A multi-port dc converter and a control method thereof

Abstract

This invention provides a multi-port DC-DC converter and its control method. The method includes: each converter controlling its own operating state based on the DC bus voltage and the deviation between the reference bus voltage and its corresponding value, so as to maintain the DC bus voltage as the voltage reference value; furthermore, the deviations of each converter are different; that is, through the coordinated control of each port controller, the control right of the DC bus voltage is autonomously switched, ensuring that the system can still maintain stable operation when any port fails. This method combines the advantages of centralized control and peer-to-peer control, does not require complex central controller logic, reduces communication workload, and maintains stable system operation to the maximum extent without increasing control complexity.

Description

Technical Field

[0001] This invention belongs to the field of DC-DC converters and related technologies, and more specifically, relates to a multi-port DC-DC converter and its control method. Background Technology

[0002] From the perspective of energy and power development, China's carbon peaking and carbon neutrality goals are forcing the energy sector to accelerate its green and low-carbon transformation, requiring high-quality energy development to be promoted in the direction of "optimizing structure, improving efficiency, ensuring safety, and reducing costs".

[0003] Existing photovoltaic power plants mainly use AC output, but AC systems have problems such as voltage exceeding limits and wide frequency range oscillations, and AC line losses also restrict the overall system efficiency and output capacity.

[0004] Compared to AC systems, DC systems offer greater transmission capacity and lower losses at the same voltage level, and avoid the effects of capacitive and inductive reactance, eliminating technical issues such as reactive power compensation and system resonance. With the development of power electronics technology, photovoltaic medium-voltage DC converters can solve the problem of photovoltaic DC transmission.

[0005] Combining photovoltaic medium-voltage DC converters with multi-port converters can enhance the power supply reliability and flexibility of the system, facilitate the access of various distributed power sources or energy storage, and facilitate the access of various types of loads, making it suitable for AC / DC hybrid power distribution applications.

[0006] In existing technologies, the power of a photovoltaic DC-DC converter is controlled based on the relationship between the output voltage and a preset upper limit voltage control, so as to enable smooth switching of the DC-DC converter's operating mode. However, this existing technology is applied to two-port photovoltaic DC-DC converters, and the control method only considers the coordination control between the two ports. For multi-port systems with three or more ports, this method cannot coordinate the switching of operating modes between the ports. Summary of the Invention

[0007] In view of this, the purpose of the present invention is to provide a multi-port DC-DC converter and its control method, which can maintain the stable operation of the system to the maximum extent without increasing the complexity of control.

[0008] The first aspect of this application discloses a control method for a multi-port DC-DC converter, wherein one side of the four converters of the multi-port DC-DC converter is connected via a DC bus, and the other side of each converter serves as a port of the multi-port DC-DC converter, respectively connected to a photovoltaic array, a medium-voltage DC distribution network, a low-voltage DC distribution network, and a low-voltage AC distribution network; the control method includes:

[0009] Each converter controls its own operating state based on the DC bus voltage and the reference bus voltage and its corresponding deviation, so as to keep the DC bus voltage as a voltage reference value; wherein the voltage reference value is the reference bus voltage, the sum of the reference bus voltage and the deviation, or the difference between the reference bus voltage and the deviation; wherein the deviation is different for each converter.

[0010] Optionally, each of the converters controls its own operating state based on the DC bus voltage and the deviation between the reference bus voltage and its corresponding value, so as to keep the DC bus voltage as the voltage reference value, including:

[0011] The photovoltaic DC / DC converter connected to the photovoltaic array controls its own operating state based on the DC bus voltage and the reference bus voltage and the first deviation, so as to keep the DC bus voltage at the voltage reference value.

[0012] Optionally, the photovoltaic DC / DC converter controls its operating state based on the DC bus voltage and the reference bus voltage and the first deviation, so as to keep the DC bus voltage at the voltage reference value, including:

[0013] The feedback value of the DC bus voltage is subtracted from the given value of the sum of the reference bus voltage and the first deviation, and then used as the input of the first proportional-integral regulator; wherein, the lower limit of the output of the first proportional-integral regulator is -1; the given value of the photovoltaic array voltage is subtracted from the feedback value of the photovoltaic array voltage and then input to the third proportional-integral regulator, and after passing through the second inverter, it is used as the upper limit of the output of the first proportional-integral regulator.

[0014] The output of the first proportional-integral regulator is connected to the first inverter;

[0015] The output of the first inverter is subtracted from the feedback value of the inductor current in the photovoltaic DC / DC converter and then used as the input of the second proportional-integral regulator.

[0016] The output of the second proportional-integral regulator is modulated by PWM to output a PWM square wave, which serves as the drive signal for each switch in the photovoltaic DC / DC converter.

[0017] Optionally, each of the converters controls its own operating state based on the DC bus voltage and the deviation between the reference bus voltage and its corresponding value, so as to keep the DC bus voltage at the voltage reference value, including:

[0018] The bidirectional DC / DC converter connected to the low-voltage DC distribution network controls its own operating state based on the DC bus voltage and the reference bus voltage and the second deviation, so as to keep the DC bus voltage at the voltage reference value.

[0019] Optionally, the bidirectional DC / DC converter controls its operating state based on the DC bus voltage and the reference bus voltage and the second deviation, so as to keep the DC bus voltage at the voltage reference value, including:

[0020] The feedback value of the DC bus voltage is subtracted from the given value of the sum of the reference bus voltage and the second deviation, and then used as the input of the fourth proportional-integral regulator; wherein, the lower limit of the output of the fourth proportional-integral regulator is -1; the upper limit of the output is the value of the given value of the inductor current after passing through the third inverter;

[0021] The feedback value of the DC bus voltage is subtracted from the given value of the difference between the reference bus voltage and the second deviation, and then used as the input of the fifth proportional-integral regulator; wherein, the upper limit of the output of the fourth proportional-integral regulator is 1; and the output of the fourth proportional-integral regulator is used as the lower limit of the output of the fifth proportional-integral regulator.

[0022] The output of the fifth proportional-integral regulator is subtracted from the feedback value of the first inductor current and then input to the sixth proportional-integral regulator; the output of the sixth proportional-integral regulator is modulated by PWM to output a PWM square wave, which serves as the drive signal for the first Boost circuit corresponding to the first inductor.

[0023] The output of the fifth proportional-integral regulator is subtracted from the feedback value of the second inductor current and then input to the seventh proportional-integral regulator. The output of the seventh proportional-integral regulator is modulated by PWM to output a PWM square wave, which serves as the drive signal for the second Boost circuit corresponding to the second inductor.

[0024] Optionally, each of the converters controls its own operating state based on the DC bus voltage and the deviation between the reference bus voltage and its corresponding value, so as to keep the DC bus voltage at the voltage reference value, including:

[0025] The DC / AC converter connected to the low-voltage AC distribution network controls its own operating state based on the DC bus voltage, the reference bus voltage, and the third deviation, so as to keep the DC bus voltage at the voltage reference value.

[0026] Optionally, the DC / AC converter controls its operating state based on the DC bus voltage and the reference bus voltage and the third deviation, so as to keep the DC bus voltage at the voltage reference value, including:

[0027] The feedback value of the DC bus voltage is subtracted from the given value of the sum of the reference bus voltage and the third deviation, and then used as the input of the eighth proportional-integral regulator; wherein, the lower limit of the output of the eighth proportional-integral regulator is -1; the upper limit of the output is the value of the given value of the d-axis component of the AC current after passing through the seventh inverter;

[0028] The feedback value of the DC bus voltage is subtracted from the given value of the difference between the reference bus voltage and the third deviation, and then used as the input of the ninth proportional-integral regulator; wherein, the upper limit of the output of the ninth proportional-integral regulator is 1; and the output of the eighth proportional-integral regulator is used as the lower limit of the output of the ninth proportional-integral regulator.

[0029] The output of the ninth proportional-integral regulator is subtracted from the feedback value of the d-axis component of the AC current and then input to the tenth proportional-integral regulator; the output of the tenth proportional-integral regulator is modulated by PWM and input to the dq / abc coordinate transformation unit.

[0030] The given value of the q-axis component of the AC current is subtracted from the feedback value of the q-axis component of the AC current, and then input to the eleventh proportional-integral regulator; the output of the eleventh proportional-integral regulator is modulated by PWM and then input to the dq / abc coordinate transformation unit.

[0031] The output of the dq / abc coordinate transformation unit is modulated again by PWM to output a PWM square wave, which serves as the drive signal for each switch in the DC / AC converter.

[0032] Optionally, each of the converters controls its own operating state based on the DC bus voltage and the deviation between the reference bus voltage and its corresponding value, so as to keep the DC bus voltage at the voltage reference value, including:

[0033] The medium-voltage DC / DC converter connected to the medium-voltage DC distribution network adopts open-loop fixed-frequency control to clamp the DC bus voltage to the voltage reference value when the medium-voltage DC converter is operating normally.

[0034] The second aspect of this application discloses a multi-port DC-DC converter, including: a photovoltaic DC / DC converter, a medium-voltage DC / DC converter, a bidirectional DC / DC converter, and a DC / AC converter;

[0035] Each converter is connected on one side via a DC bus;

[0036] The other side of the photovoltaic DC / DC converter serves as the first port of the multi-port DC converter and is connected to the photovoltaic array.

[0037] The other side of the medium-voltage DC / DC converter serves as the second port of the multi-port DC converter and is connected to the medium-voltage DC distribution network.

[0038] The other side of the bidirectional DC / DC converter serves as the third port of the multi-port DC converter and is connected to the low-voltage DC distribution network.

[0039] The other side of the DC / AC converter serves as the fourth port of the multi-port DC converter, connecting to the low-voltage AC distribution network.

[0040] The various converters are combined to implement the control method for a multi-port DC-DC converter as described in any of the first aspects of this application.

[0041] Optionally, in the above-mentioned multi-port DC-DC converter,

[0042] The photovoltaic DC / DC converter adopts a topology of multiple Boost circuits connected in parallel;

[0043] The medium-voltage DC / DC converter includes: multiple unidirectional resonant converters;

[0044] The bidirectional DC / DC converter includes: two bidirectional resonant converters connected in parallel;

[0045] The DC / AC converter includes four three-phase inverters connected in parallel.

[0046] As can be seen from the above technical solution, the control method for a multi-port DC-DC converter provided by the present invention includes: each converter controlling its own operating state based on the DC bus voltage and the deviation between the reference bus voltage and its corresponding value, so as to keep the DC bus voltage as the voltage reference value; that is, through the coordinated control of each port controller, the autonomous switching of the control right of the DC bus voltage is realized, ensuring that the system can still maintain stable operation when any port fails. This method combines the advantages of centralized control and peer-to-peer control, does not require complex central controller logic, reduces the workload of communication, and maintains the stable operation of the system to the maximum extent without increasing the complexity of control. Attached Figure Description

[0047] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0048] Figure 1 This is a flowchart of a control method for a multi-port DC-DC converter provided in an embodiment of the present invention;

[0049] Figure 2 This is a control block diagram of a photovoltaic DC / DC converter in the control method of a multi-port DC converter provided in an embodiment of the present invention;

[0050] Figure 3 This is a control block diagram of a bidirectional DC / DC inverter in the control method of a multi-port DC-DC converter provided in an embodiment of the present invention;

[0051] Figure 4 This is a control block diagram of the DC / AC converter in the control method of the multi-port DC converter provided in the embodiments of the present invention;

[0052] Figure 5 This is a schematic diagram of a multi-port DC-DC converter provided in an embodiment of the present invention;

[0053] Figure 6 This is a schematic diagram of a photovoltaic DC / DC converter in a multi-port DC-DC converter provided in an embodiment of the present invention;

[0054] Figure 7 This is a schematic diagram of a medium-voltage DC / DC converter in a multi-port DC-DC converter provided in an embodiment of the present invention;

[0055] Figure 8 This is a schematic diagram of a bidirectional DC / DC converter in a multi-port DC-DC converter provided in an embodiment of the present invention;

[0056] Figure 9 This is a schematic diagram of a DC / AC converter in a multi-port DC-DC converter provided in an embodiment of the present invention;

[0057] Figure 10 This is a control flowchart of a central controller in a multi-port DC-DC converter provided in an embodiment of the present invention;

[0058] Figure 11 This is another control flowchart of the central controller in a multi-port DC-DC converter provided in an embodiment of the present invention. Detailed Implementation

[0059] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0060] In this application, the terms "comprising," "including," or any other variations thereof are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0061] This application provides a control method for a multi-port DC-DC converter, which solves the problem that the existing control methods only consider the coordination control between two ports. For multi-port systems with three or more ports, this method cannot coordinate the switching of operating modes between the ports.

[0062] The multi-port DC converter includes four converters; one side of each converter is connected via a DC bus, and the other side of each converter serves as a port of the multi-port DC converter, connecting to the photovoltaic array, medium-voltage DC distribution network, low-voltage DC distribution network, and low-voltage AC distribution network respectively.

[0063] Specifically, the four converters are: photovoltaic DC / DC converter, medium-voltage DC / DC converter, bidirectional DC / DC converter, and DC / AC converter.

[0064] Each converter is connected on one side via a DC bus.

[0065] The other side of the photovoltaic DC / DC converter serves as the first port of the multi-port DC converter, connecting to the photovoltaic array.

[0066] The other side of the medium-voltage DC / DC converter serves as the second port of the multi-port DC converter, connecting to the medium-voltage DC distribution network.

[0067] The other side of the bidirectional DC / DC converter serves as the third port of the multi-port DC converter, connecting to the low-voltage DC distribution network.

[0068] The other side of the DC / AC converter serves as the fourth port of the multi-port DC converter, connecting to the low-voltage AC distribution network.

[0069] See Figure 1 The control method for this multi-port DC-DC converter includes:

[0070] S101. Each converter controls its own operating state based on the DC bus voltage and the deviation between the reference bus voltage and its corresponding value, so as to keep the DC bus voltage as the voltage reference value.

[0071] The voltage reference value is the reference bus voltage, the sum of the reference bus voltage and the deviation, or the difference between the reference bus voltage and the deviation.

[0072] In other words, each converter in a multi-port DC-DC converter has the function of maintaining the DC bus voltage at the reference bus voltage. Each converter also has a controller.

[0073] Specifically, the controllers of each converter use the DC bus voltage and the reference bus voltage as control parameters for the operation of each converter, thereby controlling the operating state of the converter to maintain the DC bus voltage as the reference bus voltage.

[0074] That is, each port uses its own controller to control the port's operation mode, and the control of the DC bus is autonomously coordinated and controlled by each port controller.

[0075] The reference bus low voltage can be 800V, but it can also be any value between 630V and 850V. Once the reference bus low voltage is determined, it cannot be changed.

[0076] In this embodiment, each converter controls its own operating state based on the DC bus voltage and the deviation between the reference bus voltage and its corresponding value, so as to keep the DC bus voltage as the voltage reference value. That is, through the coordinated control of each port controller, the control of the DC bus voltage is autonomously switched, ensuring that the system can still maintain stable operation when any port fails. This method combines the advantages of centralized control and peer-to-peer control, does not require complex central controller logic, reduces the workload of communication, and maintains the stable operation of the system to the maximum extent without increasing the complexity of control.

[0077] In practical applications, step S101 may include: the photovoltaic DC / DC converter connected to the photovoltaic array controls its own operating state based on the DC bus voltage and the reference bus voltage and the first deviation, so as to keep the DC bus voltage as the voltage reference value.

[0078] The value of the first deviation is not specifically limited here, but can be determined according to the actual situation, and is within the scope of protection of this application.

[0079] Specifically, such as Figure 2 As shown, the photovoltaic DC / DC converter controls its operating state based on the DC bus voltage and the first deviation between the reference bus voltage and the DC bus voltage, in order to maintain the DC bus voltage at the voltage reference value. The specific process is as follows:

[0080] The feedback value of the DC bus voltage is subtracted from the given value (the sum of the reference bus voltage and the first deviation) and used as the input to the first proportional-integral (PI) regulator. The lower limit of the first PI regulator's output is -1. The subtraction between the given value of the photovoltaic array voltage and the feedback value of the photovoltaic array voltage is input to the third PI regulator, and after passing through the second inverter, it becomes the upper limit of the first PI regulator's output.

[0081] The output of the first proportional-integral controller is connected to the second inverter.

[0082] The output of the second inverter is subtracted from the feedback value of the inductor current in the photovoltaic DC / DC converter and then used as the input of the second proportional-integral regulator.

[0083] The output of the second proportional-integral regulator is modulated by PWM to output a PWM square wave, which serves as the drive signal for each switch in the photovoltaic DC / DC converter.

[0084] Where Upv is the photovoltaic array voltage; Upv_ref is the photovoltaic array setpoint voltage; Udcline is the DC bus voltage; dU1 is the deviation voltage value, i.e., the first deviation, which can be modified in the background; I_feedback is the inductor current feedback, which is the inductor current of the basic module in the photovoltaic DC / DC converter; for example, it is the current of L11. Figure 6 The structure shown consists of multiple modules connected in parallel. Each module differs from the basic module in that it is composed of two inductors and bridge arm branches connected in parallel. Both the parallel connection of inductors and bridge arm branches and the parallel connection of modules are used to increase the converter power.

[0085] The controller of this photovoltaic DC / DC converter includes an outer voltage loop and an inner current loop. The outer voltage loop is the DC bus voltage control loop, and the upper limit of the controller is given by the output of the photovoltaic array voltage controller.

[0086] In practical applications, step S101 above may include: the medium-voltage DC / DC converter connected to the medium-voltage DC distribution network adopts open-loop fixed-frequency control so that the DC bus voltage is clamped to the voltage reference value when the medium-voltage DC converter is operating normally.

[0087] The medium-voltage DC / DC converter adopts open-loop fixed-frequency control, and clamps the intermediate bus voltage to 800V during normal operation.

[0088] In other words, the DC bus voltage is mainly maintained by the medium-voltage DC / DC converter.

[0089] like Figure 7As shown, when the medium-voltage DC / DC converter is operating normally, due to the clamping characteristics of the high-voltage side diodes of the medium-voltage DC / DC converter, the high-voltage side is clamped to 20kV. After the transformation ratio of the medium-voltage DC / DC converter is converted, the low-voltage side is 800V, thereby maintaining the DC bus voltage at 800V.

[0090] In practical applications, step S101 may include: the bidirectional DC / DC converter connected to the low-voltage DC distribution network controls its own operating state based on the DC bus voltage, the reference bus voltage and the second deviation, so as to keep the DC bus voltage as the voltage reference value.

[0091] like Figure 3 As shown, in practical applications, the bidirectional DC / DC converter controls its operating state based on the DC bus voltage and the reference bus voltage and the second deviation, so as to keep the DC bus voltage as the voltage reference value, including:

[0092] The feedback value of the DC bus voltage, subtracted from the given value (the sum of the reference bus voltage and the second deviation), is used as the input to the fourth proportional-integral (PI) regulator. The lower limit of the fourth PI regulator's output is -1. The upper limit of the output is the value of the inductor current after passing through the third inverter.

[0093] The feedback value of the DC bus voltage, subtracted from the given value of the difference between the reference bus voltage and the second deviation, is used as the input of the fifth proportional-integral (PI) controller. The upper limit of the output of the fourth PI controller is 1. The output of the fourth PI controller serves as the lower limit of the output of the fifth PI controller.

[0094] The output of the fifth proportional-integral (PI) regulator is subtracted from the feedback value of the first inductor current and then input to the sixth PI regulator. The output of the sixth PI regulator is PWM modulated to output a PWM square wave, which serves as the drive signal for the first Boost circuit corresponding to the first inductor.

[0095] The output of the fifth proportional-integral (PI) regulator is subtracted from the feedback value of the second inductor current and then input to the seventh PI regulator. The output of the seventh PI regulator is PWM modulated to output a PWM square wave, which serves as the drive signal for the second Boost circuit corresponding to the second inductor.

[0096] Where Ubst_low is the DC bus voltage; dU2 is the deviation voltage value, also known as the second deviation. dU2 and dU1 are different parameters and need to be set to different values; I_ref is the Boost inductor current setpoint, which can be given by the host computer or calculated from the power setpoint; Ibst1 is the first inductor current; as... Figure 8The current of inductor L1 is shown; Ibst2 is the current of the second inductor, as shown. Figure 8 The current in inductor L2 is shown.

[0097] The controller in this bidirectional DC / DC converter also includes an outer voltage loop and an inner current loop. The outer voltage loop uses a deviation controller, which can autonomously control the bidirectional DC / DC converter to operate in constant current mode or constant bus voltage mode based on the DC bus voltage value, so as to control the DC bus voltage stability.

[0098] When Ubst_low is greater than the upper deviation controller's voltage reference value of 800 + dU2, the lower deviation controller, due to the accumulation effect of integration, outputs the lower limit of the fourth proportional-integral controller, which is equal to the output of the upper deviation controller. Therefore, in this case, the output of the deviation controller is equal to the output of the upper deviation controller. Because Ubst_low is greater than 800 + dU2, the upper deviation controller output is negative, current flows from the DC bus to the 750V distribution network, the DC bus voltage decreases, and eventually the DC bus voltage is stabilized at the voltage reference value of 800 + dU2.

[0099] When the DC bus voltage Ubst_low is less than the lower deviation controller voltage reference value 800-dU2, the lower deviation controller output is positive, and the current flows from the 750V distribution network to the DC bus, increasing the DC bus voltage. Eventually, the DC bus voltage is stabilized at the voltage reference value 800-dU2.

[0100] When the DC bus voltage Ubst_low is less than the upper deviation controller voltage reference value 800+dU2 and greater than the lower deviation controller voltage reference value 800-dU2, the lower deviation controller, due to the integral accumulation effect, outputs the lower limit of the fourth proportional-integral controller, which is also the output value of the upper deviation controller. The upper deviation controller, due to the integral accumulation effect, outputs the upper limit of the fifth proportional-integral controller. Therefore, in this case, the voltage deviation controller output is -Iref.

[0101] In practical applications, step S101 above may include: the DC / AC converter connected to the low-voltage AC distribution network controls its own operating state based on the DC bus voltage, the reference bus voltage and the third deviation, so as to keep the DC bus voltage as the voltage reference value.

[0102] like Figure 4 As shown, in practical applications, the DC / AC converter controls its operating state based on the DC bus voltage, the reference bus voltage, and the third deviation, to maintain the DC bus voltage at the voltage reference value, including:

[0103] The feedback value of the DC bus voltage, subtracted from the given value (the sum of the reference bus voltage and the third deviation), is used as the input to the eighth proportional-integral (PI) controller. The lower limit of the eighth PI controller's output is -1. The upper limit of the output is the value of the given value of the AC current d-axis component after passing through the seventh inverter.

[0104] The feedback value of the DC bus voltage, subtracted from the given value of the difference between the reference bus voltage and the third deviation, is used as the input of the ninth proportional-integral (PI) controller. The upper limit of the ninth PI controller's output is 1. The output of the eighth PI controller serves as the lower limit of the ninth PI controller's output.

[0105] The output of the ninth proportional-integral (PI) controller is subtracted from the feedback value of the d-axis component of the AC current, and then input to the tenth PI controller. The output of the tenth PI controller is then modulated by PWM and input to the dq / abc coordinate transformation unit.

[0106] The setpoint value of the q-axis component of the AC current is subtracted from the feedback value of the q-axis component of the AC current, and then input to the eleventh proportional-integral (PI) controller. The output of the eleventh PI controller is modulated by PWM and then input to the dq / abc coordinate transformation unit.

[0107] The output of the dq / abc coordinate transformation unit is modulated by PWM again, and the output PWM square wave is used as the drive signal for each switch in the DC / AC converter.

[0108] Wherein, Udc is the DC bus voltage; dU3 is the deviation voltage value, also known as the third deviation, which is a different parameter from dU2 and dU1 and requires different values; Id_ref is the given value of the d-axis component of the AC current; Id_feedback is the d-axis component of the AC current; Iq_ref is the given value of the q-axis component of the AC current; and Iq_feedback is the q-axis component of the AC current.

[0109] The controller includes an outer voltage loop and an inner current loop. The outer voltage loop uses a deviation controller, which can autonomously control the DC / AC converter to operate in constant current mode or constant bus voltage mode based on the DC bus voltage value, so as to control the DC bus voltage stability.

[0110] Among them, the Clark transformation and Park transformation are used to transform the three-phase AC current from the three-phase stationary coordinate system to the dq rotating coordinate system, which facilitates control. This is a commonly used technique in the field of converter control.

[0111] This application provides a multi-port DC-DC converter.

[0112] like Figure 5As shown, the multi-port DC-DC converter includes: a photovoltaic DC / DC converter, a medium-voltage DC / DC converter, a bidirectional DC / DC converter, and a DC / AC converter.

[0113] Each converter is connected on one side via a DC bus.

[0114] The other side of the photovoltaic DC / DC converter serves as the first port of the multi-port DC converter, connecting to the photovoltaic array.

[0115] The other side of the medium-voltage DC / DC converter serves as the second port of the multi-port DC converter, connecting to the medium-voltage DC distribution network.

[0116] The other side of the bidirectional DC / DC converter serves as the third port of the multi-port DC converter, connecting to the low-voltage DC distribution network.

[0117] The other side of the DC / AC converter serves as the fourth port of the multi-port DC converter, connecting to the low-voltage AC distribution network.

[0118] In other words, this multi-port DC converter has four ports; the first port can be a DC 450V~850V port, connected to a photovoltaic array; the second port can be a DC ±10kV port, connected to a medium-voltage DC distribution network; the third port can be a DC ±375V port, connected to a low-voltage DC distribution network; and the fourth port can be an AC 400V port, connected to a low-voltage AC distribution network.

[0119] These four ports share a single DC 800V bus.

[0120] The various converters are combined to implement the control method for the multi-port DC-DC converter provided in the above embodiments.

[0121] The working process and principle of the control method for the multi-port DC-DC converter are not detailed here, but are all within the scope of protection of this application.

[0122] In practical applications, the structure of each converter can be:

[0123] (1) The photovoltaic DC / DC converter adopts at least one Boost circuit.

[0124] When a photovoltaic DC / DC converter uses multiple Boost circuits, the multiple Boost circuits are connected in parallel, that is, the DC / DC converter is a topology with multiple Boost circuits connected in parallel.

[0125] Specifically, such as Figure 6 As shown, each Boost circuit in a photovoltaic DC / DC converter can use two bridge arms connected in parallel with alternating connections.

[0126] Each Boost circuit includes two capacitors, four switching transistors, and two inductors. Taking one Boost circuit as an example, the two ends of inductor C11 serve as the first port, i.e., the DC 450V~850V port, connected to the photovoltaic array. The positive terminal of inductor C11 is connected to one end of inductors L12 and L11 respectively, and the other end of inductor L11 is connected to the connection point between switching transistors S11 and S12. The other end of inductor L12 is connected to the connection point between switching transistors S13 and S14. The two ends of capacitor C12 are connected to the DC bus; the positive terminal of capacitor C12 is connected to the connection point between switching transistors S11 and S13; the negative terminals of capacitor C12, capacitor C11, and the connection point between switching transistors S12 and S14 are connected.

[0127] (2) The medium-voltage DC / DC converter includes: at least one unidirectional resonant converter.

[0128] When a medium-voltage DC / DC converter includes multiple unidirectional resonant converters, the high-voltage sides of each unidirectional resonant converter are connected in series, and their low-voltage sides are connected in parallel.

[0129] The high-voltage side of the medium-voltage DC / DC converter is connected to the medium-voltage DC distribution network, and the low-voltage side of the medium-voltage DC / DC converter is connected to the DC bus.

[0130] A medium-voltage DC / DC converter can be simply referred to as a 20kV DCDC. It consists of four unidirectional resonant converters, such as... Figure 7 As shown. The low-voltage side of the unidirectional resonant converter adopts a full-bridge LLC topology with a high-frequency transformer for isolation. The high-voltage side uses a diode full-bridge rectifier. The four unidirectional resonant converters are connected in parallel on the low-voltage side and in series on the high-voltage side. Specifically, DC+ is the positive terminal of the low-voltage side of the medium-voltage DC / DC converter, and DC- is the negative terminal of the low-voltage side of the medium-voltage DC / DC converter; DC+10KV is the positive terminal of the high-voltage side of the medium-voltage DC / DC converter, with a potential of DC+10KV; DC-10KV is the negative terminal of the high-voltage side of the medium-voltage DC / DC converter, with a potential of DC-10KV.

[0131] (3) The bidirectional DC / DC converter includes: at least one bidirectional resonant converter.

[0132] When a bidirectional DC / DC converter includes multiple bidirectional resonant converters, the individual bidirectional resonant converters are connected in parallel. Figure 8 The following example uses two bidirectional resonant converters.

[0133] The high-voltage side of the bidirectional DC / DC converter is connected to the DC bus, and the low-voltage side is connected to the low-voltage DC distribution network.

[0134] like Figure 8As shown, the bidirectional resonant converter uses a full-bridge LLC topology on the low-voltage side, isolated by a high-frequency transformer. On the high-voltage side, it uses a full-bridge LLC topology cascaded with a bidirectional Boost circuit. Specifically, DC800+ is the positive terminal of the high-voltage side of the bidirectional DC / DC converter, and DC800- is the negative terminal of the high-voltage side; DC+375V is the positive terminal of the low-voltage side of the bidirectional DC / DC converter; and DC-10KV is the negative terminal of the low-voltage side of the bidirectional DC / DC converter.

[0135] (4) The DC / AC converter includes: at least one three-phase inverter.

[0136] When a DC / AC converter includes multiple three-phase inverters, the three-phase inverters are connected in parallel. Figure 9 The example will be demonstrated using four three-phase inverters.

[0137] like Figure 9 As shown, the three-phase inverter adopts a three-phase half-bridge topology, is connected to an LCL filter, and is connected to the low-voltage AC distribution network through an isolation transformer.

[0138] In practical applications, this multi-port DC-DC converter also includes a central controller.

[0139] like Figure 10 As shown, the central controller is used for:

[0140] Upon receiving the start command, the connected photovoltaic DC / DC converter is started.

[0141] Determine whether the photovoltaic DC / DC converter has completed startup and whether the DC bus voltage is greater than the reference bus voltage.

[0142] If so, control the start-up of the medium-voltage DC / DC converter. And when the medium-voltage DC / DC converter completes startup, control the start-up of the bidirectional DC / DC converter and the DC / AC converter.

[0143] like Figure 11 As shown, the central controller is also used for:

[0144] When a stop command is received, the bidirectional DC / DC converter and DC / AC converter are controlled to stop operating.

[0145] Determine whether both the bidirectional DC / DC converter and the DC / AC converter have completed shutdown.

[0146] If so, the photovoltaic DC / DC converter will be stopped, and when the photovoltaic DC / DC converter stops running, the first converter will also be stopped.

[0147] The features described in the various embodiments of this specification can be substituted for or combined with each other. Similar or identical parts between embodiments can be referred to mutually. Each embodiment focuses on describing the differences from other embodiments. In particular, for system or system embodiments, since they are basically similar to method embodiments, the description is relatively simple; relevant parts can be referred to the descriptions in the method embodiments. The systems and system embodiments described above are merely illustrative. The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the modules can be selected to achieve the purpose of this embodiment according to actual needs. Those skilled in the art can understand and implement this without creative effort.

[0148] Those skilled in the art will further recognize that the units and algorithm steps of the various examples described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, computer software, or a combination of both. To clearly illustrate the interchangeability of hardware and software, the components and steps of the various examples have been generally described in terms of functionality in the foregoing description. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementations should not be considered beyond the scope of this invention.

[0149] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A control method for a multi-port DC-DC converter, characterized in that, The four converters of the multi-port DC-DC converter are connected on one side via a DC bus, and the other side of each converter serves as a port of the multi-port DC-DC converter, connecting to a photovoltaic array, a medium-voltage DC distribution network, a low-voltage DC distribution network, and a low-voltage AC distribution network respectively; the control method includes: Each of the converters controls its own operating state based on the DC bus voltage and the deviation between the reference bus voltage and its corresponding value, so as to keep the DC bus voltage as the voltage reference value; The voltage reference value is the reference bus voltage, the sum of the reference bus voltage and the corresponding deviation, or the difference between the reference bus voltage and the corresponding deviation; the deviations corresponding to each converter are different; Each of the converters controls its operating state based on the DC bus voltage and the deviation between the reference bus voltage and its corresponding value, so as to maintain the DC bus voltage as the voltage reference value, including: The photovoltaic DC / DC converter connected to the photovoltaic array controls its own operating state based on the DC bus voltage and the reference bus voltage and the first deviation, so as to keep the DC bus voltage at the voltage reference value; The photovoltaic DC / DC converter controls its operating state based on the DC bus voltage and the reference bus voltage and a first deviation, so as to keep the DC bus voltage at the voltage reference value, including: The feedback value of the DC bus voltage is subtracted from the given value of the sum of the reference bus voltage and the first deviation, and then used as the input of the first proportional-integral regulator; wherein, the lower limit of the output of the first proportional-integral regulator is -1; the given value of the photovoltaic array voltage is subtracted from the feedback value of the photovoltaic array voltage and then input to the third proportional-integral regulator, and after passing through the second inverter, it is used as the upper limit of the output of the first proportional-integral regulator. The output of the first proportional-integral regulator is connected to the first inverter; The output of the first inverter is subtracted from the feedback value of the inductor current in the photovoltaic DC / DC converter and then used as the input of the second proportional-integral regulator. The output of the second proportional-integral regulator is modulated by PWM to output a PWM square wave, which serves as the drive signal for each switch in the photovoltaic DC / DC converter.

2. The control method for a multi-port DC-DC converter according to claim 1, characterized in that, Each of the converters controls its own operating state based on the DC bus voltage and the deviation between the reference bus voltage and its corresponding value, so as to keep the DC bus voltage at the voltage reference value, including: The bidirectional DC / DC converter connected to the low-voltage DC distribution network controls its own operating state based on the DC bus voltage and the reference bus voltage and the second deviation, so as to keep the DC bus voltage at the voltage reference value.

3. The control method for a multi-port DC-DC converter according to claim 2, characterized in that, The bidirectional DC / DC converter controls its operating state based on the DC bus voltage and the reference bus voltage and the second deviation, so as to keep the DC bus voltage at the voltage reference value, including: The feedback value of the DC bus voltage is subtracted from the given value of the sum of the reference bus voltage and the second deviation, and then used as the input of the fourth proportional-integral regulator; wherein, the lower limit of the output of the fourth proportional-integral regulator is -1; the upper limit of the output is the value of the given value of the inductor current after passing through the third inverter; The feedback value of the DC bus voltage is subtracted from the given value of the difference between the reference bus voltage and the second deviation, and then used as the input of the fifth proportional-integral regulator; wherein, the upper limit of the output of the fourth proportional-integral regulator is 1; and the output of the fourth proportional-integral regulator is used as the lower limit of the output of the fifth proportional-integral regulator. The output of the fifth proportional-integral regulator is subtracted from the feedback value of the first inductor current and then input to the sixth proportional-integral regulator; the output of the sixth proportional-integral regulator is modulated by PWM to output a PWM square wave, which serves as the drive signal for the first Boost circuit corresponding to the first inductor. The output of the fifth proportional-integral regulator is subtracted from the feedback value of the second inductor current and then input to the seventh proportional-integral regulator. The output of the seventh proportional-integral regulator is modulated by PWM to output a PWM square wave, which serves as the drive signal for the second Boost circuit corresponding to the second inductor. The photovoltaic DC / DC converter has a topology of multiple Boost circuits connected in parallel, including the first Boost circuit and the second Boost circuit.

4. The control method for a multi-port DC-DC converter according to claim 1, characterized in that, Each of the converters controls its own operating state based on the DC bus voltage and the deviation between the reference bus voltage and its corresponding value, so as to keep the DC bus voltage at the voltage reference value, including: The DC / AC converter connected to the low-voltage AC distribution network controls its own operating state based on the DC bus voltage, the reference bus voltage, and the third deviation, so as to keep the DC bus voltage at the voltage reference value.

5. The control method for a multi-port DC-DC converter according to claim 4, characterized in that, The DC / AC converter controls its operating state based on the DC bus voltage and the reference bus voltage and the third deviation, so as to keep the DC bus voltage at the voltage reference value, including: The feedback value of the DC bus voltage is subtracted from the given value of the sum of the reference bus voltage and the third deviation, and then used as the input of the eighth proportional-integral regulator; wherein, the lower limit of the output of the eighth proportional-integral regulator is -1; the upper limit of the output is the value of the given value of the d-axis component of the AC current after passing through the seventh inverter; The feedback value of the DC bus voltage is subtracted from the given value of the difference between the reference bus voltage and the third deviation, and then used as the input of the ninth proportional-integral regulator; wherein, the upper limit of the output of the ninth proportional-integral regulator is 1; and the output of the eighth proportional-integral regulator is used as the lower limit of the output of the ninth proportional-integral regulator. The output of the ninth proportional-integral regulator is subtracted from the feedback value of the d-axis component of the AC current and then input to the tenth proportional-integral regulator; the output of the tenth proportional-integral regulator is modulated by PWM and input to the dq / abc coordinate transformation unit. The given value of the q-axis component of the AC current is subtracted from the feedback value of the q-axis component of the AC current, and then input to the eleventh proportional-integral regulator; the output of the eleventh proportional-integral regulator is modulated by PWM and then input to the dq / abc coordinate transformation unit. The output of the dq / abc coordinate transformation unit is modulated again by PWM to output a PWM square wave, which serves as the drive signal for each switch in the DC / AC converter.

6. The control method for a multi-port DC-DC converter according to any one of claims 1-5, characterized in that, Each of the converters controls its own operating state based on the DC bus voltage and the deviation between the reference bus voltage and its corresponding value, so as to keep the DC bus voltage at the voltage reference value, including: The medium-voltage DC / DC converter connected to the medium-voltage DC distribution network adopts open-loop fixed-frequency control to clamp the DC bus voltage to the voltage reference value when the medium-voltage DC converter is operating normally.

7. A multi-port DC-DC converter, characterized in that, include: Photovoltaic DC / DC converters, medium-voltage DC / DC converters, bidirectional DC / DC converters, and DC / AC converters; Each converter is connected on one side via a DC bus; The other side of the photovoltaic DC / DC converter serves as the first port of the multi-port DC converter and is connected to the photovoltaic array. The other side of the medium-voltage DC / DC converter serves as the second port of the multi-port DC converter and is connected to the medium-voltage DC distribution network. The other side of the bidirectional DC / DC converter serves as the third port of the multi-port DC converter and is connected to the low-voltage DC distribution network. The other side of the DC / AC converter serves as the fourth port of the multi-port DC converter, connecting to the low-voltage AC distribution network. The various converters are combined to implement the control method for the multi-port DC-DC converter as described in any one of claims 1-6.

8. The multi-port DC-DC converter according to claim 7, characterized in that, The photovoltaic DC / DC converter employs at least one Boost circuit. The medium-voltage DC / DC converter includes: at least one unidirectional resonant converter; The bidirectional DC / DC converter includes: at least one bidirectional resonant converter; The DC / AC converter includes at least one three-phase inverter.

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