An integrated power electronic transformer and its control method

Abstract

The present invention discloses an integrated power electronic transformer and its control method. A plurality of parallel dual-active-bridge circuit modules are provided between the distribution network port and the port module. The distribution network port is connected to the input end of each dual-active-bridge circuit module through a three-phase AC / DC module. Moreover, 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, and 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. The positive terminal of the input end of each dual-active-bridge circuit module is connected to the negative terminal of the input end of the adjacent upper dual-active-bridge circuit module. The output end of the dual-active-bridge circuit module and the input end of the port module are both connected to the DC bus. The present invention has a relatively high transmission efficiency, reduces the voltage stress of the switching devices, and the dual-active-bridge circuit module adopts a current stress optimization control strategy to achieve high voltage transmission ratio and low current stress optimization control within the full operating range.

Description

Technical Field

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

[0002] With the large-scale popularization of new energy power sources such as distributed photovoltaic and wind power, and the rapid development of electric vehicles, the demand for new energy consumption and efficient and convenient charging is increasing continuously. However, affected by utilization rate and economy, the voltage stress borne by the switching devices in the traditional power electronic transformer system is large, and the conversion efficiency is not high. The existing integrated wind-solar-storage power electronic transformer has low reliability, complex structure and large device size, which is not conducive to expansion, has poor adaptability, and cannot meet the requirements of different application scenarios at the same time.

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

[0004] Technical problems to be solved by the present invention:

[0005] (1) The existing topologies of integrated wind-solar-storage-charging power electronic transformer devices generally do not have expandability, and have complex structures and poor stability.

[0006] (2) Most of the existing integrated wind-solar-storage-charging power electronic transformer devices adopt fixed energy storage battery packs, which are not conducive to maintenance or expansion. Replacing the battery pack will result in the device being unable to work for a long time, and the energy storage port and the electric vehicle charging port of the device are separately set, with a complex topology structure, high cost and being not conducive to modular simplification design, and it is also inconvenient for users to use.

[0007] In view of the above problems of the prior art, an integrated power electronic transformer and a control method thereof are provided. The integrated power electronic transformer adopts modular design, has high expandability and conversion efficiency, and uses a common interface for charging and energy storage, reducing the manufacturing cost.

[0008] To solve the above technical problems, the technical solutions adopted by the present invention are as follows:

[0009] An integrated power electronic transformer includes a distribution network port on the input side and multiple port modules on the output side. There are multiple parallel dual-active bridge circuit modules between the distribution network port and the port modules. 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 output end of the three-phase AC / DC module is connected to the positive input end of the first dual-active bridge circuit module, the negative output end of the three-phase AC / DC module is connected to the negative input end of the last dual-active bridge circuit module, and the positive input end of each dual-active bridge circuit module is connected to the negative input end of the adjacent upper dual-active bridge circuit module.

[0010] Further, 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.

[0011] Further, the port module includes a shared energy storage charging port module. The shared energy storage charging port module includes a shared energy storage charging 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 a pull-up resistor R1. The detection end of the shared port controller is also grounded through a voltage-dividing resistor R2 and a push-button switch S1 supported under the charging head provided with the shared energy storage charging port in sequence. 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 an electric vehicle or an energy storage device, the circuit between the reference voltage, the detection point, and the resistor of the electric vehicle or the energy storage device is connected.

[0012] The present invention also proposes a control method for an integrated power electronic transformer, including the step of controlling the charging and discharging of the bidirectional DC / DC module by the shared port controller, specifically including:

[0013] Obtain the voltage value of the detection end;

[0014] If the voltage value is the reference voltage value, control the bidirectional DC / DC module to turn off;

[0015] If the voltage value is [reference voltage value / (R1 + R2)] * R1, detect the PWM wave signal;

[0016] 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, then control the bidirectional DC / DC module to discharge according to the duty cycle of the PWM wave signal;

[0017] If the voltage value is [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.

[0018] Further, when controlling the bidirectional DC / DC module to discharge according to the duty cycle of the PWM wave signal, it includes:

[0019] If the duty cycle is outside the preset interval, then control the bidirectional DC / DC module to turn off;

[0020] 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;

[0021] 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;

[0022] 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;

[0023] 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.

[0024] Further, the expression of the port current corresponding to the duty cycle is as follows:

[0025]

[0026] Wherein, D represents the duty cycle.

[0027] The present invention also proposes a control method for an integrated power electronic transformer, including the steps of optimizing the control of the dual active bridge circuit module, specifically including:

[0028] Real-time obtain the output voltage, output current and input voltage of the current dual active bridge circuit module, and calculate the corresponding real-time transmission power and voltage conversion ratio;

[0029] Determine the mode suitable for the current operating condition according to the voltage conversion ratio. If the standard mode is suitable, keep the inner shift ratio as a fixed value and use PI control to adjust the outer shift ratio. If the optimal stress mode is suitable, calculate the value of the inner shift ratio when the current stress is minimized according to the real-time transmission power and the voltage conversion ratio, and use PI control to adjust the outer shift ratio.

[0030] 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, the standard mode is suitable; if the voltage conversion ratio is greater than 1, the optimal stress mode is suitable.

[0031] Furthermore, the expressions for the real-time transmission power and the voltage conversion ratio are as follows:

[0032]

[0033]

[0034] where, is the real-time transmission power, 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 device in the dual-active-bridge circuit module, is the inductor in the dual-active-bridge circuit module.

[0035] Furthermore, when calculating the value of the inner shift ratio when the current stress is minimized according to the real-time transmission power and the voltage conversion ratio, it specifically includes:

[0036] Judge whether the value of the real-time transmission power satisfies . If the value of the real-time transmission power satisfies this condition, then judge whether the value of the voltage conversion ratio satisfies . If the value of the voltage conversion ratio satisfies this condition, the value of the inner shift ratio when the current stress is minimized is the first value; if the value of the voltage conversion ratio does not satisfy , then the value of the inner shift ratio when the current stress is minimized is the second value;

[0037] If the value of the real-time transmission power does not satisfy , then judge whether the value of the real-time transmission power satisfies . If the value of the real-time transmission power satisfies this condition, then judge whether the value of the voltage conversion ratio satisfies , if the value of the voltage conversion ratio satisfies this condition, the value of the internal shift ratio when the current stress is minimized is the first value; if the value of the voltage conversion ratio does not satisfy , then it is determined whether the value of the voltage conversion ratio satisfies , if the value of the voltage conversion ratio satisfies this condition, the value of the internal shift ratio when the current stress is minimized is the first value; if the value of the voltage conversion ratio does not satisfy , then the value of the internal shift ratio when the current stress is minimized is the second value;

[0038] If the value of the real-time transmission power does not satisfy , then the value of the internal shift ratio when the current stress is minimized is the first value.

[0039] Furthermore, the expression of the first value is as follows:

[0040] ;

[0041] The expression of the second value is as follows:

[0042] ;

[0043] Among them, is the real-time transmission power, is the voltage conversion ratio.

[0044] Compared with the prior art, the advantages of the present invention are as follows:

[0045] In the present invention, the port module is directly connected to the DC bus on the output side, and the transmission efficiency is relatively high. A plurality of parallel Dual Active Bridge (DAB) modules are arranged between the input side and the output side, and the positive / negative input terminals of each DAB module are connected to the negative / positive input terminals of the adjacent DAB module, reducing the voltage stress of the switching device. In addition, the output terminals of all DAB modules are connected to the DC bus, thereby realizing large-current output.

[0046] The port module of the present invention includes different types and can adapt to different application scenarios of wind and solar loads. Among them, 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 control end of the shared port controller is connected to the bidirectional DC / DC converter. The detection end of the shared port controller is connected to the reference voltage through the pull-up resistor R1 and is also grounded through the voltage dividing resistor R2 and the push-button switch S1. It is also connected to the communication interface of the charging head provided with the energy storage charging shared port. 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 resistor 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 the working state by detecting the resistance value of the detection point and judge the type of the access device when it is in the working state, so as to realize the sharing of energy storage charging.

[0047] The DAB module of the present invention adopts a current stress optimization control strategy. By calculating the conditional parameters in real time, it determines the mode suitable for the current operating conditions. If it is suitable for the standard mode, it keeps the inner shift ratio as a fixed value and uses PI control to adjust the outer shift ratio. If it is suitable for the optimal stress mode, it calculates the inner and outer shift ratios when the stress is the smallest and adjusts the inner and outer shift ratios correspondingly, so as to realize the high voltage transfer ratio and low current stress optimization control in the full operating range. Brief Description of the Drawings

[0048] Figure 1 It is a schematic diagram of the topology structure of the power electronic transformer according to the embodiment of the present invention.

[0049] Figure 2 It is a schematic diagram of the three-phase AC / DC module circuit according to the embodiment of the present invention.

[0050] Figure 3 It is a schematic diagram of the circuit structure of the dual active bridge circuit module according to the embodiment of the present invention.

[0051] Figure 4 It is a schematic diagram of the topology structure of the dual active bridge circuit module of the power electronic transformer according to the embodiment of the present invention.

[0052] Figure 5 It is a schematic diagram of a circuit topology of the high-frequency transformer in the dual active bridge circuit module according to the embodiment of the present invention.

[0053] Figure 6 It is a schematic diagram of another circuit topology of the high-frequency transformer in the dual active bridge circuit module according to the embodiment of the present invention.

[0054] Figure 7 It is a schematic diagram of the circuit topology of the single-phase DC / DC module in the photovoltaic port module according to the embodiment of the present invention.

[0055] Figure 8Schematic diagram of the circuit topology of the bi-directional DC / DC module in the energy storage and charging common port module according to an embodiment of the present invention.

[0056] Figure 9 Schematic diagram of the energy storage and charging common port in the energy storage and charging common port module according to an embodiment of the present invention.

[0057] Figure 10 Schematic diagram of the circuit topology of the energy storage and charging common port module according to an embodiment of the present invention.

[0058] Figure 11 Flow chart for optimizing the control of the single-phase shift mode of the dual active bridge circuit module according to an embodiment of the present invention.

[0059] Figure 12 Waveform diagram of the internal and external phase shifts of the dual active bridge circuit module.

[0060] Figure 13 Flow chart of the current stress optimization control strategy for the dual active bridge circuit module according to an embodiment of the present invention.

[0061] Figure 14 Flow chart for the common port controller to control the charging and discharging of the bi-directional DC / DC module according to an embodiment of the present invention. Detailed implementation manners

[0062] The present invention will be further described below in conjunction with the accompanying drawings of the specification and specific preferred embodiments, but the protection scope of the present invention is not limited thereby.

[0063] Embodiment 1

[0064] 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 (DAB) module is provided between the distribution network port and the port modules. The output end of the dual active bridge circuit module is connected to the DC bus, and the input end of the port module is connected to the DC bus, ensuring a high transmission efficiency by directly accessing the DC bus.

[0065] As Figure 1 shown, the integrated power electronic transformer of this embodiment includes at least 4 ports. 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 and charging common 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 and charging common port of the energy storage and charging common port module is connected to the DC bus through a bi-directional DC / DC module.

[0066] In this embodiment, the number of each type of port module is not limited. According to actual needs, the number of DC / AC modules, single-phase DC / DC modules, and bidirectional DC / DC modules can be increased or decreased on the DC bus to adapt to different application scenarios of wind and solar loads.

[0067] In this embodiment, the three-phase AC / DC module can adopt Figure 2 the VSC converter shown or a converter with three-phase AC-DC conversion function. Its AC side is connected to the distribution network port and its DC side is connected to the dual active bridge circuit module. Thus, when the energy storage is insufficient, electrical energy can be input through the distribution network port to support the operation of the devices connected to the output side. When the energy storage is abundant, the three-phase AC / DC module converts direct current into three-phase alternating current and inputs it into the power grid.

[0068] In this embodiment, the circuit structure of the dual active bridge circuit module is as Figure 3 shown. The primary DC / AC module consists of a set of full-bridge inverters composed of four power switches S1, S2, S3, and S4, 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 at the same time, voltage boost or buck can be achieved. The secondary AC / DC module consists of another set of full-bridge inverters composed of four power switches S5, S6, S7, and S8, which rectifies the AC voltage on the secondary side of the high-frequency transformer back to DC output.

[0069] As Figure 4 shown, in this embodiment, multiple parallel dual active bridge circuit modules are provided. The positive pole of the output terminal of the three-phase AC / DC module is connected to the positive pole of the input terminal of the DC / AC module of the first dual active bridge circuit module, and the negative pole of the output terminal of the three-phase AC / DC module is connected to the negative pole of the input terminal of the DC / AC module of the last dual active bridge circuit module. The positive pole of the input terminal of the DC / AC module of each dual active bridge circuit module is connected to the negative pole of the input terminal of the DC / AC module of the adjacent upper dual active bridge circuit module. As Figure 4 shown, the negative pole of the input terminal of the DC / AC module of the first dual active bridge circuit module is connected to the positive pole of the input terminal of the DC / AC module of the second dual active bridge circuit module, and so on until the positive pole of the input terminal of the DC / AC module of the last dual active bridge circuit module is connected to the negative pole of the input terminal of the previous dual active bridge circuit module.

[0070] Through the above structure, the high-voltage direct current output by the three-phase AC / DC module is cascaded and divided by the DC / AC modules of each dual-active bridge circuit module, reducing the voltage stress of the switching devices. The high-frequency alternating current output by the DC / AC module is connected to the high-frequency transformer module. The high-frequency transformer can achieve 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 inside the device. The voltage output by the secondary side of the high-frequency transformer is rectified by the AC / DC module and finally connected in parallel and output to the low-voltage DC bus to achieve large-current output.

[0071] It should be noted that the connection form of each dual-active bridge circuit module can also be changed according to actual needs, adopting the form of input series output parallel or input output parallel or series-parallel connection. This embodiment does not make any limitations in this regard.

[0072] In this embodiment, the high-frequency transformer topology of the dual-active bridge circuit module is as Figure 5 shown. The high-frequency transformer topology can also adopt the topology with an LCL filter as Figure 6 shown, or the leakage inductance of the high-frequency transformer can be directly used to replace Figure 6 L2 in. The specific structure of the high-frequency transformer is not limited to this.

[0073] In this embodiment, the single-way DC / DC module of the photovoltaic port module can adopt, for example, Figure 7 the Boost circuit topology or other circuit topologies with single-phase DC / DC conversion function, which can achieve MPPT control and stably output an increased voltage.

[0074] In this embodiment, the DC / AC module of the wind power port module can also adopt, for example, Figure 2 the VSC converter shown or a converter with three-phase AC-DC conversion function. Its AC side is connected to the wind power port and its DC side is connected to the DC bus. The wind power port can be connected to a wind turbine, and generally a small wind turbine is used. In order to save costs, the switching devices that make up the VSC converter in the wind power port module are selected to have a relatively lower withstand voltage value compared to the three-phase AC / DC module of the distribution network port.

[0075] In this embodiment, the energy storage charging common port module includes an energy storage charging common port, a bidirectional DC / DC module, and a common port controller. The bidirectional DC / DC module can use, for example, Figure 8 the bidirectional buck-boost (Buck-Boost) converter or the bidirectional full bridge (H-bridge) and the bidirectional Cuk converter shown. The energy storage charging common port is as Figure 9 shown, with a total of 5 interfaces, namely DC positive pole DC+, DC negative pole DC-, communication interfaces CN1 and CN2, and common ground port PE. The left and right of the socket are symmetric structures, and the up and down adopt an asymmetric structure to prevent users from inserting the power supply positive and negative poles wrongly.

[0076] As Figure 10 shown, in this embodiment, both the DC positive electrode DC+ and the DC negative electrode DC- of the energy storage and 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. The detection end of the common port controller ( Figure 10 detection point 1 therein) is connected to the 24V reference voltage through the pull-up resistor R1. 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 charger head provided with the energy storage and charging common port. When the charger head is not in use, it is placed on the switch S1, so that the switch S1 is pressed and disconnected. When the charger head is in use, it is removed from the switch S1, so that the switch S1 is released and turned on.

[0077] As Figure 10 shown, the detection end of the common port controller is also connected to the communication interface CN2 of the charger head, so that when the charger 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 charger head, so that when the charger head is connected to the charging port of the electric vehicle, the PWM signal is obtained.

[0078] Through the above structure, the common port controller can sense the voltage change, so as to automatically identify the type of the device connected to the port and control the bidirectional DC / DC module to perform corresponding charge and discharge operations.

[0079] For example, when the energy storage and charging common port is not in use, the switch S1 is disconnected, and the voltage of the pull-up resistor R1 end can be measured as 24V at the detection point 1, and the port is in the non-working state. When the charger head is taken out from the charging device, S1 is closed. At this time, R1 and R2 are connected in series for voltage division, and the voltage measured at the detection point 1 is 12V, and the port enters the pre-working state, and starts to detect the PWM wave signal through the communication interface CN1.

[0080] When the charger head is connected to the charging port of the electric vehicle, R3 is connected, and the first voltage (for example, 8V) is obtained at the detection point 1, indicating that the plug is connected. At the same time, the voltage of the detection point 2 of the controller located in the electric vehicle changes (for example, from 12V to 8V), and the charging controller of the electric vehicle receives the plug connection signal and starts to send the PWM wave signal to control the operation of the charging port.

[0081] When the charger is connected to the charging port of the energy storage device, since the resistance value of R3 in the mobile energy storage device is different from that set in the electric vehicle, when the port is inserted, the second voltage (e.g., 3V) is obtained at the detection point 1, and the voltage at the detection point 2 of the mobile energy storage device changes (e.g., from 12V to 3V). Then it can be determined that the connected device is a mobile energy storage device, and the bidirectional DC / DC module is controlled to enter the bidirectional charge and discharge state. How to control the bidirectional DC / DC module to enter the bidirectional charge and discharge state is well known to those skilled in the art and will not be elaborated in this embodiment.

[0082] Thus, adopting the topological structure shared by electric vehicle charging and mobile energy storage devices can reduce the hardware cost of separately setting the electric vehicle charging port and the energy storage device. At the same time, it is convenient for energy storage capacity expansion and maintenance of the charging station, and improves the flexibility of the integrated power electronic transformer.

[0083] Embodiment 2

[0084] This embodiment proposes a control method for the integrated power electronic transformer described in Embodiment 1, including the steps of optimizing the control of the single-phase shift mode of the dual-active-bridge circuit module, as Figure 11 shown, specifically including:

[0085] S1) Real-time obtain the output voltage, output current and input voltage of the current dual-active-bridge circuit module, and calculate the corresponding real-time transmission power and voltage conversion ratio;

[0086] 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 phase shift ratio as a fixed value and use PI control to adjust the outer phase shift ratio. If it is suitable for the optimal stress mode, calculate the value of the inner phase shift ratio when the current stress is the smallest according to the real-time transmission power and voltage conversion ratio, and correspondingly adjust the value of the inner phase shift ratio to the value of the inner phase shift ratio when the stress is the smallest, and then use PI control to adjust the outer phase shift ratio.

[0087] 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 problems of low operating efficiency, large current stress in ordinary single-phase shift control, and only being able to operate efficiently when the voltage conversion ratio is 1, and the efficiency will be significantly reduced when the voltage amplitudes on both sides of the transformer do not match.

[0088] Specifically, as Figure 12 shown in the control waveform, D1 is the inner phase shift ratio in DAB, D2 is the outer phase shift ratio, and Ths is half a cycle. The maximum output power in the single-phase shift mode is , and the expressions of the real-time transmission power and voltage conversion ratio in step S1 are as follows:

[0089]

[0090]

[0091] Among them, is the real-time transmission power, 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 device in the dual-active-bridge circuit module, is the inductor in the dual-active-bridge circuit module.

[0092] In step S2 of this embodiment, the value of the inner shift ratio when the current stress is the smallest under the optimal stress mode is calculated according to the mathematical model of the dual-active-bridge circuit, and it is a control calculation model for the optimal stress value within the operating value range. The following is the calculation and derivation process:

[0093] From the well-known DAB transmission power and current expressions, we can obtain:

[0094]

[0095]

[0096] Combined with Figure 12 's waveform diagram and Figure 3 's DAB circuit diagram, we can obtain:

[0097]

[0098]

[0099] Assume that the DAB low-voltage DC output terminal is connected to a pure resistive load, then the above formula can be changed to:

[0100]

[0101]

[0102] Taking the rated transmission power in single-phase shift as the base value, we can obtain:

[0103]

[0104] Taking the rated transmission current in single-phase shift as the base value, we can obtain:

[0105]

[0106] It can be obtained by the transformation of formula p:

[0107]

[0108] Therefore, G can be changed to:

[0109]

[0110] In order to obtain the minimum current stresses G1min and G2min, the above formula is respectively differentiated with respect to D2 to obtain:

[0111]

[0112] Among them, for formula, from when , and when , when , according to the monotonicity of the function, it can be known that the function has a minimum point in the interval (the outward shift ratio under the minimum current stress) . Substituting it into formula, the minimum value (local minimum current stress) can be obtained ; Similarly, combining the above formula, it can be obtained that has a minimum point in the interval (the outward shift ratio under the minimum current stress) . Substituting it into formula, the minimum value (local minimum current stress) can be obtained .

[0113] 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 points D2 into the expressions of formulas G1 and G2 respectively, the minimum values , can be obtained. Substituting the same p0 and k into G1min and G2min and comparing them, it can be obtained that G1min < G2min. Therefore, the global optimal current stress value . The specific combinations of the minimum current stress shift ratios are listed as follows:

[0114] When , , the following can be obtained:

[0115]

[0116] When , , the following can be obtained:

[0117]

[0118] Among them, represents the value compared with the inner shift when the stress is the smallest, represents the value compared with the outer shift when the stress is the smallest, is the real-time transmission power, is the voltage conversion ratio.

[0119] In step S2 of this embodiment, two switching modes of current stress optimization control are involved:

[0120] When the voltage transmission ratio (i.e., the voltage conversion ratio) is close to 1, the standard control mode is adopted, where the inner shift ratio D1 is a given fixed value, and the PI control is used to adjust the outer shift ratio. Specifically, after obtaining the error ΔV2 obtained by comparing the output voltage V2 with the reference voltage V2ref, D2* is obtained through the PI regulator, and then the pulse signal 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.

[0121] When a high voltage transmission ratio and light load operation are required, the optimal stress mode is adopted. To facilitate controlling the output voltage while reducing the current stress, the inner shift ratio D1 and the outer shift ratio D2 are adjusted separately. The outer shift ratio D2 is responsible for controlling the stability of the output voltage, and the inner shift ratio D1 is responsible for optimizing the current stress. The value of the outer shift ratio D2 is the same as that in the standard control mode, and the stability of the output voltage is ensured through PI regulation. The value of the inner shift ratio D1 is the value of the inner shift ratio when the current stress is the smallest in the aforementioned optimal stress mode. The switching control of the two modes realizes the optimization of the current stress in the entire operating range, that is, it makes up for the deficiency that only when the voltage transmission ratio is 1 can the maximum power be output under single-phase shift control.

[0122] As Figure 13 shown, in step S2, in the optimal stress mode, when calculating the value of the inner shift ratio when the current stress is the smallest according to the real-time transmission power and the voltage conversion ratio, specifically, it is judged according to the calculated real-time range of the current stress optimization switch control k and p0 to obtain the corresponding control mode SFi (i = 1, 2, 3, 4), so as to obtain the value of the inner shift ratio under different control modes. Specifically:

[0123] After obtaining the real-time transmission power, judge whether the value of the real-time transmission power satisfies , if the value of the real-time transmission power satisfies this condition, then judge whether the value of the voltage conversion ratio satisfies , if the value of the voltage conversion ratio satisfies this condition, then i = 2, which is the second control mode (SF2); if the value of the voltage conversion ratio does not satisfy , then i = 1, which is the first control mode (SF1);

[0124] If the value of the real-time transmission power does not meet , then determine whether the value of the real-time transmission power meets . If the value of the real-time transmission power meets this condition, then determine whether the value of the voltage conversion ratio meets . If the value of the voltage conversion ratio meets this condition, then i = 2, which is the second control mode (SF2); if the value of the voltage conversion ratio does not meet , then determine whether the value of the voltage conversion ratio meets . If the value of the voltage conversion ratio meets this condition, then i = 2, which is the second control mode (SF2); if the value of the voltage conversion ratio does not meet , then i = 3, which is the third control mode (SF3);

[0125] If the value of the real-time transmission power does not meet , then i = 4, which is the fourth control mode (SF4).

[0126] Among them, the value of the inner and outer shift ratio when the current stress corresponding to SF2 is the smallest is , , and the value of the inner and outer shift ratio when the current stress corresponding to SF1, SF3, and SF4 is the smallest is , .

[0127] Finally, adjust the value of the inner shift ratio to the value of the inner shift ratio when the stress is the smallest, and then use PI control to adjust the outer shift ratio to obtain D 1 = D 1ref and D 2 = D 2 * value, that is, the inner and outer shift ratio in the optimal stress mode. When the converter operates at the optimal current stress point, the efficiency can usually reach the maximum value.

[0128] Example 3

[0129] This example proposes a control method for the integrated power electronic transformer described in Example 1, including the step of controlling the charging and discharging of the bidirectional DC / DC module by the common port controller, as Figure 14 shown, specifically including:

[0130] Obtain the voltage value at the detection end;

[0131] If the voltage value is the reference voltage value, then control the bidirectional DC / DC module to turn off;

[0132] If the voltage value is the first voltage value, and the first voltage value is specifically [reference voltage value / (R1 + R2)] * R1, then detect the PWM wave signal;

[0133] If the voltage value is the second voltage value, specifically [reference voltage value / (R1 + R2 * electric vehicle resistance R3 / (R2 + electric vehicle resistance R3))] * R1, and a PWM wave signal is detected, then control the two-way DC / DC module to discharge according to the duty cycle of the PWM wave signal;

[0134] If the voltage value is the third voltage value, specifically [reference voltage value / (R1 + R2 * energy storage device resistance R3 / (R2 + energy storage device resistance R3))] * R1, then control the two-way DC / DC module to perform bidirectional charging and discharging.

[0135] In this embodiment, when controlling the two-way DC / DC module to discharge according to the duty cycle of the PWM wave signal, it includes:

[0136] If the duty cycle is outside the preset interval, then control the two-way 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%;

[0137] If the duty cycle is within the first interval of the preset interval, then control the two-way DC / DC module to output a low voltage. In this embodiment, the duty cycle within the first interval specifically means that the duty cycle satisfies 5% < D < 8%, and the low voltage is specifically a voltage of ±110V;

[0138] 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 two-way DC / DC module to output a medium voltage. In this embodiment, the duty cycle within the second interval specifically means that the duty cycle satisfies 8% < D < 11%, and the medium voltage is specifically a voltage of ±200V;

[0139] 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 two-way DC / DC module to output a high voltage. In this embodiment, the duty cycle within the third interval specifically means that the duty cycle satisfies 11% < D < 15%, and the high voltage is specifically a voltage of ±375V;

[0140] 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 two-way DC / DC module to output the port current corresponding to the duty cycle. In this embodiment, the duty cycle 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:

[0141]

[0142] Among them, D represents the duty cycle.

[0143] In summary, the present invention proposes an integrated power electronic transformer. Using modular design, it can meet the requirements of different wind-solar-storage-charging application scenarios, and has the advantages of flexibility, reliability, and strong adaptability. It is directly connected to the DC bus, with high transmission efficiency. The modular design increases the reliability of the device and reduces the manufacturing cost of the device. The design of the present invention adopts a common-port topology structure, a plug-and-play port, and automatically identifies the type of the device connected to the port through the ingenious interface design of the device. This solution makes up for the disadvantages of the existing wind-solar-storage integrated devices, such as inconvenient expansion and maintenance and low flexibility, and further reduces the cost of port design and manufacturing.

[0144] The present invention also designs a corresponding control method for the proposed integrated power electronic transformer. By using the current stress optimization algorithm and switching mode control, it solves the problems of the dual-active-bridge circuit in the ordinary single-phase shift control, such as no special optimization measures for current stress, low operating efficiency, and large current stress.

[0145] The above are only the preferred embodiments of the present invention. The protection scope of the present invention is not limited to the above embodiments. All technical solutions within the idea of the present invention belong to the protection scope of the present invention. It should be pointed out that for those of ordinary skill in the art in this technical field, several improvements and refinements made 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, 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 dual active bridge circuit module, and the step of optimizing and controlling the dual active bridge circuit module specifically includes: 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.

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 in a first interval within a preset interval, the bidirectional DC / DC module is controlled to output a low voltage, where the low voltage is specifically a voltage of positive or negative 110V; 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, the bidirectional DC / DC module is controlled to output a medium voltage, where the medium voltage is specifically a voltage of plus or minus 200V; 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, the bidirectional DC / DC module is controlled to output a high voltage, and the high voltage is specifically a voltage of plus or minus 375V; 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 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 displacement when the current stress is the smallest is the first value; 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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