjunction with the floating module 1 to raise the voltage at point POC1 to approach that at point POC2. The corresponding number of capacitors are added when the voltage across the thyristor module is zero. The g2-side power transfer regulator controller determines the active power reference that needs to be transferred. P ref The line current reference is obtained through the power control. d Axis component, then with POC1 voltage phase θ poc1 Phase with POC2 voltage θ poc2 deviation θ M Based on the reference value of the floating module voltage v ref Control it to match the line current. i M Keep it vertical. During this process, the phase deviation value is... α The voltage vector of the floating module fluctuates around the line current. i M It swings left and right from a vertical position. Since phase deviation affects the phase of the reference current, it is adjusted by 90°− α and θ M The reference current phase is obtained by superimposing 1 / 2 of the phases. φ Then, by performing a coordinate transformation on the dq-axis current reference, the instantaneous current reference value can be obtained, which is then controlled by the current controller. G i,M ( s The line current is adjusted in a closed loop to obtain the reference voltage. v M,ref ; The phase-to-phase voltage equalization controller of the g2-side suspension module controller controls a single suspension module and calculates the average DC-side voltage of the g2-side suspension module. V M,dc,ave , and the actual DC side voltage V M,dc,ave,i The comparison and processing yielded the phase-to-phase voltage equalization regulation voltage. v M,dc,ave .

3. The capacitor switching control of a T-type non-isolation transformer medium-voltage flexible power transfer device according to claim 2, characterized in that: The capacitor switching control obtains the POC1 voltage amplitude through a voltage sensor and amplitude calculation. E poc1 With POC2 voltage amplitude E poc2 If the voltage amplitude at point POC1 is higher than that at point POC2 and the difference between the two voltage amplitudes is significant enough without the capacitor being engaged, the capacitor is engaged based on the deviation value. This causes the capacitor to divide the voltage with the floating module 1, reducing the voltage amplitude at point POC1 to be closer to that at point POC2. (1) In the formula, Z ref This represents the equivalent impedance value of the floating module on the g1 side. If the voltage amplitude at point POC1 is lower than that at point POC2, and the difference between the two voltage amplitudes reaches a certain level, the deviation is controlled by the controller. G Q (s) is adjusted, and the required number of capacitors is obtained through reactive power calculation. In conjunction with the floating module 1, the voltage at point POC1 is raised to be close to the voltage at point POC2. The corresponding number of capacitors are connected when the voltage across the thyristor module is zero. (2) (3) (4) (5) In the formula, k p,Q , k i,Q These are the proportional and integral coefficients of the reactive power closed-loop controller, respectively. L The inductance value is the value of the filter inductor. X For line reactance, X L For filtering inductive reactance, X C For filter capacitive reactance, C For the required capacitor size, N c represents the number of capacitors connected. C 0 represents the value of a single capacitor, and Ceil indicates rounding up; The number of capacitors to be switched is calculated, and the corresponding capacitor switch flag is set. After the flag is set, if the voltage sensor preset at both ends of the thyristor measures that the voltage across the thyristor is zero after the flag is set, then the capacitor is switched into the system.

4. The power flow transfer control method for a T-type non-isolation transformer medium-voltage flexible power flow transfer device according to claim 2, characterized in that: For the floating module on the g1 side of the power grid, the power transfer regulator determines the required power transfer. P ref The DC component of the line current on the g1 side of the power grid is obtained through power control, as shown in the following formula: (6) In the formula, k p,pN , k i,pN These are the proportional and integral coefficients of the power closed-loop controller on the g1 side, respectively. This represents the DC component of the line current on the g1 side of the power grid. With the expected impedance value of the levitation module Z ref Multiplying, we get the g1 side suspension module. d Shaft reference voltage .

5. The power flow transfer control method for a T-type non-isolation transformer medium-voltage flexible power flow transfer device according to claim 2, characterized in that: The DC-side voltage stabilization controller on the g1 side receives the DC-side voltage amplitude of the floating capacitor on the g1 side. V N,dc,ref The g1-side suspension module is obtained through DC voltage control. q Shaft reference voltage As shown in the following formula: (7) In the formula, k p,VN , k i,N These are the proportional and integral coefficients of the DC voltage regulator on the g1 side, respectively. V N,dc,ave This represents the average voltage value of the DC bus voltage of the floating module on the g1 side.

6. The power flow transfer control method for a T-type non-isolation transformer medium-voltage flexible power flow transfer device according to claim 2, characterized in that: The reference voltage phase generation controller on the g1 side generates the line current on the g1 side based on the relationship between the voltage amplitude on the g1 side and the voltage amplitude on the g2 side. i N The phase is processed to generate the reference voltage phase for the floating module on side g1. If the voltage amplitude on side g1 is lower than that on side g2, it is desirable for floating module 1 to be inductive. Therefore, the reference phase is as shown in the following formula: (8) In the formula, θ N For the phase of the line current on the g1 side, θ N,ref The reference voltage phase for the floating module; If the voltage amplitude on side g1 is higher than that on side g2, then it is desirable for the floating module 1 to be capacitive. Therefore, the reference phase is as shown in the following formula: (9) , , θ N,ref The three factors generate the reference voltage for the g1-side suspension module. v N,ref .

7. The method for phase-to-phase voltage equalization regulation and control of a T-type non-isolation transformer medium-voltage flexible power transfer device according to claim 2, characterized in that: The proposed control needs to ensure the stability of the DC-side voltage of a single floating module, and the average DC-side voltage of the floating module on side g1 should be calculated. V N,dc,ave , and the actual DC side voltage V N,dc,i The difference is calculated, and further processing is performed to obtain the phase-to-phase voltage equalization regulation voltage. v N,i,ref : (10) v N,ref and v N,i,ref The final reference voltage of the levitation module is generated by superposition. .

8. The method for regulating and controlling the power transfer on the g2 side of a T-type non-isolation transformer medium-voltage flexible power transfer device according to claim 2, characterized in that: The g2-side power transfer regulator controller determines the active power reference that needs to be transferred. P ref The line current reference is obtained through the power control. d The axial components are shown in the following formula: (11) In the formula, k p,Mp , k i,Mp These are the proportional and integral coefficients of the power closed-loop controller on the g2 side, respectively. Transmit current to the g2 side line d Axis reference, E * indicates the system's rated voltage; With the voltage phase of poc1 θ poc1 Phase with POC2 voltage θ poc2 deviation θ M Based on the reference value of the floating module voltage v ref Control it to match the line current. i M Keep it vertical. During this process, the phase deviation value is... α The voltage vector of the floating module fluctuates around the line current. i M It swings left and right from a vertical position. Since phase deviation affects the phase of the reference current, it is possible to achieve this by swinging 90°... α and θ M The reference current phase is obtained by superimposing 1 / 2 of the phases. φ Then, by performing a coordinate transformation on the dq-axis current reference, the instantaneous current reference value can be obtained: (12) (13) Then, through the current controller G i,M ( s The line current is adjusted in a closed loop to obtain the reference voltage. v M,ref； (14) In the formula, k p,Mi and k r,Mi These are the proportional coefficient and resonant coefficient of the current controller, respectively. ω b For controller bandwidth, ω 0 is the reference frequency.

9. The DC-side voltage regulation control method for a single suspended module of a T-type non-isolation transformer medium-voltage flexible power transfer device according to claim 2, characterized in that: The proposed control needs to ensure the stability of the DC-side voltage of a single floating module, and the average DC-side voltage of the floating module on side g2 should be calculated. V M,dc,ave , and the actual DC side voltage V M,dc,i The difference is calculated, and further processing is performed to obtain the phase-to-phase voltage equalization regulation voltage. v M,i,ref : (15) In the formula, θ M This refers to the phase of the line current on the g2 side.

10. The control method for a T-type non-isolation transformer medium-voltage flexible power transfer device according to claim 2, characterized in that: The g2-side suspension module controller obtains the feedforward compensation voltage by measuring the difference between the instantaneous voltage at point POC1 and point POC2, and then superimposes the aforementioned reference voltage. v M,ref and phase equalization voltage regulation v M,i,ref Obtain the converter modulation voltage : (16)。

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