A virtual space vector modulation method suitable for a parallel converter of a doubly-fed wind power generation system
By using the virtual space vector modulation method, the challenges of zero-sequence circulating current and midpoint voltage control in high-power doubly-fed wind power generation systems have been solved, thereby improving power quality and stability, extending equipment lifespan, and reducing maintenance costs.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- HUANENG RUDONG BAXIANJIAO OFFSHORE WIND POWER GENERATION CO LTD
- Filing Date
- 2025-07-01
- Publication Date
- 2026-05-26
AI Technical Summary
In high-power doubly-fed wind power generation systems, there are problems such as three-phase current imbalance, uneven DC current input and output, zero-sequence circulating current, and midpoint potential fluctuation. Traditional modulation strategies are difficult to simultaneously and effectively suppress zero-sequence circulating current and accurately control the midpoint voltage.
The virtual space vector modulation method is adopted. By redefining the voltage vector as a virtual zero vector, virtual small vector, virtual medium vector and virtual large vector, the voltage vector space is divided into six major sectors and further subdivided into five regions. The synthetic vector is selected according to the reference voltage vector region and the action time is calculated. Combined with the control factor and transformation coefficient, the midpoint voltage balance and zero-sequence circulating current suppression are achieved.
It effectively balances midpoint voltage balance and zero-sequence circulating current suppression, improves system power quality and stability, reduces equipment failure risk and maintenance costs, and enhances the system's adaptability to complex operating conditions.
Smart Images
Figure CN120582476B_ABST
Abstract
Description
Technical Field
[0001] This application relates to the field of excitation converter equipment technology for doubly fed wind power generation systems, and in particular to a virtual space vector modulation method and system applicable to parallel converters in doubly fed wind power generation systems. Background Technology
[0002] High-power doubly-fed wind power generation systems often employ back-to-back three-level converters to improve power capacity and power quality. However, due to differences in converter hardware parameters, inconsistencies in control algorithm execution, and the inherent power fluctuation characteristics of wind power generation, the system is prone to problems such as three-phase current imbalance and uneven DC-side current input and output, which in turn lead to zero-sequence circulating current, midpoint potential fluctuations, and harmonic distortion.
[0003] Traditional SVPWM strategies have limited midpoint voltage regulation capabilities when operating at high modulation speeds or low power factors, resulting in an incompletely balanced operating range. Furthermore, midpoint voltage control and zero-sequence circulating current suppression are coupled. While traditional VSVPWM strategies can achieve midpoint voltage balance across the entire range, they do not consider zero-sequence circulating current suppression, making it difficult to meet the stability and power quality requirements of high-power wind power generation systems. Therefore, there is an urgent need for a modulation strategy that can effectively suppress zero-sequence circulating current and precisely control the midpoint voltage to meet the high-performance operation requirements of high-power wind power generation systems. Summary of the Invention
[0004] The purpose of this application is to overcome the shortcomings of the prior art and provide a virtual space vector modulation method and system suitable for parallel converters in doubly fed wind power generation systems.
[0005] In a first aspect, this application provides a virtual space vector modulation method suitable for parallel converters in a doubly-fed wind power generation system, comprising the following steps:
[0006] Classify voltage vectors;
[0007] By using control factors and transformation coefficients, the voltage vector is defined as a virtual vector in the voltage vector space. The virtual vector includes a virtual zero vector, a first virtual small vector, a second virtual small vector, a virtual medium vector, a first virtual large vector, and a second virtual large vector.
[0008] The voltage vector space is divided into six sectors along the circumference, and based on the virtual space vector, the six sectors are further divided into five vector regions.
[0009] Based on the vector region where the reference voltage vector is located, the three virtual vectors that are closest to the reference voltage vector are selected as composite vectors to participate in vector synthesis, and the action time of the three composite vectors is obtained.
[0010] Depending on whether the virtual vector participates in vector synthesis, different modulation strategies are selected for control;
[0011] Calculate the midpoint voltage fluctuation value of the DC bus and set an allowable threshold for the midpoint voltage fluctuation value. Compare the midpoint voltage fluctuation value with the allowable threshold. When the midpoint voltage fluctuation value is within the allowable threshold range, perform zero-sequence circulating current suppression. When the midpoint voltage fluctuation value is outside the allowable threshold range, perform midpoint voltage control.
[0012] Optionally, classifying the voltage vector includes: dividing the voltage vector into a first vector, a second vector, a third vector, a fourth vector, and a fifth vector.
[0013] Optionally, the voltage vector space is divided into six sectors along a circumference, and based on the virtual space vector, the six sectors are further divided into five vector regions, including:
[0014] The voltage vector space is divided into six major sectors along a circle, including the first major sector, the second major sector, the third major sector, the fourth major sector, the fifth major sector, and the sixth major sector.
[0015] By using vectorized equations, the first large sector is divided into five vector regions.
[0016] By transforming the second, third, fourth, fifth, and sixth major sectors into the first major sector, and then dividing them according to the vectorized fractional equation, five vector regions are obtained.
[0017] Optionally, the voltage vector space is divided into six sectors along a circumference, including: every 60... o Divided into one large region, starting from 0 o They are numbered sequentially as follows: Ⅰ, Ⅱ, Ⅲ, Ⅳ, Ⅴ, Ⅵ.
[0018] Optionally, the step of selecting different modulation strategies for control based on whether the virtual vector participates in vector synthesis includes:
[0019] When the virtual vector does not participate in vector synthesis, control is achieved by adjusting the action time of the redundant small vectors of the first and second virtual small vectors;
[0020] When the virtual vectors participate in vector synthesis, control is achieved by adjusting the control factor.
[0021] Optionally, the zero-sequence circulation suppression includes:
[0022] When the zero-sequence circulating current is greater than zero, the control factors of the first virtual small vector and the second virtual small vector are changed to reduce the action time of the second vector, thereby reducing the zero-sequence voltage output by the parallel converter;
[0023] When the zero-sequence circulating current is less than zero, the zero-sequence voltage output by the parallel converter is increased by changing the control factors of the first virtual small vector and the second virtual small vector.
[0024] Optionally, the midpoint voltage control includes:
[0025] Based on the phase relationship between the midpoint currents of the second and third vectors, the transformation coefficients of the virtual small vector are determined.
[0026] Based on the transformation coefficients, calculate the midpoint charge output under the action of the first virtual small vector, the second virtual small vector, the virtual medium vector, the first virtual large vector, and the second virtual large vector;
[0027] Based on the midpoint charge, the values of the control factors in each vector are further determined.
[0028] Optionally, the midpoint voltage control further includes:
[0029] When the midpoint voltage fluctuation exceeds the lower limit of the allowable threshold, the lower capacitor voltage is reduced through midpoint voltage balancing control to obtain the value of the control factor.
[0030] When the midpoint voltage fluctuation exceeds the upper limit of the allowable threshold, the voltage of the upper capacitor is reduced through midpoint voltage balancing control to obtain the value of the control factor.
[0031] Optionally, the vector region is defined in the gh coordinate system.
[0032] Secondly, this application also provides a virtual space vector modulation system suitable for parallel converters in a doubly-fed wind power generation system. The virtual space vector modulation system for parallel converters in a doubly-fed wind power generation system includes: a drive circuit, a drive motor, and a modulation module. The drive circuit obtains electrical energy from the power grid via a first transformer and outputs current to the drive motor. The drive circuit includes multiple converter branches connected in parallel. The modulation module integrates a virtual space vector modulation method for parallel converters in a doubly-fed wind power generation system as described in any one of the first aspects. The modulation module is used to output the control factor and transformation coefficient to a drive signal generator, thereby driving the switches in the converter branches.
[0033] This application provides a virtual space vector modulation method and system applicable to parallel converters in doubly-fed wind power generation systems. By controlling factors and transformation coefficients, the virtual vector is redefined, and various methods are used to improve vector modulation, effectively balancing midpoint voltage balance and zero-sequence circulating current suppression. Through special partitioning and calculation methods, the amount of computation is reduced, the operation time is shortened, and the processor requirements are reduced, effectively improving the midpoint voltage balance control and zero-sequence circulating current suppression effect of parallel three-level converters in high-power doubly-fed wind power generation systems.
[0034] To make the above-mentioned features and advantages of the invention more apparent and understandable, specific embodiments are described below, and detailed descriptions are provided in conjunction with the accompanying drawings. Attached Figure Description
[0035] To more clearly illustrate the technical solutions in the embodiments or related technologies of this application, the accompanying drawings used in the description of the embodiments or related technologies will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.
[0036] Figure 1 This is a flowchart of a virtual space vector modulation method for parallel converters in a doubly fed wind power generation system, provided in one embodiment of this application.
[0037] Figure 2 This is a voltage vector space partitioning diagram of the first large sector and first vector region in step S30 of a virtual space vector modulation method for parallel converters in a doubly fed wind power generation system provided in one embodiment of this application.
[0038] Figure 3 This is a schematic diagram of a virtual space vector modulation system for parallel converters in a doubly fed wind power generation system, provided in yet another embodiment.
[0039] Figure 4 This is a simulation waveform diagram of midpoint voltage balance control provided in another embodiment of this application.
[0040] Figure 5 This is a simulation waveform diagram of zero-sequence circulating current suppression provided in another embodiment of this application. Detailed Implementation
[0041] To make the objectives and technical solutions of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this application. All other embodiments obtained by those skilled in the art based on the described embodiments of this application without creative effort are within the scope of protection of this application.
[0042] In one embodiment, see Figure 1 This application provides a virtual space vector modulation method for parallel converters in a doubly fed wind power generation system, comprising the following steps: S10~S60.
[0043] S10: Classify voltage vectors.
[0044] S20: By controlling the factor and transforming the coefficient, the voltage vector is defined as a virtual vector in the voltage vector space. The virtual vector includes a virtual zero vector, a first virtual small vector, a second virtual small vector, a virtual medium vector, a first virtual large vector, and a second virtual large vector.
[0045] S30: Divide the voltage vector space into six sectors on a circular basis, and further divide the six sectors into five vector regions based on the virtual space vector.
[0046] S40: Based on the vector region where the reference voltage vector is located, select the three virtual vectors that are closest to the reference voltage vector as composite vectors to participate in vector synthesis, and obtain the action time of the three composite vectors.
[0047] S50: Select different modulation strategies for control based on whether the virtual vector participates in vector synthesis.
[0048] S60: Calculate the midpoint voltage fluctuation value of the DC bus, and set the allowable threshold value of the midpoint voltage fluctuation value. Compare the midpoint voltage fluctuation value with the allowable threshold value. When the midpoint voltage fluctuation value is within the allowable threshold value range, perform zero-sequence circulating current suppression. When the midpoint voltage fluctuation value is outside the allowable threshold value range, perform midpoint voltage control.
[0049] This application presents a virtual space vector modulation method for parallel converters in a doubly-fed wind power generation system. By classifying voltage vectors, the characteristics of different types of voltage vectors can be clearly identified, laying the foundation for precise processing based on these characteristics. Redefining the virtual vector using control factors and transformation coefficients allows for flexible adjustment of virtual vector parameters to adapt to different operating conditions. Dividing the voltage vector space allows for precise location of the reference voltage vector region, making the selection of the nearest synthesized vector more accurate, reducing error accumulation, and improving modulation accuracy. Selecting and calculating the action time of the synthesized vector based on the reference voltage vector allows for precise allocation of vector action time according to actual needs, ensuring stable and expected output voltage and effectively reducing voltage fluctuations. Classifying the modulation region based on whether the virtual vector participates in modulation helps to formulate specific modulation rules for different regions, enhancing the targeting and effectiveness of modulation. Zero-sequence circulating current suppression reduces circulating current interference, reduces line heating and energy loss, and improves overall system energy efficiency. Midpoint voltage control allows for precise adjustment of the capacitor midpoint voltage, preventing equipment failures caused by voltage imbalance and extending equipment lifespan. The method described in this application can effectively balance the voltage balance at the capacitor midpoint and suppress zero-sequence circulating current, thereby improving the power quality and operational stability of the system, extending the service life of the equipment, reducing maintenance costs, and enhancing the system's adaptability to complex operating conditions.
[0050] In step S10, please refer to Figure 1 In step S10, the voltage vectors are classified.
[0051] As an example, the voltage vector output by the parallel converter in the basic space can be divided into zero vector, positive small vector, negative small vector, medium vector, and large vector. The five types of voltage vectors and their corresponding output voltage magnitudes are shown in Table 1.
[0052] Table 1. Five voltage vectors and their corresponding output voltage magnitudes
[0053]
[0054] Where P is the positive terminal of the DC bus, N is the negative terminal of the DC bus, and O is the midpoint of the DC bus. U dc Representing the DC bus voltage, the zero vector can include PPP, OOO, NNN; the positive small vector can include POO, PPO, OPO, OPP, OOP, POP; the negative small vector can include ONN, OON, NON, NOO, NNO, ONO; the medium vector can include PON, OPN, NPO, NOP, ONP, PNO; and the large vector can include PNN, PPN, NPN, NPP, NNP, PNP.
[0055] In step S20, please refer to Figure 1 In step S20, the voltage vector is defined as a virtual vector in the voltage vector space by controlling the factor and the transformation coefficient. The virtual vector includes a virtual zero vector, a first virtual small vector, a second virtual small vector, a virtual medium vector, a first virtual large vector, and a second virtual large vector.
[0056] As an example, using control factors k , j Transformation coefficients s Redefine the voltage vector and transform it into a virtual zero vector in the voltage vector space. First virtual small vector Second virtual small vector Virtual vector First virtual large vector Second virtual large vector This can be achieved using the following formula:
[0057]
[0058] in, For the control factors of virtual small vectors and virtual large vectors, Let be the control factor in the virtual vector, and satisfy . , Let be the transformation coefficients, and satisfy... , This is the vector in the basic space voltage vector where the output voltage magnitude is zero. , The phase difference is 60 in the basic space voltage vector o Two positive small vectors, , The phase difference is 60 in the basic space voltage vector o Two negative small vectors, , , The phase difference is 120 in the basic space voltage vector. o The three median vectors, , The phase difference is 60 in the basic space voltage vector o Two large vectors.
[0059] In step S30, please refer to Figure 1 In step S30, the voltage vector space is divided into six sectors along the circumference, and based on the virtual space vector, the six sectors are further divided into five vector regions.
[0060] As an example, the voltage vector space is divided into six sectors along the circumference, each 60... o Divided into one large region, starting from 0o They can be numbered sequentially as: Ⅰ, Ⅱ, Ⅲ, Ⅳ, Ⅴ, Ⅵ.
[0061] As an example, based on the defined virtual space vector, the voltage vector space is divided using a vector partitioning equation, resulting in five vector regions. For instance, the first large sector can be divided into vector regions: I1, I2, I3, I4, and I5. The vector partitioning equation can be expressed as follows:
[0062]
[0063] in, V g Reference voltage vector V ref The horizontal projection length in the gh coordinate system; V h Reference voltage vector V ref The vertical projection length in the gh coordinate system. The reference voltage vector can be set according to the voltage vector.
[0064] In one example, see Figure 2 This is the voltage vector space partitioning diagram for the first vector region I1 of the first large sector. It uses a virtual zero vector. V Z0 Starting from the first virtual small vector V ZS1 With the first virtual large vector V ZL1 Same direction, second virtual small vector V ZS2 With the second virtual large vector V ZL2 With the same direction, the virtual small vector and the virtual large vector form an angle of 60°. o Virtual vector V ZM Between the virtual small vector and the virtual large vector. Virtual zero vector. V Z0 Second virtual small vector V ZS2 First virtual small vector V ZS1 Forming the I1 vector region, the second virtual small vector V ZS2 First virtual small vector V ZS1 Virtual vector V ZM The endpoints form a vector region I2, the first virtual small vector. V ZS1 First virtual large vector VZL1 Virtual vector V ZM The endpoints form the I3 vector region, the second virtual small vector. V ZS2 Second virtual large vector V ZL2 Virtual vector V ZM The endpoints form the I4 vector region, the first virtual large vector. V ZL1 Second virtual large vector V ZL2 Virtual vector V ZM The endpoints form the vector region I5.
[0065] As an example, the remaining five sectors can be transformed into the first major sector I through coordinate transformation and then divided, thus obtaining five vector regions after the division.
[0066] In step S40, please refer to Figure 1 In step S40, based on the vector region where the reference voltage vector is located, three virtual vectors closest to the reference voltage vector are selected as composite vectors to participate in vector synthesis, and the action time of the three composite vectors is obtained.
[0067] As an example, based on the reference voltage vector V ref The vector region in which it is located is selected to be the same as the reference voltage vector. V ref The three most recent virtual vectors are used as the composite vectors, and the duration of action of each of the three composite vectors is calculated. The formula for calculating the duration of action is shown below:
[0068]
[0069] in, V g Reference voltage vector V ref The horizontal projection length in the gh coordinate system; V h Reference voltage vector V ref The vertical projection length in the gh coordinate system T a , T b , T c These represent the durations of action of the three composite vectors; T s One switching cycle of the parallel converter; V1g , V 2g , V 3g Let be the length of the projection of the three composite vectors onto the g-axis. V 1h , V 2h , V 3h The projection length of the three composite vectors onto the h-axis.
[0070] As an example, the duration of the three composite vectors determines the contribution of each vector to the output voltage within a switching cycle. By precisely calculating and allocating the duration, the voltage waveform output by the parallel converter can be made closer to the waveform required by the reference voltage vector, thereby achieving precise control of the output voltage. The duration of the voltage vector of the output current can be increased by adjusting the duration to compensate for the midpoint charge and restore the midpoint voltage balance.
[0071] In step S50, please refer to Figure 1 In step S50, different modulation strategies are selected for control based on whether the virtual vector participates in vector synthesis.
[0072] As an example, when the reference vector is in the I1 region with a low modulation density, the virtual vector does not participate in vector composition. This is achieved by adjusting the first virtual small vector. V ZS1 and the second virtual small vector V ZS2 The control objective is achieved by minimizing the redundancy of the small vector action time. The I1 sector can be synthesized using the following formula:
[0073]
[0074] in, V ref For the reference voltage vector, k For the control factor of the virtual small vector, s For the transformation coefficients, V Z0 For virtual zero vector, V ZS1 For the first virtual small vector, V ZS2 For the second virtual small vector, V OOO This is the vector in the basic space voltage vector where the output voltage magnitude is zero. V POO , V PPO The phase difference is 60 in the basic space voltage vector o Two positive small vectors,V OON , V ONN The phase difference is 60 in the basic space voltage vector o Two negative small vectors, T s For one switching cycle of the parallel converter, T Z0 The duration of action of the virtual zero vector. T ZS1 The duration of action of the first virtual small vector. T ZS2 The duration of action of the second virtual small vector. i a The current of phase A output from the parallel converter. i c This represents the C-phase current output from the parallel converter. When this modulation strategy is used for zero-sequence circulating current suppression, the conversion coefficient... s = k When this modulation strategy is used for midpoint voltage balancing, the transformation coefficients... s Based on phase current i a , i c The positive or negative relationship between them determines this.
[0075] As an example, when the reference vector is in the I2~I5 region with a high modulation degree, the virtual vector participates in vector synthesis. Taking I3 as an example, by adjusting the control factor... k Zero-sequence circulation suppression is achieved by altering the action times of the positive and negative small vectors in the virtual small vector, and by changing the control factor in the virtual small vector. j The midpoint voltage is controlled. Sector I3 can be synthesized using the following formula:
[0076]
[0077] in, V ref For the reference voltage vector, k For the control factor of the virtual small vector, s For the transformation coefficients, j This refers to the control factor in the virtual vector. V ZM For virtual vectors, V ZL1 This is the first virtual large vector. V ZL2 For the second virtual large vector, V POO It is a small positive vector. V ONN negative small vector ，VPON , V PNO The phase difference in the basic space voltage vector is 120. o The two median vectors, V PNN For large vectors, V OPN It is the median vector. T s For one switching cycle of the parallel converter, T Z0 The duration of action of the virtual zero vector. T ZS1 The duration of action of the first virtual small vector. T ZS2 The duration of action of the second virtual small vector. T ZL1 The duration of action of the first virtual large vector. T ZL2 The duration of action of the second virtual large vector. i a The current of phase A output from the parallel converter. i c This refers to the C-phase current output by the parallel converter.
[0078] In step S60, please refer to Figure 1 In step S60, the midpoint voltage fluctuation value of the DC bus is calculated, and the allowable threshold value of the midpoint voltage fluctuation value is set. The midpoint voltage fluctuation value is compared with the allowable threshold value. When the midpoint voltage fluctuation value is within the allowable threshold value range, zero-sequence circulating current suppression is performed. When the midpoint voltage fluctuation value is outside the allowable threshold value range, midpoint voltage control is performed.
[0079] As an example, calculate the voltage fluctuation amplitude Δ at the midpoint of the parallel converter. U And set the allowable threshold H for the midpoint voltage fluctuation value, and compare the midpoint voltage fluctuation value Δ U The relationship between the value of the control target and the allowable threshold H determines the priority of the control target.
[0080] As an example, when the midpoint voltage fluctuation amplitude Δ U Within the allowable threshold H, i.e. When zero-sequence circulating current suppression is used as the primary control objective, the virtual small vector can be used. V ZS2 Transformation coefficients in s = k .
[0081] As an example, when zero-sequence circulation i Z1 When the value is greater than 0, the first virtual small vector is changed through the PI controller. VZS1 Second virtual small vector V ZS2 medium control factor k The value of is adjusted to reduce the duration of the positive small vector, thereby lowering the zero-sequence voltage output of the parallel converter. At this time, the control factor... k The range of values can be .
[0082] As an example, when zero-sequence circulation i Z1 When <0, the first virtual small vector is changed through the PI controller. V ZS1 Second virtual small vector V ZS2 medium control factor k The value of increases the duration of the positive small vector, thereby increasing the zero-sequence voltage output of the parallel converter. At this time, the control factor... k The range of values can be .
[0083] As an example, when the midpoint voltage fluctuation amplitude Δ U Outside the allowed threshold H range, i.e. When the midpoint voltage fluctuation exceeds the allowable threshold, the midpoint voltage balance control becomes the primary task, prioritizing the stabilization of the midpoint voltage.
[0084] As an example, based on small vectors V ONN and V PPO Output the phase relationship of the midpoint current and determine the transformation coefficients in the virtual small vector. s The value of . Virtual small vector V s2 Transformation coefficients in s The value of can be obtained using the following formula:
[0085]
[0086] in, i a , i c These are the A-phase and C-phase currents output from the parallel converter, respectively. s For the transformation coefficients, k This is a control factor.
[0087] As an example, calculate the control factor. k , j When taking different values, in the first virtual small vector V ZS1 Second virtual small vector VZS2 Virtual vector V ZM First virtual large vector V ZL1 Second virtual large vector V ZS2 Midpoint charge flowing out under the action Q ZS1 , Q ZS2 , Q ZM , Q ZL1 , Q ZL2 The calculation formula is as follows:
[0088]
[0089] in, i a The current of phase A output from the parallel converter. i b The B-phase current output by the parallel converter. i c This refers to the C-phase current output by the parallel converter. k These are the control factors in the virtual small and large vectors. j This refers to the control factor in the virtual vector. s For the transformation coefficients, T ZS1 , T ZS2 , T ZM , T L1 , T L2 These are the first virtual small vectors. V ZS1 Second virtual small vector V ZS2 Virtual vector V ZM First virtual large vector V L1 Second virtual large vector V L2 The duration of action.
[0090] As an example, based on the calculation results and the midpoint voltage fluctuation, the control factors in each vector are further determined. k , j The value of . V ZS1 For example, it can be determined using the following formula:
[0091]
[0092] Where, Δ U The midpoint voltage fluctuation amplitude represents the voltage difference between the upper and lower DC bus capacitors. C This is the DC bus capacitance value. T ZS1 For the first virtual small vector V ZS1 Duration of action T ZM For virtual vectors V ZM Duration of action i a This is the A-phase current output from the parallel converter. Because... V ZS1 , V ZS2 , V ZL1 and V ZL2 Control factor k The calculation method is the same; for details, please refer to the calculation method. V ZS1 The specific methods for controlling factors will not be elaborated here.
[0093] As an example, when When the voltage deviation H between the upper and lower capacitors exceeds the lower allowable limit, midpoint voltage balance control is performed to reduce the lower capacitor voltage. At this time, the voltage is determined based on the A-phase current. i a The positive and negative states change the control factor k , j The value of . If i a If the current is >0, the output current needs to be increased. i a The duration of action of the voltage vector, then k , j The range of values can be ;like i a If the value is less than 0, the output current needs to be reduced to [value missing]. i a The duration of action of the voltage vector, then k , j The range of values can be .
[0094] As an example, when When the voltage deviation H between the upper and lower capacitors exceeds the allowable upper limit, midpoint voltage balance control is performed to reduce the voltage of the upper capacitor. At this time, the voltage is determined based on the A-phase current. i aThe positive and negative states change the control factor k , j The value of . If i a If the value is >0, the output current needs to be reduced to [value missing]. i a The duration of action of the voltage vector, then k , j The range of values can be ;like i a If the current is less than 0, then the output current needs to be increased. i a The duration of action of the voltage vector, then k , j The range of values can be .
[0095] As an example, the vector region determination described in this application can be performed in the gh coordinate system, which avoids the large number of radical and trigonometric function operations required when solving in the rectangular coordinate system, effectively shortens the system's operation time, reduces the demand on the DSP processor, and saves costs.
[0096] As an example, the method of this application can be implemented using a three-level converter based on the VSVPWM strategy, and the load can be a resistive load, an inductive load, etc.
[0097] It should be understood that although the steps in the flowcharts of the accompanying drawings are shown sequentially according to the arrows, these steps are not necessarily executed in the order indicated by the arrows. Unless explicitly stated herein, there is no strict order restriction on the execution of these steps, and they can be executed in other orders. Moreover, at least some of the steps in the accompanying drawings may include multiple sub-steps or multiple stages. These sub-steps or stages are not necessarily completed at the same time, but can be executed at different times. The execution order of these sub-steps or stages is not necessarily sequential, but can be performed alternately or in turn with other steps or at least some of the sub-steps or stages of other steps.
[0098] See another example. Figure 3 This application also provides a virtual space vector modulation system suitable for parallel converters in a doubly-fed wind power generation system. The virtual space vector modulation system may include: a drive circuit 1 and a drive motor M, wherein the drive circuit 1 obtains electrical energy from the grid via a transformer T and outputs current to the drive motor M, causing the drive motor M to operate. The drive circuit 1 includes multiple converter branches connected in parallel, such as... Figure 3As shown, the plurality of converter branches include converter branch 11 and converter branch 12. The technical solution of the present invention can effectively suppress the zero-sequence circulating current between converter branch 11 and converter branch 12. Converter branch 11 includes an AC-DC converter module 111 and a DC-AC converter module 112, which are connected in series. The output of the DC-AC converter module 112 is connected to the drive motor M through a filter module 113. Converter branch 12 includes an AC-DC converter module 121 and a DC-AC converter module 122, which are connected in series. The output of the DC-AC converter module 122 is connected to the drive motor M through a filter module 123. The virtual space vector modulation system may further include: a modulation module 2, which integrates the virtual space vector modulation method applicable to parallel converters in a doubly-fed wind power generation system. The modulation module 2 outputs control factors k, j, and transformation coefficients s to a drive signal generator R_SVPWM2. Drive signal generators G_SVPWM1, G_SVPWM2, R_SVPWM1, and R_SVPWM2 are used to generate drive signals to drive the switches in converter branches 11 and 12. The modulation module 2 uses the voltage vector at the output of the DC-AC converter module 122, according to... Figure 1 The virtual space vector modulation method shown is applicable to parallel converters in doubly-fed wind power generation systems, calculating control factors k, j, and transformation coefficients s. This invention can effectively suppress... Figure 3 The zero-sequence circulating current in the medium current loop P, the virtual space vector modulation system also includes a current-limiting reactor L, bypass switches R_CB and G_CB, a drive motor M, and a transformer T. 11 Transformer T 12 Inductor L g .
[0099] As an example, the system in this application can be based on a high-power doubly-fed wind power generation system, and the topology of converter branch 11 and converter branch 12 can adopt an NPC three-level converter. The parallel converter of the high-power doubly-fed wind power generation system is simulated and analyzed using Matlab / Simulink software to verify its control performance under conditions such as wind speed fluctuations and grid voltage imbalance.
[0100] Please refer to the simulation results. Figure 4 This demonstrates the voltage U of the upper capacitor. C1 and lower capacitor voltage U C2 The voltage U of the capacitor changes over time. C1 The lower capacitor voltage U is represented by a solid black line. C2The gray dashed line represents time, with the horizontal axis representing time in seconds (s) and the vertical axis representing capacitor voltage in volts (V). The simulation results show that initially, the capacitor voltage U... C1 The voltage was approximately 450V. Over time, the voltage of the upper capacitor began to decrease after about 0.04 seconds, reaching its lowest point and stabilizing at approximately 400V after about 0.06 seconds. From 0.06 seconds to 0.2 seconds, the voltage of the upper capacitor remained essentially at around 400V. Initially, the voltage of the lower capacitor U... C2 The voltage of the upper capacitor is approximately 350V. Over time, the lower capacitor voltage begins to rise around 0.04 seconds, reaches its peak around 0.06 seconds, and then stabilizes at approximately 400V. From 0.06 seconds to 0.2 seconds, the lower capacitor voltage remains essentially at around 400V. Therefore, within the time interval of 0-0.06 seconds, the upper capacitor voltage drops from 450V to 400V, while the lower capacitor voltage rises from 350V to 400V, indicating a shift in the midpoint voltage. From 0.06 seconds to 0.08 seconds, both the upper and lower capacitor voltages rapidly converge towards 400V and stabilize, demonstrating a relatively fast dynamic recovery speed. From 0.06 seconds to 0.2 seconds, both the upper and lower capacitor voltages stabilize at approximately 400V, indicating that the upper and lower capacitor voltages remain balanced after the circuit reaches steady state. The method of this application not only achieves midpoint voltage balance across the entire range but also maintains a relatively fast dynamic recovery speed when the midpoint voltage shifts.
[0101] Please refer to the following: Figure 5 As can be seen from the waveform diagram of zero-sequence circulating current suppression based on VSVPWM strategy, the optimized modulation strategy of this application can achieve the goal of zero-sequence circulating current suppression.
[0102] In the virtual space vector modulation method applicable to parallel converters in a doubly-fed wind power generation system proposed in this application, the virtual zero vector, virtual small vector, virtual medium vector, and virtual large vector are redefined. The synthesized vector space is divided into two regions based on whether the virtual medium vector is used as the synthesized reference vector. The method is based on the principle of canceling out the neutral point charge of the DC bus capacitor and the zero-sequence circulating current of the voltage vector during the switching cycle, and a control factor is introduced. k , j With transformation coefficients s By changing the interaction time of redundant small vectors and virtual medium vectors in the virtual small vectors, and performing vector region judgment in the gh coordinate system, the large number of radical and trigonometric function operations required when solving in the rectangular coordinate system are avoided, which effectively shortens the system's operation time, reduces the demand on the DSP processor, and saves costs.
[0103] In the aforementioned virtual space vector modulation system applicable to parallel converters in doubly-fed wind power generation systems, the modulation module 2 comprehensively plans and prioritizes the relevant vector elements, ensuring efficient and orderly modulation. It adjusts the vector action time in real-time based on the circulating current, effectively weakening the zero-sequence circulating current, reducing line heating and losses, and improving system efficiency and safety. Furthermore, it flexibly adjusts vector parameters based on the midpoint voltage, precisely balancing the capacitor midpoint voltage, avoiding equipment failures and performance degradation caused by voltage imbalance, and ensuring stable system operation. This system achieves dual-objective control of midpoint voltage balance and zero-sequence circulating current suppression, significantly improving power quality and equipment reliability.
[0104] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.
[0105] Although this application has been disclosed above with reference to embodiments, it is not intended to limit this application. Anyone skilled in the art may make some modifications and refinements without departing from the spirit and scope of this application. Therefore, the scope of protection of this application shall be determined by the appended claims.
Claims
1. A virtual space vector modulation method for parallel converters in a doubly-fed wind power generation system, characterized in that, Includes the following steps: The voltage vectors are classified into five categories: first vector, second vector, third vector, fourth vector, and fifth vector. By using control factors and transformation coefficients, the voltage vector is defined as a virtual vector in the voltage vector space. The virtual vector includes a virtual zero vector, a first virtual small vector, a second virtual small vector, a virtual medium vector, a first virtual large vector, and a second virtual large vector. The voltage vector space is divided into six sectors along the circumference, and based on the virtual space vector, the six sectors are further divided into five vector regions. Based on the vector region where the reference voltage vector is located, three virtual vectors that are closest to the reference voltage vector are selected as composite vectors to participate in vector synthesis, and the action time of the three composite vectors is obtained. Depending on whether the virtual vector participates in vector synthesis, different modulation strategies are selected for control, including: when the virtual vector does not participate in vector synthesis, control is achieved by adjusting the redundancy vector action time of the first and second virtual vectors; when the virtual vector participates in vector synthesis, control is achieved by adjusting the control factor. The midpoint voltage fluctuation value of the DC bus is calculated, and an allowable threshold for the midpoint voltage fluctuation value is set. The midpoint voltage fluctuation value is compared with the allowable threshold. When the midpoint voltage fluctuation value is within the allowable threshold range, zero-sequence circulating current suppression is performed. When the midpoint voltage fluctuation value is outside the allowable threshold range, midpoint voltage control is performed. The zero-sequence circulating current suppression includes: when the zero-sequence circulating current is greater than zero, reducing the action time of the second vector by changing the control factors of the first virtual small vector and the second virtual small vector to reduce the zero-sequence voltage output of the parallel converter; when the zero-sequence circulating current is less than zero, increasing the action time of the second vector by changing the control factors of the first virtual small vector and the second virtual small vector to increase the zero-sequence voltage output of the parallel converter.
2. The virtual space vector modulation method for parallel converters in a doubly-fed wind power generation system according to claim 1, characterized in that, The voltage vector space is divided into six sectors along a circumference, and based on the virtual space vector, the six sectors are further divided into five vector regions, including: The voltage vector space is divided into six major sectors along a circle, including the first major sector, the second major sector, the third major sector, the fourth major sector, the fifth major sector, and the sixth major sector. By using vectorized equations, the first large sector is divided into five vector regions. By transforming the second, third, fourth, fifth, and sixth major sectors into the first major sector, and then dividing them according to the vectorized fractional equation, five vector regions are obtained.
3. The virtual space vector modulation method for parallel converters in a doubly-fed wind power generation system according to claim 1, characterized in that, The voltage vector space is divided into six sectors along a circle, including: every 60 o Divided into one large region, starting from 0 o They are numbered sequentially as follows: Ⅰ, Ⅱ, Ⅲ, Ⅳ, Ⅴ, Ⅵ.
4. The virtual space vector modulation method for parallel converters in a doubly-fed wind power generation system according to claim 1, characterized in that, The midpoint voltage control includes: Based on the phase relationship of the midpoint currents output by the second and third vectors, determine the transformation coefficients of the virtual small vector; Based on the transformation coefficients, calculate the midpoint charge output under the action of the first virtual small vector, the second virtual small vector, the virtual medium vector, the first virtual large vector, and the second virtual large vector; Based on the midpoint charge, the values of the control factors in each vector are further determined.
5. The virtual space vector modulation method for parallel converters in a doubly-fed wind power generation system according to claim 1, characterized in that, The midpoint voltage control also includes: When the midpoint voltage fluctuation exceeds the lower limit of the allowable threshold, the lower capacitor voltage is reduced through midpoint voltage balancing control to obtain the value of the control factor. When the midpoint voltage fluctuation exceeds the upper limit of the allowable threshold, the voltage of the upper capacitor is reduced through midpoint voltage balancing control to obtain the value of the control factor.
6. A virtual space vector modulation method for parallel converters in a doubly-fed wind power generation system according to any one of claims 1 to 5, characterized in that, The vector region is defined in the gh coordinate system.
7. A virtual space vector modulation system suitable for parallel converters in doubly-fed wind power generation systems, characterized in that, The virtual space vector modulation system suitable for parallel converters in doubly-fed wind power generation systems includes: a drive circuit, a drive motor, and a modulation module, wherein... The drive circuit obtains electrical energy from the power grid through the first transformer and outputs current to the drive motor. The drive circuit includes multiple converter branches, which are connected in parallel. The modulation module integrates a virtual space vector modulation method for parallel converters in a doubly fed wind power generation system as described in any one of claims 1 to 6. The modulation module is used to output the control factor and transformation coefficient to the drive signal generator, thereby driving the switch in the converter branch.