Thyristor rectification system control method based on network voltage zero crossing point detection

Abstract

The invention discloses a thyristor rectification system control method based on power grid voltage zero crossing point detection. The method comprises the following steps: S1, sampling a first voltage, a second voltage and a charging current; s2, according to the effective value of any phase voltage, judging whether the three-phase alternating-current power grid has a fault or not, if the fault occurs, entering step S3, and if the fault does not occur, entering step S4; s3, a trigger pulse signal of the thyristor rectifier bridge is filled with a dead zone, and a high-magnification energy storage unit is started to supply power to a load; s4, performing zero-crossing detection according to the voltage value of any phase voltage at the current moment and the voltage value of any phase voltage at the previous moment so as to judge whether the voltage of the power grid is in a forward zero-crossing state, if so, entering step S5, and if not, entering step S5; and S5, performing phase compensation and boundary limitation on the initial trigger angle, and finally generating a trigger pulse signal of the thyristor rectifier bridge according to the trigger angle after phase compensation and boundary limitation so as to perform charging management on the high-magnification energy storage unit. The method has the advantages of high real-time performance, high robustness and high reliability.

Description

Technical Field

[0001] This invention belongs to the field of power quality management technology and relates to a control method for a thyristor rectifier system based on grid voltage zero-crossing detection. Background Technology

[0002] As a core device in modern industry and power systems, frequency converters are widely used in motor drives, energy conversion, and industrial automation. In industrial production, frequency converters play a crucial role in power conversion and precise control; their operational quality and stability directly affect production efficiency and system safety. Frequency converter operation relies on a stable DC bus power supply. However, in actual operating environments, grid faults or power fluctuations (such as voltage dips and momentary power outages) are unavoidable. These can cause significant drops in DC bus voltage, severely impacting the normal operation of the frequency converter. Mild effects may manifest as decreased operating efficiency or output fluctuations, while severe effects may lead to equipment shutdowns or even system-wide interruptions. For scenarios highly sensitive to power quality, such as semiconductor manufacturing, rail transportation, critical process production lines, and the chemical industry, the threat of these disturbances to system continuity and reliability is particularly prominent.

[0003] To address these sudden grid voltage issues, traditional solutions typically focus on the AC grid side, mitigating the impact by improving grid quality or enhancing the power system's anti-interference capabilities. However, these methods are not only costly and complex to implement, but also difficult to widely adopt in distributed power consumption environments. Therefore, thyristor rectification technology has emerged to improve DC power supply stability and ensure the continuous operation of frequency converters under grid fluctuations. Its core objective is to provide the necessary DC bus voltage support to the frequency converter during transient flashovers, deep voltage dips, or short-term grid interruptions, enabling it to maintain normal operation despite disturbances. In such systems, grid phase synchronization and trigger control are crucial components. However, existing technologies generally suffer from the following limitations:

[0004] 1. Large Phase Detection Delay: Existing solutions mostly rely on software phase-locked loop (PLL) technology. A PLL is essentially a closed-loop feedback control system. When the grid voltage changes abruptly, the PLL needs to perform several iterative calculations to relock the phase (i.e., there is a long setup time). Furthermore, a low-pass filter is typically connected in series at the front end of the PLL to filter out harmonics, which directly introduces a fixed group delay. In millisecond-level power fluctuations, this delay can easily lead to errors in the firing angle calculation, causing thyristor commutation failure.

[0005] 2. Traditional hardware detection carries the risk of misjudgment and has poor noise immunity: Traditional pure hardware zero-crossing detection circuits (such as comparator-based zero-crossing trigger circuits), while having a fast response speed, are extremely sensitive to signal quality and lack intelligent judgment mechanisms. When the mains voltage waveform is distorted, contains high-frequency noise, or oscillates near the zero point, the voltage signal may cross the zero axis multiple times in a very short period of time, causing the hardware circuit to output erroneous multiple flip pulses (i.e., "zero-crossing jitter"). This lack of judgment in hardware logic can cause the controller to fail to identify the true physical zero point, leading to thyristor mis-triggering or system logic chaos.

[0006] In summary, there is an urgent need for a power grid phase detection and control method that can both eliminate complex phase-locked loops to achieve low latency and overcome the blindness of traditional hardware detection to avoid misjudgment. Summary of the Invention

[0007] To address at least one of the aforementioned problems, this invention proposes a control method for a thyristor rectifier system based on grid voltage zero-crossing detection. By real-time detection of the grid voltage, a high-precision, low-delay grid phase reference is extracted, and abnormal operating conditions such as voltage dips, flicker, and transient impacts are quickly identified. Combined with an adaptive firing angle adjustment strategy and a closed-loop control mechanism, oscillations, overshoot, and hysteresis are effectively suppressed, achieving stable DC bus voltage output. This results in a control scheme with high real-time performance, high robustness, and stable operation under grid disturbance conditions, significantly improving the reliability of the thyristor rectifier system.

[0008] The technical solution adopted in this invention is as follows:

[0009] This application discloses a control method for a thyristor rectifier system based on grid voltage zero-crossing detection. The thyristor rectifier system includes a phase-shifting transformer, a thyristor rectifier bridge, and a high-rate energy storage unit. The primary side of the phase-shifting transformer is connected to a three-phase AC grid, and the secondary side is connected to the input terminal of the thyristor rectifier bridge. When the three-phase AC grid is not faulty, the thyristor rectifier bridge rectifies the three-phase AC power input from the three-phase AC grid into DC power and charges the high-rate energy storage unit through the DC bus. When the three-phase AC grid experiences a fault, the high-rate energy storage unit supplies power to the load. The control method includes:

[0010] S1. Sample the first voltage, the second voltage, and the charging current, and preprocess the first voltage. The first voltage is the three-phase AC voltage input from the three-phase AC grid to the primary side of the phase-shifting transformer, and the second voltage is the output bus voltage. The preprocessing includes denoising, amplitude normalization, and small delay filtering of the first voltage.

[0011] S2. Determine whether the three-phase AC power grid has a fault based on the effective value of any phase voltage in the preprocessed first voltage. If a fault occurs, proceed to step S3; if no fault occurs, proceed to step S4.

[0012] S3. If a fault occurs, the trigger pulse signal of the thyristor rectifier bridge is filled with a dead zone, and the high-rate energy storage unit is started to supply power to the load.

[0013] S4. If no fault occurs, zero-crossing detection is performed based on the voltage value of any phase voltage at the current moment and the voltage value at the previous moment to determine whether the grid voltage is in a positive zero-crossing state. If so, proceed to step S5.

[0014] S5. When the grid voltage is in a positive zero-crossing state, the instantaneous zero-crossing time of the grid voltage is calculated in real time using a linear interpolation algorithm. Then, the preliminary triggering angle is obtained based on the zero-crossing time. The preliminary triggering angle is then phase-compensated and boundary-limited. Finally, the triggering pulse signal of the thyristor rectifier bridge is generated according to the triggering angle after phase compensation and boundary limitation to manage the charging of the high-rate energy storage unit.

[0015] The load is a frequency converter.

[0016] As an optional technical solution, the fault determination in step S1 includes: if the effective value of any phase voltage is lower than the preset value of the rated grid voltage and remains so for a certain period of time, then the grid is determined to have a fault.

[0017] As an optional technical solution, the zero-crossing detection in step S4 includes:

[0018] Set the negative threshold voltage V th_neg and positive threshold voltage V th_pos ;

[0019] For any of the phase voltages, if the voltage value of that phase voltage at the current moment is greater than the positive threshold voltage V... th_pos And the voltage value at the previous moment was less than the negative threshold voltage V. th_neg If the phase voltage is at a positive zero-crossing point, then the phase voltage is determined to be at a positive zero-crossing point; if the phase voltage value at the current moment is less than the negative threshold voltage V... th_neg And the voltage value at the previous moment was greater than the positive threshold voltage V. th_neg If the phase voltage is at a negative zero-crossing point, then it is determined that the phase voltage is at a negative zero-crossing point.

[0020] As an optional technical solution, the zero-crossing time mentioned in step S5 is calculated by the following formula:

[0021]

[0022] Among them, tzero-X This represents the zero-crossing time of the current X-phase grid voltage after linear interpolation, where t represents the current time and t-1 represents the previous time. V X (t) represents the voltage value of the sampled X-phase grid voltage at the current moment after the preprocessing, V X (t-1) represents the voltage value of the sampled X-phase grid voltage at the previous moment after the preprocessing, T s The sampling period is represented by X, which can be A, B, or C, representing phase A, phase B, and phase C, respectively.

[0023] As an optional technical solution, obtaining the preliminary trigger angle based on the zero-crossing time in step S5 includes: when the system is operating in constant current mode, the charging current signal of the high-rate energy storage unit is passed through the PI controller of the voltage loop to obtain the preliminary trigger angle; when the system is operating in constant voltage mode, the charging voltage of the high-rate energy storage unit is passed through the PI controller of the current loop to obtain the preliminary trigger angle.

[0024] As an optional technical solution, step S5, which involves phase compensation and boundary limitation of the initial trigger angle, includes: performing phase compensation on the initial trigger angle to compensate for the impact of drive delay on the bus output during signal transmission; and performing boundary limitation on the compensated trigger angle to meet the limits of the minimum and maximum trigger angles.

[0025] As an optional technical solution, generating the trigger pulse signal of the thyristor rectifier bridge in step S5 includes: combining the trigger angle after phase compensation and boundary limitation with the thyristor pulse sequence relationship of the thyristor rectifier bridge to generate a trigger sequence with corresponding phase shift, and setting an interlock dead zone between the trigger pulse signals to avoid false triggering or shoot-through of the bridge arm thyristors.

[0026] The beneficial effects of this application are as follows: The thyristor rectifier system control method based on grid voltage zero-crossing detection provided by this invention can achieve millisecond-level or even microsecond-level fault response and power switching, completely isolating the interference of grid voltage fluctuations on the DC bus and ensuring uninterrupted and stable operation of downstream loads. By adopting a composite processing method combining "grid voltage filtering—threshold judgment—linear interpolation", the influence of grid noise, harmonic distortion, and electromagnetic interference on the zero-crossing detection accuracy is effectively suppressed, obtaining a high-precision, low-delay grid phase reference, providing a reliable reference for the precise control of the thyristor firing angle. In terms of control strategy, this invention combines PI steady-state regulation with an adaptive compensation mechanism based on real-time grid operating conditions to construct a dynamic-steady-state integrated composite control strategy. This strategy can significantly improve the dynamic response speed of the system under grid voltage fluctuations and rapid load changes, effectively suppress voltage oscillations, overshoot, and regulation lag in the rectification control process, and improve the stability and robustness of the system. In the thyristor pulse triggering stage, this invention introduces an interlock dead-time control mechanism to ensure that the bridge arm devices do not experience short circuits or shoot-throughs, thereby further improving the operational safety of the rectifier module and the system reliability. Attached Figure Description

[0027] Figure 1 This is the circuit diagram of a thyristor rectifier system.

[0028] Figure 2 This is a flowchart illustrating the control method of a thyristor rectifier system based on the detection of the zero-crossing point of the grid voltage.

[0029] Figure 3 This is a schematic diagram comparing the actual zero-crossing time of the A-phase grid voltage with the zero-crossing time detected by the method in this embodiment.

[0030] Figure 4 This is the timing diagram of the pulse output generated by the thyristor based on the firing angle.

[0031] Figure 5 This is a waveform diagram of the output voltage and current of a thyristor rectifier.

[0032] Figure 6 This is a flowchart illustrating the control method for a thyristor rectifier system based on zero-crossing detection of grid voltage. Detailed Implementation

[0033] The following embodiments are provided to better understand the present invention and are not limited to the following implementation methods. They do not constitute a limitation on the content and scope of protection of the present invention. Any technical solution that is the same as or similar to the present invention, derived by any person under the guidance of the present invention or by combining the features of the present invention with other prior art, falls within the protection scope of the present invention.

[0034] In the description of this invention, it should be noted that the terms "first," "second," "third," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0035] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "connected" and "linked" should be interpreted broadly. For example, they can refer to direct electrical connection or indirect electrical connection through an intermediate medium. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0036] Furthermore, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0037] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0038] Example

[0039] This embodiment uses a 20kW thyristor rectifier as an example to illustrate the control method of the thyristor rectifier system based on grid voltage zero-crossing detection. Figure 1 As shown, the thyristor rectifier system includes a phase-shifting transformer and a thyristor rectifier bridge (i.e., Figure 1 The system includes a multi-channel thyristor rectifier circuit, a filter unit LC, a high-rate energy storage unit, a diode D1, and a load. The AC currents VA, VB, and VC of each phase of the three-phase AC power grid are input to the primary side of a phase-shifting transformer. The secondary side of the phase-shifting transformer is connected to the input terminal of the thyristor rectifier bridge. The output terminal of the thyristor rectifier bridge is connected to the filter unit LC. The filter unit, the high-rate energy storage unit, and the load are connected in parallel sequentially. Diode D1 is connected in series in the parallel branch of the load. The high-rate energy storage unit can be a high-rate battery pack. The thyristor rectifier bridge uses 12 thyristors VT1-VT12. In this embodiment, when the three-phase AC power grid is functioning correctly, the thyristor rectifier bridge rectifies the three-phase AC current input from the three-phase AC power grid into DC and charges the high-rate energy storage unit through the DC bus. At this time, the load is powered by the external power grid. When the three-phase AC power grid fails, the high-rate energy storage unit supplies power to the load. Figure 6 As shown, the control method mainly includes the following steps S1-S5, and its detailed breakdown process is as follows: Figure 2 In this embodiment, the load is a frequency converter.

[0040] S1. Sample the first voltage, the second voltage, and the charging current Io, and preprocess the first voltage. The first voltage is the three-phase AC voltages VA, VB, and VC input from the three-phase AC grid to the primary side of the phase-shifting transformer. The second voltage is the output bus voltage Vo. The preprocessing includes denoising, amplitude normalization, and small-delay filtering of the first voltage to ensure the accuracy of subsequent zero-crossing detection, while minimizing the delay introduced by sampling and processing. In particular, this step only uses small-delay filtering and does not use phase-locked loop filters with large time constants to preserve the original phase characteristics of the voltage signal and reduce processing delay from the signal source.

[0041] S2. Determine whether a fault has occurred in the three-phase AC power grid based on the effective value of any phase voltage in the preprocessed first voltage. If a fault has occurred, proceed to step S3; otherwise, proceed to step S4.

[0042] As an optional implementation, the fault determination includes: if the effective value of any phase voltage is lower than a preset value of the rated grid voltage and remains so for a certain time T, then a grid fault is determined to have occurred. In this embodiment, the preset value can be 90%, and the value of the duration T can be determined according to the actual situation; this application does not impose any restrictions.

[0043] Taking the sampled phase A AC voltage VA as an example, if its effective value VA RMS If the voltage is less than 90% of the rated grid voltage and remains so for a time T, a fault is considered to have occurred.

[0044] Similarly, if the effective value of the sampled phase B AC voltage VB is VB RMS If the voltage is less than 90% of the rated grid voltage and remains so for a time T, a fault is also considered to have occurred.

[0045] Similarly, if the effective value of the sampled C-phase AC voltage VC is VC RMS If the voltage is less than 90% of the rated grid voltage and remains so for a time T, a fault is also considered to have occurred.

[0046] The rated mains voltage can be 220V.

[0047] S3. If a fault occurs, the trigger pulse signal of the thyristor rectifier bridge is filled with a dead zone, and the high-rate energy storage unit is started to supply power to the load, thereby achieving stable power supply capability at the DC end.

[0048] S4. If no fault occurs, zero-crossing detection is performed based on the voltage value of any phase voltage at the current moment and the voltage value at the previous moment to determine whether the grid voltage is in a positive zero-crossing state and to obtain a high-precision phase reference signal. If so, proceed to step S5.

[0049] As an optional implementation, the zero-crossing detection includes: setting a negative threshold voltage V. th_neg and positive threshold voltage V th_pos For any of the phase voltages, if the voltage value of that phase voltage at the current moment is greater than the positive threshold voltage V... th_pos And the voltage value at the previous moment was less than the negative threshold voltage V. th_neg If the phase voltage is at a positive zero-crossing point, then the phase voltage is determined to be at a positive zero-crossing point; if the phase voltage value at the current moment is less than the negative threshold voltage V... th_neg And the voltage value at the previous moment was greater than the positive threshold voltage V. th_neg If the phase voltage is at a negative zero-crossing point, then it is determined that the phase voltage is at a negative zero-crossing point.

[0050] Taking the sampled phase A AC voltage VA as an example, after denoising, amplitude normalization, and small delay filtering, the preprocessed phase A voltage value V at the current time t is obtained. A (t) and the voltage value V at the previous time t-1. A (t-1), if V A (t) is greater than V th_pos And V A (t-1) is less than V th_neg Then it is a positive zero-crossing state; if V A (t) is less than V th_neg And V A (t-1) is greater than V th_pos If it is, then it is a negative zero-crossing state.

[0051] Similarly, after denoising, amplitude normalization, and small-delay filtering of the sampled phase B AC voltage VB, the preprocessed phase B voltage value V at the current time t is obtained. B (t) and the voltage value V at the previous time t-1. B (t-1), if V B (t) is greater than V th_pos And V B (t-1) is less than V th_neg Then it is a positive zero-crossing state; if V B (t) is less than V th_neg And V B (t-1) is greater than V th_pos If it is, then it is a negative zero-crossing state.

[0052] Similarly, after denoising, amplitude normalization, and small-delay filtering of the sampled C-phase AC voltage VC, the preprocessed C-phase voltage value V at the current time t is obtained. C (t) and the voltage value V at the previous time t-1. C (t-1), if V C (t) is greater than Vth_pos And V C (t-1) is less than V th_neg Then it is a positive zero-crossing state; if V C (t) is less than V th_neg And V C (t-1) is greater than V th_pos If it is, then it is a negative zero-crossing state.

[0053] S5. When the grid voltage is in a positive zero-crossing state, the instantaneous zero-crossing time of the grid voltage is calculated in real time using a linear interpolation algorithm. Then, the preliminary triggering angle is obtained based on the zero-crossing time. The preliminary triggering angle is then phase-compensated and boundary-limited. Finally, the triggering pulse signal of the thyristor rectifier bridge is generated according to the triggering angle after phase compensation and boundary limitation to manage the charging of the high-rate energy storage unit.

[0054] As an optional implementation, a linear interpolation algorithm is used to calculate the instantaneous zero-crossing time of the grid voltage in real time, specifically using the following formula:

[0055]

[0056] Among them, t zero-X This represents the zero-crossing time of the current X-phase grid voltage after linear interpolation, where t represents the current time and t-1 represents the previous time. V X (t) represents the voltage value of the sampled X-phase grid voltage at the current moment after the preprocessing, V X (t-1) represents the voltage value of the sampled X-phase grid voltage at the previous moment after the preprocessing, T s The sampling period is represented by X, which can be A, B, or C, representing phase A, phase B, and phase C, respectively. In this embodiment, when the grid voltage is in a positive zero-crossing state, a linear interpolation algorithm is used to calculate the zero-crossing time of the grid voltage in real time. This method directly calculates the zero-crossing time using the linear relationship between two points, without the need for the dynamic convergence process of the PLL, thus obtaining a grid phase reference signal with extremely high precision and nanosecond-level calculation delay. Figure 3 As shown, for a phase A grid voltage, the zero-crossing time (i.e., ...) detected by the method in this embodiment is... Figure 3 The zero-crossing trigger time in the code is compared to its actual zero-crossing time (i.e., the zero-crossing trigger time in the code). Figure 3 The voltage of phase A of the power grid crosses zero at a time of only 40μs, and the angle relative to the power grid is only 0.72°, which meets the actual requirements.

[0057] As an optional implementation, obtaining the preliminary firing angle based on the zero-crossing time in step S5 includes: based on the aforementioned zero-crossing state, adjusting the output voltage (e.g., Figure 1 (i.e., Vo) and charging current (e.g.) Figure 1The initial trigger angle α signal is obtained after each of the PI compensators and constant voltage / constant current control. Specifically, when the system operates in constant current mode, the charging current signal of the high-rate energy storage unit (e.g., Io) is adjusted by its respective PI compensator and controlled by constant voltage / constant current. Figure 1 After passing through the PI controller in the voltage loop, the initial trigger angle α signal is obtained; when the system operates in constant voltage mode, the charging voltage of the high-rate energy storage unit (e.g., Io) is... Figure 1 The initial trigger angle α signal is obtained after the PI controller of the current loop (i.e., Vo) passes through the current loop.

[0058] As an optional implementation, step S5, which involves phase compensation and boundary limitation of the initial trigger angle, includes: performing phase compensation on the initial trigger angle α to compensate for the impact of drive delay on the bus output during signal transmission; and performing boundary limitation on the compensated trigger angle to meet the limits of the minimum and maximum trigger angles.

[0059] Specifically, phase compensation and boundary constraints are performed according to the following formula:

[0060]

[0061] Where, α compensated This represents the firing angle after phase compensation, where Δα represents the phase compensation amount, and α... min α represents the minimum firing angle. max This represents the maximum value of the trigger angle, min(•) represents the minimum value, and max(•) represents the maximum value. final This refers to the final firing angle obtained after phase compensation and boundary constraints.

[0062] As an optional implementation, generating the trigger pulse signal for the thyristor rectifier bridge in step S5 includes: combining the trigger angle α after phase compensation and boundary limitation. final Based on the thyristor pulse sequence relationship of the thyristor rectifier bridge, a corresponding phase shift trigger sequence is generated, such as... Figure 4 This generates a timing diagram, setting interlock dead zones between trigger pulse signals to prevent false triggering or shoot-through of the bridge arm thyristors, thus improving system operational safety. According to the control method of this embodiment, the waveforms of the thyristor rectifier's output voltage Vo and output current Io are as follows: Figure 5 .

[0063] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in this application should be included within the scope of protection of this application. All technical solutions that fall within the scope of the claims of this invention are within the scope of protection of this invention.

Claims

1. A control method of a thyristor rectifier system based on grid voltage zero-crossing detection, characterized by: The thyristor rectification system comprises a phase-shifting transformer, a thyristor rectification bridge and a high-ratio energy storage unit; the primary side of the phase-shifting transformer is connected to a three-phase AC power grid, and the secondary side of the phase-shifting transformer is connected to the input end of the thyristor rectification bridge; when the three-phase AC power grid does not fail, the thyristor rectification bridge rectifies the three-phase AC power input from the three-phase AC power grid into DC power, and charges the high-ratio energy storage unit through a DC bus; when the three-phase AC power grid fails, the high-ratio energy storage unit supplies power to the load, and the control method comprises: S1. Sampling a first voltage, a second voltage and a charging current, and preprocessing the first voltage, the first voltage being a three-phase AC voltage input from the three-phase AC power grid to the primary side of the phase-shifting transformer, and the second voltage being an output bus voltage, the preprocessing comprising denoising, amplitude normalization and small delay filtering of the first voltage; S2. Determining whether the three-phase AC power grid fails according to the effective value of any one of the preprocessed first voltages, if the three-phase AC power grid fails, proceeding to step S3, if the three-phase AC power grid does not fail, proceeding to step S4; S3. If the three-phase AC power grid fails, filling the trigger pulse signal of the thyristor rectification bridge with a dead zone, and starting the high-ratio energy storage unit to supply power to the load; S4. If the three-phase AC power grid does not fail, performing zero-crossing detection according to the voltage value of the any one of the voltages at the current time and the voltage value at the previous time to determine whether the grid voltage is in a forward zero-crossing state, if yes, proceeding to step S5; S5. When the grid voltage is in the forward zero-crossing state, using a linear interpolation algorithm to calculate the instantaneous zero-crossing time of the grid voltage in real time, then obtaining a preliminary trigger angle according to the zero-crossing time, then performing phase compensation and boundary limitation on the preliminary trigger angle, and finally generating the trigger pulse signal of the thyristor rectification bridge according to the trigger angle after the phase compensation and the boundary limitation to manage the charging of the high-ratio energy storage unit; Wherein, the load is a frequency converter.

2. The control method according to claim 1, characterized by, The determination of the fault in step S1 comprises: if the effective value of the any one of the voltages is lower than a preset value of the rated grid voltage and is maintained for a certain time, it is determined that the grid fails.

3. The control method according to claim 1, characterized by, The zero-crossing detection in step S4 comprises: A negative threshold voltage V th_neg and a positive threshold voltage V th_pos ; For any phase voltage, if the voltage value of the phase voltage at the current time is greater than the positive threshold voltage V th_pos and the voltage value at the previous time is less than the negative threshold voltage V th_neg , it is determined that the phase voltage is at a positive zero-crossing point; if the voltage value of the phase voltage at the current time is less than the negative threshold voltage V th_neg and the voltage value at the previous time is greater than the positive threshold voltage V th_neg , it is determined that the phase voltage is at a negative zero-crossing point.

4. The control method according to claim 1, characterized by, The zero-crossing time in step S5 is calculated by the following formula: Wherein, t zero-X represents the zero-crossing time of the current X-phase grid voltage after linear interpolation, t represents the current time, t-1 represents the previous time, V X (t) represents the voltage value of the sampled X-phase grid voltage after the preprocessing at the current time, V X (t-1) represents the voltage value of the sampled X-phase grid voltage after the preprocessing at the previous time, T s represents the sampling period, X can be A, B, C, representing A-phase, B-phase, C-phase respectively.

5. The control method according to claim 1, characterized by, The preliminary trigger angle obtained according to the zero-crossing time in step S5 comprises: when the system works in a constant current mode, the charging current signal of the high-ratio energy storage unit passes through a PI controller of a voltage loop to obtain the preliminary trigger angle; when the system works in a constant voltage mode, the charging voltage of the high-ratio energy storage unit passes through a PI controller of a current loop to obtain the preliminary trigger angle.

6. The control method according to claim 1, characterized by, The phase compensation and boundary limitation on the preliminary trigger angle in step S5 comprise: performing phase compensation on the preliminary trigger angle to compensate for the influence of the driving delay in the signal transmission process on the output of the bus; performing boundary limitation on the compensated trigger angle to make it meet the minimum trigger angle and the maximum trigger angle limitation.

7. The control method according to any one of claims 1 to 6, characterized by, The step S5 of generating the trigger pulse signal of the thyristor rectifier bridge comprises: combining the phase-compensated and boundary-limited trigger angle and the thyristor pulse sequence relationship of the thyristor rectifier bridge to generate a trigger sequence corresponding to the phase shift, and setting an interlocking dead zone between the trigger pulse signals to avoid mis-triggering or through of the bridge-arm thyristor.

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