An auxiliary converter control method, system and storage medium

Abstract

This invention belongs to the field of auxiliary power supply system control technology for rail vehicles, specifically relating to an auxiliary converter control method, system, and storage medium. The method includes: acquiring the three-phase output voltage of the auxiliary converter, the three-phase current on the load side, and the three-phase current on the inverter side; generating the output voltage phase angle based on the output active power; performing coordinate transformation based on the phase angle to generate voltage and current components in a synchronous rotating coordinate system; calculating reactive power based on the voltage and current components and generating the output voltage amplitude; generating a modulation wave signal based on the voltage, current, and output voltage amplitude; performing NPC modulation on the modulation wave signal to obtain four basic pulses per phase; performing logic synthesis on the basic pulses to generate six drive pulses and outputting them to a three-level NPC inverter. This invention generates six drive pulses using pure digital logic on standard NPC hardware, achieving a double-zero state effect for the ANPC, balancing internal and external transistor losses, and improving power density.

Description

Technical Field

[0001] This invention relates to the field of auxiliary power supply system control technology for rail vehicles, specifically to an auxiliary converter control method, system, and storage medium. Background Technology

[0002] Currently, to meet the growing power demands of large-formation, intelligent rail vehicles, auxiliary inverters are developing towards higher power density, higher reliability, and higher power quality. The mainstream technology path is to use a "Type I three-level" topology for power frequency auxiliary inverters, combined with a "parallel connection without interconnections" power supply architecture. Diode-clamped three-level topologies and their corresponding NPC modulation strategies are commonly employed, reducing voltage stress on power devices and improving output waveform quality by increasing the number of output levels. Simultaneously, multiple auxiliary inverters are often connected in parallel without interconnections based on traditional power droop control to achieve automatic power distribution.

[0003] However, existing technologies still have the following problems: First, conventional NPC modulation strategies result in significantly higher conduction and switching losses for the inner power switches in a three-level bridge arm compared to the outer switches. This imbalance in losses forces the heat dissipation design to be based on the highest temperature rise of the inner switches, limiting the overall current output capability and restricting further increases in power density. Second, traditional power droop control is a rigid, inertia-free static adjustment strategy. When the load changes abruptly, the system frequency fluctuates rapidly and significantly, and the output voltage amplitude after droop adjustment is lower than the rated value, especially under heavy loads. Third, the three-phase filter capacitors in LC filters are prone to local corona discharge at their "self-healing" point under alternating electric fields, leading to irreversible and slow capacitance decay. Existing systems typically lack online capacitance monitoring capabilities, making it impossible to predict capacitor aging and posing a potential risk of system failure due to capacitor failure.

[0004] Therefore, there is an urgent need for an auxiliary converter control method to systematically improve the performance, quality, and reliability of the auxiliary converter. Summary of the Invention

[0005] This invention addresses at least some of the aforementioned technical problems, providing an auxiliary converter control method, system, and storage medium. By implementing the ANPC's dual-zero state effect on a three-level NPC hardware, it balances internal and external transistor losses and improves power density.

[0006] A first aspect of the present disclosure provides an auxiliary converter control method, wherein the auxiliary converter includes a three-level NPC inverter, a transformer, an LC filter, and an output contactor connected in sequence, the LC filter being connected to an AC load via the output contactor, characterized in that the method includes: Acquire the three-phase output voltage of the auxiliary converter Three-phase current on the load side and the three-phase current on the inverter side ; Based on the three-phase output voltage and inverter side three-phase current Calculate the active power output of the auxiliary converter According to the active power Generate output voltage phase angle ; According to the output voltage phase angle For the three-phase output voltage The three-phase current on the load side Perform coordinate transformation to generate voltage components in a synchronously rotating coordinate system. , and current components , ; According to the voltage components in the synchronous rotating coordinate system , and current components , Calculate reactive power According to the reactive power Generate output voltage amplitude ; According to the voltage components in the synchronous rotating coordinate system , Current components , and the output voltage amplitude Generate modulated wave signal , ; According to the modulation wave signal , NPC modulation is performed to obtain four basic pulses per phase. , , , For the basic pulse , , , At least two of the inputs are subjected to different delays and then logically synthesized to generate six drive pulses, which are then output to the three-level NPC inverter.

[0007] The technical solution provided in this application brings at least the following beneficial effects: by generating six drive pulses through pure digital logic on standard NPC hardware, the losses of internal and external transistors are balanced, and the power density is improved.

[0008] In other embodiments of this application, the basic pulse is described. , , , At least two of the inputs are subjected to different delays and then logically synthesized to generate six drive pulses, which are then output to the three-level NPC inverter, including: For the basic pulse , The rising edge is subject to the first delay time. For the basic pulse , Apply a second delay time to the rising edge ; The delayed basic pulse , Perform an XOR operation to obtain the first intermediate signal, and then use the delayed basic pulse. , The second intermediate signal is obtained by performing an XOR operation. The first intermediate signal and the second intermediate signal are ORed to obtain the synthesized signal; A first delay time is applied to the rising edge of the synthesized signal. Then respectively with the basic pulse , Perform an OR operation to obtain two new pulses. , The basic pulse , , , and the newly added pulse , The drive pulse is output to the three-level NPC inverter.

[0009] The technical solution provided in this application has at least the following beneficial effects: by using purely digital means of differentiated delay and XOR / OR logic operations, six drive pulses with ANPC characteristics are generated on standard NPC hardware. The logic is clear, easy to implement with DSP, and does not require additional hardware costs.

[0010] In other embodiments of this application, the first delay time The dead time of the three-level NPC inverter is given.

[0011] The technical solution provided in this application has at least the following beneficial effects: using the inherent dead time of the inverter as the first delay time. No additional delay parameters need to be configured, simplifying the engineering implementation and ensuring that the minimum pulse width constraint is met between the new pulse and the original pulse.

[0012] In other embodiments of this application, the first delay time Less than the second delay time .

[0013] The technical solution provided in this application brings at least the following beneficial effects: Through the first delay time... Less than the second delay time Timing constraints ensure the correct edge timing relationship of each group of pulses in the logic synthesis, avoid race conditions in the synthesized signal, and guarantee the timing safety of the driving pulse.

[0014] In other embodiments of this application, the step of basing the active power... Generate output voltage phase angle ,include: According to the active power The calculation system outputs angular frequency commands. , in, Output angular frequency command to the system. The system's rated output angular frequency, The active power-frequency droop factor is... It is a first-order inertial element. The inertial time constant, For the Laplace operator; For the output angular frequency command Integrating, the phase angle of the output voltage is obtained. .

[0015] The technical solution provided in this application brings at least the following beneficial effects: by introducing a first-order inertial element to simulate the inertia and damping characteristics of a synchronous generator, the frequency changes smoothly when the load changes abruptly; the droop control, in conjunction with the inertial element, takes into account both steady-state power distribution and dynamic frequency stability.

[0016] In other embodiments of this application, the voltage components in the synchronously rotating coordinate system are... , and current components , Calculate reactive power According to the reactive power Generate output voltage amplitude ,include: According to the voltage components in the synchronous rotating coordinate system , and current components , Calculate reactive power ; According to the reactive power The system's rated output voltage amplitude is adjusted by reactive power droop to obtain the voltage amplitude after droop adjustment. The deviation between the droop-adjusted voltage amplitude and the output voltage setpoint is subjected to PI regulation, and the result of the PI regulation is added to the droop-adjusted voltage amplitude to obtain the output voltage amplitude. .

[0017] The technical solution provided in this application brings at least the following benefits: the reactive power is automatically and evenly distributed among parallel units through reactive power droop; the secondary voltage regulation stage compensates for voltage drops caused by reactive power disturbances through PI regulation, ensuring that the output voltage amplitude is stable at the rated level.

[0018] In other embodiments of this application, the voltage components in the synchronously rotating coordinate system are... , Current components , and the output voltage amplitude Generate modulated wave signal , ,include: According to the inductor current component in the synchronous rotating coordinate system , The impedance voltage drop compensation amount is calculated based on the inductance parameters of the LC filter. , ; According to the current components in the synchronous rotating coordinate system , Calculate the virtual impedance compensation amount using the preset virtual impedance parameters. ; The voltage component in the synchronous rotating coordinate system , As a voltage feedforward quantity, the current component in the synchronous rotating coordinate system , As the load current feedforward and the virtual impedance compensation amount A dual closed-loop control structure with an outer voltage loop and an inner current loop is adopted to generate a modulated wave signal in the synchronously rotating dq coordinate system. , .

[0019] The technical solution provided in this application brings at least the following beneficial effects: impedance voltage drop compensation ensures the consistency of output voltage when the load changes; virtual impedance reshaping of output characteristics suppresses parallel circulating current; voltage and current feedforward improves dynamic response speed; and the three synergistic effects achieve high-precision and strong anti-disturbance control.

[0020] In other embodiments of this application, the method further includes: The three-phase current on the inverter side is adjusted according to the transformer's turns ratio. The secondary current of the transformer is obtained by performing amplitude conversion and phase correction. During the period when the auxiliary converter establishes its output voltage and the output contactor of the auxiliary converter is open, the three-phase output voltage is... The fundamental voltage and fundamental current are extracted by performing Fourier decomposition on the secondary current of the transformer. The capacitance value of the three-phase filter capacitor is calculated based on the ratio of the fundamental voltage to the fundamental current. The capacitance value is compared with a preset threshold, and a warning signal is issued when the capacitance value is lower than the preset threshold.

[0021] The technical solution provided in this application brings at least the following benefits: by using the online monitoring of the filter capacitor value during the start-up no-load window, there is no need to stop the machine or add external equipment, turning regular maintenance into condition prediction, reducing maintenance costs and downtime risks.

[0022] A second aspect of the present disclosure provides a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the method described in the first aspect of the present disclosure.

[0023] A third aspect of the present disclosure provides an auxiliary converter control system for implementing the auxiliary converter control method described in the first aspect of the present disclosure, the system comprising: The acquisition unit is configured to acquire the three-phase output voltage of the auxiliary converter. Three-phase current on the load side and the three-phase current on the inverter side ; The power frequency unit, connected to the output terminal of the acquisition unit, is configured to measure the three-phase output voltage. and inverter side three-phase current Calculate the active power output of the auxiliary converter According to the active power Generate output voltage phase angle ; The conversion unit, connected to the output terminal of the acquisition unit and the output terminal of the power frequency unit, is configured to adjust the output voltage phase angle according to the phase angle of the output voltage. For the three-phase output voltage The three-phase current on the load side Perform coordinate transformation to generate voltage components in a synchronously rotating coordinate system. , and current components , ; The electrical unit, connected to the output of the conversion unit, is configured to operate according to the voltage components in the synchronous rotating coordinate system. , and current components , Calculate reactive power According to the reactive power Generate output voltage amplitude ; The control unit, connected to the output of the conversion unit and the output of the electrical unit, is configured to operate based on the voltage components in the synchronous rotating coordinate system. , Current components , and the output voltage amplitude Generate modulated wave signal , ; The modulation unit, connected to the output of the control unit, is configured to modulate the signal according to the modulation wave signal. , NPC modulation is performed to obtain four basic pulses per phase. , , , For the basic pulse , , , At least two of the inputs are subjected to different delays and then logically synthesized to generate six drive pulses, which are then output to the three-level NPC inverter.

[0024] Compared with the prior art, the present invention has the following beneficial effects: (1) By applying different delays to the basic pulse generated by NPC modulation and performing logic synthesis, six drive pulses are generated on the standard NPC hardware using pure software means, balancing the losses of internal and external tubes, and improving the power density without increasing the hardware cost.

[0025] (2) By introducing a first-order inertial element in the droop control to smooth the frequency dynamics, and combining it with the PI compensation of the secondary voltage regulation element to suppress voltage drop, the dynamic stability and power supply quality of the system are improved.

[0026] (3) By performing Fourier decomposition on the voltage and reconstructed secondary current during the no-load voltage building stage and calculating the capacitance value, the filter capacitor can be monitored online and its aging warning can be provided, thereby improving the maintainability of the system.

[0027] The above description is merely an overview of the technical solution disclosed herein. In order to better understand the technical means of this disclosure and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of this disclosure more apparent and understandable, specific embodiments of this disclosure are described below. Attached Figure Description

[0028] To more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0029] Figure 1 This is a schematic flowchart of the auxiliary converter control method according to an embodiment of this application; Figure 2 This is a topology diagram of the auxiliary converter structure according to an embodiment of this application; Figure 3 This is a block diagram of the output voltage phase angle generation control in an embodiment of this application; Figure 4 This is a block diagram of coordinate transformation and secondary current reconstruction control in an embodiment of this application; Figure 5 This is a block diagram of the output voltage amplitude generation control in an embodiment of this application; Figure 6 This is a loop control block diagram of an embodiment of this application; Figure 7 This is a block diagram of the modulation pulse synthesis logic according to an embodiment of this application; Figure 8 This is a schematic diagram of the four basic pulse waveforms in an embodiment of this application; Figure 9 This is a schematic diagram of the six-channel drive pulse waveforms in an embodiment of this application; Figure 10 This is a schematic diagram of the auxiliary converter control system structure according to an embodiment of this application. Detailed Implementation

[0030] To make the technical problems, technical solutions, and beneficial effects to be solved by this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and are not intended to limit the scope of this application.

[0031] The prefixes such as "first" and "second" used in this application embodiment are merely for distinguishing different descriptive objects and do not limit the position, order, priority, quantity, or content of the described objects. The use of ordinal numbers and other prefixes used to distinguish descriptive objects in this application embodiment does not constitute a limitation on the described objects. The description of the described objects is given in the claims or the context of the embodiments, and should not constitute unnecessary restrictions due to the use of such prefixes. Furthermore, in the description of this embodiment, unless otherwise stated, "multiple" means two or more.

[0032] The technical solutions of the embodiments of this application will be described below with reference to the accompanying drawings. In the description of the embodiments of this application, unless otherwise stated, " / " means "or," for example, A / B can mean A or B; the term "and / or" in this document is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone.

[0033] In the embodiments provided in this application, it should be understood that the disclosed systems and methods can be implemented in other ways. For example, the device embodiments described above are merely illustrative. For instance, the division of units is only a logical functional division, and in actual implementation, there may be other division methods. For example, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed. Furthermore, the coupling or direct coupling or communication connection shown or discussed may be through some interfaces; the indirect coupling or communication connection between devices or units may be electrical, mechanical, or other forms.

[0034] In this application, the terms "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which is included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0035] Existing auxiliary current limiter control schemes still have significant shortcomings in meeting the increasingly stringent comprehensive performance requirements of auxiliary power supply systems for rail vehicles. While traditional droop control can achieve power sharing, it is essentially a static mapping relationship, lacking a constraint mechanism on the rate of frequency change during load surges, leading to a degradation in dynamic frequency quality. Furthermore, the inherent characteristics of voltage droop mean that the output voltage will inevitably deviate from its rated value as reactive load increases; simply relying on droop control cannot fundamentally eliminate steady-state deviation. At the modulation level, although the NPC topology is mature and reliable, its fixed commutation path causes certain switching transistors to endure excessively high losses over long periods, becoming a bottleneck restricting power density improvement. At the maintenance level, the aging of filter capacitors is a gradual physical process, and existing systems cannot obtain information about their performance degradation before a failure occurs, resulting in reactive maintenance. Therefore, a systematic improvement to existing schemes is urgently needed to enhance the dynamic performance, power density, and maintainability of auxiliary converters.

[0036] To address the above problems, this application provides an auxiliary converter control method, system, and storage medium. The specific implementation of the technical solution of this application will be described in detail below with reference to the accompanying drawings.

[0037] The first aspect of the embodiments of this disclosure provides an auxiliary converter control method, such as... Figure 2 As shown, the auxiliary converter includes a three-level NPC inverter, a transformer, an LC filter, and an output contactor connected in sequence. The LC filter is connected to the AC load via the output contactor, as shown below. Figure 1 As shown, the method includes: S01: Acquire the three-phase output voltage of the auxiliary converter Three-phase current on the load side and the three-phase current on the inverter side .

[0038] Three-phase output voltage The three-phase voltage at the output of the LC filter (i.e., the primary side of the transformer) and the three-phase current on the load side are... The three-phase current flowing from the secondary side of the transformer to the load, and the three-phase current on the inverter side. This refers to the three-phase current at the output of a three-level NPC inverter.

[0039] S02: Based on the three-phase output voltage and inverter side three-phase current Calculate the active power output of the auxiliary converter According to active power Generate output voltage phase angle .

[0040] Active power It is a key electrical quantity characterizing the output power of the auxiliary converter, and in this invention, it is used for power droop control—when load changes cause active power fluctuations, it controls the active power output. The frequency of the output voltage is adjusted to achieve automatic equal distribution of active power among parallel units. In the embodiments of this disclosure, the active power... The instantaneous power calculation method using a stationary coordinate system is employed; specifically, active power... .

[0041] like Figure 3 As shown, in a specific illustrative embodiment, based on active power Generate output voltage phase angle ,include: S21: Based on active power The calculation system outputs angular frequency commands. , in, Output angular frequency command to the system. The system's rated output angular frequency, The active power-frequency droop factor is... It is a first-order inertial element. The inertial time constant, For the Laplace operator.

[0042] System rated output angular frequency This refers to the angular frequency value corresponding to the rated operating frequency (i.e., the power frequency of 50Hz) of the auxiliary converter. It is the reference value for the system's output angular frequency command.

[0043] Active power - frequency droop factor Reflects active power The magnitude of the frequency adjustment caused by the change is determined based on the rated power of the auxiliary converter and the allowable frequency deviation range—the larger the rated power or the smaller the allowable frequency deviation, the better. The smaller the value, the more accurate the power distribution among the parallel units.

[0044] System outputs angular frequency command It is the frequency setpoint used to generate the output voltage phase after droop control and inertial filtering.

[0045] First-order inertial element This is used to smooth the frequency command output of the droop control, so that the frequency changes gradually in an exponential manner rather than a step jump when the load changes abruptly, simulating the rotor inertial characteristics of a synchronous generator.

[0046] In this embodiment, the system's rated output angular frequency This corresponds to a power frequency of 50Hz, which is the system's rated output angular frequency. Active power-frequency droop factor The active power-frequency droop coefficient is determined based on the rated power and allowable frequency deviation range of the auxiliary converter. For example, if the rated power is 100kW and the allowable frequency deviation is ±0.5Hz, then the active power-frequency droop coefficient is... .

[0047] First-order inertial element In the time domain, it corresponds to a first-order differential equation. When a sudden change in load leads to a decrease in active power During a step change, the system outputs an angular frequency command. It will not jump immediately, but will change by a time constant. The exponential law smoothly transitions to the target value. Inertial time constant. The value is determined based on the system's requirements for dynamic frequency response, with a typical range of 0.1s to 0.5s. The larger the value, the smoother the frequency change, but the slower the response speed; The smaller the value, the faster the response speed, but the more drastic the frequency fluctuation.

[0048] S22: Output angular frequency command Integrate to obtain the output voltage phase angle. .

[0049] Specifically, the output voltage phase angle , where τ is the integration variable.

[0050] This technical solution introduces a first-order inertial element into the active power-frequency droop control to simulate the inertia and damping characteristics of a synchronous generator. This smooths out frequency changes without spikes during sudden load changes, suppressing frequency oscillations. Simultaneously, it retains the steady-state power sharing function of droop control, ensuring that each unit automatically distributes active power according to its capacity ratio when multiple generators are operating in parallel. The series connection of the first-order inertial element and droop control achieves a balance between smoothing the frequency during dynamic processes and maintaining accurate power sharing in steady state, overcoming the shortcomings of rigid frequency fluctuations in traditional droop control.

[0051] S03: Based on the output voltage phase angle For three-phase output voltage Three-phase current on the load side Inverter-side three-phase current Perform coordinate transformation to generate voltage components in a synchronously rotating coordinate system. , Current components , and inductor current component .

[0052] Specifically, such as Figure 4 As shown, the coordinate transformation uses the Park transformation to transform the three-phase output voltage in the stationary three-phase coordinate system. Three-phase current on the load side Transformed to a synchronously rotating dq coordinate system, the transformed voltage components , and current components , All are DC flow rates, which facilitates subsequent adjustment with a PI controller without steady-state error.

[0053] At the same time, the inverter-side three-phase current in the static three-phase coordinate system will be... Transform to the synchronously rotating dq coordinate system to obtain the inductor current component. It is used for feedback control of the subsequent inner current loop.

[0054] S04: Based on the voltage components in the synchronous rotating coordinate system , and current components , Calculate reactive power According to reactive power Generate output voltage amplitude .

[0055] like Figure 5 As shown, in a specific illustrative embodiment, based on the voltage components in a synchronously rotating coordinate system , and current components , Calculate reactive power According to reactive power Generate output voltage amplitude ,include: S41: Based on the voltage components in the synchronous rotating coordinate system , and current components , Calculate reactive power ; Specifically, based on instantaneous power theory, reactive power Calculate using the following formula in a synchronously rotating coordinate system:

[0056] S42: Based on reactive power The system's rated output voltage amplitude is adjusted by reactive power droop to obtain the voltage amplitude after droop adjustment. Reactive power droop adjustment is based on reactive power. For the rated output voltage amplitude of the system Adjustments are needed:

[0057] in, This is the rated output voltage amplitude of the system. The reactive power-amplitude droop factor is... This represents the voltage amplitude after reduction. Reactive power - amplitude droop factor The value is determined based on the rated reactive power and the allowable voltage deviation range. For example, if the rated reactive power is 50 kVar and the allowable voltage deviation is ±5V, Under light load ( When it is smaller, near ; under heavy load ( When it is relatively large, Below .

[0058] S43: Perform PI regulation on the deviation between the voltage amplitude after droop adjustment and the output voltage setpoint, and add the result of the PI regulation to the voltage amplitude after droop adjustment to obtain the output voltage amplitude. .

[0059] The secondary voltage regulation stage adjusts the voltage amplitude after droop adjustment. With the output voltage setpoint (usually equal to) The deviation between ) is adjusted using PI, that is:

[0060] in, This refers to the proportional coefficient of the voltage PI regulator. This represents the integral coefficient of the voltage PI regulator. The output of the PI regulator. Used to compensate for voltage drops caused by reactive load disturbances.

[0061] Final output voltage amplitude This is the sum of the voltage amplitude after droop adjustment and the result of PI adjustment, i.e.

[0062] In steady state, the integral action of the PI regulator affects the final output voltage amplitude. Approaching That is, the final output voltage amplitude It is regulated and maintained at the rated level, eliminating the voltage drop problem inherent in droop control.

[0063] This technical solution utilizes reactive power-amplitude droop control to enable each parallel unit to automatically adjust its output voltage amplitude based on its own reactive power output, achieving automatic and proportional distribution of reactive power according to capacity. This solves the problems of reactive circulating current and uneven power distribution in multi-unit parallel operation. Simultaneously, the secondary voltage regulation stage superimposes the deviation between the droop-adjusted voltage amplitude and the output voltage setpoint onto the voltage command after PI regulation. Under steady-state conditions, the PI integral action restores the output voltage amplitude to the rated value without error, fundamentally overcoming the inherent problem of traditional droop control where the output voltage is always lower than the rated value. The series combination of reactive power droop control and secondary voltage regulation allows the system to simultaneously achieve autonomous reactive power distribution and error-free output voltage amplitude adjustment without the need for interconnection communication lines, balancing the power distribution accuracy of parallel operation with the output voltage accuracy of independent operation.

[0064] S05: Based on the voltage components in the synchronous rotating coordinate system , Current components , Inductor current component and output voltage amplitude Generate modulated wave signal , .

[0065] like Figure 6 Therefore, the modulated wave signal , The generation takes into account impedance voltage drop compensation, virtual impedance compensation, and voltage and current feedforward.

[0066] In a specific illustrative embodiment, based on the voltage components in the synchronously rotating coordinate system , Current components , and output voltage amplitude Generate modulated wave signal , ,include: S51: Based on the inductor current component in the synchronously rotating coordinate system , Calculate impedance voltage drop compensation for LC filter inductance parameters. , , , , in, This represents the DC resistance of the inductor in the LC filter. This refers to the bulk inductance of the inductor in the LC filter. S52: Based on the current components in the synchronous rotating coordinate system , Calculate the virtual impedance compensation amount using the preset virtual impedance parameters. , , , in, The resistive component of the preset virtual impedance. Preset virtual impedance inductance components; S53: Transform the voltage components in the synchronous rotating coordinate system , As a voltage feedforward quantity, the current component in the synchronous rotating coordinate system , As load current feedforward and virtual impedance compensation quantity A dual closed-loop control structure with an outer voltage loop and an inner current loop is adopted to generate a modulated wave signal in a synchronously rotating dq coordinate system. , .

[0067] Specifically, the purpose of the outer voltage loop is to maintain stable output voltage and provide a reference command for the inner current loop (set as follows). and As shown below, the outer voltage loop uses a PI controller to adjust the voltage error and incorporates a load current feedforward. , Cross-decoupling with capacitor current , : d-axis voltage control:

[0068] q-axis voltage control:

[0069] The inner current loop tracks the reference command given by the outer voltage loop. The output is adjusted by the PI controller and then superimposed with a voltage component. , Cross-decoupling of inductor voltage , This generates the final modulated wave signal. , .

[0070] d-axis current control:

[0071] q-axis current control:

[0072] This application's technical solution compensates for impedance voltage drop, correcting the fundamental voltage drop across the filter inductor in real time under different load conditions. This ensures the output voltage accurately tracks the given value under various load conditions, solving the problem of severe output voltage drop under heavy loads in traditional control. By reshaping the amplitude-frequency characteristics of the inverter's equivalent output impedance using virtual impedance, it exhibits resistive-inductive characteristics, effectively suppressing circulating currents in multi-machine parallel systems and improving power sharing accuracy among parallel units. Through the synergistic introduction of voltage and current feedforward, voltage feedforward provides a fast compensation path during load changes, while current feedforward directly cancels load current disturbances, significantly shortening voltage transient recovery time and enhancing the system's immunity to impulsive loads. These three technologies are integrated into the same control loop, complementing and enhancing steady-state accuracy, parallel stability, and dynamic response, achieving a comprehensive control effect with high precision and strong anti-disturbance capabilities.

[0073] S06: Based on the modulation wave signal , NPC modulation is performed to obtain four basic pulses per phase. , , , For the basic pulse , , , At least two of the channels are subjected to different delays and then logically synthesized to generate six drive pulses, which are then output to a three-level NPC inverter.

[0074] like Figure 7 , Figure 8 As shown, the modulated wave signal output in step S05 , NPC modulation is performed, during which the three-phase modulated wave is compared with the triangular carrier wave to generate four basic pulses per phase. , , , These correspond to the four power switches (outer switches) of each phase in the NPC topology. , and inner tube , ).

[0075] like Figure 9 As shown, after applying different delays to at least two of the four basic pulses, the four pulses are combined into six drive pulses through logical operations. The six drive pulses drive six power switching transistors respectively (two additional pulses are added to the original four switching transistors in the NPC topology to achieve dual-zero state switching).

[0076] In a specific illustrative embodiment, the basic pulse , , , At least two of the inputs are subjected to different delays and then logically synthesized to generate six drive pulses, which are then output to a three-level NPC inverter, including: S61: For the basic pulse , The rising edge is subject to the first delay time. For the basic pulse , Apply a second delay time to the rising edge .

[0077] First, the rising edges of the four basic pulses are delayed. Specifically, the basic pulses... , The rising edge is subject to the first delay time. get , For the basic pulse , Apply a second delay time to the rising edge get , The purpose of rising edge delay is to stagger the timing of each pulse edge, thus avoiding race conditions during logic synthesis.

[0078] In a specific illustrative embodiment, the first delay time The dead time of the three-level NPC inverter is given.

[0079] Specifically, the dead time of a three-level inverter is a protection time set to prevent two switching transistors on the same bridge arm from being turned on simultaneously. In this embodiment, the value of the dead time is determined based on the difference between the turn-off delay and turn-on delay of the power switching transistor (IGBT or SiCMOSFET), and is typically in the range of 1μs to 5μs, depending on the model of the power switching transistor and the parameters of the drive circuit.

[0080] The technical solution of this application uses the inherent dead time of the inverter as the first delay time, which has the following engineering advantages: First, no additional delay parameters need to be configured, reducing the parameter settings of the control software; Second, the dead time has been determined by the hardware characteristics and system design, ensuring that the delay time matches the switching characteristics of the power switching transistor; Third, it ensures that the pulse width of the newly added pulse is not less than the dead time, avoiding the generation of excessively narrow pulses that could cause the switching transistor to mis-turn on or be damaged.

[0081] In a specific illustrative embodiment, the first delay time Less than the second delay time .

[0082] Preferably, the second delay time It is the first delay time twice as much as, that is This value relationship ensures the pulse after the delay. , , , The following timing constraints must be met:

[0083] Where t represents the rising edge time of each pulse. The value relationship is only a preferred example. In specific implementations, it can be appropriately adjusted according to the actual modulation strategy and switching frequency, as long as it satisfies the following conditions. The correct timing relationship can be guaranteed by meeting the conditions.

[0084] The technical solution of this application ensures the correct edge timing relationship of each group of pulses in the logic synthesis through this constraint, avoids race conditions in the synthesized signal, and guarantees the timing safety of the driving pulse.

[0085] S62: Delayed base pulse , Perform an XOR operation to obtain the first intermediate signal, and then use the delayed base pulse. , The second intermediate signal is obtained by performing an XOR operation.

[0086] The physical meaning of the XOR operation is: when two input signals are in different states, the output is high level; when they are in the same state, the output is low level.

[0087] S63: Perform an OR operation between the first intermediate signal and the second intermediate signal to obtain the synthesized signal.

[0088] The physical meaning of the OR operation is: when any one of the inputs is high, the output is high. The rising edge of this synthesized signal reflects the logical changes of the basic pulses under a specific combination.

[0089] S64: Apply a first delay time to the rising edge of the synthesized signal. Then, respectively with the basic pulse , Perform an OR operation to obtain two new pulses. , , the basic pulse , , , and new pulse , As a drive pulse output to a three-level NPC inverter.

[0090] Apply a first delay time to the rising edge of the synthesized signal. This is used to prevent short circuits caused by the simultaneous transition of a new pulse and the original pulse.

[0091] This application's technical solution targets the standard NPC hardware platform. By applying differentiated delays to the four basic pulses per phase generated by NPC modulation and performing XOR / OR logic synthesis, six drive pulses are generated using pure digital logic. This achieves the loss balancing effect of the ANPC's dual-zero state—distributing the losses originally concentrated in the inner transistors more evenly to each switching transistor, reducing the peak temperature rise of the inner transistors, and without increasing any hardware cost. It allows for a larger output current while maintaining unchanged heat dissipation conditions, thereby effectively improving the overall power density.

[0092] In other embodiments of this application, it also includes: S81: Based on the transformer turns ratio, adjust the three-phase current on the inverter side. Amplitude conversion and phase correction are performed to obtain the secondary current of the transformer; Specifically, after the auxiliary converter starts, it first establishes the output voltage. Once the output voltage stabilizes, the output contactor is closed to connect the load. During the no-load voltage build-up phase when the output voltage is established and the output contactor is open, the load side is disconnected from the converter output terminal. The transformer secondary current is the current flowing through the filter capacitor, which does not contain the load current component, providing an ideal measurement window for accurate calculation of the capacitor value.

[0093] Inverter side three-phase current This is the primary current of the transformer, which includes the transformer's magnetizing current component. To obtain the accurate filter capacitor current, it is necessary to consider the transformer turns ratio. The amplitude of the transformer primary current is calculated. Furthermore, since the transformer in this embodiment is a Dyn11 connection type transformer, there is a 30° phase difference between its primary and secondary sides. Phase correction is also performed based on this 30° phase difference. For example... Figure 4 As shown, let the transformer turns ratio be... Phase correction is introduced into the Park transform angle. The corrected secondary current , This reflects the actual current of the flow filter capacitor.

[0094] S82: During the period when the auxiliary converter establishes its output voltage and the auxiliary converter's output contactor is open, the three-phase output voltage... The fundamental voltage and fundamental current are extracted by performing Fourier decomposition on the secondary current of the transformer. S83: Calculate the capacitance value of the three-phase filter capacitor based on the ratio of fundamental voltage to fundamental current; S84: Compare the capacitance value with a preset threshold, and issue a warning signal when the capacitance value is lower than the preset threshold.

[0095] Specifically, the system issues a warning signal when the capacitance of any phase falls below a preset threshold. The preset threshold is set as a percentage of the capacitor's rated capacitance. For example, a first threshold can be set to 80% of the rated capacitance; when the capacitance falls below this value, a mild warning is issued to alert maintenance personnel. A second threshold can be set to 70% of the rated capacitance; when the capacitance falls below this value, a severe alarm is issued, recommending immediate replacement. The thresholds can be flexibly set according to the actual application scenario and the capacitor's lifespan characteristics.

[0096] A second aspect of this disclosure provides a storage medium, which may include, but is not limited to, non-transitory storage media such as read-only memory (ROM), random access memory (RAM), erasable programmable read-only memory (EPROM), flash memory, hard disk, solid-state drive (SSD), and optical disk. The storage medium may be installed in the control unit of an auxiliary converter, for example, in the external memory of a DSP or ARM processor, or packaged as a separate chip within the same module as the processor.

[0097] The computer program stored on the storage medium includes a series of program instructions that, when executed by the processor, implement all the steps of the control method described in the first aspect of the embodiments of this disclosure. After the auxiliary converter is powered on, the processor reads the program from the storage medium and loads it into memory for execution, sequentially executing steps such as data acquisition, phase generation, coordinate transformation, amplitude generation, modulation wave generation, pulse generation, and optional capacitance estimation according to the control cycle.

[0098] Because the computer program is stored in a non-transitory storage medium, it will not be lost even after the auxiliary converter is powered off, and can be directly loaded and executed upon the next power-on. In practical engineering, the program in the storage medium can be upgraded through reserved program programming interfaces (such as JTAG, UART, USB, etc.), facilitating iterative updates of control strategies.

[0099] A third aspect of the present disclosure provides an auxiliary converter control system for implementing the auxiliary converter control method described in the first aspect of the present disclosure, such as... Figure 10 As shown, the system includes a data acquisition unit, a power frequency unit, a conversion unit, an electrical unit, a control unit, and a modulation unit.

[0100] The acquisition unit is used to acquire the three-phase output voltage of the auxiliary converter. Three-phase current on the load side and the three-phase current on the inverter side .

[0101] The power frequency unit connects to the output of the acquisition unit and is used to measure the three-phase output voltage. and inverter side three-phase current Calculate the active power output of the auxiliary converter According to active power Generate output voltage phase angle .

[0102] The conversion unit connects the output terminals of the acquisition unit and the power frequency unit, and is used to determine the phase angle of the output voltage. For three-phase output voltage Three-phase current on the load side Perform coordinate transformation to generate voltage components in a synchronously rotating coordinate system. , and current components , .

[0103] The electrical unit connects to the output of the conversion unit and is used to determine the voltage components in the synchronous rotating coordinate system. , and current components , Calculate reactive power According to reactive power Generate output voltage amplitude .

[0104] The control unit connects to the output of the conversion unit and the output of the electrical unit, and is used to determine the voltage components in the synchronous rotating coordinate system. , Current components , and output voltage amplitude Generate modulated wave signal , .

[0105] The modulation unit is connected to the output of the control unit and is used to modulate the waveform signal. , NPC modulation is performed to obtain four basic pulses per phase. , , , For the basic pulse , , , At least two of the channels are subjected to different delays and then logically synthesized to generate six drive pulses, which are then output to a three-level NPC inverter.

[0106] Those skilled in the art will recognize that the modules, units, and method steps of the various examples described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementation should not be considered beyond the scope of this application.

[0107] Although embodiments of this application have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting this application. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of this application.

Claims

1. A method for controlling an auxiliary converter, wherein the auxiliary converter comprises a three-level NPC inverter, a transformer, an LC filter, and an output contactor connected in sequence, the LC filter being connected to an AC load via the output contactor, characterized in that, The method includes: Acquire the three-phase output voltage of the auxiliary converter Three-phase current on the load side and the three-phase current on the inverter side ; Based on the three-phase output voltage and inverter side three-phase current Calculate the active power output of the auxiliary converter According to the active power Generate output voltage phase angle ; According to the output voltage phase angle For the three-phase output voltage The three-phase current on the load side Perform coordinate transformation to generate voltage components in a synchronously rotating coordinate system. , and current components , ; According to the voltage components in the synchronous rotating coordinate system , and current components , Calculate reactive power According to the reactive power Generate output voltage amplitude ; According to the voltage components in the synchronous rotating coordinate system , Current components , and the output voltage amplitude Generate modulated wave signal , ; According to the modulation wave signal , NPC modulation is performed to obtain four basic pulses per phase. , , , , For the basic pulse , , , At least two of the inputs are subjected to different delays and then logically synthesized to generate six drive pulses, which are then output to the three-level NPC inverter.

2. The auxiliary converter control method according to claim 1, characterized in that, The basic pulse , , , At least two of the inputs are subjected to different delays and then logically synthesized to generate six drive pulses, which are then output to the three-level NPC inverter, including: For the basic pulse , The rising edge is subject to the first delay time. For the basic pulse , Apply a second delay time to the rising edge The delayed basic pulse , Perform an XOR operation to obtain the first intermediate signal, and then use the delayed basic pulse. , An XOR operation is performed to obtain a second intermediate signal; the first intermediate signal and the second intermediate signal are then ORed to obtain a synthesized signal; a first delay time is applied to the rising edge of the synthesized signal. Then respectively with the basic pulse , Perform an OR operation to obtain two new pulses. , The basic pulse , , , and the newly added pulse , The drive pulse is output to the three-level NPC inverter.

3. The auxiliary converter control method according to claim 2, characterized in that, First delay time The dead time of the three-level NPC inverter is given.

4. The auxiliary converter control method according to claim 2, characterized in that, First delay time Less than the second delay time .

5. The auxiliary converter control method according to claim 1, characterized in that, The active power Generate output voltage phase angle ,include: According to the active power The calculation system outputs angular frequency commands. , in, Output angular frequency command to the system. The system's rated output angular frequency, The active power-frequency droop factor is... It is a first-order inertial element. The inertial time constant, For the Laplace operator; For the output angular frequency command Integrating, the phase angle of the output voltage is obtained. .

6. The auxiliary converter control method according to claim 1, characterized in that, The voltage component in the synchronous rotating coordinate system , and current components , Calculate reactive power According to the reactive power Generate output voltage amplitude ,include: According to the voltage components in the synchronous rotating coordinate system , and current components , Calculate reactive power ; According to the reactive power The system's rated output voltage amplitude is adjusted by reactive power droop to obtain the voltage amplitude after droop adjustment. The deviation between the droop-adjusted voltage amplitude and the output voltage setpoint is subjected to PI regulation, and the result of the PI regulation is added to the droop-adjusted voltage amplitude to obtain the output voltage amplitude. .

7. The auxiliary converter control method according to claim 1, characterized in that, The voltage component in the synchronous rotating coordinate system , Current components , and the output voltage amplitude Generate modulated wave signal , ,include: According to the inductor current component in the synchronous rotating coordinate system , The impedance voltage drop compensation amount is calculated based on the inductance parameters of the LC filter. , ; According to the current components in the synchronous rotating coordinate system , Calculate the virtual impedance compensation amount using the preset virtual impedance parameters. ; The voltage component in the synchronous rotating coordinate system , As a voltage feedforward quantity, the current component in the synchronous rotating coordinate system , As the load current feedforward and the virtual impedance compensation amount A dual closed-loop control structure with an outer voltage loop and an inner current loop is adopted to generate a modulated wave signal in the synchronously rotating dq coordinate system. , .

8. The auxiliary converter control method according to claim 1, characterized in that, Also includes: The three-phase current on the inverter side is adjusted according to the transformer's turns ratio. The secondary current of the transformer is obtained by performing amplitude conversion and phase correction. During the period when the auxiliary converter establishes its output voltage and the output contactor of the auxiliary converter is open, the three-phase output voltage is... The fundamental voltage and fundamental current are extracted by performing Fourier decomposition on the secondary current of the transformer. The capacitance value of the three-phase filter capacitor is calculated based on the ratio of the fundamental voltage to the fundamental current. The capacitance value is compared with a preset threshold, and a warning signal is issued when the capacitance value is lower than the preset threshold.

9. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the program is executed by the processor, it implements the method as described in any one of claims 1 to 8.

10. An auxiliary converter control system, characterized in that, The system for implementing the auxiliary converter control method according to any one of claims 1 to 8, the system comprising: The acquisition unit is configured to acquire the three-phase output voltage of the auxiliary converter. Three-phase current on the load side and the three-phase current on the inverter side ; The power frequency unit, connected to the output terminal of the acquisition unit, is configured to measure the three-phase output voltage. and inverter side three-phase current Calculate the active power output of the auxiliary converter According to the active power Generate output voltage phase angle ; The conversion unit, connected to the output terminal of the acquisition unit and the output terminal of the power frequency unit, is configured to adjust the output voltage phase angle according to the phase angle of the output voltage. For the three-phase output voltage The three-phase current on the load side Perform coordinate transformation to generate voltage components in a synchronously rotating coordinate system. , and current components , ; The electrical unit, connected to the output of the conversion unit, is configured to operate according to the voltage components in the synchronous rotating coordinate system. , and current components , Calculate reactive power According to the reactive power Generate output voltage amplitude ; The control unit, connected to the output of the conversion unit and the output of the electrical unit, is configured to operate based on the voltage components in the synchronous rotating coordinate system. , Current components , and the output voltage amplitude Generate modulated wave signal , ; The modulation unit, connected to the output of the control unit, is configured to modulate the signal according to the modulation wave signal. , NPC modulation is performed to obtain four basic pulses per phase. , , , For the basic pulse , , , At least two of the inputs are subjected to different delays and then logically synthesized to generate six drive pulses, which are then output to the three-level NPC inverter.

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