LLC resonant circuit control method and module, storage medium and program product
By employing low-frequency narrow-pulse-width startup and fault protection methods in the LLC resonant circuit, the challenges of switching losses and drive circuit design during the initial startup phase are solved, thereby achieving the reliability and safety of the switching transistor.
Patent Information
- Application Number
- CN202410460515.3
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-04-17
- Publication Date
- 2025-10-24
AI Technical Summary
Existing LLC resonant circuits have high switching losses in the initial startup phase, which can easily lead to overheating and damage of the switching transistors. Furthermore, the design of the drive circuit is difficult, and existing soft-start methods pose risks of increased switching transistor temperature and increased short-circuit current.
A low-frequency, narrow-pulse-width startup procedure with a frequency and pulse width lower than the rated switching frequency and pulse width is adopted. The startup pulse width is set by the inductance value of the resonant inductor, the maximum turn-off current of the switching transistor, and the excitation inductor voltage. When the output voltage approaches the rated value, the frequency and pulse width are switched to the rated frequency and pulse width. The current of the switching transistor is limited by the fault protection judgment time.
It reduces hard switching losses during the initial startup phase, lowers the temperature rise of the switching transistor, simplifies the drive circuit design, ensures reliable turn-off of the switching transistor under fault conditions, and avoids damage to the switching transistor.
Smart Images
Figure CN120834709A_ABST
Abstract
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, which can reduce switching loss during the start process, simplify the design of the driving circuit and improve the reliability of the off.
[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, the LLC high frequency resonant power device 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, 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: low frequency narrow pulse width start step, driving the switching tube at start frequency lower than rated switching frequency and start pulse width lower than rated pulse width; switching step, switching the start frequency to rated switching frequency and the start pulse width to rated pulse width when the output voltage of the LLC high frequency resonant power device approaches rated output voltage.
[0012] In the above LLC resonant circuit control method, the start pulse width is set according to inductance value of resonant inductor, maximum off current of switching tube and voltage across excitation inductor.
[0013] In the above LLC resonant circuit control method, the start pulse width is determined according to the following formula,
[0014] T3 = L1 x Ipeak_max / V1
[0015] Wherein, T3 is the start pulse width, L1 is the inductance value of the resonant inductor, Ipeak_max is the maximum off current of the switching tube, V1 is the voltage across the excitation inductor.
[0016] In the above LLC resonant circuit control method, in the switching step, when the output voltage of the LLC high frequency resonant power device reaches a specified proportion of rated output voltage, the start frequency is switched to rated switching frequency and the start pulse width is switched to rated pulse width, and the specified proportion is determined in a way that instantaneous current of the switching tube at switching time does not exceed the allowed range.
[0017] In the above LLC resonant circuit control method, the start frequency is set according to the length of desired start period and temperature rise of the switching tube, and the start frequency is set to one integer multiple of the rated switching frequency.
[0018] In the above LLC resonant circuit control method, if no valid output voltage is detected within the fault protection determination time for determining whether the output circuit of the LLC high frequency resonant power device has failed, the driving of the switching tube is stopped.
[0019] In the above LLC resonant circuit control method, the LLC high-frequency resonant power device is used in a high-frequency DC / DC converter in a power supply system of a railway vehicle.
[0020] The present application provides an LLC resonant circuit control module for controlling soft start of an LLC resonant circuit in an LLC high-frequency resonant power device, the LLC high-frequency resonant power device comprising 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, 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 a low-frequency narrow-pulse-width start unit for driving the switching tubes at a start frequency lower than a rated switching frequency and at a start pulse width lower than a rated pulse width, and a switching unit for switching the start frequency to the rated switching frequency and switching the start pulse width to the rated pulse width when an output voltage of the LLC high-frequency resonant power device approaches a rated output voltage.
[0021] The present application provides a computer readable storage medium having stored thereon a computer program, characterized by the computer program being executed by a processor to implement the steps of the LLC resonant circuit control method.
[0022] The present application provides a computer program product comprising a computer program, characterized by the computer program being executed by a processor to implement the steps of the LLC resonant circuit control method.
[0023] Inventive Effects
[0024] According to the above technical solutions, although the switching action of the switching tubes is hard switching in the low-frequency narrow-pulse-width start step, the hard switching loss can be reduced compared with the prior art by using the start frequency after frequency reduction, and the problem of temperature rise caused by hard switching loss in the early start stage is solved. At the same time, compared with the case where the switching tubes use a working frequency much higher than the rated switching frequency in the start stage, the design difficulty of the driving circuit of the switching tubes as semiconductor devices is not increased. In addition, because the start pulse width of the switching tubes in the start process is less than the rated pulse width, the off current in the start process is less than or equal to the maximum off current, thereby ensuring the reliable off of the switching tubes.
[0025] Therefore, the LLC resonant circuit control method of the present application has small switching loss, simple driving circuit design, and high off reliability in the start process.
[0026] Further, since the startup pulse width is set by deriving from the parameters of the hardware circuit of the LLC resonant circuit (the inductance value of the resonant inductor, the maximum off current of the switching transistor, and the voltage across the magnetizing inductor), the off current of the switching transistor at startup can be reliably limited to be less than or equal to the maximum off current.
[0027] Even in the case where the load side is in a fault at the startup of the LLC high-frequency resonant power device, the startup pulse width set can limit the off current of the switching transistor to the maximum off current, so that the switching transistor is still in the safe operating area and can reliably turn off. Also, the fault protection determination time is set by calculating the loss of the switching transistor, thereby limiting the junction temperature of the switching transistor from further increasing, so that the switching operation of the switching transistor can be reliably performed even if a short circuit or overload or the like occurs at the early stage of startup. BRIEF DESCRIPTION OF DRAWINGS
[0028] Figure 1 is a circuit diagram showing the LLC high-frequency resonant power device of the first embodiment.
[0029] Figure 2 is a flowchart showing the startup process of the LLC high-frequency resonant power device.
[0030] Figure 3 is a time chart showing the startup process of the LLC high-frequency resonant power device.
[0031] Figure 4 is a time chart showing the case where the load side is in a fault at the startup of the LLC high-frequency resonant power device. DETAILED DESCRIPTION
[0032] 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 so-called "connection" means electrical connection unless otherwise specified.
[0033] First Embodiment
[0034] Hereinafter, the circuit structure of the LLC high-frequency resonant power device in the first embodiment will be described with reference to the drawings.
[0035] The LLC high-frequency resonant power device in the first embodiment is used to convert the electric power (direct current) from the upstream and output to the downstream (for example, an electrical load). Figure 1 is a circuit diagram showing the LLC high-frequency resonant power device of the first embodiment.
[0036] As shown in Figure 1 , the LLC high-frequency resonant power device in the first embodiment mainly includes an inverter unit InC, a transformer unit TrC, and a rectifier unit ReC.
[0037] The inverter unit InC is configured to invert a direct current input from a direct current source upstream via a positive input terminal Pi and a negative input terminal Ni into an alternating current.
[0038] Specifically, the inverter unit InC has a half-bridge inverter circuit including a first bridge arm provided with a support capacitor FC1, a second bridge arm provided with two resonance capacitors RC1, RC2, and a third bridge arm provided with two semiconductor switches SW1, SW2.
[0039] The support capacitor FC1 can eliminate ripples in the input direct current, stabilizing the direct current input voltage.
[0040] The semiconductor switches SW1, SW2 and the resonance capacitors RC1, RC2, together with the magnetizing inductance Lm and the resonance inductance Lr of a high-frequency transformer Tr included in the transformer unit TrC described later, constitute an LLC resonant circuit.
[0041] In a normal operating state, the two semiconductor switches SW1, SW2 operate at a rated switching frequency and a rated pulse width under the control of a control circuit and a drive circuit not shown, maintaining the stability of the output voltage of the LLC high-frequency resonant power device.
[0042] The semiconductor switch SW1 can be composed of a metal oxide semiconductor field effect transistor (MOSFET) and a diode connected in parallel to each other, with the drain of the metal oxide semiconductor field effect transistor connected to the cathode of the diode, the source of the metal oxide semiconductor field effect transistor connected to the anode of the diode, the switching function being realized by the metal oxide semiconductor field effect transistor, and the diode preventing reverse breakdown of the metal oxide semiconductor field effect transistor.
[0043] 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 described later and the cathode of the diode constituting the semiconductor switch SW2.
[0044] Furthermore, 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, it is easier to realize soft switching in high-frequency operation, which is conducive to 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, achieving the lightweight and miniaturization of the transformer.
[0045] Likewise, the semiconductor switch SW2 can be configured using 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 using the metal oxide semiconductor field effect transistor, and the diode prevents reverse breakdown of the metal oxide semiconductor field effect transistor.
[0046] 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.
[0047] Furthermore, as the metal oxide semiconductor field effect transistor constituting the semiconductor switch SW2, a silicon carbide field effect transistor can likewise be used.
[0048] The transformer unit TrC, on the one hand, constitutes an LLC resonant circuit together with the inverter unit InC and, on the other hand, serves for transforming the alternating current from the inverter unit InC. Furthermore, the transformer unit TrC also serves for isolating the high-voltage upstream side from the low-voltage downstream side.
[0049] The transformer unit TrC in the present embodiment comprises a high-frequency transformer Tr. One connection of the primary winding of the high-frequency transformer Tr is connected via a resonant inductance Lr to the midpoint of the two semiconductor switches SW1, SW2 on the third bridge arm of the inverter unit InC, and the other connection of the primary winding of the high-frequency transformer Tr is connected via a resonant inductance Lr2 to the midpoint of the two resonant capacitors RC1, RC2 on the second bridge arm of the inverter unit InC.
[0050] In other words, the primary winding of the high-frequency transformer Tr is connected in parallel to the magnetizing inductance Lm of the high-frequency transformer Tr and via the resonant inductance Lr to the half-bridge inverter circuit of the inverter unit InC.
[0051] The rectifier unit ReC serves for rectifying the alternating current from the high-frequency transformer Tr of the transformer unit TrC into a direct current and outputting this direct current downstream.
[0052] The rectifier unit ReC comprises a rectifier circuit, which is used to realize the rectification described above. As Figure 1As shown, the rectification circuit includes a fourth bridge arm provided with two diode switches RD1, RD3 and a fifth bridge arm provided with two diode switches RD2, RD4, constituting a full-bridge rectification circuit. In the fourth bridge arm, the cathode of diode switch RD1 is connected to the positive output terminal Po, the anode of diode switch RD1 is connected to the cathode of diode switch RD3, and the anode of diode switch RD3 is connected to the negative output terminal No. In the fifth bridge arm, the cathode of diode switch RD2 is connected to the positive output terminal Po, the anode of diode switch RD2 is connected to the cathode of diode switch RD4, and the anode of diode switch RD4 is connected to the negative output terminal No. In addition, the rectification unit ReC further includes a sixth bridge arm provided with a filter capacitor FC2.
[0053] In addition, in the rectification circuit, as the diode switch, a fast recovery diode can be used to reduce the switching loss at startup and ensure reliable operation of high-frequency rectification.
[0054] One terminal of the secondary winding of the high-frequency transformer Tr of the transformation unit TrC is connected to the midpoint of the two diode switches RD1, RD3 on the fourth bridge arm of the rectification circuit on the upper side in the figure of the rectification 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, RD4 on the fifth bridge arm of the rectification circuit.
[0055] In this way, the high-frequency transformer Tr of the transformation unit TrC is connected to the rectification circuit of the rectification unit ReC on the secondary side.
[0056] Therefore, the rectification unit ReC rectifies the alternating current from the high-frequency transformer Tr into direct current by the rectification circuit and outputs it downstream.
[0057] 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.
[0058] In this way, an LLC high-frequency resonant power device in the embodiment is constructed.
[0059] The working process of the above LLC high-frequency resonant power device is as follows.
[0060] First, the direct current from the 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.
[0061] Then, the alternating current obtained by inversion of the inverter unit InC is transformed into alternating current of the required voltage by the high-frequency transformer Tr of the transformation unit TrC.
[0062] Finally, the AC voltage after the voltage conversion by the voltage conversion unit TrC is input to the rectification circuit of the rectification unit ReC from the high-frequency transformer Tr, is rectified to DC voltage, and is output from the positive output terminal Po and the negative output terminal No.
[0063] Next, the starting process of the LLC high-frequency resonant power device will be described with reference to Figure 2 and Figure 3 .
[0064] Figure 2 is a flowchart showing the starting process of the LLC high-frequency resonant power device. Figure 3 is a time chart showing the starting process of the LLC high-frequency resonant power device.
[0065] As shown in Figure 2 , the soft starting of the LLC resonant circuit in the LLC high-frequency resonant power device is divided into a low-frequency narrow-pulse-width starting step S1, a first judgment step S2, and a switching step S3. Figure 3 The control signal SG1 of the semiconductor switch SW1, the control signal SG2 of the semiconductor switch SW2, the primary-side current I1 of the high-frequency transformer Tr, and the output voltage V of the LLC high-frequency resonant power device are shown in
[0066] The low-frequency narrow-pulse-width starting step S2 corresponds to Figure 3 in which the period T1 from the time point t1 to the time point t2 (not including the time point t2). The first judgment step S2 and the switching step S3 correspond to Figure 3 in which the period T2 after the time point t2 (including the time point t2).
[0067] In the low-frequency narrow-pulse-width starting step S2, the semiconductor switches SW1, SW2 are driven at a starting frequency lower than the rated switching frequency and at a starting pulse width T3 lower than the rated pulse width T4. Figure 3 The solid line portions of the control signal SG1 of the semiconductor switch SW1 and the control signal SG2 of the semiconductor switch SW2 in
[0068] The starting frequency of the semiconductor switches SW1, SW2 is set in accordance with the length of the desired starting period and the temperature rise of the semiconductor switches SW1, SW2, and is set to one-quarter of the rated switching frequency. In the present embodiment, the rated switching frequency of the semiconductor switches SW1, SW2 is 18 kHz, the length of the desired starting period is about 2 seconds, and the starting frequency is set to 4.5 kHz. As shown in Figure 3 , the frequency of the control signal SG1 and the control signal SG2 (the starting frequency of the semiconductor switches SW1, SW2) is one-quarter of the rated switching frequency.
[0069] In addition, the starting pulse width T3 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 V1 of the high frequency transformer Tr.
[0070] More specifically, the start pulse width T3 can be determined according to formula (1).
[0071] T3=L1×Ipeak_max / V1 (1)
[0072] Wherein, T3 is the startup pulse width of semiconductor switches SW1 and SW2, L1 is the inductance of resonant inductor Lr, Ipeak_max is the maximum off-state current of semiconductor switches SW1 and SW2, and V1 is the voltage across magnetizing inductor Lm. Since Ipeak_max is the maximum off-state current that semiconductor switches SW1 and SW2 can withstand, the startup pulse width T3 calculated thereby becomes the maximum pulse width allowed during the startup process. The startup pulse width T3 can be set to a value calculated based on equation (1) above or a value smaller than the value calculated based on equation (1) above. In this embodiment, the startup pulse width T3 is set to, for example, approximately 2.5 microseconds. At this time, the startup duty cycle of semiconductor switches SW1 and SW2 is approximately 4.5%.
[0073] like Figure 3 As shown, in the time period T1 corresponding to the low-frequency narrow-pulse-width startup step, the output voltage V of the LLC high-frequency resonant power device gradually increases. A voltage sensor for monitoring the output voltage V is provided in the LLC high-frequency resonant power device.
[0074] If the output voltage V of the LLC high-frequency resonant power device is determined to be close to the rated output voltage in the first determination step S2, a switching step S3 is executed to switch the startup frequency to the rated switching frequency and the startup pulse width T3 to the rated pulse width T4, thereby completing the startup process normally. As an example of determining whether the output voltage V of the LLC high-frequency resonant power device is close to the rated output voltage, the first determination step S2 determines whether the output voltage V of the LLC high-frequency resonant power device reaches a specified percentage of the rated output voltage. This specified percentage is determined so that the instantaneous current surge of the semiconductor switches SW1 and SW2 during switching does not exceed an allowable range, and can be, for example, 80%, 90%, 95%, or 100%. Figure 3 exemplified in FIG. 5 , where the predetermined ratio is 95% of the rated output voltage.
[0075] Specifically, in this embodiment, starting at time t2, semiconductor switches SW1 and SW2 are driven using control signals SG1 and SG2 at a rated switching frequency and a rated pulse width T4. The output voltage V of the LLC high-frequency resonant power device reaches the rated output voltage, and semiconductor switches SW1 and SW2 operate at a rated duty cycle. At this point, the switching operation of semiconductor switches SW1 and SW2 is soft switching.
[0076] The rated pulse width T4 can be determined according to formula (2).
[0077] T4=1 / fsw / 2-Td (2)
[0078] Where T4 is the rated pulse width of semiconductor switches SW1 and SW2, fsw is the rated switching frequency, and Td is the dead time of semiconductor switches SW1 and SW2. According to equation (2), the rated switching frequency T4 in this embodiment is set to approximately 27 microseconds. At this time, the rated duty cycle of semiconductor switches SW1 and SW2 is 50%.
[0079] In addition, if Figure 4 As shown, the primary side current I1 of the high frequency transformer Tr gradually decreases in the time period T1 corresponding to the low frequency and narrow pulse width starting step S1.
[0080] Figure 4 This is a timing chart showing the case where a load-side fault occurs when the LLC high-frequency resonant power device is started. Figure 4 : shows the control signal SG1 of the semiconductor switch SW1, the control signal SG2 of the semiconductor switch SW2, the primary side current I1 of the high-frequency transformer Tr, and the output voltage V of the LLC high-frequency resonant power device.
[0081] Since the load side is in a fault (such as short circuit) at startup, such as Figure 2 As shown, during time period T5, which is the duration of low-frequency, narrow-pulse-width startup step S1, the output voltage V of the LLC high-frequency resonant power device does not increase and remains at 0V. Time period T5 is the fault protection determination time used to determine whether a fault has occurred in the output circuit of the LLC high-frequency resonant power device. 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.
[0082] like Figure 4As shown, the soft start of the LLC resonant circuit in the LLC high-frequency resonant power device further includes a second judging step S4 and a stop driving step S5. In the second judging step S4, it is judged whether the valid output voltage V is detected within the time period T5 as the fault protection judging time, and in the case where the valid output voltage V is not detected (for example, the output voltage V = 0V), the stop driving step S5 is executed at the end time point t3 of the time period T5 to stop driving the semiconductor switches SW1, SW2, and the start-up abnormality is ended.
[0083] In addition, as As shown, the primary side current I1 of the high-frequency transformer Tr is always the maximum off current Ipeak_max of the semiconductor switches SW1, SW2 throughout the time period T5.
[0084] The following describes the main technical effects of the above LLC high-frequency resonant power device.
[0085] According to the above LLC high-frequency resonant power device, although the switching operation of the semiconductor switches SW1, SW2 as switching tubes in the low-frequency narrow pulse width start-up step is hard switching, by adopting the start-up frequency after the frequency reduction, the hard switching loss can be reduced compared with the prior art, and the temperature rise problem caused by the hard switching loss in the early start-up stage is solved. At the same time, compared with the case where the operating frequency of the semiconductor switches SW1, SW2 in the start-up stage is far higher than the rated switching frequency, the design difficulty of the driving circuit of the semiconductor switches SW1, SW2 is not increased. In addition, because the start-up pulse width T3 of the semiconductor switches SW1, SW2 in the start-up process is less than the rated pulse width T4, the off current in the start-up process is less than or equal to the maximum off current Ipeak_max, thereby ensuring the reliable off of the semiconductor switches SW1, SW2. Therefore, the LLC resonant circuit control method of the present application has small switching loss, simple driving circuit design and high off reliability in the start-up process.
[0086] In addition, because the start-up pulse width T3 is set by deriving the parameters (the inductance value of the resonant inductor Lr, the maximum off current Ipeak_max of the semiconductor switches SW1, SW2 and the voltage V1 across the excitation inductor Lm) of the hardware circuit of the LLC resonant circuit, the off current of the semiconductor switches SW1, SW2 at the start-up time can be reliably limited to be less than or equal to the maximum off current Ipeak_max.
[0087] Even in the case where the load side is in a fault at the time of startup of the LLC high-frequency resonant power device, the set startup pulse width T3 is able to limit the off current of the semiconductor switches SW1, SW2 to the maximum off current Ipeak_max, so that the semiconductor switches SW1, SW2 are still in the safe operating area and are able to be reliably turned off. Moreover, the fault protection determination time T5 is set by calculating the loss of the semiconductor switches SW1, SW2, whereby the junction temperature of the semiconductor switches SW1, SW2 is further limited from increasing, and the switching operation of the semiconductor switches SW1, SW2 is able to be reliably performed even in the case where a short circuit or an overload or the like occurs at the early stage of startup.
[0088] Other Embodiments
[0089] The above describes one embodiment of the present application, but the embodiment is presented for easy understanding of the present application, and the scope of protection of the present application is not limited to the embodiment. A person skilled in the art is able to make various modifications to the embodiment without departing from the technical idea of the present application. The following describes examples of the modifications.
[0090] 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 where an asymmetrical half-bridge is used, substantially the same technical effects as those of the first embodiment are able to be obtained.
[0091] Further, in the above embodiment, the half-bridge inverter circuit of the inverter unit InC can also be modified to a full-bridge inverter circuit. In the case where a full-bridge inverter circuit is used, substantially the same technical effects as those of the first embodiment are able to be obtained.
[0092] Further, in the above embodiment, the LLC resonant circuit includes one resonant inductor Lr and one magnetizing inductor Lm, but is not limited thereto, and two or more resonant inductors Lr and two or more magnetizing inductors Lm can also be included. For example, in the case where two resonant inductors Lr and two magnetizing inductors Lm are included, two or more resonant inductors Lr and two or more magnetizing inductors Lm can be connected in series, or one resonant inductor Lr and one magnetizing inductor Lm connected in series and another resonant inductor Lr and another magnetizing inductor Lm connected in series can be connected in parallel.
[0093] Further, in the above embodiment, one high-frequency transformer is provided, but is not limited thereto, and two, three, or more high-frequency transformers can also be provided. Further, in the case where two or more high-frequency transformers are provided, a rectifier circuit corresponding to the number of the high-frequency transformers can also be provided.
[0094] Further, the LLC high-frequency resonant power device in the above-described embodiments can be applied to a large-power high-frequency DC / DC conversion module or a large-power high-frequency DC / DC converter in a power supply system of a railway vehicle.
[0095] Further, in the above-described embodiments, in the circuit diagram, as the switching transistor of the semiconductor switches SW1, SW2 constituting the inverter unit InC, an N-channel field effect transistor is used, but it is not limited thereto, and a P-channel field effect transistor can also be used.
[0096] Further, in the above-described embodiments, as the switching transistor of the semiconductor switches SW1, SW2 constituting the inverter unit InC, it is not limited to a metal oxide semiconductor field effect transistor, and an insulated gate bipolar transistor (IGBT) can also be used.
Claims
1. A method of controlling soft start of an LLC resonant circuit in an LLC high-frequency resonant power device, the LLC high-frequency resonant power device 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, comprising: a low-frequency narrow-pulse-width starting step of driving the switching transistor at a starting frequency lower than a rated switching frequency and at a starting pulse width lower than a rated pulse width; a switching step of switching the starting frequency to the rated switching frequency and the starting pulse width to the rated pulse width when an output voltage of the LLC high-frequency resonant power device approaches a rated output voltage.
2. The LLC resonant circuit control method according to claim 1, wherein the starting 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 field inductor.
3. The LLC resonant circuit control method according to claim 2, wherein the starting pulse width is determined in accordance with the following equation, T3 = L1 x Ipeak_max / V1 where T3 is the starting pulse width, L1 is the inductance value of the resonant inductor, Ipeak_max is the maximum off current of the switching transistor, and V1 is the voltage across the field inductor.
4. The LLC resonant circuit control method according to claim 1, wherein in the switching step, the starting frequency is switched to the rated switching frequency and the starting pulse width is switched to the rated pulse width when the output voltage of the LLC high-frequency resonant power device reaches a prescribed proportion of the rated output voltage, and the prescribed proportion is determined in such a manner that a sudden change in an instantaneous current 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 starting frequency is set in accordance with a desired length of a starting period and a temperature rise of the switching transistor, the starting frequency is set to an integer multiple of one-tenth of the rated switching frequency.
6. The LLC resonant circuit control method according to claim 1, wherein in a case where 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 has failed, the driving of the switching transistor is stopped.
7. The LLC resonant circuit control method according to claim 1, wherein the LLC high-frequency resonant power device is used in a high-frequency DC / DC converter in a power supply system for a railway vehicle. comprising: a low-frequency narrow-pulse-width starting unit of driving the switching transistor at a starting frequency lower than a rated switching frequency and at a starting pulse width lower than a rated pulse width; 8. An LLC resonant circuit control module that controls soft start of an LLC resonant circuit in an LLC high-frequency resonant power device, the LLC high-frequency resonant power device 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, a switching unit of switching the starting frequency to the rated switching frequency and the starting pulse width to the rated pulse width when an output voltage of the LLC high-frequency resonant power device approaches a rated output voltage. The computer program is executed by a processor to implement the steps of the LLC resonant circuit control method according to claim 1. The computer program is executed by a processor to implement the steps of the LLC resonant circuit control method according to claim 1.
9. A computer-readable storage medium having stored thereon a computer program, characterized in that, 10. A computer program product comprising a computer program, characterized in that,