Integrated power electronic transformer and control method thereof

Abstract

The invention discloses an integrated power electronic transformer and a control method thereof, a plurality of parallel dual-active bridge circuit modules are arranged between a distribution network port and a port module, and the distribution network port is connected with the input end of each dual-active bridge circuit module through a three-phase AC / DC module. The output end positive electrode of the three-phase AC / DC module is connected with the input end positive electrode of the first path of dual-active bridge circuit module, and the output end negative electrode of the three-phase AC / DC module is connected with the input end negative electrode of the last path of dual-active bridge circuit module. The positive electrode of the input end of each path of dual-active bridge circuit module is connected with the negative electrode of the input end of the adjacent last path of dual-active bridge circuit module; and the output ends of the dual-active bridge circuit modules and the input end of the port module are connected with a direct-current bus. According to the invention, the transmission efficiency is high, the voltage stress of a switching device is reduced, and the dual-active bridge circuit module adopts a current stress optimization control strategy to realize high voltage transmission ratio and low current stress optimization control in a full operation range.

Description

Technical Field

[0001] The present invention relates to the electrical field, and in particular to an integrated power electronic transformer and a control method thereof. Background Art

[0002] With the widespread popularization of distributed photovoltaic, wind power and other new energy sources and the rapid development of electric vehicles, the demand for new energy consumption and efficient and convenient charging is growing. However, affected by utilization and economy, the switching devices of traditional power electronic transformer systems are subject to large voltage stress and low conversion efficiency. The existing wind, solar and storage integrated power electronic transformers have low reliability, complex structure and large device size, which is not conducive to expansion and has poor adaptability, and cannot meet the needs of different application scenarios at the same time.

[0003] As clean and renewable energy resources, wind and solar energy have great development potential. Through wind power generation and photovoltaic power generation systems, natural wind and solar energy can be converted into electrical energy to provide green energy for electric vehicles. At the same time, the continuous advancement of energy storage technology has provided solutions to the intermittent and instability problems of wind and solar power generation. However, existing energy storage devices are generally fixedly installed or placed in underground energy storage battery warehouses. This energy storage system configuration lacks flexibility and scalability, and is not easy to replace when a failure occurs. The energy storage interface and electric vehicle charging port of the general wind, solar and storage integrated interface device are set separately, and this solution will also greatly increase the cost of the device. Summary of the invention

[0004] The technical problems to be solved by the present invention are: (1) The existing wind, solar, storage and charging integrated power electronic transformer device topology is generally not scalable, and the structure is complex and has poor stability.

[0005] (2) Most of the existing wind-solar-storage-charging integrated power electronic transformer devices use fixed energy storage battery packs, which are not conducive to maintenance or expansion. Replacing the battery pack will cause the device to be unable to work for a long time. In addition, the energy storage port and the electric vehicle charging port of the device are set separately, the topology structure is complex, the cost is high, and it is not conducive to modular simplified design, which is also inconvenient for users.

[0006] In view of the above problems in the prior art, an integrated power electronic transformer and a control method thereof are provided, which adopt a modular design, have high scalability and conversion efficiency, and use a common interface for charging and energy storage, thereby reducing manufacturing costs.

[0007] In order to solve the above technical problems, the technical solution adopted by the present invention is: An integrated power electronic transformer comprises a distribution network port on an input side and a plurality of port modules on an output side, a plurality of parallel dual active bridge circuit modules are arranged between the distribution network port and the port modules, the output end of the dual active bridge circuit module is connected to a DC bus, the input end of the port module is connected to the DC bus, the distribution network port is connected to the input end of each dual active bridge circuit module through a three-phase AC / DC module, and the positive pole of the output end of the three-phase AC / DC module is connected to the positive pole of the input end of the first dual active bridge circuit module, the negative pole of the output end of the three-phase AC / DC module is connected to the negative pole of the input end of the last dual active bridge circuit module, and the positive pole of the input end of each dual active bridge circuit module is connected to the negative pole of the input end of the adjacent previous dual active bridge circuit module.

[0008] Furthermore, the port module includes a photovoltaic port module and a wind power port module, the photovoltaic port module includes a unidirectional DC / DC module and a photovoltaic port, the photovoltaic port is connected to the DC bus through the unidirectional DC / DC module, and the wind power port module includes a DC / AC module and a wind power port, and the wind power port is connected to the DC bus through the DC / AC module.

[0009] Furthermore, the port module includes an energy storage charging shared port module, the energy storage charging shared port module includes an energy storage charging shared port, a bidirectional DC / DC module and a shared port controller, the shared port controller is connected to the control end of the bidirectional DC / DC module, the detection end of the shared port controller is connected to the reference voltage through the pull-up resistor R1, the detection end of the shared port controller is also connected to the ground in sequence through the voltage divider resistor R2 and the push switch S1 supported under the charging head provided with the energy storage charging shared port, the detection end of the shared port controller is also connected to the communication interface of the charging head, so that when the charging head is connected to the charging port of the electric vehicle or the energy storage device, the circuit between the reference voltage, the detection point and the resistance of the electric vehicle or the energy storage device is connected.

[0010] The present invention also proposes a control method for an integrated power electronic transformer, including the steps of controlling the charging and discharging of a bidirectional DC / DC module by a common port controller, specifically including: Get the voltage value of the detection end; If the voltage value is the reference voltage value, the bidirectional DC / DC module is controlled to be turned off; If the voltage value is [reference voltage value / (R1+ R2)] * R1, the PWM wave signal is detected; If the voltage value is [reference voltage value / (R1+ R2*electric vehicle resistance R3 / (R2+electric vehicle resistance R3))]*R1, and a PWM wave signal is detected, the bidirectional DC / DC module is controlled to discharge according to the duty cycle of the PWM wave signal; If the voltage value is [reference voltage value / (R1+ R2*energy storage device resistance R3 / (R2+energy storage device resistance R3))]*R1, the bidirectional DC / DC module is controlled to perform bidirectional charging and discharging.

[0011] Furthermore, when the bidirectional DC / DC module is controlled to discharge according to the duty cycle of the PWM wave signal, it includes: If the duty cycle is outside the preset interval, the bidirectional DC / DC module is controlled to be turned off; If the duty cycle is within a first interval within a preset interval, controlling the bidirectional DC / DC module to output a low voltage; If the duty cycle is in a second interval within the preset interval, and the lower limit value of the second interval is the upper limit value of the first interval, controlling the bidirectional DC / DC module to output a medium voltage; If the duty cycle is in a third interval within the preset interval, and the lower limit value of the third interval is the upper limit value of the second interval, controlling the bidirectional DC / DC module to output a high voltage; If the duty cycle is in a fourth interval within the preset interval, and the lower limit value of the fourth interval is greater than the upper limit value of the third interval, the bidirectional DC / DC module is controlled to output a port current corresponding to the duty cycle.

[0012] Furthermore, the port current expression corresponding to the duty cycle is as follows:

[0013] Where D represents the duty cycle.

[0014] The present invention also proposes a control method for an integrated power electronic transformer, including the steps of optimizing and controlling a dual active bridge circuit module, specifically including: Obtain the output voltage, output current and input voltage of the current dual active bridge circuit module in real time, and calculate the corresponding real-time transmission power and voltage conversion ratio; Determine the mode suitable for the current operating conditions based on the voltage conversion ratio. If it is suitable for the standard mode, keep the inner shift ratio fixed and use PI control to adjust the outer shift ratio. If it is suitable for the optimal stress mode, calculate the value of the inner shift ratio when the current stress is minimum based on the real-time transmission power and voltage conversion ratio, and use PI control to adjust the outer shift ratio.

[0015] Furthermore, when determining the mode suitable for the current operating condition according to the voltage conversion ratio, it specifically includes: if the voltage conversion ratio is 1, it is suitable for the standard mode; if the voltage conversion ratio is greater than 1, it is suitable for the optimal stress mode.

[0016] Furthermore, the real-time transmission power and voltage conversion ratio expressions are as follows:

[0017]

[0018] in, To transfer power in real time, is the voltage conversion ratio, is the maximum power, , is the input voltage, is the output voltage, is the output current, is the turns ratio of the high frequency transformer in the dual active bridge circuit module, is the switching frequency of the switching devices in the dual active bridge circuit module, is the inductor in the dual active bridge circuit module.

[0019] Further, when calculating the value of the inner shift ratio when the current stress is minimum according to the real-time transmission power and the voltage conversion ratio, it specifically includes: Determine whether the real-time transmission power value meets If the real-time transmission power value meets this condition, then determine whether the voltage conversion ratio value meets If the voltage conversion ratio satisfies this condition, the value of the inner shift ratio when the current stress is the smallest is the first value; if the voltage conversion ratio does not satisfy , then the value of the inner displacement when the current stress is the smallest is greater than the second value; If the real-time transmission power value does not meet , then determine whether the value of real-time transmission power satisfies If the real-time transmission power value meets this condition, then determine whether the voltage conversion ratio value meets If the voltage conversion ratio satisfies this condition, the value of the inner shift ratio when the current stress is the smallest is the first value; if the voltage conversion ratio does not satisfy , then determine whether the value of the voltage conversion ratio satisfies If the voltage conversion ratio satisfies this condition, the value of the inner shift ratio when the current stress is the smallest is the first value; if the voltage conversion ratio does not satisfy , then the value of the inner displacement when the current stress is the smallest is greater than the second value; If the real-time transmission power value does not meet , then the value of the inner shift when the current stress is the smallest is the first value.

[0020] Furthermore, the expression of the first value is as follows: ; The second value expression is as follows: ; in, To transfer power in real time, is the voltage conversion ratio.

[0021] Compared with the prior art, the advantages of the present invention are: The present invention directly connects the port module to the DC bus on the output side, which has high transmission efficiency. A plurality of parallel dual active bridge circuit (DAB) modules are arranged between the input side and the output side, and the positive / negative pole of the input end of each DAB module is connected to the negative / positive pole of the input end of the adjacent DAB module, thereby reducing the voltage stress of the switching device. In addition, the output ends of all DAB modules are connected to the DC bus, thereby realizing high current output.

[0022] The port modules of the present invention include different types and can adapt to different wind and solar load application scenarios. The energy storage charging shared port module includes an energy storage charging shared port, a bidirectional DC / DC converter and a shared port controller. The shared port controller is connected to the control end of the bidirectional DC / DC converter. The detection end of the shared port controller is connected to the reference voltage through a pull-up resistor R1, and is also grounded through a voltage divider resistor R2 and a push switch S1. It is also connected to the communication interface of the charging head provided with the energy storage charging shared port, so that when the charging head is connected to the charging port of an electric vehicle or an energy storage device, the circuit between the reference voltage, the detection point and the resistance of the electric vehicle or the energy storage device is connected. The shared port controller can determine whether the energy storage charging shared port is in a working state through the resistance value of the detection point, and judge the type of access device when it is in a working state, thereby realizing energy storage charging sharing.

[0023] The DAB module of the present invention adopts a current stress optimization control strategy. By calculating the condition parameters in real time, the mode suitable for the current operating conditions is determined. If it is suitable for the standard mode, the inner shift ratio is kept at a fixed value, and the outer shift ratio is adjusted using PI control. If it is suitable for the optimal stress mode, the inner and outer shift ratios when the stress is minimum are calculated, and the inner and outer shift ratios are adjusted accordingly, thereby achieving a high voltage transmission ratio and low current stress optimization control in the full operating range. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 Schematic diagram of the topological structure of a power electronic transformer according to an embodiment of the present invention.

[0025] Figure 2 Schematic diagram of a three-phase AC / DC module circuit according to an embodiment of the present invention.

[0026] Figure 3 Schematic diagram of the circuit structure of a dual active bridge circuit module according to an embodiment of the present invention.

[0027] Figure 4The figure is a schematic diagram of the topological structure of a dual active bridge circuit module of a power electronic transformer according to an embodiment of the present invention.

[0028] Figure 5 The present invention is a schematic diagram of a circuit topology of a high frequency transformer in a dual active bridge circuit module according to an embodiment of the present invention.

[0029] Figure 6 Schematic diagram of another circuit topology of the high frequency transformer in the dual active bridge circuit module of an embodiment of the present invention.

[0030] Figure 7 Schematic diagram of the circuit topology of a single-phase DC / DC module in a photovoltaic port module according to an embodiment of the present invention.

[0031] Figure 8 Schematic diagram of the circuit topology of the bidirectional DC / DC module in the energy storage and charging shared port module according to an embodiment of the present invention.

[0032] Fig. 9 It is a schematic diagram of a shared energy storage and charging port in a shared energy storage and charging port module according to an embodiment of the present invention.

[0033] Fig.10 Schematic diagram of the circuit topology of the energy storage and charging shared port module according to an embodiment of the present invention.

[0034] Fig.11 The figure is a flow chart for optimizing control of the single phase shift mode of the dual active bridge circuit module in the embodiment of the present invention.

[0035] Fig.12 This is the internal and external phase shift waveform diagram of the dual active bridge circuit module.

[0036] Fig.13 This is a flow chart of the current stress optimization control strategy of the dual active bridge circuit module in an embodiment of the present invention.

[0037] Fig.14 This is a flow chart of a common port controller controlling the charging and discharging of a bidirectional DC / DC module according to an embodiment of the present invention. DETAILED DESCRIPTION

[0038] The present invention is further described below in conjunction with the accompanying drawings and specific preferred embodiments, but the protection scope of the present invention is not limited thereby.

[0039] Embodiment 1 This embodiment proposes an integrated power electronic transformer, which adopts a modular design and includes a distribution network port on the input side and multiple port modules on the output side. A dual active bridge circuit (DAB) module is provided between the distribution network port and the port module. The output end of the dual active bridge circuit module is connected to a DC bus, and the input end of the port module is connected to the DC bus. A higher transmission efficiency is ensured by directly connecting to the DC bus.

[0040] like Figure 1 As shown, the integrated power electronic transformer of this embodiment includes at least 4 ports, wherein the distribution network port on the input side is connected to the dual active bridge circuit module on the DC bus through a three-phase AC / DC module, and the port modules on the output side include a photovoltaic port module, a wind power port module, an energy storage charging shared port module, etc. The photovoltaic port of the photovoltaic port module is connected to the DC bus through a unidirectional DC / DC module, the wind power port of the wind power port module is connected to the DC bus through a DC / AC module, and the energy storage charging shared port of the energy storage charging shared port module is connected to the DC bus through a bidirectional DC / DC module.

[0041] In this embodiment, the number of each type of port modules is not limited. The number of DC / AC modules, single-phase DC / DC modules, and bidirectional DC / DC modules on the DC bus can be increased or decreased according to actual needs to adapt to different wind and solar load application scenarios.

[0042] In this embodiment, the three-phase AC / DC module can be used Figure 2 The VSC converter shown or the converter with three-phase AC-DC conversion function has its AC side connected to the distribution network port and its DC side connected to the dual active bridge circuit module, so that when the energy storage is insufficient, the power can be input through the distribution network port to support the operation of the equipment connected to the output side. When the energy storage is sufficient, the DC power is inverted into three-phase AC power and input into the grid through the three-phase AC / DC module.

[0043] In this embodiment, the circuit structure of the dual active bridge circuit module is as follows: Figure 3 As shown, the primary DC / AC module is composed of four power switches S1, S2, S3 and S4 to form a full-bridge inverter, which converts the DC voltage into a high-frequency square wave AC voltage. A high-frequency filter is provided in the intermediate stage to transmit the high-frequency AC voltage generated by the DC / AC module to the secondary stage, and can also achieve voltage step-up or step-down. The secondary AC / DC module is composed of four power switches S5, S6, S7 and S8 to form another full-bridge inverter, which rectifies the AC voltage of the secondary of the high-frequency transformer back to the DC output.

[0044] like Figure 4As shown, in this embodiment, a plurality of parallel dual active bridge circuit modules are provided, the positive electrode of the output end of the three-phase AC / DC module is connected to the positive electrode of the DC / AC module input end of the first dual active bridge circuit module, the negative electrode of the output end of the three-phase AC / DC module is connected to the negative electrode of the DC / AC module input end of the last dual active bridge circuit module, and the positive electrode of the DC / AC module input end of each dual active bridge circuit module is connected to the negative electrode of the DC / AC module input end of the adjacent dual active bridge circuit module, as shown in FIG. Figure 4 As shown, the negative pole of the DC / AC module input terminal of the first dual active bridge circuit module is connected to the positive pole of the DC / AC module input terminal of the second dual active bridge circuit module, and so on, the positive pole of the DC / AC module input terminal of the last dual active bridge circuit module is connected to the negative pole of the DC / AC module input terminal of the previous dual active bridge circuit module.

[0045] Through the above structure, the high-voltage direct current output by the three-phase AC / DC module is cascaded and divided through the DC / AC module of each dual-active bridge circuit module, thereby reducing the voltage stress of the switching device. The DC / AC module outputs high-frequency alternating current and is connected to the high-frequency transformer module. The high-frequency transformer can realize electrical isolation between the distribution network port on the input side and each port module on the output side, thereby realizing electrical isolation between the distribution network and the DC bus in the device. The output voltage of the secondary side of the high-frequency transformer is connected to the AC / DC module for rectification and finally output in parallel to the low-voltage DC bus to realize high-current output.

[0046] It should be noted that the connection form of each dual active bridge circuit module can also be changed according to actual needs, and the input is connected in series and the output is connected in parallel, or the input and output are connected in parallel or mixed, which is not limited in this embodiment.

[0047] In this embodiment, the high-frequency transformer topology of the dual active bridge circuit module is as follows: Figure 5 As shown, the high frequency transformer topology can also be used as Figure 6 The topology shown with LCL filter can also be directly replaced by high-frequency transformer leakage inductance Figure 6 L2 in the figure, the specific structure of the high-frequency transformer is not limited thereto.

[0048] In this embodiment, the unidirectional DC / DC module of the photovoltaic port module can be used as follows Figure 7 It is a Boost circuit topology or other circuit topologies with single-phase DC / DC conversion function, which can realize MPPT control and stably output boosted voltage.

[0049] In this embodiment, the DC / AC module of the wind power port module can also be used as follows Figure 2The VSC converter or converter with three-phase AC-DC conversion function shown has an AC side connected to a wind power port and a DC side connected to a DC bus. The wind power port can be connected to a wind turbine generator, which is generally a small wind turbine generator. In order to save costs, the switch devices constituting the VSC converter in the wind power port module are selected to have a smaller withstand voltage value than the three-phase AC / DC module of the distribution network port.

[0050] In this embodiment, the energy storage charging shared port module includes an energy storage charging shared port, a bidirectional DC / DC module and a shared port controller. The bidirectional DC / DC module can be used as follows Figure 8 The bidirectional buck-boost converter or bidirectional full bridge (H-bridge) and bidirectional Cuk converter shown in FIG. Fig. 9 As shown, there are 5 interfaces in total, namely the DC positive pole DC+, the DC negative pole DC-, the communication interfaces CN1 and CN2, and the common ground port PE. The left and right sides of the sockets are symmetrical, and the top and bottom are asymmetrical to prevent users from plugging the wrong positive and negative poles of the power supply.

[0051] like Fig.10 As shown, in this embodiment, the DC positive pole DC+ and the DC negative pole DC- of the energy storage charging common port are connected through the DC bus of the bidirectional DC / DC module, the common port controller is connected to the control end of the bidirectional DC / DC module, and the detection end ( Fig.10 The detection point 1) is connected to the reference voltage of 24V through the pull-up resistor R1, and the detection end of the common port controller is also grounded through the voltage-dividing resistor R2 and the switch S1 in sequence. The switch S1 in this embodiment is a push switch supported under the charging head provided with the energy storage charging common port. When the charging head is not in use, it is placed on the switch S1, so that the switch S1 is pressed and disconnected. When the charging head is in use, it is removed from the switch S1, so that the switch S1 is released and connected.

[0052] like Fig.10 As shown, the detection end of the common port controller is also connected to the communication interface CN2 of the charging head, so that when the charging head is connected to the charging port of the electric vehicle or the energy storage device, the circuit between the reference voltage, the detection point and the resistance of the electric vehicle or the energy storage device is connected. In addition, the signal input end of the common port controller is connected to the communication interface CN1 of the charging head, so as to obtain the PWM signal when the charging head is connected to the charging port of the electric vehicle.

[0053] Through the above structure, the common port controller can sense voltage changes, thereby automatically identifying the type of port device connected and controlling the bidirectional DC / DC module to perform corresponding charging and discharging operations.

[0054] For example, when the energy storage charging shared port is not in use, the switch S1 is disconnected, and the detection point 1 can measure the voltage of the pull-up resistor R1 end as 24V, and the port is in a non-working state. When the charging head is taken out of the charging device, S1 is closed. At this time, R1 and R2 are connected in series to divide the voltage, and the voltage measured at the detection point 1 is 12V. The port enters the pre-working state and starts to detect the PWM wave signal through the communication interface CN1.

[0055] When the charging head is connected to the charging port of the electric vehicle, R3 is connected, and detection point 1 obtains the first voltage (for example, 8V), indicating that the plug is connected. At the same time, the voltage at detection point 2 of the controller located in the electric vehicle changes (for example, from 12V to 8V). The charging controller of the electric vehicle receives the plug connection signal and starts to send a PWM wave signal to control the operation of the charging port.

[0056] When the charging head is connected to the charging port of the energy storage device, since the setting of the resistor R3 in the mobile energy storage device is different from the resistance value set in the electric vehicle, the detection point 1 obtains a second voltage (for example, 3V) when the port is inserted, and the voltage of the detection point 2 of the mobile energy storage device changes (for example, from 12V to 3V), it can be judged that the connected device is a mobile energy storage device, and the bidirectional DC / DC module is controlled to enter the bidirectional charging and discharging state. How to control the bidirectional DC / DC module to enter the bidirectional charging and discharging state is well known to those skilled in the art, and will not be repeated in this embodiment.

[0057] It can be seen that the use of a topological structure that shares electric vehicle charging and mobile energy storage devices can reduce the hardware cost of separately setting up electric vehicle charging ports and energy storage devices. At the same time, it can facilitate the expansion and maintenance of charging station energy storage and improve the flexibility of the integrated power electronic transformer.

[0058] Embodiment 2 This embodiment proposes the control method of the integrated power electronic transformer described in the first embodiment, including the step of optimizing the single phase shift mode of the dual active bridge circuit module, such as Fig.11 As shown, specifically including: S1) obtaining the output voltage, output current and input voltage of the current dual active bridge circuit module in real time, and calculating the corresponding real-time transmission power and voltage conversion ratio; S2) Determine the mode suitable for the current operating conditions according to the voltage conversion ratio. If it is suitable for the standard mode, keep the inner shift ratio as a fixed value and use PI control to adjust the outer shift ratio. If it is suitable for the optimal stress mode, calculate the value of the inner shift ratio when the current stress is minimum according to the real-time transmission power and voltage conversion ratio, and adjust the value of the inner shift ratio to the value of the inner shift ratio when the stress is minimum, and then use PI control to adjust the outer shift ratio.

[0059] Through the above steps, the method of this embodiment can not only optimize the current stress in the entire operating range, but also achieve higher efficiency than single-phase shift control under large voltage conversion ratio conditions, effectively improving the low operating efficiency and large current stress of ordinary single-phase shift control, and can only operate efficiently when the voltage conversion ratio is 1. When the voltage amplitudes on both sides of the transformer do not match, the efficiency will be significantly reduced.

[0060] Specifically, Fig.12 As shown in the control waveform, D1 is the DAB inward shift phase, D2 is the outward shift phase, and Ths is half a cycle. The maximum output power in single phase shift mode is , the real-time transmission power and voltage conversion ratio expressions in step S1 are as follows:

[0061]

[0062] in, To transfer power in real time, is the voltage conversion ratio, is the maximum power, , is the input voltage, is the output voltage, is the output current, is the turns ratio of the high frequency transformer in the dual active bridge circuit module, is the switching frequency of the switching devices in the dual active bridge circuit module, is the inductor in the dual active bridge circuit module.

[0063] In step S2 of this embodiment, the value of the inner shift ratio when the current stress is the smallest in the optimal stress mode is calculated based on the mathematical model of the dual active bridge circuit, which is a control calculation model for the optimal stress value within the operating value range. The following is the calculation derivation process: From the known DAB transmission power and current expressions, we can get:

[0064]

[0065] Combination Fig.12 The waveform diagram and Figure 3 The DAB circuit diagram can be obtained:

[0066]

[0067] Assuming that the DAB low voltage DC output terminal is connected to a pure resistive load, the above equation can be changed to:

[0068]

[0069] With the rated transmission power in a single-phase shift as the base value, we can obtain: It can be obtained as follows:

[0070] With the rated transmission current in a single-phase shift as the base value, we can obtain:

[0071] From the p-transform of the formula, we can obtain:

[0072] Therefore, G can be changed to:

[0073] In order to obtain the minimum current stresses G1min and G2min, taking the derivative of the above formula with respect to D2 respectively, we can obtain:

[0074] Among them, for formula, when , , and when , when , according to the monotonicity of the function, it can be known that the function has a minimum value point (the external phase shift ratio under the minimum current stress) in the interval . Substituting it into formula, we can obtain the minimum value (local minimum current stress) ; Similarly, combining the above formula, we can obtain has a minimum value point (the external phase shift ratio under the minimum current stress) in the interval . Substituting it into formula, we can obtain the minimum value (local minimum current stress) .

[0075] The corresponding global optimal current stress value Gmin = min{G1min, G2min} is different under different value ranges of p0 and k. For example, when , , substituting the minimum value points D2 into the expressions of formulas G1 and G2 respectively, we can obtain the minimum values , . Substituting the same p0 and k into G1min and G2min for comparison, we can obtain G1min < G2min. Therefore, the global optimal current stress value ​, the specific minimum current stress shift ratio combinations are listed as follows: when , Then you can get:

[0076] when , Then you can get:

[0077] in, It represents the value of the inward displacement ratio when the stress is minimum. It represents the value of the external displacement when the stress is minimum. To transfer power in real time, is the voltage conversion ratio.

[0078] In step S2 of this embodiment, two current stress optimization control mode switchings are involved: When the voltage transfer ratio (i.e., voltage conversion ratio) is close to 1, the standard control mode is adopted, in which the inner shift ratio D1 is a given fixed value, and the outer shift ratio is adjusted using PI control. Specifically, the error ΔV2 obtained by comparing the output voltage V2 with the reference voltage V2ref is obtained, and D2* is obtained through the PI regulator. Then, the pulse model of S5~S8 is obtained through the PWM generator to adjust the value of the output voltage V2 or the output power to ensure the normal operation of the DAB module.

[0079] When high voltage transfer ratio and light load operation are required, the optimal stress mode is adopted. In order to control the output voltage and reduce the current stress at the same time, the inner shift phase D1 and the outer shift phase D2 are adjusted separately. The outer shift phase D2 is responsible for controlling the stability of the output voltage, and the inner shift phase D1 is responsible for controlling the optimization of the current stress. The value of the outer shift phase D2 is the same as the standard control mode. The stability of the output voltage is guaranteed by PI adjustment. The value of the inner shift phase D1 is the value of the inner shift phase when the current stress is the smallest in the aforementioned optimal stress mode. The two-mode switching control realizes the optimization of current stress in the entire operating range, which makes up for the fact that the maximum power output can only be achieved when the voltage transfer ratio is 1 under single-phase control.

[0080] like Fig.13 As shown, in step S2, in the optimal stress mode, when the value of the inner shift ratio when the current stress is the smallest is calculated according to the real-time transmission power and voltage conversion ratio, the real-time range of the current stress optimization switch control k and p0 is specifically judged according to the calculated current stress, and the corresponding control mode SFi (i=1,2,3,4) is obtained, thereby obtaining the value of the inner shift ratio under different control modes, specifically: After obtaining the real-time transmission power, determine whether the value of the real-time transmission power meets the If the real-time transmission power value meets this condition, then determine whether the voltage conversion ratio value meets If the voltage conversion ratio meets this condition, then i=2, which is the second control mode (SF2); if the voltage conversion ratio does not meet this condition, then i=2, which is the second control mode (SF2). , then i=1, which is the first control mode (SF1); If the real-time transmission power value does not meet , then determine whether the value of real-time transmission power satisfies If the real-time transmission power value meets this condition, then determine whether the voltage conversion ratio value meets If the voltage conversion ratio meets this condition, then i=2, which is the second control mode (SF2); if the voltage conversion ratio does not meet this condition, then i=2, which is the second control mode (SF2). , then determine whether the value of the voltage conversion ratio satisfies If the voltage conversion ratio meets this condition, then i=2, which is the second control mode (SF2); if the voltage conversion ratio does not meet this condition, then i=2, which is the second control mode (SF2). , then i=3, which is the third control mode (SF3); If the real-time transmission power value does not meet , then i=4, which is the fourth control mode (SF4).

[0081] The value of the internal and external displacement ratio when the current stress of SF2 is the smallest is , The value of the internal and external displacement when the current stress of SF1, SF3 and SF4 is the smallest is , .

[0082] Finally, adjust the value of the inner displacement ratio to the value of the inner displacement ratio when the stress is the lowest. Then use PI control to adjust the outer displacement ratio, and get D1=D 1ref Compared with D2=D2*value, i.e., the inward and outward shift in the best stress mode, the efficiency is usually maximized when the converter operates at the current stress optimum point.

[0083] Embodiment 3 This embodiment provides a control method for the integrated power electronic transformer described in the first embodiment, including the steps of controlling the charging and discharging of the bidirectional DC / DC module by a common port controller, such as Fig.14 As shown, specifically including: Get the voltage value of the detection end; If the voltage value is the reference voltage value, the bidirectional DC / DC module is controlled to be turned off; If the voltage value is the first voltage value, and the first voltage value is specifically [reference voltage value / (R1+R2)]*R1, then the PWM wave signal is detected; If the voltage value is the second voltage value, the second voltage value is specifically [reference voltage value / (R1 + R2 * electric vehicle resistance R3 / (R2 + electric vehicle resistance R3))] * R1, and if a PWM wave signal is detected, then control the bidirectional DC / DC module to discharge according to the duty cycle of the PWM wave signal; If the voltage value is the third voltage value, the third voltage value is specifically [reference voltage value / (R1 + R2 * energy storage device resistance R3 / (R2 + energy storage device resistance R3))] * R1, then control the bidirectional DC / DC module to perform bidirectional charging and discharging.

[0084] In this embodiment, when controlling the bidirectional DC / DC module to discharge according to the duty cycle of the PWM wave signal, it includes: If the duty cycle is outside the preset interval, then control the bidirectional DC / DC module to turn off. In this embodiment, the duty cycle being outside the preset interval specifically means that the duty cycle satisfies D < 5% or D > 95%; If the duty cycle is within the first interval of the preset interval, then control the bidirectional DC / DC module to output a low voltage. In this embodiment, the duty cycle being within the first interval specifically means that the duty cycle satisfies 5% < D < 8%, and the low voltage is specifically a voltage of ±110V; If the duty cycle is within the second interval of the preset interval, and the lower limit value of the second interval is the upper limit value of the first interval, then control the bidirectional DC / DC module to output a medium voltage. In this embodiment, the duty cycle being within the second interval specifically means that the duty cycle satisfies 8% < D < 11%, and the medium voltage is specifically a voltage of ±200V; If the duty cycle is within the third interval of the preset interval, and the lower limit value of the third interval is the upper limit value of the second interval, then control the bidirectional DC / DC module to output a high voltage. In this embodiment, the duty cycle being within the third interval specifically means that the duty cycle satisfies 11% < D < 15%, and the high voltage is specifically a voltage of ±375V; If the duty cycle is within the fourth interval of the preset interval, and the lower limit value of the fourth interval is greater than the upper limit value of the third interval, then control the bidirectional DC / DC module to output the port current corresponding to the duty cycle. In this embodiment, the duty cycle being within the fourth interval specifically means that the duty cycle satisfies 20% < D < 70%, and the expression of the port current corresponding to the duty cycle is as follows:

[0085] Among them, D represents the duty cycle.

[0086] In summary, the present invention proposes an integrated power electronic transformer, which adopts a modular design and can meet the needs of different wind, solar, storage and charging application scenarios. It has the advantages of flexibility, reliability, strong adaptability, etc. It is directly connected to the DC bus, has high transmission efficiency, and adopts a modular design to increase the reliability of the device and reduce the manufacturing cost of the device. The design of the present invention adopts a shared port topology structure and a plug-and-play port. The device automatically identifies the type of access port device through the clever interface design of the device. This solution makes up for the shortcomings of the existing wind, solar and storage integrated devices, such as inconvenience in expansion and maintenance, and low flexibility, while further reducing the cost of port design and manufacturing.

[0087] The present invention also designs a corresponding control method for the proposed integrated power electronic transformer, adopts a current stress optimization algorithm and a switching mode control, and solves the problem that the dual active bridge circuit has no special optimization measures for current stress in ordinary single-phase shift control, resulting in low operating efficiency and high current stress.

[0088] The above is only a preferred embodiment of the present invention, and the protection scope of the present invention is not limited to the above embodiments. All technical solutions under the concept of the present invention belong to the protection scope of the present invention. It should be pointed out that for ordinary technicians in this technical field, some improvements and modifications without departing from the principle of the present invention should also be regarded as the protection scope of the present invention.

Claims

1. An integrated power electronic transformer, characterized in that: It includes a distribution network port on the input side and multiple port modules on the output side, multiple parallel dual active bridge circuit modules are arranged between the distribution network port and the port module, the output end of the dual active bridge circuit module is connected to the DC bus, the input end of the port module is connected to the DC bus, the distribution network port is connected to the input end of each dual active bridge circuit module through a three-phase AC / DC module, and the positive pole of the output end of the three-phase AC / DC module is connected to the positive pole of the input end of the first dual active bridge circuit module, the negative pole of the output end of the three-phase AC / DC module is connected to the negative pole of the input end of the last dual active bridge circuit module, and the positive pole of the input end of each dual active bridge circuit module is connected to the negative pole of the input end of the adjacent previous dual active bridge circuit module.

2. The integrated power electronic transformer according to claim 1, characterized in that: The port module includes a photovoltaic port module and a wind power port module. The photovoltaic port module includes a unidirectional DC / DC module and a photovoltaic port. The photovoltaic port is connected to the DC bus through the unidirectional DC / DC module. The wind power port module includes a DC / AC module and a wind power port. The wind power port is connected to the DC bus through the DC / AC module.

3. The integrated power electronic transformer according to claim 1, characterized in that: The port module includes an energy storage charging common port module, which includes an energy storage charging common port, a bidirectional DC / DC module and a common port controller. The common port controller is connected to the control end of the bidirectional DC / DC module, and the detection end of the common port controller is connected to the reference voltage through a pull-up resistor R1. The detection end of the common port controller is also connected to the ground through a voltage divider resistor R2 and a push switch S1 supported under a charging head provided with the energy storage charging common port. The detection end of the common port controller is also connected to the communication interface of the charging head, so that when the charging head is connected to the charging port of the electric vehicle or the energy storage device, the circuit between the reference voltage, the detection point and the resistance of the electric vehicle or the energy storage device is connected.

4. A control method for an integrated power electronic transformer, applied to the integrated power electronic transformer according to any one of claims 1 to 3, characterized in that: The steps of controlling the charging and discharging of the bidirectional DC / DC module by a common port controller include: Get the voltage value of the detection end; If the voltage value is the reference voltage value, the bidirectional DC / DC module is controlled to be turned off; If the voltage value is [reference voltage value / (R1+ R2)] * R1, the PWM wave signal is detected; If the voltage value is [reference voltage value / (R1+ R2*electric vehicle resistance R3 / (R2+electric vehicle resistance R3))]*R1, and a PWM wave signal is detected, the bidirectional DC / DC module is controlled to discharge according to the duty cycle of the PWM wave signal; If the voltage value is [reference voltage value / (R1+ R2*energy storage device resistance R3 / (R2+energy storage device resistance R3))]*R1, the bidirectional DC / DC module is controlled to perform bidirectional charging and discharging.

5. The control method of the integrated power electronic transformer according to claim 4, characterized in that: When the bidirectional DC / DC module discharge is controlled according to the duty cycle of the PWM wave signal, it includes: If the duty cycle is outside the preset interval, the bidirectional DC / DC module is controlled to be turned off; If the duty cycle is within a first interval within a preset interval, controlling the bidirectional DC / DC module to output a low voltage; If the duty cycle is in a second interval within the preset interval, and the lower limit value of the second interval is the upper limit value of the first interval, controlling the bidirectional DC / DC module to output a medium voltage; If the duty cycle is in a third interval within the preset interval, and the lower limit value of the third interval is the upper limit value of the second interval, controlling the bidirectional DC / DC module to output a high voltage; If the duty cycle is in a fourth interval within the preset interval, and the lower limit value of the fourth interval is greater than the upper limit value of the third interval, the bidirectional DC / DC module is controlled to output a port current corresponding to the duty cycle, and the port current expression is as follows: Where D represents the duty cycle.

6. A control method for an integrated power electronic transformer, applied to the integrated power electronic transformer according to any one of claims 1 to 3, characterized in that: The method includes the steps of optimizing and controlling the dual active bridge circuit module, specifically including: Obtain the output voltage, output current and input voltage of the current dual active bridge circuit module in real time, and calculate the corresponding real-time transmission power and voltage conversion ratio; Determine the mode suitable for the current operating conditions based on the voltage conversion ratio. If it is suitable for the standard mode, keep the inner shift ratio fixed and use PI control to adjust the outer shift ratio. If it is suitable for the optimal stress mode, calculate the value of the inner shift ratio when the current stress is minimum based on the real-time transmission power and voltage conversion ratio, and use PI control to adjust the outer shift ratio.

7. The control method of the integrated power electronic transformer according to claim 6, characterized in that: When determining the mode suitable for the current operating condition according to the voltage conversion ratio, specifically including: if the voltage conversion ratio is 1, it is suitable for the standard mode; if the voltage conversion ratio is greater than 1, it is suitable for the optimal stress mode.

8. The control method of the integrated power electronic transformer according to claim 6, characterized in that: The real-time transmission power and voltage conversion ratio expressions are as follows: in, To transfer power in real time, is the voltage conversion ratio, is the maximum power, , is the input voltage, is the output voltage, is the output current, is the turns ratio of the high frequency transformer in the dual active bridge circuit module, is the switching frequency of the switching devices in the dual active bridge circuit module, is the inductor in the dual active bridge circuit module.

9. The control method of the integrated power electronic transformer according to claim 6, characterized in that: The value of the internal shift ratio when the current stress is minimized is calculated based on the real-time transmission power and voltage conversion ratio, specifically including: Determine whether the real-time transmission power value meets If the real-time transmission power value meets this condition, then determine whether the voltage conversion ratio value meets If the voltage conversion ratio satisfies this condition, the value of the inner shift ratio when the current stress is the smallest is the first value; if the voltage conversion ratio does not satisfy , then the value of the inner displacement when the current stress is the smallest is greater than the second value; If the real-time transmission power value does not meet , then determine whether the value of real-time transmission power satisfies If the real-time transmission power value meets this condition, then determine whether the voltage conversion ratio value meets If the voltage conversion ratio satisfies this condition, the value of the inner shift ratio when the current stress is the smallest is the first value; if the voltage conversion ratio does not satisfy , then determine whether the value of the voltage conversion ratio satisfies If the voltage conversion ratio satisfies this condition, the value of the inner shift ratio when the current stress is the smallest is the first value; if the voltage conversion ratio does not satisfy , then the value of the inner displacement when the current stress is the smallest is greater than the second value; If the real-time transmission power value does not meet , then the value of the inner shift when the current stress is the smallest is the first value.

10. The control method of the integrated power electronic transformer according to claim 9, characterized in that: The expression of the first value is as follows: ； The second value expression is as follows: ； in, To transfer power in real time, is the voltage conversion ratio.

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