Pulse commutation method of static frequency converter
By dynamically switching between 12-pulse and 6-pulse pulse modes in the static inverter, and controlling the current vector according to the current frequency and rotor position, the problem of difficult low-speed start-up of the static inverter is solved, and a larger driving torque and less harmonic output are achieved.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- DONGFANG ELECTRIC AUTOMATIC CONTROL ENG CO LTD
- Filing Date
- 2026-01-06
- Publication Date
- 2026-05-15
AI Technical Summary
Existing static frequency converters cause large static friction torque when the motor is stationary or at low speed due to pulse commutation control, resulting in difficulty in starting.
When the output current frequency is lower than the set value, it starts with a 12-pulse method, forming the current vector and rotor position through the phase difference of the transformer connected by two inverter bridges, and alternately changing the current vector; when it is higher than the set value, it starts with a 6-pulse method, dynamically switching the pulse mode.
It provides greater driving torque at low speeds, overcomes static friction resistance torque, and outputs current closer to a sine wave with fewer harmonic components; it maintains a higher average torque at high frequencies and increases the proportion of current interruption time.
Smart Images
Figure CN122052655A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of motor drive and power electronics technology, and specifically relates to a pulse commutation method for a static frequency converter. Background Technology
[0002] Static frequency converters (SFDs), as core equipment in modern motor drive systems, are widely used in industrial automation, power systems, and ship propulsion. Their main function is to convert DC power into AC power with adjustable frequency, enabling stepless speed control of AC motors. In SFD systems, pulse commutation control is one of the key technologies determining motor performance, directly affecting the motor's starting characteristics, operating efficiency, and output waveform quality.
[0003] Currently, the pulse commutation control of static frequency converters mainly adopts a 6-pulse method, where the thyristors of the inverter bridge conduct in turn, switching 6 times per cycle, with each conduction current lasting for 1 / 6 of a cycle. This control method has good efficiency and stability during medium and high frequency operation and is the mainstream control method for traditional frequency converters.
[0004] In existing technologies, the pulse commutation control of frequency converters typically adopts a fixed method, that is, the same pulse switching method is used throughout the entire operating frequency range. For example, when the motor starts from a standstill, the system uses a 6-pulse control method, at which time the thyristor conduction sequence is (1,2), (2,3), (3,4), (4,5), (5,6), (6,1), and the conduction time of each interval is 1 / 6 of a cycle.
[0005] In existing pulse commutation methods, Chinese invention patent CN110535376A, titled "A Speed Control Method for the Pulse Commutation Stage of a Static Frequency Converter," discloses the following: When the output of the hysteresis comparator is 0, the output time has a lower limit Δt2, where Δt2 is the minimum time required for the current to be zero to ensure reliable thyristor turn-off; when the speed reaches a set value, the pulse output is blocked; when the speed drops to the set value due to load reasons, the commutation time is estimated; if the estimated commutation time is greater than the set value, the thyristor is turned on again; if the estimated commutation time is less than the set value, the thyristor is turned on again after the commutation time occurs. The aforementioned existing technology has the following problems: When the motor is stationary or at low speed, the pulse commutation of the above-mentioned existing technology results in a large static friction torque when the motor is stationary, which can easily lead to difficulties in starting at low speed. Summary of the Invention
[0006] The purpose of this invention is to overcome the aforementioned problems and propose a pulse commutation method for a static frequency converter, which solves the problem of large static friction torque when the motor is stationary, which easily leads to difficulties in low-speed starting.
[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A pulse commutation method for a static frequency converter is characterized in that: when the output current frequency is lower than the set value, a 12-pulse start-up method is adopted, and the current vector formed by the phase difference of the transformer connected by two inverter bridges and the rotor position are alternately changed to change the thyristors corresponding to the 12 current vectors formed by the two inverter bridges in one cycle; when the output current frequency is higher than the set value, a 6-pulse start-up method is adopted.
[0008] The current frequency setting is 1.5Hz.
[0009] The 12-pulse start-up method is described in the following steps: Step s1: Collect the three-phase induced voltage and calculate the rotor position; Step s2: Drive the first inverter bridge and the second inverter bridge to form 12 current vectors by the rotor position, divide the synchronous motor rotor position into 12 intervals, and find out the thyristors that need to be turned on in the 12 intervals corresponding to the 12 current vectors formed by the first inverter bridge and the second inverter bridge. Step s3: Turn on the corresponding thyristors of the first and second inverter bridges for a duration of 1 / 12 of the current cycle; Step s4: Turn off the corresponding thyristors of the first and second inverter bridges; Step s5: Repeat steps s1-s4, switching 12 times in one cycle to complete the pulse commutation of the static inverter.
[0010] In step s1, the three-phase induced voltages Ua, Ub, and Uc are collected, the angle α is calculated, and the rotor position is calculated by rounding down α / 30.
[0011] The formula for calculating angle α is as follows: .
[0012] The angle α ranges from 0 to 360°.
[0013] In step s2, the AC output lines of the first inverter bridge and the second inverter bridge are respectively connected to the low-voltage YD winding of the output transformer.
[0014] The first inverter bridge and the second inverter bridge are 30° out of phase with the low-voltage YD winding of the transformer they are connected to.
[0015] In step s2, when the rotor is in position 1, the first inverter bridge turns on the sixth thyristor and the first thyristor, and the second inverter bridge turns on the first thyristor and the second thyristor. When the rotor is in position 2, the first inverter bridge turns on the first thyristor and the second thyristor, and the second inverter bridge turns on the first thyristor and the second thyristor. When the rotor is in position 3, the first inverter bridge turns on the first thyristor and the second thyristor, and the second inverter bridge turns on the second thyristor and the third thyristor. When the rotor is in position 4, the first inverter bridge turns on the second and third thyristors, and the second inverter bridge turns on the second and third thyristors. When the rotor is in position 5, the first inverter bridge turns on the second and third thyristors, and the second inverter bridge turns on the third and fourth thyristors. When the rotor is in position 6, the third and fourth thyristors of the first inverter bridge are turned on, and the third and fourth thyristors of the second inverter bridge are turned on. When the rotor is in position 7, the third and fourth thyristors of the first inverter bridge are turned on, and the fourth and fifth thyristors of the second inverter bridge are turned on. When the rotor is in position 8, the first inverter bridge turns on the fourth and fifth thyristors, and the second inverter bridge turns on the fourth and fifth thyristors. When the rotor is in position 9, the first inverter bridge turns on the fourth and fifth thyristors, and the second inverter bridge turns on the fifth and sixth thyristors. When the rotor is in position 10, the fifth and sixth thyristors of the first inverter bridge are turned on, and the fifth and sixth thyristors of the second inverter bridge are turned on. When the rotor is in position 11, the fifth and sixth thyristors of the first inverter bridge are turned on, and the sixth and first thyristors of the second inverter bridge are turned on. When the rotor is in position 12, the sixth thyristor and the first thyristor of the first inverter bridge are turned on, and the sixth thyristor and the first thyristor of the second inverter bridge are turned on.
[0016] When the thyristors turned on in the first inverter bridge and the second inverter bridge are different, the current vector of the first inverter bridge lags behind the current vector of the second inverter bridge by 30°.
[0017] When the thyristors turned on by the first inverter bridge and the second inverter bridge are the same, on the transformer output side, the current vector of the first inverter bridge leads the current vector of the second inverter bridge by 30°.
[0018] The advantages of using this invention are: I. Compared with the prior art, the present invention adopts a 12-pulse inverter mode. In a range below a set value, the average driving torque of the 12-pulse mode will be greater than that of the 6-pulse mode. When the motor is stationary or at low speed, the 12-pulse mode can provide a larger driving torque and can overcome the static friction resistance torque when the motor is stationary.
[0019] Second, compared with the prior art, the 12-pulse output current of the present invention is closer to a sine wave and has fewer harmonic components than the 6-pulse output current.
[0020] Third, the present invention dynamically switches the pulse mode according to the output current frequency. As the output frequency increases, the proportion of current interruption time in the 12-pulse mode increases and the average torque decreases; switching to the 6-pulse mode can maintain a higher average torque.
[0021] Fourth, this invention calculates (α / 30) the corresponding thyristor combination based on the rotor position and connects transformer windings with a phase difference of 30° through two inverter bridges to achieve precise current vector control. Attached Figure Description
[0022] Figure 1 This is a schematic diagram of the inverter side of the static frequency converter of the present invention; Figure 2 This is a topology diagram of the thyristor bridge of the present invention; Figure 3 This is the stator current waveform of the motor of the present invention; Figure 4 This is a drag curve diagram for the present invention. Detailed Implementation
[0023] Example 1 A pulse commutation method for a static frequency converter is proposed. When the output current frequency is lower than the set value, a 12-pulse start-up method is adopted. The current vector formed by the phase difference between the two inverter bridges and the transformer and the rotor position are alternately changed to change the thyristors corresponding to the 12 current vectors formed by the two inverter bridges in one cycle. When the output current frequency is higher than the set value, a 6-pulse start-up method is adopted.
[0024] The current frequency setting is 1.5Hz.
[0025] The 12-pulse start-up method is described in the following steps: Step s1: Collect the three-phase induced voltage and calculate the rotor position; Step s2: Drive the first inverter bridge and the second inverter bridge to form 12 current vectors by the rotor position, divide the synchronous motor rotor position into 12 intervals, and find out the thyristors that need to be turned on in the 12 intervals corresponding to the 12 current vectors formed by the first inverter bridge and the second inverter bridge. Step s3: Turn on the corresponding thyristors of the first and second inverter bridges for a duration of 1 / 12 of the current cycle; Step s4: Turn off the corresponding thyristors of the first and second inverter bridges; Step s5: Repeat steps s1-s4, switching 12 times in one cycle to complete the pulse commutation of the static inverter.
[0026] In step s1, the three-phase induced voltages Ua, Ub, and Uc are collected, the angle α is calculated, and the rotor position is calculated by rounding down α / 30.
[0027] The formula for calculating angle α is as follows: .
[0028] The angle α ranges from 0 to 360°.
[0029] In step s2, the AC output lines of the first inverter bridge and the second inverter bridge are respectively connected to the low-voltage YD winding of the output transformer.
[0030] The first inverter bridge and the second inverter bridge are 30° out of phase with the low-voltage YD winding of the transformer they are connected to.
[0031] In step s2, when the rotor is in position 1, the first inverter bridge turns on the sixth thyristor and the first thyristor, and the second inverter bridge turns on the first thyristor and the second thyristor. When the rotor is in position 2, the first inverter bridge turns on the first thyristor and the second thyristor, and the second inverter bridge turns on the first thyristor and the second thyristor. When the rotor is in position 3, the first inverter bridge turns on the first thyristor and the second thyristor, and the second inverter bridge turns on the second thyristor and the third thyristor. When the rotor is in position 4, the first inverter bridge turns on the second and third thyristors, and the second inverter bridge turns on the second and third thyristors. When the rotor is in position 5, the first inverter bridge turns on the second and third thyristors, and the second inverter bridge turns on the third and fourth thyristors. When the rotor is in position 6, the third and fourth thyristors of the first inverter bridge are turned on, and the third and fourth thyristors of the second inverter bridge are turned on. When the rotor is in position 7, the third and fourth thyristors of the first inverter bridge are turned on, and the fourth and fifth thyristors of the second inverter bridge are turned on. When the rotor is in position 8, the first inverter bridge turns on the fourth and fifth thyristors, and the second inverter bridge turns on the fourth and fifth thyristors. When the rotor is in position 9, the first inverter bridge turns on the fourth and fifth thyristors, and the second inverter bridge turns on the fifth and sixth thyristors. When the rotor is in position 10, the fifth and sixth thyristors of the first inverter bridge are turned on, and the fifth and sixth thyristors of the second inverter bridge are turned on. When the rotor is in position 11, the fifth and sixth thyristors of the first inverter bridge are turned on, and the sixth and first thyristors of the second inverter bridge are turned on. When the rotor is in position 12, the sixth thyristor and the first thyristor of the first inverter bridge are turned on, and the sixth thyristor and the first thyristor of the second inverter bridge are turned on.
[0032] When the thyristors turned on in the first inverter bridge and the second inverter bridge are different, the current vector of the first inverter bridge lags behind the current vector of the second inverter bridge by 30°.
[0033] When the thyristors turned on by the first inverter bridge and the second inverter bridge are the same, on the transformer output side, the current vector of the first inverter bridge leads the current vector of the second inverter bridge by 30°.
[0034] In step s3, the thyristors corresponding to the first and second inverter bridges are turned on for a duration of 1 / 12 of the operating cycle.
[0035] The AC outputs of the first and second inverter bridges are connected to the low-voltage Y / D windings of the output transformer, respectively. The YD windings are 30° out of phase.
[0036] The transformer windings connected by the first and second inverter bridges are 30° out of phase. When the first inverter bridge turns on thyristors 6 and 1, and the second inverter bridge turns on thyristors 1 and 2, the current vector of the first inverter bridge lags behind the current vector of the second inverter bridge by 30°. When both the first and second inverter bridges turn on thyristors 1 and 2, on the transformer output side, the current vector of the first inverter bridge leads the current vector of the second inverter bridge by 30°.
[0037] like Figure 1-2 As shown in Table 1, when the frequency is below 1.5Hz, the rotor position is divided into 12 intervals.
[0038] Collect the three-phase induced voltages Ua, Ub, and Uc, and calculate the angle. The value of α ranges from 0 to 360 degrees, and the rotor position is calculated as α / 30 (rounded down).
[0039] Refer to Table 1 to find the thyristors that need to be turned on for the first and second inverter bridges.
[0040] Turn on the corresponding thyristors of the first and second inverter bridges for 1 / 12 of the current cycle.
[0041] Turn off the thyristors that are turned on in the first and second inverter bridges.
[0042] Repeat the above steps; the cycle will switch 12 times.
[0043] When the motor speed is low, the current needs to be reduced to 0 when switching thyristors. For example, when the inverter bridge switches the thyristor from (1,2) to (2,3), the rectifier bridge and inverter bridge need to be turned off, and the current needs to be reduced to 0 before the rectifier bridge and inverter bridge thyristor (2,3) are turned on again.
[0044] like Figure 3 As shown, when the output current frequency is below 1.5Hz, the synchronous motor rotor position is divided into 12 intervals, combined as shown in Table 1: Table 1 Correspondence Table of 12 Pulses
[0045] At frequencies above 1.5Hz, the rotor position is divided into 6 intervals, as shown in Table 2.
[0046] Collect the three-phase induced voltages Ua, Ub, and Uc, and calculate the angle. The value of α ranges from 0 to 360, and the rotor position is calculated as α / 60 (rounded down).
[0047] Refer to Table 1 to find the thyristors that need to be turned on for the first and second inverter bridges.
[0048] The corresponding thyristors of the first and second inverter bridges are turned on for 1 / 6 of the current cycle. Turn off the thyristors that are turned on in the first and second inverter bridges.
[0049] Repeat the above steps; the cycle will switch 6 times.
[0050] When the output current frequency is higher than 1.5Hz, the synchronous motor rotor position is divided into 6 intervals, which are combined according to Table 2:
Claims
1. A pulse commutation method for a static frequency converter, characterized in that: When the output current frequency is lower than the set value, a 12-pulse start-up method is used. The current vector formed by the phase difference between the two inverter bridges and the transformer and the rotor position are alternately changed to change the thyristors corresponding to the 12 current vectors formed by the two inverter bridges in one cycle. When the output current frequency is higher than the set value, a 6-pulse start-up method is used.
2. The pulse commutation method for a static frequency converter according to claim 1, characterized in that: The current frequency setting is 1.5Hz.
3. A pulse commutation method for a static frequency converter according to claim 1 or 2, characterized in that: The 12-pulse start-up method is described in the following steps: Step s1: Collect the three-phase induced voltage and calculate the rotor position; Step s2: Drive the first inverter bridge and the second inverter bridge to form 12 current vectors by the rotor position, divide the synchronous motor rotor position into 12 intervals, and find out the thyristors that need to be turned on in the 12 intervals corresponding to the 12 current vectors formed by the first inverter bridge and the second inverter bridge. Step s3: Turn on the corresponding thyristors of the first and second inverter bridges for a duration of 1 / 12 of the current cycle; Step s4: Turn off the corresponding thyristors of the first and second inverter bridges; Step s5: Repeat steps s1-s4, switching 12 times in one cycle to complete the pulse commutation of the static inverter.
4. The pulse commutation method for a static frequency converter according to claim 3, characterized in that: In step s1, the three-phase induced voltages Ua, Ub, and Uc are collected, the angle α is calculated, and the rotor position is calculated by rounding down α / 30.
5. The pulse commutation method for a static frequency converter according to claim 4, characterized in that: The formula for calculating angle α is as follows: 。 6. The pulse commutation method for a static frequency converter according to claim 5, characterized in that: The angle α ranges from 0 to 360°.
7. The pulse commutation method for a static frequency converter according to claim 4, characterized in that: In step s2, the AC output lines of the first inverter bridge and the second inverter bridge are respectively connected to the low-voltage YD winding of the output transformer.
8. The pulse commutation method for a static frequency converter according to claim 7, characterized in that: The first inverter bridge and the second inverter bridge are 30° out of phase with the low-voltage YD winding of the transformer they are connected to.
9. The pulse commutation method for a static frequency converter according to claim 3, characterized in that: In step s2, when the rotor is in position 1, the first inverter bridge turns on the sixth thyristor and the first thyristor, and the second inverter bridge turns on the first thyristor and the second thyristor. When the rotor is in position 2, the first inverter bridge turns on the first thyristor and the second thyristor, and the second inverter bridge turns on the first thyristor and the second thyristor. When the rotor is in position 3, the first inverter bridge turns on the first thyristor and the second thyristor, and the second inverter bridge turns on the second thyristor and the third thyristor. When the rotor is in position 4, the first inverter bridge turns on the second and third thyristors, and the second inverter bridge turns on the second and third thyristors. When the rotor is in position 5, the first inverter bridge turns on the second and third thyristors, and the second inverter bridge turns on the third and fourth thyristors. When the rotor is in position 6, the third and fourth thyristors of the first inverter bridge are turned on, and the third and fourth thyristors of the second inverter bridge are turned on. When the rotor is in position 7, the third and fourth thyristors of the first inverter bridge are turned on, and the fourth and fifth thyristors of the second inverter bridge are turned on. When the rotor is in position 8, the first inverter bridge turns on the fourth and fifth thyristors, and the second inverter bridge turns on the fourth and fifth thyristors. When the rotor is in position 9, the first inverter bridge turns on the fourth and fifth thyristors, and the second inverter bridge turns on the fifth and sixth thyristors. When the rotor is in position 10, the fifth and sixth thyristors of the first inverter bridge are turned on, and the fifth and sixth thyristors of the second inverter bridge are turned on. When the rotor is in position 11, the fifth and sixth thyristors of the first inverter bridge are turned on, and the sixth and first thyristors of the second inverter bridge are turned on. When the rotor is in position 12, the sixth thyristor and the first thyristor of the first inverter bridge are turned on, and the sixth thyristor and the first thyristor of the second inverter bridge are turned on.
10. A pulse commutation method for a static frequency converter according to claim 9, characterized in that: When the thyristors turned on in the first inverter bridge and the second inverter bridge are different, the current vector of the first inverter bridge lags behind the current vector of the second inverter bridge by 30°.
11. A pulse commutation method for a static frequency converter according to claim 10, characterized in that: When the thyristors turned on by the first inverter bridge and the second inverter bridge are the same, on the transformer output side, the current vector of the first inverter bridge leads the current vector of the second inverter bridge by 30°.