Cascade type direct current conversion equipment power unit online switching control method, device and medium

Abstract

This invention relates to an online switching control method for power units in cascaded DC-DC converter equipment. The method encompasses two control processes: soft disconnection of faulty units and soft connection of new units. Upon fault alarm, the outer loop output voltage of all power units is locked. Based on the linear relationship between output voltage and modulated DC bias, the output voltage of the faulty power unit is linearly reduced, generating a feedforward active current command. Simultaneously, the compensation voltage of the healthy power units is controlled to maintain a constant total DC voltage. Once the output voltage of the faulty power unit drops to zero, bypass electrical isolation is achieved via diode freewheeling. When a new power unit is connected, a solid-state switch is first closed at zero voltage. A smooth voltage rise is achieved through linear DC bias injection, and current transfer is completed without impact, in conjunction with synchronous voltage adjustment of the healthy power units. Finally, the closed-loop control of the outer voltage loop is restored. This invention enables uninterrupted and impact-free online switching, effectively improving the power supply reliability and maintenance flexibility of the equipment.

Description

Technical Field

[0001] This invention relates to the field of power electronics technology, and in particular to an online switching control method, device and medium for power units of a cascaded DC-DC converter. Background Technology

[0002] With the large-scale integration of new energy sources and the rapid growth of DC loads, medium-voltage DC distribution networks and DC microgrids have received wider attention. In these application scenarios, cascaded DC-DC converters, with their advantages of modular structure, easy expansion, and direct connection to medium-voltage distribution networks, have become one of the key equipment technologies. Typical 10kV AC to ±10kV DC conversion schemes include cascaded H-bridge (CHB) + DAB converters, modular multilevel converters (MMC), and three-phase bridge cascaded types.

[0003] In recent years, Active Neutral Point Clamped (ANPC) topologies have gained increasing attention due to their advantages such as uniform loss distribution, high equivalent switching frequency, and low output voltage harmonic content. Based on the concept of "three-phase to single-phase conversion," three-phase AC is decoupled into multiple single-phase isolation windings via a phase-shifting transformer. Each single-phase winding is connected to an ANPCH bridge power unit, and the DC sides of these units are then connected in series to output high-voltage DC, forming a novel cascaded DC-DC converter. This structure combines the excellent characteristics of ANPC with the voltage expansion capabilities of cascaded connections, demonstrating promising application prospects in the medium-voltage DC-DC conversion field.

[0004] However, the aforementioned cascaded DC-DC converter equipment faces a key technical challenge in actual operation: the online switching of power units. When a power unit malfunctions or experiences an anomaly (such as IGBT open circuit, overtemperature, overvoltage, or drive malfunction), it needs to be quickly removed from the DC-side series chain to ensure system safety. When maintenance is completed or online capacity expansion is required, the new unit needs to be smoothly connected to the DC-side series chain. High-quality online switching should meet requirements such as no inrush current, no voltage surges, and uninterrupted system operation.

[0005] Currently, the mainstream methods for handling power unit faults both domestically and internationally rely on bypass switches, mainly including the following:

[0006] (1) Mechanical bypass switch scheme: A mechanical contactor is connected in parallel on the AC or DC side of the power unit. When a fault occurs, the switch is closed to short-circuit the unit. However, the mechanical switch has a long operating time and generates an inrush current of 2 to 3 times the rated current at the moment of closing. At the same time, the voltage of the remaining units after bypassing needs to be redistributed, which causes voltage fluctuations. In addition, the mechanical switch has an electric arc and a limited lifespan, making it difficult to meet the requirements of frequent operation.

[0007] (2) Solid-state bypass switch scheme: solid-state switches such as thyristors or IGBTs are used to replace mechanical switches, and the response speed is improved to the microsecond level, but the voltage still changes suddenly when the switch is activated.

[0008] (3) New unit commissioning scheme: After the faulty unit is bypassed, a new unit (including redundant spare unit or replacement new unit) is commissioned. However, the DC capacitor voltage is usually zero when the new unit is commissioned, which requires complex voltage equalization control and modulation reconstruction.

[0009] In summary, the existing technologies generally have the following two common problems: (1) relying on the step switching of the bypass switch, which generates inrush current and voltage fluctuations; (2) the commissioning of new units usually requires power outage operation or has a long transient process, which affects the continuous operation of the system. Summary of the Invention

[0010] The technical problem to be solved by the present invention is to provide a method, device and medium for online switching control of power units of cascaded DC-DC converter equipment, which can realize online switching of power units of cascaded DC-DC converter equipment without impact or interruption.

[0011] The technical solution adopted by this invention to solve its technical problem is: to provide an online switching control method for power units of a cascaded DC-DC converter, comprising the following steps:

[0012] When a fault alarm is received, the regulation of the outer voltage loop of all power units is suspended, and the output value of the outer voltage loop of all power units is locked at the value before the fault occurred.

[0013] A voltage reduction command is issued to the fault power unit according to the preset voltage reduction trajectory. The DC bias of the modulation wave of the fault power unit is calculated based on the relationship between the target output voltage value of the fault power unit and the DC bias of the modulation wave. The DC bias of the modulation wave of the fault power unit is superimposed on the modulation wave of the fault power unit. At the same time, the effective value command of the feedforward active current of the fault power unit is generated according to the target output voltage value of the fault power unit.

[0014] A voltage compensation command is issued to the healthy power unit. The DC bias of the modulation wave of the healthy power unit is calculated based on the relationship between the target output voltage value of the healthy power unit and the DC bias of the modulation wave. The DC bias of the modulation wave of the healthy power unit is injected into the modulation wave of the healthy power unit. At the same time, the feedforward active current effective value command of the healthy power unit is generated based on the target output voltage value of the healthy power unit.

[0015] When the output voltage of the faulty power unit drops to zero, the drive pulses of all transistors in the faulty power unit are blocked, and the series circuit current flows through the anti-parallel diode of the faulty power unit.

[0016] The bypass switch connected in parallel with the faulty power unit is triggered to turn on, the current in the series circuit is transferred to the bypass branch, the solid-state switch connected in series on the DC side of the faulty power unit is disconnected, and the control of the voltage outer loop of all healthy power units is restored after the faulty power unit is completely isolated.

[0017] The target value of the output voltage of the fault power unit is calculated as follows: ,in, for Time fault power unit The target value of the output voltage. Fault power unit at the initial moment The output voltage, This represents the total voltage drop time.

[0018] The DC bias of the modulation wave of the fault power unit is calculated as follows: ,in, for Time fault power unit DC bias of the modulated wave. The amplitude of the triangular carrier wave. for Time fault power unit The output voltage, for Time fault power unit The target value of the output voltage.

[0019] The effective value command of the feedforward active current of the faulty power unit is calculated based on the power balance relationship between the AC and DC sides of the power unit. The specific calculation method is as follows: ,in, For faulty power units The effective value of the feedforward active current, for Time fault power unit The target value of the output voltage. For the DC current of the series circuit, For faulty power units Bus capacitor, This is the effective value of the secondary voltage of the transformer. , Fault power unit at the initial moment The output voltage, This represents the total voltage drop time.

[0020] The target value of the output voltage of the health power unit is calculated as follows: ,in, for Always-on health power unit The target value of the output voltage. Healthy power unit at the initial moment The output voltage, Healthy power units during soft cut-off of faulty power units Voltage compensation coefficient, Fault power unit at the initial moment The output voltage and Time fault power unit The difference in output voltage.

[0021] The DC bias of the modulation wave of the health power unit is calculated as follows: ,in, for Always-on health power unit DC bias of the modulated wave. The amplitude of the triangular carrier wave. for Always-on health power unit The output voltage, for Always-on health power unit The target value of the output voltage.

[0022] The effective value command of the feedforward active current of the healthy power unit is calculated based on the power balance relationship between the AC and DC sides of the power unit. The specific calculation method is as follows: ,in, For healthy power units The effective value of the feedforward active current, for Always-on health power unit The target value of the output voltage. For the DC current of the series circuit, For healthy power units Bus capacitor, This is the effective value of the secondary voltage of the transformer. , Fault power unit at the initial moment The output voltage, This represents the total voltage drop time. Healthy power units during soft cut-off of faulty power units Voltage compensation coefficient.

[0023] The technical solution adopted by this invention to solve its technical problem is: to provide an online switching control method for power units of a cascaded DC-DC converter, comprising the following steps:

[0024] When it is detected that the DC side voltage of the new power unit connected to the DC side series chain is close to the voltage across the bypass switch at the original series position, the solid-state switch connected in series on the DC side of the new power unit is closed, and the output value of the outer loop of the voltage of all power units is locked.

[0025] A voltage injection command is issued to the new power unit according to the preset voltage injection trajectory. The DC bias of the modulation wave of the new power unit is calculated based on the relationship between the target output voltage value of the new power unit and the DC bias of the modulation wave. The DC bias of the modulation wave of the new power unit is superimposed on the modulation wave of the new power unit. At the same time, the effective value command of the feedforward active current of the new power unit is generated according to the target output voltage value of the new power unit.

[0026] A voltage compensation command is issued to the healthy power unit. The DC bias of the modulation wave of the healthy power unit is calculated based on the relationship between the target output voltage value of the healthy power unit and the DC bias of the modulation wave. The DC bias of the modulation wave of the healthy power unit is injected into the modulation wave of the healthy power unit. At the same time, the feedforward active current effective value command of the healthy power unit is generated based on the target output voltage value of the healthy power unit.

[0027] When the current of the new power unit rises to the series circuit current, the original series position bypass switch is turned off, and the series circuit current is transferred to the branch where the new power unit is located.

[0028] When the output voltage of the new power unit rises to the final target voltage value, the closed-loop control of the outer voltage loop of all power units is restored.

[0029] The target value of the output voltage of the new power unit is calculated as follows: ,in, In order to be in New power unit at all times The target value of the output voltage. For the initial time of the new power unit The output voltage, For voltage injection time, For the new power unit The final target voltage value.

[0030] The DC bias of the modulation wave of the new power unit is calculated as follows: ,in, In order to be in New power unit at all times DC bias of the modulated wave. The amplitude of the triangular carrier wave. for New power unit at all times The output voltage, for New power unit at all times The target value of the output voltage.

[0031] The effective value command of the feedforward active current of the new power unit is calculated based on the power balance relationship between the AC and DC sides of the power unit. The specific calculation method is as follows: ,in, For the new power unit The effective value of the feedforward active current, for New power unit at all times The target value of the output voltage. For the DC current of the series circuit, For the new power unit Bus capacitor, This is the effective value of the secondary voltage of the transformer. , For the new power unit The final target voltage value, For voltage injection time.

[0032] The target value of the output voltage of the health power unit is calculated as follows: ,in, for Always-on health power unit The target value of the output voltage. Healthy power unit at the initial moment The output voltage, Healthy power units during soft-start of new power units Voltage compensation coefficient, for New power unit at all times The output voltage and the new power unit at the initial moment The difference in output voltage.

[0033] The DC bias of the modulation wave of the health power unit is calculated as follows: ,in, for Always-on health power unit DC bias of the modulated wave. The amplitude of the triangular carrier wave. for Always-on health power unit The output voltage, for Always-on health power unit The target value of the output voltage.

[0034] The effective value command of the feedforward active current of the healthy power unit is calculated based on the power balance relationship between the AC and DC sides of the power unit. The specific calculation method is as follows: ,in, For healthy power units The effective value of the feedforward active current, for Always-on health power unit The target value of the output voltage. For the DC current of the series circuit, For healthy power units Bus capacitor, This is the effective value of the secondary voltage of the transformer. , For the new power unit The final target voltage value, For voltage injection time, Healthy power units during soft-start of new power units Voltage compensation coefficient.

[0035] The technical solution adopted by the present invention to solve its technical problem is: to provide an electronic device, including a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes the computer program to implement the steps of the above-mentioned online switching control method for power units of cascaded DC-DC converter equipment.

[0036] The technical solution adopted by the present invention to solve its technical problem is: to provide a computer-readable storage medium on which a computer program is stored, wherein when the computer program is executed by a processor, the steps of the above-mentioned online switching control method for power units of cascaded DC-DC converter equipment are implemented.

[0037] By employing the above-mentioned technical solutions, this invention has the following advantages and positive effects compared with existing technologies: For scenarios involving the removal of faulty power units, this invention utilizes the linear correspondence between the modulated wave DC bias and the output voltage to achieve linear soft voltage reduction for the faulty unit. It synchronously generates feedforward active current commands to ensure AC / DC power matching, and combines this with synchronous voltage compensation from healthy power units to maintain a constant total DC output voltage. Finally, it transitions to bypass electrical isolation via diode freewheeling, avoiding inrush current and voltage fluctuations caused by step switching throughout the process, reducing device stress, and eliminating the need to interrupt system operation. For scenarios involving the introduction of new power units, it employs a zero-voltage closed solid-state switch combined with linear voltage injection, along with synchronous voltage reduction compensation from healthy power units, to achieve a natural and smooth transfer of current in the series circuit, eliminating surge impacts and transient disturbances, and enabling seamless integration of power units without power outages. This invention adopts an open-loop feedforward control logic, resulting in a simple architecture, fast response, no need for complex closed-loop parameter tuning, low engineering implementation difficulty, and effectively improving the power supply reliability and maintenance flexibility of cascaded DC-DC converter equipment. Attached Figure Description

[0038] Figure 1 This is a schematic diagram of a cascaded DC-DC converter in the first embodiment of the present invention;

[0039] Figure 2 This is a schematic diagram of the ANPC H-bridge topology in the first embodiment of the present invention;

[0040] Figure 3 This is a schematic diagram of control loop mode switching according to the first embodiment of the present invention;

[0041] Figure 4 This is a flowchart of the soft cut-off of the fault power unit in the first embodiment of the present invention;

[0042] Figure 5 This is a flowchart of the soft-connection of the new power unit in the first embodiment of the present invention. Detailed Implementation

[0043] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0044] The first embodiment of the present invention relates to an online switching (i.e., soft switching and soft disconnection) control method for power units of a cascaded DC-DC converter, which can be applied to, for example... Figure 1 The cascaded DC-DC converter shown has the following ANPC H-bridge topology: Figure 2As shown, this method fully utilizes the continuously adjustable voltage potential of the ANPC H-bridge topology. By injecting a linearly varying DC bias component into the modulation wave of the ANPC H-bridge power unit, it directly controls the DC output voltage to change smoothly along a preset trajectory. When a faulty power unit exits, the output voltage linearly drops to zero, and all IGBTs of the faulty power unit are locked out. Using anti-parallel diodes for freewheeling, zero-voltage soft exit is achieved. Healthy power units synchronously increase their output voltage to compensate for a constant total voltage, resulting in no impact or interruption. When a new power unit is put into operation, the solid-state switch is first closed at zero voltage, and then the voltage is linearly injected to the target value, achieving seamless online integration.

[0045] like Figure 3 As shown, in this embodiment, during normal steady-state operation, the DC bias component of the modulation wave of all power units is zero. The output voltage of each power unit is controlled by closed-loop control of voltage loop and current loop to adjust the modulation ratio and maintain the phase angle. The DC bias component is only used as a tool for transient voltage reconstruction. It is temporarily introduced during the soft disconnection of faulty power units or the soft connection of new power units to actively and linearly adjust the DC output voltage of each unit.

[0046] During the transient process, the system controller suspends the regulation of the outer voltage loop, locking its output at the value before the fault occurred. It then performs coordinated control through DC bias injection and feedforward current commands. DC bias injection involves directly superimposing a linearly varying DC component onto the modulation wave, controlling the DC output voltage in an open-loop manner. The feedforward current command dynamically calculates the active current command for each unit based on the power balance equation and sends it to the inner current loop, ensuring that the AC power matches the DC power. At the end of the transient process, the DC bias of the healthy power units naturally returns to zero according to a preset trajectory, the system controller resumes outer voltage loop control, and the system returns to the normal dual-closed-loop mode. The faulty power unit enters diode freewheeling or bypass mode after its voltage drops to zero and no longer participates in system control. During the transient process, the DC bias component changes linearly from zero; a positive DC bias component indicates a voltage increase, and a negative component indicates a voltage decrease.

[0047] Figure 4 The procedure for soft disconnection of faulty power units is given, which includes the following steps:

[0048] Step 1, Fault Detection and Reporting.

[0049] When the power unit controller detects a preset type of fault (such as IGBT open circuit, DC bus overvoltage / undervoltage, IGBT junction temperature too high, capacitor overheating, communication failure, etc.), it will respond within a certain time frame. Within 100µs, the fault type and fault parameters are reported to the system controller via fiber optic cable.

[0050] Step 2: Linear control of fault power unit voltage and generation of feedforward current command.

[0051] After receiving the fault type and fault parameters reported by the power unit, the system controller suspends the regulation of the voltage outer loop of all power units and locks the output value of the voltage outer loop of all power units at the value before the fault occurred.

[0052] Subsequently, following the set voltage reduction trajectory, the system controller issues a voltage reduction command to the faulty power unit. Based on this voltage reduction trajectory, the target output voltage value of the faulty power unit can be calculated in real time. The specific calculation method is as follows:

[0053] ;

[0054] in, for Time fault power unit The target value of the output voltage. Fault power unit at the initial moment The output voltage, This represents the total voltage drop time (e.g., 100ms).

[0055] Next, based on the linear relationship between the target output voltage of the faulty power unit and the DC bias of the modulation wave, the DC bias component of the modulation wave of the faulty power unit is calculated. The calculation method is as follows:

[0056] ;

[0057] in, The amplitude of the triangular carrier wave. for Time fault power unit The output voltage.

[0058] The DC bias component of the modulation wave of the faulty power unit was obtained. Then, it can be injected into the modulated wave, that is:

[0059] ;

[0060] in, for Time fault power unit Modulated wave, for Time fault power unit The amplitude of the modulated wave, The initial phase is used. The reconstructed modulated wave is compared with the triangular carrier wave to generate fault power units. The ANPCH bridge's switching transistors are driven by pulses, enabling the actual DC output voltage to accurately track the target value.

[0061] Meanwhile, this embodiment also generates a feedforward active current effective value command for the faulty power unit based on the target output voltage value of the faulty power unit. The generation process is based on the power balance relationship between the AC and DC sides of the power unit, specifically:

[0062] ;

[0063] in, For faulty power units The effective value of the feedforward active current, For the DC current of the series circuit, For faulty power units Bus capacitor, This is the effective value of the secondary voltage of the transformer. .

[0064] Step 3: Voltage synchronization compensation and feedforward current command generation for healthy power units.

[0065] During the voltage drop of the faulty power unit, in order to maintain a constant total DC output voltage, the system controller synchronously sends voltage compensation commands to all other healthy power units and dynamically adjusts the current commands of the healthy power units.

[0066] In this embodiment, the voltage compensation command calculates the target output voltage value of each healthy power unit in the following manner:

[0067] ;

[0068] in, for Always-on health power unit The target value of the output voltage. Healthy power unit at the initial moment The output voltage, Healthy power units during soft cut-off of faulty power units The voltage compensation coefficient is expressed as: , This represents the total number of power units. Fault power unit at the initial moment Output voltage and Time fault power unit Output voltage The difference.

[0069] Then, based on the linear relationship between the target output voltage of the health power unit and the DC bias of the modulation wave, the DC bias of the modulation wave of the health power unit is calculated. The calculation method is as follows:

[0070] ;

[0071] in, for Always-on health power unit The output voltage.

[0072] In this embodiment, the DC bias of the modulation wave of the health power unit is injected into the modulation wave of the health power unit, that is:

[0073] ;

[0074] in, for Always-on health power unit Modulated wave, for Always-on health power unit The amplitude of the modulated wave, The initial phase is used. The reconstructed modulated wave is compared with the triangular carrier wave to generate drive pulses for each switch transistor of the ANPCH bridge in each healthy power unit, thereby achieving synchronous boosting of the DC output voltage.

[0075] Meanwhile, this embodiment also generates a feedforward active current effective value command for the healthy power unit based on the target output voltage value of the healthy power unit. The generation process is based on the power balance relationship between the AC and DC sides of the power unit, specifically:

[0076] ;

[0077] in, For healthy power units The effective value of the feedforward active current, For healthy power units Bus capacitor, .

[0078] In the above process, the fault power unit The output voltage gradually decreases. When it drops to zero, proceed to step 4; otherwise, return to step 2.

[0079] Step 4, freewheeling of the faulty unit diode.

[0080] When the power unit fails When the output voltage drops to zero, the drive pulses of all IGBTs in the faulty power unit are blocked, and the series circuit current flows through the anti-parallel diode of the faulty power unit.

[0081] Step 5: Electrical isolation of the faulty unit

[0082] The bypass switch connected in parallel with the faulty power unit is triggered to turn on, and the series circuit current is transferred to the bypass branch. Then, the solid-state switch connected in series on the DC side of the faulty power unit is disconnected, completing the isolation of the faulty power unit. After that, the system controller restores the control function of the voltage outer loop of all healthy power units and enters a new normal operating mode.

[0083] It is easy to see that, for the scenario of disconnecting faulty power units, this invention achieves linear soft voltage drop of the faulty unit by relying on the linear correspondence between the DC bias of the modulation wave and the output voltage. It synchronously generates feedforward active current commands to ensure AC and DC power matching. Combined with the synchronous voltage compensation of the healthy power unit, it maintains a constant total DC output voltage. Finally, it transitions to bypass electrical isolation through diode freewheeling. The entire process avoids the inrush current and voltage fluctuations caused by step switching, reduces device stress, and does not require interruption of system operation.

[0084] Figure 5 The process for soft-connecting new power units is presented, specifically including the following steps:

[0085] Step 1: Electrically connect the new power unit.

[0086] The system controller confirms that the DC-side voltage of the new power unit is close to the voltage across the bypass switch in the original series connection. It then issues a solid-state switch closing command, closing the solid-state switch connected in series with the new power unit's DC side. At this point, the new power unit is not yet carrying current, and the current in the series loop still flows entirely through the original bypass switch. The system controller also locks the output values ​​of the outer loop voltage for all power units.

[0087] Step 2: Linear injection of the new unit's DC output voltage and generation of feedforward current commands.

[0088] In this step, the system controller sends voltage injection commands to the new power unit according to the preset voltage injection trajectory.

[0089] The target output voltage of the new power unit can be calculated in real time based on the preset voltage injection trajectory. The specific calculation method is as follows:

[0090] ;

[0091] in, In order to be in New power unit at all times The target value of the output voltage. For the initial time of the new power unit The output voltage, The voltage injection time (e.g., 100ms). For the new power unit The final target voltage value.

[0092] Next, the DC bias of the modulation wave of the new power unit is calculated based on the linear relationship between the target output voltage of the new power unit and the DC bias of the modulation wave. The calculation method is as follows:

[0093] ;

[0094] in, In order to be in New power unit at all times DC bias of the modulated wave. for New power unit at all times The output voltage.

[0095] After obtaining the DC bias of the modulation wave of the new power unit, it can be injected into the modulation wave, that is:

[0096] ;

[0097] in, for New power unit at all times Modulated wave, for New power unit at all times The amplitude of the modulated wave, The initial phase is used. The reconstructed modulated wave is compared with the triangular carrier wave to generate a new power unit. The ANPC H-bridge drives the switching transistors with pulses, enabling the actual DC output voltage to accurately track the target value.

[0098] Meanwhile, this embodiment also generates a feedforward active current effective value command for the new power unit based on the target output voltage value of the new power unit. The generation process is based on the power balance relationship between the AC and DC sides of the power unit, specifically:

[0099] ;

[0100] in, For the new power unit The effective value of the feedforward active current, For the new power unit Bus capacitor, .

[0101] Step 3: Voltage synchronization compensation and feedforward current command generation for healthy power units.

[0102] During the voltage injection process of the new power unit, in order to maintain a constant total DC output voltage, the system controller synchronously sends voltage compensation commands to the existing healthy power units.

[0103] In this embodiment, the voltage compensation command calculates the target output voltage value of each healthy power unit in the following manner:

[0104] ;

[0105] in, for Always-on health power unit The target value of the output voltage. Healthy power unit at the initial moment The output voltage, Healthy power units during soft-start of new power units The voltage compensation coefficient is expressed as: , for New power unit at all times Output voltage New power unit at the initial moment Output voltage The difference.

[0106] Then, based on the linear relationship between the target output voltage of the health power unit and the DC bias of the modulation wave, the DC bias of the modulation wave of the health power unit is calculated. The calculation method is as follows:

[0107] ;

[0108] in, for Always-on health power unit The DC bias of the modulated wave.

[0109] After obtaining the DC bias of the modulation wave of the healthy power unit, it can be injected into the modulation wave, that is:

[0110] ;

[0111] The reconstructed modulated wave is compared with the triangular carrier wave to generate drive pulses for each switch of the ANPC H-bridge in each healthy power unit, thereby achieving synchronous boosting of the DC output voltage.

[0112] Meanwhile, this embodiment also generates a feedforward active current effective value command for the healthy power unit based on the target output voltage value of the healthy power unit. The generation process is based on the power balance relationship between the AC and DC sides of the power unit, specifically:

[0113] ;

[0114] in, For healthy power units The effective value of the feedforward active current, .

[0115] When the current of the new power unit rises to the series circuit current (i.e., the current of the original bypass switch branch drops to 0), the system controller turns off the original bypass switch, and the series circuit current is completely transferred to the new power unit branch.

[0116] Step 4: Continue to boost the voltage to the target voltage.

[0117] When the output voltage of the new power unit rises to the final target voltage value If the condition is met, proceed to step 5; otherwise, return to step 2.

[0118] Step 5: Restore normal control.

[0119] In this step, the system controller restores the closed-loop control of the voltage outer loop of all power units and enters a new normal operating mode.

[0120] Therefore, this invention, for the scenario of new power unit deployment, adopts a zero-voltage closed solid-state switch combined with linear voltage injection, and with synchronous voltage reduction compensation of healthy power units, to achieve natural and smooth transfer of current in the series circuit, eliminate surge impact and transient disturbance, and complete the seamless connection of power units without power outage.

[0121] The second embodiment of the present invention relates to an electronic device, including a memory, a processor, and a computer program stored in the memory and executable on the processor. When the processor executes the computer program, it implements the steps of the online switching control method for power units of the cascaded DC-DC converter of the first embodiment.

[0122] The third embodiment of the present invention relates to a computer-readable storage medium having a computer program stored thereon, wherein the computer program, when executed by a processor, implements the steps of the online switching control method for power units of a cascaded DC-DC converter according to the first embodiment.

[0123] Those skilled in the art will understand that embodiments of this application can be provided as methods, systems, or computer program products. Therefore, this application can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, this application can take the form of a computer program product implemented on one or more computer-usable storage media (including, but not limited to, disk storage and optical storage) containing computer-usable program code.

[0124] This application is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of this application. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart... Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0125] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to operate in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction methods implemented in a process. Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0126] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0127] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for online switching control of power units in a cascaded DC-DC converter, characterized in that, Includes the following steps: When a fault alarm is received, the regulation of the outer voltage loop of all power units is suspended, and the output value of the outer voltage loop of all power units is locked at the value before the fault occurred. A voltage reduction command is issued to the fault power unit according to the preset voltage reduction trajectory. The DC bias of the modulation wave of the fault power unit is calculated based on the relationship between the target output voltage value of the fault power unit and the DC bias of the modulation wave. The DC bias of the modulation wave of the fault power unit is superimposed on the modulation wave of the fault power unit. At the same time, the effective value command of the feedforward active current of the fault power unit is generated according to the target output voltage value of the fault power unit. A voltage compensation command is issued to the healthy power unit. The DC bias of the modulation wave of the healthy power unit is calculated based on the relationship between the target output voltage value of the healthy power unit and the DC bias of the modulation wave. The DC bias of the modulation wave of the healthy power unit is injected into the modulation wave of the healthy power unit. At the same time, the feedforward active current effective value command of the healthy power unit is generated based on the target output voltage value of the healthy power unit. When the output voltage of the faulty power unit drops to zero, the drive pulses of all transistors in the faulty power unit are blocked, and the series circuit current flows through the anti-parallel diode of the faulty power unit. The bypass switch connected in parallel with the faulty power unit is triggered to turn on, the current in the series circuit is transferred to the bypass branch, the solid-state switch connected in series on the DC side of the faulty power unit is disconnected, and the control of the voltage outer loop of all healthy power units is restored after the faulty power unit is completely isolated.

2. The online switching control method for power units of cascaded DC-DC converter equipment according to claim 1, characterized in that, The target value of the output voltage of the fault power unit is calculated as follows: ,in, for Time fault power unit The target value of the output voltage. Fault power unit at the initial moment The output voltage, This represents the total voltage drop time.

3. The online switching control method for power units of cascaded DC-DC converter equipment according to claim 1, characterized in that, The DC bias of the modulation wave of the fault power unit is calculated as follows: ,in, for Time fault power unit DC bias of the modulated wave. The amplitude of the triangular carrier wave. for Time fault power unit The output voltage, for Time fault power unit The target output voltage value.

4. The online switching control method for power units of cascaded DC-DC converter equipment according to claim 1, characterized in that, The effective value command of the feedforward active current of the faulty power unit is calculated based on the power balance relationship between the AC and DC sides of the power unit. The specific calculation method is as follows: ,in, For faulty power units The effective value of the feedforward active current, for Time fault power unit The target value of the output voltage. For the DC current of the series circuit, For faulty power units Bus capacitor, This is the effective value of the secondary voltage of the transformer. , Fault power unit at the initial moment The output voltage, This represents the total voltage drop time.

5. The online switching control method for power units of cascaded DC-DC converter equipment according to claim 1, characterized in that, The target value of the output voltage of the health power unit is calculated as follows: ,in, for Always-on health power unit The target value of the output voltage. Healthy power unit at the initial moment The output voltage, Healthy power units during soft cut-off of faulty power units Voltage compensation coefficient, Fault power unit at the initial moment The output voltage and Time fault power unit The difference in output voltage.

6. The online switching control method for power units of cascaded DC-DC converter equipment according to claim 1, characterized in that, The DC bias of the modulation wave of the health power unit is calculated as follows: ,in, for Always-on health power unit DC bias of the modulated wave. The amplitude of the triangular carrier wave. for Always-on health power unit The output voltage, for Always-on health power unit The target value of the output voltage.

7. The online switching control method for power units of cascaded DC-DC converter equipment according to claim 1, characterized in that, The effective value command of the feedforward active current of the healthy power unit is calculated based on the power balance relationship between the AC and DC sides of the power unit. The specific calculation method is as follows: ,in, For healthy power units The effective value of the feedforward active current, for Always-on health power unit The target value of the output voltage. For the DC current of the series circuit, For healthy power units Bus capacitor, This is the effective value of the secondary voltage of the transformer. , Fault power unit at the initial moment The output voltage, This represents the total voltage drop time. Healthy power units during soft cut-off of faulty power units Voltage compensation coefficient.

8. A method for online switching control of power units in a cascaded DC-DC converter, characterized in that, Includes the following steps: When it is detected that the DC side voltage of the new power unit connected to the DC side series chain is close to the voltage across the bypass switch at the original series position, the solid-state switch connected in series on the DC side of the new power unit is closed, and the output value of the outer loop of the voltage of all power units is locked. A voltage injection command is issued to the new power unit according to the preset voltage injection trajectory. The DC bias of the modulation wave of the new power unit is calculated based on the relationship between the target output voltage value of the new power unit and the DC bias of the modulation wave. The DC bias of the modulation wave of the new power unit is superimposed on the modulation wave of the new power unit. At the same time, the effective value command of the feedforward active current of the new power unit is generated according to the target output voltage value of the new power unit. A voltage compensation command is issued to the healthy power unit. The DC bias of the modulation wave of the healthy power unit is calculated based on the relationship between the target output voltage value of the healthy power unit and the DC bias of the modulation wave. The DC bias of the modulation wave of the healthy power unit is injected into the modulation wave of the healthy power unit. At the same time, the feedforward active current effective value command of the healthy power unit is generated based on the target output voltage value of the healthy power unit. When the current of the new power unit rises to the series circuit current, the original series position bypass switch is turned off, and the series circuit current is transferred to the branch where the new power unit is located. When the output voltage of the new power unit rises to the final target voltage value, the closed-loop control of the outer voltage loop of all power units is restored.

9. The online switching control method for power units of cascaded DC-DC converter equipment according to claim 8, characterized in that, The target value of the output voltage of the new power unit is calculated as follows: ,in, In order to be in New power unit at all times The target value of the output voltage. For the initial time of the new power unit The output voltage, For voltage injection time, For the new power unit The final target voltage value.

10. The online switching control method for power units of a cascaded DC-DC converter according to claim 8, characterized in that, The DC bias of the modulation wave of the new power unit is calculated as follows: ,in, In order to be in New power unit at all times DC bias of the modulated wave. The amplitude of the triangular carrier wave. for New power unit at all times The output voltage, for New power unit at all times The target value of the output voltage.

11. The online switching control method for power units of a cascaded DC-DC converter according to claim 8, characterized in that, The effective value command of the feedforward active current of the new power unit is calculated based on the power balance relationship between the AC and DC sides of the power unit. The specific calculation method is as follows: ,in, For the new power unit The effective value of the feedforward active current, for New power unit at all times The target value of the output voltage. For the DC current of the series circuit, For the new power unit Bus capacitor, This is the effective value of the secondary voltage of the transformer. , For the new power unit The final target voltage value, For voltage injection time.

12. The online switching control method for power units of a cascaded DC-DC converter according to claim 8, characterized in that, The target value of the output voltage of the health power unit is calculated as follows: ,in, for Always-on health power unit The target value of the output voltage. Healthy power unit at the initial moment The output voltage, Healthy power units during soft-start of new power units Voltage compensation coefficient, for New power unit at all times The output voltage and the new power unit at the initial moment The difference in output voltage.

13. The online switching control method for power units of a cascaded DC-DC converter according to claim 8, characterized in that, The DC bias of the modulation wave of the health power unit is calculated as follows: ,in, for Always-on health power unit DC bias of the modulated wave. The amplitude of the triangular carrier wave. for Always-on health power unit The output voltage, for Always-on health power unit The target value of the output voltage.

14. The online switching control method for power units of a cascaded DC-DC converter according to claim 8, characterized in that, The effective value command of the feedforward active current of the healthy power unit is calculated based on the power balance relationship between the AC and DC sides of the power unit. The specific calculation method is as follows: ,in, For healthy power units The effective value of the feedforward active current, for Always-on health power unit The target value of the output voltage. For the DC current of the series circuit, For healthy power units Bus capacitor, This is the effective value of the secondary voltage of the transformer. , For the new power unit The final target voltage value, For voltage injection time, Healthy power units during soft-start of new power units Voltage compensation coefficient.

15. An electronic device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that, When the processor executes the computer program, it implements the steps of the online switching control method for power units of the cascaded DC-DC converter as described in any one of claims 1-14.

16. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the computer program is executed by the processor, it implements the steps of the online switching control method for power units of the cascaded DC-DC converter as described in any one of claims 1-14.

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