Power Conversion Equipment

Abstract

To provide a power conversion device that can improve stability of an output voltage in a case in which a plurality of power conversion units are included.SOLUTION: A power conversion device 100 includes: a first power conversion unit 10 configured to convert DC power into DC power of a first voltage; a second power conversion unit 20 provided on an output side of the first power conversion unit 10 and configured to convert the DC power converted by the first power conversion unit 10 into DC power of a second voltage; a control unit 30 configured to control driving of the first power conversion unit 10 based on a voltage output from the first power conversion unit 10; and a voltage detection unit 40 configured to detect a voltage output from the second power conversion unit 20. Then, the voltage detection unit 40 outputs, to the control unit 30, a signal for reducing the voltage output from the first power conversion unit 10 in a case in which the voltage detected by the voltage detection unit 40 exceeds a predetermined threshold value Th.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a power conversion device, and more particularly to a power conversion device including a plurality of power conversion units. [Background technology]

[0002] 2. Description of the Related Art Conventionally, a power conversion device including a plurality of power conversion units is known (see, for example, Patent Document 1).

[0003] The power conversion device of Patent Document 1 is provided with a chopper circuit that converts DC power. A DC-DC converter is provided on the output side of the chopper circuit. A transformer is provided on the output side of the DC-DC converter. Furthermore, in the power conversion device of Patent Document 1, the output voltage of the transformer is detected. Then, feedback control is performed based on the output voltage to adjust the output voltage of the chopper circuit. Furthermore, the output voltage of the transformer is supplied to a load.

[0004] Moreover, in the power conversion device described in the above Patent Document 1, a control circuit is required for each of the chopper circuit and the DC-DC converter, which increases the number of parts and the cost. If high accuracy is not required for the output voltage, a method of configuring a simple power conversion circuit can be considered in which either the chopper circuit or the DC-DC converter is driven by a fixed PWM without feedback. In this case, when the load factor (the ratio of the average power to the maximum power in a certain period) of the load is relatively small, the output voltage of the transformer tends to rise. In the above Patent Document 1, the chopper circuit and the DC-DC converter each have a control circuit, so that it is possible to ensure the stability of the output voltage. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2019-83658 A Summary of the Invention [Problem to be solved by the invention]

[0006] Also, in order to ensure the stability of the output voltage, a method can be considered in which the output voltage of the DC-DC converter (rather than the output voltage of the chopper circuit itself) is fed back to the control circuit of the chopper circuit. In this case, the stability of the feedback control may deteriorate in response to voltage changes in the low load rate region, so it is desirable to improve the stability of the output voltage.

[0007] The present invention has been made to solve the above-mentioned problems, and one object of the present invention is to provide a power conversion device that is capable of improving the stability of the output voltage when it is equipped with multiple power conversion units. [Means for solving the problem]

[0008] In order to achieve the above object, a power conversion device according to one aspect of the present invention includes a first power conversion unit that boosts DC power and converts it into DC power of a first voltage, a second power conversion unit that is provided on an output side of the first power conversion unit and boosts the DC power converted by the first power conversion unit and converts it into DC power of a second voltage, a control unit that controls driving of one of the first power conversion unit and the second power conversion unit based on a voltage output from one of the first power conversion unit and the second power conversion unit, and a detection unit that detects a voltage or a current output from the other of the first power conversion unit and the second power conversion unit, and the detection unit detects whether the voltage or the current detected by the detection unit is: Has a hysteresis characteristic that includes two thresholds Prescribed Two Threshold The threshold value set on the side with the smaller load factor. If the difference exceeds the threshold voltage, a signal is output to the control unit to reduce the voltage output from one of the first power conversion unit that boosts the DC power and the second power conversion unit that boosts the DC power without stopping the boost operation.

[0009] In the power conversion device according to one aspect of the present invention, as described above, when the voltage or current detected by the detection unit exceeds a predetermined threshold, the detection unit outputs a signal to the control unit to reduce the voltage output from one of the first power conversion unit and the second power conversion unit. As a result, even if the load factor becomes relatively small and the output voltage or output current of the other of the first power conversion unit and the second power conversion unit increases, the output voltage of one of the first power conversion unit and the second power conversion unit is reduced. Therefore, the output voltage of the other of the first power conversion unit and the second power conversion unit is reduced. Also, in the power conversion device according to one aspect of the present invention, as described above, the control unit controls the driving of one of the first power conversion unit and the second power conversion unit based on the voltage output from one of the first power conversion unit and the second power conversion unit. As a result, the driving of the power conversion unit of the control unit itself is controlled based on the voltage output from its own power conversion unit (one of the first power conversion unit and the second power conversion unit). Therefore, unlike the case where the driving of the power conversion unit is controlled based on the voltage output from another power conversion unit, the control gain is prevented from becoming large. As a result, when a plurality of power conversion units are provided, the stability of the output voltage can be improved.

[0010] Furthermore, by configuring the detection unit to output a signal to the control unit to reduce the voltage output from one of the first power conversion unit and the second power conversion unit, the configuration of the detection unit is relatively simple, and therefore the configuration of the power conversion device can be simplified compared to a case where a control unit that controls the drive (such as feedback control to adjust the PWM signal) is provided for each of the first power conversion unit and the second power conversion unit.

[0011] In the power conversion device according to the above aspect, preferably, the detection unit detects a voltage or a current output from the other of the first power conversion unit and the second power conversion unit, and when the detected voltage or current exceeds a predetermined threshold, outputs a signal to the control unit to reduce the voltage output from one of the first power conversion unit and the second power conversion unit. With this configuration, since the detection unit detects the voltage, the number of parts is relatively small compared to the case where the detection unit detects the current. As a result, it is possible to improve the stability of the output voltage while suppressing an increase in the number of parts.

[0012] In the power conversion device according to the above aspect, preferably, when the voltage detected by the detection unit exceeds a predetermined threshold, the control unit linearly reduces the voltage output from one of the first power conversion unit and the second power conversion unit so that the voltage or current output from the other of the first power conversion unit and the second power conversion unit becomes approximately constant. With this configuration, unlike a case in which the voltage output from one of the first power conversion unit and the second power conversion unit is reduced in a stepwise manner, the voltage output from the other of the first power conversion unit and the second power conversion unit can be accurately kept approximately constant.

[0013] In the power conversion device according to the above aspect, preferably, when the voltage or current detected by the detection unit exceeds a predetermined threshold, the control unit reduces the voltage output from one of the first power conversion unit and the second power conversion unit by a preset amount. With this configuration, unlike a case where the voltage output from one of the first power conversion unit and the second power conversion unit is changed continuously (smoothly), it is possible to easily reduce the voltage output from one of the first power conversion unit and the second power conversion unit. As a result, it is possible to suppress an increase in the control load of the control unit.

[0014] In this case, the predetermined threshold value is preferably: As two thresholds,The power converter has a hysteresis characteristic including a first voltage threshold and a second voltage threshold smaller than the first voltage threshold, and the control unit reduces the voltage output from one of the first power conversion unit and the second power conversion unit by a preset amount when the voltage detected by the detection unit increases and becomes larger than the first voltage threshold, and increases the voltage output from one of the first power conversion unit and the second power conversion unit by a preset amount when the voltage detected by the detection unit decreases and becomes smaller than the second voltage threshold. With this configuration, when the voltage detected by the detection unit is between the first voltage threshold and the second voltage threshold, control to reduce or increase the voltage output from one of the first power conversion unit and the second power conversion unit is not performed. In other words, a dead zone is generated. As a result, it is possible to suppress frequent control to reduce or increase the voltage output from one of the first power conversion unit and the second power conversion unit.

[0015] In the power conversion device in which the control unit reduces the voltage by a preset amount, preferably, the predetermined threshold value is As two thresholds, The power converter has a hysteresis characteristic including a first current threshold and a second current threshold smaller than the first current threshold, and the control unit reduces the voltage output from one of the first power conversion unit and the second power conversion unit by a preset amount when the current detected by the detection unit decreases and becomes smaller than the second current threshold, and increases the voltage output from one of the first power conversion unit and the second power conversion unit by a preset amount when the current detected by the detection unit increases and becomes larger than the first current threshold. With this configuration, when the current detected by the detection unit is between the first current threshold and the second current threshold, control to reduce or increase the voltage output from one of the first power conversion unit and the second power conversion unit is not performed. In other words, a dead zone is generated. As a result, it is possible to suppress frequent control to reduce or increase the voltage output from one of the first power conversion unit and the second power conversion unit.

[0016] In the power conversion device according to the above aspect, preferably, the first power conversion unit includes a non-insulated power conversion unit, and the second power conversion unit includes an insulated power conversion unit. With this configuration, since the first power conversion unit is a non-insulated power conversion unit, the parasitic inductance can be reduced compared to an insulated power conversion unit. Therefore, the current increase rate (current slope, di / dt) does not become sluggish. This allows the first power conversion unit to convert the current or voltage quickly. As a result, the first power conversion unit can be driven at a high frequency. Therefore, the processing power within a drive cycle is reduced, and the elements constituting the first power conversion unit can be made smaller. This allows the first power conversion unit to be made smaller. In addition, since the degree of power conversion of the second power conversion unit is reduced by the amount that the first power conversion unit converts power, the switching elements included in the second power conversion unit can be operated at high speed. That is, the second power conversion unit can be driven at a high frequency. As a result, the processing power within a drive cycle is reduced, and the elements constituting the second power conversion unit can be made smaller. This allows the second power conversion section to be made smaller in size. Also, since the current flowing through the switching element is reduced, loss in the switching element can be reduced.

[0017] In the power conversion device according to the above aspect, preferably, the first power conversion unit and the second power conversion unit are driven based on a PWM signal, and the duty ratio of the PWM signal that drives the other of the first power conversion unit and the second power conversion unit that is not controlled by the control unit is fixed. With this configuration, the configuration and control of the power conversion device can be simplified compared to a case in which the duty ratio of the PWM signal that drives the other of the first power conversion unit and the second power conversion unit is variable. Effect of the Invention

[0018] According to the present invention, as described above, when a plurality of power conversion units are provided, it is possible to improve the stability of the output voltage. [Brief description of the drawings]

[0019] [Figure 1] 1 is a block diagram showing a configuration of a power conversion device according to a first embodiment. [Diagram 2] 1 is a circuit diagram showing a configuration of a power conversion device according to a first embodiment. [Diagram 3] FIG. 2 is a diagram for explaining the operation of the power conversion device according to the first embodiment. [Figure 4] FIG. 11 is a block diagram showing a configuration of a power conversion device according to a second embodiment. [Diagram 5] FIG. 11 is a diagram for explaining the operation of the power conversion device according to the second embodiment. [Figure 6] FIG. 11 is a block diagram showing a configuration of a power conversion device according to a third embodiment. [Figure 7] FIG. 11 is a diagram for explaining the operation of the power conversion device according to the third embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings.

[0021] [First embodiment] The configuration of a power conversion device 100 according to a first embodiment will be described with reference to FIGS. 1 to 3.

[0022] 1, the power conversion device 100 includes a first power conversion unit 10. The first power conversion unit 10 converts DC power from a DC power source 1 into DC power of a first voltage. The DC power source 1 has a voltage of, for example, 20V to 28V.

[0023] In the first embodiment, the first power conversion unit 10 is a non-insulated power conversion unit. For example, the first power conversion unit 10 is configured with a boost chopper. The first power conversion unit 10 boosts a voltage of 24V to 100V, for example.

[0024] 2, the first power conversion unit 10 includes a capacitor C1, a reactor L1, a switching element SW1, and a diode D1. The switching element SW1 is, for example, a MOSFET. In the following description, "connected" means "electrically connected."

[0025] The positive and negative sides of the capacitor C1 are connected to the positive and negative sides of the DC power supply 1, respectively. The positive side of the capacitor C1 is connected to one end of the reactor L1. The other end of the reactor L1 is connected to the drain of the switching element SW1 and the anode of the diode D1. The cathode of the diode D1 is connected to the positive side of the capacitor C2, the positive side of the capacitor C3, and the drain of the switching element SW2 of the second power conversion unit 20. The source of the switching element SW1 is connected to the negative side of the DC power supply 1. In addition, the first power conversion unit 10 (switching element SW1) is driven based on a PWM signal.

[0026] As shown in FIG. 1, the power conversion device 100 includes a second power conversion unit 20. The second power conversion unit 20 is provided on the output side of the first power conversion unit 10. The second power conversion unit 20 converts the DC power converted by the first power conversion unit 10 into DC power of a second voltage. In this way, by boosting the voltage in two stages by the two first power conversion units 10 and the second power conversion unit 20, it is possible to reduce the size and increase the efficiency of the power conversion device 100 compared to the case of boosting the voltage by one power conversion unit. For example, compared to the case of directly boosting the voltage from 24V to 400V, it is possible to select the optimal switching elements (SW1, SW2, and SW3) for each boost stage by boosting the voltage from 24V to 100V and then boosting the voltage from 100V to 400V in two stages. This makes it possible to reduce switching loss and saturation loss. In addition, magnetic components can also be made smaller. This makes it possible to reduce the size and increase the efficiency of the power conversion device 100.

[0027] 1, in the first embodiment, the second power conversion unit 20 is an insulating type power conversion unit. The second power conversion unit 20 is, for example, a two-transistor forward type insulating type DC / DC converter. The second power conversion unit 20 boosts a voltage of, for example, 100V to 400V. Then, the second power conversion unit 20 outputs a DC voltage of 400V to the load 2.

[0028] 2, the second power conversion unit 20 includes a capacitor C2, a capacitor C3, a capacitor C4, a switching element SW2, a switching element SW3, a transformer T, a rectifier unit 21, a reactor L2, and a smoothing capacitor C5. The switching elements SW2 and SW3 are each formed of, for example, a MOSFET.

[0029] The positive side of the capacitor C2, the positive side of the capacitor C3, and the drain of the switching element SW2 are connected to the positive output (cathode of the diode D1) of the first power conversion unit 10. The negative side of the capacitor C2, the negative side of the capacitor C4, and the source of the switching element SW3 are connected to the negative output of the first power conversion unit 10.

[0030] The negative side of the capacitor C3 and the positive side of the capacitor C4 are connected to one end of the primary winding of the transformer T. The source of the switching element SW2 and the drain of the switching element SW3 are connected to each other. The source of the switching element SW2 and the drain of the switching element SW3 are connected to the other end of the primary winding of the transformer T. A rectifier 21 is connected to the secondary winding of the transformer T.

[0031] The positive side of the rectifier 21 is connected to one end of the reactor L2. The other end of the reactor L2 is connected to the positive side of the smoothing capacitor C5. The negative side of the rectifier 21 is connected to the negative side of the smoothing capacitor C5.

[0032] The second power conversion unit 20 also includes a switching element drive unit 22. The switching element drive unit 22 drives the switching elements SW2 and SW3. The second power conversion unit 20 (the switching elements SW2 and SW3) are driven based on a PWM signal.

[0033] In the first embodiment, the duty ratio of the PWM signal that drives the second power conversion unit 20, which is not controlled by the control unit 30, is fixed. That is, the switching element drive unit 22 controls the driving of the switching elements SW2 and SW3 in a state in which the duty ratio of the PWM signal that drives the switching elements SW2 and SW3 is fixed. In addition, since the duty ratio of the PWM signal is fixed, the voltage input to the second power conversion unit 20 is boosted at a fixed ratio (100V to 400V). Note that the duty ratio of the PWM and the turns ratio of the transformer T are selected to values ​​that optimize the efficiency of the second power conversion unit 20.

[0034] In the first embodiment, the power conversion device 100 includes a control unit 30. The control unit 30 controls the driving of the first power conversion unit 10 based on the voltage output from the first power conversion unit 10. Specifically, the control unit 30 receives the voltage output from the first power conversion unit 10 and performs feedback control based on the input voltage. Then, the control unit 30 adjusts a PWM signal that drives the switching element SW1 of the first power conversion unit 10 so as to stabilize the voltage output from the first power conversion unit 10. That is, the control unit 30 adjusts the PWM signal so that the output voltage from the first power conversion unit 10 becomes 100V.

[0035] Moreover, in the first embodiment, the power conversion device 100 includes a voltage detection unit 40. The voltage detection unit 40 detects the voltage output from the second power conversion unit 20. The voltage detection unit 40 is configured with a relatively small number of components (such as a reference voltage and a comparator, or an operational amplifier and a voltage dividing resistor). The voltage detection unit 40 is an example of a "detection unit" in the claims.

[0036] Here, in the insulated second power conversion unit 20, when the load factor (the ratio of average power to maximum power in a certain period) of the load 2 to which power is supplied from the second power conversion unit 20 is relatively small, the output voltage of the second power conversion unit 20 tends to increase.

[0037] Therefore, in the first embodiment, the voltage detection unit 40 detects the voltage output from the second power conversion unit 20. When the detected voltage exceeds a predetermined threshold Th (see FIG. 3), the voltage detection unit 40 outputs a signal to the control unit 30 to reduce the voltage output from the first power conversion unit 10. The "signal to reduce" is a signal to instruct the control unit 30 to reduce the voltage output from the first power conversion unit 10, or a signal indicating that the voltage detected by the voltage detection unit 40 exceeds the predetermined threshold Th. When the voltage detected by the voltage detection unit 40 exceeds the predetermined threshold Th, the control unit 30 linearly reduces the voltage output from the first power conversion unit 10 so that the voltage output from the second power conversion unit 20 becomes approximately constant.

[0038] For example, as shown in FIG. 3, the voltage output from the second power conversion unit 20 gradually increases with a decrease in the load factor of the load 2. If the voltage output from the first power conversion unit 10 is not decreased, the voltage output from the second power conversion unit 20 continues to increase, as shown by the dotted line in FIG. 3. On the other hand, in the first embodiment, if the voltage output from the second power conversion unit 20 exceeds a predetermined threshold Th, the voltage detection unit 40 outputs a signal to the control unit 30 to decrease the voltage output from the first power conversion unit 10. As a result, the control unit 30 generates a PWM signal so as to linearly decrease the voltage output from the first power conversion unit 10 as the load factor decreases. As a result, in a region where the voltage output from the second power conversion unit 20 exceeds the predetermined threshold Th (a region where the load factor is small), the voltage output from the second power conversion unit 20 becomes approximately constant regardless of the load factor.

[0039] (Effects of the first embodiment) In the first embodiment, the following effects can be obtained.

[0040] In the first embodiment, as described above, when the voltage detected by the voltage detection unit 40 exceeds a predetermined threshold value Th, the voltage detection unit 40 outputs a signal to the control unit 30 to lower the voltage output from the first power conversion unit 10. As a result, even if the load factor becomes relatively small and the output voltage of the second power conversion unit 20 rises, the output voltage of the first power conversion unit 10 is reduced. Therefore, the output voltage of the second power conversion unit 20 is reduced. Also, in the first embodiment, as described above, the control unit 30 controls the drive of the first power conversion unit 10 based on the voltage output from the first power conversion unit 10. As a result, the drive of the first power conversion unit 10 is controlled based on the voltage output from the first power conversion unit 10. Therefore, unlike the case where the drive of the first power conversion unit 10 is controlled (feedback control) based on the voltage output from another second power conversion unit 20, the control gain is suppressed from becoming large. As a result, in the case where a plurality of first power conversion units 10 and second power conversion units 20 are provided, the stability of the output voltage can be improved.

[0041] Furthermore, in the first embodiment, as described above, the voltage detection unit 40 is configured to output a signal to the control unit 30 to lower the first power conversion unit 10. This makes the configuration of the voltage detection unit 40 relatively simple, and therefore the configuration of the power conversion device 100 can be simplified compared to the case where a control unit that controls the drive (such as feedback control to adjust the PWM signal) is provided for each of the first power conversion unit 10 and the second power conversion unit 20.

[0042] In the first embodiment, as described above, the voltage detection unit 40 detects a voltage, so the number of parts is relatively small compared to when the voltage detection unit 40 detects a current. As a result, it is possible to improve the stability of the output voltage while suppressing an increase in the number of parts.

[0043] Furthermore, in the first embodiment, as described above, when the voltage detected by the voltage detection unit 40 exceeds the predetermined threshold value Th, the control unit 30 linearly reduces the voltage output from the first power conversion unit 10 so that the voltage output from the second power conversion unit 20 becomes approximately constant. This makes it possible to accurately keep the voltage output from the second power conversion unit 20 approximately constant, unlike the case where the voltage or current output from the first power conversion unit 10 is reduced in a stepwise manner.

[0044] In the first embodiment, as described above, the first power conversion unit 10 includes a non-insulated power conversion unit, and the second power conversion unit 20 includes an insulated power conversion unit. As a result, since the first power conversion unit 10 is a non-insulated power conversion unit, the parasitic inductance can be reduced compared to an insulated power conversion unit. Therefore, the current increase rate (current slope, di / dt) does not become sluggish. As a result, the first power conversion unit 10 can convert the voltage quickly. As a result, the first power conversion unit 10 can be driven at a high frequency. Therefore, the processing power within the drive cycle is reduced, and the elements constituting the first power conversion unit 10 can be made smaller. As a result, the first power conversion unit 10 can be made smaller. Also, since the degree of power conversion of the second power conversion unit 20 is reduced by the amount that the first power conversion unit 10 converts power, the switching element SW2 and the switching element SW3 included in the second power conversion unit 20 can be operated at high speed. In other words, the second power conversion unit 20 can be driven at a high frequency. As a result, the processing power within a drive cycle is reduced, making it possible to reduce the size of the elements constituting the second power conversion unit 20. This makes it possible to reduce the size of the second power conversion unit 20. In addition, the current flowing through the switching elements SW2 and SW3 is reduced, making it possible to reduce losses in the switching elements SW2 and SW3.

[0045] In the first embodiment, as described above, the duty ratio of the PWM signal that drives the second power conversion unit 20, which is not controlled by the control unit 30, is fixed. This simplifies the configuration and control of the power conversion device 100 compared to the case where the duty ratio of the PWM signal that drives the second power conversion unit 20 is variable.

[0046] [Second embodiment] The configuration of a power conversion device 200 according to the second embodiment will be described with reference to FIGS.

[0047] 4, the power conversion device 200 includes a control unit 130. The control unit 130 controls the driving of the first power conversion unit 10 based on the voltage output from the first power conversion unit 10.

[0048] In the second embodiment, when the voltage detected by the voltage detection unit 40 exceeds a predetermined threshold (first voltage threshold Th1, see FIG. 5), the control unit 130 reduces the voltage output from the first power conversion unit 10 by a preset magnitude (ΔV1). Specifically, the predetermined threshold has a hysteresis characteristic including the first voltage threshold Th1 and a second voltage threshold Th2 smaller than the first voltage threshold Th1.

[0049] In the second embodiment, as shown in Fig. 5, when the voltage detected by the voltage detection unit 40 increases and becomes larger than the first voltage threshold Th1, the control unit 130 reduces the voltage output from the first power conversion unit 10 by a preset magnitude (ΔV1). Also, when the voltage detected by the voltage detection unit 40 decreases and becomes smaller than the second voltage threshold Th2, the control unit 130 increases the voltage output from the first power conversion unit 10 by a preset magnitude (ΔV1). That is, when the load factor decreases and the voltage output from the second power conversion unit 20 becomes larger than the first voltage threshold Th1, the control unit 130 reduces the voltage output from the first power conversion unit 10 by a preset magnitude (ΔV1). In addition, when an increase in the load factor causes the voltage output from the second power conversion unit 20 to become smaller than the second voltage threshold Th2, the control unit 130 increases the voltage output from the first power conversion unit 10 by a predetermined amount (ΔV1).

[0050] Other configurations of the second embodiment are similar to those of the first embodiment.

[0051] (Effects of the second embodiment) In the second embodiment, the following effects can be obtained.

[0052] In the second embodiment, as described above, when the voltage detected by the voltage detection unit 40 exceeds a predetermined threshold (first voltage threshold Th1), the control unit 130 reduces the voltage output from the first power conversion unit 10 by a preset magnitude (ΔV1). This makes it possible to easily reduce the voltage output from the first power conversion unit 10, unlike the case where the voltage output from the first power conversion unit 10 is changed continuously (smoothly). As a result, it is possible to suppress an increase in the control load of the control unit 130.

[0053] In the second embodiment, as described above, the predetermined threshold has a hysteresis characteristic including a first voltage threshold Th1 and a second voltage threshold Th2 smaller than the first voltage threshold Th1. When the voltage detected by the voltage detection unit 40 increases and becomes larger than the first voltage threshold Th1, the control unit 130 reduces the voltage or current output from the first power conversion unit 10 by a preset magnitude (ΔV1). When the voltage detected by the voltage detection unit 40 decreases and becomes smaller than the second voltage threshold Th2, the control unit 130 increases the voltage output from the first power conversion unit 10 by a preset magnitude (ΔV1). As a result, when the voltage detected by the voltage detection unit 40 is between the first voltage threshold Th1 and the second voltage threshold Th2, control to reduce or increase the voltage output from the first power conversion unit 10 is not performed. That is, a dead zone is generated. As a result, it is possible to suppress frequent control to reduce or increase the voltage output from the first power conversion unit 10.

[0054] [Third embodiment] The configuration of a power conversion device 400 according to the third embodiment will be described with reference to FIGS.

[0055] 6, the power conversion device 400 is provided with a control unit 330. The control unit 330 controls the driving of the first power conversion unit 10 based on the voltage output from the first power conversion unit 10.

[0056] The power conversion device 400 is also provided with a current detection unit 340 that detects a current output from the second power conversion unit 20. In the third embodiment, the predetermined threshold has a hysteresis characteristic including a first current threshold Th11 (see FIG. 7) and a second current threshold Th12 that is smaller than the first current threshold Th11. When the current detected by the current detection unit 340 decreases and becomes smaller than the second current threshold Th12, the control unit 330 decreases the voltage output from the first power conversion unit 10 by a preset magnitude (ΔV2). When the current detected by the current detection unit 340 increases and becomes larger than the first current threshold Th11, the control unit 330 increases the voltage output from the first power conversion unit 10 by a preset magnitude (ΔV2). The first current threshold Th11 and the second current threshold Th12 are determined based on an inflection point of a curve (graph) showing the relationship between the current flowing through the load 2 and the output voltage. Moreover, the current detection section 340 is an example of the "detection section" in the claims.

[0057] (Effects of the third embodiment) In the third embodiment, the following effects can be obtained.

[0058] In the third embodiment, as described above, when the current detected by the current detection unit 340 becomes smaller than the second current threshold Th12, the current detection unit 340 outputs a signal to the control unit 330 to reduce the voltage output from the first power conversion unit 10. As a result, even if the load factor becomes relatively small and the output current of the second power conversion unit 20 increases, the output voltage of the first power conversion unit 10 is reduced. Therefore, the output voltage (output current) of the second power conversion unit 20 is reduced. Also, in the third embodiment, as described above, the control unit 330 controls the drive of the first power conversion unit 10 based on the voltage output from the first power conversion unit 10. As a result, the drive of the first power conversion unit 10 of the control unit 330 is controlled based on the voltage output from the first power conversion unit 10 of the control unit 330. Therefore, unlike the case where the drive of the first power conversion unit 10 of the control unit 3 ... As a result, when a plurality of first power conversion units 10 and second power conversion units 20 are provided, the stability of the output voltage can be improved.

[0059] In the third embodiment, as described above, the predetermined threshold has a hysteresis characteristic including the first current threshold Th11 and the second current threshold Th12 smaller than the first current threshold Th11. This makes it possible to suppress frequent control to decrease or increase the voltage output from the first power conversion unit 10.

[0060] [Variations] The embodiments disclosed herein should be considered to be illustrative and not restrictive in all respects. The scope of the present invention is indicated by the claims, not by the description of the embodiments above, and further includes all modifications (variations) within the meaning and scope of the claims.

[0061] For example, in the first to third embodiments described above, the first power conversion unit 10 is a boost chopper, but the present invention is not limited to this. In the present invention, the first power conversion unit 10 may be a non-insulated power conversion unit other than a boost chopper.

[0062] In the above first to third embodiments, the second power conversion unit 20 is an insulating DC / DC converter of a two-transistor forward system, but the present invention is not limited to this. In the present invention, the second power conversion unit 20 may be an insulating power conversion unit other than an insulating DC / DC converter of a two-transistor forward system.

[0063] In the above first to third embodiments, the power conversion device 100 (200 and 400) is provided with two power conversion units, the first power conversion section 10 and the second power conversion section 20, but the present invention is not limited to this. In the present invention, the power conversion device may be provided with three or more power conversion sections.

[0064] In the above first embodiment, when the voltage detected by the voltage detection unit 40 exceeds a predetermined threshold value Th, the voltage output from the first power conversion unit 10 is linearly reduced so that the voltage output from the second power conversion unit 20 becomes substantially constant, but the present invention is not limited to this. In the present invention, when the voltage detected by the voltage detection unit 40 exceeds a predetermined threshold value Th, the voltage output from the first power conversion unit 10 may be reduced in a stepwise manner.

[0065] In the second embodiment, the predetermined threshold has a hysteresis characteristic (one-stage hysteresis characteristic) including the first voltage threshold Th1 and the second voltage threshold Th2, but the present invention is not limited to this. In the present invention, the predetermined threshold may have a two or more stages of hysteresis characteristic having a third threshold and a fourth threshold in addition to the first voltage threshold Th1 and the second voltage threshold Th2.

[0066] In the above first to third embodiments, the output voltage is stabilized by adjusting the PWM signal for the first power conversion unit 10 (second power conversion unit 20), but the present invention is not limited to this. In the present invention, the output voltage may be stabilized by a method other than adjusting the PWM signal.

[0067] In the third embodiment, the predetermined thresholds (first current threshold Th11 and second current threshold Th12) have a hysteresis characteristic, but the present invention is not limited to this. In the present invention, the current threshold may be composed of one value, as in the first embodiment.

[0068] In the above third embodiment, the current detection unit 340 detects the current output from the second power conversion unit 20, but the present invention is not limited to this. In the present invention, the current detection unit 340 may be configured to detect the current output from the first power conversion unit 10 as in the third embodiment.

[0069] In the above first to third embodiments, an example has been shown in which the driving of the first power conversion unit is controlled based on the voltage (current) output from the second power conversion unit, but the present invention is not limited to this. For example, the driving of the second power conversion unit may be controlled based on the voltage (current) output from the first power conversion unit. In other words, when the voltage (current) of the first power conversion unit detected by the detection unit exceeds a predetermined threshold, the voltage output from the second power conversion unit may be reduced. [Explanation of symbols]

[0070] 10 First power conversion unit 20 Second power conversion section 30, 130, 330 Control section 40 Voltage detection unit (detection unit) 100, 200, 400 Power Converter 340 Current detection unit (detection unit) Th Predetermined threshold Th1 First voltage threshold Th2 Second voltage threshold Th11 First current threshold Th12 Second current threshold

Claims

1. a first power conversion unit that boosts DC power and converts it into DC power of a first voltage; a second power conversion unit provided on an output side of the first power conversion unit and configured to boost the DC power converted by the first power conversion unit and convert the DC power into DC power of a second voltage; a control unit that controls driving of one of the first power conversion unit and the second power conversion unit based on a voltage output from one of the first power conversion unit and the second power conversion unit; a detection unit that detects a voltage or a current output from the other of the first power conversion unit and the second power conversion unit, a first power conversion unit that converts a first voltage into a second voltage and a second voltage into a third voltage, and a voltage output from the first power conversion unit that converts a first voltage into a second voltage and a voltage output from the second power conversion unit that converts a first voltage into a second voltage and a voltage output from the second power conversion unit that converts a first voltage into a second voltage and a voltage output from the second power conversion unit that converts a first voltage into a second voltage and a voltage output from the second power conversion unit that converts a second voltage into a second voltage,

2. 2. The power conversion device according to claim 1, wherein the detection unit detects a voltage output from the other of the first power conversion unit and the second power conversion unit, and when the detected voltage or current exceeds the predetermined threshold, outputs a signal to the control unit to reduce the voltage output from one of the first power conversion unit and the second power conversion unit.

3. 3. The power conversion device according to claim 1, wherein when the voltage or current detected by the detection unit exceeds the predetermined threshold, the control unit linearly reduces the voltage output from one of the first power conversion unit and the second power conversion unit so that the voltage or current output from the other of the first power conversion unit and the second power conversion unit becomes approximately constant.

4. 3. The power conversion device according to claim 1, wherein when the voltage or current detected by the detection unit exceeds the predetermined threshold, the control unit reduces the voltage output from one of the first power conversion unit and the second power conversion unit by a preset amount.

5. the predetermined threshold has a hysteresis characteristic including a first voltage threshold and a second voltage threshold lower than the first voltage threshold as the two thresholds, The control unit is When the voltage detected by the detection unit increases and becomes greater than the first voltage threshold, a voltage output from one of the first power conversion unit and the second power conversion unit is reduced by a preset magnitude; 5. The power conversion device according to claim 4, wherein when the voltage detected by the detection unit drops and becomes smaller than the second voltage threshold, the voltage output from one of the first power conversion unit and the second power conversion unit is increased by a preset magnitude.

6. the predetermined threshold has a hysteresis characteristic including a first current threshold and a second current threshold smaller than the first current threshold as the two thresholds, The control unit is When the current detected by the detection unit decreases and becomes smaller than the second current threshold, a voltage output from one of the first power conversion unit and the second power conversion unit is reduced by a preset magnitude; 5. The power conversion device according to claim 4, wherein when the current detected by the detection unit increases and becomes greater than the first current threshold, a voltage output from one of the first power conversion unit and the second power conversion unit is increased by a preset magnitude.

7. The first power conversion unit includes a non-insulated power conversion unit, The power conversion device according to claim 1 , wherein the second power conversion section includes an insulating type power conversion section.

8. the first power conversion unit and the second power conversion unit are driven based on a PWM signal; The power conversion device according to any one of claims 1 to 7, wherein a duty ratio of the PWM signal that drives the other of the first power conversion unit and the second power conversion unit that is not controlled by the control unit is fixed.

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