Power conversion device

Abstract

A power conversion device (100) of the present disclosure is provided with: a transformer (12); an inverter circuit (11) connected to the primary side of the transformer (12); a rectifier circuit (13) connected to the secondary side of a transformer (12); a snubber circuit (15) that is connected to the rectifier circuit (13) and comprises a snubber capacitor Csnb; a voltage detection unit (17) that detects the voltage of the output end of the rectifier circuit (13) and thereby detects the voltage of the snubber capacitor Csnb, and that generates a detection signal; and a control unit (16) for controlling the rectifier circuit (13) on the basis of the detection signal obtained by detection by the voltage detection unit (17).

Description

Power conversion device

[0001] This disclosure relates to a power conversion device.

[0002] An isolated DC / DC converter has a function of converting an input voltage to a target output voltage while ensuring electrical isolation between the input and output, and is thus used in various applications. The characteristics required for an isolated DC / DC converter include miniaturization and high efficiency.

[0003] In the case of an application where the output on the secondary side of the transformer uses a low voltage and a large current, in order to achieve the above requirements, it is important to reduce the conduction loss of the switching element that constitutes the rectifier circuit connected to the secondary side of the transformer. In order to achieve the reduction of the conduction loss of the switching element in the secondary-side rectifier circuit, the following items can be mentioned. (1) Lower the current value flowing through the switching element. (2) Select a switching element with a low on-resistance. (3) Shorten the asynchronous rectification period and increase the synchronous rectification period.

[0004] When a full-bridge type isolated DC / DC converter is selected, it is possible to reduce the current flowing through the switching element of the rectifier circuit connected to the secondary side of the transformer with respect to the DAB converter and the LLC converter. On the other hand, in a full-bridge type isolated DC / DC converter, a surge voltage is generated in the switching element of the rectifier circuit on the secondary side of the transformer. Therefore, it is necessary to select a switching element with a high breakdown voltage, and there is a problem that the on-resistance of the switching element becomes high. In order to avoid such a problem, it is necessary to suppress the surge voltage using a snubber circuit, select a switching element with a low breakdown voltage, and reduce the on-resistance of the switching element.

[0005] However, in a typical RCD snubber circuit, energy caused by surge voltage is consumed by the resistor, hindering efficiency improvements. On the other hand, by applying a lossless snubber circuit that does not use resistors as the circuit configuration, surge voltage can be suppressed while suppressing losses in the snubber circuit, making it possible to select switching elements with low on-resistance. As a method to achieve further loss reduction, one can shorten the asynchronous rectification period and increase the synchronous rectification period. For example, one could consider applying a synchronous rectification method that adds an auxiliary winding to the transformer, as disclosed in Patent Document 1 for the switching power supply device.

[0006] Patent No. 4529181

[0007] In an isolated DC / DC converter that incorporates a lossless snubber circuit as part of its configuration, when using a synchronous rectification method such as that disclosed in Patent Document 1, depending on the operating conditions, synchronous rectification may occur while the charge stored in the snubber capacitor is not completely released. As a result, the charge passes through the switching element and the snubber diode. In other words, the snubber capacitor enters a short-circuit mode.

[0008] In short-circuit mode, the short-circuit current is determined by the parasitic resistance and snubber capacitor voltage along the short-circuit path. In short-circuit mode, a large current flows instantaneously, which can cause the switching element and snubber diode to fail. To avoid this problem, if many switching elements and snubber diodes are connected in parallel, a new problem arises: the power converter becomes larger.

[0009] This disclosure is made to solve the problems described above, and aims to provide a power converter that uses a lossless snubber circuit as part of its circuit configuration, which enables miniaturization and reduced losses by extending the synchronous rectification period while avoiding short-circuit mode.

[0010] The power conversion device according to this disclosure comprises: a transformer having a primary winding on the primary side and a secondary winding on the secondary side that are electromagnetically coupled to each other; an inverter circuit connected to the primary side of the transformer and converting DC power to AC power; a rectifier circuit connected to the secondary side of the transformer and rectifying the AC generated in the secondary winding; a snubber circuit connected to the rectifier circuit and having a snubber capacitor; a voltage detection unit that detects the voltage of the snubber capacitor and generates a detection signal by detecting the voltage at the output terminal of the rectifier circuit; and a control unit that controls the rectifier circuit based on the detection signal detected by the voltage detection unit.

[0011] The power converter according to this disclosure controls the timing of synchronous rectification while suppressing short-circuit current based on the snubber capacitor voltage of the snubber capacitor constituting the snubber circuit, thereby providing the effect of obtaining a power converter that can be miniaturized and has low losses.

[0012] This is a circuit diagram showing the configuration of the power converter according to Embodiment 1. This is a circuit diagram for explaining the difference between synchronous rectification and asynchronous rectification. This is a circuit diagram showing an RC snubber circuit as a comparative example. This is a circuit diagram showing another example of an RC snubber circuit as a comparative example. This is a circuit diagram showing an RCD snubber circuit as a comparative example. This is a circuit diagram showing a lossless snubber circuit of the power converter according to Embodiment 1. This is a circuit diagram showing another example of a lossless snubber circuit of the power converter according to Embodiment 1. This is a diagram explaining the operating state of the switching elements of the rectifier circuit on the secondary side of the power converter according to Embodiment 1 and the lossless snubber circuit. This is a diagram explaining the operating state of the switching elements of the rectifier circuit on the secondary side of the power converter according to Embodiment 1 and the lossless snubber circuit. This is a diagram explaining the operating state of the switching elements of the rectifier circuit on the secondary side of the power converter according to Embodiment 1 and the lossless snubber circuit. This is a diagram showing the operating waveform of the power converter according to Embodiment 1. This is a circuit diagram showing the configuration of the power converter according to Embodiment 2.

[0013] Embodiment 1. Figure 1 is a circuit diagram showing the configuration of a power converter 100 according to Embodiment 1. The power converter 100 includes a primary inverter circuit 11 which is a DC / AC converter, a transformer 12 connected to the AC output terminal of the inverter circuit 11 and having a primary winding on the primary side and a secondary winding on the secondary side that are electromagnetically coupled to each other, a rectifier circuit 13 which is an AC / DC converter connected to the secondary side of the transformer 12, a smoothing LC filter circuit 14 connected to the DC output terminal of the rectifier circuit 13, a lossless snubber circuit 15 for surge voltage suppression connected to the DC output terminal of the rectifier circuit 13 and the smoothing LC filter circuit 14, a control unit 16 that controls the on / off timing of the switching elements, and a voltage detection unit 17 that detects the voltage at the DC output terminal of the rectifier circuit 13. The voltage detection unit 17 can also detect the voltage of the snubber capacitor Csnb of the lossless snubber circuit 15 by detecting the voltage at the DC output terminal of the rectifier circuit 13.

[0014] In Figure 1, the area on the left side of the transformer 12 where the inverter circuit 11 is located is called the primary side, and the area on the right side of the transformer 12 where the rectifier circuit 13, LC filter circuit 14, and lossless snubber circuit 15 are located is called the secondary side.

[0015] In the power conversion device 100 according to Embodiment 1, the inverter circuit 11 and the rectifier circuit 13 are each configured as full-bridge circuits.

[0016] The inverter circuit 11 outputs a DC to AC voltage waveform and inputs it to the primary winding on the primary side of the transformer 12. The secondary winding on the secondary side of the transformer 12 outputs an AC voltage multiplied by the turns ratio. This AC voltage is rectified by the rectifier circuit 13.

[0017] By inputting the rectified voltage to the LC filter circuit 14, a smoothed voltage is output to the output terminal of the LC filter circuit 14. The switching elements 11a to 11d that constitute the inverter circuit 11, which is composed of a full-bridge circuit, and the switching elements 13a to 13d that constitute the rectifier circuit 13 are controlled on / off based on the gate signals output from the control unit 16. Although diodes are connected in parallel to each switching element, in the following explanation, the connected diodes will also be described as part of the switching element.

[0018] The full-bridge circuit, which is the specific configuration of the rectifier circuit 13, is for rectification purposes, and therefore the same function can be achieved with diodes. However, by performing synchronous rectification using MOSFETs (Metal Oxide Semiconductor Field Effect Transistors), which are unipolar elements, the effect of reducing conduction losses can be achieved.

[0019] Figure 2A is a diagram illustrating the rectification method of asynchronous rectification using diodes. If the forward voltage is Vf and the current is I, the loss P is determined by the following equation (1): P = Vf × I (1)

[0020] Figure 2B is a diagram illustrating a synchronous rectification method using unipolar elements such as MOSFETs. If the on-resistance is Ron, the loss P is determined by the following equation (2): P = Ron × I 2 (2)

[0021] In low-voltage, high-current applications, synchronous rectification losses are smaller than those of asynchronous rectification, so synchronous rectification is sometimes used to achieve loss reduction. However, achieving synchronous rectification requires precise control of the on / off operation of the switching element according to the current polarity.

[0022] Ideally, synchronous rectification over the entire period would minimize losses the most. However, considering nonlinear elements such as the on-time and off-time of the switching elements, as well as other error factors, it becomes necessary to shorten the synchronous rectification period and lengthen the asynchronous rectification period. As a result, losses generated in the switching elements increase.

[0023] The lossless snubber circuit 15 connected to the secondary side plays a role in suppressing the surge voltage generated when the switching element is turned off due to the leakage inductance of the transformer 12 and the recovery phenomenon of the diodes in the rectifier circuit 13. By suppressing the surge voltage, it is possible to prevent the switching element from being damaged by overvoltage. In addition to this effect, it also becomes possible to use switching elements with low voltage resistance.

[0024] The on-resistance of a MOSFET, a switching element, is approximately proportional to its breakdown voltage. Therefore, by reducing the breakdown voltage of the MOSFET, the on-resistance can also be reduced. If low on-resistance switching elements become applicable, the losses of the switching elements can be reduced, enabling miniaturization of power conversion devices.

[0025] The function of the snubber circuit is as described above. To realize the function of the snubber circuit, there are the RC snubber circuit shown in Figures 3A and 3B, and the RCD snubber circuit shown in Figure 3C, which consume surge energy through a resistor within the snubber circuit, as well as the lossless snubber circuit 15 shown in Figures 3D and 3E described above. Note that the RC snubber circuit and the RCD snubber circuit are comparative examples. On the other hand, in the power converter 100 according to Embodiment 1, the lossless snubber circuit 15 is used as the snubber circuit.

[0026] The specific configuration of the lossless snubber circuit 15 shown in Figure 3D is as follows: One end of the snubber capacitor Csnb is connected to one end of the DC output terminal of the rectifier circuit 13. The cathode of the snubber diode D1 is connected to one end of the DC output terminal of the rectifier circuit 13 via the inductor Lf of the LC filter circuit 14. The cathode of the snubber diode D2 is connected to the anode of the snubber diode D1, and the anode of the snubber diode D2 is connected to the other end of the DC output terminal of the rectifier circuit 13. The other end of the snubber capacitor Csnb is connected to the connection point of the snubber diodes D1 and D2.

[0027] The specific configuration of another example of the lossless snubber circuit 15 shown in Figure 3E is as follows: One end of the snubber capacitor Csnb1 is connected to one end of the DC output terminal of the rectifier circuit 13. One end of the snubber inductor Lsnb is connected to one end of the DC output terminal of the rectifier circuit 13 via the inductor Lf of the LC filter circuit 14. One end of the snubber capacitor Csnb2 is connected to the other end of the snubber inductor Lsnb. The other end of the snubber capacitor Csnb2 is connected to the other end of the DC output terminal of the rectifier circuit 13.

[0028] The other end of snubber capacitor Csnb1 is connected to the anode of snubber diode D1 and the cathode of snubber diode D2. The cathode of snubber diode D2 is connected to the other end of the output terminal of rectifier circuit 13. The cathode of snubber diode D1 is connected to the connection point of snubber inductor Lsnb and snubber capacitor Csnb2.

[0029] In the comparative examples, the RC snubber circuit and the RCD snubber circuit store the energy of the leakage inductance in the snubber capacitor Csnb and dissipate it through the resistor to suppress surge voltage. Therefore, to enhance the surge voltage suppression effect, it is necessary to increase the power dissipation in the resistor. Increasing the power dissipation in the resistor leads to larger resistors, larger power conversion devices due to the larger resistors, and a decrease in efficiency. In particular, solving the above-mentioned problems becomes important when the power band is large.

[0030] On the other hand, the lossless snubber circuit 15, which is part of the circuit configuration of the power converter 100 according to Embodiment 1, has the above-described circuit configuration, and therefore, by storing surge energy in the snubber capacitor Csnb and then supplying it to the load, it is possible to suppress surge voltage. In other words, the lossless snubber circuit 15 has the excellent feature that no loss occurs in the snubber circuit because the energy due to the surge voltage is not consumed by the resistor and is supplied to the load. Furthermore, since the lossless snubber circuit 15 requires fewer components to make up the circuit, the power converter 100 can be made smaller.

[0031] Let's consider the case where synchronous rectification is started while charge exists in the snubber capacitor Csnb. In the comparative example RC snubber circuit shown in Figures 3A and 3B, a snubber resistor Rsnb is connected in series with the snubber capacitor Csnb. Therefore, even if there is charge in the snubber capacitor Csnb, the current is limited by the snubber resistor Rsnb. For this reason, damage to the switching element due to short-circuit current is unlikely to occur.

[0032] Furthermore, in the comparative example RCD snubber circuit shown in Figure 3C, the current is blocked by the snubber diode Dsnb, so no short circuit path is generated.

[0033] On the other hand, the lossless snubber circuit 15 has no external resistors connected to the snubber capacitor Csnb, nor is there any blocking of the short-circuit path by the snubber diode. Therefore, if the start timing of synchronous rectification is not appropriate, a short-circuit path may be formed, and the switching elements 13a to 13d and snubber diodes D1 and D2 of the secondary rectifier circuit 13 may be damaged by overcurrent due to the short-circuit current. For this reason, since the lossless snubber circuit 15 may generate a short-circuit current if a conventional synchronous rectification method is used, a synchronous rectification method suitable for the lossless snubber circuit 15 is required.

[0034] A suitable synchronous rectification method for the lossless snubber circuit 15 is described below. First, the output voltage vs of the rectifier circuit 13 is detected as a detection signal by a voltage detection unit 17 provided at the output terminal of the rectifier circuit 13. Based on the output voltage vs of the rectifier circuit 13, the snubber capacitor voltage of the snubber capacitor Csnb of the lossless snubber circuit 15 can be detected. The detection signal is taken into the control unit 16 to determine the timing of synchronous rectification, and gate signals are generated for the switching elements 13a to 13d of the secondary side rectifier circuit 13. This makes it possible to reduce losses due to synchronous rectification while avoiding short-circuit current.

[0035] Figures 4A, 4B, and 4C illustrate the operating states of the switching elements 13a to 13d and the lossless snubber circuit 15 of the secondary rectifier circuit 13 of the power converter 100 according to Embodiment 1, respectively.

[0036] Figure 4A shows the state in which the switching elements 13a to 13d of the secondary rectifier circuit 13 are suppressing surge voltage. The current generated on the secondary side of the transformer 12 flows through the switching element 13a of the rectifier circuit 13 to the snubber capacitor Csnb of the lossless snubber circuit 15. The current then flows through the snubber diode D1, the inductor Lf and capacitor Cf of the LC filter circuit 14, and then through the switching element 13d to the transformer 12.

[0037] In the state shown in Figure 4A, the gate signals from the control unit 16 cause switching elements 13a and 13d to be in the ON state, while switching elements 13b and 13c are in the OFF state.

[0038] The operation shown in FIG. 4A will be described in detail below. By turning on the opposing arms of the full-bridge circuit that constitutes the primary-side inverter circuit 11, a voltage is generated on the secondary side of the transformer 12. The differential voltage between the voltage on the secondary side of the transformer 12 and the output voltage of the LC filter circuit 14 is applied to the snubber capacitor Csn of the lossless snubber circuit 15, and a current flows transiently. Here, the current flowing through the inductor Lf of the LC filter circuit 14 can be considered as a current source because the time constant of the LC filter circuit 14 is sufficiently large and much smaller than the wiring inductance component of the path of the snubber capacitor Csn.

[0039] Since the impedance of the snubber capacitor Csn is low for high-frequency components, it is sufficiently large compared to the parasitic capacitances of the switching elements 13a to 13d of the secondary-side rectifier circuit 13. Therefore, the energy of the parasitic inductor is stored in the snubber capacitor Csn, and it becomes possible to suppress the surge voltage generated in the switching elements 13a to 13d of the secondary-side rectifier circuit 13.

[0040] FIG. 4B shows a state in which the switching elements 13a to 13d of the secondary-side rectifier circuit 13 are in the off state and the snubber capacitor Csn is discharging. A part of the inductor current due to the inductor Lf of the LC filter circuit 14 flows through the snubber diode D2 to the snubber capacitor Csn and refluxes to the inductor Lf. The remaining part of the inductor current due to the inductor Lf of the LC filter circuit 14 flows through the rectifier circuit 13 and refluxes to the LC filter circuit 14.

[0041] The operation shown in FIG. 4B will be described in detail below. The inductor current due to the inductor Lf of the LC filter circuit 14 refluxes through the rectifier circuit 13 and the lossless snubber circuit 15. At this time, the charge stored in the snubber capacitor Csn discharges, and the snubber capacitor voltage decreases. The speed at which the charge escapes depends on the inductor current value, and when the inductor current is small, the speed at which the charge escapes becomes slow. That is, the decrease in the snubber capacitor voltage depends on the magnitude of the inductor current. Here, the inductor current depends on the output power of the load.

[0042] Figure 4C shows a state where the switching elements 13a to 13d of the secondary rectifier circuit 13 are in an off state, and further, the snubber capacitor Csn is in a state where the discharge of the charge is completed. The inductor current by the inductor Lf of the LC filter circuit 14 flows into the rectifier circuit 13 and refluxes to the LC filter circuit 14. On the other hand, the lossless snubber circuit 15 no longer contributes to the reflux of the inductor current.

[0043] Hereinafter, the operation shown in FIG. 4C will be described in detail below. In order to reduce the loss by synchronous rectification, the opposing arms of the switching elements 13a to 13d of the secondary rectifier circuit 13 are set to an on state. That is, all of the switching elements 13a to 13d of the secondary rectifier circuit 13 are set to an on state. At this time, when the snubber capacitor voltage is greater than 0 V, the charge of the snubber capacitor Csn is short-circuited through the switching elements ① to 13d of the secondary rectifier circuit 13 and the snubber diodes D1 and D2. That is, there is a short-circuit path in the circuit loop of the secondary rectifier circuit 13 and the snubber capacitor Csn of the lossless snubber circuit 15. The short-circuit current is I = V / R according to Ohm's law. Here, V is the snubber capacitor voltage, and R is the resistance component of the short-circuit path.

[0044] Since the resistance component R is the on-resistance of the switching elements 13a to 13d and the wiring resistance, it is very small. Therefore, in order to reduce the short-circuit current, it is necessary to lower the snubber capacitor voltage. For this reason, when the snubber capacitor voltage becomes less than or equal to the threshold voltage, all of the switching elements 13a to 13d of the secondary rectifier circuit 13 are set to an on state to determine the synchronous rectification period while avoiding the short-circuit current. As an example of the threshold voltage, for example, +0.1 V can be cited.

[0045] For this purpose, the snubber capacitor voltage is detected through the voltage detection unit 17, and when the detected voltage becomes a voltage less than or equal to the threshold voltage set using a comparator or the like, the voltage detection unit 17 outputs a detection signal. The control unit <16> controls the on / off timing of the switching elements 13a to 13d of the secondary rectifier circuit 13 based on the detection signal sent from the voltage detection unit 17.

[0046] It should be noted that there is an unclear "①" in the content of item [3], which may be an error or an unclear mark in the original text. If there is any other specific requirement or correction information, please feel free to let me know.Figure 5 is a diagram showing the operating waveform of the power converter 100 according to Embodiment 1. Specifically, Figure 5 shows an example of how the detection signal output from the voltage detection unit 17 is generated and reflected in the gate signals of the switching elements 13a to 13d of the secondary rectifier circuit 13.

[0047] In Figure 5, from top to bottom, the waveforms are: the gate signal input to the switching elements 11a to 11d of the full-bridge circuit constituting the primary inverter circuit 11; the primary voltage v1 of the transformer 12; the current i1 flowing through the primary side of the transformer 12; the secondary voltage v2 of the transformer 12; the output voltage vs after rectification by the rectifier circuit 13; the current i2 flowing through the switching elements of the secondary rectifier circuit 13; and the snubber capacitor voltage v of the snubber capacitor Csnb. b The figures show the detection signal detected by the voltage detection unit 17 and the gate signals input to the switching elements 13a to 13d of the secondary rectifier circuit 13, respectively. The hatched areas in Figure 5 represent the short-circuit period.

[0048] A gate signal sent to the switching elements 11a to 11d of the primary inverter circuit 11 applies a voltage v1 to the primary side of the transformer 12, causing a current i1 to flow. A voltage v2, which is the primary transformer voltage multiplied by the turns ratio, is output to the secondary side of the transformer 12. A surge voltage is superimposed on the output voltage vs after rectification by the rectifier circuit 13, resulting in the waveform shown in Figure 5.

[0049] As shown in Figure 4A, when a surge voltage occurs, current flows to the output side through the snubber capacitor Csnb to suppress the surge voltage, thus reducing the snubber capacitor voltage v b The voltage increases. According to the operation shown in Figure 4B, when the rectified output voltage vs approaches 0V, the snubber capacitor voltage v b The voltage gradually decreases. At this time, if all the switching elements 13a to 13d of the secondary rectifier circuit 13 are turned on, a short-circuit current flows due to the energy stored in the snubber capacitor Csnb. Therefore, by providing the voltage detection unit 17, the short-circuit current can be avoided.

[0050] In other words, by providing the voltage detection unit 17 at the position shown in the circuit diagram in Figure 1, the voltage between the drain and source of the switching elements 13a to 13d of the secondary rectifier circuit 13 can be detected, thus enabling zero-voltage switching operation during synchronous rectification. Here, zero-voltage switching operation refers to the snubber capacitor voltage v b This means that when the voltage is 0V or less, the switching elements 13a to 13d are turned on.

[0051] In Figure 5, an example of the operation of the power converter 100 is explained with the threshold voltage of the voltage detection unit 17 set to 0V. The snubber capacitor voltage v b When the snubber capacitor voltage v falls below 0V, the voltage detection unit 17 outputs a High signal, which is a detection signal. However, b It does not need to be below 0V, but it is sufficient if it is close to 0V. Specifically, the snubber capacitor voltage v b However, if the voltage is, for example, +0.1V or lower, it is acceptable to output a High signal.

[0052] Based on this High signal, the control unit 16 controls the turn-on timing of the gate signals of the switching elements 13a to 13d of the secondary rectifier circuit 13. In ideal synchronous rectification, the period during which current flows through the switching elements 13a to 13d of the secondary rectifier circuit 13 and the period during which the secondary gate signal is a High signal are the same. In other words, it is preferable that the waveforms shown by the dotted lines in Figure 5 change at the same timing.

[0053] In the comparative example RCD snubber circuit shown in Figure 3C, the switching element of the secondary rectifier circuit is turned on after a dead time has been introduced. On the other hand, when applying a lossless snubber circuit 15, such as the power converter 100 according to Embodiment 1, it is necessary to further consider the snubber capacitor voltage. Since the amount of change in the snubber capacitor voltage over time changes depending on the load current and the snubber capacitor capacity, it is possible to estimate it from the inductor current value, but a short-circuit current will be generated due to factors such as transient fluctuations of the load and estimation errors.

[0054] In one example of the circuit configuration of the power converter 100 according to Embodiment 1 shown in Figure 1, the output voltage vs of the rectifier circuit 13, that is, the input voltage to the lossless snubber circuit 15, is detected. However, it is also possible to directly detect the voltage of the snubber capacitor Csnb or the snubber diode D2. A specific configuration will be described in Embodiment 2 below.

[0055] In the example of the circuit configuration of the power converter 100 according to Embodiment 1 shown in Figure 1, an example is shown in which the secondary rectifier circuit 13 is configured as a full-bridge circuit. However, any rectifier circuit that converts AC to DC, such as a center-tapped configuration with an intermediate tap on the secondary winding of the transformer 12, is acceptable, and the specific configuration of the rectifier circuit 13 is not limited.

[0056] In the example of the circuit configuration of the power converter 100 according to Embodiment 1 shown in Figure 1, the lossless snubber circuit 15 is configured with two snubber diodes D1 and D2 and one snubber capacitor Csnb. However, the circuit configuration is not limited to the lossless snubber circuit described above; any snubber circuit that generates a short circuit path in the snubber capacitor Csnb depending on the operating mode of the secondary rectifier circuit 13 is acceptable. Although the circuit diagram symbolizes only one capacitor, the snubber capacitor Csnb may consist of multiple capacitors in series and parallel, or diodes in series and parallel.

[0057] In the example of the circuit configuration of the power converter 100 according to Embodiment 1 shown in Figure 1, the switching element of the full-bridge circuit constituting the secondary rectifier circuit 13 is shown as a MOSFET. However, the switching element is not limited to a MOSFET. That is, it may be an IGBT (Insulated Gate Bipolar Transistor) and a diode connected in antiparallel to the IGBT, or a combination of a MOSFET and an external diode, or a diode as a separate element.

[0058] The semiconductor material constituting the switching element described above is not limited to silicon (Si). Wide-bandgap semiconductor materials with a wider bandgap than silicon, such as silicon carbide (SiC), gallium nitride (GaN), and gallium oxide (Ga2O3), may also be used.

[0059] In other words, the switching element can be a Si-MOSFET, Si-IGBT, SiC-MOSFET, SiC-IGBT, GaN power transistor, Ga2O3 power transistor, etc. By using a wide-bandgap semiconductor material for the switching element, an inverter circuit and rectifier circuit can be obtained that have high voltage resistance, good heat dissipation, and high-speed switching capabilities.

[0060] Although the circuit diagram symbol illustrates a single switching element, multiple switching elements may be arranged in multiple parallel or multiple series configurations to increase current capacity and voltage withstand capability. When multiple switching elements are arranged in multiple parallel or multiple series configurations, the switching elements may be a mixture of the aforementioned Si-IGBTs, Si-MOSFETs, SiC-MOSFETs, etc.

[0061] The control unit 16, which constitutes the power conversion device 100 according to Embodiment 1 shown in Figure 1, includes analog circuits such as operational amplifiers and comparators, a processor such as a CPU (Central Processing Unit), a memory for exchanging data with the processor, and an input / output interface for inputting and outputting signals between the processor and the outside.

[0062] The processor may include an ASIC (Application Specific Integrated Circuit), an IC (Integrated Circuit), a DSP (Digital Signal Processor), an FPGA (Field Programmable Gate Array), a microcontroller, and various signal processing circuits.

[0063] Embodiment 2. Figure 6 is a circuit diagram showing the configuration of the power converter 150 according to Embodiment 2. The power converter 150 according to Embodiment 2 is characterized in that, in addition to the circuit configuration of the power converter 100 according to Embodiment 1, it further has a voltage sensor 18 that detects the snubber capacitor voltage of the snubber capacitor Csnb of the lossless snubber circuit 15. The snubber capacitor voltage of the snubber capacitor Csnb detected by the voltage sensor 18 is sent to the control unit 16 as a detection signal, and the control unit 16 controls the on / off timing of the gate signals of the switching elements 13a to 13d of the rectifier circuit 13 based on the detection signal.

[0064] In the power conversion device 150 according to Embodiment 2, the voltage sensor 18 detects the snubber capacitor voltage of the snubber capacitor Csnb of the lossless snubber circuit 15. When the voltage detected by the voltage sensor 18 falls below a threshold voltage, a gate signal from the control unit 16 turns on all the switching elements of the rectifier circuit 13.

[0065] In the power conversion device 150 according to Embodiment 2, the snubber capacitor voltage of the snubber capacitor Csnb is directly detected by the voltage sensor 18, which has the effect of enabling more accurate zero-voltage switching operation during synchronous rectification.

[0066] In the power conversion device 150 according to Embodiment 2, the snubber capacitor voltage of the snubber capacitor Csnb is directly detected by the voltage sensor 18, so the voltage detection unit 17 is not an essential component and may be omitted. In this case, the circuit configuration is further simplified.

[0067] <Summary of the various aspects of this application> The various aspects of this application are summarized below as an appendix.

[0068] (Note 1) A power conversion device comprising: a transformer having a primary winding on the primary side and a secondary winding on the secondary side that are electromagnetically coupled to each other; an inverter circuit connected to the primary side of the transformer and converting DC power to AC power; a rectifier circuit connected to the secondary side of the transformer and rectifying the AC generated in the secondary winding; a snubber circuit connected to the rectifier circuit and having a snubber capacitor; a voltage detection unit that detects the voltage of the snubber capacitor and generates a detection signal by detecting the voltage at the output terminal of the rectifier circuit; and a control unit that controls the rectifier circuit based on the detection signal detected by the voltage detection unit.

[0069] (Note 2) The power conversion device according to Note 1, characterized in that the snubber circuit is a lossless snubber circuit.

[0070] (Note 3) The power conversion device according to Note 2, characterized in that a short circuit exists in the circuit loop between the rectifier circuit and the snubber capacitor of the lossless snubber circuit when synchronous rectification is performed by the rectifier circuit.

[0071] (Note 4) The power conversion device according to any one of Notes 1 to 3, characterized in that the rectifier circuit is composed of a full bridge circuit.

[0072] (Note 5) The power conversion device according to any one of Notes 1 to 4, characterized in that it controls the on / off timing of the switching elements of the rectifier circuit that performs synchronous rectification based on the detected value output by the voltage detection unit.

[0073] (Note 6) The power conversion device according to Note 5, characterized in that when the detection signal of the voltage detection unit falls below a set threshold voltage, the on / off timing of the switching element of the rectifier circuit that performs synchronous rectification is controlled.

[0074] (Note 7) The power conversion device according to any one of Notes 1 to 6, characterized in that it controls the timing for turning on all switching elements of the rectifier circuit that performs synchronous rectification based on the detected value of the voltage detection unit.

[0075] (Note 8) The power conversion device according to any one of Notes 1 to 7, characterized in that an LC filter circuit is further connected to the output terminal of the rectifier circuit.

[0076] (Note 9) The power conversion device according to Note 2 or 3, further comprising a voltage sensor for detecting the voltage of the snubber capacitor of the lossless snubber circuit, wherein all switching elements of the rectifier circuit turn on when the voltage detected by the voltage sensor falls below a threshold voltage.

[0077] While this disclosure describes various exemplary embodiments and examples, the various features, aspects, and functions described in one or more embodiments are not limited to the application of a particular embodiment, but can be applied individually or in various combinations to the embodiments.

[0078] Accordingly, countless variations not illustrated are conceivable within the scope of the art of this disclosure. These include, for example, modifying, adding or omitting at least one component, or extracting at least one component and combining it with components of other embodiments.

[0079] 11 Inverter circuit, 11a-11d, 13a-13d Switching elements, 12 Transformer, 13 Rectifier circuit, 14 LC filter circuit, 15 Lossless snubber circuit, 16 Control unit, 17 Voltage detection unit, 18 Voltage sensor, 100, 150 Power converter, Csnb, Csnb1, Csnb2 Snubber capacitor, D1, D2, Dsnb Snubber diode, Lf Inductor, R Resistive component

Claims

1. A power conversion device comprising: a transformer having a primary winding on the primary side and a secondary winding on the secondary side that are electromagnetically coupled to each other; an inverter circuit connected to the primary side of the transformer and converting DC power to AC power; a rectifier circuit connected to the secondary side of the transformer and rectifying the AC generated in the secondary winding; a snubber circuit connected to the rectifier circuit and having a snubber capacitor; a voltage detection unit that detects the voltage of the snubber capacitor and generates a detection signal by detecting the voltage at the output terminal of the rectifier circuit; and a control unit that controls the rectifier circuit based on the detection signal detected by the voltage detection unit.

2. The power conversion device according to claim 1, characterized in that the snubber circuit is a lossless snubber circuit.

3. The power conversion device according to claim 2, characterized in that a short circuit exists in the circuit loop between the rectifier circuit and the snubber capacitor of the lossless snubber circuit when synchronous rectification is performed by the rectifier circuit.

4. The power conversion device according to any one of claims 1 to 3, characterized in that the rectifier circuit is configured as a full-bridge circuit.

5. The power conversion device according to any one of claims 1 to 4, characterized in that it controls the on / off timing of the switching elements of the rectifier circuit that performs synchronous rectification based on the detected value output by the voltage detection unit.

6. The power conversion device according to claim 5, characterized in that when the detection signal of the voltage detection unit falls below a set threshold voltage, the on / off timing of the switching element of the rectifier circuit that performs synchronous rectification is controlled.

7. The power conversion device according to any one of claims 1 to 6, characterized in that it controls the timing for turning on all switching elements of the rectifier circuit that performs synchronous rectification based on the detected value of the voltage detection unit.

8. The power conversion device according to any one of claims 1 to 7, characterized in that an LC filter circuit is further connected to the output terminal of the rectifier circuit.

9. The power conversion device according to claim 2 or 3, further comprising a voltage sensor for detecting the voltage of the snubber capacitor of the lossless snubber circuit, wherein all switching elements of the rectifier circuit turn on when the voltage detected by the voltage sensor falls below a threshold voltage.

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