Extensible three-level bidirectional converter with multi-stage parallel communication

Abstract

The extensible three-level bidirectional converter comprises a three-level conversion unit, a main control unit, a multi-level optical fiber communication module and a current sharing control module, the three-level conversion unit comprises at least one basic unit group, each basic unit group is expanded to N-level expansion unit groups, N is greater than or equal to 2, and the main control unit is connected with the multi-level optical fiber communication module. The basic unit group and the expansion unit group are consistent in structure and realize cascade communication through the multi-stage optical fiber communication module; the multi-stage optical fiber communication module comprises an integrated optical fiber interface board card, a signal conversion circuit and an optical fiber link, through the integrated optical fiber interface board card and a multi-stage cascade architecture, N-stage (N > = 1) parallel expansion can be realized, a communication link does not need to be redesigned, the anti-electromagnetic interference capability is obviously superior to that of traditional cable / bus communication, the communication delay is less than or equal to 10 microseconds, the packet loss rate is less than or equal to 0.01%, and the communication efficiency is greatly improved. Data synchronization and reliability are guaranteed, the continuous operation rate of the system is larger than or equal to 99.9%, the current sharing precision is smaller than or equal to 3%, and equipment damage caused by local overload is avoided.

Description

Technical Field

[0001] This invention relates to the field of bidirectional converter technology, and more specifically to a three-level bidirectional converter with multi-stage parallel communication and scalability. Background Technology

[0002] As a core device for energy conversion and transmission, bidirectional converters are widely used in new energy power generation, energy storage, and rail transportation. With the increasing demand for power capacity in various applications, a single converter can no longer meet the high power output requirements. Therefore, connecting multiple converters in parallel to expand capacity has become the mainstream solution.

[0003] Existing parallel converter technologies mostly employ cable communication or ordinary bus communication (such as CAN bus, RS485), which has the following shortcomings: First, cable communication and ordinary bus communication have weak electromagnetic interference resistance. In high-power converter scenarios, they are easily affected by electromagnetic radiation generated by the high-frequency operation of switching devices, leading to communication delays, data packet loss, and consequently, synchronization imbalance between parallel modules and decreased current sharing accuracy. Second, the expansion levels of traditional parallel architectures are limited, mostly in a "master-single-level slave" mode, making it difficult to achieve multi-level expansion of 3 levels or more. Moreover, expansion requires rebuilding the communication link, which is complex. Third, most current mainstream parallel converters adopt a two-level topology. In high-voltage, high-power scenarios, switching losses are high and output harmonic content is high, requiring additional filtering devices, resulting in increased equipment size and cost. Therefore, a three-level bidirectional converter with multi-level parallel communication and scalability is needed. Summary of the Invention

[0004] To address the problems existing in the prior art, this invention provides a three-level bidirectional converter with multi-level parallel communication scalability. By combining an integrated fiber optic interface design, a multi-level fiber optic communication architecture, and a three-level topology, the converter can be flexibly expanded in multiple parallel stages, while ensuring communication stability and conversion efficiency, thus meeting the needs of high-power capacity applications.

[0005] To achieve the above objectives, the present invention is implemented through the following technical solution: a three-level bidirectional converter with multi-level parallel communication scalability, comprising a three-level converter unit, a main control unit, a multi-level optical fiber communication module and a current sharing control module, wherein the three-level converter unit comprises at least one set of basic unit groups, each set of basic unit groups is extended to N levels of extended unit groups, and N≥2, the basic unit groups and the extended unit groups have the same structure and are cascaded through the multi-level optical fiber communication module; The main control unit includes a main control board, which has a built-in main controller for generating system-level control commands and communicating with the basic unit group via optical fiber for direct control of the basic unit group. The current sharing control module includes a current sharing command generation unit and a current sharing adjustment unit; the current sharing command generation unit is located on the main control board in the main control unit, and the current sharing adjustment unit is located on the control chip at each unit level. The current sharing command generation unit calculates the rated output current (I_ref=I_total / N) of each unit based on the total number of parallel units (N) and the total power given value, and sends it to each unit through optical fiber; The current sharing adjustment unit receives the AC current sampling value (I_actual) and the rated output current (I_ref) of its own unit. It adopts droop control combined with an active current sharing compensation algorithm. When the deviation between I_actual and I_ref exceeds 5%, it adjusts the duty cycle of the PWM drive signal at the unit level to make the output current of each unit tend to be consistent, with a current sharing accuracy of ≤3%.

[0006] Furthermore, both the basic unit group and the expansion unit group adopt the NPC midpoint clamping topology, including four IGBT power switching transistors (numbered: S1, S2, S3, S4), two clamping diodes (numbered: D1, D2), and two DC-side voltage divider capacitors (numbered: C1, C2). Among them, S1 and S2 are connected in series, and S3 and S4 are connected in series. The two sets of series branches are connected in parallel and then connected to both ends of the DC bus formed by C1 and C2 in series on the DC side. One end of D1 is connected to the series node of S1 and S2, and the other end of D1 is connected to the midpoint of the series clamping of C1 and C2. One end of D2 is connected to the series node of S3 and S4, and the other end of D2 is connected to the midpoint of the series clamping of C1 and C2. The AC side is led out through the series node of S2 and S3 for bidirectional AC-DC conversion.

[0007] Furthermore, each group of three-level converter units also includes a sampling circuit, a driving circuit, and a unit-level control chip. The unit-level control chip is set in the basic unit group. The sampling circuit includes a DC voltage sampling module, an AC current sampling module, and an IGBT temperature sampling module. The DC voltage sampling module is used to collect the voltage of C1 and C2 and the total voltage of the DC bus. The AC current sampling module is used to collect the AC side output current. The IGBT temperature sampling module is used to collect the case temperature of the IGBT power switching transistors S1 to S4 and transmit the sampled data in the sampling circuit to the unit-level control chip. The drive circuit receives the PWM drive signal from the unit-level control chip and controls the on / off state of the IGBT power switch to realize the three-level converter function. Furthermore, the main control unit also includes a human-machine interaction module and a system protection module. The human-machine interaction module includes a touch screen and buttons for displaying system operating parameters and setting control parameters. The system protection module includes overvoltage protection, overcurrent protection, overtemperature protection, and communication fault protection. When an abnormal signal is detected (such as the DC bus voltage exceeding 110% of the rated value, the IGBT temperature exceeding 125°C, or the communication interruption exceeding 50ms), a shutdown command is immediately sent to each unit to ensure system safety.

[0008] Furthermore, the multi-level optical fiber communication module includes an integrated optical fiber interface board, a signal conversion circuit, and an optical fiber link, which are integrated on the housing of each group of three-level converter units to realize cascaded communication between the main control unit and each unit group, and between each unit group. The integrated fiber optic interface board adopts a PCB integrated design and is directly soldered onto the circuit board where the unit-level control chip is located. The integrated fiber optic interface board is equipped with two fiber optic interfaces (an "input interface" and an "output interface"), eliminating the need for an external communication module and reducing signal conversion steps. The signal conversion circuit is integrated inside the unit-level control chip and uses a high-speed serial communication protocol to convert the control signals sent by the main control unit into optical signals transmitted through optical fibers. At the same time, it converts the sampled data of this unit into optical signals and feeds them back to the upper-level unit or the main control unit.

[0009] Furthermore, the number of expansion unit groups in the Nth level expansion unit group increases in increments of N+1. The multi-level optical fiber communication module also includes optical fiber links. The connection method of the optical fiber links is as follows: the main control board is connected to the "input interface" of the basic unit group (group 1) via optical fiber, the "output interface" of the basic unit group (group 1) is connected to the "input interface" of the first level expansion unit group (group 2) via optical fiber, the "output interface" of the first level expansion unit group (group 2) can be further connected to the "input interface" of the second level expansion unit group (group 3), and so on, to achieve N-level expansion.

[0010] Preferably, the optical fiber is a single-mode silica fiber with a transmission rate of ≥1Gbps and a transmission distance of ≤100m, which meets the requirements of short-distance parallel connection of multiple units.

[0011] In summary, this invention provides a three-level bidirectional converter with multi-stage parallel communication for scalability, and compared with existing technologies, the beneficial effects achieved are as follows: 1. High flexibility for expansion: Through integrated fiber optic interface cards and multi-level cascading architecture, N-level (N≥1) parallel expansion can be achieved without redesigning the communication link. The expansion process only requires connecting the fiber optic cable, which is simple to operate and meets different power capacity requirements. 2. Strong communication stability: Utilizing fiber optic communication and a high-speed serial protocol, its anti-electromagnetic interference capability is significantly superior to that of traditional cable / bus communication. Communication delay is ≤10μs, and packet loss rate is ≤0.01%, ensuring the reliability of synchronization and data transmission between parallel modules. 3. High converter efficiency: Adopting the NPC three-level topology, the switching loss is reduced by 30%-40% compared with the two-level converter, the AC side THD is ≤3%, no need to add a large-capacity filter device, the equipment size is reduced by 20%, and the cost is reduced by 15%; 4. High operational reliability: It has multi-level protection and fault redundancy functions. When one unit fails, the other units automatically take over the load. The system has a continuous operation rate of ≥99.9% and a current sharing accuracy of ≤3%, avoiding equipment damage caused by local overload. Attached Figure Description

[0012] Figure 1 This is a diagram of the multi-level optical fiber communication architecture of the present invention; Figure 2 This is a topology diagram of the three-level commutator circuit of the present invention; Figure 3 This is a schematic diagram of the flow sharing control principle of the present invention; Detailed Implementation

[0013] The invention will now be further described with reference to the accompanying drawings.

[0014] like Figures 1 to 3 As shown: This invention relates to a three-level bidirectional converter with multi-level parallel communication and scalability. It comprises a three-level converter unit, a main control unit, a multi-level fiber optic communication module, and a current sharing control module. At least one set of three-level converter units is provided (defined as a "basic unit group"). The converter can be expanded to N levels (N≥2, defined as an "extended unit group"). Each group of units has the same structure and achieves cascaded communication through the multi-level fiber optic communication module. The specific structure is as follows: 1. Three-level converter unit like Figure 2 As shown, each three-level converter unit includes a three-level commutation circuit, a drive circuit, a sampling circuit, and a unit-level control chip. The three-level commutation circuit adopts an NPC (neutral point clamping) topology, including four IGBT power switches (S1, S2, S3, S4), two clamping diodes (D1, D2), and DC-side voltage divider capacitors (C1, C2). S1 and S2 are connected in series, and S3 and S4 are connected in series. The two series branches are connected in parallel to the DC side (both ends of the DC bus formed by C1 and C2 in series). One end of D1 is connected to the series node of S1 and S2, and the other end is connected to the midpoint (clamping midpoint) of the series connection of C1 and C2. One end of D2 is connected to the series node of S3 and S4, and the other end is connected to the clamping midpoint. The AC side is led out through the series node of S2 and S3 to realize bidirectional AC-DC conversion. The sampling circuit includes a DC voltage sampling module (collecting the voltages of C1 and C2 and the total DC bus voltage), an AC current sampling module (collecting the AC side output current), and an IGBT temperature sampling module (collecting the case temperature of S1-S4). The sampled data is transmitted to the unit-level control chip. The drive circuit receives the PWM drive signal from the unit-level control chip and controls the on / off state of the IGBT power switch to realize the three-level converter function.

[0015] 2. Main Control Unit The main control unit includes a main control board, a human-machine interaction module, and a system protection module; The main control board has a built-in main controller, which uses a 32-bit DSP chip to generate system-level control instructions (such as converter mode switching instructions, power setting instructions, and parallel expansion instructions). It communicates with the unit-level control chip of the basic unit group (Group 1) through optical fiber to realize direct control of the basic unit group. The human-machine interaction module includes a touch screen and buttons, used to display system operating parameters (such as the output power of each unit, DC bus voltage, and communication status) and set control parameters (such as the number of parallel units and the current sharing error threshold). The system protection module includes overvoltage protection, overcurrent protection, overtemperature protection, and communication fault protection. When an abnormal signal is detected (such as the DC bus voltage exceeding 110% of the rated value, the IGBT temperature exceeding 125°C, or the communication interruption exceeding 50ms), a shutdown command is immediately sent to each unit to ensure system safety.

[0016] 3. Multi-level fiber optic communication module like Figure 1 As shown, the multi-level optical fiber communication module includes an integrated optical fiber interface board, a signal conversion circuit, and an optical fiber link, which are integrated on the housing of each group of three-level converter units to realize cascaded communication between the main control unit and each unit group, and between each unit group. The integrated fiber optic interface board adopts a PCB integrated design and is directly soldered onto the circuit board where the unit-level control chip is located. The board is equipped with two fiber optic interfaces (an "input interface" and an "output interface"), eliminating the need for an external communication module and reducing signal conversion steps. The signal conversion circuit is integrated inside the unit-level control chip and uses a high-speed serial communication protocol to convert the control signals (such as PWM synchronization signals and power command signals) sent by the main control unit into optical signals transmitted through optical fiber. At the same time, it converts the sampled data of this unit (such as current, voltage, and temperature) into optical signals and feeds them back to the upper-level unit or the main control unit. The fiber optic link is connected as follows: the main control board is connected to the "input interface" of the basic unit group (group 1) via fiber optic cable; the "output interface" of the basic unit group (group 1) is connected to the "input interface" of the first expansion unit group (group 2) via fiber optic cable; the "output interface" of the first expansion unit group (group 2) can be further connected to the "input interface" of the second expansion unit group (group 3), and so on, to achieve N-level expansion; the fiber optic cable is a single-mode silica fiber with a transmission rate ≥1Gbps and a transmission distance ≤100m, which meets the requirements of short-distance parallel connection of multiple units.

[0017] 4. Flow sharing control module like Figure 1 As shown, the current sharing control module includes a current sharing command generation unit (located on the main control board) and a current sharing adjustment unit (located in each unit-level control chip). The current sharing command generation unit calculates the rated output current (I_ref=I_total / N) of each unit based on the total number of parallel units (N) and the total power given value, and sends it to each unit through optical fiber; The current sharing adjustment unit receives the AC current sampling value (I_actual) and the rated output current (I_ref) of its own unit. It adopts the "droop control + active current sharing compensation" algorithm. When the deviation between I_actual and I_ref exceeds 5%, it adjusts the duty cycle of the PWM drive signal at the unit level to make the output current of each unit tend to be consistent, with a current sharing accuracy of ≤3%.

[0018] The technical effects achieved through the above embodiments are as follows: (N≥1) Parallel expansion requires no redesign of the communication link; the expansion process only requires connecting optical fibers, making it easy to operate and meeting different power capacity requirements. Strong communication stability: Utilizing fiber optic communication and a high-speed serial protocol, its anti-electromagnetic interference capability is significantly superior to that of traditional cable / bus communication, with a communication delay ≤10μs and a packet loss rate ≤0.01%, ensuring the reliability of synchronization and data transmission between parallel modules; High converter efficiency: Adopting NPC three-level topology, the switching loss is reduced by 30%-40% compared with two-level converter, the AC side THD is ≤3%, no need to add a large-capacity filter device, the equipment size is reduced by 20%, and the cost is reduced by 15%; High operational reliability: It has multi-level protection and fault redundancy functions. When one unit fails, the other units automatically take over the load. The system has a continuous operation rate of ≥99.9% and a current sharing accuracy of ≤3%, avoiding equipment damage caused by local overload.

[0019] The embodiments described in this invention are for illustrative purposes only and do not constitute a limitation on the scope of the claims. Other substantially equivalent substitutions that can be conceived by those skilled in the art are all within the scope of protection of this invention.

Claims

1. A three-level bidirectional converter with multi-stage parallel communication expansion capability, characterized in that, It includes a three-level converter unit, a main control unit, a multi-level optical fiber communication module and a current sharing control module. The three-level converter unit includes at least one set of basic unit groups, each set of basic unit groups is extended to N levels of extended unit groups, and N≥2. The basic unit groups and the extended unit groups have the same structure and achieve cascaded communication through the multi-level optical fiber communication module. The main control unit includes a main control board, which has a built-in main controller for generating system-level control commands and communicating with the basic unit group via optical fiber for direct control of the basic unit group. The current sharing control module includes a current sharing command generation unit and a current sharing adjustment unit; the current sharing command generation unit is located on the main control board in the main control unit, and the current sharing adjustment unit is located on the control chip at each unit level. The current sharing command generation unit calculates the rated output current (I_ref=I_total / N) of each unit based on the total number of parallel units (N) and the total power given value, and sends it to each unit through optical fiber; The current sharing adjustment unit receives the AC current sampling value (I_actual) and the rated output current (I_ref) of its own unit. It adopts droop control combined with an active current sharing compensation algorithm. When the deviation between I_actual and I_ref exceeds 5%, it adjusts the duty cycle of the PWM drive signal at the unit level to make the output current of each unit tend to be consistent, with a current sharing accuracy of ≤3%.

2. A three-level bidirectional converter with multi-stage parallel communication scalability as described in claim 1, characterized in that, Both the basic unit group and the expansion unit group adopt the NPC midpoint clamping topology, including four IGBT power switching transistors (numbered: S1, S2, S3, S4), two clamping diodes (numbered: D1, D2), and two DC-side voltage divider capacitors (numbered: C1, C2). Among them, S1 and S2 are connected in series, and S3 and S4 are connected in series. The two sets of series branches are connected in parallel and then connected to both ends of the DC bus formed by C1 and C2 in series on the DC side. One end of D1 is connected to the series node of S1 and S2, and the other end of D1 is connected to the midpoint of the series clamping of C1 and C2. One end of D2 is connected to the series node of S3 and S4, and the other end of D2 is connected to the midpoint of the series clamping of C1 and C2. The AC side is led out through the series node of S2 and S3 for bidirectional AC-DC conversion.

3. A three-level bidirectional converter with multi-stage parallel communication scalability according to claim 2, characterized in that, Each three-level converter unit also includes a sampling circuit, a driving circuit, and a unit-level control chip. The unit-level control chip is set in the basic unit group. The sampling circuit includes a DC voltage sampling module, an AC current sampling module, and an IGBT temperature sampling module. The DC voltage sampling module is used to collect the voltage of C1 and C2 and the total voltage of the DC bus. The AC current sampling module is used to collect the AC side output current. The IGBT temperature sampling module is used to collect the case temperature of the IGBT power switching transistors S1 to S4. The sampling data in the sampling circuit is transmitted to the unit-level control chip. The drive circuit receives the PWM drive signal from the unit-level control chip and controls the on / off state of the IGBT power switch to realize the three-level converter function.

4. A three-level bidirectional converter with multi-stage parallel communication scalability according to claim 3, characterized in that, The main control unit also includes a human-machine interaction module and a system protection module. The human-machine interaction module includes a touch screen and buttons, which are used to display system operating parameters and set control parameters. The system protection module includes overvoltage protection, overcurrent protection, overtemperature protection, and communication fault protection. When an abnormal signal is detected (such as the DC bus voltage exceeding 110% of the rated value, the IGBT temperature exceeding 125°C, or the communication interruption exceeding 50ms), a shutdown command is immediately sent to each unit to ensure system safety.

5. A three-level bidirectional converter with multi-stage parallel communication scalability according to claim 3, characterized in that, The multi-level optical fiber communication module includes an integrated optical fiber interface board, a signal conversion circuit, and an optical fiber link, which are integrated on the housing of each group of three-level converter units to realize cascaded communication between the main control unit and each unit group, and between each unit group. The integrated fiber optic interface board adopts a PCB integrated design and is directly soldered onto the circuit board where the unit-level control chip is located. The integrated fiber optic interface board is equipped with two fiber optic interfaces (an "input interface" and an "output interface"), eliminating the need for an external communication module and reducing signal conversion steps. The signal conversion circuit is integrated inside the unit-level control chip and uses a high-speed serial communication protocol to convert the control signals sent by the main control unit into optical signals transmitted through optical fibers. At the same time, it converts the sampled data of this unit into optical signals and feeds them back to the upper-level unit or the main control unit.

6. A three-level bidirectional converter with multi-stage parallel communication scalability according to claim 5, characterized in that, The number of expansion unit groups in the Nth level expansion unit group increases in increments of N+1. The multi-level optical fiber communication module also includes optical fiber links. The connection method of the optical fiber links is as follows: the main control board is connected to the "input interface" of the basic unit group (group 1) via optical fiber. The "output interface" of the basic unit group (group 1) is connected to the "input interface" of the first level expansion unit group (group 2) via optical fiber. The "output interface" of the first level expansion unit group (group 2) can be further connected to the "input interface" of the second level expansion unit group (group 3), and so on, to achieve N-level expansion.

7. A three-level bidirectional converter with multi-stage parallel communication scalability according to claim 6, characterized in that, The optical fiber uses single-mode silica fiber, with a transmission rate of ≥1Gbps and a transmission distance of ≤100m, meeting the requirements for short-distance parallel connection of multiple units.

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