Converter control method and system, and storage medium

Abstract

NOT VISIBLE DUE TO STATUS OF PATENT

Description

Converter control method, system and storage medium

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to Chinese patent application No. 202410244167.6, filed on February 29, 2024, entitled “Control method, system and storage medium for converter”, the entire contents of which are incorporated herein by reference. Technical Field

[0003] The present application relates to the field of renewable energy power generation, and in particular to a control method, system and storage medium for a converter. Background Art

[0004] With the promotion of renewable energy, the capacity demand for renewable energy energy conversion equipment is increasing. As an important component of energy conversion equipment, the converter also has a demand for capacity expansion. The converter can adopt a modular design and achieve converter capacity expansion by connecting converter modules in parallel. In order to improve the control accuracy of the converter module, each converter module in the converter can be controlled separately. The control unit used to execute the control algorithm assumes the control algorithm of multiple converter modules and sends down the modulation waves of multiple converter modules. The current of multiple converter modules is prone to current mutation at the commutation point, resulting in uneven current of multiple converter modules. It may also trigger converter faults, reducing the safety of the converter. Summary of the Invention

[0005] In order to solve the above technical problems, embodiments of the present application provide a control method, system, and storage medium for a converter, which can improve the current balance of converter modules connected in parallel in the converter.

[0006] In a first aspect, an embodiment of the present application provides a control method for a converter, wherein the converter includes N converter modules connected in parallel, where N is an integer greater than 1, and the converter module has an AC end. The method includes: a converter control device obtains a three-phase modulation wave voltage based on the three-phase current, a d-axis current given value, and a q-axis current given value of the AC end of the converter module at a time corresponding to a most recently passed inflection point of a predetermined carrier; the converter control device obtains a three-phase modulation wave incremental voltage of each converter module based on the three-phase current of the AC end of the converter module at a time corresponding to a most recently passed inflection point of a predetermined carrier; when the three-phase modulation wave voltage and the voltage at the inflection point of the predetermined carrier meet a balanced adjustment condition, the converter control device generates a pulse control signal corresponding to each converter module based on the three-phase modulation wave voltage and the three-phase modulation wave incremental voltage of each converter module, and controls the corresponding converter module using the pulse control signal.

[0007] In a second aspect, an embodiment of the present application provides a control system for a converter, comprising: a converter, comprising N converter modules connected in parallel, N being an integer greater than 1, and the converter module having an AC end; a converter control device, configured to obtain a three-phase modulated wave voltage based on the three-phase current, a d-axis current given value, and a q-axis current given value from the AC end of the converter module at the time corresponding to the inflection point of the most recently passed predetermined carrier; and, obtaining a three-phase modulated wave incremental voltage of each converter module based on the three-phase current of the AC end of the converter module at the time corresponding to the inflection point of the closest predetermined carrier; and, when the three-phase modulated wave voltage and the voltage at the inflection point of the predetermined carrier meet a balanced adjustment condition, generating a pulse control signal corresponding to each converter module based on the three-phase modulated wave voltage and the three-phase modulated wave incremental voltage of each converter module, and utilizing the pulse control signal to control the corresponding converter module.

[0008] In a third aspect, an embodiment of the present application provides a computer-readable storage medium having computer program instructions stored thereon. When the computer program instructions are executed by a processor, the control method of the converter according to the first aspect is implemented.

[0009] Embodiments of the present application provide a control method, system, and storage medium for a converter. A converter control device can obtain a three-phase modulated wave voltage based on the three-phase current at the AC end of each converter module at the time corresponding to the inflection point of the most recently passed predetermined carrier, and obtain a three-phase modulated wave incremental voltage of each AC module based on the three-phase current at the AC end of each converter module at the time corresponding to the inflection point of the predetermined carrier. When the three-phase modulated wave voltage and the voltage at the inflection point of the predetermined carrier meet a balanced adjustment condition, a pulse control signal can be generated based on the three-phase modulated wave incremental voltage and the three-phase modulated wave voltage. The three-phase modulated wave incremental voltage can compensate for the current difference between the parallel converter modules, and the three-phase modulated wave voltage and the voltage at the inflection point of the predetermined carrier meet the balanced adjustment condition. The three-phase modulated wave voltage after processing with the three-phase modulated wave incremental voltage does not exceed the voltage range of the predetermined carrier. The current difference of the parallel converter modules controlled by the generated pulse control signal is reduced, and the current of the converter modules at the commutation point does not experience a sudden change, thereby improving the current balance of the converter modules and thereby improving the safety of the converter. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following is a brief introduction to the drawings required for use in the embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0011] FIG1 is a schematic diagram of an example of a converter provided in an embodiment of the present application;

[0012] FIG2 is a flow chart of a method for controlling a converter according to an embodiment of the present application;

[0013] FIG3 is a schematic diagram of an example of current of a converter module that is not controlled by the converter control method provided in an embodiment of the present application;

[0014] FIG4 is a schematic diagram of an example of current of a converter module controlled by the converter control method provided in an embodiment of the present application;

[0015] FIG5 is a schematic diagram of another example of the current of a converter module that is not controlled by the converter control method provided in the embodiment of the present application;

[0016] FIG6 is a schematic diagram of another example of current of a converter module controlled by the converter control method provided in an embodiment of the present application;

[0017] FIG7 is a flow chart of a method for controlling a converter according to another embodiment of the present application;

[0018] FIG8 is a logic diagram of an example of obtaining the average value of the d-axis current provided by an embodiment of the present application;

[0019] FIG9 is a logic diagram of an example of obtaining the average value of the q-axis current provided by an embodiment of the present application;

[0020] FIG10 is a logic diagram of an example of obtaining a three-phase modulated wave voltage according to an embodiment of the present application;

[0021] FIG11 is a logic diagram of an example of obtaining a current difference according to an embodiment of the present application;

[0022] FIG12 is a schematic diagram of an example of control logic for a converter provided in an embodiment of the present application;

[0023] FIG13 is a schematic structural diagram of a control system of a converter provided in one embodiment of the present application. DETAILED DESCRIPTION

[0024] The features and exemplary embodiments of various aspects of the present application will be described in detail below. In order to make the purpose, technical solutions and advantages of the present application clearer, the present application will be further described in detail below in conjunction with the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only intended to explain the present application, rather than to limit the present application. For those skilled in the art, the present application can be implemented without the need for some of these specific details. The following description of the embodiments is merely to provide a better understanding of the present application by illustrating the examples of the present application.

[0025] With the promotion of renewable energy, the capacity demand for renewable energy energy conversion equipment is increasing. As an important component of energy conversion equipment, the converter also has a demand for capacity expansion. The converter can adopt a modular design and achieve converter capacity expansion by connecting converter modules in parallel. In order to improve the control accuracy of the converter module, each converter module in the converter can be controlled separately. The control unit used to execute the control algorithm assumes the control algorithm of multiple converter modules and sends down the modulation waves of multiple converter modules. The current of multiple converter modules is prone to current mutation at the commutation point, resulting in uneven current of multiple converter modules. It may also trigger converter faults, reducing the safety of the converter.

[0026] In the embodiments of the present application, the converter may include but is not limited to a photovoltaic converter matched with a photovoltaic device, a wind power converter matched with a wind turbine generator set, etc. The type of converter is not limited here. For example, the converter may include but is not limited to a doubly fed converter, a full power converter, etc. The converter includes N converter modules connected in parallel, where N is an integer greater than 1. The converter module has an AC end, and the AC end can input or output three-phase current. In some examples, the converter module may include a machine-side rectifier module or a grid-side inverter module. The machine-side rectifier module is a converter module electrically connected to the power generation structure of the energy conversion device, and can convert the AC power generated by the power generation structure in the energy conversion device into DC power. Specifically, the AC end of the machine-side rectifier module can be electrically connected to the power generation structure of the energy conversion device. The grid-side inverter module is a conversion module electrically connected to the grid side. The grid-side inverter module is electrically connected to the machine-side rectifier module and can convert the DC power output by the machine-side rectifier module into AC power for transmission to the grid. Specifically, the AC end of the grid-side inverter module can be electrically connected to the grid side.

[0027] For example, FIG1 is a schematic diagram of an example of a converter provided in an embodiment of the present application. As shown in FIG1 , the converter 11 may include a machine-side rectifier module 111 and a grid-side inverter module 112. The machine-side rectifier module 111 may be electrically connected to the grid-side inverter module 112 via a DC bus. The converter shown in FIG1 includes two parallel machine-side rectifier modules 111. Each machine-side rectifier module 111 is electrically connected to the power generation structure 12 via a filter reactor L1 and a filter reactor L2. The grid-side inverter module 112 is connected to the power grid 14 via a filter L3 and a transformer 13. The machine-side rectifier module 111 and the grid-side inverter module 112 may share a conversion control device, that is, the machine-side rectifier module 111 and the grid-side inverter module 112 are controlled by the same conversion control device.

[0028] The converter modules in a converter can be connected to filter reactors. For example, the generator-side rectifier module in the converter can be electrically connected to the power generation structure via the filter reactor, and the grid-side inverter module in the converter can be electrically connected to the grid via the filter reactor. Ideally, in multiple converter modules connected in parallel, parameters such as the filter reactors connected to different converter modules and the reactance of the circuits in which the converter modules reside should be identical. This allows a single control algorithm and modulation wave to ensure consistent current across the multiple converter modules connected in parallel. However, due to manufacturing process errors, the filter reactors connected to different converter modules in parallel can have different inductances, the reactance of the circuits in which different converter modules reside can vary, and the control circuits of different converter modules can have different control delays. These differences can lead to current differences between the converter modules connected in parallel. Specifically, the currents of the parallel AC modules are uneven, resulting in sudden current changes. These sudden current changes can easily trigger the current safety margins of the converter modules, thereby affecting the service life of the power devices in the converter modules and even triggering faults that cause the energy conversion equipment to shut down. For example, a sudden change in current at the commutation point is likely to cause the converter module to shut down, leading to a fault.

[0029] The control method, system and storage medium of the converter provided in the embodiment of the present application can be applied to the scenario of N machine-side rectifier modules connected in parallel in the converter, and can also be applied to the scenario of N grid-side inverter modules connected in parallel in the converter, and are not limited here. If the converter includes N machine-side rectifier modules connected in parallel and N grid-side inverter modules connected in parallel, the control method of the converter provided in the embodiment of the present application can be used for the N machine-side rectifier modules connected in parallel, and the control method of the converter provided in the embodiment of the present application can be used for the N grid-side inverter modules connected in parallel. In the embodiment of the present application, the converter modules connected in parallel share a three-phase modulation wave voltage, and each converter module has its own corresponding three-phase modulation wave incremental voltage. When the balanced adjustment condition is met, the three-phase modulation wave voltage is reduced by the three-phase modulation wave incremental voltage, and then a pulse control signal corresponding to each converter module is generated. The three-phase modulated wave incremental voltage is generated for each AC module. The pulse control signal generated by the three-phase modulated wave voltage and the three-phase modulated wave incremental voltage can reduce the difference between the currents of the parallel AC modules, improve the current balance of the parallel AC modules, avoid voltage mutations in the AC modules, and improve the safety of the converter.

[0030] The control method of the converter provided in the embodiment of the present application can be executed by a converter control device. The converter control device may include a universal converter controller, which can be used to collect data, run control algorithms, perform fault protection, control the converter module, and upload status information of the converter controller. The universal converter controller can control power devices such as insulated gate bipolar transistors (IGBTs) in the converter module by outputting pulse control signals, such as pulse width modulation (PWM) signals, to control the converter module. The universal converter controller may include a control unit and a computing unit. The control unit may be implemented as, but not limited to, a microcontroller unit (MCU), and the computing unit may be implemented as, but not limited to, a field programmable gate array (FPGA). The converter control device may also include a power interface unit and a drive control unit. The power interface unit and the drive control unit may be implemented as, but not limited to, an integrated circuit board. The power interface unit converts the pulse control signals output by the universal converter controller into drive signals suitable for the converter module. It also converts converter module status signals, such as fault signals and thermal signals, into signals suitable for the universal converter controller. The power interface unit also isolates the converter module from the universal converter controller, improving the converter control device's anti-interference capability and reliability. The drive control unit converts and processes the drive signals output by the power interface unit. The drive signals output by the drive control unit are used to drive the power devices in the converter module. The drive control unit also monitors short circuits in the converter module's power devices and uploads temperature information from the converter module's power devices to the universal converter controller.

[0031] The control method, system and storage medium of the converter provided in this application are described below respectively.

[0032] In a first aspect, the present application provides a method for controlling a converter, which can be executed by a converter control device to control the N converter modules connected in parallel in the above-described embodiment. FIG2 is a flow chart of a method for controlling a converter according to an embodiment of the present application. As shown in FIG2 , the method for controlling a converter can include steps S201 to S203.

[0033] In step S201, the current conversion control device obtains a three-phase modulated wave voltage based on the three-phase current, the d-axis current given value, and the q-axis current given value at the AC end of the current conversion module at the time corresponding to the inflection point of the most recently passed predetermined carrier.

[0034] The predetermined carrier is a pre-set carrier with periodicity. The predetermined carrier and the modulated wave work together to obtain a pulse control signal. The maximum value of the modulated wave working together is less than or equal to the maximum value of the predetermined carrier, and the minimum value of the modulated wave working together is greater than or equal to the minimum value of the predetermined carrier. In some examples, the maximum value of the modulated wave can be equal to the maximum value of the predetermined carrier, and the minimum value of the modulated wave can be equal to the minimum value of the predetermined carrier. The predetermined carrier can be set according to the scenario, requirements, experience, etc. For example, the predetermined carrier may include a triangular wave. The inflection point of the predetermined carrier may include a peak point and a valley point. The peak point of the predetermined carrier is the maximum value of the predetermined carrier, and the valley point of the predetermined carrier is the minimum value of the predetermined carrier. The three-phase current at the AC end of the converter module at the time corresponding to the inflection point of the predetermined carrier most recently passed can be the three-phase voltage at the AC end of the AC module at the time corresponding to the inflection point in the predetermined carrier closest to the current moment. For example, if the predetermined carrier wave is a triangular wave, and the current time is at the rising edge of the predetermined carrier wave, the most recently passed inflection point of the predetermined carrier wave is the valley point, and the three-phase current used is the three-phase current of the AC end of the AC module at the time of the valley point of the predetermined carrier wave; if the current time is at the falling edge of the predetermined carrier wave, the most recently passed inflection point of the predetermined carrier wave is the peak point, and the three-phase current used is the three-phase current of the AC end of the AC module at the time of the peak point of the predetermined carrier wave. The current conversion control device can latch the three-phase current of the current conversion module at the peak point and valley point of the predetermined carrier wave, so as to obtain the three-phase modulated wave voltage by using the latched three-phase current of the current conversion module, the d-axis current set value, and the q-axis current set value. In the embodiment of the present application, it is necessary to obtain the three-phase current of the AC end of each current conversion module in the N parallel current conversion modules at the time corresponding to the most recently passed inflection point of the predetermined carrier wave. For example, if the converter includes two converter modules connected in parallel, the two converter modules are converter module 1 and converter module 2, then the three-phase current i of the AC end of converter module 1 at the time corresponding to the inflection point of the most recently passed predetermined carrier is obtained. 1a,1b,1c , obtain the three-phase current i of the AC end of the conversion module 2 at the time corresponding to the inflection point of the most recently passed predetermined carrier 2a,2b,2c .

[0035] The d-axis current given value is the d-axis reference current given in the two-phase rotating coordinate system, and the q-axis current given value is the q-axis reference current given in the two-phase rotating coordinate system. The specific settings can be based on scenarios, requirements, experience, etc., and are not limited here.

[0036] The three-phase current at the AC end of each converter module at the time corresponding to the inflection point of the most recently passed predetermined carrier can be converted into the d-axis current and q-axis current in a two-phase rotating coordinate system. Then, the three-phase modulated wave voltage is obtained by processing the d-axis current, q-axis current, d-axis current set value, and q-axis current set value. The three-phase modulated wave voltage can represent the modulated wave.

[0037] In step S202 , the converter control device obtains a three-phase modulation wave incremental voltage of each converter module based on the three-phase current at the AC end of the converter module at a time corresponding to the inflection point of the most recently passed predetermined carrier.

[0038] The current conversion control device can latch the three-phase current of the current conversion module at the peak point and valley point of the predetermined carrier to obtain the three-phase modulated wave incremental voltage.

[0039] The three-phase modulation wave incremental voltage of each of the N parallel-connected converter modules can be obtained based on the average value of the three-phase currents at the AC terminals of the N parallel-connected converter modules at the time corresponding to the most recently passed inflection point of the predetermined carrier, and the three-phase currents at the AC terminals of each of the N converter modules at the time corresponding to the most recently passed inflection point of the predetermined carrier, through proportional integral (PI) processing, etc. The three-phase modulation wave incremental voltage of the converter module can compensate for the current difference between the converter module and other converter modules connected in parallel with the converter module.

[0040] In step S203, when the three-phase modulation wave voltage and the voltage of the inflection point of the predetermined carrier meet the balanced adjustment conditions, the converter control device generates a pulse control signal corresponding to each converter module based on the three-phase modulation wave voltage and the three-phase modulation wave incremental voltage of each converter module, and uses the pulse control signal to control the corresponding converter module.

[0041] The three-phase modulated wave voltage and the three-phase modulated wave incremental voltage cannot work together unconditionally. If the three-phase modulated wave voltage and the three-phase modulated wave incremental voltage work together unconditionally, the three-phase modulated wave voltage after processing with the three-phase modulated wave incremental voltage is likely to exceed the predetermined carrier voltage range at the peak and valley points of the three-phase modulated wave (i.e., the commutation points). This can cause some converter modules to have pulse signals while others do not, leading to current abrupt changes and current imbalance in multiple converter modules connected in parallel. Therefore, the three-phase modulated wave voltage after processing with the three-phase modulated wave incremental voltage cannot exceed the predetermined carrier voltage range. The balancing adjustment condition includes the condition that the three-phase modulated wave voltage and the three-phase modulated wave incremental voltage can work together. If the voltage at the inflection point of the three-phase modulated wave voltage and the predetermined carrier satisfies the balancing adjustment condition, the three-phase modulated wave voltage after processing with the three-phase modulated wave incremental voltage will not exceed the predetermined carrier voltage range, thereby ensuring that the current of the converter module at the commutation point does not abruptly change, thereby ensuring the safety of the converter module. The three-phase modulated wave voltage of each converter module is processed using the incremental three-phase modulated wave voltage to obtain a new three-phase modulated wave voltage corresponding to each converter module. Based on this new three-phase modulated wave voltage, a pulse control signal corresponding to each converter module is generated, thereby controlling the corresponding converter module. The current differences between converter modules controlled by the pulse control signal are reduced, and the current balance of the N converter modules connected in parallel is improved.

[0042] When the voltage at the inflection point of the three-phase modulated wave voltage and the predetermined carrier does not meet the balanced adjustment condition, a pulse control signal corresponding to the converter module is generated based on the three-phase modulated wave voltage. In this case, the three-phase modulated wave incremental voltage does not participate in the generation of the pulse control signal to avoid the three-phase modulated wave voltage after being processed by the three-phase modulated wave incremental voltage exceeding the voltage range of the predetermined carrier, and to avoid a sudden change in the current of the converter module at the commutation point.

[0043] In an embodiment of the present application, the converter control device can obtain a three-phase modulated wave voltage based on the three-phase current at the AC end of each converter module at the time corresponding to the inflection point of the most recently passed predetermined carrier, and obtain a three-phase modulated wave incremental voltage of each AC module based on the three-phase current at the AC end of each converter module at the time corresponding to the inflection point of the predetermined carrier. When the three-phase modulated wave voltage and the voltage at the inflection point of the predetermined carrier meet a balanced adjustment condition, a pulse control signal can be generated based on the three-phase modulated wave incremental voltage and the three-phase modulated wave voltage. The three-phase modulated wave incremental voltage can compensate for the current difference between the parallel converter modules, and the three-phase modulated wave voltage and the voltage at the inflection point of the predetermined carrier meet a balanced adjustment condition. The three-phase modulated wave voltage after being processed by the three-phase modulated wave incremental voltage will not exceed the voltage range of the predetermined carrier. The difference in current of the parallel converter modules controlled by the generated pulse control signal is reduced, and the current of the converter modules at the commutation point will not undergo a sudden change, thereby improving the current balance of the converter modules and thereby improving the safety of the converter.

[0044] Figure 3 is a schematic diagram illustrating an example of the current of a converter module without using the converter control method provided in an embodiment of the present application. Figure 4 is a schematic diagram illustrating an example of the current of a converter module with using the converter control method provided in an embodiment of the present application. The experimental conditions for the current of the converter modules shown in Figures 3 and 4 are the same.

[0045] The two-color curves in Figure 3 represent the currents of the two parallel converter modules in the converter. It can be seen from Figure 3 that if the control method of the converter provided in the embodiment of the present application is not adopted, it is very easy for some converter modules to have pulse signals and some converter modules to have no pulse signals at the commutation points of the modulation wave, that is, the peak points and valley points. The currents of the two parallel converter modules suddenly change in the peak area, resulting in a large difference in the currents of the two parallel converter modules at this point, resulting in a sudden waveform of current imbalance as shown in Figure 3.

[0046] The two-color curves in Figure 4 represent the currents of the two parallel converter modules in the converter. It can be seen from Figure 4 that, by adopting the converter control method provided in the embodiment of the present application, the current of the converter module basically does not undergo sudden changes, and the current balance of the two converter modules is better.

[0047] FIG5 is a schematic diagram of another example of the current of the converter module that is not controlled by the control method of the converter provided in the embodiment of the present application, and FIG6 is a schematic diagram of another example of the current of the converter module that is controlled by the control method of the converter provided in the embodiment of the present application. The experimental conditions for the current of the converter module shown in FIG5 and FIG6 are the same, and the experimental conditions for the current of the converter module shown in FIG5 and FIG3 are different. The two-color curves in FIG5 represent the currents of the two parallel converter modules in the converter. It can be seen from FIG5 that without adopting the control method of the converter provided in the embodiment of the present application, the current of the converter module undergoes a sudden change in the peak area, and the current difference between the two converter modules here is relatively large. The two-color curves in FIG6 represent the currents of the two parallel converter modules in the converter. It can be seen from FIG6 that with adopting the control method of the converter provided in the embodiment of the present application, the current of the converter module basically does not undergo a sudden change, and the current balance of the two converter modules is better.

[0048] It can be seen from the current schematic diagram of the above-mentioned converter module that the converter control method provided in the embodiment of the present application can avoid sudden changes in the current of the converter modules connected in parallel in the converter, thereby improving the current balance of the converter modules connected in parallel.

[0049] Figure 7 is a flowchart of a control method for a converter provided in another embodiment of the present application. The difference between Figure 7 and Figure 2 is that step S201 in Figure 2 can be specifically refined into steps S2011 to S2013 in Figure 7, step S202 in Figure 2 can be specifically refined into steps S2021 and S2022 in Figure 7, and step S203 in Figure 2 can be specifically refined into steps S2031 and S2032 in Figure 7.

[0050] In step S2011 , the d-axis current and q-axis current of each converter module in a two-phase rotating coordinate system are converted based on the three-phase current of the converter module at the time corresponding to the inflection point of the most recently passed predetermined carrier.

[0051] The three-phase current here refers to the three-phase current in a three-phase stationary coordinate system. By transforming between the three-phase stationary coordinate system and the two-phase rotating coordinate system, the three-phase current at the AC end of each converter module at the time corresponding to the inflection point of the most recently passed predetermined carrier is converted into the d-axis current and q-axis current of each converter module. Each of the N converter modules connected in parallel has its own d-axis current and q-axis current.

[0052] In step S2012 , the average d-axis current and the average q-axis current of the N converter modules are obtained according to the d-axis current and the q-axis current of each converter module in the two-phase rotating coordinate system.

[0053] The average value of the d-axis current is the average value of the d-axis currents of the N converter modules. The average value of the q-axis current is the average value of the q-axis currents of the N converter modules. For example, FIG8 and FIG9 are respectively a logic diagram of an example of obtaining the average value of the d-axis current and a logic diagram of an example of obtaining the average value of the q-axis current provided in an embodiment of the present application. The converter includes two converter modules connected in parallel, the two converter modules being converter module 1 and converter module 2, and the d-axis current i of converter module 1 being 1d The d-axis current of the converter module 2 is i 2d Superposition and averaging are performed to obtain the average d-axis current i df ; q-axis current i of converter module 1 1q And the q-axis current of the converter module 2 is i 2q Superposition and averaging are performed to obtain the average value of the q-axis current i qf .

[0054] In step S2013 , a three-phase modulated wave voltage is obtained according to the d-axis current average value, the q-axis current average value, the d-axis current given value, and the q-axis current given value.

[0055] The d-axis reference voltage can be obtained based on the given d-axis current value and the average d-axis current. The q-axis reference voltage can be obtained based on the given q-axis current value and the average q-axis current. The d-axis reference voltage and q-axis reference voltage are subjected to coordinate system transformation and space vector pulse width modulation (SVPWM) processing to obtain a three-phase modulated wave voltage. This three-phase modulated wave voltage is common to the N parallel AC modules.

[0056] For example, FIG10 is a logic diagram of an example of obtaining a three-phase modulated wave voltage according to an embodiment of the present application. As shown in FIG10 , the d-axis current is given a value i dr * and the average d-axis current i df The difference is processed by proportional integral (PI) and limiting to obtain the d-axis reference voltage V dr *; Set the q-axis current to a given value i qr * and the average value of q-axis current i qf The difference is processed by proportional integration and limiting to obtain the q-axis reference voltage V qr *. For d-axis reference voltage V dr * and q-axis reference voltage V qr *Perform Park inverse transform to obtain the α-axis reference voltage V in the two-phase stationary coordinate system α * and β-axis reference voltage V β *. Reference voltage for α axis V α * and β-axis reference voltage V β*Perform SVPWM processing to obtain the three-phase modulation wave voltage V xmod , where x can take values ​​of a, b, and c, representing phase a, phase b, and phase c.

[0057] In step S2021 , an average value of the three-phase currents of the N converter modules is obtained based on the three-phase currents of the AC terminals of the converter modules at the time corresponding to the inflection point of the most recently passed predetermined carrier.

[0058] The three-phase current used here refers to the three-phase current at the converter end of the converter module latched by the converter control device at the time corresponding to the inflection point of the predetermined carrier. The average value of the three-phase current at the AC end of the N converter modules at the time corresponding to the most recently passed inflection point of the predetermined carrier can be used as a reference current to be used in subsequent steps to measure the three-phase current at the AC end of each converter module at the time corresponding to the most recently passed inflection point of the predetermined carrier.

[0059] In step S2022, based on the current difference between the three-phase current of each conversion module and the average value of the three-phase current, a three-phase modulation wave incremental voltage of each conversion module is obtained through proportional integration processing.

[0060] The current difference between the three-phase current at the AC end of each converter module at the time corresponding to the inflection point of the predetermined carrier that has passed most recently and the average value of the three-phase current can reflect the difference between the current of each converter module and the reference current. Each converter module has a corresponding current difference. For example, FIG11 is a logic diagram of an example of obtaining a current difference provided in an embodiment of the present application. If the converter includes two converter modules connected in parallel, the two converter modules are converter module 1 and converter module 2 respectively; the three-phase current i at the AC end of converter module 1 at the time corresponding to the inflection point of the predetermined carrier that has passed most recently is 1a,1b,1c The three-phase current i of the AC end of the converter module 2 at the time corresponding to the inflection point of the predetermined carrier most recently passed 2a,2b,2c After superposition, the average processing is performed to obtain the average value of the three-phase current; the three-phase current i of the converter module 1 1a,1b,1c Differing from the average value of the three-phase current, the current difference i of the converter module 1 is obtained. 1xdiff ; The three-phase current i of the converter module 2 2a,2b,2c Differing from the average value of the three-phase current, the current difference i of the converter module 2 is obtained. 2xdiff .

[0061] After the current difference is processed by proportional integration, it can also be limited to obtain the three-phase modulation wave incremental voltage of the conversion module.

[0062] In step S2031, when the three-phase modulation wave voltage and the voltage of the inflection point of the predetermined carrier meet the balance adjustment condition, the modulation wave voltage difference between the three-phase modulation wave voltage and the three-phase modulation wave incremental voltage of each conversion module is calculated respectively.

[0063] The inflection points include peak points and valley points, and the equalization adjustment conditions may include: the voltage difference between the peak point of the predetermined carrier and the voltage of the three-phase modulation wave is greater than or equal to the preset adjustment threshold, and the voltage difference between the three-phase modulation wave voltage and the valley point of the predetermined carrier is greater than or equal to the preset adjustment threshold. The preset adjustment threshold is the threshold value at which the three-phase modulation wave voltage processed by the three-phase modulation wave incremental voltage does not exceed the maximum value of the predetermined carrier, which can be set according to the scenario, requirements, experience, etc., and is not limited here. Correspondingly, if the voltage difference between the peak point of the predetermined carrier and the voltage of the three-phase modulation wave is less than the preset adjustment threshold, or the difference between the three-phase modulation wave voltage and the valley point of the predetermined carrier is less than the preset adjustment threshold, then the three-phase modulation wave incremental voltage does not participate in the generation of the pulse control signal.

[0064] Each converter module corresponds to a modulation wave voltage difference, which is the difference between the three-phase modulation wave voltage and the three-phase modulation wave incremental voltage of the converter module.

[0065] In step S2032, pulse conversion processing is performed on the modulation wave voltage difference of each converter module to generate a pulse control signal corresponding to each converter module, and the pulse control signal is used to control the corresponding converter module.

[0066] The modulated wave voltage difference of the converter module can be input into a PWM generator, and the signal output by the PWM generator can be used as a pulse control signal. This pulse control signal can be used to control the corresponding converter module. In some examples, the modulated wave voltage difference corresponding to different converter modules may be different. If the modulated wave voltage difference is different, the pulse width of the pulse control signal corresponding to the converter module will be different. In this case, when using the pulse control signal to control the converter module, it is necessary to simultaneously turn on the power devices in different converter modules. That is, the turn-on edge of the pulse control signal of different converter modules corresponds to the same time. The turn-on edge of the pulse control signal is the starting edge of the signal that controls the turn-on of the power devices in the converter module. The turn-on edge of the pulse control signal of different converter modules corresponds to the same time. The pulse width of the pulse control signal of different converter modules may be different. Therefore, the turn-off edge of the pulse control signal of different converter modules may be different. This is equivalent to adjusting the end time of the pulse control signal.

[0067] For example, FIG12 is a schematic diagram of an example of the control logic of the converter provided in an embodiment of the present application. Taking the converter including two parallel converter modules as an example, the two parallel converter modules are converter module 1 and converter module 2, and the logic portion for obtaining the three-phase modulated wave voltage is consistent with the content shown in FIG10, and the logic portion for obtaining the voltage difference is consistent with the content shown in FIG11. The logic for obtaining the three-phase modulated wave voltage and the logic for obtaining the voltage difference are not repeated here. As shown in FIG12, the current difference i corresponding to converter module 1 is 1xdiff Perform PI processing and amplitude limiting processing to obtain the three-phase modulation wave incremental voltage of the converter module 1; the current difference i corresponding to the converter module 2 2xdiff Perform PI processing and amplitude limiting processing to obtain the three-phase modulated wave incremental voltage of the converter module 2. Subtract the three-phase modulated wave voltage from the three-phase modulated wave incremental voltage of the converter module 1 to obtain the modulated wave voltage difference corresponding to the converter module 1. The modulated wave voltage difference corresponding to the converter module 1 is input into the PWM generator 1 to obtain the pulse control signal output by the PWM generator 1. The pulse control signal is used to control the converter module 1. The three-phase current i at the AC end of the controlled converter module 1 at the time corresponding to the inflection point of the most recently passed predetermined carrier is 1a,1b,1c Perform coordinate system transformation to obtain the d-axis current i 1d and q-axis current i 1q , participate in the next round of converter control. The three-phase modulated wave voltage is subtracted from the three-phase modulated wave incremental voltage of the converter module 2 to obtain the modulated wave voltage difference corresponding to the converter module 2. The modulated wave voltage difference corresponding to the converter module 2 is input into the PWM generator 2 to obtain the pulse control signal output by the PWM generator 2. The pulse control signal is used to control the converter module 2. The three-phase current i at the AC end of the controlled converter module 2 at the time corresponding to the inflection point of the most recently passed predetermined carrier is 2a,2b,2c Perform coordinate system transformation to obtain the d-axis current i 2d and q-axis current i 2q , participate in the next round of converter control.

[0068] In some embodiments, the converter control device includes a control unit and a computing unit. The control unit can be implemented as, but not limited to, an MCU, and the computing unit can be implemented as, but not limited to, an FPGA. The process of obtaining a three-phase modulated wave voltage based on data such as three-phase current can be executed by the control unit, that is, the control unit obtains the three-phase modulated wave voltage based on the three-phase current, a given d-axis current value, and a given q-axis current value. The process of obtaining a three-phase modulated wave incremental voltage and generating a pulse control signal based on the three-phase current can be executed by the computing unit, that is, the computing unit obtains a three-phase modulated wave incremental voltage for each converter module based on the three-phase current, generates a pulse control signal based on the three-phase modulated wave voltage and the three-phase modulated wave incremental voltage of each converter module, and uses the pulse control signal to control the corresponding converter module.

[0069] Compared with the technical solution in which each of the N parallel converter modules adopts a set of control algorithms, in the embodiment of the present application, the control unit executes the process of obtaining the three-phase modulated wave voltage, and the three-phase modulated wave voltage is common to the N parallel converter modules, that is, for the N parallel converter modules, the control unit only needs to execute a set of control algorithms, obtain the three-phase modulated wave incremental voltage through the calculation unit, and adjust the driving pulse level of the pulse control signal through the three-phase modulated wave incremental voltage and the three-phase modulated wave voltage to achieve the current equalization control of the current of the N parallel converter modules. Implementing the current equalization control algorithm through the calculation unit has a faster response and can avoid the situation in which the control unit bears the control algorithms of multiple converter modules, releases the resources of the control unit, reduces the load of the control unit, and avoids the situation in which the control unit is overloaded.

[0070] A second aspect of the present application provides a converter control system. FIG13 is a schematic diagram of the structure of a converter control system provided in an embodiment of the present application. As shown in FIG13 , the converter control system may include a converter 31 and a converter control device 32 .

[0071] The converter 31 may include N converter modules 311 connected in parallel, where N is an integer greater than 1. The converter module 311 has an AC terminal, and the AC terminal of the converter module 311 can input or output three-phase current.

[0072] The converter control device 32 can be configured to obtain a three-phase modulated wave voltage based on the three-phase current, d-axis current given value and q-axis current given value at the AC end of the converter module at the time corresponding to the inflection point of the most recently passed predetermined carrier; and obtain a three-phase modulated wave incremental voltage of each converter module based on the three-phase current at the AC end of the converter module at the time corresponding to the inflection point of the most recently passed predetermined carrier; and, when the three-phase modulated wave voltage and the voltage at the inflection point of the predetermined carrier meet the balanced adjustment condition, generate a pulse control signal corresponding to each converter module based on the three-phase modulated wave voltage and the three-phase modulated wave incremental voltage of each converter module, and use the pulse control signal to control the corresponding converter module.

[0073] The converter control device 32 may be configured to execute the converter control method in the above embodiment. For details, please refer to the relevant contents in the above embodiment, which will not be described again here.

[0074] In some examples, the variable flow control device 32 may include a control unit 321 and a calculation unit 322 .

[0075] The control unit 321 can be configured to obtain the three-phase modulated wave voltage based on the three-phase current, the d-axis current set value, and the q-axis current set value at the AC end of the converter module at the time corresponding to the most recently passed inflection point of the predetermined carrier. Similarly, the control unit can also be configured to perform a detailed step of obtaining the three-phase modulated wave voltage based on the three-phase current, the d-axis current set value, and the q-axis current set value at the AC end of the converter module at the time corresponding to the most recently passed inflection point of the predetermined carrier. For details, please refer to the relevant content of the above embodiment and will not be repeated here.

[0076] The calculation unit 322 can be configured to obtain a three-phase modulation wave incremental voltage for each converter module based on the three-phase current at the AC end of the converter module at the time corresponding to the inflection point of the most recently passed predetermined carrier; and, if the three-phase modulation wave voltage and the voltage at the inflection point of the predetermined carrier meet a balanced adjustment condition, generate a pulse control signal corresponding to each converter module based on the three-phase modulation wave voltage and the three-phase modulation wave incremental voltage of each converter module, and use the pulse control signal to control the corresponding converter module. Similarly, the control unit can also be configured to perform a detailed step of obtaining a three-phase modulation wave incremental voltage for each converter module based on the three-phase current at the AC end of the converter module at the time corresponding to the inflection point of the most recently passed predetermined carrier, and also to perform a detailed step of generating a pulse control signal corresponding to each converter module based on the three-phase modulation wave voltage and the three-phase modulation wave incremental voltage of each converter module, and use the pulse control signal to control the corresponding converter module, if the three-phase modulation wave voltage and the voltage at the inflection point of the predetermined carrier meet a balanced adjustment condition. For details, please refer to the relevant content of the above embodiment and will not be repeated here.

[0077] In a third aspect of the present application, a computer-readable storage medium is provided, on which computer program instructions are stored. When the computer program instructions are executed by a processor, the control method of the converter in the above-mentioned embodiment can be implemented, and the same technical effect can be achieved. To avoid repetition, the above-mentioned computer-readable storage medium may include a non-transitory computer-readable storage medium, such as a read-only memory (ROM), a random access memory (RAM), a magnetic disk, or an optical disk, etc., which is not limited here.

[0078] An embodiment of the present application provides a computer program product, which includes a computer program. When the computer program is executed by a processor, it implements the control method of the converter in the above embodiment and can achieve the same technical effect. To avoid repetition, it will not be described here.

[0079] It should be understood that the various embodiments in this specification are described in a progressive manner, and the same or similar parts between the various embodiments can be referred to each other, and each embodiment focuses on the differences from other embodiments. For system embodiments, computer-readable storage medium embodiments, and computer program products, relevant parts can be found in the description of the method embodiments. This application is not limited to the specific steps and structures described above and shown in the figures. Those skilled in the art can make various changes, modifications, and additions, or change the order of the steps after understanding the spirit of this application. In addition, for the sake of brevity, a detailed description of known method technologies is omitted here.

[0080] Aspects of the present application have been described above with reference to the flowcharts and / or block diagrams of the methods, devices (systems) and computer program products according to the embodiments of the present application. It should be understood that each box in the flowchart and / or block diagram and the combination of each box in the flowchart and / or block diagram can be implemented by computer program instructions. These computer program instructions can be provided to the processor of a general-purpose computer, a special-purpose computer or other programmable data processing device to produce a machine so that these instructions executed via the processor of the computer or other programmable data processing device enable the implementation of the function / action specified in one or more boxes of the flowchart and / or block diagram. This processor can be, but is not limited to, a general-purpose processor, a special-purpose processor, a special application processor or a field programmable logic circuit. It is also understood that each box in the block diagram and / or the flowchart and the combination of the boxes in the block diagram and / or the flowchart can also be implemented by the dedicated hardware that performs the specified function or action, or can be implemented by the combination of dedicated hardware and computer instructions.

[0081] Those skilled in the art should understand that the above embodiments are exemplary rather than restrictive. Different technical features appearing in different embodiments can be combined to achieve beneficial effects. Based on a study of the drawings, specifications and claims, those skilled in the art should be able to understand and implement other variations of the disclosed embodiments. In the claims, the term "comprising" does not exclude other devices or steps; when an item is not modified by a quantifier, it is intended to include one / kind or more / kinds of items and can be used interchangeably with "one / kind or more / kinds of items"; the terms "first" and "second" are used to identify names rather than to indicate any specific order. Any figure marks in the claims should not be understood as limiting the scope of protection. The functions of multiple parts appearing in the claims can be implemented by a separate hardware or software module. The fact that certain technical features appear in different dependent claims does not mean that these technical features cannot be combined to achieve beneficial effects.

Claims

1. A method for controlling a converter, wherein the converter comprises N converter modules connected in parallel, where N is an integer greater than 1, and the converter modules have AC terminals. The method comprises: The current conversion control device obtains a three-phase modulated wave voltage based on the three-phase current, the d-axis current given value, and the q-axis current given value of the AC end of the conversion module at the time corresponding to the inflection point of the most recently passed predetermined carrier; The current conversion control device obtains the three-phase modulation wave incremental voltage of each current conversion module according to the three-phase current at the AC end of the current conversion module at the time corresponding to the inflection point of the predetermined carrier most recently passed; When the three-phase modulation wave voltage and the voltage of the inflection point of the predetermined carrier meet the balanced adjustment conditions, the current conversion control device generates a pulse control signal corresponding to each current conversion module based on the three-phase modulation wave voltage and the three-phase modulation wave incremental voltage of each current conversion module, and uses the pulse control signal to control the corresponding current conversion module.

2. The method according to claim 1, wherein The step of obtaining the three-phase modulation wave incremental voltage of each of the conversion modules according to the three-phase current at the AC end of the conversion module at a time corresponding to the inflection point of the predetermined carrier most recently passed comprises: Obtaining an average value of the three-phase currents of N of the conversion modules according to the three-phase currents at the AC end of the conversion module at a time corresponding to an inflection point of a predetermined carrier that has recently passed; Based on the current difference between the three-phase current of each of the conversion modules and the three-phase current average value, the three-phase modulation wave incremental voltage of each of the conversion modules is obtained through proportional integration processing.

3. The method according to claim 1, wherein The inflection points include peak points and valley points, and the equilibrium adjustment conditions include: The voltage difference between the peak point of the predetermined carrier and the voltage of the three-phase modulation wave is greater than or equal to a preset adjustment threshold, and the voltage difference between the three-phase modulation wave voltage and the valley point of the predetermined carrier is greater than or equal to the preset adjustment threshold.

4. The method according to claim 1, wherein The step of generating a pulse control signal corresponding to each of the conversion modules based on the three-phase modulation wave voltage and the three-phase modulation wave incremental voltage of each of the conversion modules includes: respectively calculating the modulation wave voltage difference between the three-phase modulation wave voltage and the three-phase modulation wave incremental voltage of each of the conversion modules; The modulation wave voltage difference of each of the conversion modules is subjected to pulse conversion processing to generate the pulse control signal corresponding to each of the conversion modules.

5. The method according to claim 1, wherein The time corresponding to the conduction edge of the pulse control signal of different converter modules is the same.

6. The method according to claim 1, wherein The method of obtaining a three-phase modulated wave voltage based on the three-phase current, the d-axis current given value, and the q-axis current given value at the AC end of the conversion module at a time corresponding to an inflection point of a predetermined carrier that has recently passed by the AC end of the conversion module comprises: Converting the three-phase current of the AC end of the conversion module at the time corresponding to the inflection point of the most recently passed predetermined carrier to obtain the d-axis current and q-axis current of each of the conversion modules in a two-phase rotating coordinate system; Obtaining an average d-axis current and an average q-axis current of the N converter modules according to the d-axis current and the q-axis current of each converter module in the two-phase rotating coordinate system; A three-phase modulated wave voltage is obtained according to the d-axis current average value, the q-axis current average value, the d-axis current given value, and the q-axis current given value.

7. The method according to claim 1, wherein The variable current control device includes a control unit and a calculation unit; The current conversion control device obtains a three-phase modulated wave voltage based on the three-phase current, the d-axis current given value, and the q-axis current given value at the time corresponding to the inflection point of the most recently passed predetermined carrier from the AC end of the conversion module, including: The control unit obtains the three-phase modulated wave voltage based on the three-phase current, the d-axis current given value, and the q-axis current given value; The current conversion control device obtains the three-phase modulation wave incremental voltage of each of the current conversion modules based on the three-phase current at the AC end of the current conversion module at a time corresponding to an inflection point of a predetermined carrier that has recently passed, including: The calculation unit obtains the three-phase modulation wave incremental voltage of each of the conversion modules according to the three-phase current; The current conversion control device generates a pulse control signal corresponding to each current conversion module based on the three-phase modulation wave voltage and the three-phase modulation wave incremental voltage of each current conversion module, and controls the corresponding current conversion module using the pulse control signal, including: The calculation unit generates the pulse control signal based on the three-phase modulation wave voltage and the three-phase modulation wave incremental voltage of each of the conversion modules, and uses the pulse control signal to control the corresponding conversion module.

8. The method according to claim 1, wherein The conversion module includes a machine-side rectifier module or a grid-side inverter module.

9. A control system for a converter, comprising: A converter, comprising N converter modules connected in parallel, where N is an integer greater than 1, and each converter module has an AC terminal; The current conversion control device is configured to obtain a three-phase modulated wave voltage based on the three-phase current, d-axis current given value and q-axis current given value at the time corresponding to the inflection point of the most recently passed predetermined carrier from the AC end of the conversion module; and obtain a three-phase modulated wave incremental voltage of each of the conversion modules based on the three-phase current at the time corresponding to the inflection point of the closest predetermined carrier from the AC end of the conversion module; and, when the three-phase modulated wave voltage and the voltage at the inflection point of the predetermined carrier meet the balance adjustment condition, generate a pulse control signal corresponding to each of the conversion modules based on the three-phase modulated wave voltage and the three-phase modulated wave incremental voltage of each of the conversion modules, and use the pulse control signal to control the corresponding conversion module.

10. A computer-readable storage medium, wherein: The computer-readable storage medium stores computer program instructions, and when the computer program instructions are executed by a processor, the method for controlling the converter according to any one of claims 1 to 8 is implemented.