Bidirectional soft start circuit and bidirectional soft start protection method thereof

Abstract

The invention is suitable for the technical field of power supplies, and provides a bidirectional soft start circuit and a bidirectional soft start protection method thereof. The method comprises the following steps: performing bidirectional soft start control on a bus capacitor according to a soft start driving signal; acquiring the accumulated energy of the soft start resistor in the current time period; obtaining the critical energy of the soft start resistor in the current time period; the accumulated energy is compared with the critical energy, and if it is detected that the energy is larger than the critical energy, soft start driving protection is carried out. By the adoption of the mode, bidirectional soft start can be achieved, the use scene of a machine is widened, the phenomenon of fault misjudgment caused by voltage pits is avoided, and the reliability and stability of the soft start circuit are greatly improved.

Description

Technical Field

[0001] The present application belongs to the technical field of power supply, and more specifically, relates to a bidirectional soft-start circuit and a bidirectional soft-start protection method thereof. Background Art

[0002] In the commonly used conversion circuits of power electronics, when the boost circuit and half-bridge circuit are used for boosting, the output voltage must be greater than the input voltage, resulting in the inability of the DC voltage at the output port to start slowly from zero. Common single-stage power modules, such as DC-DC (DCDC) converters, rectifiers, and energy storage converters can be regarded as derivative circuits of the boost circuit or the half-bridge circuit, and all have the problem that the DC output voltage on the high-voltage side cannot be soft-started directly from zero. When the external load is a large capacitive load, or there is a fault that causes the resistance to be too small or even a short circuit, directly attracting the relay or contactor to output the target DC voltage will cause a huge instantaneous impact on the power module, causing the relay to stick and the device to be overstressed. In severe cases, it may even damage the power module or the load.

[0003] In view of the problem that the DC voltage output by the above power module cannot be slowly started from zero, a common solution is to add a soft start circuit inside the power module. When the output starts, the soft start circuit is started first to slowly increase the external port voltage until the difference between the external port voltage and the output target voltage is small, and then close the main power contactor or relay to reduce the instantaneous current impact, thereby achieving the soft start effect. Figure 1-2 As shown, taking a common single-stage rectifier as an example, Figure 1 a is a common single-stage rectifier circuit diagram. Figure 1 b is the corresponding voltage output range, Figure 2 a is the ideal soft-start output voltage and current waveform. Figure 2 b is the output voltage and current waveform without soft start.

[0004] In some working conditions, for example, when the external load needs to supply power to the auxiliary source at the same time, the soft-start voltage may drop temporarily, and the drop position may be random. The voltage drop may cause the software to misjudge. Summary of the invention

[0005] The purpose of the embodiments of the present application is to provide a bidirectional soft-start circuit and a bidirectional soft-start protection method thereof, aiming to solve the above-mentioned technical problems in the prior art.

[0006] To achieve the above-mentioned purpose, according to one aspect of the present application, a bidirectional soft-start protection method is provided, which is applied to a bidirectional soft-start circuit, including: performing bidirectional soft-start control on the bus capacitor according to a soft-start drive signal; obtaining the accumulated energy of the soft-start resistor in the current time period; obtaining the critical energy of the soft-start resistor in the current time period; comparing the accumulated energy with the critical energy, and performing soft-start drive protection if it is detected that the energy is greater than the critical energy.

[0007] Optionally, obtaining the accumulated energy of the soft-start resistor in the current time period includes: determining the voltage across the soft-start resistor based on the bidirectional soft-start circuit; determining the cycle length of the current time period; and calculating the voltage and the cycle length to determine the accumulated energy of the soft-start resistor in the current time period.

[0008] Optionally, determining the voltage across the soft-start resistor based on the bidirectional soft-start circuit includes: calculating the voltage across the soft-start resistor based on the bidirectional soft-start circuit by applying the following relationship:

[0009]

[0010] Among them, U0 is the voltage of the low voltage port, τ is the time constant, t is the time, U R (t) is the voltage across the soft-start resistor.

[0011] Optionally, determining the cycle length of the current time period includes: determining the number of discrete reference calculation cycles included in the current time period, the reference calculation cycle being smaller than the control cycle of the DSP controller; and determining the cycle length of the current time period based on the number and the reference calculation cycle.

[0012] Optionally, calculating the voltage and the cycle length to determine the accumulated energy of the soft-start resistor in the current time period includes: calculating the voltage and the resistance value of the soft-start resistor to calculate the instantaneous power consumed by the soft-start resistor; integrating and solving the instantaneous power according to the cycle length to obtain the accumulated energy of the soft-start resistor in the current time period.

[0013] Optionally, the critical energy of the soft-start resistor in the current time period is obtained, including: integrating the time according to the instantaneous power of the soft-start resistor to obtain the cumulative energy value of the soft-start resistor over time; dividing the entire process of bidirectional soft-start control of the bus capacitor into multiple time periods; and obtaining the critical energy of the current time period by the difference between the cumulative energy value at the end time of the current time period and the cumulative energy value at the end time of the previous time period of the current time period.

[0014] To achieve the above-mentioned purpose, according to one aspect of the present application, a bidirectional soft-start circuit is provided, comprising: a relay, a first MOS tube, a second MOS tube, a soft-start resistor, a bus capacitor and a DSP controller; the control end of the relay, the gate of the first MOS tube and the gate of the second MOS tube are connected to the DSP controller, the drain of the first MOS tube and the first end of the relay are externally connected to the positive electrode of a high-voltage power supply, the source of the first MOS tube is connected to the source of the second MOS tube, the drain of the second MOS tube is connected to the first end of the bus capacitor through the soft-start resistor, the second end of the relay is connected to the first end of the bus capacitor, and the second end of the bus capacitor is connected to the negative electrode of the high-voltage power supply.

[0015] Optionally, the bus capacitor includes a first bus capacitor and a second bus capacitor connected in series.

[0016] Optionally, the bidirectional soft start circuit also includes: a third MOS tube, a fourth MOS tube and an inductor; the drain of the third MOS tube is connected to the first end of the bus capacitor, the source of the third MOS tube is connected to the positive electrode of the low voltage port through the inductor, the source of the third MOS tube is also connected to the drain of the fourth MOS tube, the source of the fourth MOS tube is connected to the negative electrode of the low voltage port, and the low voltage port is used to connect a load.

[0017] Optionally, the DSP controller is used to receive a soft-start drive signal, control the first MOS tube and the second MOS tube to be turned on in sequence, and perform a bidirectional soft-start on the bus capacitor through the soft-start resistor.

[0018] The beneficial effect of the bidirectional soft-start circuit provided in the present application is that compared with the prior art, the present application determines whether soft-start protection is needed by calculating the energy of the soft-start resistor, thereby realizing bidirectional soft-start, broadening the use scenarios of the machine, avoiding the phenomenon of misjudgment of faults caused by voltage pits, and greatly increasing the reliability and stability of the soft-start circuit. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the technical features of the embodiments of the present application, the drawings required for use in the embodiments of the present application will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For those skilled in the art, other drawings can be obtained based on these drawings without paying any creative work.

[0020] Figure 1 is a schematic diagram of a rectifier system;

[0021] Figure 2 Output voltage and current waveforms with and without soft start;

[0022] Figure 3 This is a simplified diagram of the soft start circuit;

[0023] Figure 4 It is a schematic diagram comparing the actual soft start curve and the critical curve;

[0024] Figure 5 A schematic diagram of the structure of a bidirectional soft-start circuit provided in an embodiment of the present application;

[0025] Figure 6 A schematic diagram of a voltage variation curve across a soft-start resistor provided in an embodiment of the present application;

[0026] Figure 7 A schematic diagram of an energy accumulation curve of a soft-start resistor provided in an embodiment of the present application;

[0027] Figure 8 A schematic diagram of a segmented energy criterion soft start protection provided in an embodiment of the present application;

[0028] Fig. 9 A schematic diagram of a soft start protection method provided in an embodiment of the present application;

[0029] Fig.10 A flow chart of a bidirectional soft-start protection method applied to a bidirectional soft-start circuit provided in an embodiment of the present application. DETAILED DESCRIPTION

[0030] In order to have a clearer understanding of the technical features, purposes and effects of the present application, the specific implementation methods of the present application are further described in detail below in conjunction with the accompanying drawings and Examples. The following examples are only used to illustrate the present application, but are not used to limit the scope of protection of the present application. Based on the embodiments of the present application, other embodiments obtained by those skilled in the art without paying creative work should all belong to the scope of protection of the present application.

[0031] In the description of the present application, it should be noted that the terms "upper", "lower", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present application.

[0032] In the description of this application, it should be understood that the numbers in this document, such as "first", "second", etc., are only used to distinguish the objects described, have no sequential or technical meaning, and cannot be understood as stipulating or implying the importance of the objects described.

[0033] In the description of this application, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in this application can be understood according to specific circumstances.

[0034] In the description of this application, the term "plurality" refers to two or more than two. In addition, the term "and / or" is only a description of the association relationship of associated objects, indicating that there can be three relationships. For example, A and / or B can mean: A exists alone, A and B exist at the same time, and B exists alone. In addition, the character " / " in this article generally indicates that the associated objects before and after are in an "or" relationship.

[0035] In the description of this application, it should be noted that, unless otherwise defined, all technical and scientific terms used in this application have the same meaning as those commonly understood by those skilled in the art. The terms used in the specification of this application are only for the purpose of describing specific embodiments and are not intended to limit this application. For those of ordinary skill in the art, the specific meanings of the above terms in this application can be understood by specific circumstances.

[0036] When a soft start fault occurs, the traditional protection method is to calculate a soft start critical curve based on the actual situation, and implement this critical curve in the control chip. dc If the voltage rise curve is below the calculated critical curve, a fault shutdown is reported. Figure 3 The soft start diagram shown in the figure, R s is the soft-start resistor, U bus is the high-voltage bus voltage, R0 is the load, and C0 is the maximum capacitance allowed. The corresponding time constant can be calculated based on the critical value. The software uses interrupt counting as time t to calculate the time at different bus voltages U bus , the critical port voltage at the corresponding moment is calculated in real time: According to the above, the soft start relationship of the high-voltage side port voltage is: The program limits the exponential values ​​of time t and e and calculates the critical port voltage U c And with the actual U dc For comparison and fault judgment, refer to the soft start critical curve Figure 4 , the area below the curve is the fault area, and the area above the curve is the normal area.

[0037] Reference Figure 5According to one aspect of the present application, an embodiment of the present application provides a bidirectional soft-start circuit, including: a relay K, a first MOS tube Q1, a second MOS tube Q2, a soft-start resistor Rs, a bus capacitor and a DSP controller.

[0038] The control end of the relay K, the gate of the first MOS tube Q1 and the gate of the second MOS tube Q2 are connected to the DSP controller, the drain of the first MOS tube Q1 and the first end of the relay K are externally connected to the positive electrode of the high-voltage power supply, the source of the first MOS tube Q1 is connected to the source of the second MOS tube Q2, the drain of the second MOS tube Q2 is connected to the first end of the bus capacitor through the soft-start resistor, the second end of the relay K is connected to the first end of the bus capacitor, and the second end of the bus capacitor is connected to the high-voltage power supply U dc The first MOS tube Q1 and the second MOS tube Q2 are preferably MOSFET tubes.

[0039] The DSP controller receives the soft-start driving signal, controls the first MOS transistor Q1 and the second MOS transistor Q2 to be turned on in sequence, and performs a bidirectional soft-start on the bus capacitor through the soft-start resistor Rs.

[0040] The bus capacitor includes a first bus capacitor C1 and a second bus capacitor C2 connected in series.

[0041] The bidirectional soft start circuit also includes: a third MOS tube Q3, a fourth MOS tube Q4 and an inductor L; the drain of the third MOS tube Q3 is connected to the first end of the bus capacitor, the source of the third MOS tube Q3 is connected to the positive electrode of the low voltage port through the inductor L, the source of the third MOS tube Q3 is also connected to the drain of the fourth MOS tube Q4, the source of the fourth MOS tube Q4 is connected to the negative electrode of the low voltage port, and the low voltage port is used to connect a load.

[0042] The process of bidirectional soft start is that when the DSP controller receives the high-voltage side start command, i.e. the soft start drive signal, the DSP controller sends the first MOS tube Q1 drive signal to turn on, so as to realize U dc High voltage side external voltage to internal U bus Bus soft start, when the power module is at the low voltage side, the DSP controller sends the second MOS tube Q2 to drive and open, to achieve U bus Internal bus voltage to external U dc The external load on the high voltage side is soft-started. dc Voltage and U bus When the voltages are similar, the DSP controller sends a relay K closing signal through the serial port, relay K closes, and the low-voltage port finally outputs U0.

[0043] The embodiment of the present invention calculates the soft-start resistance R by fitting the voltage soft-start critical curve under severe working conditions. s Voltage variation curve U at both ends R (t), such as Figure 6 As shown by the dotted line, Figure 6 The solid line in is the soft start critical curve.

[0044] In the embodiment of the present application, the reference calculation cycle of the soft start drive protection control is determined. T a It is a discretized period, which is shorter than the control period of the DSP controller. The reference calculation period is smaller than the control period of the DSP controller.

[0045] Determine the number of discretization periods, for example n = 1, 2, ..., 10000. Discretization period energy W R (n) Calculate the following relationship:

[0046]

[0047] The corresponding energy accumulation W tal (n) Calculate the following relationship:

[0048]

[0049] In the embodiment of the present application, the soft start resistor R s The voltage change curve at both ends is processed by discrete integration to obtain the energy accumulation curve of the soft-start resistor. Figure 7 As shown by the solid line in .

[0050] The accumulated energy is processed in time periods. The more time periods there are, the shorter the protection time is. Each time period corresponds to a different level of critical energy. A small amount of margin can be added as critical judgment energy according to the hardware's tolerance. The critical judgment energy of each section is used as the criterion for fault. When the accumulated energy in a certain period is greater than the critical energy of that period, the chip controls the machine to shut down quickly for protection. For the schematic diagram of segmented energy judgment soft start protection, see Figure 8 Where T b The period of the divided time period is:

[0051]

[0052] λ is the number of reference calculation cycles included in the current period. The number of periods included in the entire two-way soft start protection process, that is, the number of parameter segments k = 1, 2, ..., 30. Critical energy ΔW R (k) = W tal (k.λ)-W tal [(k-1).λ], and then determine the critical judgment energy curve W limit(k) From Fig. 9 It can be seen that the energy does not change much after the 10th period, so the energy accumulation can be approximately considered to be the same after the 10th period, and the minimum critical energy limit can be added after the 10th period. Fig. 9 This is a complete schematic diagram of the two-way soft-start protection method. The soft-start drive signal is turned on, that is, the DSP controller receives the soft-start drive signal. The voltage difference across the soft-start resistor is calculated, and the energy accumulation is calculated. Then the time period is counted. When the count reaches the current period, the critical energy and cumulative energy of the current period are calculated to determine whether the accumulated parameters are greater than the critical energy. If not, the count value is reset to zero, indicating that the current period is normal. If yes, it means that soft-start protection is required, wave sealing processing, soft-start drive is turned off, and the machine alarm is shut down.

[0053] The embodiment of the present invention realizes bidirectional soft start, broadens the use scenarios of the machine, avoids the phenomenon of fault misjudgment caused by voltage pits, and greatly increases the reliability and stability of the soft start circuit. It should be noted that the algorithm of the soft start resistor energy of the present application can be calculated by collecting the current flowing through the soft start resistor, and the soft start circuit part can be made of a low-power BUCK circuit to increase the soft start power and improve the working efficiency of the circuit.

[0054] In summary, the bidirectional soft-start circuit of the embodiment of the present application includes: a relay, a first MOS tube, a second MOS tube, a soft-start resistor, a bus capacitor and a DSP controller; the control end of the relay, the gate of the first MOS tube and the gate of the second MOS tube are connected to the DSP controller, the drain of the first MOS tube and the first end of the relay are connected to the positive electrode of the high-voltage power supply, the source of the first MOS tube is connected to the source of the second MOS tube, the drain of the second MOS tube is connected to the first end of the bus capacitor through the soft-start resistor, the second end of the relay is connected to the first end of the bus capacitor, and the second end of the bus capacitor is connected to the negative electrode of the high-voltage power supply, which can realize bidirectional soft start, broaden the use scenarios of the machine, avoid the phenomenon of misjudgment of faults caused by voltage pits, and greatly increase the reliability and stability of the soft-start circuit.

[0055] like Fig.10 As shown, the present application also provides a bidirectional soft start protection method applied to the aforementioned bidirectional soft start circuit, which is applied to a DSP controller in the bidirectional soft start circuit. The method includes:

[0056] Step S11: performing bidirectional soft-start control on the bus capacitor according to the soft-start drive signal.

[0057] The DSP controller in the bidirectional soft start circuit receives the soft start drive signal and performs bidirectional soft start control on the bus capacitor according to the soft start drive signal. Specifically, first, the DSP controller sends a drive signal to the first MOS tube Q1 to turn on, so as to realize U dc High voltage side external voltage to internal U bus Bus soft start, when the power module is at the low voltage side, the DSP controller sends the second MOS tube Q2 to drive and open, to achieve U bus Internal bus voltage to external U dc The external load on the high voltage side is soft-started. dc Voltage and U bus When the voltages are similar, the DSP controller sends a relay K closing signal through the serial port, relay K closes, and the low-voltage port finally outputs U0.

[0058] Step S12: Obtain the accumulated energy of the soft-start resistor in the current period.

[0059] Optionally, firstly, the voltage across the soft-start resistor is determined based on the bidirectional soft-start circuit. Specifically, the voltage across the soft-start resistor is calculated based on the bidirectional soft-start circuit by applying the following relationship:

[0060]

[0061] Among them, U0 is the voltage of the low voltage port, τ is the time constant, t is the time, U R (t) is the voltage across the soft-start resistor.

[0062] Then determine the cycle length of the current period. Optionally, determine the number of discretized reference calculation cycles included in the current period, λ is the number of reference calculation cycles included in the current period, T a It is the reference calculation cycle, which is smaller than the control cycle of the DSP controller. It can be set specifically. b The cycle length T of the current period is determined according to the number and the reference calculation period. b .

[0063] Then the voltage and the cycle length are calculated to determine the accumulated energy of the soft-start resistor in the current period. Optionally, the voltage and the resistance of the soft-start resistor are calculated to calculate the instantaneous power consumed by the soft-start resistor. The instantaneous power is integrated and solved according to the cycle length to obtain the accumulated energy of the soft-start resistor in the current time period.

[0064] Step S13: Obtain the critical energy of the soft-start resistor in the current period.

[0065] Optionally, the instantaneous power of the soft-start resistor is integrated over time to obtain the cumulative energy value of the soft-start resistor over time; the entire process of bidirectional soft-start control of the bus capacitor is divided into multiple time periods; the difference between the cumulative energy value at the end of the current time period and the cumulative energy value at the end of the previous time period of the current time period is obtained to obtain the critical energy of the current time period. For more details, refer to the previous embodiment.

[0066] Step S14: Compare the accumulated energy with the critical energy, and if it is detected that the energy is greater than the critical energy, perform soft start drive protection.

[0067] Compare the accumulated energy with the critical energy to determine whether the accumulated parameter is greater than the critical energy. If not, the count value is reset to zero, indicating that the current period is normal. If yes, it means that soft start protection, wave blocking processing, soft start drive shutdown, and machine alarm shutdown are required.

[0068] The above is only a preferred implementation of the present application, but the protection scope of the present application is not limited thereto. It should be pointed out that for those skilled in the art, several equivalent obvious variations and / or equivalent replacements can be made without departing from the technical principles of the present application. These obvious variations and / or equivalent replacements should also be regarded as the protection scope of the present application.

Claims

1. A two-way soft start protection method, characterized in that: Applied to a bidirectional soft-start circuit, the bidirectional soft-start protection method includes: Perform bidirectional soft-start control on the bus capacitor according to the soft-start drive signal; Obtain the accumulated energy of the soft-start resistor in the current period; Obtain the critical energy of the soft-start resistor in the current period; The accumulated energy is compared with the critical energy, and if it is detected that the energy is greater than the critical energy, soft start driving protection is performed.

2. The bidirectional soft start protection method according to claim 1, characterized in that: The step of obtaining the accumulated energy of the soft-start resistor in the current period includes: Determining a voltage across the soft-start resistor based on the bidirectional soft-start circuit; Determining the cycle length of the current period; The voltage and the cycle length are calculated to determine the accumulated energy of the current period of the soft-start resistor.

3. The bidirectional soft start protection method according to claim 2, characterized in that: Determining the voltage across the soft-start resistor based on the bidirectional soft-start circuit includes: The voltage across the soft-start resistor is calculated based on the bidirectional soft-start circuit using the following relationship: Among them, U0 is the voltage of the low voltage port, τ is the time constant, t is the time, U R (t) is the voltage across the soft-start resistor.

4. The bidirectional soft start protection method according to claim 2, characterized in that: The determining the cycle length of the current time period includes: Determine the number of discretized reference calculation cycles included in the current period, wherein the reference calculation cycle is less than a control cycle of the DSP controller; The cycle length of the current period is determined according to the number and the reference calculation cycle.

5. The bidirectional soft start protection method according to claim 2, characterized in that: The step of calculating the voltage and the cycle length to determine the accumulated energy of the soft-start resistor during the current period includes: Calculate the voltage and the resistance of the soft-start resistor to calculate the instantaneous power consumed by the soft-start resistor; The instantaneous power is integrated and solved according to the cycle length to obtain the accumulated energy of the soft-start resistor in the current time period.

6. The bidirectional soft start protection method according to claim 5, characterized in that: The step of obtaining the critical energy of the soft-start resistor in the current period includes: Integrate the instantaneous power of the soft-start resistor over time to obtain the accumulated energy value of the soft-start resistor over time; The whole process of bidirectional soft-start control of bus capacitor is divided into multiple time periods; The critical energy of the current period is obtained by taking the difference between the cumulative energy value at the end time of the current period and the cumulative energy value at the end time of the previous period of the current period.

7. A bidirectional soft-start circuit, characterized in that: The bidirectional soft-start circuit comprises: a relay, a first MOS tube, a second MOS tube, a soft-start resistor, a bus capacitor and a DSP controller; The control end of the relay, the gate of the first MOS tube and the gate of the second MOS tube are connected to the DSP controller, the drain of the first MOS tube and the first end of the relay are externally connected to the positive electrode of the high-voltage power supply, the source of the first MOS tube is connected to the source of the second MOS tube, the drain of the second MOS tube is connected to the first end of the bus capacitor through the soft-start resistor, the second end of the relay is connected to the first end of the bus capacitor, and the second end of the bus capacitor is connected to the negative electrode of the high-voltage power supply.

8. The bidirectional soft-start circuit according to claim 7, characterized in that: The bus capacitor includes a first bus capacitor and a second bus capacitor connected in series.

9. The bidirectional soft-start circuit according to claim 7, characterized in that: The bidirectional soft start circuit also includes: a third MOS tube, a fourth MOS tube and an inductor; the drain of the third MOS tube is connected to the first end of the bus capacitor, the source of the third MOS tube is connected to the positive electrode of the low voltage port through the inductor, the source of the third MOS tube is also connected to the drain of the fourth MOS tube, the source of the fourth MOS tube is connected to the negative electrode of the low voltage port, and the low voltage port is used to connect a load.

10. The bidirectional soft-start circuit according to claim 7, characterized in that: The DSP controller is used to receive a soft-start driving signal, control the first MOS tube and the second MOS tube to be turned on in sequence, and perform a bidirectional soft start on the bus capacitor through the soft-start resistor.

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