Synchronous modulation method for low switching frequency bus clamp of dual three-phase permanent magnet wind driven generator

Abstract

The invention discloses a low-switching-frequency bus clamp synchronous modulation method for double three-phase permanent magnet wind driven generators. The method comprises the following steps of 1, deducing a symmetry constraint condition of output voltage of a six-phase inverter; 2, according to the symmetry constraint condition, the number, position and vector sequence of sampling points of the six-phase inverter are constructed; 3, deducing a decoupled six-phase inverter reference voltage vector according to the fundamental wave plane reference voltage vector and the harmonic wave plane reference voltage vector; 4, according to the amplitude and the phase of the reference voltage vector of the six-phase inverter, the action time of the selected voltage vector is calculated, and PWM modulation is carried out. According to the bus clamp modulation method provided by the invention, the problem of overlarge output voltage distortion under low switching frequency in the existing modulation method is solved, and high-efficiency operation of the dual three-phase permanent magnet wind driven generator under the working condition of low switching frequency is ensured.

Description

Technical Field

[0001] The present invention belongs to the technical field of renewable energy power generation control, and in particular relates to a low switching frequency bus clamping synchronous modulation technology for a dual three-phase permanent magnet wind turbine. Background Art

[0002] The dual three-phase permanent magnet synchronous generator has excellent characteristics such as high power density, high efficiency, and high fault tolerance operation capability. It has good engineering value and application prospects in large-capacity offshore wind farms. However, due to the high power level of large-capacity offshore wind turbines, the switching frequency of its supporting converter needs to be limited to a low level considering factors such as switching loss and heat dissipation conditions. The number of converter output pulses decreases within a fundamental cycle at a low switching frequency, and the output voltage waveform is significantly distorted; in addition, the dual three-phase permanent magnet synchronous motor has an inherent low harmonic impedance characteristic. The combination of these two factors leads to serious output current distortion, increased system additional losses, and reduced operating efficiency. By optimizing the modulation strategy of the DTP-PMSG machine-side converter, it is possible to optimize the generator output current harmonics while keeping the switching frequency unchanged, thereby improving the generator operating efficiency.

[0003] The DTP-PMSG machine-side converter is a dual three-phase voltage source converter. Common modulation strategies include carrier phase shift pulse width modulation (CPSPWM) and space vector pulse width modulation (SVPWM). Studies have shown that compared with CPSPWM, SVPWM has a higher DC voltage utilization rate and is more widely used in the field of wind power generation. However, the traditional SVPWM is essentially asynchronous modulation, and its output voltage waveform is significantly distorted at low switching frequencies. In order to improve the output performance of the generator under low switching frequency constraints, some scholars have proposed current harmonic minimization modulation technology and selective harmonic elimination modulation technology to optimize the output performance. However, this method has a large amount of algorithm calculation, which is not conducive to the implementation of digital processors.

[0004] In summary, when DTP-PMSG operates at low switching frequency, the output voltage of the converter is severely distorted, which affects the operating efficiency of the generator. The traditional SVPWM and optimized pulse width modulation methods cannot achieve a balance between output voltage harmonic optimization and algorithm calculation. Therefore, how to design a synchronous modulation strategy to achieve harmonic optimization of the output voltage at low switching frequency while having a lower algorithm calculation is the key to achieving high-efficiency operation of DTP-PMSG at low switching frequency. Summary of the invention

[0005] The purpose of the present invention is to overcome the shortcomings of the existing modulation methods, such as serious output voltage distortion at low switching frequency and excessive algorithm calculation, and propose a low switching frequency bus clamping synchronous modulation method for a dual three-phase permanent magnet wind generator to ensure that the dual three-phase permanent magnet wind generator can still operate smoothly and efficiently at a low switching frequency.

[0006] The technical solution adopted by the present invention is: a low switching frequency bus clamping synchronous modulation method for a dual three-phase permanent magnet wind turbine generator, comprising the following steps:

[0007] Step 1: Derive the output voltage symmetry constraint of the six-phase inverter;

[0008] Step 2: According to the symmetry constraint condition and the clamping method, the number, position and vector sequence of sampling points of the six-phase inverter are constructed;

[0009] Step 3: derive a decoupled six-phase inverter reference voltage vector according to the fundamental plane and the harmonic plane reference voltage vectors;

[0010] Step 4: Calculate the action time of the selected voltage vector according to the amplitude and phase of the reference voltage vector of the six-phase inverter, and calculate the duty cycle of each phase according to the vector sequence to perform PWM modulation.

[0011] Furthermore, the specific process of step 1 is as follows:

[0012] The machine-side converter of the dual three-phase permanent magnet wind turbine generator is used as two sets of three-phase inverters with a common DC bus to work together. In order to make the output voltage of the six-phase inverter have six-phase symmetry, half-wave odd symmetry and quarter-cycle even symmetry, the two sets of three-phase inverters are required to meet three-phase symmetry, half-wave odd symmetry and quarter-cycle even symmetry respectively, so that the second set of inverters and the first set of inverters must have the same number of sampling points and sampling positions, and the output voltage waveform satisfies the phase shift relationship of 30 degrees. The symmetry constraint conditions are as follows:

[0013] The two sets of three-phase inverters have the same number of sampling points, and the number of sampling points in each sector must be an even number, and the positions of the sampling points must be symmetrical about the middle of the sector;

[0014] The voltage vectors selected at the two sampling points S1 and S2 that are symmetrical about the middle of the sector also need to be symmetrical about the middle of the sector. That is, if S1 selects a boundary voltage vector, S2 needs to select another boundary voltage vector; if S1 selects a zero vector, S2 needs to select another zero voltage vector.

[0015] Furthermore, the specific process of step 2 is as follows:

[0016] According to the symmetry constraint condition, the number of sampling points of the two sets of three-phase inverters is determined to be N;

[0017] N = 2n, n is a positive integer; (1)

[0018] Determine the sampling point positions α of the two sets of six-phase inverters

[0019]

[0020] Wherein, i is a positive integer, i=1,…,n;

[0021] According to the symmetry constraint and the clamping mode, the vector sequences of the two three-phase inverters are determined; when the number of sampling points N = 4n-2, the clamping modes include 30° clamping and 60° clamping;

[0022] In the 30° clamping mode, the vector sequence corresponding to the first N / 2 sampling points of the first sector of the first three-phase inverter is 0-4-6, 6-4-0, ..., 0-4-6, and the vector sequence corresponding to the last N / 2 sampling points is "4-6-7, 7-6-4, ..., 4-6-7";

[0023] In the 60° clamping mode, the vector sequence corresponding to the first N / 2 sampling points of the first sector of the first three-phase inverter is 7-6-4, 4-6-7, ..., 7-6-4, and the vector sequence corresponding to the last N / 2 sampling points is "6-4-0, 0-4-6, ..., 6-4-0";

[0024] When the number of sampling points N=4n, the clamping mode has only 60° clamping. The vector sequence corresponding to the first N / 2 sampling points of the first sector of the first three-phase inverter is 4-6-7, 7-6-4, …, 4-6-7, 7-6-4, and the vector sequence corresponding to the last N / 2 sampling points is 6-4-0, 0-4-6, …, 6-4-0, 0-4-6. The vector sequence of the second three-phase inverter is obtained by phase shifting the first three-phase inverter by 30°.

[0025] According to the vector sequences of the two sets of three-phase inverters, the vector sequence of the six-phase inverter is derived. When the number of sampling points N=4n-2, the vector sequence corresponding to the first N / 2 sampling points of the first sector in the 30° clamping mode is 05-44-60, 60-44-05, …, 05-44-60, and the vector sequence corresponding to the last N / 2 sampling points is 40-64-76, 76-64-40, …, 40-64-76.

[0026] When the number of sampling points N=4n-2, the vector sequence corresponding to the first N / 2 sampling points of the first sector in the 60° clamping mode is 74-65-47, 47-65-74, ..., 74-65-47, and the vector sequence corresponding to the last N / 2 sampling points is 67-46-04, 04-46-67, ..., 67-46-04;

[0027] When the number of sampling points N=4n, the vector sequence corresponding to the first N / 2 sampling points of the first sector in the 60° clamping mode is 44-65-77, 77-65-44, …, 44-65-77, 77-65-44, and the vector sequence corresponding to the last N / 2 sampling points is 64-46-07, 07-46-64, …, 64-46-07, 07-46-64.

[0028] Furthermore, the specific process of step 3 is as follows:

[0029] According to the fundamental plane reference voltage vector With harmonic plane reference voltage vector Derivation of two sets of decoupled three-phase inverter reference voltage vectors and

[0030]

[0031] Let the harmonic plane reference voltage vector but

[0032]

[0033] Furthermore, the specific process of step 4 is as follows:

[0034] Through two sets of three-phase inverter reference voltage vector and The action time of the selected voltage vector is derived from the volt-second balance principle

[0035]

[0036] Where k = 1, 2, and It indicates the kth set of three-phase windings in the αβ component; They are the two boundary vector αβ components of the sector where the reference voltage vector is located, t1 and t2 are their action times, and it can be deduced that

[0037]

[0038] According to the calculated voltage vector action time and the vector sequence of the six-phase inverter, the duty cycle of each phase of the six-phase inverter is calculated, and the output is compared with the triangular carrier to perform PWM modulation.

[0039] Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

[0040] (1) The bus clamp synchronous modulation strategy designed in the present invention has lower switching frequency and lower output voltage harmonics under the same number of sampling points.

[0041] (2) The synchronous modulation strategy designed in the present invention has a simple algorithm architecture, does not require complex calculation processes, does not involve matrix operations, and does not involve solving transcendental equations. It is more convenient to execute in digital microprocessors commonly used in dual three-phase permanent magnet wind turbines.

[0042] (3) The low switching frequency bus clamping synchronous modulation method for dual three-phase permanent magnet wind turbines proposed in the present invention can output a voltage waveform that satisfies six-phase symmetry, half-wave odd symmetry, and quarter-cycle even symmetry; at the same time, it can be seen from the output spectrum that the proposed method eliminates even-order harmonics and the voltage THD is effectively suppressed. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 This is a circuit topology diagram of a dual three-phase permanent magnet wind generator of the present invention;

[0044] Figure 2 is a voltage vector distribution diagram of a six-phase inverter of the present invention;

[0045] Figure 3 It is the voltage vector distribution diagram of two sets of three-phase inverters of decoupled type of the present invention;

[0046] Figure 4 This is a structural diagram of the control system of the dual three-phase permanent magnet generator of the present invention;

[0047] Figure 5 The output voltage waveform under bus clamp synchronous modulation of the present invention;

[0048] Figure 6 This is the output voltage waveform diagram under bus clamp synchronous modulation of the present invention;

[0049] Figure 7 This is the output voltage spectrum diagram under bus clamp synchronous modulation of the present invention;

[0050] Figure 8 It is a flow chart of the present invention. DETAILED DESCRIPTION

[0051] It should be noted that the following embodiments can enable those skilled in the art to more fully understand the present invention, but do not limit the present invention in any way.

[0052] The following is combined with Figure 1-Figure 8 The present invention is further described with a technical solution, a low switching frequency bus clamping synchronous modulation method of a dual three-phase permanent magnet wind turbine generator mainly comprises the following steps:

[0053] Step 1: Derive the output voltage symmetry constraints of the six-phase inverter.

[0054] like Figure 1As shown, the six-phase converter on the machine side of the dual three-phase permanent magnet wind turbine generator is regarded as two sets of three-phase inverters with a common DC bus working together. In order to make the output voltage of the six-phase inverter have six-phase symmetry, half-wave odd symmetry and quarter-cycle even symmetry, the two sets of three-phase inverters are required to meet the three-phase symmetry, half-wave odd symmetry and quarter-cycle even symmetry respectively. At the same time, the second set of inverters and the first set of inverters must have the same number of sampling points and sampling positions, and the output voltage waveform must meet the phase shift relationship of 30 degrees. The constraints are as follows:

[0055] Constraint 1: The two sets of three-phase inverters have the same number of sampling points, and the number of sampling points in each sector must be an even number, and the positions of the sampling points must be symmetrical about the middle of the sector.

[0056] Constraint 2: The voltage vectors selected at the two sampling points S1 and S2 that are symmetrical about the middle of the sector must also be symmetrical about the middle of the sector, that is, if S1 selects a boundary voltage vector, then S2 must select another boundary voltage vector; if S1 selects a zero vector, then S2 must select another zero voltage vector.

[0057] Step 2: According to the symmetry constraint and clamping method, the number, position and vector sequence of sampling points of the six-phase inverter are constructed. Specifically:

[0058] According to the symmetry constraint condition derived in step 1, the number of sampling points of the two sets of three-phase inverters is determined to be N.

[0059] N=2n; (1)

[0060] Wherein, n is a positive integer.

[0061] According to the symmetry constraint condition, the sampling point positions α of the two sets of six-phase inverters are determined;

[0062]

[0063] Wherein, i is a positive integer, i=1,…,n.

[0064] According to the symmetry constraints and clamping methods described in 2, the vector sequences of the two sets of three-phase inverters and the corresponding vector sequences of the six-phase inverters are determined, as shown in Table 1:

[0065]

[0066]

[0067] Table 1 Bus clamp modulation strategy (first sector)

[0068] The vector sequence numbers in Table 1 are abbreviations of the voltage vectors of the three-phase inverter and the six-phase inverter. The voltage vector distribution is as follows: Figure 2-Figure 4 shown.

[0069] As shown in Table 1, when the number of sampling points N=4n-2, the clamping modes include 30° clamping and 60° clamping.

[0070] In the 30° clamping mode, the vector sequence corresponding to the first N / 2 sampling points of the first sector of the first three-phase inverter is "0-4-6, 6-4-0, ..., 0-4-6", and the vector sequence corresponding to the last N / 2 sampling points is "4-6-7, 7-6-4, ..., 4-6-7".

[0071] In the 60° clamping mode, the vector sequence corresponding to the first N / 2 sampling points of the first sector of the first three-phase inverter is "7-6-4, 4-6-7, ..., 7-6-4", and the vector sequence corresponding to the last N / 2 sampling points is "6-4-0, 0-4-6, ..., 6-4-0".

[0072] When the number of sampling points N = 4n, the clamping mode has only 60° clamping. The vector sequence corresponding to the first N / 2 sampling points of the first sector of the first three-phase inverter is "4-6-7, 7-6-4, ..., 4-6-7, 7-6-4", and the vector sequence corresponding to the last N / 2 sampling points is "6-4-0, 0-4-6, ..., 6-4-0, 0-4-6". The vector sequence of the second three-phase inverter is obtained by phase shifting the first three-phase inverter by 30°.

[0073] According to the vector sequences of the two sets of three-phase inverters, the vector sequence of the six-phase inverter is derived: when the number of sampling points N=4n-2, the vector sequence corresponding to the first N / 2 sampling points of the first sector in the 30° clamping mode is “05-44-60, 60-44-05, …, 05-44-60”, and the vector sequence corresponding to the last N / 2 sampling points is “40-64-76, 76-64-40, …, 40-64-76”.

[0074] When the number of sampling points N=4n-2, the vector sequence corresponding to the first N / 2 sampling points of the first sector in the 60° clamping mode is "74-65-47, 47-65-74, ..., 74-65-47", and the vector sequence corresponding to the last N / 2 sampling points is "67-46-04, 04-46-67, ..., 67-46-04".

[0075] When the number of sampling points N=4n, the vector sequence corresponding to the first N / 2 sampling points of the first sector in the 60° clamping mode is "44-65-77, 77-65-44, ..., 44-65-77, 77-65-44", and the vector sequence corresponding to the last N / 2 sampling points is "64-46-07, 07-46-64, ..., 64-46-07, 07-46-64".

[0076] Step 3: Derivation of the decoupled six-phase inverter reference voltage vector based on the fundamental plane and harmonic plane reference voltage vectors. Specifically:

[0077] like Figure 4 As shown, the fundamental plane reference voltage vector is obtained by the dual three-phase permanent magnet synchronous generator controller With harmonic plane reference voltage vector according to and Derivation of two sets of decoupled three-phase inverter reference voltage vectors and

[0078]

[0079] Let the harmonic plane reference voltage vector but

[0080]

[0081] It can be seen from equation (4) that the reference voltage vector amplitudes of the two sets of three-phase inverters are the same, and the phase difference is 30°, as shown in Figure 3 The reference voltage vector is shown in FIG.

[0082] Step 4: Calculate the action time of the selected voltage vector according to the six-phase inverter reference voltage vector, and calculate the duty cycle of each phase according to the vector sequence for PWM modulation. Specifically:

[0083] According to two sets of three-phase inverter reference voltage vector and The action time of the selected voltage vector is derived from the volt-second balance principle

[0084]

[0085] Where k = 1, 2, and It indicates the kth set of three-phase windings in the αβ component; They are the two boundary vector αβ components of the sector where the reference voltage vector is located, t1 and t2 are their action times, and it can be deduced that

[0086]

[0087] According to the calculated voltage vector action time and the designed vector sequence of the six-phase inverter, the duty cycle of each phase of the six-phase inverter can be calculated. Figure 5 As shown, taking the vector sequence 44-65-77, 77-65-44 as an example, the duty cycle of each phase of the six-phase inverter is

[0088]

[0089] like Figure 5 As shown, the duty cycle of each phase is compared with the triangular carrier and output, and PWM modulation is performed to drive the six-phase inverter, thereby supplying power to the dual three-phase permanent magnet wind turbine generator.

[0090] The effectiveness of the low switching frequency bus clamping synchronous modulation method for dual three-phase permanent magnet wind turbine generator proposed in the present invention is verified by MATLAB / Simu link simulation experiment. The simulation experiment results are as follows: Figure 6-Figure 7 As shown, the DC bus voltage is 1200V.

[0091] Figure 6 The output line voltage waveforms are shown in Figure 1 for N=4, N=6, 30° clamping mode, and N=6, 60° clamping mode. The corresponding line voltage spectra are shown in Figure 11. Figure 7 shown.

[0092] Depend on Figure 6-Figure 7 It can be seen that the low switching frequency bus clamping synchronous modulation method for the dual three-phase permanent magnet wind turbine proposed in the present invention can output a voltage waveform that satisfies six-phase symmetry, half-wave odd symmetry and quarter-cycle even symmetry; at the same time, it can be seen from the output spectrum diagram that the proposed method eliminates even-order harmonics and the voltage THD is effectively suppressed.

[0093] The above descriptions are merely embodiments of the present invention and are not intended to limit the patent scope of the present invention. Any equivalent structure or equivalent process transformation made using the contents of the present invention specification and drawings, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present invention.

Claims

1. A low switching frequency busbar clamping synchronous modulation method for a dual three-phase permanent magnet wind turbine generator, characterized in that: The following steps are involved: Step 1: Derive the output voltage symmetry constraint of the six-phase inverter; Step 2: According to the symmetry constraint condition and the clamping method, the number, position and vector sequence of sampling points of the six-phase inverter are constructed; Step 3: derive a decoupled six-phase inverter reference voltage vector according to the fundamental plane and the harmonic plane reference voltage vectors; Step 4: Calculate the action time of the selected voltage vector according to the amplitude and phase of the reference voltage vector of the six-phase inverter, and calculate the duty cycle of each phase according to the vector sequence to perform PWM modulation.

2. A low switching frequency bus clamping synchronous modulation method for a dual three-phase permanent magnet wind turbine according to claim 1, characterized in that: The specific process of step 1 is as follows: The machine-side converter of the dual three-phase permanent magnet wind turbine generator is used as two sets of three-phase inverters with a common DC bus to work together. The two sets of three-phase inverters meet three-phase symmetry, half-wave odd symmetry and quarter-cycle even symmetry respectively, so that the second set of inverters and the first set of inverters must have the same number of sampling points and sampling positions, and the output voltage waveform meets the phase shift relationship of 30 degrees. The symmetry constraint conditions are as follows: The two sets of three-phase inverters have the same number of sampling points, and the number of sampling points in each sector must be an even number, and the positions of the sampling points must be symmetrical about the middle of the sector; The voltage vectors selected at the two sampling points S1 and S2 that are symmetrical about the middle of the sector also need to be symmetrical about the middle of the sector.

3. A low switching frequency bus clamping synchronous modulation method for a dual three-phase permanent magnet wind turbine generator according to claim 2, characterized in that: The specific process of step 2 is as follows: According to the symmetry constraint condition, the number of sampling points of the two sets of three-phase inverters is determined to be N; N = 2n, n is a positive integer; (1) Determine the sampling point positions α of the two sets of six-phase inverters Wherein, i is a positive integer, i=1,…,n; According to the symmetry constraint and the clamping mode, the vector sequences of the two three-phase inverters are determined; when the number of sampling points N = 4n-2, the clamping modes include 30° clamping and 60° clamping; In the 30° clamping mode, the vector sequence corresponding to the first N / 2 sampling points of the first sector of the first three-phase inverter is 0-4-6, 6-4-0, …, 0-4-6, and the vector sequence corresponding to the last N / 2 sampling points is "4-6-7, 7-6-4, …, 4-6-7"; In the 60° clamping mode, the vector sequence corresponding to the first N / 2 sampling points of the first sector of the first three-phase inverter is 7-6-4, 4-6-7, ..., 7-6-4, and the vector sequence corresponding to the last N / 2 sampling points is "6-4-0, 0-4-6, ..., 6-4-0"; When the number of sampling points N=4n, the clamping mode has only 60° clamping. The vector sequence corresponding to the first N / 2 sampling points of the first sector of the first three-phase inverter is 4-6-7, 7-6-4, …, 4-6-7, 7-6-4, and the vector sequence corresponding to the last N / 2 sampling points is 6-4-0, 0-4-6, …, 6-4-0, 0-4-6. The vector sequence of the second three-phase inverter is obtained by phase shifting the first three-phase inverter by 30°. According to the vector sequences of the two sets of three-phase inverters, the vector sequence of the six-phase inverter is derived. When the number of sampling points N=4n-2, the vector sequence corresponding to the first N / 2 sampling points of the first sector in the 30° clamping mode is 05-44-60, 60-44-05, …, 05-44-60, and the vector sequence corresponding to the last N / 2 sampling points is 40-64-76, 76-64-40, …, 40-64-76. When the number of sampling points N=4n-2, the vector sequence corresponding to the first N / 2 sampling points of the first sector in the 60° clamping mode is 74-65-47, 47-65-74, ..., 74-65-47, and the vector sequence corresponding to the last N / 2 sampling points is 67-46-04, 04-46-67, ..., 67-46-04; When the number of sampling points N=4n, the vector sequence corresponding to the first N / 2 sampling points of the first sector in the 60° clamping mode is 44-65-77, 77-65-44, …, 44-65-77, 77-65-44, and the vector sequence corresponding to the last N / 2 sampling points is 64-46-07, 07-46-64, …, 64-46-07, 07-46-64.

4. A low switching frequency bus clamping synchronous modulation method for a dual three-phase permanent magnet wind turbine generator according to claim 3, characterized in that: The specific process of step 3 is as follows: According to the fundamental plane reference voltage vector With harmonic plane reference voltage vector Derivation of two sets of decoupled three-phase inverter reference voltage vectors and Let the harmonic plane reference voltage vector but 5. A low switching frequency bus clamping synchronous modulation method for a dual three-phase permanent magnet wind turbine generator according to claim 4, characterized in that: The specific process of step 4 is as follows: Through two sets of three-phase inverter reference voltage vector and The action time of the selected voltage vector is derived from the volt-second balance principle Where k = 1, 2, and It indicates the kth set of three-phase windings in αβ components; They are the two boundary vector αβ components of the sector where the reference voltage vector is located, t1 and t2 are their action times, and it can be deduced that According to the calculated voltage vector action time and the vector sequence of the six-phase inverter, the duty cycle of each phase of the six-phase inverter is calculated, and the output is compared with the triangular carrier to perform PWM modulation.

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