LLC resonant circuit control method and module, storage medium and program product

Abstract

An LLC resonant circuit control method, a control module, a storage medium and a program product are used for controlling soft start of an LLC high-frequency resonant power device for an electric locomotive, the device comprises an inversion unit for inverting a direct current into an alternating current, a transformation unit for transforming the alternating current and a rectification unit for rectifying the transformed alternating current into the direct current, wherein the switching tube, the resonant capacitor, the resonant inductor and the excitation inductor form an LLC resonant circuit, and the method comprises the following steps: a starting earlier stage step: connecting a pre-charging circuit between a direct current source and an inversion unit, and driving the switching tube with a starting frequency lower than a rated switching frequency and a starting pulse width lower than a rated pulse width; starting a later step: directly and electrically connecting the direct current source with the inverter unit when the voltage at the two ends of the support capacitor is close to the rated input voltage, and disconnecting the pre-charging circuit; and a switching step: when the output voltage is close to the rated output voltage, switching to the rated switching frequency and the rated pulse width.

Description

TECHNICAL FIELD

[0001] The present application relates to an LLC resonant circuit control method, in particular to a control method, a control module, a storage medium and a program product for soft starting of a high-power LLC high-frequency resonant circuit. BACKGROUND

[0002] An LLC resonant circuit can be used in an LLC high-frequency resonant power device. As an example of the LLC high-frequency resonant power device, a high-frequency DC / DC converter in a power supply system of a railway vehicle can be mentioned. Such an LLC high-frequency resonant power device generally includes an inverter unit that inverts direct current from an upstream into alternating current, a transformer unit that transforms the alternating current from the inverter unit using a high-frequency transformer, and a rectifier unit that rectifies the transformed alternating current into direct current and outputs the direct current to a downstream, wherein a switching transistor, a resonant capacitor, a resonant inductor, and an excitation inductor in the inverter unit and the transformer unit constitute an LLC resonant circuit.

[0003] Since the LLC resonant circuit is a hard switching process at the initial stage of starting, and the switching frequency is high (for example, above 18 kHz), the switching loss at the initial stage of starting is large, which easily causes the switching transistor to overheat and be damaged. In order to cope with such a situation, currently, the LLC resonant circuit mainly has the following several soft starting methods.

[0004] As a first method of the soft starting method, the switching duty cycle of the switching transistor is kept at the switching duty cycle (for example, 50%) at normal working time during the starting process of the LLC resonant circuit, and the starting of the LLC resonant circuit is performed using a switching frequency (for example, a switching frequency of 3 times or more than the rated resonant frequency of the LLC resonant circuit) much higher than the rated resonant frequency of the LLC resonant circuit, thereby increasing the resonant impedance during the starting process and reducing the starting current. After a certain period of time, when the output voltage of the LLC high-frequency resonant power device gradually reaches the rated output voltage, the switching frequency is gradually reduced to the rated resonant frequency.

[0005] As a second method of the soft starting method, the switching frequency can be kept at the rated resonant frequency during the starting process of the LLC resonant circuit, and the switching duty cycle of the switching transistor is controlled to gradually increase from 0% to the switching duty cycle (for example, 50%) at normal working time. Considering that the charging current is large at the initial stage of starting, the charging current is reduced after the output voltage is slowly established at the later stage of starting, the switching duty cycle can be appropriately increased to achieve fast starting, thereby being able to reduce the starting current at the initial stage of starting.

[0006] As the third mode of the soft start mode, the switching duty ratio of the switching transistor can be kept at the normal working switching duty ratio (e.g. 50%) during the start of the LLC resonant circuit, and the front-end input of the LLC resonant circuit can adopt a chopper circuit, so that the switching voltage of the switching transistor starts from a low voltage (e.g. 0V) and slowly rises, thereby reducing the start current.

[0007] In the first mode, since a switching frequency much higher than the rated resonant frequency (e.g. 3 times or 5 times the frequency) is used during the start, the design of the driving circuit of the switching transistor (MOSFET, IGBT, etc.) is difficult to control the heat generation of the driving circuit, and the design of the driving circuit is also difficult. In addition, when a switching frequency much higher than the rated resonant frequency (e.g. 3 times or 5 times the frequency) is used during the start, since the duty ratio is still 50% and the pulse width is still wide, the hard-off current of the switching transistor is still large at the initial stage of the start, and the switching frequency is also high, so the switching transistor will generate a lot of heat.

[0008] In the second mode, since the entire start process is hard switching and the switching frequency is the rated switching frequency, the temperature of the switching transistor will rise, and the switching loss will be large. Moreover, if a short circuit occurs on the load side at the initial stage of the start, the gradual increase of the switching duty ratio will exacerbate the increase of the short circuit current, which may cause damage to the switching transistor.

[0009] In the third mode, although the addition of the chopper circuit to the front end can solve the problem of excessive start current, it also increases the cost, size and weight of the chopper circuit. SUMMARY

[0010] The present application is proposed in view of the above, and aims to provide an LLC resonant circuit control method, LLC resonant circuit control module, storage medium and program product capable of small current impact and small hard switching loss during the start process.

[0011] The present application provides a LLC resonant circuit control method for controlling soft start of LLC resonant circuit in LLC high frequency resonant power device for electric locomotive, the LLC high frequency resonant power device for electric locomotive comprises an inverter unit for inverting DC current from upstream into AC current, a transformer unit for transforming AC current from the inverter unit using high frequency transformer, and a rectifier unit for rectifying the transformed AC current into DC current and outputting to downstream, and the switching tube, resonant capacitor, resonant inductor and excitation inductor in the inverter unit and the transformer unit constitute the LLC resonant circuit, characterized by comprising: a pre-start step, when receiving the start signal of the LLC high frequency resonant power device for electric locomotive, connecting a pre-charge circuit between the DC source in upstream and the inverter unit, and driving the switching tube at a start frequency lower than the rated switching frequency and a start pulse width lower than the rated pulse width; a post-start step, when the voltage across the support capacitor in the inverter unit approaches the rated input voltage, directly connecting the DC source in upstream and the inverter unit, and disconnecting the pre-charge circuit; a switching step, when the output voltage of the LLC high frequency resonant power device for electric locomotive approaches the rated output voltage, switching the start frequency to the rated switching frequency, and switching the start pulse width to the rated pulse width.

[0012] In the above LLC resonant circuit control method, the pre-charge circuit has a first switch and a resistor connected in series with the first switch, in the pre-start step, the first switch is on, and the resistor is connected in series with the inverter unit, in the post-start step, a second switch connected between the DC source in upstream and the inverter unit is on, and the first switch is off.

[0013] In the above LLC resonant circuit control method, the pre-charge circuit is the pre-charge circuit already existing in the power supply system of railway vehicle.

[0014] In the above LLC resonant circuit control method, in the post-start step, when the voltage across the support capacitor in the inverter unit reaches the first specified proportion of the rated input voltage, the DC source in upstream and the inverter unit are directly connected, and the pre-charge circuit is disconnected, and the first specified proportion is determined in a manner that the instantaneous current jump of the support capacitor at the time of switching does not cause overcurrent protection, in the switching step, when the output voltage of the LLC high frequency resonant power device for electric locomotive reaches the second specified proportion of the rated output voltage, the start frequency is switched to the rated switching frequency, and the start pulse width is switched to the rated pulse width, and the second specified proportion is determined in a manner that the instantaneous current jump of the switching tube at the time of switching does not exceed the allowable range.

[0015] In the LLC resonant circuit control method, when no valid output voltage is detected within a fault protection determination time for determining whether a fault occurs in an output circuit of the LLC high-frequency resonant power device for electric locomotive, the driving of the switching tube is stopped.

[0016] In the LLC resonant circuit control method, the starting pulse width is set according to the inductance value of the resonant inductor, the maximum off current of the switching tube and the voltage across the excitation inductor, and the starting frequency is set according to the length of the desired starting period and the temperature rise of the switching tube.

[0017] In the LLC resonant circuit control method, the LLC high-frequency resonant power device for electric locomotive is used in a high-frequency DC / DC converter in a power supply system of a railway vehicle.

[0018] The present application provides an LLC resonant circuit control module for controlling the soft start of an LLC resonant circuit in an LLC high-frequency resonant power device for electric locomotive, which comprises an inverter unit for inverting DC power from an upstream into AC power, a transformer unit for transforming the AC power from the inverter unit using a high-frequency transformer, and a rectifier unit for rectifying the transformed AC power into DC power and outputting the DC power to a downstream, and the switching tube, resonant capacitor, resonant inductor and excitation inductor in the inverter unit and the transformer unit constitute the LLC resonant circuit, characterized by comprising: a pre-starting unit for connecting a pre-charging circuit between a DC source in the upstream and the inverter unit when a starting signal of the LLC high-frequency resonant power device for electric locomotive is received, and driving the switching tube at a starting frequency lower than a rated switching frequency and a starting pulse width lower than a rated pulse width; a post-starting unit for directly electrically connecting the DC source in the upstream and the inverter unit and disconnecting the pre-charging circuit when the voltage across a support capacitor in the inverter unit approaches a rated input voltage; and a switching unit for switching the starting frequency to the rated switching frequency and the starting pulse width to the rated pulse width when the output voltage of the LLC high-frequency resonant power device for electric locomotive approaches a rated output voltage.

[0019] The present application provides a computer readable storage medium having a computer program stored thereon, characterized in that the computer program, when executed by a processor, implements the steps of the LLC resonant circuit control method.

[0020] The present application provides a computer program product comprising a computer program, characterized in that the computer program, when executed by a processor, implements the steps of the LLC resonant circuit control method.

[0021] Inventive effects

[0022] Before the inverter unit is powered on, the support capacitor in the inverter unit is in a zero-voltage state, i.e. no energy in the capacitor, and at the moment of power-on, due to the step change in voltage, the support capacitor is equivalent to a short-circuit state, the higher the voltage across the support capacitor, the greater the current flowing through the support capacitor, and if a pre-charge circuit is not connected before starting, the large current will cause current impact on the support capacitor and the switching tube, and easily trigger the over-current protection of the input current.

[0023] The application connects a pre-charge circuit, and uses the resistance in the pre-charge circuit to limit the current when charging the support capacitor, changes the time constant when charging the support capacitor, so that the voltage of the support capacitor can slowly increase in the pre-starting period. Because the voltage of the support capacitor slowly increases in the pre-starting period, the turn-off current of the switching tube in the pre-starting period can also be greatly reduced.

[0024] Moreover, when the voltage across the support capacitor increases to near the rated input voltage in the post-starting period, the input voltage will suddenly change to the rated input voltage after the pre-charge circuit is disconnected, at this time the voltage mutation rate is small, and the current impact on the support capacitor and the switching tube is small.

[0025] On the other hand, although the switching action of the switching tube in the pre-starting period and the post-starting period is hard switching, by using the reduced starting frequency, the hard switching loss can be reduced compared with the past, and the problem of temperature rise caused by hard switching loss in the pre-starting period is solved. At the same time, compared with the case where the switching tube uses a working frequency much higher than the rated switching frequency in the starting stage, the design difficulty of the driving circuit of the switching tube as a semiconductor device is not increased.

[0026] In addition, because the starting pulse width of the switching tube in the pre-starting period and the post-starting period is smaller than the rated pulse width, the turn-off current in the starting process is less than or equal to the maximum turn-off current, thereby ensuring the reliable turn-off of the switching tube.

[0027] When the output voltage of the LLC high-frequency resonant power device for electric locomotive approaches the rated output voltage, because the output voltage has been basically established, even if the starting frequency is switched to the rated switching frequency and the starting pulse width is switched to the rated pulse width, the current mutation of the switching tube is also very small.

[0028] Because the input voltage slowly rises in the pre-starting period, the output voltage slowly rises in the pre-starting period and the post-starting period, and the low-frequency narrow-pulse-width starting mode is used in the pre-starting period, the current when charging the support capacitor and the turn-off current of the switching tube are maximally reduced, the hard switching loss is reduced, and the problem of excessive junction temperature and device damage caused by large hard switching loss in the early starting stage is avoided.

[0029] In addition, since the pre-charge circuit is an existing circuit in the power supply system of the railway vehicle, no additional hardware cost is required, and the control strategy is simply adjusted on the basis of the existing vehicle main circuit to achieve the control method. Therefore, the control method is simple and the hardware cost is low.

[0030] In addition, even in the case of a fault at the load side during startup of the LLC high-frequency resonant power device for electric locomotives, the increase in the junction temperature of the switching tube can be suppressed due to the reduction in the off current of the switching tube caused by the connection of the pre-charge circuit. The set startup pulse width can also limit the off current of the switching tube to the maximum off current, so that the switching tube remains in the safe operating area and can be reliably turned off. Moreover, the fault protection determination time is set by calculating the loss of the switching tube, thereby limiting the further increase in the junction temperature of the switching tube, and the switching operation of the switching tube can be reliably performed even if a short circuit or overload fault occurs during the early startup period. BRIEF DESCRIPTION OF DRAWINGS

[0031] Figure 1 is a circuit diagram of the LLC high-frequency resonant power device for electric locomotives of the first embodiment.

[0032] Figure 2 is a flowchart showing the startup process of the LLC high-frequency resonant power device for electric locomotives.

[0033] Figure 3 is a time chart showing the startup process of the LLC high-frequency resonant power device for electric locomotives.

[0034] Figure 4 is a time chart showing the case of a fault at the load side during startup of the LLC high-frequency resonant power device for electric locomotives. DETAILED DESCRIPTION

[0035] Hereinafter, embodiments of the present application will be described. Note that the following embodiments are given to facilitate understanding of the present application and are not intended to limit the present application. In addition, the term "connected" means electrically connected unless otherwise specified.

[0036] First Embodiment

[0037] Hereinafter, the circuit structure of the LLC high-frequency resonant power device for electric locomotives and the pre-charge circuit in the first embodiment will be described with reference to the drawings.

[0038] The LLC high-frequency resonant power device for electric locomotives in the first embodiment is used to convert the power (direct current) from the upstream and output it to the downstream (e.g., an electrical load). Figure 1 is a circuit diagram of the LLC high-frequency resonant power device for electric locomotives and the pre-charge circuit of the first embodiment. is a circuit diagram of the LLC high-frequency resonant power device for electric locomotives and the pre-charge circuit of the first embodiment.

[0039] As Figure 1 shown, the LLC high-frequency resonant power device for electric locomotive in the first embodiment mainly comprises an inverter unit InC, a transformer unit TrC and a rectifier unit ReC.

[0040] In addition, a pre-charge circuit PcC is provided between the upstream DC source (not shown) and the inverter unit InC, and the pre-charge circuit PcC has a first switch K1 and a resistor R1 connected in series with the first switch K1. A second switch K2 is also provided between the upstream DC source and the inverter unit InC, and the second switch K2 is connected in parallel with the pre-charge circuit PcC.

[0041] The inverter unit InC is used to invert the DC power input from the upstream DC source via the positive input terminal Pi and the negative input terminal Ni into AC power, and the DC power is input to the positive input terminal Pi via the pre-charge circuit PcC or the second switch K2 before being input to the positive input terminal Pi.

[0042] Specifically, the inverter unit InC has a half-bridge inverter circuit comprising a first bridge arm provided with a support capacitor FC1, a second bridge arm provided with two resonant capacitors RC1, RC2 and a third bridge arm provided with two semiconductor switches SW1, SW2.

[0043] The support capacitor FC1 can eliminate the ripple in the input DC and stabilize the DC input voltage.

[0044] The semiconductor switches SW1, SW2 and the resonant capacitors RC1, RC2, together with the magnetizing inductance Lm and the resonant inductance Lr of the high-frequency transformer Tr comprised in the transformer unit TrC described later, constitute an LLC resonant circuit.

[0045] In the normal working state, the two semiconductor switches SW1, SW2 work at the rated switching frequency and the rated pulse width under the control of the control circuit and the drive circuit not shown, so as to maintain the stability of the output voltage of the LLC high-frequency resonant power device for electric locomotive.

[0046] The semiconductor switch SW1 can be composed of a metal oxide semiconductor field effect transistor (MOSFET) and a diode connected in parallel with each other, wherein the drain of the metal oxide semiconductor field effect transistor is connected to the cathode of the diode, the source of the metal oxide semiconductor field effect transistor is connected to the anode of the diode, the switching function is realized by using the metal oxide semiconductor field effect transistor, and the reverse breakdown of the metal oxide semiconductor field effect transistor is prevented by using the diode.

[0047] In addition, the drain of the metal oxide semiconductor field effect transistor constituting the semiconductor switch SW1 and the cathode of the diode constituting the semiconductor switch SW1 are commonly connected to the positive input terminal Pi, and the source of the metal oxide semiconductor field effect transistor constituting the semiconductor switch SW1 and the anode of the diode constituting the semiconductor switch SW1 are commonly connected to the drain of the metal oxide semiconductor field effect transistor constituting the semiconductor switch SW2 and the cathode of the diode constituting the semiconductor switch SW2 described later.

[0048] Further, as the metal oxide semiconductor field effect transistor constituting the semiconductor switch SW1, a silicon carbide field effect transistor (SiC-MOSFET) can be used. In this way, soft switching in a high frequency operation can be more easily realized, and the reduction of the core volume and the number of turns of the winding of the high frequency transformer Tr of the transformer unit TrC described later is facilitated, and the weight and size of the transformer are reduced.

[0049] Similarly, the semiconductor switch SW2 can be constituted by a metal oxide semiconductor field effect transistor and a diode connected in parallel to each other, wherein the drain of the metal oxide semiconductor field effect transistor is connected to the cathode of the diode, the source of the metal oxide semiconductor field effect transistor is connected to the anode of the diode, the switching function is realized by the metal oxide semiconductor field effect transistor, and the diode prevents the metal oxide semiconductor field effect transistor from being reverse-broken down.

[0050] In addition, the source of the metal oxide semiconductor field effect transistor and the anode of the diode in the semiconductor switch SW2 are commonly connected to the negative input terminal Ni.

[0051] Further, as the metal oxide semiconductor field effect transistor constituting the semiconductor switch SW2, a silicon carbide field effect transistor can also be used.

[0052] The transformer unit TrC constitutes an LLC resonant circuit with the inverter unit InC on one hand, and is used to transform the alternating current from the inverter unit InC on the other hand. In addition, the transformer unit TrC also functions to isolate the high-voltage upstream side from the low-voltage downstream side.

[0053] The transformer unit TrC in the present embodiment includes one high frequency transformer Tr. One terminal of the primary winding of the high frequency transformer Tr is connected to the midpoint of the two semiconductor switches SW1, SW2 on the third bridge arm of the inverter unit InC via the resonant inductor Lr, and the other terminal of the primary winding of the high frequency transformer Tr is connected to the midpoint of the two resonant capacitors RC1, RC2 on the second bridge arm of the inverter unit InC via the resonant inductor Lr2.

[0054] In other words, the primary winding of the high-frequency transformer Tr is connected in parallel with the magnetizing inductance Lm of the high-frequency transformer Tr and is connected to the half-bridge inverter circuit of the inverter unit InC via the resonant inductance Lr.

[0055] The rectifier unit ReC is configured to rectify the alternating current from the high-frequency transformer Tr of the transformer unit TrC into direct current and output the direct current downstream.

[0056] The rectifier unit ReC includes a rectifier circuit, and the rectification is achieved by the rectifier circuit. As shown in Figure 1 The rectifier circuit includes a fourth bridge arm provided with two diode switches RD1 and RD3 and a fifth bridge arm provided with two diode switches RD2 and RD4, forming a full-bridge rectifier circuit. In the fourth bridge arm, the cathode of the diode switch RD1 is connected to the positive output terminal Po, the anode of the diode switch RD1 is connected to the cathode of the diode switch RD3, and the anode of the diode switch RD3 is connected to the negative output terminal No. In the fifth bridge arm, the cathode of the diode switch RD2 is connected to the positive output terminal Po, the anode of the diode switch RD2 is connected to the cathode of the diode switch RD4, and the anode of the diode switch RD4 is connected to the negative output terminal No. In addition, the rectifier unit ReC further includes a sixth bridge arm provided with a filter capacitor FC2.

[0057] In addition, in the rectifier circuit, a fast recovery diode can be used as the diode switch, reducing the switching loss at startup and ensuring reliable operation of the high-frequency rectifier.

[0058] One terminal of the secondary winding of the high-frequency transformer Tr of the transformer unit TrC is connected to the midpoint of the two diode switches RD1 and RD3 on the fourth bridge arm of the rectifier circuit on the upper side in the diagram of the rectifier unit ReC, and the other terminal of the secondary winding of the high-frequency transformer Tr is connected to the midpoint of the two diode switches RD2 and RD4 on the fifth bridge arm of the rectifier circuit.

[0059] In this way, the high-frequency transformer Tr of the transformer unit TrC is connected to the rectifier circuit of the rectifier unit ReC on the secondary side.

[0060] Therefore, the rectifier unit ReC rectifies the alternating current from the high-frequency transformer Tr into direct current by the rectifier circuit and outputs the direct current downstream.

[0061] In addition, the positive input terminal Pi and the negative input terminal Ni are used to connect the direct current source upstream, and the positive output terminal Po and the negative output terminal No can be connected to the electrical load downstream.

[0062] In this way, an LLC high-frequency resonant power device for electric locomotives is constructed in the embodiment.

[0063] The working process of the above-mentioned LLC high-frequency resonant power device for electric locomotives is as follows.

[0064] First, direct current from upstream is input from the positive input terminal Pi and the negative input terminal Ni, and is inverted into alternating current by the half-bridge inverter circuit of the inverter unit InC.

[0065] Then, the AC power obtained by the inversion of the inverter unit InC is transformed into AC power of a required voltage by the high-frequency transformer Tr of the transformer unit TrC.

[0066] Finally, the AC power transformed by the transformation unit TrC is input from the high-frequency transformer Tr to the rectifier circuit of the rectifier unit ReC, rectified into DC power, and output from the positive output terminal Po and the negative output terminal No.

[0067] Below, refer to Figure 2 and Figure 3 , the starting process of LLC high-frequency resonant power equipment for electric locomotives is explained.

[0068] Figure 2 This is a flowchart showing the startup process of the LLC high-frequency resonant power device for electric locomotives. Figure 3 This is a timing chart showing the startup process of the LLC high-frequency resonant power device for electric locomotives.

[0069] like Figure 2 As shown, the soft start of the LLC resonant circuit in the LLC high-frequency resonant power device for electric locomotives is divided into an early start step S1, a first judgment step S2, a late start step S3, a second judgment step S4 and a switching step S5. Figure 3 Figure 1 shows control signal SG1 for semiconductor switch SW1, control signal SG2 for semiconductor switch SW2, primary current I1 of high-frequency transformer Tr, output voltage V1 across filter capacitor FC2, and input voltage V2 across support capacitor FC1. Primary current I1 flowing through high-frequency transformer Tr is also the off-state current flowing through semiconductor switch SW1 or SW2.

[0070] The initial step S1 corresponds to Figure 3 The first judgment step S2 and the start-up later step S3 correspond to the time period T1 from the time point t1 to the time point t2 (excluding the time point t2). Figure 3 The second judgment step S4 and the switching step S5 correspond to the time period T2 from the time point t2 to the time point t3 (excluding the time point t3). Figure 3 The time period T3 after the time point t3 (including the time point t3).

[0071] In the early startup step S1, when a startup signal from the LLC high-frequency resonant power device for electric locomotives is received, the first switch K1 is turned on, a pre-charging circuit PcC is connected between the upstream DC source and the inverter unit InC, and the semiconductor switches SW1 and SW2 are driven at a startup frequency lower than the rated switching frequency and a startup pulse width T4 lower than the rated pulse width T5.

[0072] At this time, due to the connection of the first switch K1, the resistor R1 is connected in series with the inverter unit InC, and the support capacitor FC1 starts to charge. Figure 3 As shown, during time period T1 corresponding to the early startup step S1, the voltage across support capacitor FC1, i.e., input voltage V2, slowly rises. The voltage across filter capacitor FC2, i.e., output voltage V1, also slowly rises in tandem with input voltage V2. At this time, because the starting voltage of semiconductor switches SW1 and SW2 is low, the primary-side current I1 of high-frequency transformer Tr slowly increases in tandem with the rising input voltage. The LLC high-frequency resonant power system for electric locomotives is equipped with voltage sensors for monitoring output voltage V1 and input voltage V2.

[0073] Figure 3 The solid line portion of the control signal SG1 of the semiconductor switch SW1 and the control signal SG2 of the semiconductor switch SW2 in FIG. 5 represents the actual control signal, and the dotted line portion represents the control signal under an assumed rated switching frequency.

[0074] The starting frequency of the semiconductor switches SW1 and SW2 is set according to the desired starting period and the temperature rise of the semiconductor switches SW1 and SW2. The starting frequency is set to an integer multiple of the rated switching frequency. In this embodiment, the rated switching frequency of the semiconductor switches SW1 and SW2 is 18 kHz, the desired starting period is about 2 seconds, and the starting frequency is set to 4.5 kHz. Figure 3 As shown, the frequency of the control signal SG1 and the control signal SG2 (the activation frequency of the semiconductor switches SW1 and SW2 ) is one quarter of the rated switching frequency.

[0075] In addition, the starting pulse width T4 of the semiconductor switches SW1 and SW2 is set according to the resonant inductance Lr, the maximum off-state current of the semiconductor switches SW1 and SW2, and the voltage across the excitation inductance Lm. Figure 3 The duration of the high level portion of each cycle of the control signal SG1 and the control signal SG2 in FIG. Furthermore, the voltage across the magnetizing inductor Lm is the same as the primary side voltage V3 of the high frequency transformer Tr.

[0076] More specifically, the start pulse width T4 can be determined according to formula (1).

[0077] T4 = L1 x Ipeak_max / V3 (1)

[0078] where T4 is the start-up pulse width of the semiconductor switches SW1, SW2, L1 is the inductance value of the resonance inductor Lr, Ipeak_max is the maximum off current of the semiconductor switches SW1, SW2, and V3 is the voltage across the exciting inductor Lm. Since Ipeak_max is the maximum off current that the semiconductor switches SW1, SW2 can tolerate, the start-up pulse width T4 calculated from the above equation (1) becomes the maximum pulse width allowed during the start-up process. The start-up pulse width T4 can be set to a value calculated based on the above equation (1) or a value smaller than the value calculated based on the above equation (1). In the present embodiment, the start-up pulse width T4 is set to, for example, about 2.5 microseconds. At this time, the start-up duty ratio of the semiconductor switches SW1, SW2 is about 4.5%.

[0079] Next, when it is determined in the first determination step S2 that the voltage across the support capacitor in the inverter unit InC is close to the rated input voltage, the post-start-up step S3 is executed to turn on the second switch K2, to electrically connect the upstream DC source directly to the inverter unit InC, and to turn off the first switch K1, so that the DC current no longer flows through the pre-charge circuit PcC. As an example of determining whether the voltage across the support capacitor in the inverter unit InC is close to the rated input voltage, it is determined in the first determination step S2 whether the voltage across the support capacitor reaches a first prescribed ratio of the rated input voltage. The first prescribed ratio is determined in such a manner that the sudden change in the instantaneous current of the support capacitor FC1 at the time of switching does not cause overcurrent protection, and can be, for example, 80%, 90%, 95%, 100%, or the like. Figure 3 An example in which the first prescribed ratio is 90% of the rated input voltage is shown in FIG. 10.

[0080] Further, in the time period T2 corresponding to the post-start-up step S3, the semiconductor switches SW1, SW2 are still driven at a start-up frequency lower than the rated switching frequency and at a start-up pulse width T4 lower than the rated pulse width T5, and the output voltage V1 continues to rise. Further, as shown in FIG. 11, in the time period T2, the input voltage V2 is maintained at the rated input voltage, and the primary-side current I1 of the high-frequency transformer Tr gradually decreases. Figure 3

[0081] ​Next, when it is determined in the second determination step S4 that the output voltage (i.e., the voltage across the filter capacitor FC2) VI of the LLC high-frequency resonant power device for electric locomotive approaches the rated output voltage, the switching step S3 is executed to switch the start-up frequency to the rated switching frequency and switch the start-up pulse width T4 to the rated pulse width T5, and the start-up is ended. As an example of determining whether the output voltage VI of the LLC high-frequency resonant power device for electric locomotive approaches the rated output voltage, it is determined in the second determination step S4 whether the output voltage VI of the LLC high-frequency resonant power device for electric locomotive reaches the second prescribed ratio of the rated output voltage. The second prescribed ratio is determined in such a manner that the instantaneous current of the semiconductor switches SW1 and SW2 at the time of switching does not exceed the allowable range, and for example, can be 80%, 90%, 95%, 100%, or the like. Figure 4 An example in which the second prescribed ratio is 100% of the rated output voltage is shown in FIG. 8.

[0082] That is, in the present embodiment, from the time point t3, the semiconductor switches SW1 and SW2 are driven by the control signals SG1 and SG2 at the rated switching frequency and the rated pulse width T5, the output voltage VI of the LLC high-frequency resonant power device for electric locomotive becomes the rated output voltage, and the semiconductor switches SW1 and SW2 operate at the rated duty ratio. At this time, the switching operation of the semiconductor switches SW1 and SW2 is soft switching.

[0083] The rated pulse width T5 can be determined according to Equation (2).

[0084] T5 = 1 / fsw / 2 - Td (2)

[0085] where T5 is the rated pulse width of the semiconductor switches SW1 and SW2, fsw is the rated switching frequency, and Td is the dead time of the semiconductor switches SW1 and SW2. According to Equation (2), the rated switching frequency T5 in the present embodiment is set to about 27 microseconds. At this time, the rated duty ratio of the semiconductor switches SW1 and SW2 is 50%.

[0086] Figure 4 is a time chart showing a case in which the load side is in a fault (e.g., short circuit) at the time of start-up of the LLC high-frequency resonant power device for electric locomotive. Figure 4 An example in which the load side is in a fault (e.g., short circuit) at the time of start-up of the LLC high-frequency resonant power device for electric locomotive is shown in FIG. 8.

[0087] Since the load side is in a fault (e.g., short circuit) at the time of start-up, as shown in FIG. 8, the output voltage VI of the LLC high-frequency resonant power device for electric locomotive is not increased to the rated output voltage, and the semiconductor switches SW1 and SW2 do not operate at the rated duty ratio. Figure 2As shown, during time period T1, which continues during the initial startup step S1, the output voltage V1 of the LLC high-frequency resonant power device for electric locomotives does not increase and remains at 0V. Time period T6 is the fault protection determination time, which is used to determine whether a fault has occurred in the output circuit of the LLC high-frequency resonant power device for electric locomotives. Faults in this context include abnormalities such as a short circuit or overload in the output circuit. The temperature rise can be calculated based on the losses of the semiconductor switches SW1 and SW2. The fault protection determination time is determined so that the junction temperature of the semiconductor switches SW1 and SW2 does not exceed the rated maximum value during this fault protection determination time.

[0088] like Figure 4 As shown, the soft start of the LLC resonant circuit in the LLC high-frequency resonant power device for electric locomotives further includes a third determination step S6 and a drive stop step S7. In the third determination step S6, a determination is made as to whether a valid output voltage V1 is detected within a time period T6, which serves as a fault protection determination time. If a valid output voltage V1 is not detected (e.g., output voltage V≈0 V), the drive stop step S5 is executed at time t4, the end of time period T6, to stop driving the semiconductor switches SW1 and SW2, and the abnormal start is terminated.

[0089] In addition, if ​ As shown, during the time period T1 corresponding to the initial startup step S1, if there is a load short circuit or other situation, the output voltage V1 cannot be established (output voltage V≈0V). As the input voltage V2 slowly rises, the primary side current I1 flowing through the high-frequency transformer Tr and the semiconductor switches SW1 and SW2 will also slowly rise.

[0090] Because output voltage V1 cannot reach above 95% of the rated output voltage, semiconductor switches SW1 and SW2 continue to operate in low-frequency, narrow pulse mode. After time t2, input voltage V2 reaches the rated input voltage. However, due to the limitations of the low-frequency, narrow pulse, the off-current of semiconductor switches SW1 and SW2 remains constant, remaining at the maximum off-current Ipeak_max of semiconductor switches SW1 and SW2.

[0091] Hereinafter, the main technical effects of the above-mentioned LLC high-frequency resonant power device for electric locomotives will be described.

[0092] Before the inverter unit InC is powered on, the support capacitor FC1 in the inverter unit InC is in a zero voltage state, i.e. no energy in the capacitor, and at the moment of power-on, due to the step change in voltage, the support capacitor FC1 is equivalent to a short circuit state, the higher the voltage across the support capacitor FC1, the greater the current flowing through the support capacitor FC1, and if a pre-charge circuit PcC is not connected before starting, then the large current will cause a current surge to the support capacitor FC1 and the semiconductor switches SW1, SW2 as switching tubes, and the input current overcurrent protection is easily triggered.

[0093] The present application connects the pre-charge circuit PcC, and uses the resistor R1 in the pre-charge circuit PcC to limit the current when charging the support capacitor FC1, changes the time constant when charging the support capacitor FC1, so that the voltage of the support capacitor FC1 can slowly increase in the pre-starting period. Because the voltage of the support capacitor FC1 slowly increases in the pre-starting period, the turn-off current of the semiconductor switches SW1, SW2 in the pre-starting period can be greatly reduced. Generally, the time constant τ = RC when charging the capacitor, R represents the resistance in the circuit, C represents the capacity of the capacitor, and the greater the time constant τ, the longer the time to charge to the predetermined voltage.

[0094] Furthermore, when the voltage across the support capacitor FC1 increases to near the rated input voltage in the post-starting period, the input voltage will suddenly change to the rated input voltage after the pre-charge circuit PcC is disconnected, at this time the voltage mutation rate is small, and the current surge to the support capacitor FC1 and the semiconductor switches SW1, SW2 is small.

[0095] On the other hand, although the switching action of the semiconductor switches SW1, SW2 in the pre-starting period step S1 and the post-starting period step S3 is hard switching, by using the reduced frequency starting frequency, the hard switching loss can be reduced compared with the past, and the temperature rise problem caused by the hard switching loss in the pre-starting period is solved. At the same time, compared with the case where the semiconductor switches SW1, SW2 use a working frequency much higher than the rated switching frequency during the starting stage, the design difficulty of the drive circuit of the semiconductor switches SW1, SW2 as semiconductor devices is not increased.

[0096] In addition, because the starting pulse width T4 of the semiconductor switches SW1, SW2 in the pre-starting period step S1 and the post-starting period step S3 is less than the rated pulse width T5, the turn-off current I1 during the starting process is less than or equal to the maximum turn-off current Ipeak_max, thereby ensuring the reliable turn-off of the semiconductor switches SW1, SW2.

[0097] When the output voltage V1 of the LLC high-frequency resonant power device for electric locomotive approaches the rated output voltage, since the output voltage V1 has been substantially established, even if the starting frequency is switched to the rated switching frequency and the starting pulse width T4 is switched to the rated pulse width T5, the current of the semiconductor switches SW1 and SW2 is small.

[0098] Because the input voltage V2 slowly rises in the starting early stage, the output voltage V1 slowly rises in the starting early stage and the starting late stage, and the starting mode of low frequency and narrow pulse width is adopted in the starting early stage, the current when charging the support capacitor FC1 and the turn-off current of the semiconductor switches SW1 and SW2 are maximally reduced, the hard switching loss is reduced, and the problem that the hard switching loss is large in the starting early stage and the junction temperature is excessively high to damage the device is avoided.

[0099] In addition, because the pre-charge circuit PcC is an existing circuit in the power supply system of the railway vehicle, no additional hardware cost is needed, and the control strategy is simply adjusted on the basis of the existing vehicle main circuit to achieve the control method. Therefore, the control method is simple and the hardware cost is low.

[0100] In addition, even if the load side is in failure when the LLC high-frequency resonant power device for electric locomotive starts, because the pre-charge circuit PcC reduces the turn-off current of the semiconductor switches SW1 and SW2, the increase speed of the junction temperature of the semiconductor switches SW1 and SW2 is inhibited. The starting pulse width T4 set can limit the turn-off current I1 of the semiconductor switches SW1 and SW2 to the maximum turn-off current Ipeak_max, so that the semiconductor switches SW1 and SW2 are still in the safe working area and can be reliably turned off. Moreover, the failure protection determination time is set by calculating the loss of the semiconductor switches SW1 and SW2, so that the junction temperature of the semiconductor switches SW1 and SW2 is further limited to increase, and even if the failure such as short circuit or overload occurs in the starting early stage, the switching operation of the semiconductor switches SW1 and SW2 can be reliably performed.

[0101] Other embodiments

[0102] The above describes one embodiment of the present application, but the embodiment is proposed for easy understanding of the present application, and the protection scope of the present application is not limited to the embodiments. Those skilled in the art can make various modifications to the embodiment without departing from the technical idea of the present application. Hereinafter, the modifications are exemplified.

[0103] In the above embodiment, the half-bridge inverter circuit of the inverter unit InC is a symmetrical half-bridge, but is not limited thereto, and an asymmetrical half-bridge can also be used. In the case of using the asymmetrical half-bridge, substantially the same technical effects as the first embodiment can be obtained.

[0104] Further, in the above-described embodiment, the half-bridge inverter circuit of the inverter unit InC can also be modified to a full-bridge inverter circuit. The use of a full-bridge inverter circuit also enables approximately the same technical effects as the first embodiment.

[0105] Further, in the above-described embodiment, the LLC resonant circuit includes one resonant inductor Lr and one magnetizing inductor Lm, but is not limited thereto and can include two or more resonant inductors Lr and two or more magnetizing inductors Lm. For example, in the case where two resonant inductors Lr and two magnetizing inductors Lm are included, the two or more resonant inductors Lr and the two or more magnetizing inductors Lm can be connected in series, or one resonant inductor Lr and one magnetizing inductor Lm connected in series can be connected in parallel with another resonant inductor Lr and another magnetizing inductor Lm connected in series.

[0106] Further, in the above-described embodiment, one high-frequency transformer is provided, but is not limited thereto and two, three, or more high-frequency transformers can be provided. Further, in the case where two or more high-frequency transformers are provided, a number of rectifier circuits corresponding to the number of high-frequency transformers can also be provided.

[0107] Further, the LLC high-frequency resonant power device for electric locomotives in the above-described embodiment can be applied to a high-power high-frequency DC / DC conversion module or a high-power high-frequency DC / DC converter in a power supply system of a railway vehicle.

[0108] Further, in the above-described embodiment, in the circuit diagram, an N-channel field effect transistor is used as a switching transistor that constitutes the semiconductor switches SW1 and SW2 in the inverter unit InC, but is not limited thereto and a P-channel field effect transistor can also be used.

[0109] Further, in the above-described embodiment, as the switching transistor that constitutes the semiconductor switches SW1 and SW2 in the inverter unit InC, a metal oxide semiconductor field effect transistor is not limited and an insulated gate bipolar transistor (IGBT) can also be used.

Claims

1. A method of controlling an LLC resonant circuit, which controls soft start of an LLC resonant circuit in an LLC high-frequency resonant power device for electric locomotive, the LLC high-frequency resonant power device for electric locomotive including an inverter unit that inverts direct current from an upstream into alternating current, a transformer unit that transforms the alternating current from the inverter unit using a high-frequency transformer, and a rectifier unit that rectifies the transformed alternating current into direct current and outputs to a downstream, and the LLC resonant circuit being constituted by switching tubes, a resonant capacitor, a resonant inductor, and an excitation inductor in the inverter unit and the transformer unit, characterized in that, comprises: a pre-starting step of connecting a pre-charge circuit between an upstream DC source and the inverter unit and driving the switching transistor at a start-up frequency lower than a rated switching frequency and a start-up pulse width lower than a rated pulse width when a start-up signal of the LLC high-frequency resonant power device for electric locomotive is received; a post-starting step of directly connecting the upstream DC source and the inverter unit and disconnecting the pre-charge circuit when a voltage across a support capacitor in the inverter unit approaches a rated input voltage; a switching step of switching the start-up frequency to the rated switching frequency and the start-up pulse width to the rated pulse width when an output voltage of the LLC high-frequency resonant power device for electric locomotive approaches a rated output voltage.

2. The LLC resonant circuit control method according to claim 1, wherein the pre-charge circuit has a first switch and a resistor connected in series to the first switch, the first switch is turned on and the resistor is connected in series to the inverter unit in the pre-starting step, and a second switch provided between the upstream DC source and the inverter unit is turned on and the first switch is turned off in the post-starting step.

3. The LLC resonant circuit control method according to claim 1, wherein the pre-charge circuit is a pre-charge circuit already provided in a power supply system of a railway vehicle.

4. The LLC resonant circuit control method according to claim 1, wherein the upstream DC source and the inverter unit are directly connected and the pre-charge circuit is disconnected when a voltage across a support capacitor in the inverter unit reaches a first prescribed ratio of the rated input voltage in the post-starting step, and the first prescribed ratio is determined in such a manner that an instantaneous current surge of the support capacitor at the time of switching does not cause overcurrent protection, and the start-up frequency is switched to the rated switching frequency and the start-up pulse width is switched to the rated pulse width when an output voltage of the LLC high-frequency resonant power device for electric locomotive reaches a second prescribed ratio of the rated output voltage in the switching step, and the second prescribed ratio is determined in such a manner that an instantaneous current surge of the switching transistor at the time of switching does not exceed an allowable range.

5. The LLC resonant circuit control method according to claim 1, wherein the driving of the switching transistor is stopped when no valid output voltage is detected within a fault protection determination time for determining whether an output circuit of the LLC high-frequency resonant power device for electric locomotive has failed.

6. The LLC resonant circuit control method according to claim 1, wherein the start-up pulse width is set in accordance with an inductance value of the resonant inductor, a maximum off current of the switching transistor, and a voltage across the exciting inductor, and the start-up frequency is set in accordance with a desired length of a start-up period and a temperature rise of the switching transistor.

7. The LLC resonant circuit control method according to claim 1, wherein ​ ​ ​ ​ ​ ​ ​ ​ ​ The LLC high-frequency resonant power device for electric locomotive is used in a high-frequency DC / DC converter in a power supply system of a railway vehicle.

8. An LLC resonant circuit control module that controls soft start of an LLC resonant circuit in an LLC high-frequency resonant power device for an electric locomotive, the LLC high-frequency resonant power device for the electric locomotive including an inverter unit that inverts direct current from an upstream into alternating current, a transformer unit that transforms the alternating current from the inverter unit using a high-frequency transformer, and a rectifier unit that rectifies the transformed alternating current into direct current and outputs the direct current to a downstream, the LLC resonant circuit being constituted by switching tubes, a resonant capacitor, a resonant inductor, and a magnetizing inductor in the inverter unit and the transformer unit, characterized by, The LLC high-frequency resonant power device for electric locomotive comprises: a pre-start-up unit, which, when receiving a start-up signal of the LLC high-frequency resonant power device for electric locomotive, connects a pre-charging circuit between an upstream DC source and the inverter unit, and drives the switching tube at a start-up frequency lower than a rated switching frequency and a start-up pulse width lower than a rated pulse width; a post-start-up unit, which, when a voltage across a support capacitor in the inverter unit approaches a rated input voltage, directly connects the upstream DC source and the inverter unit, and disconnects the pre-charging circuit; and a switching unit, which, when an output voltage of the LLC high-frequency resonant power device for electric locomotive approaches a rated output voltage, switches the start-up frequency to the rated switching frequency, and switches the start-up pulse width to the rated pulse width. The computer program is executed by a processor to implement the steps of the LLC resonant circuit control method of claim 1.

9. A computer readable storage medium having stored thereon a computer program, characterized in that, The computer program is executed by a processor to implement the steps of the LLC resonant circuit control method of claim 1.

10. A computer program product comprising a computer program, characterized in that, ​

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