Modular bidirectional converter and phase-locked method thereof

Abstract

The embodiment of the application discloses a modular bidirectional converter and a phase locking method thereof. The bidirectional converter comprises a conversion circuit composed of multiple modules; each module corresponds to a module control card; a first end of the conversion circuit is connected with a direct-current traction network, and a second end of the conversion circuit is connected with an alternating-current power grid; a system control card is configured to, in a post-buffer starting stage, perform phase locking on the alternating-current power grid to obtain a first phase, and synchronize the first phase to the module control card, so that the module control card controls the output voltage of the module based on the first phase; the post-buffer starting stage represents that the voltage of a direct-current side bus of the conversion circuit has been buffered to a first threshold value, and the buffer starting stage comprises the post-buffer starting stage; the module control card is configured to, in a non-buffer starting stage, perform phase locking on the alternating-current power grid to obtain a second phase, and control the output voltage of the module based on the second phase; and the non-buffer starting stage represents a state in which the alternating-current side of the bidirectional converter is completed and the module control card can sample the alternating current.

Description

Technical Field

[0001] This application relates to, but is not limited to, the field of train regenerative braking energy feedback technology, and particularly to a modular bidirectional converter and its phase-locking method. Background Technology

[0002] A bidirectional converter is a power electronic converter that enables bidirectional energy flow, allowing for the conversion of energy between direct current (DC) and alternating current (AC) or between different DC voltage levels. Bidirectional converters are widely used in electric vehicles, energy storage systems, and distributed generation. Particularly in rail transit traction applications, bidirectional converters typically rely on phase-locked loops (PLLs) via module power control cards. Each power control card requires AC voltage input, resulting in complex signal transmission and high circuit costs. Summary of the Invention

[0003] In view of this, embodiments of this application provide at least one modular bidirectional converter and its phase-locked loop method.

[0004] The technical solution of this application embodiment is implemented as follows:

[0005] On the one hand, embodiments of this application provide a modular bidirectional converter, which includes a conversion circuit composed of multiple modules; each module corresponds to a module control card; the first end of the conversion circuit is connected to the DC traction network, and the second end of the conversion circuit is connected to the AC power grid;

[0006] The system control card is configured to obtain the first phase by phase-locking the AC power grid during the post-slow start phase, and synchronize the first phase to the module control card so that the module control card controls the output voltage of the module based on the first phase; the post-slow start phase indicates that the voltage of the DC side bus of the conversion circuit has been buffered to a first threshold; wherein, the slow start phase includes the post-slow start phase;

[0007] The module control card is configured to obtain a second phase by phase-locking with the AC grid during the non-soft start phase, and control the output voltage of the module based on the second phase; the non-soft start phase represents the state of the bidirectional converter's AC side completing grid connection and the module control card being able to sample the AC power.

[0008] In some embodiments, the bidirectional converter includes a buffer circuit; the buffer circuit is connected to different paths between the conversion circuit and the DC traction network; the system control card is configured to control the buffer circuit to conduct when the path between the bidirectional converter and the DC traction network and the AC grid is open, so as to supply power to the DC side bus through the buffer circuit until the voltage of the DC side bus is buffered to a first threshold and enters the post-slow start stage.

[0009] In some embodiments, a first switch is connected between the conversion circuit and the AC power grid; a module control card is configured to perform forward inversion based on the first phase control module, so that the inverter voltage is gradually buffered to a second threshold; when the inverter voltage is the second threshold, the voltage difference across the first switch reaches a first difference threshold; a system control card is configured to control the first switch to close when the voltage difference across the first switch reaches the first difference threshold, thereby achieving AC side grid connection; and control the buffer circuit to turn off.

[0010] In some embodiments, a second switch is connected between the DC traction network and the conversion circuit; a module control card is configured to control the module to perform reverse rectification and control the voltage of the DC side bus to stabilize to a third threshold; the voltage of the DC side bus is the third threshold, and the voltage difference between the DC side bus and the DC traction network reaches a second difference threshold; a system control card is configured to control the second switch to close when the voltage difference between the DC side bus and the DC traction network reaches the second difference threshold, thereby realizing DC side grid connection and soft start-up completion.

[0011] In some embodiments, the module control card is configured to elect a host during the non-soft start phase based on a module sovereignty value determined by the system soft start state, module state, bus sampling state, host flag, module online flag, weight of each state, and weight of each flag; the host is configured to control the phase synchronization of multiple modules.

[0012] In some embodiments, the priority of the system soft start state is higher than the priority of the module state, the priority of the module state is higher than the priority of the bus sampling state, the priority of the bus sampling state is higher than the priority of the host flag, and the priority of the host flag is higher than the priority of the module online flag.

[0013] In some embodiments, during the soft start phase, the system soft start state is a first value, and the system control card is elected as the host; during the non-soft start phase, the system soft start state is a second value, and the system control card is removed from the election; the first value is greater than the second value.

[0014] In some embodiments, the module control card is configured to perform data interaction and sovereignty contention among multiple modules via the current sharing controller local area network bus; the host is configured to control the phase synchronization and carrier synchronization of multiple modules via the synchronization controller local area network bus.

[0015] In some embodiments, the buffer circuit includes a low-voltage AC power supply, a third switch, and a rectifier circuit; the first end of the rectifier circuit is connected to a different path between the conversion circuit and the DC traction network, the first end of the third switch is connected to the second end of the rectifier circuit, and the second end of the third switch is connected to the low-voltage AC power supply; when the third switch is closed and the conduction angle of the rectifier circuit is gradually opened, the low-voltage AC power supply supplies power to the DC side bus through the third switch and the rectifier circuit until the conduction angle reaches the fourth threshold and the voltage of the DC side bus is buffered to the first threshold.

[0016] On the other hand, embodiments of this application provide a phase-locked method for a modular bidirectional converter, applied to the aforementioned bidirectional converter. The phase-locked method includes:

[0017] In the post-slow start phase, the system control card performs phase-locking with the AC power grid to obtain the first phase and synchronizes the first phase to the module control card, so that the module control card controls the output voltage of the module based on the first phase; the post-slow start phase indicates that the voltage of the DC side bus of the conversion circuit has been buffered to the first threshold; wherein, the slow start phase includes the post-slow start phase;

[0018] During the non-soft start phase, the module control card performs phase-locking with the AC grid to obtain the second phase, and controls the output voltage of the module based on the second phase; the non-soft start phase represents the state where the AC side of the bidirectional converter has completed grid connection and the module control card can sample the AC power.

[0019] In some embodiments, the phase-locked loop method includes: when the system control card is conducting the path between the bidirectional converter and the DC traction network and the AC power grid, controlling the buffer circuit to conduct so as to supply power to the DC side bus through the buffer circuit until the voltage of the DC side bus is buffered to a first threshold and enters the post-slow start stage.

[0020] In some embodiments, the phase-locked loop method includes: a module control card performing forward inversion based on a first phase control module, so that the inverter voltage is gradually buffered to a second threshold; when the inverter voltage is the second threshold, the voltage difference across the first switch reaches a first difference threshold; when the voltage difference across the first switch reaches the first difference threshold, the system control card controls the first switch to close, thereby achieving AC side grid connection; and controls the buffer circuit to turn off.

[0021] In some embodiments, the phase-locked loop method includes: the module control card controls the module to perform reverse rectification and controls the voltage of the DC bus to stabilize to a third threshold; the voltage of the DC bus is the third threshold, and the voltage difference between the DC bus and the DC traction network reaches a second difference threshold; when the voltage difference between the DC bus and the DC traction network reaches the second difference threshold, the system control card controls the second switch to close, realizes DC side grid connection, and the soft start is completed.

[0022] In some embodiments, during the non-soft start phase, the module control card elects a host based on the module sovereignty value determined by the system soft start state, module state, bus sampling state, host flag, module online flag, weight of each state, and weight of each flag; the host controls the phase synchronization of multiple modules.

[0023] In some embodiments, the priority of the system soft start state is higher than the priority of the module state, the priority of the module state is higher than the priority of the bus sampling state, the priority of the bus sampling state is higher than the priority of the host flag, and the priority of the host flag is higher than the priority of the module online flag.

[0024] In some embodiments, during the soft start phase, the system soft start state is a first value, and the system control card is elected as the host; during the non-soft start phase, the system soft start state is a second value, and the system control card is removed from the election; the first value is greater than the second value.

[0025] In some embodiments, the phase-locked loop method includes: the host performing data interaction and sovereignty contention among multiple modules via a current sharing controller local area network bus; and the host controlling phase synchronization and carrier synchronization of multiple modules via a synchronization controller local area network bus.

[0026] In this embodiment, during the system soft start-up phase (post-soft start-up phase), the system control card performs phase locking and synchronizes the first phase locked to multiple module control cards. The module control cards then control the output voltage of their respective modules based on the first phase. In this way, the system control card samples the external AC power grid, while the module control cards only need to sample the inverter voltage. Compared to having all modules perform phase locking, this saves circuit costs and reduces wiring complexity. After the soft start-up is complete, the module control cards automatically perform phase locking and control the output voltage of their respective modules based on the second phase locked, enabling precise control. This not only saves circuit costs and reduces wiring complexity but also ensures the control accuracy of the modules.

[0027] It should be understood that the above general description and the following detailed description are merely exemplary and explanatory, and are not intended to limit the technical solutions of this application. Attached Figure Description

[0028] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with this application and, together with the specification, serve to explain the technical solutions of this application.

[0029] Figure 1 A schematic diagram of the composition structure of a bidirectional converter provided in this application embodiment. Figure 1 ;

[0030] Figure 2A schematic diagram of the composition structure of a bidirectional converter provided in this application embodiment. Figure 2 ;

[0031] Figure 3 A schematic diagram illustrating the implementation process of a phase-locked loop method provided in an embodiment of this application;

[0032] Figure 4 This is a schematic diagram of the composition structure of a phase-locked system provided in an embodiment of this application;

[0033] Figure 5 A schematic diagram of the composition structure of a bidirectional converter provided in this application embodiment. Figure 3 ;

[0034] Figure 6 A schematic diagram of the composition structure of a bidirectional converter provided in this application embodiment. Figure 4 ; . Detailed Implementation

[0035] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions of this application are further described in detail below with reference to the accompanying drawings and embodiments. The described embodiments should not be regarded as limitations on this application. All other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0036] In the following description, references are made to “some embodiments,” which describe a subset of all possible embodiments. However, it is understood that “some embodiments” may be the same subset or different subsets of all possible embodiments and may be combined with each other without conflict.

[0037] The terms “first / second / third” are used merely to distinguish similar objects and do not represent a specific ordering of objects. It is understood that “first / second / third” may be interchanged in a specific order or sequence where permitted, so that the embodiments of this application described herein can be implemented in an order other than that illustrated or described herein.

[0038] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains. The terminology used herein is for descriptive purposes only and is not intended to limit the scope of this application.

[0039] Currently, most rail transit power supply systems use unidirectional rectifiers to convert three-phase AC power into DC power to provide DC power to rail transit vehicles. To achieve bidirectional energy flow between the DC and AC sides of the rail transit power supply system and provide a stable DC contact voltage, a rechargeable bidirectional traction power supply device has been introduced into this system. The AC side of the rechargeable bidirectional traction power supply device is connected to the AC power grid, and the DC side is connected to the DC traction network. When the rail transit vehicle is in traction mode, the power supply device operates in rectification mode, converting the AC power from the AC power grid into DC power to supply the DC traction network. When the rail transit vehicle is in braking mode, the power supply device operates in inverter mode, converting the DC power from the DC traction network back into AC power and feeding it back to the AC power grid.

[0040] This application provides a modular bidirectional converter, such as... Figure 1 As shown, the bidirectional converter 10 includes a conversion circuit 11 composed of multiple modules; each module corresponds to a module control card;

[0041] The first end of the conversion circuit 11 is connected to the DC traction network, and the second end of the conversion circuit 11 is connected to the AC power grid.

[0042] The system control card is configured to, during the post-slow start phase, perform phase-locking on the AC power grid to obtain a first phase, and synchronize the first phase to the module control card, so that the module control card controls the output voltage of the module based on the first phase; the post-slow start phase indicates that the voltage of the DC side bus of the conversion circuit 11 has been buffered to a first threshold; wherein, the slow start phase includes the post-slow start phase;

[0043] The module control card is configured to perform phase-locking with the AC grid to obtain a second phase during the non-soft start phase, and control the output voltage of the module based on the second phase; the non-soft start phase represents the state where the AC side of the bidirectional converter 10 is connected to the grid and the module control card can sample the AC power.

[0044] like Figure 1 As shown, the first sub-terminal of the conversion circuit 11 is connected to the first end (positive pole) of the DC traction network, and the second sub-terminal of the conversion circuit 11 is connected to the second end (negative pole) of the DC traction network; the third, fourth and fifth sub-terminals of the conversion circuit 11 are all connected to the three-phase AC power grid.

[0045] The bidirectional converter 10 is used to invert energy from the DC traction grid to the AC grid and to rectify energy from the AC grid to the DC traction grid. In other words, the bidirectional converter regulates the power output of the power distribution network (AC and DC grids). For example, when the train is in traction mode, the bidirectional converter operates in rectification mode, absorbing electrical energy from the AC grid and rectifying it into DC power to provide a stable traction power supply for the train. When the train brakes, the bidirectional converter switches to inverter mode, inverting the regenerative electrical energy generated during braking back to the AC grid, thus achieving energy recovery and reuse.

[0046] The conversion circuit 11 is used to realize bidirectional conversion between AC and DC power. The conversion circuit 11 adopts a modular design, with each module corresponding to a module control card, which is used to control the ANPC circuit. Multiple modules in the conversion circuit 11 communicate via a Controller Area Network (CAN) bus.

[0047] For example, the conversion circuit 11 can be an active neutral point clamped (ANPC) circuit. Each module in the ANPC circuit can include multiple devices such as switching devices (Sa, Sb, Sc), inductors (L), and flying capacitors (F). The module control card can be a power control card.

[0048] Buffer circuit 12 is used to charge the DC-side bus. The DC-side bus is the conductive path connecting a DC power source (such as a battery, DC traction network, or rectifier output) to the inverter input. The DC-side bus is used to provide a stable DC voltage for conversion to AC output.

[0049] The system control card is the control core of the bidirectional converter 10, responsible for the overall control logic and parameter settings, and controlling the buffer circuit 12 and various switches. Based on the grid status, load demand, and other system parameters, the system control card calculates the phase and frequency of the inverter's required output voltage and sends this information as control signals to each module in the conversion circuit 11.

[0050] The post-slow start phase indicates that the voltage of the DC side bus of the conversion circuit 11 is buffered to the first threshold and begins to enter the slow start grid connection phase. At this time, the system control card can perform phase locking and share the phase locked out with multiple module control cards so that multiple module control cards can control the output voltage of the corresponding module (ANPC circuit) based on the phase locked out.

[0051] The first phase refers to the phase locked out by the system control card. The first threshold refers to the normal value of the DC bus voltage. For example, the first threshold can be set based on the target voltage of the rectifier circuit 123. Specifically, if the rectifier circuit 123 is a single-phase bridge circuit, the first threshold can be set to = 0.85 * 1.414 * (1000 / 220) * target voltage. The target voltage (mains power) will fluctuate. Based on a lower limit of 10%, the bus voltage can be calculated to be greater than 1082V. Therefore, the first threshold value is greater than 1000V, and can be 1082V, 1250V (volts), etc.

[0052] The non-soft start phase indicates that the AC side of the bidirectional converter 10 has been connected to the grid and the module control card can sample the AC power. At this time, the module control card can automatically lock the phase and control the output voltage of the corresponding module based on the phase locked out. The second phase refers to the phase locked out by the module control card.

[0053] In some implementations, the voltage of the DC bus of the conversion circuit 11 can be buffered to a first threshold by the buffer circuit 12. At this time, the system control card locks the AC power grid and synchronizes the first phase locked out to the module control card through the synchronous CAN bus, so that the module control card controls the output voltage of the corresponding module based on the first phase.

[0054] In some implementations, the module control card can perform inverter operation based on the phase locked out by the system control card, controlling the inverter voltage to slowly increase from 0 until the AC side of the bidirectional converter 10 is connected to the grid. At this time, the module control card can sample the AC voltage, and therefore, the module control card can lock the phase itself and control the output voltage of the corresponding module based on the phase locked out.

[0055] In this embodiment, during the system soft start-up phase (post-soft start-up phase), the system control card performs phase locking and synchronizes the first phase locked to multiple module control cards. The module control cards then control the output voltage of their respective modules based on the first voltage. In this way, the system control card samples the external AC power grid, while the module control cards only need to sample the inverter voltage. Compared to having all modules perform phase locking, this saves circuit costs and reduces wiring complexity. After the soft start-up is complete, the module control cards automatically perform phase locking and control the output voltage of the corresponding modules based on the second phase locked, achieving precise control. This not only saves circuit costs and reduces wiring complexity but also ensures the control accuracy of the modules.

[0056] In some embodiments, such as Figure 1As shown, the bidirectional converter 10 includes a buffer circuit 12; the buffer circuit 12 is connected to different paths between the conversion circuit 11 and the DC traction network; the system control card is configured to control the buffer circuit 12 to conduct when the path between the bidirectional converter 10 and the DC traction network and the AC power grid is open, so as to supply power to the DC side bus through the buffer circuit 12 until the voltage of the DC side bus is buffered to the first threshold and enters the soft start stage.

[0057] like Figure 1 As shown, the first sub-terminal of the buffer circuit 12 is connected to the first path, and the second sub-terminal of the buffer circuit 12 is connected to the second path.

[0058] In some embodiments, such as Figure 2 As shown, the buffer circuit 12 includes a low-voltage AC power supply 121, a third switch 122, and a rectifier circuit 123. The first end of the rectifier circuit 123 is connected to different paths between the conversion circuit 11 and the DC traction network. The first end of the third switch 122 is connected to the second end of the rectifier circuit 123, and the second end of the third switch 122 is connected to the low-voltage AC power supply 121. When the third switch 122 is closed and the conduction angle of the rectifier circuit 123 is gradually opened, the low-voltage AC power supply 121 supplies power to the DC side bus through the third switch 122 and the rectifier circuit 123 until the conduction angle reaches a fourth threshold and the voltage of the DC side bus is buffered to a first threshold.

[0059] Rectifier circuit 123 can be a phase-bridge fully controlled rectifier circuit. The target voltage can be 220Vac.

[0060] In some implementations, such as Figure 5 and 6 As shown, the third switch 122 may include a slow-start contactor and a slow-start miniature circuit breaker (referred to as a slow-start miniature circuit breaker). At this time, when the slow-start miniature circuit breaker closes, the slow-start contactor closes, and the conduction angle of the rectifier circuit 123 gradually opens, 220Vac supplies power to the DC side bus through the slow-start miniature circuit breaker, the slow-start contactor, and the rectifier circuit 123.

[0061] The fourth threshold refers to the maximum value of the conduction angle of the rectifier circuit. The rectifier circuit refers to a single-phase bridge fully controlled rectifier circuit. The conduction angle refers to the on-state of the drive signal in a single-phase bridge circuit.

[0062] In some implementations, such as Figure 2As shown, a first transformer (1000V:220V in the figure) is connected between the third switch 122 and the rectifier circuit 123. The system control card controls the third switch 122 to close and controls the rectifier circuit 123 to gradually open the conduction angle. The 220Vac voltage slowly charges the DC bus through the step-up transformer and the rectifier circuit 123. When the conduction angle reaches its maximum value (at this time, the rectifier circuit is similar to a single-phase bridge diode uncontrolled rectifier), the bus voltage reaches 1250V.

[0063] In some implementations, such as Figure 2 As shown, the bidirectional converter 10 may include a disconnecting switch, which is used for electrical isolation and operational control. In this case, not only must the DC switchgear circuit breaker and the AC switchgear circuit breaker be turned off, but the disconnecting switch must also be turned off in order to enable the buffer circuit 12 to conduct.

[0064] In some implementations, such as Figure 2 As shown, a DC switchgear can be installed between the DC traction network and the bidirectional converter 10, and an AC switchgear can be installed between the AC power grid and the bidirectional converter 10. In this case, the closure of the DC switchgear circuit breaker and the AC switchgear circuit breaker signifies that the path between the bidirectional converter 10 and both the DC traction network and the AC power grid is established. Both the AC and DC switchgear circuit breakers are used to connect and disconnect circuits, and also to automatically disconnect circuits in case of faults to protect the safe operation of the equipment.

[0065] It should be noted that the purpose of using the buffer circuit 12 to buffer the DC bus voltage to the first threshold (normal value) is to prevent the DC bus voltage from rising instantaneously when the AC frame is directly closed, which would cause the bus capacitor, switching devices, etc. to suffer a large current surge. By gradually charging to the normal value, this surge can be effectively reduced, thus protecting the equipment.

[0066] In some embodiments, such as Figure 1 and Figure 2 As shown, a first switch 13 is connected between the conversion circuit 11 and the AC power grid; the module control card is configured to perform forward inversion based on the first phase, so that the inverter voltage is gradually buffered to a second threshold; the inverter voltage is the second threshold, and the voltage difference across the first switch 13 reaches a first difference threshold; the system control card is configured to control the first switch 13 to close when the voltage difference across the first switch 13 reaches the first difference threshold, thereby achieving AC side grid connection; and control the buffer circuit 12 to turn off.

[0067] The first switch 13 is used to automatically disconnect the circuit when the current in the circuit exceeds the rated current, so as to prevent the equipment from being damaged due to overload. The first switch 13 can be a frame circuit breaker or an AC switch cabinet circuit breaker.

[0068] The first difference threshold is used to determine when the buffer circuit 12 is turned off. For example, the first difference threshold can be 50V. The second threshold refers to the inverter voltage value when the voltage difference across the first switch 13 reaches the first difference threshold.

[0069] In some implementations, the module control card performs inverter operation based on the phase and frequency of the phase-locked output from the system control card, controlling the inverter voltage to slowly increase from 0 until the voltage difference across the first switch 13 is less than 50V. At this point, the system control card controls the first switch 13 to close, and the AC side of the bidirectional converter 10 completes grid connection.

[0070] like Figure 1 and Figure 2 As shown, a second transformer (900V: 35kV in the figure) can be connected between the first switch 13 (frame circuit breaker) and the AC power grid.

[0071] In some embodiments, such as Figure 1 and Figure 2 As shown, a second switch 14 is connected between the DC traction network and the conversion circuit 11; the module control card is configured to control the module to perform reverse rectification and control the voltage of the DC side bus to stabilize to a third threshold; the voltage of the DC side bus is the third threshold, and the voltage difference between the DC side bus and the DC traction network reaches a second difference threshold; the system control card is configured to control the second switch 14 to close when the voltage difference between the DC side bus and the DC traction network reaches the second difference threshold, thereby realizing DC side grid connection and soft start-up completion.

[0072] The conversion circuit 11 can operate bidirectionally; rectification can be achieved by controlling the direction of the inverter current. The second switch 14 is used to connect and disconnect the DC circuit. The second switch 14 can be a DC contactor or a DC switchgear circuit breaker. The third threshold refers to the voltage value of the traction network. The second differential threshold is used to determine the closing timing of the second switch 14.

[0073] In some implementations, the module control card controls the module to perform reverse rectification and stabilize the DC bus voltage. The target voltage for stabilization is the traction network voltage. The system control card determines the voltage difference between the DC bus and the traction network. When the voltage difference is less than 20V, the system control card controls the second switch 14 to close, and the DC side of the bidirectional converter is connected to the grid, thus completing the soft start process.

[0074] It should be noted that stabilizing the voltage of the DC bus at the traction network voltage value is to reduce voltage fluctuations and ensure stable operation of the equipment.

[0075] In some embodiments, the module control card is configured to elect a host based on a module sovereignty value determined by the system soft start state, module state, bus sampling state, host flag, module online flag, weight of each state, and weight of each flag during the non-soft start phase.

[0076] The system soft-start state is used to characterize whether the system is in the soft-start phase. In some implementations, during the soft-start phase, the system soft-start state is a first value, and the system control card is elected as the host; during the non-soft-start phase, the system soft-start state is a second value, and the system control card is de-elected; the first value is greater than the second value. For example, the first value can be 1, and the second value can be 0.

[0077] As shown in Table 1 below, during the soft start phase, the system soft start state value is 1; during the non-soft start phase, the system soft start state value is 0. The module soft start state is always 0.

[0078] The module status is used to indicate whether the corresponding module is under shutdown protection. For example, as shown in Table 1 below, if no fault occurs that would cause the module to be under shutdown protection, the module is considered to be operating normally, and the value of the module status can be 1; if the module is under shutdown protection, the value of the module status can be 0.

[0079] The bus sampling status is used to characterize whether the bus sampling is abnormal. Operating mode control, midpoint balancing loop, and ripple suppression loop control all involve bus sampling and are quite important; therefore, it is essential to ensure that the host's bus sampling is normal to guarantee the effectiveness of the host's sampling. For example, as shown in Table 1 below, if the bus sampling is normal, the value of the bus sampling status can be 1; if the bus sampling is abnormal, the value of the bus sampling status can be 0.

[0080] The host flag is used to indicate whether the corresponding module is the host. For example, as shown in Table 1 below, if the module is the host, the host flag is 1; if the module is a slave, the host flag is 0. It should be noted that, under the same conditions, the host should be maintained as much as possible to reduce host switching.

[0081] The module online flag is used to indicate whether the module is offline. For example, as shown in Table 1, if the module is online, the module online status is 1; if the module is offline, the module online status is 0.

[0082] Table 1

[0083]

[0084] In some implementations, it can be determined whether the bus sampling is abnormal based on the difference between the DC bus voltage and the median value of the system DC bus voltage within the filtering time and its relationship with a first voltage threshold.

[0085] In some implementations, the filtering time can be 5 seconds and the first voltage threshold can be 40V. In this case, if the difference between the DC bus voltage and the median value of the system DC bus voltage is greater than the first voltage threshold (40V) and the filtering time reaches 5 seconds, it is judged that the bus sampling is abnormal.

[0086] In some implementations, the weight of the system soft start state can be 512, the weight of the module state can be 256, the weight of the bus sampling state can be 128, the weight of the host flag can be 64, and the weight of the module online flag can be 32 - module address. In this case, the formula for calculating the module sovereignty value can be: Module sovereignty value = [System soft start state * 512 + Module state * 256 + Bus sampling state * 128 + Host flag * 64 + (32 - Module address)] * Module online flag.

[0087] In some implementations, the priority of the system soft start state is higher than the priority of the module state, the priority of the module state is higher than the priority of the bus sampling state, the priority of the bus sampling state is higher than the priority of the host flag, and the priority of the host flag is higher than the priority of the module online flag.

[0088] Among them, the priority and weight of the status (including status and flag) are positively correlated. For example, the system soft start status has the highest priority and its weight can be set to 512. The module status has the next highest priority and its weight can be set to 256. The bus sampling status has the next lowest priority and its weight can be set to 128. The host flag has the next lowest priority and its weight can be set to 64. The module online status has the lowest priority and its weight can be set to 32 - module address. Since the system soft start status has the highest priority, when the system soft start status is the first value (1), the system control card directly competes to become the host, and when the system soft start status is the second value (0), the system control card withdraws from the host competition.

[0089] In some implementations, the weight of the online flag is negatively correlated with the module's address; when multiple modules are in the same state and there is no host, the module with the smallest address is the host.

[0090] In some embodiments, the module control card is configured to perform data interaction and sovereignty contention among multiple modules via a current sharing controller local area network bus; the host is configured to control the phase synchronization and carrier synchronization of multiple modules via a synchronization controller local area network bus.

[0091] In some implementations, the data required for sovereignty competition can be transmitted via a current-sharing CAN bus. Synchronization-related control information can also be transmitted via a synchronization CAN bus.

[0092] It should be noted that, in order to achieve a smooth transition of the PLL host from the soft start phase to the normal operation phase, the system control card is included in the sovereignty competition (the system control card and all module control cards compete for sovereignty in real time), ensuring that a new host can take over control if the host fails. The sovereignty competition formula remains consistent at all times. The system soft start state is included in the sovereignty competition formula, and the weight coefficient is the largest (512), so that the system control card becomes the host during the soft start phase. In the non-soft start phase, the value of the system soft start state is 0. At this time, the system control card withdraws from the sovereignty competition, and multiple module control cards compete for the host; thus, a smooth transition is achieved.

[0093] This application provides a phase-locked loop (PLL) method for a modular bidirectional converter, applicable to bidirectional converters. For example... Figure 3 As shown, the method includes the following steps 301 to 302:

[0094] Step 301: In the post-slow start phase, the system control card performs phase-locking with the AC power grid to obtain the first phase, and synchronizes the first phase to the module control card, so that the module control card controls the output voltage of the module based on the first phase; the post-slow start phase indicates that the voltage of the DC side bus of the conversion circuit has been buffered to the first threshold; wherein, the slow start phase includes the post-slow start phase.

[0095] Step 302: In the non-soft start phase, the module control card performs phase-locking with the AC grid to obtain the second phase, and controls the output voltage of the module based on the second phase; the non-soft start phase represents the state where the AC side of the bidirectional converter is connected to the grid and the module control card can sample the AC power.

[0096] In some embodiments, the phase-locked loop method provided in this application further includes the following step 303:

[0097] Step 303: When the bidirectional converter is connected to the DC traction network and the AC power grid, the system control card controls the buffer circuit to be turned on so as to supply power to the DC side bus through the buffer circuit until the voltage of the DC side bus is buffered to the first threshold and enters the soft start stage.

[0098] In some implementations, as the third switch is closed and the conduction angle of the rectifier circuit gradually increases, the low-voltage AC power supplies the DC-side bus via the third switch and the rectifier circuit until the conduction angle reaches a fourth threshold and the voltage of the DC-side bus is buffered to a first threshold.

[0099] In some embodiments, the phase-locked loop method provided in this application further includes the following steps 304 to 305:

[0100] Step 304: The module control card controls the module to perform forward inversion based on the first phase, so that the inverter voltage is gradually buffered to the second threshold; the inverter voltage is the second threshold, and the voltage difference across the first switch of the frame reaches the first difference threshold.

[0101] Step 305: When the voltage difference across the first switch reaches the first difference threshold, the system control card controls the first switch to close, thereby achieving AC side grid connection; and controls the buffer circuit to turn off.

[0102] In some embodiments, the phase-locked loop method provided in this application further includes the following steps 306 to 307:

[0103] Step 306: The module control card controls the module to perform reverse rectification and controls the voltage of the DC side bus to stabilize to the third threshold; the voltage of the DC side bus is the third threshold, and the voltage difference between the DC side bus and the DC traction network reaches the second difference threshold.

[0104] Step 307: When the voltage difference between the DC bus and the DC traction network reaches the second difference threshold, the system control card controls the second switch to close, realizing DC side grid connection and completing the soft start.

[0105] In some embodiments, the phase-locked loop method provided in this application further includes the following steps 308 to 309:

[0106] Step 308: In the non-soft start phase, the module control card elects a host based on the module sovereignty value determined by the system soft start state, module state, bus sampling state, host flag, module online flag, the weight of each state, and the weight of each flag.

[0107] In some implementations, the weight of the online flag is negatively correlated with the address of the module, and when the states of the multiple modules are consistent and there is no host, the module with the smallest address is the host.

[0108] In some implementations, during the non-soft start phase, the system soft start state is a second value, and the system control card exits the election; the first value is greater than the second value.

[0109] Step 309: The host controls the phase synchronization of multiple modules.

[0110] In some embodiments, the phase-locked loop method provided in this application further includes the following steps 310 to 311:

[0111] Step 310: The module control card performs data interaction and sovereignty competition among multiple modules through the current sharing controller local area network bus;

[0112] Step 311: The host controls the phase synchronization and carrier synchronization of multiple modules through the local area network bus of the synchronization controller.

[0113] It should be noted that the phase-locked method provided in this application embodiment belongs to the same inventive concept as the aforementioned bidirectional converter. Therefore, the phase-locked method may also include other possible steps to achieve the functions and effects that the aforementioned bidirectional converter can achieve. Similarly, the bidirectional converter may also include other possible components to execute any step of the phase-locked method in this application embodiment, and this application embodiment does not limit this.

[0114] Furthermore, the modular bidirectional converter and its phase-locked method provided in this application are not only applicable to rail transit traction scenarios, but also to other scenarios with bidirectional operating conditions.

[0115] The following describes the application of the phase-locked loop method provided in the embodiments of this application in a real-world scenario.

[0116] like Figure 4 As shown, this application embodiment provides a phase-locked system (PLS) for a modular bidirectional converter. The PLS includes a monitoring host, a system control card, and multiple power control cards. The monitoring host can detect the operating status of the system control card and the multiple power control cards via a monitoring CAN bus. The system control card can achieve synchronous control of the multiple power control cards via a synchronization CAN bus, and the multiple module control cards can achieve data exchange between modules via a current-sharing CAN bus.

[0117] In some implementations, the monitoring host can be connected to a 10-inch touchscreen so that users can view the operating status of the equipment. The monitoring host can also be connected to a power grid traction power monitoring system and a Power Supervisory Control and Data Acquisition (PSCADA) system. PSCADA is an automated system used for real-time monitoring and control of power system operation. By collecting operating data and status information from power equipment and analyzing and processing this data, PSCADA achieves centralized monitoring, automated control, and data analysis of the power system, thereby improving the operating efficiency, reliability, and safety of the power system. The power grid traction power monitoring system is an automated monitoring system specifically designed for railway and urban rail transit traction power supply systems.

[0118] The system control card includes multiple interfaces with different functions. For example, the system control card may include interfaces such as ADC, CANB, GPIO, SCIB, SPIA, EMIF, PWM, GPIO, SPIB, and CANA. Among them, the Analog-to-Digital Converter (ADC) is used to convert analog signals to digital signals. The Controller Area Network B (CANB) is used to collect the status of each control card. General Purpose Input / Output (GPIO) is used for simple digital signal control and status detection, and also for connecting short-circuit modules. The Serial Communication Interface B (SCIB) is used for communication with the debugging platform. The Serial Peripheral Interface A (SPIA) is used to connect external flash memory. The External Memory Interface (EMIF) is used to connect external Static Random Access Memory (SRAM). Pulse Width Modulation (PWM) is used to connect a soft-start module. The Serial Peripheral Interface B (SPIB) is used for current sharing among multiple power control cards. The Controller Area Network A (CANA) is used for synchronization among multiple power control cards. Similarly, a power control card can also include multiple interfaces such as ADC, CANB, GPIO, SCIB, SPIA, EMIF, PWM, GPIO, SPIB, and CANA.

[0119] like Figure 5 As shown, one implementation process of the phase-locked loop (PLL) method may include the following steps:

[0120] Step 1 (1 in the figure): Close the DC switchgear circuit breaker and the AC switchgear circuit breaker to ensure that the external power has been connected to the bidirectional controller.

[0121] Step 2 (2 in the figure): Close the bidirectional converter isolation switch.

[0122] Step 3 (3 in the figure): Slowly open the micro-break closure.

[0123] Step 4 (4 in the diagram) (Busbar Buffer Stage): The system control card controls the slow-start contactor to close, and the system control card controls the single-phase bridge fully controlled rectifier circuit to gradually open the conduction angle, passing through the 220Vac step-up transformer and the single-phase bridge fully controlled rectifier circuit (corresponding to...). Figure 1 The rectified current 123) in the middle slowly charges the DC side bus. After the conduction angle reaches the maximum value and the bus voltage is normal (1250V), it proceeds to the next step.

[0124] Step 5 (5 in the diagram) (Inverter slow start-up and grid connection stage): The system control card performs phase locking with the 35kV power grid and performs phase synchronization via synchronous CAN. The power control card (module in conversion circuit 11) performs inverter operation according to the phase and frequency of the system control card, controlling the inverter voltage to slowly increase from 0 until the frame circuit breaker (corresponding to Figure 1 When the voltage difference between the two ends of the first switch 13 is less than 50V, the system control card judges the voltage difference between the inverter voltage of the module and the 900V voltage of the transformer. When the voltage difference is less than 50V, the control frame circuit breaker closes and the bidirectional converter AC side completes grid connection.

[0125] Step 6 (6 in the figure): The system control card shuts down the single-phase bridge fully controlled rectifier circuit drive and disconnects the soft-start contactor.

[0126] Step 7 (7 in the figure): The module (power control card) automatically locks in phase and the module host performs phase synchronization. The module performs reverse rectification and stabilizes the DC bus voltage. The target value for stabilization is the traction network voltage. The system control card judges the voltage difference between the DC bus and the traction network. When the voltage difference is less than 20V, the system control card controls the DC contactor to close, and the DC side of the bidirectional converter completes grid connection. The soft start process is completed.

[0127] After the soft start process is completed, the module can operate in the rectification direction or the inverter direction, or switch between the two directions, depending on actual needs. No restrictions are imposed here.

[0128] like Figure 6 As shown, another implementation of the phase-locked loop (PLL) method may include the following steps:

[0129] Step 1 (1 in the figure): Close the bidirectional converter isolation switch.

[0130] Step 2 (2 in the figure): Slowly open the micro-break closure.

[0131] Step 3 (Figure (3)) (Bus Buffer Stage): The system control card controls the slow-start contactor to close, and charges the DC bus slowly through a 220Vac step-up transformer and rectifier circuit. The system control card outputs a square wave signal to directly control the single-phase bridge fully controlled rectifier circuit (SCR), using pure open-loop control. The trigger angle is gradually opened from 0 degrees until it reaches its maximum value. When the trigger angle reaches its maximum value and the bus voltage is normal, the next step begins.

[0132] Step 4 (4 in the figure) (AC grid connection stage): The system control card controls the AC switch cabinet circuit breaker to close, and the bidirectional converter AC side completes grid connection.

[0133] Step 5 (5 in the figure): The system control card shuts down the single-phase bridge fully controlled rectifier circuit drive and disconnects the slow-start contactor.

[0134] Step 6 (6 in the figure) (Reverse rectification traction network connection stage): The module locks in phase by itself and performs reverse rectification by the module host alone to stabilize the DC bus voltage. The stabilized bus voltage value is issued by the system control card, and the other modules do not work. The system control card judges the voltage difference between the DC bus and the traction network. When the voltage difference is less than a certain value, the system control card controls the DC switch cabinet circuit breaker to close, and the DC side of the bidirectional converter completes the grid connection. The slow start process is completed.

[0135] It should be noted that the switching devices in the bidirectional converter can be flexibly configured and selected according to requirements. This application does not limit the type, quantity, or location of the switching devices, and its phase-locked control strategy has high compatibility.

[0136] The phase-locked loop (PLL) strategy can be as follows: During the system's soft start-up phase, the system control card performs PLL and shares the phase with the module control card. The goal is to reduce circuit costs and wiring complexity by requiring only the system control card to sample the external AC grid and the power control card to sample the inverter voltage. Once the soft start-up is complete, the module control card takes over the AC PLL function, independently competing for the module master position and controlling the phase synchronization of all modules.

[0137] To achieve a smooth transition from the soft start phase to the normal operation phase of the PLL master, the system control card is included in the sovereignty competition (both the system control card and all module control cards compete for sovereignty in real time), ensuring that a new master can take over control if the master fails. The sovereignty competition formula remains consistent, incorporating the system soft start state into the formula with the largest weight coefficient (512), so that the system control card becomes the master during the soft start phase; in the non-soft start phase, the system soft start state value is 0, at which point the system control card withdraws from the sovereignty competition, and multiple module control cards compete for the master position; thus, a smooth transition is achieved.

[0138] The formula for sovereignty competition is: Module sovereignty value = [System soft start status * 512 + Module status * 256 + Bus sampling status * 128 + Host flag * 64 + (32 - Module address)] * Module online flag.

[0139] It should be noted that, in this document, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Unless otherwise specified, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes that element.

[0140] In the several embodiments provided in this application, it should be understood that the disclosed devices and methods can be implemented in other ways. The device embodiments described above are merely illustrative. For example, the division of units is only a logical functional division, and in actual implementation, there may be other division methods, such as: multiple units or components can be combined, or integrated into another system, or some features can be ignored or not executed. In addition, the coupling, direct coupling, or communication connection between the various components shown or discussed can be through some interfaces, and the indirect coupling or communication connection between devices or units can be electrical, mechanical, or other forms.

[0141] The units described above as separate components may or may not be physically separate, and the components shown as units may or may not be physical units; they may be located in one place or distributed across multiple network units; some or all of the units may be selected to achieve the purpose of this embodiment according to actual needs. Furthermore, the functional units in the embodiments of this application may all be integrated into one processing unit, or each unit may be a separate unit, or two or more units may be integrated into one unit; the integrated unit may be implemented in hardware or in a combination of hardware and software functional units.

[0142] The above description is merely an embodiment of this application, but the scope of protection of this application is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application.

Claims

1. A modular bidirectional converter, characterized by, The bidirectional converter comprises a conversion circuit composed of a plurality of modules; each module corresponds to a module control card; a first switch is connected between the conversion circuit and an AC power grid; A first end of the conversion circuit is connected to a DC traction grid, and a second end of the conversion circuit is connected to the AC power grid; The system control card is configured to, in a post-buffer starting phase, perform phase locking on the AC power grid to obtain a first phase, synchronize the first phase to the module control card, and control the module control card to control output voltages of the modules based on the first phase; the post-buffer starting phase represents that a voltage of a DC side bus of the conversion circuit has been buffered to a first threshold value; wherein the buffer starting phase includes the post-buffer starting phase; after the post-buffer starting phase ends, the first switch is closed; The module control card is configured to, in a non-buffer starting phase, perform phase locking on the AC power grid to obtain a second phase, and control the output voltages of the modules based on the second phase; the non-buffer starting phase represents a state in which the AC side of the bidirectional converter is completed and the module control card can sample AC power.

2. The bidirectional converter of claim 1, wherein, The bidirectional converter comprises a buffer circuit; the buffer circuit is connected to different paths between the conversion circuit and the DC traction grid and the AC power grid; The system control card is configured to, when a path between the bidirectional converter and the DC traction grid and the AC power grid is conducted, control the buffer circuit to be conducted, so as to supply power to the DC side bus through the buffer circuit, until the voltage of the DC side bus is buffered to the first threshold value, and the post-buffer starting phase is entered.

3. A bidirectional converter according to claim 2, characterized in that The conversion circuit is connected with a first switch between the conversion circuit and the AC power grid; The module control card is configured to control the modules to perform forward inversion based on the first phase, so that an inversion voltage is gradually buffered to a second threshold value; when the inversion voltage is the second threshold value, a voltage difference between the first switch reaches a first difference threshold value; The system control card is configured to, when the voltage difference between the first switch reaches the first difference threshold value, control the first switch to be closed, so as to realize AC side grid connection; and control the buffer circuit to be turned off.

4. A bidirectional converter according to claim 3, characterized in that The DC traction grid is connected with a second switch between the DC traction grid and the conversion circuit; The module control card is configured to control the modules to perform reverse rectification, and control the voltage of the DC side bus to be stable to a third threshold value; when the voltage of the DC side bus is the third threshold value, a voltage difference between the DC side bus and the DC traction grid reaches a second difference threshold value; The system control card is configured to, when the voltage difference between the DC side bus and the DC traction grid reaches the second difference threshold value, control the second switch to be closed, so as to realize DC side grid connection and complete buffer starting.

5. The bidirectional converter according to any one of claims 1 to 4, wherein The module control card is configured to, in a non-buffer starting phase, determine a module master value based on a system buffer starting state, a module state, a bus sampling state, a host flag, a module online flag, a weight of each state, and a weight of each flag, and compete for a host based on the module master value; The host is configured to control phase synchronization of a plurality of modules.

6. A bidirectional converter according to claim 5, characterized in that The priority of the system slow start state is higher than the priority of the module state, the priority of the module state is higher than the priority of the bus sampling state, the priority of the bus sampling state is higher than the priority of the host flag, and the priority of the host flag is higher than the priority of the module online flag.

7. The bidirectional converter of claim 5, wherein, In the slow start phase, the system slow start state is a first value, and the system control card competes to be the host; In the non-slow start phase, the system slow start state is a second value, and the system control card exits the competition; The first value is greater than the second value.

8. The bidirectional converter of claim 5, wherein, The module control card is configured to perform data interaction and master competition of a plurality of the modules through a current sharing controller area network bus; The host is configured to control phase synchronization and carrier synchronization of a plurality of the modules through a synchronous controller area network bus.

9. The bidirectional converter of claim 2, wherein, The buffer circuit comprises a low-voltage alternating current, a third switch, and a rectifier circuit; A first end of the rectifier circuit is connected to a different path between the conversion circuit and the DC traction network, a first end of the third switch is connected to a second end of the rectifier circuit, and a second end of the third switch is connected to the low-voltage alternating current; When the third switch is closed and a conduction angle of the rectifier circuit is gradually opened, the low-voltage alternating current supplies power to the DC side bus through the third switch and the rectifier circuit until the conduction angle reaches a fourth threshold value and the voltage of the DC side bus is buffered to a first threshold value.

10. A method of phase locking a modular bidirectional converter, characterized by, The phase-locked method is applied to the bidirectional converter of any one of claims 1 to 9, and the phase-locked method comprises: In a post slow start phase, a system control card performs phase locking on an alternating current network to obtain a first phase, and synchronizes the first phase to a module control card, so that the module control card controls an output voltage of a module based on the first phase; the post slow start phase represents that the voltage of the DC side bus of the conversion circuit has been buffered to a first threshold value; wherein the slow start phase includes the post slow start phase; In a non-slow start phase, the module control card performs phase locking on the alternating current network to obtain a second phase, and controls the output voltage of the module based on the second phase; the non-slow start phase represents that the AC side of the bidirectional converter completes grid connection, and the module control card can sample the alternating current.

Images