Converter control method and control system, converter, and wind turbine

Abstract

The present disclosure provides a converter control method and control system, a converter, and a wind turbine. The method comprises: determining the current rotor speed of a double-fed induction generator; and in response to the difference between the rotor speed and the synchronous speed of the double-fed induction generator being less than a preset threshold, for each three-level bridge arm, controlling the states of a plurality of switching transistors in the three-level bridge arm in the following manner: in response to receiving a first modulation signal for switching the output level of the three-level bridge arm from a positive level to a midpoint level or a second modulation signal for switching from a negative level to the midpoint level, turning off the currently turned-on outer transistor, and turning on each clamping transistor and each inner transistor when the turned-on outer transistor has been turned off. The present disclosure solves the problem that the thermal stress of a power device is excessively large near the synchronous speed, and can effectively disperse the thermal stress of the inner transistor by optimizing modulation logic, so that the thermal distribution of the power device of each switching transistor is more uniform, and the problem that the thermal stress of the power device is excessively large is alleviated.

Description

Control methods and systems for converters, converters and wind turbine generator sets

[0001] This application claims priority to Chinese Patent Application No. 202411870542.4, filed on December 17, 2024, entitled "Control Method and Control System for Converter, Converter and Wind Turbine Generator", the entire contents of which are incorporated herein by reference. Technical Field

[0002] This disclosure relates to the field of wind power generation, and more specifically, to a control method for a converter, a control system, a converter, and a wind turbine generator set. Background Technology

[0003] A double-fed induction generator (DFIG) is a commonly used type of wind turbine. The stator winding of a DFIG can be directly connected to the power grid, while its rotor winding can be connected to a converter via slip rings. The converter can precisely control the frequency and amplitude of the rotor current to control the speed and output power of the wind turbine.

[0004] Converters used in doubly-fed wind turbines can be three-level active neutral-point clamped (ANPC) topologies. Compared to two-level converters, three-level converters offer higher voltage ratings, lower switching losses, and lower harmonic distortion. Therefore, three-level converters are more reliable and advantageous when used in doubly-fed wind turbines. Summary of the Invention

[0005] For doubly-fed wind turbines, the torque capability near the generator's synchronous speed affects the overall performance of the doubly-fed wind turbine system. Therefore, unlike general converter control schemes, this disclosure recognizes that converter control near the generator's synchronous speed may be one of the keys to improving the performance of the power generation system.

[0006] Specifically, near the synchronous speed of a doubly-fed wind turbine, the rotor speed is close to the synchronous speed, the slip is very small, and the rotor current frequency is very low. When the rotor speed is equal to the synchronous speed, the slip is zero, and the rotor current is DC. This disclosure recognizes that when the rotor speed is close to or equal to the synchronous speed, the zero-level duration of the converter during modulation will be longer. In this case, if the power devices of the converter are still modulated according to traditional methods such as normal modulation for ANPC topologies, it will lead to untimely commutation of certain power devices, resulting in excessive thermal stress. This necessitates reducing the torque of the wind turbine to address the problem of excessive thermal stress on the power devices near the synchronous speed, which inevitably affects power generation.

[0007] Given that existing control schemes for converters in doubly fed wind turbines cannot adequately address the problem of excessive thermal stress on power devices near synchronous speed, this disclosure proposes a converter control method, a control system, a converter, and a wind turbine generator set to solve or at least alleviate the aforementioned problem.

[0008] The first aspect of this disclosure provides a control method for a converter applied to a doubly-fed wind turbine. The converter includes multiple three-level arms, each three-level arm including multiple switching transistors, the multiple switching transistors including two inner transistors, two outer transistors, and two clamping transistors. The control method includes: determining the current rotor speed of the doubly-fed wind turbine; and, in response to a difference between the rotor speed and the synchronous speed of the doubly-fed wind turbine being less than a preset threshold, controlling the state of the multiple switching transistors in each three-level arm in the following manner: in response to receiving a first modulation signal for switching the output level of the three-level arm from a positive level to a midpoint level or a second modulation signal for switching the output level of the three-level arm from a negative level to a midpoint level, turning off the currently conducting outer transistors, and turning on each clamping transistor and each inner transistor when the conducting outer transistors are turned off.

[0009] A second aspect of this disclosure provides a control system for a converter, the control system comprising: a processor; and a memory for storing processor-executable instructions, wherein the processor-executable instructions, when executed by the processor, cause the processor to perform a converter control method according to an embodiment of this disclosure.

[0010] A third aspect of this disclosure provides a converter that includes a control system for the converter according to embodiments of this disclosure.

[0011] A fourth aspect of this disclosure provides a wind turbine generator set, the wind turbine generator set including a doubly fed wind turbine generator and a converter according to embodiments of this disclosure.

[0012] A fifth aspect of this disclosure provides a computer-readable storage medium that, when instructions in the computer-readable storage medium are executed by a processor of an electronic device, enables the electronic device to perform a converter control method according to embodiments of this disclosure.

[0013] A sixth aspect of this disclosure provides a computer program product including computer-executable instructions that, when executed by at least one processor, implement the converter control method according to embodiments of this disclosure.

[0014] According to the control scheme of the converter disclosed herein, the current rotor speed of the doubly-fed wind turbine can be determined. When the difference between the rotor speed and the synchronous speed of the doubly-fed wind turbine is less than a preset threshold, for each three-level bridge arm, in response to receiving a first modulation signal for switching the output level of the three-level bridge arm from a positive level to a midpoint level or a second modulation signal for switching the output level of the three-level bridge arm from a negative level to a midpoint level, the currently conducting outer tube is turned off. And when the conducting outer tube is turned off, each clamping tube and each inner tube are turned on. Thus, by optimizing the converter's control algorithm, under the modulation signal at the midpoint level, the current stress borne by a single inner tube and a single clamping tube in related technologies can be controlled to be borne jointly by two clamping tubes and two inner tubes. Thus, even when the midpoint level of zero level lasts for a long time near synchronous speed, it can alleviate the problem of excessive thermal stress on power devices, effectively disperse the thermal stress of the inner tube, and make the heat distribution of the power devices of the switching transistor more uniform. This scheme can solve the problem of excessive thermal stress on the power devices of the converter without losing power generation by optimizing the modulation logic. It is also universal, suitable for the design and application of new units, and easy to improve existing units. It has good control effect and high application value. Attached Figure Description

[0015] Figure 1 is a schematic diagram illustrating the structure of a doubly fed wind turbine according to an exemplary embodiment of the present disclosure.

[0016] Figure 2 is a topological schematic diagram illustrating the three-level bridge arm of a converter according to an exemplary embodiment of the present disclosure.

[0017] Figure 3 is a schematic diagram illustrating an example of the switching state switching mode of a three-level bridge arm of a converter according to an exemplary embodiment of the present disclosure.

[0018] Figures 4A to 4G are schematic diagrams illustrating the current paths of the three-level bridge arms of a converter in different states according to exemplary embodiments of the present disclosure.

[0019] Figure 5 is a schematic flowchart illustrating a control method for a converter near synchronous speed according to an exemplary embodiment of the present disclosure.

[0020] Figure 6 is a schematic diagram illustrating another example of the switching state switching mode of the three-level bridge arm of a converter according to an exemplary embodiment of the present disclosure.

[0021] Figure 7 is an example illustrating a PWM waveform diagram of a converter according to an exemplary embodiment of the present disclosure.

[0022] Figure 8 is a schematic flowchart illustrating an example of generating a PWM waveform in a control method for a converter according to an exemplary embodiment of the present disclosure.

[0023] Figure 9 is another example illustrating a PWM waveform diagram of a converter according to an exemplary embodiment of the present disclosure.

[0024] Figure 10 is a schematic flowchart illustrating another example of generating a PWM waveform in a control method for a converter according to an exemplary embodiment of the present disclosure.

[0025] Figures 11A and 11B are schematic diagrams illustrating the effects of a control method for a converter according to exemplary embodiments of the present disclosure. Detailed Implementation

[0026] The following detailed embodiments are provided to aid the reader in gaining a comprehensive understanding of the methods, apparatus, and / or systems described herein. However, various changes, modifications, and equivalents of the methods, apparatus, and / or systems described herein will become apparent upon understanding this disclosure. For example, the order of operations described herein is merely illustrative and is not limited to those orders set forth herein, but may be changed as will become clear upon understanding this disclosure, except for operations that must occur in a specific order. Furthermore, for clarity and conciseness, descriptions of features known in the art may be omitted.

[0027] The features described herein may be implemented in different forms and should not be construed as limited to the examples described herein. Rather, the examples described herein are provided only to illustrate some of the many feasible ways of implementing the methods, apparatus, and / or systems described herein, which will become clear upon understanding the disclosure of this application.

[0028] As used herein, the term “and / or” includes any one of the associated listed items and any combination of any two or more.

[0029] Although terms such as “first,” “second,” and “third” may be used herein to describe various components, assemblies, regions, layers, or parts, these components, assemblies, regions, layers, or parts should not be limited by these terms. Rather, these terms are used only to distinguish one component, assembly, region, layer, or part from another. Thus, without departing from the teaching of the examples described herein, the first component, first assembly, first region, first layer, or first part referred to as the first component, first assembly, first region, first layer, or first part may also be referred to as the second component, second assembly, second region, second layer, or second part.

[0030] In the specification, when an element (such as a layer, region, or substrate) is described as being "on" another element, "connected to," or "bonded to" another element, the element may be directly "on" another element, directly "connected to," or "bonded to" the other element, or one or more other elements may be present in between. Conversely, when an element is described as being "directly on" another element, "directly connected to," or "directly bonded to" another element, no other elements may be present in between.

[0031] The terminology used herein is for the purpose of describing various examples only and is not intended to limit disclosure. Unless the context clearly indicates otherwise, the singular form is intended to include the plural form as well. The terms “comprising,” “including,” and “having” indicate the presence of the described features, quantities, operations, components, elements, and / or combinations thereof, but do not preclude the presence or addition of one or more other features, quantities, operations, components, elements, and / or combinations thereof.

[0032] Unless otherwise defined, all terms used herein (including technical and scientific terms) shall have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure pertains upon understanding this disclosure. Unless expressly defined herein, terms (such as those defined in a general dictionary) shall be interpreted as having a meaning consistent with their meaning in the context of the relevant field and in this disclosure, and shall not be interpreted in an idealized or overly formalistic manner.

[0033] Furthermore, in the description of the examples, detailed descriptions of well-known related structures or functions will be omitted when it is believed that such detailed descriptions would lead to a vague interpretation of this disclosure.

[0034] As mentioned earlier, for doubly fed wind turbines, the zero-level duration of the converter during modulation is relatively long, which can lead to untimely commutation of certain power devices and excessive thermal stress. Existing control schemes cannot properly solve the problem of excessive thermal stress on power devices near synchronous speed.

[0035] In view of these problems, this disclosure provides a control method for a converter, a control system for a converter, a converter, a wind turbine generator set, a computer-readable storage medium, and a computer program product to solve or at least alleviate the above-mentioned problems.

[0036] To better understand the embodiments of this disclosure, before describing the control scheme of the converter, we will first describe the topology example of the converter of the doubly fed wind turbine, the switching state switching example, and the current path example under different states with reference to Figures 1 to 4G.

[0037] As shown in Figure 1, a doubly-fed induction generator (DFIG) wind turbine generator set may include a wind turbine generator 110, two parallel-connected turbine-side filter reactors 120, two parallel-connected turbine-side converters 130, a grid-side converter 140, a grid-side filter 150, and a transformer 160. The electrical energy output from the wind turbine generator 110 can enter the corresponding turbine-side converter 130 through the two turbine-side filter reactors 120, and after rectification by the turbine-side converter, enter the grid-side converter 140. The current inverted by the grid-side converter 140 passes through the grid-side filter 150 (e.g., an inductor-capacitor-inductor (LCL) type filter) and is connected to the low-voltage side of the transformer 160 to feed into the power grid 170. Although a topology example with two turbine-side converters in parallel is described here with reference to Figure 1, the converter topology is not limited to this; for example, embodiments of this disclosure are also applicable to topologies employing a single turbine-side converter.

[0038] In the example above, the two machine-side converters and the grid-side converter can be controlled by the same control system, which may include a converter controller, a power interface board, and a drive control board.

[0039] Here, the converter controller can be used to collect converter data, implement control algorithms, implement fault protection, control power devices, and upload status information.

[0040] The power interface board can convert modulation signals such as pulse width modulation (PWM) output from the converter controller into drive signals suitable for power devices and braking units on the drive control board. It can also convert status signals of power devices and braking units (such as fault signals, sensing signals from negative temperature coefficient (NTC) thermistors, etc.) into level signals suitable for the converter controller. The power interface board can also isolate the signals of power devices from intelligent core components, improve the anti-interference capability of the control system, and improve the reliability of the control system.

[0041] The drive control board can convert the modulation signal output from the power interface board into a drive signal for the Insulated-Gate Bipolar Transistor (IGBT), enabling short-circuit monitoring of the IGBT and real-time uploading of the internal temperature of the IGBT.

[0042] According to embodiments of this disclosure, the converter is applied to a doubly-fed wind turbine. The converter includes multiple three-level bridge arms, each of which includes multiple switching transistors, including two inner transistors, two outer transistors, and two clamping transistors. Furthermore, each three-level bridge arm may include an upper half-bridge arm and a lower half-bridge arm, each of which may include one inner transistor, one outer transistor, and one clamping transistor. Here, the upper and lower half-bridge arms refer to those located between the positive terminal of the DC bus (see NP in Figure 2) and the midpoint of the DC bus, with the midpoint of the DC bus as the boundary. The lower half-bridge arm is located between the midpoint of the DC bus and the negative terminal of the DC bus (see DC- in Figure 2).

[0043] As an example, the converter can be a grid-connected ANPC (active clamping) three-level converter. For instance, this converter can be used as a grid-connected converter in various fields such as photovoltaics, wind power, energy storage, and hydrogen production.

[0044] Specifically, the converter may include multiple three-level bridge arms with the same structure, such as an ANPC-type three-level circuit topology. Figure 2 shows an example of the topology of the three-level bridge arms of a converter according to an exemplary embodiment of the present disclosure.

[0045] As shown in Figure 2, each three-level bridge arm may include multiple switching transistors (IGBTs). The switching transistors may include a first external transistor T1, a first internal transistor T2, a second internal transistor T3, a second external transistor T4, a first clamping transistor T5, and a second clamping transistor T6. The first internal transistor T2, the first external transistor T1, and the first clamping transistor T5 may be located in the upper half of the bridge arm, while the second internal transistor T3, the second external transistor T4, and the second clamping transistor T6 may be located in the lower half of the bridge arm.

[0046] In addition, each three-level bridge arm may also include a fast recovery freewheeling diode connected in reverse parallel with each switching transistor. Specifically, it includes: diode D1 connected in reverse parallel with the first external transistor T1, diode D2 connected in reverse parallel with the first internal transistor T2, diode D3 connected in reverse parallel with the second internal transistor T3, diode D4 connected in reverse parallel with the second external transistor T4, diode D5 connected in reverse parallel with the first clamping transistor T5, and diode D6 connected in reverse parallel with the second clamping transistor T6. Furthermore, each three-level bridge arm may also include a first DC capacitor C1 and a second DC capacitor C2, both having a voltage Udc. The DC bus of the three-level bridge arm is composed of upper and lower DC capacitors C1 and C2, respectively. The voltages of the upper and lower DC capacitors are equal and both have Udc, forming three voltages: DC+, NP, and DC-. When different current paths are conducting, the AC terminal can output a positive level, a negative level, and a midpoint level. Specifically, the AC terminal can output a 1- level, a 1+ level, a 0+ level, and a 0- level.

[0047] Based on the analysis of the commutation process of positive level, negative level and midpoint level, according to the commutation principle of "shortest commutation loop", the modulation of the three-level bridge arm topology can be divided into 7 switching states, namely positive 1 state, positive 1 dead zone state, positive 0 state, positive 0 negative 0 state, negative 0 state, negative 1 dead zone state and negative 1 state.

[0048] Figure 3 shows an example of the three-level bridge arm switching between these 7 switching states. As shown in Figure 3, the switching state switching methods of the three-level bridge arm can include: switching between positive 1 state and positive 1 dead zone state, switching between positive 1 dead zone state and positive 0 state, switching between positive 0 state and positive 0 negative 0 state, switching between negative 1 state and negative 1 dead zone state, switching between negative 1 dead zone state and negative 0 state, and switching between negative 0 state and positive 0 negative 0 state.

[0049] Figures 4A to 4G show the current paths for each switching state. The dotted dashed lines and short dashed horizontal lines represent the current paths that are turned on in each switching state, respectively. The short dashed horizontal lines indicate current outflow, and the dotted dashed lines indicate current inflow.

[0050] As shown in Figure 4A, by turning on the first outer tube T1 and the first inner tube T2 and turning off the other switching tubes, the AC terminal can output a positive bus voltage, thereby switching the switch state to the positive 1 state.

[0051] As shown in Figure 4B, by turning off both the first external tube T1 and the first clamping tube T5, the switch state is switched to the positive 1 dead zone state, preventing short circuits from occurring during the switching process between the positive 1 state and the positive 0 state.

[0052] As shown in Figure 4C, by turning on the first inner tube T2 and the first clamping tube T5 and turning off the other switching tubes, the AC terminal can output the midpoint level, thereby switching the switch state to the positive 0 state.

[0053] As shown in Figure 4D, by turning on the first inner tube T2, the second inner tube T3, the first clamping tube T5, and the second clamping tube T6, while turning off the other switching tubes, the switching state is switched to a 0 positive 0 negative state, thereby increasing the current carrying capacity at the midpoint level (zero level). The 0 positive 0 negative state can be an intermediate state between switching from a positive 0 state to a negative 0 state or vice versa.

[0054] As shown in Figure 4E, by turning on the second inner tube T3 and the second clamping tube T6 and turning off the other switching tubes, the AC terminal can output the midpoint level, thereby switching the switch state to the negative 0 state.

[0055] As shown in Figure 4F, by turning off both the second clamping tube T6 and the second external tube T4, the switch state is switched to the negative 1 dead zone state, preventing short circuits from occurring during the switching process between the negative 1 state and the negative 0 state.

[0056] As shown in Figure 4G, by turning on the second inner tube T3 and the second outer tube T4 and turning off the other switching tubes, the AC terminal can output a negative bus voltage, thereby switching the switch state to the negative 1 state.

[0057] The on / off state of each switch in the above states can be shown in Table 1 below, where "1" indicates on and "0" indicates off.

[0058] Table 1

[0059] In the example above, the converter's modulation logic can switch between positive and negative states based on the positive and negative states of the modulation wave issued by the control algorithm. When the modulation wave is positive, the modulation logic can switch between a positive 1 state, a positive 1 dead zone state, and a positive 0 state; when the modulation wave is negative, the modulation logic can switch between a negative 0 state, a negative 1 dead zone state, and a negative 1 state. The zero level, which serves as the midpoint level, can include three states: positive 0 state, positive 0 negative 0 state, and negative 0 state.

[0060] In response, this disclosure reveals that when the rotor speed is close to the synchronous speed, the slip is very small and the rotor current frequency is very low; when the rotor speed is equal to the synchronous speed, the slip is zero and the rotor current is DC. To address the problem of excessive thermal stress in power devices, a modulation optimization strategy near the synchronous speed can be activated when the rotor speed is close to the synchronous speed, thus resolving the issue of excessive thermal stress in power devices without reducing torque.

[0061] As shown in Figure 5, the control method of the converter according to an embodiment of the present disclosure may include the following steps:

[0062] In step S510, the current rotor speed of the doubly fed wind turbine can be determined.

[0063] In step S520, in response to the difference between the rotor speed and the synchronous speed of the doubly fed wind turbine being less than a preset threshold, for each three-level bridge arm, the state of multiple switching transistors in the three-level bridge arm is controlled in the following manner: in response to receiving a first modulation signal for switching the output level of the three-level bridge arm from a positive level to a midpoint level or a second modulation signal for switching from a negative level to a midpoint level, the currently conducting outer transistor is turned off, and when the conducting outer transistor is turned off, each clamping transistor and each inner transistor are turned on.

[0064] Specifically, when the generator rotor speed is close to or equal to the synchronous speed, the frequency of each phase current of the generator-side doubly fed converter is low or all are DC current. The modulation wave of the generator-side converter is much smaller than that in the case of asynchronous speed. Correspondingly, the duration of the midpoint level in the modulation state of the three-level bridge arm topology is longer. The midpoint level includes positive 0 state, positive 0 negative 0 state and negative 0 state.

[0065] In conventional modulation logic, when entering synchronization speed, if the machine-side current is positive and the positive 0 state lasts for a long time, the current stress on the first inner transistor T2 and the first clamping transistor T5 increases, resulting in significant heat generation. If this continues for too long, the power devices will experience overheating failure. Similarly, when entering synchronization speed, if the machine-side current is negative and the negative 0 state lasts for a long time, the current stress on the second inner transistor T3 and the second clamping transistor T6 increases, resulting in significant heat generation. If this continues for too long, the power devices will also experience overheating failure.

[0066] In step S520 above, in response to the difference between the rotor speed and the synchronous speed of the doubly fed wind turbine being less than a preset threshold, for each three-level bridge arm, the outer tube (e.g., the first outer tube T1 corresponding to the positive level and the positive 1 state or the second outer tube T4 corresponding to the negative level and the negative 1 state) that is currently conducting can be turned off according to the first modulation signal or the second modulation signal. And when the conducting outer tube is turned off, for example after passing through the positive 1 dead zone state or the negative 1 dead zone state, each clamping tube (e.g., the first clamping tube T5 and the second clamping tube T6) and each inner tube (e.g., the first inner tube T2 and the second inner tube T3) can then be turned on.

[0067] In the above process, the preset threshold can be set according to actual needs, for example, it can be determined based on the measurement error of the rotor speed.

[0068] As shown in Figure 6, by means of the above method, when switching from a positive or negative level to the midpoint level, it can directly switch from a positive 1 state through a positive 1 dead zone state to a positive 0 or negative 0 state, or from a negative 1 state through a negative 1 dead zone state to a positive 0 or negative 0 state, instead of switching from a positive 1 state through a positive 1 dead zone state to a positive 0 state, or from a negative 1 state through a negative 1 dead zone state to a negative 0 state, as shown in Figure 3. This ensures that near the synchronization speed, the zero level only includes the positive 0 and negative 0 states, without experiencing the positive 0 and negative 0 states. In the positive 0 and negative 0 states, the current stress can be shared by the two clamping transistors and the two inner transistors, which is four switching transistors. Compared with the scheme shown in Figure 3 where the current stress is shared by one clamping transistor and one inner transistor, the overheating problem of the power devices can be solved simply by optimizing the modulation logic, effectively dispersing the thermal stress of the switching transistors and making the heat distribution of the power devices of each switching transistor more uniform.

[0069] Furthermore, as shown in Figure 6, in the embodiments of this disclosure, near the synchronization speed, the level can be switched from the midpoint level to a positive level or a negative level.

[0070] Specifically, in response to the difference between the rotor speed and the synchronous speed of the doubly-fed wind turbine being less than a preset threshold, the state of multiple switching transistors in each three-level bridge arm can be controlled in the following way:

[0071] In response to receiving a third modulation signal for switching the output level of the three-level bridge arm from the midpoint level to the positive level, the second inner tube (e.g., the second inner tube T3) and each clamping tube (e.g., the first clamping tube T5 and the second clamping tube T6) of the three-level bridge arm are turned off, and with the second inner tube and each clamping tube turned off, for example after a positive 1 dead zone state, the first outer tube (e.g., the first outer tube T1) of the three-level bridge arm is turned on.

[0072] In response to receiving a fourth modulation signal for switching the output level of the three-level bridge arm from the midpoint level to the negative level, the first inner tube (e.g., the first inner tube T2) and each clamping tube (e.g., the first clamping tube T5 and the second clamping tube T6) of the three-level bridge arm can be turned off, and with the first inner tube and each clamping tube turned off, for example after passing through the negative 1 dead zone state, the second outer tube (e.g., the second outer tube T4) of the three-level bridge arm can be turned on.

[0073] Using the above method, when the difference between the rotor speed and the synchronous speed of the doubly fed wind turbine is less than a preset threshold (or near the synchronous speed), as shown in Figure 6 and Table 2 below, the modulation of the three-level bridge arm topology can be divided into 5 switching states, namely positive 1 state, positive 1 dead zone state, positive 0 negative 0 state, negative 1 dead zone state and negative 1 state.

[0074] As shown in Figure 6, the switching modes of the three-level bridge arm can include: switching between positive 1 state and positive 1 dead zone state, switching between positive 1 dead zone state and positive 0 / negative 0 state, switching between negative 1 state and negative 1 dead zone state, and switching between negative 1 dead zone state and positive 0 / negative 0 state.

[0075] Table 2

[0076] Furthermore, in the converter control method of the embodiments of this disclosure, when the rotor speed is asynchronous, different control modes can be adopted as needed, such as the mode shown in FIG3 or the mode shown in FIG6.

[0077] Specifically, in one example, the control method of the converter may further include: in response to the difference between the rotor speed and the synchronous speed of the doubly-fed wind turbine being greater than the aforementioned preset threshold, for each three-level bridge arm, the state of multiple switching transistors in that three-level bridge arm can be controlled in the following manner:

[0078] In response to receiving a first modulation signal or a second modulation signal, the outer tube (e.g., the first outer tube T1 corresponding to the positive level and the positive 1 state or the second outer tube T4 corresponding to the negative level and the negative 1 state) that was turned on in the current state (e.g., the positive 1 state corresponding to the positive level or the negative 1 state) can be turned off, and after passing through the positive 1 dead zone state or the negative 1 dead zone state, each clamping tube (e.g., the first clamping tube T5 and the second clamping tube T6) and each inner tube (e.g., the first inner tube T2 and the second inner tube T3) can be turned on.

[0079] Specifically, in this example, the control mode shown in Figure 6 can be used for both the rotor speed near the synchronous speed and the rotor speed at asynchronous speed. The modulation of the three-level bridge arm topology switches between five switching states. Among them, "near the synchronous speed" indicates a speed range where the difference between the rotor speed and the synchronous speed is less than or equal to 50 revolutions; "asynchronous speed" indicates a speed range where the difference between the rotor speed and the synchronous speed is greater than 50 revolutions.

[0080] In another example, the control method for the converter may further include: in response to the difference between the rotor speed and the synchronous speed of the doubly-fed wind turbine being greater than a preset threshold, controlling the state of multiple switches in each three-level bridge arm in the following manner:

[0081] In response to receiving a first modulation signal or a second modulation signal, the currently conducting outer tube is turned off, and when the conducting outer tube is turned off, each clamping tube and each inner tube are turned on.

[0082] In this example, when the difference is less than the aforementioned preset threshold, the state of each three-level bridge arm can be controlled based on the first control mode; when the difference is greater than the aforementioned preset threshold, the state of each three-level bridge arm can be controlled based on the second control mode. The state of a three-level bridge arm can refer to a combination of the sub-states of each of the multiple switching transistors in the three-level bridge arm. The sub-state of each switching transistor refers to its on / off state.

[0083] Here, the number of states each three-level bridge arm switches between in the first control mode can differ from the number of states switched between in the second control mode. In the first control mode, when the modulation wave is positive, the converter's modulation logic switches between a positive 1 state, a positive 1 dead-time state, and a positive 0 / negative 0 state; when the modulation wave is negative, the converter's modulation logic switches between a positive 0 / negative 0 state, a negative 1 dead-time state, and a negative 1 state. The zero level may only include the positive 0 / negative 0 state. In the second control mode, when the modulation wave is positive, the modulation logic can switch between a positive 1 state, a positive 1 dead-time state, and a positive 0 state; when the modulation wave is negative, the modulation logic can switch between a negative 0 state, a negative 1 dead-time state, and a negative 1 state. The zero level may include the positive 0 state, the positive 0 / negative 0 state, and the negative 0 state.

[0084] Specifically, different control modes can be adopted for two speed states: when the rotor speed is near the synchronous speed and when the rotor speed is asynchronous. When the rotor speed is close to or equal to the synchronous speed, the modulation of the three-level bridge arm topology can be switched between the five switching states shown in Figure 6. When the rotor speed is asynchronous, the modulation of the three-level bridge arm topology can be switched between the seven switching states shown in Figure 3.

[0085] Specifically, when the difference is less than the preset threshold and the output level of the three-level bridge arm is at the midpoint level, each switch can be controlled to be in the first state; when the difference is greater than the preset threshold and the output level of the three-level bridge arm is at the midpoint level, each switch can be controlled to be in the first state or the second state.

[0086] In the first state, the first inner tube T2, the second inner tube T3, the first clamping tube T5, and the second clamping tube T6 can be in a conducting state, and the first outer tube T1 and the second outer tube T4 can be in a closed state. In the second state, the first inner tube and the first clamping tube can be in a conducting state, and all other switching tubes except the first inner tube T2 and the first clamping tube T5 can be in a closed state; or, the second inner tube T3 and the second clamping tube T6 can be in a conducting state, and all other switching tubes except the second inner tube T3 and the second clamping tube T6 can be in a closed state.

[0087] Furthermore, in embodiments of this disclosure, the rotor speed can be determined by receiving sensing signals from an encoder installed on the doubly-fed wind turbine; and determining the rotor speed based on the sensing signals. Specifically, the encoder can sense the rotational speed of the wind turbine, and the converter's control system can communicate with the encoder to receive the sensed signals from the encoder, determine the current rotor speed, and thus switch to the corresponding control mode according to the rotor speed.

[0088] The control logic of the converter according to embodiments of the present disclosure at different rotor speeds has been described above. The specific process example of implementing the on / off control of each switch tube will be described below with reference to Figures 7 to 10.

[0089] During the control process of the converter, a three-phase modulation wave corresponding to each three-level bridge arm can be generated based on the operating data of the three-level converter.

[0090] As an example, the parameters of the three-phase modulation wave corresponding to the three-level bridge arm can be determined first based on the operating data of the three-level converter, and the corresponding three-phase modulation wave can be generated based on these parameters. Here, the operating data of the three-level converter may include, but is not limited to, at least one of the following: DC bus voltage, generator-side AC voltage, grid-side AC voltage, and output current of the three-level bridge arm.

[0091] Furthermore, the three-phase modulated wave can be, for example, including but not limited to, a sine wave, or other types of three-phase modulated waves. Parameters of the three-phase modulated wave can include, for example, amplitude, phase, and frequency.

[0092] Based on the three-phase modulation wave and carrier wave corresponding to each three-level bridge arm, modulation signals for controlling each switching transistor of the three-level bridge arm can be generated. For example, each switching transistor can be controlled by a PWM waveform.

[0093] Here, a corresponding carrier can be generated based on the carrier's parameters. For example, carrier parameters can include amplitude, phase, frequency, etc. The type of carrier can include, but is not limited to, two layers of triangular carriers with the same frequency and phase, or other types of carriers can be used.

[0094] As an example, as shown in Figure 7, the three-phase modulated wave Us can be generated based on the grid-side voltage using coordinate transformations such as the dq coordinate system. Specifically, data such as the DC voltage Udc of the converter, the AC voltage Uabc of the machine side and the grid side, and the module current Iabc can be collected by an analog-to-digital converter, and the three-phase modulated wave data can be generated after calculation by a preset internal control algorithm.

[0095] In addition, a co-directional carrier modulation method can be used to obtain the driving pulse for the power device. When the amplitude of the positive half-wave of the modulation wave is greater than that of the upper carrier wave, a positive level is output; when the amplitude of the negative half-wave of the modulation wave is less than that of the lower carrier wave, a negative level is output; otherwise, a 0 level is output.

[0096] For example, after comparing the modulated wave with the carrier wave, initial PWM waveforms of the first outer transistor T1, the first inner transistor T2, and the second clamping transistor T6 can be generated. After adding a dead time, PWM waveforms of the first clamping transistor T5, the second inner transistor T3, and the second outer transistor T4 can be generated. The pulses of the first outer transistor T1 and the first clamping transistor T5 are complementary, the pulses of the second clamping transistor T6 and the second outer transistor T4 are complementary, and the pulses of the first inner transistor T2 and the second inner transistor T3 are complementary.

[0097] Specifically, the pulse generation method of the three-level converter in the exemplary embodiment of this disclosure is as follows: During the positive half-cycle of the modulation wave, when the modulation wave is greater than the triangular carrier wave, a positive level is output, switches T1 and T2 are turned on, and other switches are turned off; when the modulation wave is less than the triangular carrier wave, a 0 level is output, switches T2, T3, T5, and T6 are turned on, and other switches are turned off. During the negative half-cycle of the modulation wave, when the modulation wave is less than the triangular carrier wave, a negative level is output, switches T3 and T4 are turned on, and other switches are turned off; when the modulation wave is greater than the triangular carrier wave, a 0 level is output, switches T2, T3, T5, and T6 are turned on, and other switches are turned off.

[0098] As an example, as shown in Figure 8, the PWM waveforms used to control each switching transistor can be generated in the following way:

[0099] In step S810, based on the comparison result of the three-phase modulation wave and the carrier wave, a PWM waveform for controlling the first outer tube T1 during the positive half-cycle of the three-phase modulation wave and a PWM waveform for controlling the first inner tube T2 during the positive half-cycle can be generated.

[0100] In step S820, a PWM waveform for controlling the first clamping transistor T5 in the positive half-cycle can be generated based on the PWM waveform used to control the first external transistor T1 in the positive half-cycle.

[0101] In step S830, a PWM waveform for controlling the second inner tube T3 in the positive half-cycle can be generated based on the PWM waveform used to control the first inner tube T2 in the positive half-cycle.

[0102] In step S840, a PWM waveform for turning off the second external transistor T4 during the positive half-cycle and a PWM waveform for turning off the second clamping transistor T6 during the positive half-cycle can be generated.

[0103] As an example, the PWM waveform used to control the first outer transistor T1 is complementary to the PWM waveform used to control the first clamping transistor T5; the PWM waveform used to control the first inner transistor T2 is complementary to the PWM waveform used to control the second inner transistor T3; in addition, the PWM waveform used to control the second outer transistor T4 is complementary to the PWM waveform used to control the second clamping transistor T6, which is turned off in the positive half-cycle and is complementary in the negative half-cycle.

[0104] As shown in Figure 9, S1, S2, S3, S4, S5, and S6 represent the PWM waveforms for switching transistors T1, T2, T3, T4, T5, and T6, respectively. Ao The voltage waveform of phase A is represented. During the positive half-cycle of the modulation wave, the first inner transistor T2 is always on according to the comparison result between the modulation wave and the upper half-carrier. The first outer transistor T1 is controlled to turn on and off according to the comparison result between the modulation wave and the upper half-carrier. That is, the initial PWM waveforms T1 and T2 are generated after the modulation wave is compared with the carrier. After adding the dead time, the PWM waveforms of the first clamping transistor T5 and the second inner transistor T3 are generated. The pulses of the first outer transistor T1 and the first clamping transistor T5 are complementary, and the pulses of the first inner transistor T2 and the second inner transistor T3 are complementary, thus forming the control pulses of T1 / T2 / T3 / T5.

[0105] As an example, as shown in Figure 10, PWM waveforms for controlling each switching transistor can also be generated in the following way:

[0106] In step S1010, based on the comparison result of the three-phase modulation wave and the carrier wave, a PWM waveform for controlling the second clamping tube T6 during the negative half-cycle of the three-phase modulation wave and a PWM waveform for controlling the second inner tube T3 during the negative half-cycle can be generated.

[0107] In step S1020, a PWM waveform for controlling the second external transistor T4 in the negative half-cycle can be generated based on the PWM waveform used to control the second clamping transistor T6 in the negative half-cycle.

[0108] In step S1030, a PWM waveform for controlling the first inner tube T2 in the negative half-cycle can be generated based on the PWM waveform used to control the second inner tube T3 in the negative half-cycle.

[0109] In step S1040, a PWM waveform for turning off the first external transistor T1 during the negative half-cycle and a PWM waveform for turning off the first clamping transistor T5 during the negative half-cycle can be generated.

[0110] As an example, the PWM waveform used to control the second outer tube T4 is complementary to the PWM waveform used to control the second clamping tube T6; the PWM waveform used to control the second inner tube T3 is complementary to the PWM waveform used to control the first inner tube T2.

[0111] Figures 11A and 11B are schematic diagrams illustrating the effects of a control method for a converter according to exemplary embodiments of the present disclosure. Figure 11A shows test results obtained using a conventional control algorithm, and Figure 11B shows test results obtained using a control algorithm according to the present disclosure. The horizontal axis represents time (in seconds), and the vertical axis represents temperature (in degrees Celsius).

[0112] As shown in Figure 11A, in the modulation method of the related technology, the highest temperature of the switching transistor in the three-level bridge arm can reach 73.6 degrees Celsius, which is close to the preset over-temperature protection value of 75 degrees Celsius for power devices. However, as shown in Figure 11B, when using the control method of the exemplary embodiment of this disclosure, the highest temperature of the switching transistor in the three-level bridge arm is reduced to 58 degrees Celsius. Therefore, it can be seen that the above-described control method according to the embodiments of this disclosure can solve the problem of localized overheating of the switching transistor at synchronous speed by optimizing the modulation logic of the three-level bridge arm.

[0113] A second aspect of the present disclosure provides a control system for a converter, the control system comprising: a processor; and a memory for storing processor-executable instructions, wherein the processor-executable instructions, when executed by the processor, cause the processor to perform a control method for the converter according to an embodiment of the present disclosure.

[0114] As an example, the control system may include an electronic device having the aforementioned processor and memory. This electronic device may be a PC, tablet, personal digital assistant, smartphone, or other device capable of executing the aforementioned set of instructions. Here, the electronic device is not necessarily a single device; it may be any collection of devices or circuits capable of executing the aforementioned instructions (or instruction sets) individually or in combination. The electronic device may also be part of an integrated control system or system manager, or may be configured to interface with a portable electronic device locally or remotely (e.g., via wireless transmission).

[0115] In electronic devices, a processor may include a central processing unit (CPU), a graphics processing unit (GPU), a programmable logic device, a dedicated processor system, a microcontroller, or a microprocessor. By way of example and not limitation, a processor may also include analog processors, digital processors, microprocessors, multi-core processors, processor arrays, network processors, etc.

[0116] The processor can execute instructions or code stored in memory, which can also store data. Instructions and data can also be sent and received over a network via a network interface device, which can employ any known transport protocol.

[0117] Memory can be integrated with the processor; for example, RAM or flash memory can be housed within an integrated circuit microprocessor. Alternatively, memory can comprise a separate device, such as an external disk drive, storage array, or other storage device that can be used by any database system. Memory and processor can be operatively coupled, or can communicate with each other, for example, via I / O ports, network connections, etc., enabling the processor to read files stored in the memory.

[0118] In addition, electronic devices may include video displays (such as liquid crystal displays) and user interaction interfaces (such as keyboards, mice, touch input devices, etc.). All components of the electronic device may be interconnected via buses and / or networks.

[0119] A third aspect of an embodiment of the present disclosure provides a converter, the converter including a control system for the converter according to an embodiment of the present disclosure.

[0120] A fourth aspect of the embodiments of the present disclosure provides a wind turbine generator set, the wind turbine generator set including a doubly fed wind turbine generator and a converter according to the embodiments of the present disclosure.

[0121] A fifth aspect of the present disclosure provides a computer-readable storage medium that, when instructions in the computer-readable storage medium are executed by a processor of an electronic device, enables the electronic device to perform a control method for a converter according to an embodiment of the present disclosure.

[0122] Specifically, the converter control method according to embodiments of the present disclosure can be programmed into a computer program and stored on a computer-readable storage medium. When the instructions in the computer-readable storage medium are executed by at least one processor, the at least one processor is caused to perform the converter control method according to exemplary embodiments of the present disclosure. Examples of computer-readable storage media include: read-only memory (ROM), random access programmable read-only memory (PROM), electrically erasable programmable read-only memory (EEPROM), random access memory (RAM), dynamic random access memory (DRAM), static random access memory (SRAM), flash memory, non-volatile memory, CD-ROM, CD-R, CD+R, CD-RW, CD+RW, DVD-ROM, DVD-R, DVD+R, DVD-RW, DVD+RW, DVD-RAM, BD-ROM, BD-R, BD-R LTH, BD-RE, Blu-ray or optical disc storage, hard disk drive (HDD), solid-state drive (SSD), card storage (such as multimedia cards, secure digital (SD) cards, or ultra-fast digital (XD) cards), magnetic tape, floppy disk, magneto-optical data storage device, optical data storage device, hard disk, solid-state drive, and any other device configured to store a computer program and any associated data, data files, and data structures in a non-transitory manner and to provide the computer program and any associated data, data files, and data structures to a processor or computer so that the processor or computer can execute the computer program. In one example, the computer program and any associated data, data files, and data structures are distributed across a networked computer system, such that the computer program and any associated data, data files, and data structures are stored, accessed, and executed in a distributed manner through one or more processors or computers.

[0123] A sixth aspect of the present disclosure provides a computer program product including computer-executable instructions that, when executed by at least one processor, implement the converter control method according to the embodiments of the present disclosure.

[0124] The specific embodiments of this disclosure have been described in detail above. Although some embodiments have been shown and described, those skilled in the art should understand that modifications and variations can be made to these embodiments without departing from the principles and spirit of this disclosure, which are defined by the claims and their equivalents. Such modifications and variations should also be within the protection scope of the claims of this disclosure.

Claims

1. A control method for a converter, characterized in that, The converter is applied to a doubly-fed wind turbine. The converter includes multiple three-level bridge arms, each three-level bridge arm including multiple switching transistors, the multiple switching transistors including two inner transistors, two outer transistors, and two clamping transistors. The control method includes: Determine the current rotor speed of the doubly-fed wind turbine; and In response to the difference between the rotor speed and the synchronous speed of the doubly-fed wind turbine being less than a preset threshold, the state of multiple switching transistors in each three-level bridge arm is controlled in the following manner: In response to receiving a first modulation signal for switching the output level of the three-level bridge arm from a positive level to a midpoint level or a second modulation signal for switching the output level from a negative level to a midpoint level, the currently conducting outer tube is turned off, and each clamping tube and each inner tube is turned on when the conducting outer tube is turned off.

2. The control method according to claim 1, characterized in that, Each three-level bridge arm includes an upper half-bridge arm and a lower half-bridge arm. The upper half-bridge arm includes a first inner tube of the two inner tubes, a first outer tube of the two outer tubes, and a first clamping tube of the two clamping tubes. The lower half-bridge arm includes a second inner tube of the two inner tubes, a second outer tube of the two outer tubes, and a second clamping tube of the two clamping tubes. The control method further includes: In response to the difference between the rotor speed and the synchronous speed of the doubly-fed wind turbine exceeding a preset threshold, the state of multiple switching transistors in each three-level bridge arm is controlled in the following manner: In response to receiving the first modulation signal, the first outer tube is turned off, and while the first outer tube is turned off, the first clamping tube is turned on; and while the first clamping tube is turned on, the second clamping tube and the two inner tubes are turned on; and In response to receiving the second modulation signal, the second outer tube is turned off, and the second clamping tube is turned on when the second outer tube is turned off; and the first clamping tube and the two inner tubes are turned on when the second clamping tube is turned on.

3. The control method according to claim 1, characterized in that, The control method further includes: In response to the difference between the rotor speed and the synchronous speed of the doubly-fed wind turbine exceeding a preset threshold, the state of multiple switching transistors in each three-level bridge arm is controlled in the following manner: In response to receiving the first modulation signal or the second modulation signal, the currently conducting outer tube is turned off, and when the conducting outer tube is turned off, each clamping tube and each inner tube are turned on.

4. The control method according to any one of claims 1 to 3, characterized in that, In response to the difference being less than the preset threshold, for each three-level bridge arm, the state of multiple switching transistors in that three-level bridge arm is also controlled in the following manner: In response to receiving a third modulation signal for switching the output level of the three-level bridge arm from the midpoint level to the positive level, the second inner tube and each clamping tube of the three-level bridge arm are turned off, and the first outer tube of the three-level bridge arm is turned on while the second inner tube and each clamping tube are turned off; as well as In response to receiving a fourth modulation signal for switching the output level of the three-level bridge arm from the midpoint level to the negative level, the first inner tube and each clamping tube of the three-level bridge arm are turned off, and the second outer tube of the three-level bridge arm is turned on while the first inner tube and each clamping tube are turned off.

5. The control method according to claim 1, characterized in that, Each three-level bridge arm includes an upper bridge arm and a lower bridge arm. The upper bridge arm includes a first inner tube of the two inner tubes, a first outer tube of the two outer tubes, and a first clamping tube of the two clamping tubes. The lower bridge arm includes a second inner tube of the two inner tubes, a second outer tube of the two outer tubes, and a second clamping tube of the two clamping tubes. Specifically, when the difference is less than the preset threshold and the output level of the three-level bridge arm is the midpoint level, each switch is controlled to be in the first state. When the difference is greater than the preset threshold and the output level of the three-level bridge arm is the midpoint level, each switch is controlled to be in the first state or the second state, and In the first state, the first inner tube, the second inner tube, the first clamping tube, and the second clamping tube are in a conductive state, while the first outer tube and the second outer tube are in a closed state. In the second state, the first inner tube and the first clamping tube are in a conducting state, and all other switching tubes except the first inner tube and the first clamping tube are in a turning-off state; or, the second inner tube and the second clamping tube are in a conducting state, and all other switching tubes except the second inner tube and the second clamping tube are in a turning-off state.

6. The control method according to claim 1, characterized in that, When the difference is less than the preset threshold, the state of each three-level bridge arm is controlled based on the first control mode, and If the difference exceeds the preset threshold, the state of each three-level bridge arm is controlled based on the second control mode. The state of the three-level bridge arm refers to the combination of the sub-states of each of the multiple switching transistors in the three-level bridge arm. The number of states that each three-level bridge arm switches to in the first control mode is different from the number of states that switch to in the second control mode.

7. The control method according to claim 1, characterized in that, The rotor speed is determined in the following manner: Receive sensing signals from the encoder installed on the doubly-fed wind turbine; and The rotor speed is determined based on the sensed signal.

8. The control method according to claim 1, characterized in that, Each three-level bridge arm includes an upper half-bridge arm and a lower half-bridge arm. The upper half-bridge arm includes a first inner tube among the two inner tubes, a first outer tube among the two outer tubes, and a first clamping tube among the two clamping tubes. The lower half-bridge arm includes a second inner tube among the two inner tubes, a second outer tube among the two outer tubes, and a second clamping tube among the two clamping tubes. The modulation signal is generated based on a three-phase modulation wave and a carrier wave, and each switching transistor is controlled by a pulse width modulation (PWM) waveform. Specifically, for each three-level bridge arm, the PWM waveform used to control multiple switching transistors in that three-level bridge arm is generated in the following manner: Based on the comparison result between the three-phase modulation wave and the carrier wave, a PWM waveform for controlling the first outer tube during the positive half-cycle of the three-phase modulation wave and a PWM waveform for controlling the first inner tube during the positive half-cycle are generated. Based on the PWM waveform used to control the first external transistor in the positive half-cycle, a PWM waveform used to control the first clamping transistor in the positive half-cycle is generated. Based on the PWM waveform used to control the first inner transistor during the positive half-cycle, a PWM waveform used to control the second inner transistor during the positive half-cycle is generated; and Generate a PWM waveform for turning off the second external transistor and the second clamping transistor during the positive half-cycle.

9. The control method according to claim 8, characterized in that, For each three-level bridge arm, a PWM waveform for controlling multiple switching transistors in that three-level bridge arm is also generated in the following manner: Based on the comparison result of the three-phase modulation wave and the carrier wave, a PWM waveform for controlling the second clamping transistor during the negative half-cycle of the three-phase modulation wave and a PWM waveform for controlling the second inner transistor during the negative half-cycle are generated. Based on the PWM waveform used to control the second clamping transistor in the negative half-cycle, a PWM waveform used to control the second external transistor in the negative half-cycle is generated. Based on the PWM waveform used to control the second inner transistor during the negative half-cycle, a PWM waveform used to control the first inner transistor during the negative half-cycle is generated; and Generate a PWM waveform for turning off the first external transistor during the negative half-cycle and a PWM waveform for turning off the first clamping transistor during the negative half-cycle.

10. A control system for a converter, characterized in that, The control system includes: Processor; and Memory used to store processor-executable instructions. Wherein, when the processor executes the processor instructions, it causes the processor to perform the converter control method according to any one of claims 1 to 9.

11. A converter, characterized in that, The converter includes a control system for the converter according to claim 10.

12. A wind turbine generator set, characterized in that, The wind turbine generator set includes a doubly fed wind turbine generator and a converter according to claim 11.

13. A computer-readable storage medium, characterized in that, When the instructions in the computer-readable storage medium are executed by the processor of the electronic device, the electronic device is able to perform the control method of the converter according to any one of claims 1 to 9.

14. A computer program product comprising computer-executable instructions, characterized in that, When the computer-executable instructions are executed by at least one processor, they implement the control method for the converter according to any one of claims 1 to 9.

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