A control method and system for realizing soft start of thyristor rectifier bridge

Abstract

The application discloses a control method and system for realizing soft starting of a thyristor rectifier bridge, and belongs to the technical field of power generation, power transformation or power distribution. According to the real-time obtained power grid voltage parameters and the power grid voltage frequency, the application introduces specific logic to accurately identify the half-cycle position of the power grid voltage, reduces the frequency measurement error caused by power grid voltage distortion, accurately generates the thyristor driving pulse according to the obtained power grid voltage frequency, introduces a thyristor turn-off point automatic correction algorithm, automatically adjusts the phase of the thyristor driving pulse cycle by cycle, avoids the failure of the thyristor slow starting, and thus ensures the reliable and accurate generation of the thyristor driving pulse.

Description

Technical Field

[0001] This invention discloses a control method and system for achieving soft starting of a thyristor rectifier bridge, belonging to the technical field of power generation, power transformation or power distribution. Background Technology

[0002] Thyristor semi-controlled rectifier bridges are widely used in the front stage of AC / DC converters, typically to rectify AC voltage into rectified voltage. Figure 1A A circuit diagram of a thyristor semi-controlled rectifier bridge system is given, which mainly consists of an input AC power supply V. AC Diodes D1 and D2, Q1 and Q2, and output capacitor C. o It consists of a DC-to-DC converter and other components. A semi-controlled rectifier bridge, composed of the first diode D1, the second diode D2, the first thyristor Q1, and the second thyristor Q2, is used to convert the input AC voltage V... AC The voltage is rectified to DC voltage vb. The key to thyristor-controlled rectification lies in the reasonable and effective control of the turn-on and turn-off times of the first thyristor Q1 and the second thyristor Q2. If the control is improper, at the initial start-up of the circuit, due to the output capacitor C... o If the voltage is zero and the first thyristor Q1 and the second thyristor Q2 are not properly controlled, it will cause the output capacitor C to... o The initial charging current is too large, which on the one hand affects the input AC voltage source v AC This can cause excessive inrush current pressure, and on the other hand, excessive charging current may damage power devices.

[0003] Existing technologies, such as US Patent US2017324350A1 and Chinese Patent CN111342436A, provide drive signals v for the first thyristor Q1 and the second thyristor Q2. gT The ideal way to produce it, such as Figure 1B As shown. In an ideal driving mode, a driving pulse is generated for each half-wave of the grid voltage. This pulse is generated only during the 1 / 4 half-cycle of the grid voltage drop. The driving pulse has two aspects: firstly, its rising edge gradually "moves forward" until it reaches the peak of the grid voltage; secondly, its falling edge remains essentially constant, meaning the pulse width of the thyristor driving pulse gradually increases. For example... Figure 1C As shown, a key technical challenge in generating ideal drive pulses lies in accurately setting the rising edge timing of each drive pulse of the thyristor, and this rising edge needs to be gradually "moved forward," typically with sufficiently fine step sizes. Furthermore, another key technical challenge in generating ideal drive pulses is rationally setting the falling edge of each drive pulse, i.e., the thyristor's turn-off point. This falling edge must be ensured to fall within one-quarter of the voltage drop cycle of the mains voltage. Figure 1C, usually with a margin, the drive pulse turn-off point is set at the t2 time point, and the drive pulse turn-off point is at most at the t3 time point, and if it is moved further back, the thyristor cannot be turned off within the current grid voltage half-wave, resulting in failure of the soft start function and causing overcurrent stress problems. It should be pointed out that the front rising edge and the rear falling edge of the drive pulse are strongly coupled with the frequency of the grid voltage. In addition, the thyristor drive pulse usually needs to last for tens of grid cycles, and during this process, if the grid voltage is distorted or the frequency drifts, it will pose a great challenge to the thyristor drive pulse.

[0004] Chinese invention patent CN111342436A proposes to determine the front rising edge time point of the drive pulse by sampling the form of the grid voltage, that is, the absolute value of the input grid voltage corresponding to the front edge of the nth drive pulse is greater than the absolute value of the input grid voltage corresponding to the front edge of the n-1 drive pulse. This scheme has great limitations, on the one hand, the voltage difference of the grid voltage corresponding to the adjacent two drive pulses is usually small, and it is easy to misjudge; in addition, when the grid voltage is distorted, this scheme is invalid. US2017324350A1 addresses the problem and does not provide a specific implementation scheme, only an ideal drive pulse waveform is given.

[0005] In summary, for the problem of thyristor rectifier soft start drive pulse generation, the present application aims to provide a drive pulse generation method for realizing reliable soft start of thyristor rectifier. SUMMARY

[0006] The application aims to solve the technical problems of failure of the soft start of the thyristor rectifier bridge due to distortion of the grid voltage or frequency drift.

[0007] The application adopts the following technical solutions to achieve the above application purposes:

[0008] A control method for realizing soft start of a thyristor rectifier bridge, comprising the following three steps:

[0009] A. Obtain grid voltage parameters from the real-time sampled grid voltage signal, the grid voltage parameters including grid voltage mean value, grid voltage maximum value, and grid voltage minimum value;

[0010] B. When the real-time sampled grid voltage is within 1 / 4 of the grid voltage rise cycle and the sampled grid voltage value exceeds the first reference voltage, the number of sampling cycles is recorded. After the real-time sampled grid voltage sequentially reaches the maximum grid voltage, is less than the first reference voltage, is less than the second reference voltage, and exceeds the first reference voltage, the sampled cycle value that has been experienced is assigned to the grid voltage frequency count value. The first and second reference voltages are determined based on the maximum grid voltage, and the second reference voltage is less than the first reference voltage. The criterion that the real-time sampled grid voltage is within 1 / 4 of the grid voltage rise cycle is determined based on the average grid voltage.

[0011] C. When the real-time sampled grid voltage is within 1 / 4 of the grid voltage drop cycle, initialize the thyristor pulse turn-on and turn-off points, obtain the minimum grid voltage between the thyristor pulse turn-on and turn-off points, and obtain the minimum grid voltage within 1 / 4 of the grid voltage cycle after the thyristor pulse turn-off point. When the minimum grid voltage between the thyristor pulse turn-on and turn-off points is less than the minimum grid voltage within 1 / 4 of the grid voltage cycle after the thyristor pulse turn-off point, perform a phase shift operation on the turn-on and turn-off points of the next thyristor pulse. When the minimum grid voltage between the thyristor pulse turn-on and turn-off points is greater than the minimum grid voltage within half a grid voltage cycle after the thyristor pulse turn-off point, only advance the turn-on time of the next thyristor pulse. The criterion that the real-time sampled grid voltage is within 1 / 4 of the grid voltage drop cycle is determined based on the maximum and minimum grid voltage values.

[0012] Furthermore, in a control method for achieving soft start of a thyristor rectifier bridge, the specific implementation method of step A is as follows:

[0013] A-1. Wait for the grid voltage sampling to complete;

[0014] A-2, Accumulate the loop counter value;

[0015] A-3. If the loop count value exceeds the count threshold, proceed to A-9; otherwise, proceed to A-4.

[0016] A-4. Add the current sampled value of the grid voltage to the total grid voltage value;

[0017] A-5. If the current sampled value of the grid voltage is greater than the maximum value of the grid voltage, proceed to A-7; otherwise, proceed to A-6.

[0018] A-6. If the current sampled value of the grid voltage is less than the minimum value of the grid voltage, proceed to A-8; otherwise, jump to A-1.

[0019] A-7 assigns the current sampled value of the grid voltage to the maximum value of the grid voltage;

[0020] A-8. Assign the current sampled value of the grid voltage to the minimum grid voltage value;

[0021] A-9. Calculate the average grid voltage based on the current total grid voltage value and the counting threshold, and use the current maximum and minimum grid voltage values ​​as the final maximum and minimum grid voltage values.

[0022] A-10. Set the total grid voltage and the maximum grid voltage to zero, assign the rated peak grid voltage to the minimum grid voltage, and jump to A-1.

[0023] Furthermore, in a control method for achieving soft starting of a thyristor rectifier bridge, the specific implementation method of step B is as follows:

[0024] B-1. Wait for the grid voltage sampling to complete;

[0025] B-2, Accumulate the loop counter value;

[0026] B-3. ​​For branches with a status flag value less than 2, if the current sampled value of the grid voltage is less than the average value of the grid voltage, set the status flag value to 2 and jump to B-1; otherwise, jump directly to B-1.

[0027] B-4, the branch with a status flag value of 2: if the current sampled value of the grid voltage is greater than the average value of the grid voltage, set the status flag value to 3 and jump to B-1; otherwise, jump directly to B-1.

[0028] B-5, branch with status flag value of 3: If the current sampled value of the grid voltage is greater than the first reference voltage, set the status flag value to 4, set the cycle count value to zero, and jump to B-1; otherwise, jump directly to B-1. The first reference voltage is (0.8~0.9)×v. gmax v gmax This represents the maximum grid voltage.

[0029] B-6, the branch with a status flag value of 4: when the current sampled value of the grid voltage is less than the first reference voltage, set the status flag value to 5 and jump to B-1; otherwise, jump directly to B-1.

[0030] B-7, branch with status flag value of 5: If the current sampled value of the grid voltage is less than the second reference voltage, set the status flag value to 6 and jump to B-1; otherwise, jump directly to B-1. The second reference voltage is (0.3~0.6)×v. gmax ;

[0031] B-8, the branch with a status flag value of 6: when the current sampled value of the grid voltage is greater than the second reference voltage, set the status flag value to 2, assign the current loop count value to the grid voltage frequency count value, and jump to B-1; otherwise, jump directly to B-1.

[0032] Furthermore, in a control method for achieving soft starting of a thyristor rectifier bridge, the specific implementation method of step C is as follows:

[0033] C-1. Wait for the grid voltage sampling to complete;

[0034] C-2, Accumulate the loop counter value;

[0035] C-3. If the cycle count value exceeds the grid voltage frequency count value, proceed to C-4; otherwise, proceed to C-5.

[0036] C-4. Clear the loop counter value to zero;

[0037] C-5. If the grid voltage frequency count value is within the preset grid frequency range, proceed to C-6; otherwise, jump to C-1.

[0038] C-6. For branches with a status flag value less than 3, if the current sampled value of the grid voltage is greater than the first reference value, set the status flag value to 3 and jump to C-1; otherwise, jump directly to C-1. The first reference value is (0.8~0.9)×v. gmax v gmax This represents the maximum grid voltage.

[0039] C-7. For branches with a status flag value of 3, when the current sampled value of the grid voltage is less than the second reference value, set the status flag value to 4, assign the grid voltage frequency count value to the loop count value, initialize the thyristor pulse's on / off point, and set the second reference value to (0.1~0.2)×v. gmin v gmin This is the minimum grid voltage.

[0040] C-8, the branch with a status flag value of 4, when the loop count value is greater than the thyristor pulse turn-on point, sets the status flag value to 5, assigns the peak value of the rated grid voltage to the first auxiliary signal, sets the thyristor drive signal to high level, and starts soft start; otherwise, jumps to C-1.

[0041] C-9, the branch with a status flag value of 5: when the current sampled value of the grid voltage is less than the first auxiliary signal, the current sampled value of the grid voltage is assigned to the first auxiliary signal; otherwise, when the current cycle count value reaches the thyristor pulse turn-off point, the status flag value is set to 6, the thyristor drive signal is set to low level, and the peak value of the grid voltage is assigned to the second auxiliary signal; when the current cycle count value does not reach the thyristor pulse turn-off point, the branch directly jumps to C-1.

[0042] C-10, the branch with a status flag value of 6: when the current sampled value of the grid voltage is less than the second auxiliary signal, the current sampled value of the grid voltage is assigned to the second auxiliary signal; otherwise, when the current cycle count value exceeds half of the grid voltage frequency count value and the current cycle count value has not reached the thyristor pulse turn-off point, the status flag value is set to 7 and the branch jumps to C-1; when the current cycle count value does not exceed half of the grid voltage frequency count value or the current cycle count value reaches the thyristor pulse turn-off point, the branch jumps directly to C-1.

[0043] C-11, the branch with a status flag value of 7, when the current value of the first auxiliary signal is less than the current value of the second auxiliary signal, performs a phase shift operation on the turn-on and turn-off points of the next thyristor pulse; otherwise, only the turn-on time of the next thyristor pulse is shifted forward, the status flag value is set to 4, and the process proceeds to C-12.

[0044] C-12. When the current thyristor pulse activation point is less than half of the grid voltage frequency count value, set the status flag value to 0, set the thyristor drive signal to always high, and end the soft start.

[0045] Furthermore, in a control method for achieving soft start of a thyristor rectifier bridge, the sampling frequency of the grid voltage is more than 500 times the rated frequency of the grid.

[0046] Furthermore, in a control method for achieving soft start of a thyristor rectifier bridge, the counting threshold is 2 to 3 cycles of the lowest grid voltage.

[0047] Furthermore, in a control method for soft-starting a thyristor rectifier bridge, in step C-7, the expression for the initialization point and turn-off point of the thyristor pulse is P. on =N pd -N ont P off =N pd -N oft , where P on P off N represents the turn-on and turn-off points of the thyristor pulse. pd N represents the grid voltage frequency count value. ont N oft N represents the bias points for the thyristor pulse turn-on and turn-off points, respectively. ont = 0.05 × N pd N oft = 0.05 × N pd .

[0048] Furthermore, in a control method for achieving soft start of a thyristor rectifier bridge, in step C-11, the expression for performing a phase shift operation on the turn-on and turn-off points of the next thyristor pulse is P.on =P on -N onx -N phase P off = P off -N phase The expression for shifting the turn-on time of the next thyristor pulse forward only is P. on =P on -N onx P off = P off , where P on P off N represents the turn-on and turn-off points of the thyristor pulse. onx N is the step size for advancing the turn-on time of the next thyristor pulse. phase It is the step size of the phase shift operation.

[0049] Furthermore, in a control method for achieving soft start of a thyristor rectifier bridge, N phase =(0.01~0.05)×N pd or N phase = k × (v gW_min - v gP_min ), where k is the proportionality coefficient, v gP_min v gW_min These are the first and second auxiliary signals.

[0050] A control system for implementing soft starting of a thyristor rectifier bridge includes:

[0051] The grid voltage parameter acquisition module acquires grid voltage parameters from real-time sampled grid voltage signals. The grid voltage parameters include the average grid voltage, the maximum grid voltage, and the minimum grid voltage.

[0052] The real-time grid voltage frequency acquisition module starts recording the number of sampling periods when the sampled grid voltage is within 1 / 4 of the grid voltage rise cycle and the sampled grid voltage value exceeds the first reference voltage. After the real-time sampled grid voltage sequentially reaches its maximum value, falls below the first reference voltage, falls below the second reference voltage, and exceeds the first reference voltage, the module assigns the already experienced sampling period values ​​to the grid voltage frequency count value. The first and second reference voltages are determined based on the maximum grid voltage value, and the second reference voltage is less than the first reference voltage. The criterion that the real-time sampled grid voltage is within 1 / 4 of the grid voltage rise cycle is determined based on the average grid voltage value.

[0053] The thyristor pulse generation module initializes the thyristor pulse turn-on and turn-off points when the real-time sampled grid voltage is within 1 / 4 of the grid voltage drop cycle. It then obtains the minimum grid voltage between the thyristor pulse turn-on and turn-off points, and the minimum grid voltage within 1 / 4 of the grid voltage cycle after the thyristor pulse turn-off point. If the minimum grid voltage between the thyristor pulse turn-on and turn-off points is less than the minimum grid voltage within 1 / 4 of the grid voltage cycle after the thyristor pulse turn-off point, it performs a phase shift operation on the turn-on and turn-off points of the next thyristor pulse. If the minimum grid voltage between the thyristor pulse turn-on and turn-off points is greater than the minimum grid voltage within half a grid voltage cycle after the thyristor pulse turn-off point, it only advances the turn-on time of the next thyristor pulse. The criterion that the real-time sampled grid voltage is within 1 / 4 of the grid voltage drop cycle is determined based on the maximum and minimum grid voltage values.

[0054] The present invention, by adopting the above technical solution, has the following beneficial effects:

[0055] (1) The thyristor rectifier bridge soft start scheme proposed in this invention can adapt to changes in grid voltage and grid frequency. By acquiring key information such as grid voltage peak value and average value in real time, and further automatically acquiring grid frequency in real time based on the acquired key information, the thyristor drive pulse is reliably and accurately generated.

[0056] (2) In the case of grid voltage distortion, the present invention introduces specific logic to accurately identify the grid voltage half-cycle, reduce the frequency measurement error caused by grid voltage distortion, and accurately generate thyristor drive pulses based on the obtained grid voltage frequency to ensure the reliability of thyristor pulse drive.

[0057] (3) In the case of power grid voltage and frequency changes, the present invention introduces an automatic thyristor turn-off point correction algorithm to automatically adjust the phase of the thyristor drive pulse cycle by cycle, avoid thyristor soft start failure, and greatly improve reliability. Attached Figure Description

[0058] Figure 1A This is the circuit diagram of a thyristor semi-controlled rectifier bridge system. Figure 1B A schematic diagram illustrating the generation of an ideal thyristor drive signal using existing technology. Figure 1C This is a schematic diagram showing the gradual forward movement of the rising edge of an ideal driving pulse.

[0059] Figure 2A This is a circuit diagram of a thyristor semi-controlled rectifier bridge system and a mains voltage sampling circuit. Figure 2B This is a block diagram of the control system for implementing soft start of the thyristor rectifier bridge according to the present invention.

[0060] Figure 3 The flowchart shows the specific implementation process for the power grid parameter acquisition module to obtain the maximum, minimum, and average values ​​of the power grid voltage.

[0061] Figure 4A and Figure 4B The flowchart and corresponding waveform diagram show the specific implementation process for the real-time grid voltage frequency acquisition module to obtain the frequency count value of the grid voltage. Figure 4C This is a waveform diagram for measuring the grid frequency under grid voltage distortion conditions.

[0062] Figure 5A and Figure 5B The flowchart and corresponding waveform diagram show the specific implementation of the thyristor pulse generation module for generating thyristor pulses. Figure 5C This is a schematic diagram illustrating the correction of the thyristor drive pulse by combining the first auxiliary voltage and the second auxiliary voltage.

[0063] Figure 6 The waveform of the thyristor drive pulse generated by the control method of the present invention is shown.

[0064] Explanation of the labels in the diagram: D1, D2, D3, and D4 are the first, second, third, and fourth diodes, respectively; Q1 and Q2 are the first and second thyristors, respectively; C... o R1 and R2 are the output capacitor and the first and second sampling resistors, respectively. Detailed Implementation

[0065] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the listed embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of the present invention.

[0066] like Figure 2A As shown, the main power circuit of the thyristor semi-controlled rectifier bridge system consists of an input AC voltage source AC, a first thyristor Q1, a second thyristor Q2, a first diode D1, a second diode D2, and an output capacitor C. o The system consists of a DC-DC converter and a thyristor-controlled rectifier bridge composed of first thyristor Q1, first thyristor Q2, first diode D1, and second diode D2. A mains voltage sampling circuit, composed of third diode D3, fourth diode D4, first sampling resistor R1, and second sampling resistor R2, samples the input AC voltage V. AC Rectified into a steampunk wave signal v g Steamed bun wave signal v g Input to the control system.

[0067] like Figure 2BAs shown, the input signal of the control system is the grid voltage waveform signal v. g The output signal is the drive pulse signal v of the first thyristor Q1 and the second thyristor Q2 in the main power circuit. gT and the identification signal v ct ; Identification signal v ct The signal is active high to indicate the end of the thyristor semi-controlled rectification soft start. The control system consists of three parts: a grid voltage parameter acquisition module, a grid voltage frequency real-time acquisition module, and a thyristor pulse generation module. In this embodiment, the grid voltage waveform signal v input to the control system... g After processing by the grid voltage parameter acquisition module, the maximum value v of the grid voltage is obtained. gmax Minimum value v gmin Average value v gavg The maximum value of the grid voltage, v. gmax Minimum value v gmin and average v gavg and the grid voltage waveform signal v g The input is sent to the real-time grid voltage and frequency acquisition module to obtain the frequency count value N of the grid voltage. pd The frequency count value N of the grid voltage. pd Maximum grid voltage v gmax Minimum grid voltage v gmin and the real-time grid voltage waveform signal v g The input is sent to the thyristor pulse generation module, which generates thyristor pulses and performs real-time correction.

[0068] Figure 2B The grid voltage parameter acquisition module shown obtains the maximum value v of the grid voltage. gmax Minimum value v gmin Average value v gavg The specific implementation flowchart is as follows Figure 3 As shown, it is mainly divided into steps 201 to 210.

[0069] Step 201: Wait for the grid voltage waveform sampling to complete. After sampling, proceed to step 202. It should be noted that in this embodiment of the invention, the grid voltage waveform is sampled at a fixed sampling frequency, typically more than 500 times the rated frequency of the grid.

[0070] Step 202, loop count value C yc Accumulate.

[0071] Step 203, determine the count value C yc Does it exceed the counting threshold N? cyc If yes, proceed to step 209; otherwise, proceed to step 204. It should be noted that the counting threshold N...cyc This typically corresponds to 2 to 3 periods of lowest grid voltage.

[0072] Step 204: Accumulate the current grid voltage sample value v g (k), i.e., v gsumT =v gsumT +v g (k). Wherein, v g (k) refers to the sampled value of the current k-th grid voltage waveform. After step 204, proceed to step 205.

[0073] Step 205: Determine the current grid voltage sampling value v g (k) Is it greater than the maximum grid voltage v? gmaxT If so, proceed to step 207 and assign the current grid voltage sample value to v. gmaxT If not, proceed to step 206.

[0074] Step 206: Determine the current grid voltage sampling value v g (k) Is it less than the minimum grid voltage v? gminT If so, proceed to step 208 and assign the current grid voltage sample value to v. gminT If not, proceed to the waiting step 201.

[0075] Step 209, store relevant data, wherein the average grid voltage is determined by v gsum =v gsumT / N cyc Simultaneously, the final values ​​of the maximum and minimum grid voltages are assigned to v respectively. gmax and v gmin Then proceed to step 210;

[0076] Step 210, variable reset, v gsum and v gmax Reset to 0, v gminT Reset to V m V m It is the rated peak value of the power grid voltage.

[0077] Figure 2 shows the specific implementation process and corresponding waveforms for the real-time grid voltage frequency acquisition module to acquire the frequency count value of the grid voltage. Figure 4A and Figure 4B As shown, the specific implementation process of the acquisition module to acquire the frequency count value of the grid voltage includes steps 301 to 315.

[0078] Step 301: Wait for the grid voltage waveform sampling to complete. After sampling, proceed to step 302. It should be noted that in this embodiment of the invention, the grid voltage waveform is sampled at a fixed sampling frequency, typically more than 500 times the rated frequency of the grid.

[0079] Step 302, loop count value N cnt Accumulate.

[0080] Step 303, based on status flag S ys The value determines the branch to execute. There are a total of S... ys <2 branches, S ys =2 branches, S ys =3 branches, S ys =4 branches, S ys =5 branches, S ys =6 branches, which are six code execution branches.

[0081] S ys <2 logic branches. Step 304, determine the current sampled value v of the grid voltage waveform. g (k) Is it less than the average grid voltage v? g_avg If so, proceed to step 310 and set the status flag signal S. ys =2, then jump to waiting step 301; otherwise, jump directly to waiting step 301.

[0082] S ys =2 logic branches. Step 305, the current sampled value v of the grid voltage waveform. g (k) Is it greater than the average grid voltage v? g_avg If so, proceed to step 311 and set the status flag signal S. ys =3, then jump to waiting step 301; otherwise, jump directly to waiting step 301.

[0083] S ys =3 logic branches. Step 306, the current sampled value v of the grid voltage waveform. g (k) Is it greater than the grid voltage reference value v? g_hsd Baseline value v g_hsd Based on actual operating conditions, the recommended value for v in this embodiment of the invention is... g_hsd = (0.8~0.9)×v gmax If so, proceed to step 312 and set the status flag signal S. ys = 4 and set the loop counter value N cnt = 0, then jump to waiting step 301; otherwise, jump directly to waiting step 301.

[0084] S ys=4 logic branches. Step 307, the current sampled value v of the grid voltage waveform. g (k) Is it less than the grid voltage reference value v? g_hsd If so, proceed to step 313 and set the status flag signal S. ys =5, then jump to waiting step 301; otherwise, jump directly to waiting step 301.

[0085] S ys =5 logic branches. Step 307, the current sampled value v of the grid voltage waveform. g (k) Is it less than the grid voltage reference value v? g_lsd Baseline value v g_lsd Based on actual operating conditions, the recommended value for v in this embodiment of the invention is... g_lsd =(0.3~0.6)×v gmax If so, proceed to step 314 and set the status flag signal S. ys =6, then jump to waiting step 301; otherwise, jump directly to waiting step 301.

[0086] S ys =6 logic branches. Step 309, the current sampled value v of the grid voltage waveform. g (k) Is it greater than the grid voltage reference value v? g_hsd If so, proceed to step 315 and set the status indicator signal S. ys =2 and read the current loop count value N pd =N cnt N pd If the current grid voltage cycle is measured, then proceed to the waiting step 301; otherwise, proceed directly to the waiting step 301.

[0087] Figure 4A The logical representation of the execution block diagram is as follows: Figure 4B As shown. The cycle count value N cnt Continuous accumulation, N is calculated after each grid voltage sampling. cnt Perform an increment operation. First, monitor the real-time sampling value v of the grid voltage waveform. g (k), first find t 40 Point, i.e., the real-time value of the grid voltage v g (k) is greater than the average grid voltage v g_avg After locating the voltage point, continue monitoring the grid voltage sampling value v. g (k), when v g (k) is greater than the first baseline value v g_hsd t 41 Point, reset the cycle count value N to zero. cnt and the t 41The point is used as the starting point for measuring the grid voltage cycle. First reference point v g_hsd Typically, a point with a relatively high grid voltage is selected; in this embodiment of the invention, a value of v is recommended. g_hsd =(0.8~0.9)×v gmax First reference point v g_hsd Second reference point v g_lsd Used to calculate the power grid frequency. The reason for choosing t is... 41 There are two reasons for using a point as the starting point of the cycle: 1) To improve reliability and avoid misjudgment. When the grid voltage is relatively high, the grid voltage distortion is usually small, thus avoiding the selection of the wrong starting point of the cycle; 2) To improve accuracy. When the grid voltage is relatively high, the rate of change of the grid voltage is relatively small, and the impact of the inaccuracy of the starting point of the cycle caused by the sampling error of the control system on the accuracy of frequency measurement is relatively small.

[0088] See Figure 4B Select the starting point t for periodic measurement 41 The next step is to determine the end point t of the cycle. 44 Traditional frequency measurement methods typically involve directly detecting the grid voltage sample value (V) in real time. g (k) until v appears again g (k) is greater than the first reference point v g_hsd While traditional methods are simple and convenient, they are prone to frequency measurement errors under conditions of grid voltage distortion. (See also...) Figure 4C This paper presents one possible scenario for grid voltage distortion. After determining t... 51 After determining the start point of the cycle, according to the traditional method, the end point of the power grid cycle is easily determined as t. 52 This is clearly incorrect, demonstrating the low reliability of traditional period measurement schemes and their susceptibility to period calculation errors. This invention addresses this by introducing an additional condition for determining the midpoint of the period, namely… Figure 4B t in 42 Point and t 43 Point, that is Figure 4C t in 52 Point and t 53 This method effectively avoids errors in periodic measurements, significantly improves reliability, and better adapts to scenarios with power grid distortion. See embodiments of this invention for details. Figure 4B In determining the real-time value of the grid voltage v g (k) Descends to the second baseline v g_lsd Only then will the final cycle end point be determined to improve reliability.

[0089] Figure 2A The flowchart and corresponding waveform diagram of the thyristor pulse generation module for generating thyristor pulses are shown below. Figure 5A andFigure 5B As shown, Figure 5A The specific implementation process shown consists of 28 steps, from step 501 to step 527.

[0090] Step 501: Wait for the grid voltage waveform sampling to complete. After sampling, proceed to step 502. It should be noted that in this embodiment of the invention, the grid voltage waveform is sampled at a fixed sampling frequency, typically more than 500 times the rated frequency of the grid.

[0091] Step 502, loop count value P cyc Accumulate.

[0092] Step 503, determine the count value P cyc Does it exceed the threshold N? pd N pd That is Figure 4A The obtained grid voltage frequency count value, i.e., the real-time periodic value of the grid voltage. If so, proceed to step 504 to clear the count value P. cyc Otherwise, proceed to step 505.

[0093] Step 505, determine the power grid frequency count value N. pd If the frequency is within the preset power grid frequency range, proceed to step 506; otherwise, proceed to the waiting step 501.

[0094] Step 506, determine the status flag P ys The value, based on the stated P ys The specific value, selectively execute P ys <3、P ys = 3, P ys = 4、P ys = 5、P ys = 6、P ys = 7, etc., 6 branches.

[0095] P ys <3 logic branches. Step 507, determine the current grid voltage sampling value v. g (k) Is it greater than the first baseline value v? p_hsd If so, continue to step 513 and set the status flag P. ys If the value is assigned to 3, then the program jumps to the 501 branch. Otherwise, it jumps directly to the 501 branch. The first baseline value is v. p_hsd The recommended value is (0.8~0.9)×v gmax .

[0096] P ys = 3 logic branches. Step 508, determine the current grid voltage sampling value v. g (k) Is it less than the second benchmark value v?p_lsd If yes, continue to step 514; otherwise, jump to the waiting branch 501. Second baseline value v p_lsd The recommended value is (0.1~0.2)×v gmin First baseline value v p_hsd Second benchmark value v p_lsd Used to determine the relative position of the thyristor's initial pulse. The relevant variables in step 514 are operated as shown in equation (1).

[0097] P ys =4, P cyc =N pd P on =N pd -N ont P off =N pd -N oft (1)

[0098] In equation (1), P on and P off These represent the turn-on and turn-off points of the thyristor pulse, respectively. ont and N oft These are the bias points, which can be adjusted according to actual working conditions. The recommended value N in this invention is... ont = 0.05 × N pd N oft = 0.05 × N pd .

[0099] like Figure 5B As shown, P ys <3 logical branches and P ys The purpose of the =3 logic branch is to accurately find the 1 / 4 cycle of the grid voltage drop, that is... Figure 5B t 601 ~t 611 In addition to the time period, a reasonable cycle count P also needs to be selected. cyc The starting point. To improve reliability, this embodiment of the invention proposes prioritizing finding t. 60 The point, that is, the moment when the grid voltage is relatively high, is at t. 60 After time point P, find a time when the grid voltage is relatively low and use it as the cycle count P. cyc The counting starting point is determined in this way, which effectively avoids selecting the wrong starting point. Furthermore, the cycle count P selected in this invention... cyc The starting point is set at t 61 Point, that is, the grid voltage is lower than the second reference point v. p_lsd The second reference point can be selected based on actual working conditions; the recommended value in this invention is (0.1~0.2)×v. gmin It should be noted that the counting starting point t 61It must be at the zero-crossing point t of the grid voltage 611 Maintain a certain distance to prevent errors in the thyristor pulse turn-off point due to inaccuracies in the power grid frequency calculation. After selecting and determining the cycle count P... cyc After determining the counting start point, the turn-on and turn-off points of the thyristor pulses can be determined based on the real-time P. cyc The count value is determined. The on and off points are P in the above equation (1). on and P off Point, it should be noted that P on and P off Adjustments are made after each thyristor turn-on and turn-off, as described in this embodiment of the invention. Figure 5B Corresponding P ys =4、P ys =5、P ys =6、P ys =7 and other logical branches.

[0100] P ys = 4 logical branches; Step 509, determine the loop counter value P cyc Is it greater than the thyristor turn-on point P? on If so, then assign the value P. ys =5, assign the first auxiliary signal v gP_min =V mx At the same time, the thyristor turn-on signal v gT Set the level high; the thyristor will begin a slow start. Otherwise, proceed to step 501 to wait. V mx It is the peak value of the grid voltage rating.

[0101] P ys = 5 logic branches; Step 510, determine the current real-time value of the grid voltage v g (k) Is it less than the first auxiliary signal v? gP_min If so, proceed to step 516 and change the real-time grid voltage value v. g (k) is assigned to v gP_min Otherwise, proceed to step 517 to determine whether the current count value has reached the thyristor turn-off point P. off Otherwise, proceed to step 501, etc.; if yes, execute step 518 and operate according to formula (2).

[0102] P ys =6, v gT =0, v gW_min =V mx (2)

[0103] v gW_min It is the second auxiliary signal, V mx It is the peak value of the grid voltage rating.

[0104] Pys = 6 logic branches; Step 511, determine the current real-time value of the grid voltage v g (k) Is it less than the second auxiliary signal v? gW_min If so, proceed to step 519 and change the real-time grid voltage value v. g (k) is assigned to v gW_min Otherwise, proceed to step 520. Otherwise, jump directly to step 520 to determine if the current count value satisfies P. cyc >0.5N pd And P cyc <P off If so, proceed to step 521 and assign a value to the status indicator signal P. ys = 7, then proceed to step 501 to wait. Otherwise, proceed directly to step 501 to wait.

[0105] P ys = 7 logic branches; Step 512, determine the first auxiliary signal v gP_min Is it less than the second auxiliary signal v? gW_min If yes, proceed to step 522; otherwise, proceed to step 523. Steps 522 and 523 are performed according to equations (3) and (4) respectively.

[0106] P on =P on -N onx -N phase P off = P off -N phase (3)

[0107] P on =P on -N onx P off = P off (4)

[0108] Where N onx This is the step size by which the thyristor drive turn-on point moves forward each time. It determines the soft-start time and the grid inrush current during the soft-start process, and needs to be determined according to the specific operating conditions. In this embodiment of the invention, it is recommended to select N. onx = 0.01×N pd N pd This represents the periodic value of the grid voltage. N phase This is the step size for phase adjustment. This variable is used to adjust the overall phase of the thyristor drive's turn-on and turn-off points, and is used to correct the phase of each drive pulse of the thyristor in real time. The underlying adjustment mechanism will be discussed below. Figure 5C In detail, step 524 assigns a value to P. ys = 4, then execute step 525 to determine the current thyristor turn-on point P.on Is it less than 0.5N? pd If the signal indicates that the thyristor's turn-on point has reached the peak of the mains voltage, proceed to step 526, clear the status indicator signal, and reset the thyristor drive signal V. gT Set to constant high. Continue to step 527, triggering the soft start end signal v. cT Set to high, slow start ends.

[0109] See Figure 5C This invention provides an adaptive solution to improve reliability in situations where grid frequency fluctuations may cause errors in the thyristor drive pulse turn-off point. The solution relies on... Figure 5B The first auxiliary signal v gP_min Second auxiliary signal v gW_min The first auxiliary signal originates from the real-time grid voltage V during the high-level period of each thyristor drive signal. g The minimum value of (k), similarly, the second auxiliary signal originates from the individual thyristor drive off-state point P. off Count to 0.5N in cycles. pd Real-time voltage v of the power grid during the corresponding time period g The minimum value of (k). See also Figure 5C During the k-th thyristor drive, under normal operating conditions, since the thyristor turn-off point is located to the left of the grid voltage zero-crossing point, the first auxiliary signal v must be satisfied. gP_min Greater than the second auxiliary signal v gW_min Therefore, based on the first and second auxiliary signals, it is possible to indirectly determine whether the thyristor drive pulse has a turn-off point lag problem. For example, suppose that due to grid frequency fluctuations (sudden frequency increase) or frequency measurement errors, at the k+1th thyristor drive pulse, the thyristor drive pulse v... gT The breakpoint t 74 If the thyristor is located to the right of the grid voltage zero-crossing point and the thyristor drive pulse is not subsequently corrected, the thyristor may fail to turn off. In this case, Figure 5C In the process, the first auxiliary signal v will inevitably appear. gP_min Less than the second auxiliary signal v gW_min Based on this judgment condition, this invention patent will, within the next (k+2)th drive pulse time, set the thyristor's turn-on and turn-off point P. on (k+2) and P off (k+2) is shifted forward appropriately, as shown in equation (3) above, with a left shift phase value of N. phase It is recommended that the value N be taken as follows. phase =(0.01~0.05)×N pd It should be noted that, in this embodiment of the invention, the phase left shift is a fixed value N. phaseAlternatively, a variable value can be used, as shown in equation (5).

[0110] N phase = k × (v gW_min - v gP_min (5)

[0111] That is, left-shifted phase N phase and the first and second auxiliary signals v gP_min v gW_min The difference is proportional; further, the left-shifted phase N phase It can also be generated in a non-linear manner. See also Figure 5C After a phase shift to the left by N phase After adjustment, the thyristor drive pulse corrects the signal after k+2 pulse cycles, thereby realizing the second auxiliary signal v. gW_min Less than the first auxiliary signal v gP_min .

[0112] The adaptive correction scheme for thyristor pulses proposed in this invention can effectively solve the impact of factors such as power grid frequency fluctuations, frequency measurement errors, and errors introduced by power grid voltage distortion on thyristor driving, significantly improve the reliability of driving pulse generation, and effectively avoid the problem of thyristor turn-off point lag. In addition, in this invention, the power grid frequency is acquired in real time (see Figure 2) and the thyristor driving pulse is generated based on the real-time acquired power grid frequency, further improving system reliability and avoiding thyristor driving signal errors under extreme operating conditions.

[0113] To verify the effectiveness of the embodiments of the present invention, an experimental platform was built, and the experimental waveforms are as follows. Figure 6 As shown, it can be seen that each thyristor pulse drives v gT All were generated as expected, bus voltage v b The current rises slowly, with the maximum grid inrush current around 15A, verifying the feasibility of this invention patent.

[0114] The scope of protection of this invention is not limited to the above embodiments; all technical solutions falling within the scope of this invention's concept are also within its protection. It should be noted that for those skilled in the art, any improvements and modifications made without departing from the principles of this invention should be considered within its protection scope.

Claims

1. A control method for achieving soft start of a thyristor rectifier bridge, characterized in that, It includes the following three steps: A. Obtain grid voltage parameters from real-time sampled grid voltage signals, including the average grid voltage, maximum grid voltage, and minimum grid voltage. B. When the real-time sampled grid voltage is within 1 / 4 of the grid voltage rise cycle and the sampled grid voltage value exceeds the first reference voltage, the number of sampling cycles is recorded. After the real-time sampled grid voltage sequentially reaches the maximum grid voltage, is less than the first reference voltage, is less than the second reference voltage, and exceeds the first reference voltage, the sampled cycle value that has been experienced is assigned to the grid voltage frequency count value. The first and second reference voltages are determined based on the maximum grid voltage, and the second reference voltage is less than the first reference voltage. The criterion that the real-time sampled grid voltage is within 1 / 4 of the grid voltage rise cycle is determined based on the average grid voltage. C. When the real-time sampled grid voltage is within 1 / 4 of the grid voltage drop cycle, initialize the thyristor pulse turn-on and turn-off points, obtain the minimum grid voltage between the thyristor pulse turn-on and turn-off points, and obtain the minimum grid voltage within 1 / 4 of the grid voltage cycle after the thyristor pulse turn-off point. When the minimum grid voltage between the thyristor pulse turn-on and turn-off points is less than the minimum grid voltage within 1 / 4 of the grid voltage cycle after the thyristor pulse turn-off point, perform a phase shift operation on the turn-on and turn-off points of the next thyristor pulse. When the minimum grid voltage between the thyristor pulse turn-on and turn-off points is greater than the minimum grid voltage within half a grid voltage cycle after the thyristor pulse turn-off point, only advance the turn-on time of the next thyristor pulse. The criterion that the real-time sampled grid voltage is within 1 / 4 of the grid voltage drop cycle is determined by the maximum and minimum grid voltage values.

2. The control method for soft-starting a thyristor rectifier bridge according to claim 1, characterized in that, The specific implementation method of step A is as follows: A-1. Wait for the grid voltage sampling to complete; A-2, Accumulate the loop counter value; A-3. If the loop count value exceeds the count threshold, proceed to A-9; otherwise, proceed to A-4. A-4. Add the current sampled value of the grid voltage to the total grid voltage value; A-5. If the current sampled value of the grid voltage is greater than the maximum value of the grid voltage, proceed to A-7; otherwise, proceed to A-6. A-6. If the current sampled value of the grid voltage is less than the minimum value of the grid voltage, proceed to A-8; otherwise, jump to A-1. A-7 assigns the current sampled value of the grid voltage to the maximum value of the grid voltage; A-8. Assign the current sampled value of the grid voltage to the minimum grid voltage value; A-9. Calculate the average grid voltage based on the current total grid voltage value and the counting threshold, and use the current maximum and minimum grid voltage values ​​as the final maximum and minimum grid voltage values. A-10. Set the total grid voltage and the maximum grid voltage to zero, assign the rated peak grid voltage to the minimum grid voltage, and jump to A-1.

3. The control method for soft-starting a thyristor rectifier bridge according to claim 1, characterized in that, The specific implementation method of step B is as follows: B-1. Wait for the grid voltage sampling to complete; B-2, Accumulate the loop counter value; B-3. ​​For branches with a status flag value less than 2, if the current sampled value of the grid voltage is less than the average value of the grid voltage, set the status flag value to 2 and jump to B-1; otherwise, jump directly to B-1. B-4, the branch with a status flag value of 2: if the current sampled value of the grid voltage is greater than the average value of the grid voltage, set the status flag value to 3 and jump to B-1; otherwise, jump directly to B-1. B-5, the branch with status flag value of 3: If the current sampled value of the grid voltage is greater than the first reference voltage, set the status flag value to 4, set the loop count value to zero, and jump to B-1; otherwise, jump directly to B-1. The first reference voltage is (0.8~0.9)×v. gmax v gmax This represents the maximum grid voltage. B-6, the branch with a status flag value of 4: when the current sampled value of the grid voltage is less than the first reference voltage, set the status flag value to 5 and jump to B-1; otherwise, jump directly to B-1. B-7, branch with status flag value of 5: If the current sampled value of the grid voltage is less than the second reference voltage, set the status flag value to 6 and jump to B-1; otherwise, jump directly to B-1. The second reference voltage is (0.3~0.6)×v. gmax ; B-8, the branch with a status flag value of 6: when the current sampled value of the grid voltage is greater than the second reference voltage, set the status flag value to 2, assign the current loop count value to the grid voltage frequency count value, and jump to B-1; otherwise, jump directly to B-1.

4. The control method for soft-starting a thyristor rectifier bridge according to claim 1, characterized in that, The specific implementation method of step C is as follows: C-1. Wait for the grid voltage sampling to complete; C-2, Accumulate the loop counter value; C-3. If the cycle count value exceeds the grid voltage frequency count value, proceed to C-4; otherwise, proceed to C-5. C-4. Clear the loop counter value to zero; C-5. If the grid voltage frequency count value is within the preset grid frequency range, proceed to C-6; otherwise, jump to C-1. C-6. For branches with a status flag value less than 3, if the current sampled value of the grid voltage is greater than the first reference value, set the status flag value to 3 and jump to C-1; otherwise, jump directly to C-1. The first reference value is (0.8~0.9)×v. gmax v gmax This represents the maximum grid voltage. C-7. For branches with a status flag value of 3, when the current sampled value of the grid voltage is less than the second reference value, set the status flag value to 4, assign the grid voltage frequency count value to the loop count value, initialize the thyristor pulse's on / off point, and the second reference value is (0.1~0.2)×v. gmin v gmin This is the minimum grid voltage. C-8, the branch with a status flag value of 4, when the loop count value is greater than the thyristor pulse turn-on point, sets the status flag value to 5, assigns the peak value of the rated grid voltage to the first auxiliary signal, sets the thyristor drive signal to high level, and starts soft start; otherwise, jumps to C-1. C-9, the branch with a status flag value of 5: when the current sampled value of the grid voltage is less than the first auxiliary signal, the current sampled value of the grid voltage is assigned to the first auxiliary signal; otherwise, when the current cycle count value reaches the thyristor pulse turn-off point, the status flag value is set to 6, the thyristor drive signal is set to low level, and the peak value of the grid voltage is assigned to the second auxiliary signal; when the current cycle count value does not reach the thyristor pulse turn-off point, the branch directly jumps to C-1. C-10, the branch with a status flag value of 6: when the current sampled value of the grid voltage is less than the second auxiliary signal, the current sampled value of the grid voltage is assigned to the second auxiliary signal; otherwise, when the current cycle count value exceeds half of the grid voltage frequency count value and the current cycle count value has not reached the thyristor pulse turn-off point, the status flag value is set to 7 and the branch jumps to C-1; when the current cycle count value does not exceed half of the grid voltage frequency count value or the current cycle count value reaches the thyristor pulse turn-off point, the branch jumps directly to C-1. C-11, the branch with a status flag value of 7, when the current value of the first auxiliary signal is less than the current value of the second auxiliary signal, performs a phase shift operation on the turn-on and turn-off points of the next thyristor pulse; otherwise, only the turn-on time of the next thyristor pulse is shifted forward, the status flag value is set to 4, and the process proceeds to C-12. C-12. When the current thyristor pulse activation point is less than half of the grid voltage frequency count value, set the status flag value to 0, set the thyristor drive signal to always high, and end the soft start.

5. The control method for soft-starting a thyristor rectifier bridge according to claim 1, characterized in that, The frequency at which the grid voltage is sampled in real time is more than 500 times the rated frequency of the grid.

6. The control method for achieving soft start of a thyristor rectifier bridge according to claim 2, characterized in that, The counting threshold is 2 to 3 cycles of the lowest grid voltage.

7. The control method for soft-starting a thyristor rectifier bridge according to claim 4, characterized in that, In step C-7, the expressions for initializing the turn-on and turn-off points of the thyristor pulse are P. on =N pd -N ont P off =N pd -N oft , where P on P off N represents the turn-on and turn-off points of the thyristor pulse. pd N represents the grid voltage frequency count value. ont N oft N represents the bias points for the thyristor pulse turn-on and turn-off points, respectively. ont = 0.05 × N pd N oft = 0.05 × N pd .

8. The control method for soft-starting a thyristor rectifier bridge according to claim 4, characterized in that, In step C-11, the expression for the phase-shifting operation of the turn-on and turn-off points of the next thyristor pulse is P. on =P on -N onx -N phase P off = P off -N phase The expression for shifting the turn-on time of the next thyristor pulse forward only is P. on =P on -N onx P off = P off , where P on P off N represents the turn-on and turn-off points of the thyristor pulse. onx N is the step size for advancing the turn-on time of the next thyristor pulse. phase It is the step size of the phase shift operation.

9. The control method for soft-starting a thyristor rectifier bridge according to claim 8, characterized in that, N phase =(0.01~0.05)×N pd or N phase = k × (v gW_min - v gP_min ), where k is the proportionality coefficient, v gP_min v gW_min These are the first and second auxiliary signals.

10. A control system for implementing soft starting of a thyristor rectifier bridge, characterized in that, include: The power grid voltage parameter acquisition module acquires power grid voltage parameters from real-time sampled power grid voltage signals. The power grid voltage parameters include the average power grid voltage, the maximum power grid voltage, and the minimum power grid voltage. The real-time grid voltage frequency acquisition module starts recording the number of sampling periods when the sampled grid voltage is within 1 / 4 of the grid voltage rise cycle and the sampled grid voltage value exceeds a first reference voltage. After the real-time sampled grid voltage sequentially reaches its maximum value, falls below the first reference voltage, falls below the second reference voltage, and exceeds the first reference voltage, the module assigns the already experienced sampling period values ​​to the grid voltage frequency count value. The first and second reference voltages are determined based on the maximum grid voltage value, and the second reference voltage is less than the first reference voltage. The criterion that the real-time sampled grid voltage is within 1 / 4 of the grid voltage rise cycle is determined based on the average grid voltage value. The thyristor pulse generation module initializes the thyristor pulse turn-on and turn-off points when the real-time sampled grid voltage is within 1 / 4 of the grid voltage drop cycle. It then obtains the minimum grid voltage between the thyristor pulse turn-on and turn-off points, and the minimum grid voltage within 1 / 4 of the grid voltage cycle after the thyristor pulse turn-off point. If the minimum grid voltage between the thyristor pulse turn-on and turn-off points is less than the minimum grid voltage within 1 / 4 of the grid voltage cycle after the thyristor pulse turn-off point, it performs a phase shift operation on the turn-on and turn-off points of the next thyristor pulse. If the minimum grid voltage between the thyristor pulse turn-on and turn-off points is greater than the minimum grid voltage within half a grid voltage cycle after the thyristor pulse turn-off point, it only advances the turn-on time of the next thyristor pulse. The criterion that the real-time sampled grid voltage is within 1 / 4 of the grid voltage drop cycle is determined based on the maximum and minimum grid voltage values.

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