Rectifier power supply slow start circuit and control method

Abstract

The application relates to the technical field of power grid power conversion, and provides a rectifier power supply slow start circuit and a control method, which comprises a power supply unit, an EMI filter, a slow start switch unit, a slow start drive unit, a slow start drive control unit, a circuit control unit and a rectifier circuit; the circuit control unit comprises a phase-locked unit and a rectifier circuit control unit; the power supply unit is electrically connected with the phase-locked unit and the EMI filter; the EMI filter is electrically connected with the slow start switch unit; the slow start switch unit is electrically connected with the slow start drive unit and the rectifier circuit; the slow start drive unit is electrically connected with the slow start drive control unit; the slow start drive control unit is electrically connected with the rectifier circuit control unit; and the rectifier circuit control unit is electrically connected with the rectifier circuit. The control method of the slow start circuit is simple and reliable, can be realized through a simple CPU, has low requirements on calculation speed and precision, and simplifies the slow start operation.

Description

Technical Field

[0001] This invention relates to the field of power grid power conversion technology, and in particular to a rectifier power supply soft-start circuit and control method. Background Technology

[0002] Existing soft-start circuits, when performing power supply soft-start operations, suffer from significant drawbacks. Most rectifier sources contain uncontrolled rectifier diodes, and the presence of rectifier filter capacitors during startup results in a very large starting current, potentially damaging the rectifier diodes. Furthermore, common rectifier soft-start circuits, composed of relays / contactors and soft-start resistors, cannot achieve soft-start under load, and the reliability of the soft-start resistors is low. Summary of the Invention

[0003] To solve the above-mentioned technical problems, the present invention provides a rectifier power supply soft-start circuit, comprising: a power supply unit, an EMI filter, a soft-start switch unit, a soft-start drive unit, a soft-start drive control unit, a circuit control unit, and a rectifier circuit;

[0004] The circuit control unit includes: a phase-locked loop unit and a rectifier circuit control unit;

[0005] The power supply unit is electrically connected to the phase-locked unit and the EMI filter. The EMI filter is electrically connected to the soft-start switch unit. The soft-start switch unit is electrically connected to the soft-start drive unit and the rectifier circuit. The soft-start drive unit is electrically connected to the soft-start drive control unit. The soft-start drive control unit is electrically connected to the rectifier circuit control unit. The rectifier circuit control unit is electrically connected to the rectifier circuit.

[0006] Preferably, the power supply unit is a single-phase power supply, and the soft-start switch unit is a single-channel soft-start switch;

[0007] The soft-start switch includes: a first NPN MOSFET and a second NPN MOSFET;

[0008] The L line of the single-phase power supply is electrically connected to pin 2 of the first NPN MOSFET through an EMI filter. Pins 3 of the first NPN MOSFET and pins 3 of the second NPN MOSFET are electrically connected to the soft-start drive unit. Pin 2 of the second NPN MOSFET is electrically connected to the rectifier circuit. Pins 1 of the first NPN MOSFET and pins 1 of the second NPN MOSFET are electrically connected to the soft-start drive unit.

[0009] The neutral (N) line of a single-phase power supply is electrically connected to the rectifier circuit via an EMI filter.

[0010] Preferably, the power supply unit is a three-phase power supply, including: a first power supply, a second power supply and a third power supply;

[0011] The slow-start switch unit is a three-way slow-start switch, including: a first slow-start switch, a second slow-start switch and a third slow-start switch;

[0012] The first soft-start switch includes: a first NPN MOSFET and a second NPN MOSFET;

[0013] The second soft-start switch includes: a third NPN MOSFET and a fourth NPN MOSFET;

[0014] The third soft-start switch includes: the fifth NPN MOSFET and the sixth NPN MOSFET;

[0015] The Ua line of the first power supply is electrically connected to pin 2 of the first NPN MOSFET through an EMI filter. Pins 3 of the first NPN MOSFET and pins 3 of the second NPN MOSFET are electrically connected to the soft-start drive unit. Pin 2 of the second NPN MOSFET is electrically connected to the rectifier circuit. Pins 1 of the first NPN MOSFET and pins 1 of the second NPN MOSFET are electrically connected to the soft-start drive unit.

[0016] The Ub line of the second power supply is electrically connected to pin 2 of the third NPN MOSFET through an EMI filter. Pins 3 of the third NPN MOSFET and pin 3 of the fourth NPN MOSFET are electrically connected to the soft-start drive unit. Pin 2 of the fourth NPN MOSFET is electrically connected to the rectifier circuit. Pins 1 of the third NPN MOSFET and pin 1 of the fourth NPN MOSFET are electrically connected to the soft-start drive unit.

[0017] The Uc line of the third power supply is electrically connected to pin 2 of the fifth NPN MOSFET through an EMI filter. Pins 3 of the fifth NPN MOSFET and pin 3 of the sixth NPN MOSFET are electrically connected to the soft-start drive unit. Pin 2 of the sixth NPN MOSFET is electrically connected to the rectifier circuit. Pins 1 of the fifth NPN MOSFET and pin 1 of the sixth NPN MOSFET are electrically connected to the soft-start drive unit.

[0018] The neutral (N) line of the three-phase power supply is electrically connected to the rectifier circuit through an EMI filter.

[0019] A control method for a rectifier power supply soft-start circuit includes:

[0020] S1: Perform a slow start pre-check. If the slow start pre-check is abnormal, the slow start is determined to have failed and the process ends. If the slow start pre-check is normal, proceed to step S2.

[0021] S2: Determine the type of power supply unit. If the power supply unit is a single-phase power supply, the first slow-start procedure is used. If the power supply unit is a three-phase power supply, the second slow-start procedure is used.

[0022] Preferably, the pre-start check includes:

[0023] S11: Determine if the grid voltage is normal. If the grid voltage is normal, proceed to step S12; otherwise, determine that the slow start has failed and end the process.

[0024] S12: Determine if the phase-locked unit is ready. If yes, repeat step S12. If yes, proceed to step S2.

[0025] Preferably, the first slow start process is as follows:

[0026] S211: Use the L line of the single-phase power supply as the slow-start enable branch, connect the slow-start enable branch, and the slow-start drive unit controls the slow-start switch to perform the slow-start operation. The slow-start starting point is located at 0° or 180° of the grid voltage waveform of that phase.

[0027] S212: The slow start duty cycle of the slow start enable branch is accumulated according to the slow start step size. It is accumulated once for each cycle or half cycle of the power grid. It is determined whether the slow start duty cycle is 1. If it is, proceed to step S213; otherwise, repeat step S212.

[0028] S213: Determine whether the bus voltage meets the slow-start requirement; if yes, the slow-start is successful and the process ends; otherwise, proceed to step S214.

[0029] S214: Determine if the maximum slow-start time has been reached; if so, determine that the slow-start has failed and end the process; otherwise, return to step S213.

[0030] Preferably, the second delayed start process is as follows:

[0031] S221: Use any one of the Ua, Ub and Uc lines as the slow start enable branch, and the other two as non-slow start branches. Connect the slow start enable branch and close the non-slow start branches. The slow start drive unit controls the slow start switch corresponding to the slow start enable branch to perform the slow start operation. The slow start starting point is located at 0° or 180° of the enable phase grid voltage waveform.

[0032] S222: The slow start duty cycle of the slow start enable branch is accumulated according to the slow start step size. It is accumulated once for each cycle or half cycle of the power grid. It is determined whether the slow start duty cycle is 1. If it is, proceed to step S223; otherwise, repeat step S222.

[0033] S223: Determine whether the bus voltage meets the slow start requirement. If yes, proceed to step S225; otherwise, proceed to step S224.

[0034] S224: Determine if the maximum slow-start time has been reached; if yes, determine that the slow-start has failed and end the process; otherwise, return to step S223.

[0035] S225: Connect the non-soft start branch, determine that the soft start is successful, and end the process.

[0036] The present invention has the following beneficial effects:

[0037] 1. The soft-start switch unit eliminates the need for a soft-start resistor, reducing components and simplifying the overall design;

[0038] 2. The soft-start circuit does not need to consider the load condition. It can charge the DC bus capacitor under both full load and no load, realize the soft-start function, and improve reliability.

[0039] 3. When a single-phase or three-phase power supply starts slowly, only one pulse drive is needed, while the other circuits remain constantly off, making it simple to implement;

[0040] 4. The control method of the soft-start circuit is simple and reliable, and can be implemented with a simple CPU. It does not have high requirements for calculation speed and accuracy, thus simplifying the soft-start operation.

[0041] 5. Applicable to various single-phase / three-phase four-wire rectifier circuits, with a wide range of applications. Attached Figure Description

[0042] Figure 1 This is a schematic diagram of the overall structure of the rectifier power supply soft-start circuit.

[0043] Figure 2 This is a structural diagram of the first embodiment of the rectifier power supply soft-start circuit;

[0044] Figure 3 This is a structural diagram of a second embodiment of the rectifier power supply soft-start circuit;

[0045] Figure 4 The waveform diagram shows the start-up point of the rectifier circuit at 0° of the enable phase grid voltage waveform.

[0046] Figure 5 The waveform diagram shows the start-up point of the rectifier circuit at 180° of the enable phase grid voltage waveform.

[0047] The realization of the objective, functional features and advantages of the present invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0048] It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0049] Reference Figure 1This invention provides a rectifier power supply soft-start circuit, which is applicable to various single-phase / three-phase four-wire rectifier circuits, including: uncontrolled rectifier / multi-pulse rectifier circuits, PFC circuits, PWM rectifier circuits, Vienna rectifier circuits, etc., and has a wide range of applications;

[0050] Includes: power supply unit, EMI filter, soft-start switch unit, soft-start drive unit, soft-start drive control unit, circuit control unit, and rectifier circuit;

[0051] The circuit control unit includes: a phase-locked loop unit and a rectifier circuit control unit;

[0052] The power supply unit is electrically connected to the phase-locked unit and the EMI filter. The EMI filter is electrically connected to the soft-start switch unit. The soft-start switch unit is electrically connected to the soft-start drive unit and the rectifier circuit. The soft-start drive unit is electrically connected to the soft-start drive control unit. The soft-start drive control unit is electrically connected to the rectifier circuit control unit. The rectifier circuit control unit is electrically connected to the rectifier circuit.

[0053] Specifically, the phase-locked unit is used to collect the real-time amplitude, frequency and phase of the input grid voltage. The circuit control unit and the slow-start drive control unit work together to complete the real-time calculation of the slow-start drive and output the slow-start drive control signal. The slow-start drive unit is used to connect the slow-start switch unit and the slow-start drive control unit, and acts on the slow-start switch in real time to drive the slow-start switch to finally realize the slow-start function.

[0054] The soft-start drive unit is used to drive the soft-start switch. Each switch consists of two MOSFETs connected in reverse series. A general MOSFET drive circuit can be used. Since there is no high-frequency switch, the drive loss is small. Furthermore, for the soft-start circuit of this invention, only single-channel and three-channel drives are required for the single-channel and three-channel types, respectively, but the drives need to be isolated from each other.

[0055] The slow-start drive control unit is a drive control circuit that, together with the circuit control unit, calculates and issues drive signal pulses.

[0056] The circuit control unit can work together with the rectifier circuit control unit and utilize the CPU resources of the rectifier circuit control unit, including input three-phase voltage sampling, soft-start operation, and single or three-channel drive output (EPWM port or IO port).

[0057] refer to Figure 2 In the first embodiment, the power supply unit is a single-phase power supply, and the slow-start switch unit is a single-channel slow-start switch.

[0058] The soft-start switch includes: a first NPN MOSFET and a second NPN MOSFET;

[0059] The L line of the single-phase power supply is electrically connected to pin 2 of the first NPN MOSFET through an EMI filter. Pins 3 of the first NPN MOSFET and pins 3 of the second NPN MOSFET are electrically connected to the soft-start drive unit. Pin 2 of the second NPN MOSFET is electrically connected to the rectifier circuit. Pins 1 of the first NPN MOSFET and pins 1 of the second NPN MOSFET are electrically connected to the soft-start drive unit.

[0060] The neutral (N) line of a single-phase power supply is electrically connected to the rectifier circuit via an EMI filter.

[0061] Specifically, the soft-start switch uses two NPN MOSFETs connected in reverse series, eliminating the need for a soft-start resistor. For single-phase / three-phase four-wire rectifier circuits, either a single or three-way soft-start switch can achieve the soft-start function. The soft-start switch is located between the EMI filter and the rectifier circuit. Due to the low on-resistance of the MOSFETs (the on-resistance of SiC MOSFETs is in the milliohm range), the switch operates once per power grid cycle, resulting in negligible losses. After the soft-start is complete, the switch is fully open, with only conduction losses, resulting in very high soft-start efficiency.

[0062] refer to Figure 3 In the second embodiment, the power supply unit is a three-phase power supply, including: a first power supply, a second power supply and a third power supply;

[0063] The slow-start switch unit is a three-way slow-start switch, including: a first slow-start switch, a second slow-start switch and a third slow-start switch;

[0064] The first soft-start switch includes: a first NPN MOSFET and a second NPN MOSFET;

[0065] The second soft-start switch includes: a third NPN MOSFET and a fourth NPN MOSFET;

[0066] The third soft-start switch includes: the fifth NPN MOSFET and the sixth NPN MOSFET;

[0067] The Ua line of the first power supply is electrically connected to pin 2 of the first NPN MOSFET through an EMI filter. Pins 3 of the first NPN MOSFET and pins 3 of the second NPN MOSFET are electrically connected to the soft-start drive unit. Pin 2 of the second NPN MOSFET is electrically connected to the rectifier circuit. Pins 1 of the first NPN MOSFET and pins 1 of the second NPN MOSFET are electrically connected to the soft-start drive unit.

[0068] The Ub line of the second power supply is electrically connected to pin 2 of the third NPN MOSFET through an EMI filter. Pins 3 of the third NPN MOSFET and pin 3 of the fourth NPN MOSFET are electrically connected to the soft-start drive unit. Pin 2 of the fourth NPN MOSFET is electrically connected to the rectifier circuit. Pins 1 of the third NPN MOSFET and pin 1 of the fourth NPN MOSFET are electrically connected to the soft-start drive unit.

[0069] The Uc line of the third power supply is electrically connected to pin 2 of the fifth NPN MOSFET through an EMI filter. Pins 3 of the fifth NPN MOSFET and pin 3 of the sixth NPN MOSFET are electrically connected to the soft-start drive unit. Pin 2 of the sixth NPN MOSFET is electrically connected to the rectifier circuit. Pins 1 of the fifth NPN MOSFET and pin 1 of the sixth NPN MOSFET are electrically connected to the soft-start drive unit.

[0070] The neutral (N) line of the three-phase power supply is electrically connected to the rectifier circuit through an EMI filter.

[0071] This invention provides a control method for a rectifier power supply soft-start circuit, comprising:

[0072] S1: Perform a slow start pre-check. If the slow start pre-check is abnormal, the slow start is determined to have failed and the process ends. If the slow start pre-check is normal, proceed to step S2.

[0073] S2: Determine the type of power supply unit. If the power supply unit is a single-phase power supply, the first slow-start procedure is used. If the power supply unit is a three-phase power supply, the second slow-start procedure is used.

[0074] Furthermore, the pre-launch checks for delayed start-up are as follows:

[0075] S11: Determine if the grid voltage is normal. If the grid voltage is normal, proceed to step S12; otherwise, determine that the slow start has failed and end the process.

[0076] S12: Determine if the phase-locked unit is ready. If yes, repeat step S12. If yes, proceed to step S2.

[0077] Furthermore, the first phase of the delayed restart process is as follows:

[0078] S211: Use the L line of the single-phase power supply as the slow-start enable branch, connect the slow-start enable branch, and the slow-start drive unit controls the slow-start switch to perform the slow-start operation. The slow-start starting point is located at 0° or 180° of the grid voltage waveform of that phase.

[0079] S212: The slow start duty cycle of the slow start enable branch is accumulated according to the slow start step size. It is accumulated once for each cycle or half cycle of the power grid. It is determined whether the slow start duty cycle is 1. If it is, proceed to step S213; otherwise, repeat step S212.

[0080] S213: Determine whether the bus voltage meets the slow-start requirement; if yes, the slow-start is successful and the process ends; otherwise, proceed to step S214.

[0081] S214: Determine if the maximum slow-start time has been reached; if so, determine that the slow-start has failed and end the process; otherwise, return to step S213.

[0082] Furthermore, the second delayed start process is as follows:

[0083] S221: Use any one of the Ua, Ub and Uc lines as the slow start enable branch, and the other two as non-slow start branches. Connect the slow start enable branch and close the non-slow start branches. The slow start drive unit controls the slow start switch corresponding to the slow start enable branch to perform the slow start operation. The slow start starting point is located at 0° or 180° of the enable phase grid voltage waveform.

[0084] Specifically, the soft-start starting point of a single-phase / three-phase four-wire rectifier circuit is located at 0° of the enable phase grid voltage waveform, as shown in the waveform diagram. Figure 4 As shown, the soft-start starting point of a single-phase / three-phase four-wire rectifier circuit is located at 180° of the enable phase grid voltage waveform. Figure 5 As shown;

[0085] S222: The slow start duty cycle of the slow start enable branch is accumulated according to the slow start step size. It is accumulated once for each cycle or half cycle of the power grid. It is determined whether the slow start duty cycle is 1. If it is, proceed to step S223; otherwise, repeat step S222.

[0086] Specifically, by adjusting the slow-start step size, the slow-start current can be adjusted. The slow-start current must be within the tolerance range of the rectifier tube or filter in the rectifier circuit. The smaller the slow-start step size, the smaller the slow-start current and the longer the slow-start time under the same rectifier circuit. Conversely, the larger the slow-start current and the shorter the slow-start time.

[0087] S223: Determine whether the bus voltage meets the slow start requirement. If yes, proceed to step S225; otherwise, proceed to step S224.

[0088] S224: Determine if the maximum slow-start time has been reached; if yes, determine that the slow-start has failed and end the process; otherwise, return to step S223.

[0089] S225: Connect the non-soft start branch, determine that the soft start is successful, and end the process.

[0090] It should be noted that, in this document, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or system that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or system. Unless otherwise specified, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or system that includes that element.

[0091] The sequence numbers of the above embodiments of the present invention are for descriptive purposes only and do not represent the superiority or inferiority of the embodiments. In the unit claims listing several devices, several of these devices may be embodied by the same hardware item. The use of the terms first, second, and third, etc., does not indicate any order and can be interpreted as identifiers.

[0092] The above are merely preferred embodiments of the present invention and do not limit the scope of the patent. Any equivalent structural or procedural transformations made based on the description and drawings of the present invention, or direct or indirect applications in other related technical fields, are similarly included within the scope of patent protection of the present invention.

Claims

1. A rectifier power supply soft-start circuit, characterized in that, include: Power supply unit, EMI filter, soft-start switch unit, soft-start drive unit, soft-start drive control unit, circuit control unit, and rectifier circuit; The circuit control unit includes: a phase-locked loop unit and a rectifier circuit control unit; The power supply unit is electrically connected to the phase-locked unit and the EMI filter. The EMI filter is electrically connected to the soft-start switch unit. The soft-start switch unit is electrically connected to the soft-start drive unit and the rectifier circuit. The soft-start drive unit is electrically connected to the soft-start drive control unit. The soft-start drive control unit is electrically connected to the rectifier circuit control unit. The rectifier circuit control unit is electrically connected to the rectifier circuit. The power supply unit is a single-phase power supply, and the soft-start switch unit is a single-channel soft-start switch. The soft-start switch includes: a first NPN MOSFET and a second NPN MOSFET; The L line of the single-phase power supply is electrically connected to pin 2 of the first NPN MOSFET through an EMI filter. Pins 3 of the first NPN MOSFET and pins 3 of the second NPN MOSFET are electrically connected to the soft-start drive unit. Pin 2 of the second NPN MOSFET is electrically connected to the rectifier circuit. Pins 1 of the first NPN MOSFET and pins 1 of the second NPN MOSFET are electrically connected to the soft-start drive unit. The neutral (N) line of a single-phase power supply is electrically connected to the rectifier circuit via an EMI filter. The power supply unit is a three-phase power supply, including: a first power supply, a second power supply, and a third power supply; The slow-start switch unit is a three-way slow-start switch, including: a first slow-start switch, a second slow-start switch and a third slow-start switch; The first soft-start switch includes: a first NPN MOSFET and a second NPN MOSFET; The second soft-start switch includes: a third NPN MOSFET and a fourth NPN MOSFET; The third soft-start switch includes: the fifth NPN MOSFET and the sixth NPN MOSFET; The Ua line of the first power supply is electrically connected to pin 2 of the first NPN MOSFET through an EMI filter. Pins 3 of the first NPN MOSFET and pins 3 of the second NPN MOSFET are electrically connected to the soft-start drive unit. Pin 2 of the second NPN MOSFET is electrically connected to the rectifier circuit. Pins 1 of the first NPN MOSFET and pins 1 of the second NPN MOSFET are electrically connected to the soft-start drive unit. The Ub line of the second power supply is electrically connected to pin 2 of the third NPN MOSFET through an EMI filter. Pins 3 of the third NPN MOSFET and pin 3 of the fourth NPN MOSFET are electrically connected to the soft-start drive unit. Pin 2 of the fourth NPN MOSFET is electrically connected to the rectifier circuit. Pins 1 of the third NPN MOSFET and pin 1 of the fourth NPN MOSFET are electrically connected to the soft-start drive unit. The Uc line of the third power supply is electrically connected to pin 2 of the fifth NPN MOSFET through an EMI filter. Pins 3 of the fifth NPN MOSFET and pin 3 of the sixth NPN MOSFET are electrically connected to the soft-start drive unit. Pin 2 of the sixth NPN MOSFET is electrically connected to the rectifier circuit. Pins 1 of the fifth NPN MOSFET and pin 1 of the sixth NPN MOSFET are electrically connected to the soft-start drive unit. The neutral (N) line of the three-phase power supply is electrically connected to the rectifier circuit through an EMI filter.

2. A control method for a rectifier power supply soft-start circuit as described in claim 1, characterized in that, include: S1: Perform a pre-start check. If the pre-start check is abnormal, the start-up is determined to have failed and the process ends. If the pre-start check is normal, proceed to step S2; S2: Determine the type of power supply unit. If the power supply unit is a single-phase power supply, the first slow-start procedure is used. If the power supply unit is a three-phase power supply, the second slow-start procedure is used.

3. The control method for the rectifier power supply soft-start circuit according to claim 2, characterized in that, The specific pre-start checks are as follows: S11: Determine if the grid voltage is normal. If the grid voltage is normal, proceed to step S12; otherwise, determine that the slow start has failed and end the process. S12: Determine if the phase-locked unit is ready. If yes, repeat step S12. If yes, proceed to step S2.

4. The control method for the rectifier power supply soft-start circuit according to claim 2, characterized in that, The first slow start procedure is as follows: S211: Use the L line of the single-phase power supply as the slow-start enable branch, connect the slow-start enable branch, and the slow-start drive unit controls the slow-start switch to perform the slow-start operation. The slow-start starting point is located at 0° or 180° of the grid voltage waveform of that phase. S212: The slow start duty cycle of the slow start enable branch is accumulated according to the slow start step size. It is accumulated once for each cycle or half cycle of the power grid. It is determined whether the slow start duty cycle is 1. If it is, proceed to step S213; otherwise, repeat step S212. S213: Determine if the bus voltage meets the slow-start requirement; if so, the slow-start is successful and the process ends. Otherwise proceed to step S214; S214: Determine if the maximum slow-start time has been reached; if so, determine that the slow-start has failed and end the process. Otherwise, return to step S213.

5. The control method for the rectifier power supply soft-start circuit according to claim 2, characterized in that, The second delayed start process is as follows: S221: Use any one of the Ua, Ub and Uc lines as the slow start enable branch, and the other two as non-slow start branches. Connect the slow start enable branch and close the non-slow start branches. The slow start drive unit controls the slow start switch corresponding to the slow start enable branch to perform the slow start operation. The slow start starting point is located at 0° or 180° of the enable phase grid voltage waveform. S222: The slow start duty cycle of the slow start enable branch is accumulated according to the slow start step size. It is accumulated once for each cycle or half cycle of the power grid. It is determined whether the slow start duty cycle is 1. If it is, proceed to step S223; otherwise, repeat step S222. S223: Determine whether the bus voltage meets the slow start requirement. If yes, proceed to step S225; otherwise, proceed to step S224. S224: Determine if the maximum slow-start time has been reached; if yes, determine that the slow-start has failed and end the process; otherwise, return to step S223. S225: Connect the non-soft start branch, determine that the soft start is successful, and end the process.

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