Thyristor control method for marine medium and high voltage soft starters

Abstract

This invention relates to a thyristor control method for a marine medium-high voltage soft starter. The marine power grid supplies power to a three-phase motor via a controllable thyristor. During the motor startup phase, the controller sets a fixed-frequency interrupt (f). Upon entering the interrupt, thyristor control is completed, and the number of cycles is set to f ÷ 50Hz. In each interrupt, a dual-dq conversion phase-locked loop (PLL) technique, capable of resisting harmonic interference, is used to perform phase tracking of the marine power grid, obtaining the three-phase input phase angle of the thyristor. In each power cycle, a step function is used to process the startup voltage feedback deviation during startup, calculate the trigger angle, and update the trigger angle. The phase and trigger angle are compared based on line voltage triggering logic, and a high-frequency PWM pulse is used to trigger the thyristor, with synchronous calibration of the PWM. In the marine power grid, this method reduces the impact of poor power quality on the soft starter control, ensuring accurate thyristor control.

Description

Technical Field

[0001] This invention relates to a control technology, and more particularly to a thyristor control method for marine medium and high voltage soft starters. Background Technology

[0002] Limited by current semiconductor device manufacturing capabilities, the voltage withstand rating of thyristors is limited; 6kV medium voltage has essentially reached the limit for thyristors. Furthermore, in marine applications, the small capacity of the ship's electrical grid and the complexity of its electrical equipment result in relatively poor power quality. Moreover, the confined space inside ship cabins makes equipment repair difficult if it malfunctions, and damage during navigation is even more problematic. Therefore, reliability is paramount in medium- and high-voltage applications on ships, and since the core of a soft starter is the thyristor, accurate and error-free control of the thyristor becomes a crucial factor in the reliable operation of the equipment. Summary of the Invention

[0003] To address the stability issues of medium- and high-voltage soft starters, a thyristor control method for marine medium- and high-voltage soft starters is proposed, which effectively improves the reliability and stability of thyristor control for soft starters.

[0004] The technical solution of this invention is as follows: a thyristor control method for a marine medium-high voltage soft starter. The marine power grid supplies power to a three-phase motor through a controllable thyristor. During the motor startup phase, the controller sets a fixed-frequency interrupt f. After entering the interrupt, the thyristor control is completed, and the number of times in one electrical cycle is set to f ÷ 50Hz. In each interrupt, a dual dq conversion phase-locked loop technology that can resist harmonic interference is used to perform phase tracking of the marine power grid to obtain the three-phase input phase angle of the thyristor. In each electrical cycle, a step function is used to process the startup voltage feedback deviation during startup, calculate the trigger angle, and update the trigger angle once. The phase and trigger angle are compared according to the line voltage triggering logic. A high-frequency PWM pulse is used to trigger the thyristor, and the PWM is synchronously calibrated.

[0005] Furthermore, the three-phase input phase angle of the thyristor is calculated as follows:

[0006] The dual dq conversion phase-locked loop technology performs phase tracking on the ship's power grid, obtaining an angle of wt, where wt ranges from 0 to 2π, and converting 0 to 2π into 0 to 360 degrees.

[0007] Detect the zero crossing point where Uab changes from positive to negative. Starting from this zero crossing point, compare the magnitudes of Ubc and Uca within 60 degrees. If Ubc > Uca, it is positive sequence. The phase angle AngleAB of line voltage Uab = wt + 90, the phase angle AngleBC of line voltage Ubc = AngleAB - 120, and the phase angle AngleCA of line voltage Uca = AngleBC - 120. If the calculation results of AngleAB, AngleBC, and AngleCA > 360 degrees, then the calculation result - 360. If the calculation results of AngleAB, AngleBC, and AngleCA < 0 degrees, then the calculation result + 360;

[0008] Detect the zero crossing point where Uab changes from positive to negative. Starting from this zero crossing point, compare the magnitudes of Ubc and Uca within 60 degrees. If Ubc < Uca, it is negative sequence. The phase angle AngleAB of line voltage Uab = wt + 90, the phase angle AngleCA of line voltage Uca = AngleAB - 120, and the phase angle AngleBC of line voltage Ubc = AngleCA - 120. If the calculation results of AngleAB, AngleBC, and AngleCA > 360 degrees, then the calculation result - 360. If the calculation results of AngleAB, AngleBC, and AngleCA < 0 degrees, then the calculation result + 360.

[0009] Furthermore, the calculation of the firing angle is as follows:

[0010] First, use the step function to process the difference between the given voltage and the actual voltage to obtain the curve γ, γ = sgn(given voltage - actual voltage). Then, perform a PI calculation on γ once per electrical cycle to obtain the curve β, β = Kp×γ + Ki×Σγ. If β > 120, then β = 120, where Kp and Ki are the proportionality coefficient and the integral coefficient respectively, and the default values of Kp and Ki are 120÷(expected starting time (seconds) × 50). Finally, subtract β from the maximum firing angle of 150 degrees to obtain the firing angle α, α = 150 - β.

[0011] Furthermore, the thyristor firing logic is as follows:

[0012] It is stipulated that in each phase, the thyristor with the anode facing the power supply and the cathode facing the motor is the positive tube, and vice versa is the negative tube; the trigger logic of the thyristor is: AngleAB, AngleBC, and AngleCA are compared with the trigger angle α in turn. When α < AngleAB < 150, trigger the positive tube of phase A and the negative tube of phase B; when (α + 180) < AngleAB < 330, trigger the negative tube of phase A and the positive tube of phase B; when α < AngleBC < 150, trigger the positive tube of phase B and the negative tube of phase C; when (α + 180) < AngleBC < 330 degrees, trigger the negative tube of phase B and the positive tube of phase C; when α < AngleCA < 150, trigger the positive tube of phase C and the negative tube of phase A; when (α + 180) < AngleCA < 330 degrees, trigger the negative tube of phase C and the positive tube of phase A;

[0013] The thyristor is triggered by a double-pulse high-frequency PWM signal. The specific triggering method is as follows: After each interruption, first set the PWM duty cycle of all thyristors to 0%, then judge which thyristor should be triggered according to the thyristor trigger logic, and finally set the PWM duty cycle of the triggered thyristor to 50%; at the same time, if the used controller has the function of automatically synchronizing each PWM, synchronous setting should be carried out. If there is no automatic synchronization function, programming should be used to keep each PWM synchronized.

[0014] Furthermore, the thyristor control is completed after the interruption, and the specific steps are as follows:

[0015] 1) Enter the interruption, sample voltage and current, including the input voltage, output voltage, and output current of the thyristor, and then enter step 2);

[0016] 2) Judge whether the phase sequence detection is completed. If not, continue with the phase sequence detection, exit this interruption, and wait for the next interruption to enter; if the phase sequence detection has been completed, enter step 3);

[0017] 3) Phase-lock the input voltage of the thyristor, use the double dq transformation phase-locked loop method, output the angular velocity w, multiply w by the time t to get the angle wt, and then enter step 4);

[0018] 4) Based on the wt obtained in step 3), calculate the phases of the input three-phase voltages Uab, Ubc, and Uca of the thyristor input voltage, and then enter step 5);

[0019] 5) Accumulate and increment the number of times of entering this interruption by 1, and then enter step 6);

[0020] 6) Judge whether the accumulated value of the number of times of entering the interruption reaches the number of times in one electrical cycle. The number of times in one electrical cycle is f÷50Hz. If the number of times has reached, enter step 7). If the number of times has not reached, enter step 9);

[0021] 7) Calculate and update the trigger angle, and then enter step 8);

[0022] 8) Clear the accumulated interrupt count to zero, then proceed to 9);

[0023] 9) Compare the phases of the input three-phase voltages Uab, Ubc and Uca obtained in step 4) with the trigger angles in step 7). Based on the comparison results, set the PWM duty cycle of each thyristor according to the trigger logic, and exit the interrupt.

[0024] The beneficial effects of this invention are as follows: the thyristor control method for marine medium and high voltage soft starters of this invention reduces the impact of poor power quality on the control of soft starters in the ship's power grid, making the control of thyristors accurate and error-free. Attached Figure Description

[0025] Figure 1 This is a flowchart of the thyristor control process for the marine medium- and high-voltage soft starter of the present invention.

[0026] Figure 2 This invention provides the input voltage positive sequence determination, phase-locked loop output, and three-phase line voltage angle diagram.

[0027] Figure 3 This invention relates to input voltage negative sequence determination, phase-locked loop output, and three-phase line voltage angle diagram;

[0028] Figure 4 This is a diagram showing the firing angle calculation for this invention, using voltage ramp start as an example;

[0029] Figure 5 This is a schematic diagram of the thyristor in the main circuit of the soft starter of this invention;

[0030] Figure 6 This is a thyristor trigger pulse diagram for the present invention, taking a trigger angle of 100 degrees as an example. Detailed Implementation

[0031] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. These embodiments are based on the technical solution of the present invention and provide detailed implementation methods and specific operating procedures. However, the scope of protection of the present invention is not limited to the following embodiments.

[0032] A method for controlling thyristors in marine medium- and high-voltage soft starters is proposed. First, a dual-dq conversion phase-locked loop (PLL) technique capable of resisting strong harmonic interference is used to perform phase tracking on the ship's power grid, which has poor power quality, to obtain an accurate phase angle. Then, a step function is used to process the feedback deviation and calculate the trigger angle, enabling the thyristor's trigger angle to move unidirectionally and stably. The trigger angle is updated once in each electrical cycle. Finally, based on the line voltage triggering logic, a high-frequency PWM pulse is used to trigger the thyristor, and the PWM is synchronously calibrated.

[0033] Figure 1The diagram shows the thyristor control flowchart. The controller is configured with a fixed-frequency interrupt (typically set to 10kHz, but adjustable based on the processor's processing power). Upon entering the interrupt, thyristor control is completed. The specific control flow is as follows:

[0034] Step 1: Enter the interrupt, sample the voltage and current, including the thyristor input voltage, output voltage, and output current, and then proceed to Step 2;

[0035] Step 2: Determine if the phase sequence detection is complete. If not, continue with the phase sequence detection, exit the current interrupt, and wait for the next interrupt. If the phase sequence detection is complete, proceed to Step 3.

[0036] Step 3: Phase-locked loop is applied to the thyristor input voltage using the double dq transformation phase-locked loop method. The output angular velocity w is obtained by multiplying w by time t, and then proceeding to Step 4.

[0037] Step 4: Based on the wt obtained in Step 3, calculate the phase of the three-phase input voltages Uab, Ubc and Uca from the thyristor input voltage, and then proceed to Step 5;

[0038] Step 5: Increment the number of times this interrupt has been entered by 1, and then proceed to Step 6;

[0039] Step 6: Determine if the accumulated interrupt count has reached the number of interrupts in one electrical cycle. For example, if the interrupt frequency is set to 10kHz, then the number of interrupts in one electrical cycle is 10kHz ÷ 50Hz = 200. If the number has been reached, proceed to step 7; otherwise, proceed to step 9.

[0040] Step 7: Calculate and update the trigger angle, then proceed to Step 8;

[0041] Step 8: Clear the accumulated interrupt count to zero, and then proceed to step 9;

[0042] Step 9: Compare the phases of the input three-phase voltages Uab, Ubc, and Uca obtained in Step 4 with the trigger angles in Step 7. Based on the comparison results, set the PWM duty cycle of each thyristor according to the trigger logic, and exit the interrupt.

[0043] Figure 2Shown is the diagram of positive-sequence judgment of input voltage, PLL output, and three-phase line voltage angles. After the three-phase power supply of the device's main circuit is connected, the three-phase line voltage inputs Uab, Ubc, and Uca are collected. The zero-crossing point where Uab changes from positive to negative is detected. Starting from this zero-crossing point, the magnitudes of Ubc and Uca within 60 degrees are compared. If Ubc > Uca, it is positive sequence. After the phase-sequence detection is completed, the phase-sequence detection will not be performed again until the next power-on. After the phase-sequence detection is completed, the dual dq transformation PLL technology is used to track the phase of the three-phase line voltage, obtaining wt, where the range of wt is 0 - 2π. For convenient use, 0 - 2π is converted to 0 - 360 degrees. The phase angle of line voltage Uab, AngleAB = wt + 90, the phase angle of line voltage Ubc, AngleBC = AngleAB - 120, and the phase angle of line voltage Uca, AngleCA = AngleBC - 120. If the calculation results of AngleAB, AngleBC, and AngleCA > 360 degrees, the calculation results are - 360. If the calculation results of AngleAB, AngleBC, and AngleCA < 0 degrees, the calculation results are + 360.

[0044] Figure 3 Shown is the diagram of negative-sequence judgment of input voltage, PLL output, and three-phase line voltage angles. After the three-phase power supply of the device's main circuit is connected, the three-phase line voltage inputs Uab, Ubc, and Uca are collected. The zero-crossing point where Uab changes from positive to negative is detected. Starting from this zero-crossing point, the magnitudes of Ubc and Uca within 60 degrees are compared. If Ubc < Uca, it is negative sequence. After the phase-sequence detection is completed, the phase-sequence detection will not be performed again until the next power-on. After the phase-sequence detection is completed, the dual dq transformation PLL technology is used to track the phase of the three-phase line voltage, obtaining wt, where the range of wt is 0 - 2π. For convenient use, 0 - 2π is converted to 0 - 360 degrees. The phase angle of line voltage Uab, AngleAB = wt + 90, the phase angle of line voltage Uca, AngleCA = AngleAB - 120, and the phase angle of line voltage Ubc, AngleBC = AngleCA - 120. If the calculation results of AngleAB, AngleBC, and AngleCA > 360 degrees, the calculation results are - 360. If the calculation results of AngleAB, AngleBC, and AngleCA < 0 degrees, the calculation results are + 360.

[0045] Figure 4The figure shows a trigger angle calculation diagram taking the voltage ramp start as an example. In medium and high voltage, marine applications, smooth start and reliability are more important than start speed. Therefore, to avoid overcurrent at the initial stage of start and too slow voltage increase at the later stage of start, and to avoid motor oscillation caused by reciprocating movement of the trigger angle back and forth, the measures taken are as follows: First, use the step function to process the difference between the given voltage and the actual voltage to obtain the curve γ, γ = sgn(given voltage - actual voltage); then perform a PI calculation on γ once per electrical cycle (the PI calculation inputs the deviation step curve γ and outputs the phase shift angle β) to obtain the curve β, β = Kp×γ + Ki×Σγ. If β > 120, then β = 120, where Kp and Ki are the proportionality coefficient and the integral coefficient respectively. The default values of Kp and Ki are 120÷(expected start time (seconds) × 50). If you want to accelerate the start, you can appropriately increase Kp and Ki. If you want a smoother start, you can appropriately decrease Kp and Ki; finally, subtract β from the maximum trigger angle of 150 degrees to obtain the trigger angle α, α = 150 - β.

[0046] Figure 5 It is the schematic diagram of the thyristor in the main circuit of the soft starter. For the convenience of description, it is stipulated that in each phase, the thyristor with the anode facing the power supply and the cathode facing the motor is the positive tube, and vice versa is the negative tube. The trigger logic of the thyristor is as follows: AngleAB, AngleBC, and AngleCA are compared with the trigger angle α in turn. When α < AngleAB < 150, trigger the positive tube of phase A and the negative tube of phase B; when (α + 180) < AngleAB < 330, trigger the negative tube of phase A and the positive tube of phase B; when α < AngleBC < 150, trigger the positive tube of phase B and the negative tube of phase C; when (α + 180) < AngleBC < 330 degrees, trigger the negative tube of phase B and the positive tube of phase C; when α < AngleCA < 150, trigger the positive tube of phase C and the negative tube of phase A; when (α + 180) < AngleCA < 330 degrees, trigger the negative tube of phase C and the positive tube of phase A. The thyristor is triggered by a double dq transformation phase-locked loop technology that can resist strong harmonic interference instead of the zero-crossing timing method to perform phase tracking on the marine power grid with poor power quality to obtain accurate phase angles, providing necessary conditions for accurately triggering the thyristor;

[0047] Figure 6 It is the trigger pulse schematic diagram drawn according to the above thyristor trigger logic and trigger method taking the trigger angle of 100 degrees as an example.

[0048] Use the double dq transformation phase-locked loop technology that can resist strong harmonic interference to replace the zero-crossing timing method to perform phase tracking on the marine power grid with poor power quality to obtain accurate phase angles, providing necessary conditions for accurately triggering the thyristor;

[0049] The trigger angle calculation process uses a step function to make the trigger angle of the thyristor move unidirectionally and update the trigger angle once per electrical cycle, so as to achieve a smooth start-up process in the early stage and a smooth start-up process in the middle and late stages, and avoid motor oscillation caused by the back-and-forth movement of the trigger angle.

[0050] The trigger logic is determined by directly using the line voltage angle, avoiding the accuracy loss caused by the line voltage to phase voltage transition. High-frequency PWM pulses are used to trigger the thyristor, and the PWM is synchronously calibrated to ensure the reliability and accuracy of the final triggering step in the thyristor control process.

[0051] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A thyristor control method for a marine medium-high voltage soft starter, wherein the marine power grid supplies power to a three-phase motor via a controllable thyristor, characterized in that... The controller is set to a fixed frequency during the motor startup phase. f Interrupt, after entering the interrupt, complete the thyristor control and set the number of times in one electrical cycle. f ÷50Hz; each interrupt uses a dual-channel system capable of resisting harmonic interference. dq Phase-locked loop (PLL) technology is used for phase tracking of the ship's electrical network to obtain the phase angle of the three-phase input of the thyristors. In each electrical cycle, a step function is used to process the startup voltage feedback deviation during startup, calculate the trigger angle, and update the trigger angle. The comparison between phase and trigger angle is based on line voltage triggering logic, using high frequency... PWM The pulse triggers the thyristor and... PWM Perform synchronous calibration; calculate the three-phase input phase angle of the thyristor: pair dq Phase-locked loop (PLL) technology is used for phase tracking of the ship's electrical network to obtain the angle. wt , wt The range is 0 - 2 π , will 0 - 2 π Convert to 0-360 degrees; Detection Uab Starting from the zero-crossing point where the positive value changes to the negative value, compare the values ​​within 60 degrees from that point. UBC and Uca The size, if Ubc> Uca This is the positive sequence, line voltage. Uab phase angle AngleAB=wt+ 90, line voltage UBC phase angle AngleBC=AngleAB -120, line voltage Uca phase angle AngleCA=AngleBC -120; like AngleAB, AngleBC, AngleCA If the calculated result is greater than 360 degrees, then the calculated result is -360. AngleAB, AngleBC, AngleCA If the calculated result is less than 0 degrees, then the calculated result is +360. Detection Uab Starting from the zero-crossing point where the positive value changes to the negative value, compare the values ​​within 60 degrees from that point. UBC and Uca The size, if UBC< Uca Then it is negative sequence, line voltage Uab phase angle AngleAB = wt + 90 Line voltage Uca phase angle AngleCA=AngleAB- 120 Line voltage UBC phase angle AngleBC=AngleCA-120 ; like AngleAB, AngleBC, AngleCA If the calculated result is greater than 360 degrees, then the calculated result is -360. AngleAB, AngleBC, AngleCA If the calculated result is less than 0 degrees, then the calculated result is +360.

2. The thyristor control method for marine medium- and high-voltage soft starters according to claim 1, characterized in that, The trigger angle calculation: First, a step function is used to process the difference between the given voltage and the actual voltage, resulting in the curve γ, where γ = sgn(given voltage - actual voltage). Then, a PI calculation is performed on γ for each electrical cycle, yielding the curve... β , β=Kp×γ+Ki×Σ γ ,like β> 120, then β =120, where Kp, Ki These are the proportional coefficient and the integral coefficient, respectively. Kp, Ki The default value is 120 ÷ (expected startup time (seconds) × 50); finally, subtract the maximum trigger angle of 150 degrees. β Get the trigger angle α，α= 150 -β .

3. The thyristor control method for marine medium- and high-voltage soft starters according to claim 1 or 2, characterized in that, The thyristor triggering logic is as follows: In each phase, the thyristor with its anode facing the power supply and its cathode facing the motor is designated as a positive thyristor, and vice versa. The triggering logic for the thyristors is as follows: AngleAB, AngleBC, AngleCA sequentially with trigger angle α When making comparisons, α < AngleAB < 150 This triggers the positive phase A transistor and the negative phase B transistor; when ( α+ 180)< AngleAB <330, triggers phase A reverse transistor and phase B forward transistor; when α <AngleBC < 150, triggering the B-phase positive tube and the C-phase negative tube; when( α+ 180)< AngleBC <330 degrees, triggering phase B reverse tube and phase C forward tube; when α < AngleCA < 150 This triggers the C-phase positive tube and the A-phase reverse tube; when ( α+ 180)< AngleCA <330 degrees, triggering the C phase reverse tube and the A phase forward tube; The thyristor uses a dual-pulse high frequency. PWM The signal triggers the interrupt, specifically by setting the parameters of all thyristors after each interrupt is entered. PWM The duty cycle is 0%, then the thyristor triggering logic determines which thyristor should be triggered, and finally the thyristor to be triggered is set. PWM The duty cycle is 50%; simultaneously, if the controller used has automatic synchronization of each channel... PWM The function should be synchronized. If there is no automatic synchronization function, then programming should be used to synchronize each channel. PWM Keep in sync.

4. The thyristor control method for marine medium- and high-voltage soft starters according to claim 3, characterized in that, The thyristor control is completed after the interruption, and the specific steps are as follows: 1) Enter interrupt, sample voltage and current, including thyristor input voltage, output voltage, and output current, then enter 2). 2) Determine whether the phase sequence detection is complete. If not, continue the phase sequence detection, exit the current interrupt, and wait for the next interrupt. If phase sequence detection has been completed, proceed to step 3). 3) Phase-locked loop (PLL) is applied to the thyristor input voltage using a dual-phase method. dq Transformation phase-locked loop method, output angular velocity w , w Multiply by time t Obtaining the angle wt Then proceed to step 4). 4) Based on the results obtained in step 3) wt The input three-phase voltage is calculated from the thyristor input voltage. Uab, Ubc and Uca The phase, then enter 5); 5) Accumulate the number of times this interrupt has been entered by 1, then proceed to 6). 6) Determine if the accumulated interrupt count has reached the count for one electrical cycle. The count for one electrical cycle is... f ÷50Hz, if the number of times has been reached, proceed to step 7); if the number of times has not been reached, proceed to step 9). 7) Calculate and update the trigger angle, then proceed to 8). 8) Clear the accumulated interrupt count to zero, then proceed to 9). 9) The input three-phase voltage obtained in step 4) Uab, Ubc and Uca The phase of the thyristor is compared with the trigger angle in step 7), and the comparison result is used to set the trigger logic for each thyristor. PWM Duty cycle, exit interrupt.

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