Power conversion device

Abstract

To provide a power conversion device in which surge energy is efficiently regenerated such that the conversion efficiency can be improved.SOLUTION: A power conversion device 1 includes an AC-DC conversion unit 20 that converts an AC voltage to a DC voltage, an energy storage unit 30 that is connected to the AC-DC conversion unit 20 and stores surge energy, a discharge resistor 16 that is connected in parallel with the energy storage unit 30 and is connected in series with a load 12, a first smooth capacitor 15 that is connected in series with the discharge resistor 16 and is connected in parallel with the load 12, electrical path switch units 40, 40A that perform switching between first current paths 30, 41, 15 which are connected in series with the energy storage unit 30 and is connected in series with the first smooth capacitor 15, and second current paths 42, 30, 16, 15 which are connected in series with the energy storage unit 30 and is connected in parallel with the first smooth capacitor 15, and a control circuit 13 that controls operation of the AC-DC conversion unit 20.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a power conversion device. [Background technology]

[0002] 2. Description of the Related Art A DC-DC converter is known that converts a DC voltage into an AC voltage, and then steps up or steps down the converted AC voltage, rectifies it, and outputs it.

[0003] In DC-DC converters, low-voltage rectifier elements are used, and the surge voltages generated across the elements are sometimes suppressed by voltage clamp snubber circuits.

[0004] Patent Document 1 describes a technique in which a series circuit consisting of a first capacitor and a first diode is connected to the output terminal of a rectifier circuit, and a voltage control unit is connected between the connection point between the first capacitor and the first diode and the connection point between the smoothing inductor and the smoothing capacitor of the rectifier circuit. The voltage control unit performs control using a predetermined formula, thereby suppressing the peak voltage Ecp of the surge. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 5516055 Summary of the Invention [Problem to be solved by the invention]

[0006] Because the voltage of the snubber capacitor, which is the storage means of the snubber circuit, is higher than the steady-state applied voltage to the rectifier element, it has been difficult to efficiently regenerate the energy stored in the snubber capacitor (hereinafter referred to as surge energy) to the load.

[0007] In the technique described in Patent Document 1, the peak voltage of a surge is suppressed, but no consideration is given to efficiently regenerating the surge energy and improving the efficiency of regeneration of the surge energy.

[0008] An object of the present invention is to provide a power conversion device capable of efficiently regenerating surge energy and improving conversion efficiency. [Means for solving the problem]

[0009] In order to achieve the above object, the present invention is configured as follows.

[0010] The power conversion device includes an AC / DC conversion unit that converts an AC voltage into a DC voltage, an energy storage unit connected to the AC / DC conversion unit and that stores surge energy, a discharge resistor connected in parallel to the energy storage unit and in series with a load, a first smoothing capacitor connected in series to the discharge resistor and in parallel with the load, a current path switching unit that switches between a first current path connected in series with the energy storage unit and in series with the first smoothing capacitor and a second current path connected in series with the energy storage unit and in parallel with the first smoothing capacitor, and a control circuit that controls operation of the AC / DC conversion unit. Effect of the Invention

[0011] According to the present invention, it is possible to provide a power conversion device capable of efficiently regenerating surge energy and improving conversion efficiency. [Brief description of the drawings]

[0012] [Figure 1] 1 is a circuit configuration diagram of a power conversion device according to a first embodiment. [Diagram 2] 3 is an operational waveform diagram of the power conversion device. FIG. [Diagram 3] FIG. 2 is a diagram showing a current path when surge energy is stored in a snubber capacitor. [Figure 4]FIG. 2 is a diagram showing a current path when energy stored in a snubber capacitor is discharged. [Diagram 5] FIG. 11 is a circuit configuration diagram of a power conversion device according to a second embodiment. [Figure 6] FIG. 11 is a circuit configuration diagram of a power conversion device according to a third embodiment. [Figure 7] FIG. 11 is an operational waveform diagram when a switching element of the power conversion device of the third embodiment is always in an on state. [Figure 8] FIG. 11 is an operational waveform diagram when controlling the switching elements of the power conversion device of the third embodiment. [Figure 9] FIG. 11 is a circuit configuration diagram of a power conversion device 4 according to a fourth embodiment. [Figure 10] FIG. 11 is an operational waveform diagram when a switching element of the power conversion device of the fourth embodiment is in an on state. [Figure 11] FIG. 13 is a diagram showing an example of a condition for turning on a switching element of a power conversion device according to a fourth embodiment. [Figure 12] FIG. 13 is a circuit configuration diagram of a power conversion device according to a fifth embodiment. [Figure 13] FIG. 13 is an operational waveform diagram when smoothing capacitors of the power conversion device of the fifth embodiment are connected in parallel without an inductor. [Figure 14] FIG. 13 is an operational waveform diagram when the smoothing capacitor of the fifth embodiment is connected in parallel via an inductor. [Figure 15] FIG. 2 is a circuit configuration diagram of a power conversion device according to a different example (comparative example) from the present invention. [Figure 16] FIG. 11 is an operational waveform diagram of a comparative example of the present invention. [Figure 17] FIG. 11 is a diagram showing a current path when surge energy is stored in a snubber capacitor in a comparative example of the present invention. [Figure 18] FIG. 11 is a diagram showing a current path when surge energy stored in a snubber capacitor is discharged in a comparative example of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] Hereinafter, embodiments of the present invention will be described with reference to the drawings. EXAMPLES

[0014] Example 1 FIG. 1 is a circuit configuration diagram of a power conversion device 1 according to a first embodiment of the present invention.

[0015] In Fig. 1, a DC power supply 10 is connected to switching elements 21, 22, 23, and 24 that constitute an inverter, and is converted into an AC voltage, which is then stepped up or down by a transformer 11. The transformer 11 is connected to an AC / DC conversion unit 20 (rectifier circuit) that is constituted by switching elements 25 and 26, and to diodes 27 and 28 that constitute a snubber circuit described below. A connection point between the diodes 27 and 28 is connected to one end (positive pole side) of a load 12 and a smoothing capacitor 15 via a discharge resistor 16. In addition, one end (positive pole side) of the load 12 and the smoothing capacitor 15 is connected to a secondary winding of the transformer 11 via a smoothing inductor 14. The other end (negative pole side) of the load 12 and the smoothing capacitor 15 is connected to the source sides of the switching elements 25 and 26.

[0016] In addition, the connection point between diodes 27 and 28 is connected to one end (positive side) of snubber capacitor 31 that constitutes energy storage section 30, and the other end (negative side) of snubber capacitor 31 is connected to load 12 and one end (positive side) of smoothing capacitor 15 via electrical path switching section 40, as well as to the source sides of switching elements 25 and 26.

[0017] The electric path switching unit 40 has a diode 41 (first diode) and a diode 42 (second diode). The anode of the diode 41 is connected to the snubber capacitor 31, and the cathode of the diode 42 is connected to the snubber capacitor 31. A connection point between the diodes 41 and 42 is an input terminal of the electric path switching means 40, the cathode of the diode 41 is a first output terminal, and the anode of the diode 42 is a second output terminal. The first output terminal of the electric path switching means 40 is connected to one end of the load 12 and the smoothing capacitor 15, and the second output terminal is connected to the other end of the load 12 and the smoothing capacitor 15.

[0018] A snubber circuit is formed by diodes 27 and 28, snubber capacitor 31, discharge resistor 16, and diodes 41 and 42. The snubber circuit shown in FIG. 1 suppresses the surge voltage applied to switching elements 25 and 26, and also effectively regenerates the surge energy to load 12.

[0019] The connection of the snubber circuit will be described. A first end of the energy storage unit 30 is connected to the drain terminals of the switching elements 25 and 26 via diodes 27 and 28, respectively. A second end of the energy storage unit 30 is connected to the input end of the electric path switching unit 40. A first output end of the electric path switching unit 40 is connected to the positive electrode side of the smoothing capacitor 15, and a second output end of the electric path switching unit 40 is connected to the negative electrode side of the smoothing capacitor 15. A discharge resistor 16 is connected to the first end of the energy storage unit 30 and the positive electrode of the smoothing capacitor 15.

[0020] For the sake of convenience in explaining the operation, the connection point corresponding to the ground on the output side of the power conversion device 1 is designated as point a, and the connection point between the cathodes of the diodes 27 and 28 and the snubber capacitor 31 is designated as point b.

[0021] The control circuit 13 switches on and off the switching elements 21 to 24 to convert the DC voltage of the DC power supply 10 into a pulsed AC voltage (pulse AC voltage). This pulsed AC voltage is applied to the primary winding of the transformer 11, stepped down or stepped up by the transformer 11, and output to the secondary winding.

[0022] Control circuit 13 switches switching elements 25 and 26 to rectify the pulse AC voltage output to the secondary winding of transformer 11 into a DC voltage. The pulse-like ripple contained in this DC voltage is sufficiently smoothed by smoothing inductor 14 and smoothing capacitor 15, and then output to load 12. Control circuit 13 detects the voltage and current of DC power supply 10 and load 12, and controls switching elements 21 to 24 to regulate the output voltage to load 12 to a predetermined value.

[0023] In the above-mentioned operation, a surge voltage may occur due to the switching operation across the switching elements 25 and 26. This surge voltage is suppressed by a snubber circuit.

[0024] Fig. 2 is an operational waveform diagram of the power conversion device 1. Fig. 3 is a diagram showing a current path when surge energy is accumulated, i.e., charged, in the snubber capacitor 31. Fig. 4 is a diagram showing a current path when the energy accumulated in the snubber capacitor 31 is discharged. Note that in Figs. 3 and 4, the circuit parts on the primary side from the transformer 11 of the power conversion device 1 are omitted.

[0025] 2 shows the voltage Vb at point b in FIG. 1 relative to point a, and the voltage at the drain terminal of switching element 25. Note that the operation of switching element 26 is symmetrical to that of switching element 25, so a description thereof will be omitted.

[0026] Between times t0 and t2, switching element 25 is kept in the off state by control circuit 13, and a voltage is applied to its drain terminal from the secondary winding of transformer 11. Between times t2 and t3, no voltage is applied from transformer 11 to switching element 25. During this period, control circuit 13 turns switching element 25 on to rectify the aforementioned pulse AC voltage into DC, i.e., synchronously rectify it.

[0027] 2, when a voltage is induced in the secondary winding of transformer 11, a surge voltage higher than the voltage amplitude value Vt of the secondary winding of transformer 11 is generated at the drain terminal of switching element 25 due to the influence of parasitic inductor components and parasitic capacitance components on the circuit. At this time, when the drain voltage of switching element 25 reaches the sum of voltage Vsc of snubber capacitor 31 and voltage Vout of smoothing capacitor 15, diode 41 becomes conductive. Then, a current is generated in the path of the secondary winding of transformer 11, diode 27, snubber capacitor 31, diode 41, and smoothing capacitor 15, as shown in FIG.

[0028] In other words, the diode 41 forms a current path that connects the snubber capacitor 31 and the smoothing capacitor 15 in series, and the surge energy is stored and regenerated to the load 12 at the same time.

[0029] Furthermore, the voltage Vb becomes the sum of the voltage Vsc of the snubber capacitor 31 and the voltage Vout of the smoothing capacitor 15, and the drain voltage of the switching element 25 is clamped at the voltage Vb. Here, consider a power conversion device different from the present invention in which the electric path switching unit 40 is omitted from the power conversion device 1. In the power conversion device different from the present invention, for example, the snubber capacitor 31 is connected to the negative electrode of the smoothing capacitor 15, and the maximum value of the voltage Vb is set to be equal to the voltage Vb of the power conversion device 1 by adjusting the resistance value of the discharge resistor 16 or the like. In this case, the voltage Vsc of the snubber capacitor 31 of the power conversion device 1 becomes a lower voltage value obtained by subtracting the voltage Vout than that of the power conversion device different from the present invention described above. The power conversion device different from the present invention will be described as the power conversion device 6 in the comparative example section after describing the embodiment of the present invention.

[0030] For convenience of explanation, the forward voltage of the diode 27 is ignored.

[0031] 2, when the accumulation of surge energy in snubber capacitor 31 ends, the drain voltage of switching element 25 converges to the amplitude value Vt induced in the secondary winding of transformer 11. After time t1, diode 42 becomes conductive, and a current is generated in the path of snubber capacitor 31, discharge resistor 16, and smoothing capacitor 15, as shown in FIG.

[0032] That is, a current path is formed by the diode 42 from the snubber capacitor 31 to the smoothing capacitor 15 via the discharge resistor 16, and the surge energy is regenerated to the load 12. Here, the voltage Vsc of the snubber capacitor 31 in the first embodiment is a lower voltage value than the same portion of the power conversion device different from the present invention described above, so that the loss generated in the discharge resistor 16 due to the regeneration of the surge energy is reduced, and the efficiency of regeneration of the surge energy is improved.

[0033] As described above, the snubber circuit of the power conversion device 1 clamps the surge voltage applied to the switching element with the sum of the voltage of the snubber capacitor 31 and the smoothing capacitor 15, and at the same time regenerates the surge energy, by the action of the electric path switching means 40. Compared to the above-mentioned power conversion devices different from the present invention, the power conversion device 1 according to the first embodiment of the present invention is capable of simultaneously storing and regenerating surge energy when a surge voltage occurs, and reducing the voltage of the snubber capacitor 31 to reduce the loss occurring in the discharge resistor, thereby achieving the effect of improving the power conversion efficiency.

[0034] That is, according to the first embodiment of the present invention, it is possible to provide a power conversion device capable of efficiently regenerating surge energy and improving conversion efficiency.

[0035] Although MOSFETs are used for the switching elements 25 and 26 in the first embodiment, IGBTs with diodes connected in inverse parallel may also be used.

[0036] Example 2 Next, a second embodiment of the present invention will be described.

[0037] Fig. 5 is a circuit configuration diagram of a power conversion device 2 according to a second embodiment of the present invention. In Fig. 5, the circuit portion on the primary side from a transformer 11 is similar to that of the power conversion device 1 according to the first embodiment, and is therefore not shown. Also, a description of the points common to the power conversion device 1 will be omitted.

[0038] The power conversion device 2 includes an energy storage unit 30A different from the power conversion device 1 of the embodiment 1. The energy storage unit 30A of the embodiment 2 is a split rectifier circuit configured with a snubber capacitor 31 (first snubber capacitor), a snubber capacitor 32 (second snubber capacitor), and diodes 33 (third diode), 34 (fourth diode), and 35 (fifth diode).

[0039] In the dividing rectifier circuit that is the energy storage unit 30A, the voltage during surge energy discharge is lower than the voltage during surge energy storage.

[0040] The connection of the energy storage unit 30A in the second embodiment will be described.

[0041] The negative electrode of the snubber capacitor 31 is connected to the anode of the diode 34, and the cathode of the diode 34 is connected to the positive electrode of the snubber capacitor 32. The positive electrode of the snubber capacitor 31 is connected to the cathode of the diode 35, and the cathode of the diode 34 is connected to the anode of the diode 35. The anode of the diode 34 is connected to the cathode of the diode 33, and the negative electrode of the snubber capacitor 32 is connected to the anode of the diode 33. A first end of the energy storage unit 30A is the positive electrode of the snubber capacitor 31, and a second end of the energy storage unit 30A is the negative electrode of the snubber capacitor 32.

[0042] The operation of the second embodiment will be described. When a surge voltage occurs at the drain terminal of the switching element 25 or 26 and reaches the sum of the voltages of the snubber capacitors 31 and 32 and the smoothing capacitor 15, the diodes 34 and 41 become conductive. Then, a current is generated in the path of the secondary winding of the transformer 11, the diode 27 or 28, the snubber capacitor 31, the diode 34, the snubber capacitor 32, the diode 41, and the smoothing capacitor 15.

[0043] In other words, when storing surge energy, snubber capacitors 31 and 32 are equivalent to being connected in series, and the voltage of energy storage unit 30A is the sum of the voltages of snubber capacitors 31 and 32. Furthermore, a current path is formed that connects energy storage unit 30A in series with smoothing capacitor 15, and storage of surge energy and regeneration to the load 12 side are performed simultaneously. This operation is the same as that of power conversion device 1 in the first embodiment.

[0044] Next, when the generation of the surge voltage ends, the diodes 33, 35, and 42 become conductive. The stored energy in the snubber capacitor 31 is regenerated to the load via the diodes 33, 42 and the discharge resistor 16, and the stored energy in the snubber capacitor 32 is regenerated to the load via the diodes 35, 42 and the discharge resistor 16.

[0045] In other words, when the surge energy is discharged, the snubber capacitors 31 and 32 are equivalent to being connected in parallel, and the voltage of the energy storage unit 30A when discharging is reduced to half of the voltage when energy is stored.

[0046] As a result, the loss generated in the discharge resistor 16 during surge energy regeneration in the power conversion device 2 of the second embodiment is reduced compared to the power conversion device 1 of the first embodiment, increasing the efficiency of surge energy regeneration and improving the conversion efficiency.

[0047] According to the second embodiment of the present invention, in addition to being able to obtain the same effects as those of the first embodiment, as described above, it is possible to achieve the effects of increasing the efficiency of regeneration of surge energy and increasing conversion efficiency.

[0048] Example 3 Next, a third embodiment of the present invention will be described.

[0049] Fig. 6 is a circuit configuration diagram of a power conversion device 3 according to a third embodiment of the present invention. In Fig. 6, the circuit portion on the primary side from the transformer 11 is similar to that of the power conversion device 1 of the first embodiment, and is therefore not shown. Also, a description of the points common to the power conversion device 1 will be omitted.

[0050] 6, the power conversion device 3 includes a switching element 29 (discharge path interruption switching element) that electrically interrupts the electric path via the discharge resistor 16 depending on the situation. The other configurations are the same as those of the first embodiment. The switching element 29 is connected between the electric path switching unit 40, to which the energy storage unit 30 is connected, and the smoothing capacitor 15, and is connected in series with the discharge resistor 16. The gate terminal of the switching element 29 is connected to the control circuit 13 and is controlled by the control circuit 13. By appropriately controlling the switching element 29, it is possible to improve the regeneration efficiency of surge energy.

[0051] FIG. 7 is an operational waveform diagram when the switching element 29 of the power conversion device 3 of the third embodiment is always in the ON state.

[0052] In order to easily explain the operation of the third embodiment, the following description will be given separately for the case where the switching element 29 is constantly in the ON state and the case where the switching element 29 is controlled.

[0053] 8 is an operational waveform diagram when controlling switching element 29. The operation of power conversion device 3 will be described with reference to FIGS.

[0054] First, the operation when switching element 29 is always in the on state will be described. In this case, power conversion device 3 becomes a circuit equivalent to power conversion device 1 of embodiment 1. Fig. 7 shows voltage Vb at point b when point a in Fig. 6 is used as a reference, and the voltage of the drain terminal of switching element 25. As switching element 26 operates symmetrically to switching element 25, a description thereof will be omitted.

[0055] Depending on the interrelationships between the input voltage of the power conversion device 3 (the voltage of the DC power source 10, not shown), the turns ratio between the primary and secondary of the transformer 11, and the withstand voltages of the switching elements 25 and 26, there may be cases where a sufficient difference cannot be set between the maximum value of the surge voltage and the voltage of the secondary winding of the transformer 11.

[0056] 7 shows operational waveforms under conditions in which the maximum value of the surge voltage is suppressed to a value lower than that of Fig. 2 in Example 1 by adjusting the discharge resistor 16 or the like, and the voltage Vsc of the snubber capacitor 31 is reduced to a voltage equal to the voltage amplitude value Vt of the secondary winding of the transformer 11. In this case, the secondary winding of the transformer 11 and the snubber capacitor 31 function as a voltage source, and are equivalent to a state in which they are connected in parallel.

[0057] For this reason, while the surge voltage from time t1 to time t2 converges and a voltage with an amplitude of Vt is generated in the secondary winding of the transformer 11, currents are generated in the following two paths.

[0058] The path 1 includes the snubber capacitor 31, the discharge resistor 16, the switching element 29, the smoothing capacitor 15, and the diode .

[0059] The path 2 is a path that includes the secondary winding of the transformer 11, the diode 27, the discharge resistor 16, the switching element 29, and the smoothing capacitor 15.

[0060] In path 1, surge energy is regenerated to load 12 via discharge resistor 16, whereas path 2 corresponds to supplying a portion of the power output from transformer 11 to load 12 via discharge resistor 16. This results in higher loss than when power is supplied from transformer 11 to load 12 via switching elements 25 and 26, smoothing inductor 14, and smoothing capacitor 15, and may reduce the conversion efficiency of power conversion device 3.

[0061] Next, the operation when the switching element 29 is controlled will be described.

[0062] Fig. 8 shows the voltage at the gate terminal of switching element 29, the voltage Vb at point b when point a in Fig. 6 is used as a reference, and the voltages at the drain terminals of switching elements 25 and 26. As with Fig. 7 described above, Fig. 8 shows operation waveforms under conditions in which the maximum value of the surge voltage is suppressed lower than that of the example shown in Fig. 2 in the first embodiment by adjusting discharge resistor 16 or the like, and voltage Vsc of snubber capacitor 31 is reduced to a voltage value equal to the voltage amplitude Vt of the secondary winding of transformer 11.

[0063] Between times t0 and t2 and between times t21 and t22, a voltage is induced in the secondary winding of the transformer 11 and is applied to the drain terminals of the switching elements 25 and 26.

[0064] 8, in the periods from time t0 to t2 and from time t21 to t22 when a voltage is induced in the secondary winding of the transformer 11, the power conversion device 3 turns off the switching element 29 to cut off the electric path from the snubber capacitor 31 to the smoothing capacitor 15 via the discharge resistor 16. This operation prevents the power supply via the above-mentioned path 2, which occurs when the switching element 29 is always on, and reduces loss.

[0065] As described above, the power conversion device 3 controls the switching element 29 to be in the off state during the period in which a voltage is induced in the secondary winding of the transformer 11, thereby enabling the regeneration of surge energy via the aforementioned path 1, thereby improving the conversion efficiency.

[0066] According to the third embodiment of the present invention, in addition to being able to obtain the same effects as those of the first embodiment, it is possible to achieve an effect of increasing the efficiency of regeneration of surge energy and thus increasing conversion efficiency.

[0067] The energy storage unit 30 in the third embodiment can be replaced with the energy storage unit 30A in the second embodiment.

[0068] Moreover, the off period of the switching element 29 does not need to completely coincide with the period during which a voltage is induced in the secondary winding of the transformer 11. By turning off the switching element during a period that includes the period during which a voltage is induced in the secondary winding of the transformer 11, it is possible to obtain the effect of improving the conversion efficiency.

[0069] Example 4 Next, a fourth embodiment of the present invention will be described.

[0070] Fig. 9 is a circuit configuration diagram of a power conversion device 4 according to a fourth embodiment of the present invention. In Fig. 9, the circuit portion on the primary side from the transformer 11 is similar to that of the power conversion device 1 of the first embodiment, and is therefore not shown. Also, a description of the points common to the power conversion device 1 will be omitted.

[0071] 9, the power conversion device 4 includes an electric path switching unit 40A that newly includes a switching element 43 (current-passing switching element) instead of the diode 42 that is a part of the electric path switching unit 40 in the power conversion device 1 of the first embodiment. A gate terminal of the switching element 43 is connected to the control circuit 13, and the switching element 43 is controlled by the control circuit 13. When the switching element 43 is turned off, the switching element 43 functions as a diode, and the circuit and operation of the power conversion device 4 become equivalent to those of the power conversion device 1 of the first embodiment.

[0072] On the other hand, when the switching element 43 is turned on, it is equivalent to the connection point between the snubber capacitor 31 and the diode 41 being connected to the negative electrode of the smoothing capacitor 15, and the circuit and operation of the power conversion device 4 become equivalent to a power conversion device different from the present invention described above.

[0073] The power conversion device 4 can suppress surge voltages and improve conversion efficiency by controlling the switching element 43 in response to the input voltage and output voltage to switch the operation of the circuit.

[0074] FIG. 10 is an operational waveform diagram when the switching element 43 of the power conversion device 4 of the fourth embodiment is in the on state.

[0075] In order to easily understand the operation of the fourth embodiment, the operation will be described separately for a case where the switching element 43 is always in an OFF state and a case where the switching element 43 is controlled.

[0076] The operation of the power conversion device 4 will be described with reference to FIG. 7 used in the description of the third embodiment above, and FIGS. 9 and 10 of the fourth embodiment.

[0077] First, the operation when the switching element 43 is in the off state will be described. In this case, the switching element 43 functions as a diode, and the operation is the same as that of the power conversion device 1 of the first embodiment. Here, as shown in Fig. 7, when the voltage of the snubber capacitor 31 is set to a voltage equal to the voltage amplitude value Vt of the secondary winding of the transformer in order to suppress the surge voltage, a path is formed for supplying power from the secondary winding of the transformer 11 to the load 12 via the discharge resistor 16, and loss increases.

[0078] Therefore, the power conversion device 4 of the fourth embodiment turns on the switching element 43 under the conditions shown in Fig. 7. Fig. 10 shows an operation waveform diagram of the power conversion device 4 when the switching element 43 is turned on under the conditions shown in Fig. 7. As shown in Fig. 10, the voltage Vsc of the snubber capacitor 31 exceeds the voltage amplitude Vt of the secondary winding of the transformer 11. As a result, a path for supplying power from the transformer 11 to the load 12 via the discharge resistor 16 is not formed, and an increase in loss can be avoided. At the same time, the function of the snubber circuit for suppressing the surge voltage becomes effective.

[0079] Fig. 11 shows an example of conditions for turning on the switching element 43 of the power conversion device 4. In Fig. 11, the vertical axis and the horizontal axis respectively represent the output voltage and the input voltage of the power conversion device 4. The upper limit of the output voltage specification is Vomax, the lower limit is Vomin, and the upper limit of the input voltage specification is Vimax, the lower limit is Vimin.

[0080] 11 is the range of input / output voltages in which the voltage of snubber capacitor 31 becomes equal to the voltage amplitude of the secondary winding of transformer 11 when switching element 43 of power conversion device 4 is turned off. Therefore, in power conversion device 4, the switching element 43 is set to be turned on in the range surrounded by points a', b, c, d', which includes the range surrounded by points a, b, c, d. Through these controls, the voltage of snubber capacitor 31 in the power conversion device 4 exceeds the secondary winding voltage of transformer 11 over the entire input / output voltage range, and power is not supplied via discharge resistor 16, thereby reducing losses and improving conversion efficiency.

[0081] According to the fourth embodiment of the present invention, the electric path switching unit 40A has a first operation mode in which, when the energy storage unit 30 stores surge energy, the energy storage unit 30 and the smoothing capacitor 15 are connected in series, and when the surge energy is discharged, the energy storage unit 30 is connected to the smoothing capacitor 15 via the discharge resistor 16, and a second operation mode in which, when the energy storage unit 30 stores surge energy, the energy storage unit 30 and the AC-DC conversion unit 20 are connected without the smoothing capacitor 15, and when the surge energy is discharged, the energy storage unit 30 is connected to the smoothing capacitor 15 via the discharge resistor 16, and the control circuit 13 is configured to switch between the first operation mode and the second operation mode based on the input voltage and output voltage of the AC-DC conversion unit 20. Therefore, in addition to obtaining the same effects as those of the first embodiment, the regeneration efficiency of surge energy is improved, and the effect of improving the conversion efficiency can be achieved.

[0082] The energy storage unit 30 in the fourth embodiment can be replaced with the energy storage unit 30A in the second embodiment.

[0083] Example 5 Next, a fifth embodiment of the present invention will be described.

[0084] Fig. 12 is a circuit configuration diagram of a power conversion device 5 according to a fifth embodiment of the present invention. In Fig. 12, the circuit portion on the primary side from the transformer 11 is similar to that of the power conversion device 1 of the first embodiment, and therefore the diagram is omitted. Also, a description of the points common to the power conversion device 1 is omitted.

[0085] As described above, the power conversion device 1 of the first embodiment has an effect of increasing the power conversion efficiency by simultaneously storing and regenerating surge energy when a surge voltage occurs, by including the electric path switching unit 40. However, there is a risk of voltage fluctuation occurring in the smoothing capacitor 15 due to the effect of regenerating part of the surge energy in the smoothing capacitor 15 at the same time as the surge voltage occurs.

[0086] In order to avoid voltage fluctuations in smoothing capacitor 15 due to the occurrence of a surge voltage, power conversion device 5 includes smoothing capacitors 15 and 17 which are divided into two systems and connected in parallel via inductor 18. The connection of smoothing capacitor 17 will be described. Smoothing capacitor 15 (first smoothing capacitor) is connected in parallel with load 12.

[0087] The positive electrode of the first smoothing capacitor 15 is connected to the positive electrode of a smoothing capacitor 17 (second smoothing capacitor) via an inductor 18. The negative electrode of the smoothing capacitor 15 is connected to the negative electrode of the smoothing capacitor 17. The positive electrode of the smoothing capacitor 17 is connected to a connection point between the cathode of a diode 41, which corresponds to a first output terminal of the current path switching unit 40, and the discharge resistor 16.

[0088] In other words, the inductor 18 is connected between the connection point between the discharge resistor 16 and the electrical path switching unit 40 and the positive electrode side of the smoothing capacitor 15, and the smoothing capacitor 17 is connected between the connection point between the discharge resistor 16 and the electrical path switching unit 40 and the negative electrode side of the smoothing capacitor 15.

[0089] In the fifth embodiment, the inductor 18 is disposed between the positive electrodes of the smoothing capacitors 15 and 17, but the same effect can be obtained even if the inductor 18 is disposed between the negative electrodes of the smoothing capacitors 15 and 17.

[0090] FIG. 13 is an operational waveform diagram when the smoothing capacitor 15 and the smoothing capacitor 17 of the power conversion device 5 of the fifth embodiment are connected in parallel without the inductor 18 therebetween.

[0091] In order to easily explain the operation of the fifth embodiment, the following description will be given for a case where the smoothing capacitor 15 and the smoothing capacitor 17 are connected in parallel without the inductor 18, and a case where the smoothing capacitor 15 and the smoothing capacitor 17 are connected in parallel via the inductor 18. The operation of the power conversion device 5 will be described with reference to Fig. 12 and Figs. 13 and 14 described later.

[0092] FIG. 13 is an operational waveform diagram when the smoothing capacitor 15 and the smoothing capacitor 17 are connected in parallel without the inductor 18. In this case, the power conversion device 5 has a circuit and operation equivalent to the power conversion device 1 of the first embodiment. FIG. 13 shows the drain terminal voltage of the switching element 25 and the ripple voltage, which is an AC voltage component of the smoothing capacitor 15. As shown in FIG. 13, a surge voltage occurs at the drain terminal of the switching element 25, and at the same time, an edge-shaped voltage fluctuation occurs in the smoothing capacitor 15. This edge-shaped voltage waveform may contain frequency components several tens to several hundreds times higher than the fundamental frequency due to the switching operation. There is a risk that noise propagated or radiated from the power conversion device 5 due to this may cause damage to other devices.

[0093] FIG. 14 is an operational waveform diagram when the smoothing capacitor 15 and the smoothing capacitor 17 are connected in parallel via the inductor 18. FIG. 14 shows the drain terminal voltage of the switching element 25 and the ripple voltages of the smoothing capacitors 15 and 17. Here, an operational waveform example is shown when the capacitance ratio of the smoothing capacitor 15 and the smoothing capacitor 17 is set to about 10:1. Compared with the above-mentioned FIG. 13, it can be confirmed that there is no edge-shaped voltage fluctuation in the voltage waveform of the smoothing capacitor 15 in FIG. 14. On the other hand, the voltage waveform of the smoothing capacitor 17 is sawtooth-shaped. In the smoothing capacitor 17 connected from the snubber capacitor 31 via the electric path switching unit 40, voltage fluctuation occurs due to the influence of regeneration of surge energy when a surge voltage occurs, but the inductor 18 and the smoothing capacitor 15 act as a low-pass filter, and have the effect of suppressing the amplitude of the ripple voltage of the smoothing capacitor 15. This reduces noise propagated or radiated from the power conversion device 5.

[0094] As a general method example different from the fifth embodiment, a ripple voltage can also be suppressed by disposing a low-pass filter made up of an inductor and a capacitor between the smoothing capacitor 15 and the load 12.

[0095] However, since a current equivalent to the load current flows through the inductor used in this case, a magnetic core of the same size as the smoothing inductor 14 is required to prevent magnetic saturation.

[0096] On the other hand, a current caused by surge energy is generated in the inductor 18 used in the fifth embodiment, but the current value is sufficiently low compared to the load current. Therefore, the fifth embodiment can use the inductor 18 having a smaller magnetic body compared to the smoothing inductor 14, and has an effect of reducing costs compared to the above-mentioned general method example.

[0097] According to the fifth embodiment of the present invention, in addition to being able to obtain the same effects as the first embodiment, it is possible to provide a power conversion device at low cost that has the effect of increasing the regeneration efficiency of surge energy and increasing the conversion efficiency.

[0098] The energy storage unit 30 in the fifth embodiment can be replaced with the energy storage unit 30A in the second embodiment.

[0099] Moreover, it is also possible to add the smoothing capacitor 17 and the inductor 18 having the connection relationship shown in FIG.

[0100] (Comparative Example) Next, an example different from the present invention and for comparison with the present invention will be described.

[0101] FIG. 15 is a circuit configuration diagram of a power conversion device 6 that is different from the power conversion device 1 of the first embodiment of the present invention.

[0102] 15, a difference from the power conversion device 1 according to the first embodiment of the present invention shown in FIG. 1 is that the power conversion device 6 does not include the electric path switching unit 40 of the power conversion device 1. In the power conversion device 6, the diodes 27 and 28, the capacitor 31, and the discharge resistor 16 correspond to a snubber circuit that suppresses a surge voltage applied to the switching elements 25 and 26.

[0103] The control circuit 13 of the power conversion device 6 performs the same control operation as the control circuit 3 of the power conversion device 1.

[0104] In the control operation of the power conversion device 6, a surge voltage may occur due to the switching operation across the switching elements 25 and 26. The surge voltage is suppressed by the above-mentioned snubber circuit.

[0105] The operation of the snubber circuit of the power conversion device 6 will be described with reference to FIGS.

[0106] Fig. 16 is an operational waveform diagram of the power conversion device 6. Fig. 17 is a diagram showing a current path when surge energy is accumulated, i.e., charged, in the snubber capacitor 31. Fig. 18 is a diagram showing a current path when the surge energy accumulated in the snubber capacitor 31 is discharged. Note that in Figs. 17 and 18, the circuit parts on the primary side from the transformer 11 of the power conversion device 6 are omitted.

[0107] Fig. 16 shows the voltage Vb at point b in Fig. 14 relative to point a, and the voltage at the drain terminal of switching element 25. Note that voltage Vb of power conversion device 6 is the voltage of snubber capacitor 31. As switching element 26 operates in a symmetrical manner to switching element 25, a description thereof will be omitted.

[0108] Between times t0 and t2, switching element 25 is kept in the off state by control circuit 13, and a voltage is applied to its drain terminal from the secondary winding of transformer 11. Between times t2 and t3, no voltage is applied from transformer 11 to switching element 25. During this period, control circuit 13 turns switching element 25 on, and rectifies the aforementioned pulse AC voltage to DC, i.e., synchronously rectifies it.

[0109] 16, when a voltage is induced in the secondary winding of transformer 11, a surge voltage higher than the voltage amplitude value Vt of the secondary winding of transformer 11 is generated at the drain terminal of switching element 25 due to parasitic inductor components, parasitic capacitance components, etc. on the circuit. At this time, when the drain voltage of switching element 25 reaches the voltage value Vsc of snubber capacitor 31, a current is generated in the path of the secondary winding of transformer 11, diode 27, and snubber capacitor 31, as shown in FIG. 17, and surge energy accumulates in snubber capacitor 31.

[0110] Then, the drain voltage of the switching element 25 is limited (clamped) to the voltage Vsc of the snubber capacitor 31. For convenience of explanation, the forward voltage of the diode 27 is ignored.

[0111] 16, when the accumulation of surge energy in snubber capacitor 31 ends, the drain voltage of switching element 25 converges to the voltage amplitude Vt of the secondary winding of transformer 11. After time t1, a current is generated in the path of snubber capacitor 31, discharge resistor 16, and smoothing capacitor 15, as shown in FIG.

[0112] As described above, the snubber circuit of the power conversion device 6 has the effect of clamping the surge voltage applied to the switching element with the voltage of the snubber capacitor and regenerating the surge energy to the load. This action suppresses the peak voltage of the surge and improves the efficiency of the power conversion device 6.

[0113] However, in the comparative power conversion device 6, no consideration is given to efficiently regenerating surge energy and improving the efficiency of regeneration of surge energy, making it difficult to improve the efficiency of regeneration of surge energy.

[0114] In contrast, in the power conversion devices 1 to 5 according to the first to fifth embodiments of the present invention, an ionization switching unit 40 that switches between a path for storing surge energy and a path for discharging the surge energy is provided.

[0115] According to the present invention, during the period when a surge voltage occurs, snubber capacitors 31, 32 and smoothing capacitor 15 on the load 12 side are connected in series to store surge energy and regenerate it to the load 12 side at the same time, thereby reducing the voltage of snubber capacitor 31. During the period when no surge voltage occurs, surge energy is efficiently regenerated from snubber capacitor 31 to smoothing capacitor 15 via discharge resistor 16.

[0116] As a result, the present invention can provide a power conversion device that can reduce the loss in the snubber capacitor 31, efficiently regenerate surge energy, and improve conversion efficiency. [Explanation of symbols]

[0117] 1, 2, 3, 4, 5...power conversion device, 10...DC power supply, 11...transformer, 12...load, 13...control circuit, 14...smoothing inductor, 15, 17...smoothing capacitor, 16...discharge resistor, 18...inductor, 20...AC / DC conversion section (rectifier circuit), 21, 22, 23, 24, 25, 26, 29, 43...switching element, 27, 28...diode, 30, 30A...energy storage section, 31, 32...snubber capacitor, 40, 40A...current path switching section, 33, 34, 35, 41, 42...diode

Claims

1. an AC / DC converter that converts AC voltage into DC voltage; an energy storage unit connected to the AC / DC converter and configured to store surge energy; A discharge resistor connected in parallel with the energy storage unit and in series with a load; a first smoothing capacitor connected in series to the discharge resistor and in parallel to the load; a current path switching unit that switches between a first current path that is connected in series with the energy storage unit and in series with the first smoothing capacitor and a second current path that is connected in series with the energy storage unit and in parallel with the first smoothing capacitor; A control circuit for controlling the operation of the AC / DC converter; A power conversion device comprising:

2. 2. The power conversion device according to claim 1, the electric path switching unit has a first diode and a second diode, an anode of the first diode and a cathode of the second diode are connected to the energy storage unit, a cathode of the first diode is connected to a positive electrode side of the first smoothing capacitor, and an anode of the second diode is connected to a negative electrode side of the first smoothing capacitor.

3. 2. The power conversion device according to claim 1, The electrical path switching unit is a first operation mode in which the energy storage unit and the first smoothing capacitor are connected in series when the surge energy is stored in the energy storage unit, and the energy storage unit is connected to the first smoothing capacitor via the discharge resistor when the surge energy is discharged; a second operation mode in which the energy storage unit and the AC / DC converter are connected to each other without passing through the first smoothing capacitor when storing surge energy in the energy storage unit, and the energy storage unit is connected to the first smoothing capacitor via the discharge resistor when discharging the surge energy; having The power conversion device, wherein the control circuit switches between the first operation mode and the second operation mode based on an input voltage and an output voltage of the AC / DC conversion unit.

4. The power conversion device according to claim 2 or 3, A power conversion device, wherein the energy storage section has a split rectifier circuit whose voltage during discharge of surge energy is lower than the voltage during storage of surge energy.

5. In the power conversion device according to any one of claims 1 to 3, a discharge path cutoff switching element connected between the energy storage unit and the first smoothing capacitor and connected in series with the discharge resistor; The power conversion device according to claim 1, wherein the control circuit turns off the discharge path interruption switching element during a period in which an AC voltage is applied to the AC / DC conversion unit.

6. In the power conversion device according to any one of claims 1 to 3, an inductor connected between a connection point between the discharge resistor and the current path switching unit and a positive electrode side of the first smoothing capacitor; a second smoothing capacitor connected to a connection point between the discharge resistor and the current path switching unit and to a negative electrode side of the first smoothing capacitor; A power conversion device comprising:

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