A bidirectional flexible voltage regulating device and control method for power distribution networks

Abstract

This application provides a bidirectional flexible voltage regulation device and control method for a distribution network, comprising: a direct AC / AC type unidirectional voltage regulation topology connected to the grid side and load side of the distribution network for voltage regulation; and a mode switching switch connected to the direct AC / AC type unidirectional voltage regulation topology to control the switching of the operating mode of the direct AC / AC type unidirectional voltage regulation topology. The direct AC / AC type unidirectional voltage regulation topology is partially connected in series in the low-voltage distribution network lines through the mode switching switch to achieve bidirectional flexible voltage regulation when the low-voltage distribution network voltage fluctuates or exceeds limits. This application achieves bidirectional flexible voltage regulation of the distribution network voltage exceeding limits based on the direct AC / AC type unidirectional voltage regulation topology and the mode switching switch in coordination, eliminating the need for a large-volume transformer and DC link. By detecting the grid voltage to control the operation of the mode switching switch, and by using closed-loop control to achieve real-time adjustment of the output voltage, it realizes bidirectional flexible voltage regulation of the distribution network voltage exceeding limits based on the direct AC / AC type unidirectional voltage regulation topology and the switch in coordination.

Description

Technical Field

[0001] This application relates to the fields of flexible voltage regulation in low-voltage distribution networks and power electronics technology, specifically to a bidirectional flexible voltage regulation device and control method for distribution networks. Background Technology

[0002] In recent years, with the continuous advancement of the "dual carbon" target and the in-depth development of new power systems, new renewable energy sources such as distributed photovoltaics, wind power, energy storage, and electric vehicle charging facilities have been massively integrated into low-voltage distribution networks. Distribution networks are gradually transforming from traditional unidirectional power supply networks to a multi-interactive system of "source-grid-load-storage." However, the large-scale integration of new energy sources also means that the operating environment faced by low-voltage distribution networks is becoming increasingly severe. The voltage at low-voltage distribution line nodes is extremely sensitive to power fluctuations from these new sources and loads, easily leading to frequent voltage fluctuations, exceeding limits, three-phase imbalance, and low power factor. This not only affects the power supply quality for regional users but also limits the distribution network's ability to absorb and integrate these new sources and loads. Among these issues, the problem of bidirectional voltage exceeding limits in the distribution network is particularly prominent. During the day, when user electricity consumption is low, photovoltaic power output is excessive, causing the distribution network voltage to exceed the upper limit. This can not only damage equipment but also affect the stability of grid operation. At night, when user electricity consumption reaches its peak, photovoltaic power output is insufficient, causing the distribution network voltage to exceed the lower limit, affecting the normal power supply for regional users. Therefore, how to effectively solve the problem of bidirectional voltage over-limit in the power distribution network has become a key technical challenge that the power industry urgently needs to address.

[0003] However, in the specific implementation of bidirectional flexible voltage regulation in low-voltage distribution networks, traditional open-loop control strategies rely on preset fixed parameters and unidirectional command transmission, lacking the ability to perceive and dynamically correct the system output in real time. In direct AC / AC type unidirectional voltage regulation topology scenarios, if open-loop control is used, the system can only roughly adjust the output voltage based on the initially set duty cycle. Dynamic factors such as grid impedance changes, load fluctuations, and the randomness of distributed energy output are ignored, resulting in insufficient voltage regulation accuracy, weak anti-interference capability, and a tendency to induce voltage oscillations or even instability. In addition, the voltage fluctuations of new distribution networks exhibit bidirectional and polymorphic characteristics. The single operating mode of the direct AC / AC type unidirectional voltage regulation topology cannot cover all operating scenarios. If the mode switching switch cannot flexibly switch the operating mode of the bidirectional flexible voltage regulation device according to the voltage fluctuations of the distribution network, it will lead to voltage regulation failure and even equipment damage. Summary of the Invention

[0004] In view of one of the defects in the prior art, the purpose of this application is to provide a bidirectional flexible voltage regulating device for power distribution networks.

[0005] A first aspect of this application provides a bidirectional flexible voltage regulating device for a power distribution network, comprising:

[0006] A direct AC / AC type unidirectional voltage regulation topology, wherein the two ends of the direct AC / AC type unidirectional voltage regulation topology are respectively connected to the grid side and the load side of the low-voltage distribution network, and are used to regulate the voltage of the distribution network;

[0007] A mode switching switch is connected to the direct AC / AC type unidirectional voltage regulating topology and is used to control the switching of the working mode of the direct AC / AC type unidirectional voltage regulating topology.

[0008] The direct AC / AC type unidirectional voltage regulation topology is connected in series in the low-voltage distribution network through the mode switching switch to realize bidirectional flexible voltage regulation when the voltage of the low-voltage distribution network fluctuates or exceeds the limit.

[0009] Optionally, the mode switching switch includes: a high-voltage side switching switch and a low-voltage side switching switch;

[0010] One end of the direct AC / AC type unidirectional voltage regulation topology is the high-voltage side, and the other end is the low-voltage side;

[0011] The high-voltage side of the direct AC / AC type unidirectional voltage regulation topology is connected to the grid side and the load side of the distribution network respectively through the high-voltage side switching switch;

[0012] The low-voltage side of the direct AC / AC type unidirectional voltage regulation topology is connected to the grid side and the load side of the distribution network respectively through the low-voltage side switching switch.

[0013] Optionally, the high-voltage side switching switch includes a first grid-side switch and a first load-side switch;

[0014] The low-voltage side switching switch includes a second grid-side switch and a second load-side switch;

[0015] The first grid-side switch is connected to the grid side of the low-voltage distribution network, and the first load-side switch is connected to the load side of the low-voltage distribution network.

[0016] The second grid-side switch is connected to the grid side of the low-voltage distribution network, and the second load-side switch is connected to the load side of the low-voltage distribution network.

[0017] Optionally, the direct AC / AC type unidirectional voltage regulation topology includes: a high-voltage side filter capacitor, an IGBT-based bidirectional switch, an inductor, and a low-voltage side filter capacitor;

[0018] The bidirectional switching transistor includes: a main control transistor and a freewheeling transistor;

[0019] The high-voltage side filter capacitor is connected in parallel across both sides of the high-voltage side port, and the low-voltage side filter capacitor is connected in parallel across both sides of the low-voltage side port. One end of the main control transistor of the bidirectional switch is connected in series with one end of the inductor, and the other end of the inductor is connected to one end of the low-voltage side filter capacitor and then connected to the low-voltage side port. The other end of the main control transistor is connected to one end of the high-voltage side filter capacitor and then connected to the high-voltage side port. One end of the freewheeling diode of the bidirectional switch is connected between the main control transistor and the inductor, and the other end of the freewheeling diode is connected to both the high-voltage side port and the low-voltage side port.

[0020] Optionally, the main control transistor of the bidirectional switching transistor is composed of a set of IGBT anti-parallel diodes S1 and S2 connected in series with common emitters. The direct AC / AC type unidirectional voltage regulation topology regulates the output voltage by controlling the conduction time of the main control transistors S1 and S2 within one switching cycle.

[0021] Optionally, the freewheeling diode of the bidirectional switching transistor is composed of a set of IGBT anti-parallel diodes S3 and S4 connected in series with common emitters, which is used to provide a freewheeling path for the current.

[0022] A second aspect of this application provides a control method for a bidirectional flexible voltage regulating device in a power distribution network, comprising:

[0023] The voltage value of the low-voltage distribution network is collected and compared with the set upper and lower voltage limits to determine whether the voltage of the low-voltage distribution network is within the set voltage range. If it is, the network is considered to be operating normally and the bidirectional flexible voltage regulating device does not need to be connected to the low-voltage distribution network for voltage regulation. If not, the operating mode of the bidirectional flexible voltage regulating device is determined according to the voltage deviation from the upper and lower limits.

[0024] Based on the operating mode of the bidirectional flexible voltage regulator of the power distribution network, a corresponding closed-loop control strategy is determined, and the duty cycle of the bidirectional switching transistor in the bidirectional flexible voltage regulator of the power distribution network is calculated through the control strategy. The output voltage of the bidirectional flexible voltage regulator of the power distribution network is adjusted through the duty cycle.

[0025] Optionally, determining the operating mode of the bidirectional flexible voltage regulating device for the distribution network based on the deviation of the low-voltage distribution network voltage from the set range includes:

[0026] The voltage value of the low-voltage distribution network is collected and compared with the set upper and lower voltage limits to determine whether the voltage of the low-voltage distribution network is within the set voltage range. If it is, the network is considered to be operating normally and the bidirectional flexible voltage regulating device does not need to be connected to the low-voltage distribution network for voltage regulation. If not, the operating mode of the bidirectional flexible voltage regulating device is determined according to the voltage deviation from the upper and lower limits.

[0027] Wherein, when the voltage of the low-voltage distribution network exceeds the upper limit value, the bidirectional flexible voltage regulating device of the distribution network is connected in series between the input network and the output load of the low-voltage distribution network in Buck mode;

[0028] When the voltage of the low-voltage distribution network is lower than the lower limit, the bidirectional flexible voltage regulating device of the distribution network is connected in series between the input network and the output load in Boost mode.

[0029] Optionally, when the voltage of the low-voltage distribution network exceeds the upper limit value, the bidirectional flexible voltage regulating device of the distribution network is connected in series between the input power supply and the output load in Buck mode, including:

[0030] The second load-side switch of the low-voltage side switching switch and the first grid-side switching switch of the high-voltage side switching switch in the mode switching device of the power distribution network bidirectional flexible voltage regulation device are turned to the on state;

[0031] The first load-side switch of the high-voltage side switching switch and the second grid-side switch of the low-voltage side switching switch are switched to the off state.

[0032] In this device, the high-voltage side port of the direct AC / AC type unidirectional voltage regulation topology of the distribution network bidirectional flexible voltage regulation device is connected to the grid side of the low-voltage distribution network through the first grid side switch, and the low-voltage side port is connected to the load side of the low-voltage distribution network through the second load side switch. The distribution network bidirectional flexible voltage regulation device is connected in series between the input grid and the output load in Buck mode.

[0033] Optionally, when the voltage of the low-voltage distribution network exceeds the upper limit value, the bidirectional flexible voltage regulating device of the distribution network is connected in series between the input power supply and the output load in Buck mode;

[0034] The Buck modes include: Mode 1 power transfer mode and Mode 2 freewheeling mode;

[0035] The mode-1 power transmission mode is characterized by the main control tube of the direct AC / AC type unidirectional voltage regulation topology being turned on and the freewheeling tube being turned off, at which point the circuit is in power transmission mode.

[0036] The modal two freewheeling mode is characterized by the main control transistor being turned off and the freewheeling transistor being turned on, with the circuit in freewheeling mode.

[0037] Optionally, in the mode-one power transfer mode, the power supply u i Power is supplied to the load, and the load voltage u o =u i Load current i oAs the voltage rises exponentially, the inductors and capacitors of the direct AC / AC type unidirectional voltage regulation topology absorb energy, and the voltage rises. Depending on the direction of the inductor current, the energy is transferred from the input power supply to the output load or fed back from the output load to the input power supply.

[0038] In the modal two freewheeling mode, the load voltage u o Approximately 0, the load current decreases exponentially, the inductor and the capacitor supply power to the load and release energy, the voltage drops, and the inductor current continues through the freewheeling tube.

[0039] Optionally, when the voltage of the low-voltage distribution network is lower than the lower limit, the bidirectional flexible voltage regulating device of the distribution network is connected in series between the input power supply and the output load in Boost mode;

[0040] The second grid-side switch of the low-voltage side switching switch and the first load-side switch of the high-voltage side switching switch in the mode switching device of the power distribution network are switched to the on state; the first grid-side switch of the high-voltage side switching switch and the second load-side switch of the low-voltage side switching switch are switched to the off state.

[0041] The high-voltage side port of the direct AC / AC type unidirectional voltage regulation topology of the distribution network bidirectional flexible voltage regulation device is connected to the load side of the low-voltage distribution network through the second load side switch of the high-voltage side switching switch, and the low-voltage side port is connected to the grid side of the low-voltage distribution network through the first grid side switch of the low-voltage side switching switch. The distribution network bidirectional flexible voltage regulation device is connected in series between the input grid and the output load in Boost mode.

[0042] Optionally, when the voltage of the low-voltage distribution network is lower than the lower limit, the bidirectional flexible voltage regulating device of the distribution network is connected in series between the input network and the output load in Boost mode;

[0043] The Boost mode includes: Mode 1 freewheeling mode and Mode 2 power transfer mode;

[0044] The modal freewheeling mode is defined as follows: when the main control transistor of the direct AC / AC type unidirectional voltage regulation topology is turned off and the freewheeling transistor is turned on, the circuit is in freewheeling mode.

[0045] The modal two power transmission mode is such that when the main control transistor is turned on and the freewheeling transistor is turned off, the circuit is in power transmission mode.

[0046] Optionally, in the mode-one freewheeling mode, the power supply u i When power is supplied to an inductor, the inductor stores energy, the inductor voltage rises, the current increases, and the high-voltage side filter capacitor supplies power to the load.

[0047] In the mode two power transmission mode, the power supply and the energy storage inductor supply power to the load. The inductor releases energy, the voltage drops, and depending on the direction of the inductor current, the energy is transferred from the input power supply to the load or fed back from the load to the input power supply.

[0048] Optionally, the step of determining a corresponding closed-loop control strategy based on the operating mode of the bidirectional flexible voltage regulator of the distribution network, calculating the duty cycle of the bidirectional switching transistor in the bidirectional flexible voltage regulator of the distribution network through the control strategy, and adjusting the output voltage of the bidirectional flexible voltage regulator of the distribution network through the duty cycle includes:

[0049] The deviation between the actual output voltage value and the reference value of the low-voltage distribution network is detected, and the duty cycle of the bidirectional switching transistor in the bidirectional flexible voltage regulating device of the distribution network under the corresponding working mode is obtained through PI control.

[0050] The output voltage of the bidirectional flexible voltage regulator in the power distribution network is adjusted by the duty cycle to maintain a stable output voltage on the load side.

[0051] Optionally, the closed-loop control strategy includes a modulation stage and a delay stage.

[0052] This application provides a bidirectional flexible voltage regulating device for distribution networks, which adopts a direct AC / AC type unidirectional voltage regulating topology combined with mode switching technology. The direct AC / AC type unidirectional voltage regulating topology can achieve low-cost, compact, and flexible voltage regulation when the voltage fluctuates or exceeds the limit in low-voltage distribution networks. Unlike existing flexible voltage regulating equipment, it does not require a transformer or DC link, and only needs to achieve voltage regulation through direct AC / AC conversion. This bidirectional flexible voltage regulating device for distribution networks based on the direct AC / AC type unidirectional voltage regulating topology and the mode switching switch works together to realize the switching of the working mode of the bidirectional flexible voltage regulating device under different operating conditions, thereby realizing bidirectional flexible voltage regulation of the distribution network when it exceeds the limit.

[0053] Other technical effects resulting from the additional features will be further illustrated in the corresponding embodiments. Attached Figure Description

[0054] Other features, objects, and advantages of this application will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings:

[0055] Figure 1 This is a schematic diagram of the structure of a bidirectional flexible voltage regulating device for a power distribution network according to an exemplary embodiment;

[0056] Figure 2 This is a schematic diagram of a direct AC / AC type unidirectional voltage regulation topology module of a bidirectional flexible voltage regulation device for a distribution network, according to an exemplary embodiment.

[0057] Figure 3 This is a schematic diagram of the mode switching switch section module of a bidirectional flexible voltage regulating device for a power distribution network, according to an exemplary embodiment.

[0058] Figure 4 This is a schematic diagram of the equivalent circuit structure of a direct AC / AC type unidirectional voltage regulation topology of a bidirectional flexible voltage regulation device for a distribution network operating in Buck mode, according to an exemplary embodiment.

[0059] Figure 5 This is a block diagram of a Buck mode closed-loop control in a bidirectional flexible voltage regulating device for a power distribution network, according to an exemplary embodiment.

[0060] Figure 6 This is a schematic diagram of the equivalent circuit structure of different modes of the direct AC / AC type unidirectional voltage regulation topology of the distribution network bidirectional flexible voltage regulation device when it is operating in Boost mode, according to an exemplary embodiment of the closed-loop control strategy and mode switching method of the distribution network bidirectional flexible voltage regulation device.

[0061] Figure 7 This is a block diagram of the Boost mode closed-loop control in the closed-loop control strategy and mode switching method of a bidirectional flexible voltage regulator for a power distribution network, according to an exemplary embodiment.

[0062] Figure 8 This is a timing diagram of the bidirectional switch operation of the direct AC / AC type unidirectional voltage regulation topology of the bidirectional flexible voltage regulation device in the closed-loop control strategy and mode switching method of the bidirectional flexible voltage regulation device in the distribution network according to an exemplary embodiment.

[0063] Figure 9 This is a schematic diagram of the various states of the mode switching switch section in the closed-loop control strategy and mode switching method of the bidirectional flexible voltage regulating device for a distribution network, according to an exemplary embodiment.

[0064] Figure 10 This is a schematic diagram of mode switching in the closed-loop control strategy and mode switching method of a bidirectional flexible voltage regulating device for a power distribution network, according to an exemplary embodiment.

[0065] Figure 11 This is a diagram of the mode switching switch action signal in the closed-loop control strategy and mode switching method of a bidirectional flexible voltage regulating device for a power distribution network, according to an exemplary embodiment.

[0066] Figure 12 The graph shows the voltage and current curves on the grid side and load side of the bidirectional flexible voltage regulator in Buck mode, according to a closed-loop control strategy and mode switching method of the bidirectional flexible voltage regulator in a distribution network, as illustrated in an exemplary embodiment.

[0067] Figure 13 This is a graph showing the voltage and current curves on the grid side and load side of the bidirectional flexible voltage regulator in Boost mode, according to a closed-loop control strategy and mode switching method of the bidirectional flexible voltage regulator in a distribution network, as illustrated in an exemplary embodiment.

[0068] In the diagram: 100, Direct AC / AC type unidirectional voltage regulation topology; 100a, High-voltage side of the direct AC / AC type unidirectional voltage regulation topology; 100b, Low-voltage side of the direct AC / AC type unidirectional voltage regulation topology; 101, High-voltage side filter capacitor; 102, Bidirectional switching transistor; 102a, Main control bidirectional transistor; 102b, Freewheeling bidirectional transistor; 103, Inductor; 104, Low-voltage side filter capacitor;

[0069] 200, Mode switching switch; 201, High-voltage side switching switch; 201a, First grid side switch; 201b, First load side switch; 202, Low-voltage side switching switch; 202a, Second grid side switch; 202b, Second load side switch. Detailed Implementation

[0070] The present application will now be described in detail with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present application, but do not limit the present application in any way. It should be noted that those skilled in the art can make several modifications and improvements without departing from the concept of the present application, and these all fall within the protection scope of the present application. Parts not described in detail in the following embodiments can be implemented using existing technology.

[0071] In the description of the embodiments of this application, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "bottom", "inner", "outer", "clockwise", "counterclockwise", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings. They are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application.

[0072] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined with "first" or "second" may explicitly or implicitly include one or more of that feature.

[0073] In the description of the embodiments in this application, "multiple" means two or more, unless otherwise explicitly specified. In this application, unless otherwise explicitly specified and limited, the terms "installed," "connected," "linked," "fixed," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances.

[0074] The terms "comprising" and "having," and any variations thereof, in the embodiments of this application are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or device that includes a series of steps or units is not limited to the steps or units listed, but may optionally include steps or units not listed, or may optionally include other steps or units inherent to such processes, methods, products, or devices.

[0075] In the implementation of bidirectional flexible voltage regulation in low-voltage distribution networks, traditional open-loop control strategies rely on preset fixed parameters and unidirectional command transmission, lacking real-time perception and dynamic correction capabilities for system output. In direct AC / AC type unidirectional voltage regulation topology scenarios, if open-loop control is used, the system can only roughly adjust the output voltage based on the initially set duty cycle. Dynamic factors such as grid impedance changes, load fluctuations, and the randomness of distributed energy output are ignored, resulting in insufficient voltage regulation accuracy, weak anti-interference capability, and a tendency to induce voltage oscillations or even instability. Based on the above problems, this application provides a bidirectional flexible voltage regulation device for distribution networks to solve these issues.

[0076] Reference Figure 1 As shown in one embodiment of this application, a bidirectional flexible voltage regulating device for a power distribution network includes: a direct AC / AC type unidirectional voltage regulating topology 100 and a mode switching switch 200.

[0077] The two ends of the direct AC / AC type unidirectional voltage regulating topology 100 are connected to the grid side and the load side of the low-voltage distribution network, respectively, for voltage regulation of the distribution network; the mode switching switch 200 is connected to the direct AC / AC type unidirectional voltage regulating topology 100 and is used to control the switching of the working mode of the direct AC / AC type unidirectional voltage regulating topology 100.

[0078] Among them, the direct AC / AC type unidirectional voltage regulation topology 100 is connected in series in the low-voltage distribution network line through the mode switching switch 200 to realize bidirectional flexible voltage regulation when the low-voltage distribution network voltage fluctuates or exceeds the limit.

[0079] It should be noted that the grid side is the power supply side; the load side is the load side.

[0080] The above embodiments of this application describe a bidirectional flexible voltage regulation device for distribution networks based on a direct AC / AC type unidirectional voltage regulation topology and coordinated with a switch. The device consists of a direct AC / AC type unidirectional voltage regulation topology 100 and a mode switching switch 200. The direct AC / AC type unidirectional voltage regulation topology 100 is used to achieve compact, low-cost, and flexible voltage regulation when the distribution network voltage fluctuates or exceeds limits. The mode switching switch 200 is used to switch the operating mode of the direct AC / AC type unidirectional voltage regulation topology 100. By detecting the grid-side voltage, the mode switching switch is activated, thereby achieving bidirectional flexible voltage regulation of the distribution network voltage that exceeds limits in coordination with the switch, based on the direct AC / AC type unidirectional voltage regulation topology.

[0081] In order to achieve the goal of bidirectional over-limit flexible voltage regulation of distribution network based on direct AC / AC type unidirectional voltage regulation topology and coordinated with the switch, in some specific embodiments of this application, the mode switching switch 200 includes: high-voltage side switching switch 201 and low-voltage side switching switch 202.

[0082] One end of the direct AC / AC type unidirectional voltage regulating topology 100 is the high-voltage side 100a, and the other end is the low-voltage side 100b. The high-voltage side 100a of the direct AC / AC type unidirectional voltage regulating topology is connected to the grid side and the load side of the distribution network through the high-voltage side switching switch 201. The low-voltage side 100b of the direct AC / AC type unidirectional voltage regulating topology is connected to the grid side and the load side of the distribution network through the low-voltage side switching switch 202.

[0083] Specifically, the mode switching switch 200 consists of a high-voltage side switching switch 201 and a low-voltage side switching switch 202. The high-voltage side switching switch 201 is connected to the high-voltage side 100a port of the direct AC / AC type unidirectional voltage regulating topology 100, wherein the grid-side switch 201a of the high-voltage side switching switch is connected to the grid side of the low-voltage distribution network, and the load-side switch 201b of the high-voltage side switching switch is connected to the load side of the low-voltage distribution network; the low-voltage side switching switch 202 is connected to the low-voltage side 100b port of the direct AC / AC type unidirectional voltage regulating topology 100, wherein the grid-side switch 202a of the low-voltage side switching switch is connected to the grid side of the low-voltage distribution network, and the load-side switch 202b of the low-voltage side switching switch is connected to the load side of the low-voltage distribution network, thus constituting the mode switching switch 200.

[0084] In the above embodiments of this application, the mode switching switch 200 controls the switching on and off by detecting the grid voltage, thereby realizing the mode switching of the direct AC / AC type unidirectional voltage regulation topology 100 to access the low-voltage distribution network, and thus realizing bidirectional over-limit flexible voltage regulation of the low-voltage distribution network.

[0085] In some specific embodiments of this application, the high-voltage side switching switch 201 includes a first grid-side switch 201a and a first load-side switch 201b; the low-voltage side switching switch 202 includes a second grid-side switch 202a and a second load-side switch 202b.

[0086] The first grid-side switch 201a is connected to the grid side of the low-voltage distribution network, and the first load-side switch 201b is connected to the load side of the low-voltage distribution network; the second grid-side switch 202a is connected to the grid side of the low-voltage distribution network, and the second load-side switch 202b is connected to the load side of the low-voltage distribution network.

[0087] The mode switching section 200 of the bidirectional flexible voltage regulating device for the power distribution network, such as... Figure 3 As shown, it consists of a high-voltage side switching switch 201 and a low-voltage side switching switch 202. The high-voltage side switching switch 201 is connected to the high-voltage side 100a port of the direct AC / AC type unidirectional voltage regulating topology 100, wherein the first grid side switch 201a of the high-voltage side switching switch is connected to the grid side of the low-voltage distribution network, and the first load side switch 201b of the high-voltage side switching switch is connected to the load side of the low-voltage distribution network; the low-voltage side switching switch 202 is connected to the low-voltage side 100b port of the direct AC / AC type unidirectional voltage regulating topology 100, wherein the second grid side switch 202a of the low-voltage side switching switch is connected to the grid side of the low-voltage distribution network, and the second load side switch 202b of the low-voltage side switching switch is connected to the load side of the low-voltage distribution network.

[0088] In some specific embodiments of this application, the direct AC / AC type unidirectional voltage regulation topology 100 includes: a high-voltage side filter capacitor 101, an IGBT-based bidirectional switch 102, an inductor 103, and a low-voltage side filter capacitor 104.

[0089] The bidirectional switching transistor 102 includes a main control bidirectional switching transistor 102a and a freewheeling bidirectional switching transistor 102b. A high-voltage side filter capacitor 101 is connected in parallel across the ports of the high-voltage side 100a, and a low-voltage side filter capacitor 104 is connected in parallel across the ports of the low-voltage side 100b. One end of the main control bidirectional switching transistor 102a is connected in series with one end of an inductor 103. The other end of the inductor 103 is connected to one end of the low-voltage side filter capacitor 104 and then to the port of the low-voltage side 100b. The other end of the main control bidirectional switching transistor 102a is connected to one end of the high-voltage side filter capacitor 101 and then to the port of the high-voltage side 100a. One end of the freewheeling bidirectional switching transistor 102b is connected between the main control bidirectional switching transistor 102a and the inductor 103. The other end of the freewheeling bidirectional switching transistor 102b is connected to both the port of the high-voltage side 100a and the port of the low-voltage side 100b.

[0090] Specifically, the direct AC / AC type unidirectional voltage regulation topology 100 consists of a high-voltage side filter capacitor 101, an IGBT-based bidirectional switch 102, an inductor 103, and a low-voltage side filter capacitor 104. The high-voltage side filter capacitor 101 is connected in parallel on both sides of the high-voltage side 100a port; the low-voltage side filter capacitor 104 is connected in parallel on both sides of the low-voltage side 100b port; the main control bidirectional switch 102a of the bidirectional switch is connected in series with the inductor 103, and one side is connected to the high-voltage side 100a; the freewheeling bidirectional switch 102b of the bidirectional switch is connected between the main control switch 102a of the bidirectional switch and the inductor 103, thus forming the direct AC / AC type unidirectional voltage regulation topology 100.

[0091] In some specific embodiments of this application, the main control bidirectional switch 102a in the two sets of bidirectional switches 102 is composed of a set of IGBT anti-parallel diodes S1 and S2 connected in series with common emitters. The direct AC / AC type unidirectional voltage regulation topology 100 regulates the output voltage by controlling the conduction time of the main control bidirectional switches S1 and S2 within one switching cycle.

[0092] It should be noted that the bidirectional switch 102 refers to a switching device composed of two IGBTs connected in anti-parallel with diodes connected in series with their common emitters. S1 and S2 are two IGBTs connected in anti-parallel with one diode, and S1 and S2 are connected in series with their common emitters to form a bidirectional switch.

[0093] In some specific embodiments of this application, the freewheeling bidirectional switching transistor 102b of the two sets of bidirectional switching transistors is composed of a set of IGBT anti-parallel diodes S3 and S4 connected in series with common emitters, which is used to provide a freewheeling path for current and ensure the release of inductor energy storage.

[0094] In the above embodiments of this application, the IGBT-based bidirectional switch 102 of the direct AC / AC type unidirectional voltage regulation topology includes: the main control bidirectional switch 102a of the direct AC / AC type unidirectional voltage regulation topology 102 is composed of a set of IGBT anti-parallel diodes S1 and S2 connected in series with common emitters; the output voltage is regulated by controlling the conduction time of the main control bidirectional switch S1 and S2 within one cycle; the freewheeling bidirectional switch 102b of the direct AC / AC type unidirectional voltage regulation topology 102 includes: a set of IGBT anti-parallel diodes S3 and S4 connected in series with common emitters; the freewheeling bidirectional switch 102b provides a freewheeling path for current and ensures the release of inductor energy storage.

[0095] A second aspect of this application provides a control method for a bidirectional flexible voltage regulating device in a power distribution network, comprising:

[0096] S1. Collect the voltage value of the low-voltage distribution network and compare it with the set upper and lower voltage limits to determine whether the voltage of the low-voltage distribution network is within the set voltage range. If yes, the network is considered to be operating normally and the bidirectional flexible voltage regulating device of the distribution network does not need to be connected to the low-voltage distribution network for voltage regulation. If no, the working mode of the bidirectional flexible voltage regulating device of the distribution network is determined according to the voltage deviation from the upper and lower limits.

[0097] S2. Determine the corresponding closed-loop control strategy based on the working mode of the bidirectional flexible voltage regulating device of the distribution network.

[0098] S3. Calculate the duty cycle of the bidirectional switching transistor in the bidirectional flexible voltage regulator of the power distribution network using a closed-loop control strategy, and adjust the output voltage of the bidirectional flexible voltage regulator of the power distribution network using the duty cycle.

[0099] The main method of mode switching is to determine the working mode of the bidirectional flexible voltage regulator of the distribution network based on the voltage deviation of the low-voltage distribution network from the set range, and switch the corresponding control strategy to control the output voltage of the distribution network.

[0100] The embodiments described above in this application eliminate the need for transformers and DC links, achieving low-cost, compact, and flexible voltage regulation for low-voltage distribution network voltage fluctuations or bidirectional over-limit situations simply through direct AC / AC conversion. The closed-loop control strategy of this bidirectional flexible voltage regulation device enables real-time, precise, and flexible voltage regulation of the output voltage, maintaining stable voltage on the user side. The mode switching method of this bidirectional flexible voltage regulation device allows the control mode switching switch to operate according to the type of voltage over-limit when the distribution network voltage exceeds its limit, thereby achieving mode switching of the bidirectional flexible voltage regulation device and ensuring reliable switch operation.

[0101] In some specific embodiments of this application, the operating mode of the bidirectional flexible voltage regulating device for the distribution network is determined based on the deviation of the low-voltage distribution network voltage from the set range, including:

[0102] The voltage value of the low-voltage distribution network is collected and compared with the set upper and lower voltage limits to determine whether the voltage of the low-voltage distribution network is within the set voltage range. If it is, the network is considered to be operating normally and the bidirectional flexible voltage regulating device of the distribution network does not need to be connected to the low-voltage distribution network for voltage regulation. If not, the working mode of the bidirectional flexible voltage regulating device of the distribution network is determined according to the voltage deviation from the upper and lower limits.

[0103] When the voltage of the low-voltage distribution network exceeds the upper limit, the bidirectional flexible voltage regulating device of the distribution network is connected in series between the input network and the output load in Buck mode;

[0104] When the voltage of the low-voltage distribution network is lower than the lower limit, the bidirectional flexible voltage regulating device of the distribution network is connected in series between the input network and the output load in Boost mode.

[0105] It should be noted that the output load refers to the load side.

[0106] In some specific embodiments of this application, when the voltage of the low-voltage distribution network exceeds the upper limit, the bidirectional flexible voltage regulating device of the distribution network is connected in series between the input power supply and the output load in Buck mode;

[0107] The second load-side switch of the low-voltage side switching switch and the first grid-side switching switch of the high-voltage side switching switch in the mode switching device of the distribution network are turned on; the first load-side switch of the high-voltage side switching switch and the second grid-side switch of the low-voltage side switching switch are turned off.

[0108] In this device, the high-voltage side port of the direct AC / AC type unidirectional voltage regulation topology of the distribution network bidirectional flexible voltage regulation device is connected to the grid side of the low-voltage distribution network through the first grid side switch, and the low-voltage side port is connected to the load side of the low-voltage distribution network through the second load side switch. The distribution network bidirectional flexible voltage regulation device is connected in series between the input grid and the output load in Buck mode.

[0109] In some specific embodiments of this application, when the voltage of the low-voltage distribution network exceeds the upper limit, the bidirectional flexible voltage regulating device of the distribution network is connected in series between the input power supply and the output load in Buck mode; the Buck mode includes: mode one power transmission mode and mode two freewheeling mode.

[0110] In Mode 1, the power transmission mode is a direct AC / AC type unidirectional voltage regulation topology. When the main control bidirectional switch is turned on and the freewheeling bidirectional switch is turned off, the circuit is in power transmission mode. In Mode 2, the freewheeling mode is a freewheeling mode. When the main control bidirectional switch is turned off and the freewheeling bidirectional switch is turned on, the circuit is in freewheeling mode.

[0111] It should be noted that when the circuit is in power transmission mode, the entire circuit is in power transmission mode, meaning that there is a power flow between the power grid and the load.

[0112] In some specific embodiments of this application, in mode-one power transfer mode, the power supply u i Power is supplied to the load, and the load voltage u o =u i Load current i o As the voltage rises exponentially, the inductors and capacitors in the direct AC / AC type unidirectional voltage regulation topology absorb energy, causing the voltage to rise. Depending on the direction of the inductor current, the energy is transferred from the input power supply to the output load or fed back from the output load to the input power supply.

[0113] In the modal two freewheeling mode, the load voltage U oWhen the current is approximately zero, the load current decreases exponentially. The inductor and capacitor supply power to the load and release energy, causing the voltage to drop. The inductor current then continues through the freewheeling diode.

[0114] Specifically, the two operating modes of the bidirectional flexible voltage regulating device for the power distribution network in Buck mode include:

[0115] In mode one, during the time period [t0-t1] of one switching cycle, when the main control bidirectional switches S1 and S2 are turned on and the freewheeling bidirectional switches S3 and S4 are turned off, the circuit is in power transfer mode. The equivalent circuit diagram is as follows: Figure 4 As shown in (a), depending on the direction of the inductor current, energy is transferred from the input power supply to the output load or fed back from the output load to the input power supply.

[0116] Mode 2: During the time period [t1-t2] within one switching cycle, when the main control bidirectional switches S1 and S2 are off and the freewheeling bidirectional switches S3 and S4 are on, the circuit is in freewheeling mode. The equivalent circuit diagram is as follows: Figure 4 As shown in (b), the inductor current freewheels through the switching transistors S3 and S4.

[0117] In the mode 1 power transfer mode and the mode 2 freewheeling mode, the power frequency input voltage is assumed to be u. i (t)=U i ·sin(ωt), where the angular frequency ω=2πf remains constant, and the amplitude U i It may contain random disturbances. The conduction ratio of the main control transistor is d(t), and its steady-state value is D;

[0118] To obtain accurate and stable power frequency output u o (t)=U o sin(ωt), requiring a very good sine degree and an amplitude U o Constant, frequency and phase are related to the input voltage u i (t) have the same fundamental frequency.

[0119] It should be noted that the above embodiments are intended to provide initial conditions and variable descriptions for the mathematical model to be established later.

[0120] The two operating modes represent different operating states of the topology within a single switching cycle, and their corresponding expressions differ. It is necessary to derive the state-space average equation of the topology within one switching cycle based on these two sets of expressions. The transfer function can be obtained by superimposing a small disturbance onto the state-space average equation and performing a Laplace transform. The open-loop transfer function of the output voltage and duty cycle represents the relationship between them. The input to the closed-loop control strategy is the deviation between the actual and reference values ​​of the output voltage. After passing through the PI controller, the corresponding actual duty cycle can be obtained. Describing the transfer function can be used to calculate the PI parameters for PI control.

[0121] In some specific implementations, based on the operating mode of the bidirectional flexible voltage regulator in the distribution network, a corresponding closed-loop control strategy is determined. The duty cycle of the bidirectional switching transistor in the bidirectional flexible voltage regulator is calculated using this control strategy, and the output voltage of the bidirectional flexible voltage regulator is adjusted based on the duty cycle. This includes:

[0122] The deviation between the actual output voltage of the low-voltage distribution network and the reference value is detected, and the duty cycle of the bidirectional switch in the bidirectional flexible voltage regulator of the distribution network under the corresponding working mode is obtained through PI control; the output voltage of the bidirectional flexible voltage regulator of the distribution network is adjusted by the duty cycle to maintain a stable output of the load side voltage.

[0123] The closed-loop control strategy is a voltage single closed-loop control strategy.

[0124] It should be noted that the closed-loop control strategy logic is the same for different operating modes, namely, a voltage single closed-loop control strategy is adopted. By detecting the difference between the output voltage reference value and the actual value, the real-time duty cycle is obtained through the PI controller, and then the output voltage is controlled. However, the circuits, transfer functions, and parameters of the PI controller are different for different operating modes.

[0125] Furthermore, the closed-loop control strategy includes a modulation stage and a delay stage.

[0126] In Buck mode, when the inductor current is in the positive half-cycle, the expressions for the inductor voltage, output capacitor current, and input power supply current in mode-1 power transfer mode are as follows:

[0127]

[0128] i s (t)=i L (t);

[0129] In the formula, u i (t) represents the input voltage, u o (t) represents the output voltage, i s (t) represents the input current, i L (t) represents the inductor current, L represents the filter inductance, C represents the low-voltage side filter capacitor, and R represents the load resistance;

[0130] In mode two freewheeling, the expressions for the inductor voltage, output capacitor current, and input power supply current are:

[0131]

[0132] i s (t)=i L (t).

[0133] In the formula, u i (t) represents the input voltage, u o (t) represents the output voltage, i s (t) represents the input current, i L (t) represents the inductor current, L represents the filter inductance, C represents the low-voltage side filter capacitor, and R represents the load resistance;

[0134] Calculate the state-space average equation of the converter, taking any switching period (T) s The average value of each state quantity within) As a new state variable, the average state-space equation of the converter can be obtained as follows:

[0135]

[0136] In the formula, T s For the switching cycle, This represents the average value of the input-side voltage during any given switching cycle. This represents the average value of the output voltage during any switching cycle. This represents the average value of the input-side current during any switching cycle. The average value of the inductor current during any switching cycle is given by L, where L is the filter inductance, C is the low-voltage side filter capacitor, and R is the load resistance.

[0137] Small-signal disturbances are superimposed on the static DC components of each major variable, i.e.

[0138]

[0139] In the formula, U i U o I L I s These are the static DC components of the input voltage, output voltage, inductor current, and input current, respectively. These are the small-signal disturbance components of the input voltage, output voltage, inductor current, input current, and the conduction ratio of the main control bidirectional switch of the converter, respectively.

[0140] Substituting the above equation into the state-averaged equation, if and only if Time (i.e., input voltage u) i (t) is outside the sufficiently small locality of zero, and both sides of the equation are equal. They can be canceled out; further, zero-valued terms can be eliminated. and (DU) i -U o (and ignore nonlinear terms) The small-signal state equation of the system can be obtained as follows:

[0141]

[0142] Performing a Laplace transform on the equation, we obtain

[0143]

[0144] In the formula, These are complex frequency domain models of small-signal disturbance components, namely, input voltage, output voltage, inductor current, input current, and the conduction ratio of the main bidirectional switch of the converter.

[0145] eliminate The following open-loop transfer function can be obtained:

[0146] The transfer function from input voltage to output voltage;

[0147]

[0148] The transfer function from duty cycle to output voltage;

[0149]

[0150] Output impedance;

[0151]

[0152] It should be noted that the three open-loop transfer functions are in parallel, mainly indicating the relationship between input voltage and output voltage, the relationship between duty cycle and output voltage, and output impedance, respectively. They all belong to the mathematical model of the circuit and express the circuit characteristics.

[0153] In the above implementation process, the transfer function from duty cycle to output voltage can only derive the relationship between duty cycle and output voltage. The duty cycle value and the output voltage value correspond one-to-one. If open-loop control is performed, that is, given a fixed output voltage value, a fixed duty cycle is calculated according to the transfer function. This method can control the output voltage, but it cannot change the duty cycle in real time to control the output voltage to keep it stable in response to the dynamic fluctuations of the output voltage.

[0154] In this application, a PI controller is used for single-loop instantaneous voltage value control, and the output voltage U is controlled by the PI controller. o Feedback is sent to the input terminal, forming a negative feedback system. The PI controller uses the instantaneous error e = U between the actual and desired output voltage values. o.ref -U o Dynamically adjust the duty cycle d to ensure U o Fast and accurate tracking of U o.ref When load / input changes cause U o When voltage fluctuations occur, the system automatically corrects the duty cycle through error feedback to maintain voltage stability.

[0155] Reference Figure 5As shown, the block diagram of the Buck mode closed-loop control in the bidirectional flexible voltage regulating device of the distribution network is shown. The single closed-loop control is divided into output voltage sampling, error signal generation, controller processing, PWM modulation, delay stage, circuit dynamic model and output voltage feedback in sequence.

[0156] The specific process includes: first, collecting the output voltage U of the bidirectional flexible voltage regulating device in the power distribution network. o Calculate U o With a given voltage reference value U o.ref The error signal e = U o.ref -U o Next, the error signal e is sent to the PI controller for proportional-integral calculation to obtain the control voltage U. c The U obtained from PI control is used as a control variable to drive subsequent stages; then the U obtained from PI control is... c Through PWM modulation, i.e. K pwm The module converts the duty cycle signal d. pwm After a delay, G... delay The duty cycle d after the output delay simulates the control delay in the actual system; finally, the duty cycle d outputs the actual output voltage U through the main circuit. o Transfer function G od (s) represents the change in the main circuit from the control-generated duty cycle d to the generated output voltage U. o The dynamic process.

[0157] The core of closed-loop control is the generated output voltage U. o The data is sampled in real time and enters the error signal generation stage, along with U. o.ref Continuous comparison forms a closed-loop control, enabling dynamic voltage regulation.

[0158] In this approach, a single closed-loop voltage control strategy is employed, typically using a PI controller. The proportional gain K is adjusted accordingly. p and integral coefficient K i This improves the system's steady-state and dynamic performance. A modulation stage and a delay stage are added; the modulation stage is set to have a gain of K. pwm Control K pwm The value is 1, and the delay element G delay (s) includes the sampling calculation step T s and PWM control loop 0.5T s ;

[0159]

[0160] In the formula, T delay For the delay period, T s The switching cycle.

[0161] The open-loop transfer function of voltage single-loop control can be expressed as:

[0162]

[0163] In the formula, K p K is the proportionality coefficient. i is the integral coefficient.

[0164] The PI parameters of the voltage loop are designed based on the switching frequency f. s Set the open-loop cutoff frequency f cr and PI transition frequency f zt ;

[0165]

[0166] Based on the definition of open-loop cutoff frequency, a system of equations can be established, and then the PI controller parameter K can be solved. p and K i ;

[0167]

[0168] In some specific embodiments of this application, when the voltage of the low-voltage distribution network is lower than the lower limit, the bidirectional flexible voltage regulating device of the distribution network is connected in series between the input power supply and the output load in Boost mode;

[0169] The second grid-side switch of the low-voltage side switching switch and the first load-side switch of the high-voltage side switching switch in the mode switching device of the distribution network are switched to the on state; the first grid-side switch of the high-voltage side switching switch and the second load-side switch of the low-voltage side switching switch are switched to the off state.

[0170] The high-voltage side port of the direct AC / AC type unidirectional voltage regulation topology of the distribution network bidirectional flexible voltage regulation device is connected to the load side of the low-voltage distribution network through the second load side switch of the high-voltage side switching switch, and the low-voltage side port is connected to the grid side of the low-voltage distribution network through the first grid side switch of the low-voltage side switching switch. The distribution network bidirectional flexible voltage regulation device is connected in series between the input grid and the output load in Boost mode.

[0171] In some specific embodiments of this application, when the voltage of the low-voltage distribution network is lower than the lower limit, the bidirectional flexible voltage regulating device of the distribution network is connected in series between the input network and the output load in Boost mode;

[0172] Boost modes include: Mode 1 freewheeling mode and Mode 2 power transfer mode.

[0173] In the first mode of freewheeling, when the main control bidirectional switch of the direct AC / AC type unidirectional voltage regulation topology is turned off and the freewheeling bidirectional switch is turned on, the circuit is in freewheeling mode.

[0174] The mode two power transmission mode is that when the main control bidirectional switch is turned on and the freewheeling bidirectional switch is turned off, the circuit is in power transmission mode.

[0175] Specifically, in mode one, during the [t0-t1] time period within one switching cycle, when the main control bidirectional switches S1 and S2 are off and the freewheeling bidirectional switches S3 and S4 are on, the circuit is in freewheeling mode. The equivalent circuit diagram is as follows: Figure 6 As shown in (a).

[0176] Mode 2: During the [t1-t2] time period within one switching cycle, when the main control bidirectional switches S1 and S2 are turned on and the freewheeling bidirectional switches S3 and S4 are turned off, the circuit is in power transfer mode. The equivalent circuit diagram is as follows: Figure 6 As shown in (b), depending on the direction of the inductor current, energy is transferred from the input power supply to the output load or fed back from the output load to the input power supply.

[0177] The closed-loop control strategy of the bidirectional flexible voltage regulating device in the distribution network adopts a single closed-loop voltage control strategy. The controller is generally a PI controller, with additional modulation and delay stages. The control block diagram is shown below. Figure 7 As shown.

[0178] In some specific embodiments of this application, in mode-one freewheeling mode, the power supply u i When power is supplied to an inductor, the inductor stores energy, the inductor voltage rises, the current increases, and the high-voltage side filter capacitor supplies power to the load.

[0179] In the two-mode power transfer mode, the power supply and the energy storage inductor supply power to the load. The inductor releases energy, the voltage drops, and depending on the direction of the inductor current, the energy is transferred from the input power supply to the load or fed back from the load to the input power supply.

[0180] Specifically, when the bidirectional flexible voltage regulator of the distribution network operates in Boost mode, under the complementary high-frequency conduction of S1, S2 and S3, S4, the circuit has two operating modes. The initial conditions are: assuming the power frequency input voltage is u... i (t)=U i ·sin(ωt), where the angular frequency ω=2πf remains constant, and the amplitude U i It may contain random disturbances. The conduction ratio of switching transistors S3 and S4 is d(t), and their steady-state value is D. The control objective of this system is to obtain a precise and stable power frequency output u. o (t)=U o sin(ωt), requiring a very good sine degree and an amplitude U o Constant, frequency and phase are related to the input voltage u i(t) The fundamental frequency is the same. The state equations for the two operating modes are as follows:

[0181] In mode one, during the [t0-t1] time period within a switching cycle, when the main control bidirectional switches S1 and S2 are off and the freewheeling bidirectional switches S3 and S4 are on, the circuit is in freewheeling mode, and the power supply u... i When power is supplied to an inductor, the inductor stores energy, the inductor voltage rises, the current increases, and the high-voltage side filter capacitor supplies power to the load.

[0182] When the inductor current is in the positive half-cycle, the expressions for the inductor voltage, the low-side capacitor current, and the input power supply current are:

[0183]

[0184] i s (t)=i L (t);

[0185] In the formula, u i (t) represents the input voltage, u o (t) represents the output voltage, i s (t) represents the input current, i L (t) represents the inductor current, L represents the energy storage inductor, C represents the high-voltage side filter capacitor, and R represents the load resistance.

[0186] In Mode 2, during the [t1-t2] time period within a switching cycle, when the main control bidirectional switches S1 and S2 are turned on and the freewheeling bidirectional switches S3 and S4 are turned off, the circuit is in power transfer mode. The power supply and energy storage inductor supply power to the load, the inductor releases energy, and the voltage drops. Depending on the direction of the inductor current, energy is transferred from the input power supply to the load or fed back from the load to the input power supply.

[0187] When the inductor current is in the positive half-cycle, the expressions for the inductor voltage, output capacitor current, and input power supply current are:

[0188]

[0189] i s (t)=i L (t);

[0190] In the formula, u i (t) represents the input voltage, u o (t) represents the output voltage, t s (t) represents the input current, i L (t) represents the inductor current, L represents the energy storage inductor, C represents the high-voltage side filter capacitor, and R represents the load resistance;

[0191] In Boost mode, when calculating the duty cycle, the average value of each state quantity within any switching cycle (Ts) is taken. As a new state variable, the average state-space equation of the converter can be obtained as follows:

[0192]

[0193] In the formula, T s For the switching cycle, This represents the average value of the input-side voltage during any given switching cycle. This represents the average value of the output voltage during any switching cycle. This represents the average value of the input-side current during any switching cycle. The average value of the inductor current during any switching cycle is given by L, where L is the filter inductance, C is the low-voltage side filter capacitor, and R is the load resistance.

[0194] Small-signal disturbances are superimposed on the static DC components of each major variable, i.e.

[0195]

[0196] In the formula, U i U o I L I s These are the static DC components of the input voltage, output voltage, inductor current, and input current, respectively. These are the small-signal disturbance components of the input voltage, output voltage, inductor current, input current, and the conduction ratio of the main control bidirectional switch of the converter, respectively.

[0197] Substituting into the state-averaged equation, if and only if Time (i.e., input voltage u) i (t) is outside the sufficiently small locality of zero, and both sides of the equation are equal. They can be canceled out; further, zero-valued terms can be eliminated. and U i -(1-D)U o And ignore nonlinear terms The small-signal state equation of the system can be obtained as follows:

[0198]

[0199] Applying the Laplace transform to the equation, we get...

[0200]

[0201] In the formula, These are complex frequency domain models of small-signal disturbance components, namely, input voltage, output voltage, inductor current, input current, and the conduction ratio of the converter freewheeling bidirectional switch.

[0202] eliminate The following open-loop transfer function can be obtained:

[0203] (1) Transfer function from input voltage to output voltage:

[0204]

[0205] (2) Transfer function from duty cycle to output voltage:

[0206]

[0207] (3) Output impedance:

[0208]

[0209] In Boost mode, a single-loop voltage control strategy is also employed, typically using a PI controller. Adjusting the proportional and integral coefficients improves the system's steady-state and dynamic performance. A modulation and delay stage are also added. The modulation stage is set to a gain of K. pwm Control K pwm The value is 1, and the delay element G delay (s) includes the sampling calculation step T s and PWM control loop 0.5T s .

[0210]

[0211] In the formula, T delay This refers to the time for the delay phase.

[0212] The open-loop transfer function of a single closed-loop control can be expressed as:

[0213]

[0214] In the formula, K p K is the proportionality coefficient. i Integral coefficient

[0215] The PI parameters of the voltage loop are designed based on the switching frequency f. s Set the open-loop cutoff frequency f cr and PI transition frequency f zt ;

[0216]

[0217] Based on the definition of open-loop cutoff frequency, a system of equations can be established, and then the PI controller parameter K can be solved. p and K i

[0218]

[0219] In Boost mode, the transfer function expression from input voltage to output voltage shows that by controlling the duty cycle of the bidirectional switching transistor, the direct AC / AC type unidirectional voltage regulation topology can regulate the voltage on the output load side; through the voltage single closed-loop control strategy, the direct AC / AC type unidirectional voltage regulation topology can adjust the duty cycle of the switching transistor in real time according to the instantaneous value of the output voltage, thereby achieving precise regulation and smooth voltage regulation of the output voltage.

[0220] Reference Figure 7 As shown, the single-loop closed-loop control is divided into output voltage sampling, error signal generation, controller processing, PWM modulation, delay stage, circuit dynamic model, and output voltage feedback in sequence. The specific process includes: firstly, acquiring the output voltage U of the bidirectional flexible voltage regulator in the distribution network. o Calculate U o With a given voltage reference value U o.ref The error signal e = U o.ref -U o Next, the error signal e is sent to the PI controller for proportional-integral calculation to obtain the control voltage U. c The U obtained from PI control is used as a control variable to drive subsequent stages; then the U obtained from PI control is... c Through PWM modulation, i.e. K pwm The module converts the duty cycle signal d. pwm After a delay, G... delay The duty cycle d after the output delay simulates the control delay in the actual system; finally, the duty cycle d outputs the actual output voltage U through the main circuit. o Transfer function G od (s) represents the change in the main circuit from the control-generated duty cycle d to the generated output voltage U. o The dynamic process. The core of closed-loop control is the generated output voltage U. o The data is sampled in real time and enters the error signal generation stage, along with U. o.ref Continuous comparison forms a closed-loop control, enabling dynamic voltage regulation.

[0221] In this application, when the circuit is determined to be operating normally, the bidirectional flexible voltage regulating device of the power distribution network is connected in series between the input power grid and the output load in a direct-through mode.

[0222] In the case where the bidirectional flexible voltage regulator of the distribution network is connected in series between the input power supply and the output load in a direct-through mode, the high-voltage side switching switches of the mode switching switch are all in the on state, the low-voltage side switching switches are all in the off state, the main control bidirectional switch tube of the direct AC / AC type unidirectional voltage regulation topology remains in the on state, the freewheeling bidirectional switch tube remains in the off state, the input power supply and the output load are directly connected, the bidirectional flexible voltage regulator of the distribution network operates in the direct-through mode, and the load side voltage is the low-voltage distribution network line voltage.

[0223] Specifically, refer to Figure 9 As shown, the control method includes the following: Under operating condition one, when the voltage of the low-voltage distribution network line is within the allowable voltage deviation range, the circuit operates normally. The high-voltage side switching switches (201a, 201b) are kept in the on state, and the low-voltage side switching switches (202a, 202b) are kept in the off state. The main control bidirectional switching transistors (S1, S2) of the bidirectional flexible voltage regulator of the distribution network are kept in the on state, and the freewheeling bidirectional switching transistors (S3, S4) are kept in the off state. At this time, the input power supply and the output load are directly connected, the bidirectional flexible voltage regulator of the distribution network is in the direct-through mode, and the output load voltage is the low-voltage distribution network line voltage.

[0224] Operating Condition 2: When the voltage of the low-voltage distribution network line fluctuates or exceeds the upper limit, the system detects that the line voltage deviates from the set upper limit value. After controlling the load-side switch 202b of the low-voltage side switching switch to the on state, the system controls the load-side switch 201b of the high-voltage side switching switch to the off state. Other mode switching switches maintain their original switching states, that is, the grid-side switch 201a of the high-voltage side switching switch remains on state, and the grid-side switch 202a of the low-voltage side switching switch remains off state. At this time, the bidirectional flexible voltage regulator of the distribution network is connected between the input power supply and the output load in Buck mode. The system releases the lockout state of the bidirectional flexible voltage regulator of the distribution network, detects the deviation between the output voltage and the set value, and switches the control strategy of the bidirectional flexible voltage regulator of the distribution network. The two sets of bidirectional switches are switched on and off complementaryly according to the duty cycle obtained by the Buck mode closed-loop control strategy. The bidirectional flexible voltage regulator of the distribution network performs voltage reduction regulation to maintain a stable output voltage on the load side.

[0225] Under operating condition 3, when the voltage of the low-voltage distribution network line fluctuates or exceeds the lower limit, the system detects that the line voltage deviates from the set lower limit value. After controlling the grid-side switch 202a of the low-voltage side switching switch to the conducting state, the system controls the grid-side switch 201a of the high-voltage side switching switch to the off state. Other mode switching switches maintain their original switching states, that is, the load-side switch 201b of the high-voltage side switching switch remains in the conducting state, and the load-side switch 202b of the low-voltage side switching switch remains in the off state. At this time, the bidirectional flexible voltage regulator of the distribution network is connected between the input power supply and the output load in Boost mode. The system releases the lockout state of the bidirectional flexible voltage regulator of the distribution network, detects the deviation between the output voltage and the set value, and switches the control strategy of the bidirectional flexible voltage regulator of the distribution network. The two sets of bidirectional switches are switched on and off complementaryly according to the duty cycle obtained by the Boost mode closed-loop control strategy. The bidirectional flexible voltage regulator of the distribution network performs voltage boost regulation to maintain a stable output voltage on the load side.

[0226] Condition 4: When the voltage of the low-voltage distribution network line recovers to the allowable deviation range and the detected line voltage recovers to the set voltage range, the main control switch (S1, S2) of the distribution network bidirectional flexible voltage regulator is switched to a continuously conducting state, and the freewheeling bidirectional switch (S3, S4) is switched to a continuously off state. The distribution network bidirectional flexible voltage regulator is disengaged from voltage regulation, and the high-voltage side switching switch (201a, 201b) is switched to a conducting state, while the low-voltage side switching switch (202a, 202b) is switched to a off state. At this time, the input power supply and the output load are directly connected, and the distribution network bidirectional voltage regulator is in a direct-through mode.

[0227] The timing sequence of the switching transistors during the bidirectional switching process of the bidirectional flexible voltage regulating device in the distribution network is as follows: Figure 8 As shown.

[0228] For the status of each state of the mode switching switch section of the bidirectional flexible voltage regulating device for the power distribution network, please refer to [link / reference]. Figure 9 As shown, when the low-voltage distribution network voltage is within the allowable deviation range, the direct AC / AC type unidirectional voltage regulating topology operates in straight-through mode, such as... Figure 9 As shown in (a); when the voltage of the low-voltage distribution network exceeds the upper limit, the topology operates in Buck mode, as follows: Figure 9 As shown in (b); when the voltage of the low-voltage distribution network exceeds the lower limit, the topology operates in Boost mode, as follows: Figure 9 As shown in (c). A schematic diagram of the mode switching method is shown below. Figure 10 As shown, after comparing the input voltage with the set upper and lower voltage limits, the operating mode of the topology is determined to be either Buck mode or Boost mode. The corresponding closed-loop control strategy is then selected to calculate the duty cycle and control the output voltage. The control signal generation section is the PWM signal generation section of the topology's bidirectional switching transistor, controlled by both input voltage zero-crossing comparison and duty cycle.

[0229] The preferred features in the above embodiments can be used individually in any embodiment, or in any combination thereof, provided they do not conflict with each other. Furthermore, parts not described in detail in the embodiments can be implemented using existing technologies.

[0230] The following examples and comparative examples will be used to further illustrate this application in order to better understand the above-mentioned technical solutions. It should be understood that the following are only some examples and are not intended to limit this application.

[0231] This application discloses a closed-loop control device and control method for a bidirectional flexible voltage regulating device in a power distribution network. The bidirectional flexible voltage regulating device in the power distribution network, as shown in the example... Figure 1 As shown, the bidirectional flexible voltage regulation device for the distribution network consists of a direct AC / AC type unidirectional voltage regulation topology 100 and a mode switching switch 200. The high-voltage side 100a of the direct AC / AC type unidirectional voltage regulation topology is connected to the grid side and load side of the low-voltage distribution network through the high-voltage side switching switch 201; the low-voltage side 100b of the direct AC / AC type unidirectional voltage regulation topology is connected to the grid side and load side of the low-voltage distribution network through the low-voltage side switching switch 202; the direct AC / AC type unidirectional voltage regulation topology 100 is connected in series in the low-voltage distribution network line through the mode switching switch 200 to realize bidirectional flexible voltage regulation when the low-voltage distribution network voltage fluctuates or exceeds the limit.

[0232] Direct AC / AC type unidirectional voltage regulation topology of distribution network bidirectional flexible voltage regulation device 100 Figure 2 As shown, it consists of a high-voltage side filter capacitor 101, an IGBT-based bidirectional switch 102, an inductor 103, and a low-voltage side filter capacitor 104. The high-voltage side filter capacitor 101 is connected in parallel across the two sides of the high-voltage side 100a port; the low-voltage side filter capacitor 104 is connected in parallel across the two sides of the low-voltage side 100b port; the main control bidirectional switch 102a of the two sets of bidirectional switches is connected in series with the inductor 103, with one side connected to the high-voltage side and the other side connected to the low-voltage side; one side of the freewheeling bidirectional switch 102b of the two sets of bidirectional switches is connected between the main control bidirectional switch and the inductor.

[0233] Mode switching section 200 of the bidirectional flexible voltage regulating device for power distribution network Figure 3As shown, it consists of a high-voltage side switching switch 201 and a low-voltage side switching switch 202. The high-voltage side switching switch 201 is connected to the high-voltage side 100a port of the direct AC / AC type unidirectional voltage regulating topology, wherein the grid side switch 201a of the high-voltage side switching switch is connected to the grid side of the low-voltage distribution network, and the load side switch 201b of the high-voltage side switching switch is connected to the load side of the low-voltage distribution network; the low-voltage side switching switch 202 is connected to the low-voltage side 100b port of the direct AC / AC type unidirectional voltage regulating topology 100, wherein the grid side switch 202a of the low-voltage side switching switch is connected to the grid side of the low-voltage distribution network, and the load side switch 202b of the low-voltage side switching switch is connected to the load side of the low-voltage distribution network.

[0234] Application Example 1:

[0235] Reference Figure 11 , Figure 12 and Figure 13 This is one embodiment of the present application, which illustrates the control method of the present application to verify the actual effect of the method.

[0236] The closed-loop control strategy and mode switching method of the bidirectional flexible voltage regulating device for the distribution network are implemented using MATLAB / Simulink software. Figure 1 The structure shown is used to perform simulation verification for this topology. The simulation parameters are shown in Table 1 below.

[0237] Table 1: Simulation parameters of closed-loop control strategy and mode switching method for bidirectional flexible voltage regulating device in distribution network

[0238] parameter value parameter value Grid voltage 220V, 264V, 176V Load voltage 220V Switching frequency 10kHz Grid frequency 50Hz Transmission power 10kW

[0239] Under the operating conditions shown in the table above, the rated transmission power is 10kW, the rated voltage is 220V (1p.u.), the switching frequency is set to 10kHz, and the grid frequency is 50Hz. When the bidirectional flexible voltage regulator of the distribution network operates in Buck mode, the grid voltage remains at 1p.u. from 0 to 0.3s; from 0.3s to 0.6s, the grid voltage rises to 1.2pu; and from 0.6s to 1s, the grid voltage drops back to 1p.u. The simulation results are as follows: Figure 11 (a) and Figure 12 As shown in the figure. When the bidirectional flexible voltage regulator of the distribution network operates in Boost mode, the grid voltage remains at 1 p.u. from 0 to 0.4 s; from 0.4 s to 0.7 s, the grid voltage rises to 1.2 p.u.; and from 0.7 s to 1 s, the grid voltage drops back to 1 p.u. The simulation results are as follows. Figure 11 (b) and Figure 13 As shown.

[0240] Figure 11In the implementation of this invention, when the voltage of the low-voltage distribution network line fluctuates or exceeds the limit, the action signals of each switch in the mode switching switch section are shown. It can be seen that through switch switching control, when different types of voltage exceed the limit occur, the mode switching achieves reliable operation, realizing reliable switching of the working mode of the bidirectional flexible voltage regulating device of the distribution network.

[0241] Figure 12 The figures show the voltage and current curves of the grid side and the load side when the bidirectional flexible voltage regulating device of the distribution network operates in Buck mode in the embodiment of the present invention. It can be seen that by using the closed-loop control strategy and mode switching method of the proposed bidirectional flexible voltage regulating device of the distribution network, the device can complete accurate and rapid voltage regulation when the voltage of the low-voltage distribution network exceeds the upper limit, and maintain the voltage stability of the load side.

[0242] Figure 13 The figures show the voltage and current curves of the grid side and the load side when the bidirectional flexible voltage regulating device of the distribution network operates in Boost mode in the embodiment of the present invention. It can be seen that by using the closed-loop control strategy and mode switching method of the proposed bidirectional flexible voltage regulating device of the distribution network, the device can complete accurate and rapid voltage regulation when the voltage of the low-voltage distribution network exceeds the lower limit, and maintain the voltage stability of the load side.

[0243] The above examples demonstrate that the closed-loop control strategy and mode switching method of the bidirectional flexible voltage regulating device for distribution networks implemented in this example are as follows: The bidirectional flexible voltage regulating device is used to achieve compact, low-cost, and flexible voltage regulation and switch operation switching when the distribution network voltage fluctuates or exceeds limits; the flexible voltage regulation closed-loop control strategy is used to achieve fast, flexible, and accurate voltage regulation when the distribution network voltage fluctuates or exceeds limits; and the mode switching method is used to control the switch to operate according to the type of exceedance when the distribution network voltage fluctuates or exceeds limits, thereby realizing the switching of the bidirectional flexible voltage regulating device and ensuring reliable switch operation.

[0244] The foregoing has described some specific embodiments of this application. It should be understood that this application is not limited to the specific embodiments described above, and those skilled in the art can make various modifications or variations within the scope of the claims, which do not affect the substantive content of this application. The above-described preferred features can be used in any combination without conflict.

Claims

1. A bidirectional flexible voltage regulating device for power distribution network, characterized in that, include: A direct AC / AC type unidirectional voltage regulation topology, wherein the two ends of the direct AC / AC type unidirectional voltage regulation topology are respectively connected to the grid side and the load side of the low-voltage distribution network, and are used to regulate the voltage of the distribution network; A mode switching switch is connected to the direct AC / AC type unidirectional voltage regulating topology and is used to control the switching of the working mode of the direct AC / AC type unidirectional voltage regulating topology. The direct AC / AC type unidirectional voltage regulation topology is connected in series in the low-voltage distribution network through the mode switching switch to realize bidirectional flexible voltage regulation when the voltage of the low-voltage distribution network fluctuates or exceeds the limit. The mode switching switch includes: a high-voltage side switching switch and a low-voltage side switching switch; One end of the direct AC / AC type unidirectional voltage regulation topology is the high-voltage side, and the other end is the low-voltage side; The high-voltage side of the direct AC / AC type unidirectional voltage regulation topology is connected to the grid side and the load side of the distribution network respectively through the high-voltage side switching switch; The low-voltage side of the direct AC / AC type unidirectional voltage regulation topology is connected to the grid side and the load side of the distribution network respectively through the low-voltage side switching switch; The high-voltage side switching switch includes a first grid-side switch and a first load-side switch; The low-voltage side switching switch includes a second grid-side switch and a second load-side switch; The first grid-side switch is connected to the grid side of the low-voltage distribution network, and the first load-side switch is connected to the load side of the low-voltage distribution network. The second grid-side switch is connected to the grid side of the low-voltage distribution network, and the second load-side switch is connected to the load side of the low-voltage distribution network. The direct AC / AC type unidirectional voltage regulation topology includes: a high-voltage side filter capacitor, an IGBT-based bidirectional switch, an inductor, and a low-voltage side filter capacitor; The bidirectional switching transistor includes: a main control transistor and a freewheeling transistor; The high-voltage side filter capacitor is connected in parallel across both sides of the high-voltage side port, and the low-voltage side filter capacitor is connected in parallel across both sides of the low-voltage side port. One end of the main control transistor of the bidirectional switch is connected in series with one end of the inductor, and the other end of the inductor is connected to one end of the low-voltage side filter capacitor and then connected to the low-voltage side port. The other end of the main control transistor is connected to one end of the high-voltage side filter capacitor and then connected to the high-voltage side port. One end of the freewheeling diode of the bidirectional switch is connected between the main control transistor and the inductor, and the other end of the freewheeling diode is connected to both the high-voltage side port and the low-voltage side port.

2. The bidirectional flexible voltage regulating device of a power distribution network according to claim 1, characterized in that, The main control transistor of the bidirectional switching transistor is composed of a set of IGBT anti-parallel diodes S1 and S2 connected in series with common emitters. The direct AC / AC type unidirectional voltage regulation topology regulates the output voltage by controlling the conduction time of the main control transistors S1 and S2 within one switching cycle.

3. The bidirectional flexible voltage regulating device for a power distribution network according to claim 1, characterized in that, The freewheeling diode of the bidirectional switching transistor is composed of a set of IGBT anti-parallel diodes S3 and S4 connected in series with common emitter, which is used to provide a freewheeling path for current.

4. A control method for a bidirectional flexible voltage regulating device for a power distribution network as described in any one of claims 1-3, characterized in that, include: The voltage value of the low-voltage distribution network is collected and compared with the set upper and lower voltage limits to determine whether the voltage of the low-voltage distribution network is within the set voltage range. If yes, the power grid is considered to be operating normally, and the bidirectional flexible voltage regulating device of the distribution network does not need to be connected to the low-voltage distribution network for voltage regulation; if no, the operating mode of the bidirectional flexible voltage regulating device of the distribution network is determined according to the voltage deviation from the upper and lower limits. Based on the working mode of the bidirectional flexible voltage regulating device for the power distribution network, the corresponding closed-loop control strategy is determined; The duty cycle of the bidirectional switch in the bidirectional flexible voltage regulator of the power distribution network is calculated using the closed-loop control strategy, and the output voltage of the bidirectional flexible voltage regulator of the power distribution network is adjusted using the duty cycle.

5. The control method for a bidirectional flexible voltage regulating device for a power distribution network according to claim 4, characterized in that, The step of determining the operating mode of the bidirectional flexible voltage regulating device for the distribution network based on the voltage deviation from the set range includes: The voltage value of the low-voltage distribution network is collected and compared with the set upper and lower voltage limits to determine whether the voltage of the low-voltage distribution network is within the set voltage range. If it is, the network is considered to be operating normally and the bidirectional flexible voltage regulating device does not need to be connected to the low-voltage distribution network for voltage regulation. If not, the operating mode of the bidirectional flexible voltage regulating device is determined according to the voltage deviation from the upper and lower limits. Wherein, when the voltage of the low-voltage distribution network exceeds the upper limit value, the bidirectional flexible voltage regulating device of the distribution network is connected in series between the input network and the output load of the low-voltage distribution network in Buck mode; When the voltage of the low-voltage distribution network is lower than the lower limit, the bidirectional flexible voltage regulating device of the distribution network is connected in series between the input network and the output load in Boost mode.

6. The control method for a bidirectional flexible voltage regulating device in a power distribution network according to claim 5, characterized in that, When the voltage of the low-voltage distribution network exceeds the upper limit value, the bidirectional flexible voltage regulating device of the distribution network is connected in series between the input power supply and the output load in Buck mode, including: The second load-side switch of the low-voltage side switching switch and the first grid-side switching switch of the high-voltage side switching switch in the mode switching device of the power distribution network bidirectional flexible voltage regulation device are turned to the on state; The first load-side switch of the high-voltage side switching switch and the second grid-side switch of the low-voltage side switching switch are switched to the off state. In this device, the high-voltage side port of the direct AC / AC type unidirectional voltage regulation topology of the distribution network bidirectional flexible voltage regulation device is connected to the grid side of the low-voltage distribution network through the first grid side switch, and the low-voltage side port is connected to the load side of the low-voltage distribution network through the second load side switch. The distribution network bidirectional flexible voltage regulation device is connected in series between the input grid and the output load in Buck mode.

7. The control method for a bidirectional flexible voltage regulating device for a power distribution network according to claim 6, characterized in that, When the voltage of the low-voltage distribution network exceeds the upper limit value, the bidirectional flexible voltage regulating device of the distribution network is connected in series between the input power supply and the output load in Buck mode; The Buck modes include: Mode 1 power transfer mode and Mode 2 freewheeling mode; The mode-1 power transmission mode is characterized by the main control tube of the direct AC / AC type unidirectional voltage regulation topology being turned on and the freewheeling tube being turned off, at which point the circuit is in power transmission mode. The modal two freewheeling mode is characterized by the main control transistor being turned off and the freewheeling transistor being turned on, with the circuit in freewheeling mode.

8. The control method for a bidirectional flexible voltage regulating device in a power distribution network according to claim 7, characterized in that, In the aforementioned mode-one power transfer mode, the power supply Power supply to the load, load voltage Load current As the voltage rises exponentially, the inductors and capacitors of the direct AC / AC type unidirectional voltage regulation topology absorb energy, and the voltage rises. Depending on the direction of the inductor current, the energy is transferred from the input power supply to the output load or fed back from the output load to the input power supply. In the modal two freewheeling mode, the load voltage Approximately 0, the load current decreases exponentially, the inductor and the capacitor supply power to the load and release energy, the voltage drops, and the inductor current continues through the freewheeling tube.

9. The control method for a bidirectional flexible voltage regulating device for a power distribution network according to claim 5, characterized in that, When the voltage of the low-voltage distribution network is lower than the lower limit, the bidirectional flexible voltage regulating device of the distribution network is connected in series between the input power supply and the output load of the low-voltage distribution network in Boost mode; The second grid-side switch of the low-voltage side switching switch and the first load-side switch of the high-voltage side switching switch in the mode switching device of the power distribution network are switched to the on state; the first grid-side switch of the high-voltage side switching switch and the second load-side switch of the low-voltage side switching switch are switched to the off state. The high-voltage side port of the direct AC / AC type unidirectional voltage regulation topology of the distribution network bidirectional flexible voltage regulation device is connected to the load side of the low-voltage distribution network through the second load side switch of the high-voltage side switching switch, and the low-voltage side port is connected to the grid side of the low-voltage distribution network through the first grid side switch of the low-voltage side switching switch. The distribution network bidirectional flexible voltage regulation device is connected in series between the input grid and the output load in Boost mode.

10. The control method for a bidirectional flexible voltage regulating device for a power distribution network according to claim 9, characterized in that, When the voltage of the low-voltage distribution network is lower than the lower limit, the bidirectional flexible voltage regulating device of the distribution network is connected in series between the input network and the output load in Boost mode; The Boost mode includes: Mode 1 freewheeling mode and Mode 2 power transfer mode; The modal freewheeling mode is defined as follows: when the main control transistor of the direct AC / AC type unidirectional voltage regulation topology is turned off and the freewheeling transistor is turned on, the circuit is in freewheeling mode. The modal two power transmission mode is such that when the main control transistor is turned on and the freewheeling transistor is turned off, the circuit is in power transmission mode.

11. The control method for a bidirectional flexible voltage regulating device for a power distribution network according to claim 10, characterized in that, In the aforementioned mode-one freewheeling mode, the power supply When power is supplied to an inductor, the inductor stores energy, the inductor voltage rises, the current increases, and the high-voltage side filter capacitor supplies power to the load. In the mode two power transmission mode, the power supply and the energy storage inductor supply power to the load. The inductor releases energy, the voltage drops, and depending on the direction of the inductor current, the energy is transferred from the input power supply to the load or fed back from the load to the input power supply.

12. The control method for a bidirectional flexible voltage regulating device in a power distribution network according to claim 5, characterized in that, The step of determining a corresponding closed-loop control strategy based on the operating mode of the bidirectional flexible voltage regulator of the power distribution network, calculating the duty cycle of the bidirectional switching transistor in the bidirectional flexible voltage regulator of the power distribution network using the control strategy, and adjusting the output voltage of the bidirectional flexible voltage regulator of the power distribution network using the duty cycle includes: The deviation between the actual output voltage value and the reference value of the low-voltage distribution network is detected, and the duty cycle of the bidirectional switching transistor in the bidirectional flexible voltage regulating device of the distribution network under the corresponding working mode is obtained through PI control. The output voltage of the bidirectional flexible voltage regulator in the power distribution network is adjusted by the duty cycle to maintain a stable output voltage on the load side.

13. The control method for a bidirectional flexible voltage regulating device for a power distribution network according to claim 12, characterized in that, The closed-loop control strategy includes a modulation stage and a delay stage.

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