Power conversion device

Abstract

To protect a device from an input voltage of reverse polarity without significantly increasing heat generation and losses.SOLUTION: A diode D1 is connected between a DC power supply 2 and switching elements TR1 and TR2, and has a forward direction from the DC power supply 2 toward the switching elements TR1 and TR2. A relay 11 is connected in parallel to the diode D1. A relay control circuit controls the relay 11 so as to turn off the relay 11 when starting to apply an input voltage VIN to the power conversion device 1, and turn on the relay 11 when a forward voltage is applied to the diode D1.SELECTED DRAWING: Figure 1

Description

[Technical field]

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

[0002] Patent Document 1 discloses a power supply circuit that generates DC power from supplied AC power. This power supply circuit includes a rectifier including a diode bridge to full-wave rectify the supplied AC power. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 2916393 Summary of the Invention [Problem to be solved by the invention]

[0004] A diode has a certain resistance even when a current flows in the forward direction. Therefore, when a circuit includes a diode bridge as in Patent Document 1, the diode bridge may generate heat and cause losses. For this reason, for example, by using a DC power distribution network instead of an AC power distribution network, rectification (i.e., a diode bridge) is not required at the input stage of each electric device connected to the power distribution network, and heat generation and losses can be reduced.

[0005] However, an electric device that operates on a supplied DC power may include a diode to protect the electric device from an input voltage of wrong polarity. Even such a diode may generate heat and loss. Therefore, it is required to protect the electric device from an input voltage of reverse polarity without increasing heat generation and loss significantly.

[0006] An object of the present disclosure is to provide a power conversion device that converts an input voltage supplied from a DC power source into a predetermined output voltage, and that can protect the device from an input voltage of reverse polarity without significantly increasing heat generation and loss. [Means for solving the problem]

[0007] A power conversion device according to a first aspect of the present disclosure includes: A power conversion device that converts an input voltage supplied from a DC power source into a predetermined output voltage, At least one switching element; a first diode connected between the DC power supply and the switching element, the first diode having a forward direction from the DC power supply to the switching element; a relay connected in parallel with the first diode; and a relay control circuit that controls the relay so that the relay is turned off when application of the input voltage to the power conversion device begins and so that the relay is turned on when a forward voltage is applied to the first diode.

[0008] This allows the device to be protected from reverse polarity input voltages without significantly increasing heat generation and losses.

[0009] According to the power conversion device according to the second aspect of the present disclosure, in the power conversion device according to the first aspect, The relay control circuit turns on the relay when a voltage at a node between the switching element and the relay exceeds a predetermined threshold.

[0010] This allows the relay to be turned on when a forward voltage is applied to the first diode.

[0011] According to a power conversion device according to a third aspect of the present disclosure, in the power conversion device according to the first aspect, The power conversion device further includes a transformer having a primary winding connected to the switching element, a secondary winding, and an auxiliary winding electromagnetically coupled to the primary winding and the secondary winding, The relay control circuit turns on the relay when the voltage developed across the auxiliary winding exceeds a predetermined threshold.

[0012] This allows the relay to be turned on when a forward voltage is applied to the first diode.

[0013] According to a fourth aspect of the present disclosure, in the power conversion device according to one of the first to third aspects, The power conversion device is a capacitor connected so that the input voltage is applied from the DC power supply via the first diode or the relay; a resistor connected in series with the first diode; The relay is connected in parallel to the first diode and the resistor.

[0014] This makes it possible to reduce the ripple voltage and also to mitigate the inrush current to the capacitor.

[0015] According to a power conversion device according to a fifth aspect of the present disclosure, in the power conversion device according to the fourth aspect, The device further includes a second diode connected in parallel with the capacitor.

[0016] This can improve the reverse breakdown voltage of the capacitor and other components. Effect of the Invention

[0017] According to a power conversion device according to an aspect of the present disclosure, the device can be protected from a reverse polarity input voltage without significantly increasing heat generation and loss. [Brief description of the drawings]

[0018] [Figure 1] 1 is a circuit diagram showing an example of a configuration of a power conversion device 1 according to an embodiment. [Diagram 2] 2 is a timing chart showing an example of the operation of the power conversion device 1 of FIG. [Diagram 3] 1 is a circuit diagram showing an example of a configuration of a power conversion device 1A according to a first modified example of an embodiment. [Figure 4] FIG. 11 is a circuit diagram showing an example of a configuration of a power conversion device 1B according to a second modified example of the embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] [Embodiment] Hereinafter, an embodiment according to one aspect of the present disclosure will be described with reference to the drawings. In each drawing, the same reference numerals denote similar components.

[0020] [Configuration example of embodiment] 1 is a circuit diagram showing an example of the configuration of a power conversion device 1 according to an embodiment. The power conversion device 1 converts an input voltage VIN supplied from a DC power source 2 into a predetermined output voltage VOUT and supplies the output voltage VOUT to a load device 3. The DC power source 2 may be, for example, a storage battery, a combination of an AC power source and a rectifier, or a DC power distribution network. The load device 3 is, for example, an electric device that operates on DC power.

[0021] The power conversion device 1 includes a relay 11, a comparator 12, a drive circuit 13, a rectifier circuit 14, a capacitor C1, a capacitor C2, a diode D1, a reference voltage source E1, resistors R1 to R5, a transformer T1, and switching elements TR1 to TR3.

[0022] The switching elements TR1 and TR2 are connected in series to each other between a positive bus connected to the positive electrode of the DC power supply 2 and a negative bus connected to the negative electrode of the DC power supply 2. The switching elements TR1 and TR2 are configured as, for example, a half-bridge type circuit. The switching elements TR1 and TR2 are, for example, field effect transistors.

[0023] The diode D1 and the resistor R1 are connected in series with each other between the DC power source 2 and the switching elements TR1 and TR2. The diode D1 has a forward direction from the DC power source 2 toward the switching elements TR1 and TR2. FIG. 1 shows an example in which the diode D1 and the resistor R1 are inserted in the positive bus. The relay 11 is connected in parallel with the diode D1 and the resistor R1. The relay 11 includes a switch SW and a coil L that moves a movable contact of the switch SW. When the switch SW is turned off, a current I1 flows through the diode D1 and the resistor R1. On the other hand, when the switch SW is turned on, a current I2 flows through the relay 11. When the switch SW is turned on, the relay 11 has a resistance much smaller than the forward resistance of the diode D1.

[0024] The capacitor C1 is connected across the positive bus and the negative bus so that the input voltage VIN is applied from the DC power supply 2 via a diode D1 and a resistor R1 or via a relay 11. The capacitor C1 is, for example, an electrolytic capacitor.

[0025] The transformer T1 has a primary winding w1 connected across the switching element TR2 and a secondary winding w2 connected to a rectifier circuit 14. The capacitor C2 is connected between the switching element TR2 and the primary winding w1 of the transformer T1. The rectifier circuit 14 rectifies the AC voltage generated in the secondary winding w2 of the transformer T1 to generate an output voltage VOUT.

[0026] The resistors R2 and R3 generate a voltage V2 obtained by dividing the voltage V1 at the node between the switching elements TR1 and TR2 and the relay 11, and apply the voltage V2 to the non-inverting input terminal of the comparator 12. The reference voltage source E1 generates a predetermined reference voltage Vref and applies the voltage V2 to the inverting input terminal of the comparator 12. The reference voltage Vref is set corresponding to a predetermined threshold voltage Vth indicating the minimum value of the voltage V1 to be applied to the switching elements TR1 and TR2. When the input voltage VIN is 380V, the threshold voltage Vth may be set to, for example, 370V. The comparator 12 outputs a signal S0 indicating whether the voltage V2 is higher than the reference voltage Vref, i.e., whether the voltage V1 is higher than the threshold voltage Vth. When V2≦Vref, the signal S0 becomes low level, and when V2>Vref, the signal S0 becomes high level.

[0027] The drive circuit 13 generates control signals S1 and S2 to alternately turn on the switching elements TR1 and TR2 at a predetermined duty ratio and applies the control signals to the control terminals (gates) of the switching elements TR1 and TR2. The drive circuit 13 may generate the control signals S1 and S2 according to the signal S0 so as to keep both the switching elements TR1 and TR2 off immediately after starting to apply the input voltage VIN to the power conversion device 1, and to start the operation of the switching elements TR1 and TR2 after the voltage V1 becomes higher than the threshold voltage Vth.

[0028] Resistors R4 and R5 divide the signal S0 and apply it to the control terminal of the switching element TR3. When the switching element TR3 is turned on, a current flows through the coil L of the relay 11 and the switch SW is turned on. On the other hand, when the switching element TR3 is turned off, the switch SW is also turned off. The switching element TR3 is, for example, a bipolar transistor.

[0029] The resistors R4 and R5 and the switching element TR3 are an example of a relay control circuit that controls the relay 11 in accordance with the signal S0.

[0030] [Operation of the embodiment] FIG. 2 is a timing chart showing an example of the operation of the power conversion device 1 of FIG.

[0031] At time t1, the input voltage VIN starts to be applied from the DC power supply 2 to the power conversion device 1. Immediately after the input voltage VIN starts to be applied to the power conversion device 1, V1≦Vth, so the signal S0 is at a low level. At this time, both switching elements TR1 and TR2 are maintained off. Also, at this time, the switch SW of the relay 11 is turned off, and a current I1 flows through the diode D1 and resistor R1. As the capacitor C1 is charged by the current I1, the voltage V1 gradually increases and the current I1 gradually decreases.

[0032] When the voltage V1 reaches the threshold voltage Vth at time t2, the signal S0 transitions from low level to high level. At this time, the switching elements TR1 and TR2 are alternately turned on at a predetermined duty ratio in accordance with the control signals S1 and S2. Also, at this time, the switch SW of the relay 11 is turned on, and a current I2 flows through the relay 11 instead of the current I1. Since power is supplied from the power conversion device 1 to the load device 3 after time t2, the current I2 becomes larger than the current I1 immediately before the switch SW of the relay 11 is turned on. Strictly speaking, the current I2 includes a ripple component, but in FIG. 2, the fluctuation due to the ripple component is omitted for the sake of simplicity.

[0033] The relay control circuit controls the relay 11 so that the relay 11 is turned off when the input voltage VIN is not applied to the power conversion device 1 and when the input voltage VIN starts to be applied to the power conversion device 1. After that, the relay control circuit controls the relay 11 so that the relay 11 is turned on when a forward voltage is applied to the diode D1. In detail, the relay control circuit turns on the relay 11 when an input voltage VIN of the correct polarity is applied to the power conversion device 1, and as a result, a certain amount of charge is accumulated in the capacitor C1 and the voltage V1 exceeds the threshold voltage Vth. When an input voltage VIN of the reverse polarity is applied to the power conversion device 1, the power conversion device 1 is protected by the diode D1. Also, as described above, the relay 11 has a resistance much smaller than the forward resistance of the diode D1 when the switch SW is turned on. Therefore, by turning on the relay 11 when an input voltage VIN of the correct polarity is applied to the power conversion device 1, heat generation and loss can be reduced compared to when the current I1 flows through the diode D1 and the resistor R1. In this way, by using the diode D1 and the relay 11, the power conversion device 1 can protect the device from the input voltage VIN of reverse polarity without significantly increasing heat generation and loss.

[0034] [Modification of the embodiment] Fig. 3 is a circuit diagram showing an example of a configuration of a power conversion device 1A according to a first modified example of the embodiment. The power conversion device 1A includes a diode D2 connected in parallel to the capacitor C1 in addition to the components of the power conversion device 1 in Fig. 1. By including the diode D2, it is possible to improve the reverse withstand voltage to the capacitor C1 and other components.

[0035] FIG. 4 is a circuit diagram showing an example of the configuration of a power conversion device 1B according to a second modified example of the embodiment. The power conversion device 1B includes a transformer T2 instead of the transformer T1 of FIG. 1, and further includes a capacitor C3 and a diode D3. The transformer T2 has an auxiliary winding w3 electromagnetically coupled to the primary winding w1 and the secondary winding w2 in addition to the primary winding w1 and the secondary winding w2. One end of the auxiliary winding w3 is connected to a resistor R4 via a diode D3, and the other end is grounded. A node between the diode D3 and the resistor R4 is grounded via a capacitor C3. The diode D3, the capacitor C3, the resistors R4 and R5, and the switching element TR3 are an example of a relay control circuit that controls the relay 11 according to the voltage generated in the auxiliary winding w3. When the input voltage VIN starts to be applied to the power conversion device 1B, both of the switching elements TR1 and TR2 are kept off, so that the voltage generated in the auxiliary winding w3 is zero, and the relay control circuit turns off the relay 11. Thereafter, when the voltage V1 reaches the threshold voltage Vth, the switching elements TR1 and TR2 start to operate, and the voltage generated in the auxiliary winding w3 gradually increases. The relay control circuit turns on the relay 11 when the voltage generated in the auxiliary winding w3 exceeds a predetermined threshold. In other words, the relay control circuit turns on the relay 11 when a forward voltage is applied to the diode D1 and the switching elements TR1 and TR2 are operating. According to the power conversion device 1B of FIG. 4, the relay 11 can be controlled by detecting the voltage generated in the auxiliary winding w3.

[0036] [Effects of the embodiment] The power conversion device 1 according to the embodiment includes the diode D1, and thus can protect the device from a reverse polarity input voltage. For example, an input voltage of reverse polarity may be applied to the power conversion device 1 due to an erroneous connection between the power conversion device 1 and the DC power source 2. When an input voltage of reverse polarity is applied, the relay 11 is not turned on, and the current is blocked by the diode D1.

[0037] The power conversion device 1 according to the embodiment includes the capacitor C1, thereby making it possible to reduce the ripple voltage. Also, the power conversion device 1 according to the embodiment includes the resistor R1, thereby making it possible to mitigate the inrush current to the capacitor C1.

[0038] When a forward current flows through the diode D1 and when a current flows through the resistor R1, the diode D1 and the resistor R1 may heat up, causing a loss. The power conversion device 1 according to the embodiment includes a relay 11, and by turning on the relay 11 when a forward voltage is applied to the diode D1 and the switching elements TR1 and TR2 are operating, it is possible to reduce heat generation and loss. For example, even if the resistor R1 has a thermal fuse, a current flows through the resistor R1 only immediately after the input voltage VIN starts to be applied to the power conversion device 1 (i.e., when the capacitor C1 is charged), so that the resistor R1 will not melt.

[0039] According to the power conversion device 1 according to the embodiment, the switching elements TR1 and TR2 operate only when the voltage V1 is sufficiently large (V1>Vth), and therefore an overcurrent can be prevented.

[0040] Since the power conversion device 1 according to the embodiment operates using DC power supplied from the DC power source 2, there is no need to provide a diode bridge at the input stage, which makes it possible to avoid heat generation and loss due to the diode bridge and also reduces the circuit size.

[0041] A technology called "DC industry" has been proposed that realizes energy saving by providing electric devices and a DC power distribution network that operate on a DC voltage of 300 to 400 V instead of conventional electric devices that operate on an AC voltage of 100 to 200 V. The power conversion device 1 according to the embodiment is applicable to electric devices for the DC industry, for example. The power conversion device 1 according to the embodiment can reduce the size and improve the efficiency compared to a power conversion device that converts both AC and DC input voltages to a predetermined output voltage. Furthermore, the power conversion device 1 according to the embodiment can reduce the size compared to a conventional power conversion device that converts a DC input voltage to a predetermined output voltage.

[0042] As described above, the power conversion device 1 according to the embodiment can protect the device from a reverse polarity input voltage without significantly increasing heat generation and loss.

[0043] [Other variations] Although the embodiment of the present disclosure has been described in detail above, the above description is merely an example of the present disclosure in every respect. It goes without saying that various improvements and modifications can be made without departing from the scope of the present disclosure. For example, the following modifications are possible. In the following, the same reference numerals are used for the same components as in the above embodiment, and the description of the same points as in the above embodiment is omitted as appropriate. The following modifications can be combined as appropriate.

[0044] The power conversion device may include an additional capacitor in parallel with the resistor R3. This allows the switching elements TR1 and TR2 to start operating and the relay 11 to be turned on after a predetermined time has elapsed since an inrush current flows through the capacitor C1. For example, if the input voltage VIN is 390V and the reference voltage Vref is set to a value corresponding to Vth=370V, the signal S0 transitions from a low level to a high level when the voltage V1 reaches 390V due to the delay of the additional capacitor.

[0045] Capacitor C1 and resistor R1 may be omitted.

[0046] Diode D1, resistor R1 and relay 11 may be inserted in the negative bus instead of in the positive bus.

[0047] The power conversion device may supply an output voltage to a load device that operates on AC power instead of a load device that operates on DC power, in which case the rectifier circuit 14 on the secondary side of the transformer can be eliminated.

[0048] The power conversion device may be configured as an asynchronous rectification converter including at least one switching element and a diode, instead of a synchronous rectification converter including a plurality of field effect transistors or bipolar transistors.

[0049] The power conversion device may include one or more switching elements configured as a forward circuit, a flyback circuit, or a full-bridge circuit, instead of the switching elements TR1, TR2 configured as a half-bridge circuit.

[0050] The power conversion device may be configured as a non-insulated converter that does not include a transformer, instead of an isolated converter that includes a transformer.

[0051] [summary] A power conversion device according to each aspect of the present disclosure may be expressed as follows.

[0052] A power conversion device 1 according to one aspect of the present disclosure is a power conversion device 1 that converts an input voltage VIN supplied from a DC power source 2 into a predetermined output voltage VOUT, and includes at least one switching element TR1, TR2, a diode D1 connected between the DC power source 2 and the switching elements TR1, TR2 and having a forward direction from the DC power source 2 toward the switching elements TR1, TR2, a relay 11 connected in parallel to the diode D1, and a relay control circuit that controls the relay 11. The relay control circuit controls the relay 11 so that the relay 11 is turned off when application of the input voltage VIN to the power conversion device 1 begins, and so that the relay 11 is turned on when a forward voltage is applied to the diode D1.

[0053] In the power conversion device 1 according to one aspect of the present disclosure, the relay control circuit turns on the relay 11 when the voltage at the node between the switching elements TR1, TR2 and the relay 11 exceeds a predetermined threshold value.

[0054] A power conversion device 1B according to an aspect of the present disclosure further includes a transformer T2 having a primary winding w1 connected to switching elements TR1 and TR2, a secondary winding w2, and an auxiliary winding w3 electromagnetically coupled to the primary winding w1 and the secondary winding w2. A relay control circuit turns on a relay 11 when a voltage generated in the auxiliary winding w3 exceeds a predetermined threshold value.

[0055] The power conversion device 1 according to one aspect of the present disclosure further includes a capacitor C1 connected so that an input voltage VIN is applied from a DC power supply 2 via a diode D1 or a relay 11, and a resistor R1 connected in series with the diode D1. The relay 11 is connected in parallel with the diode D1 and the resistor R1.

[0056] A power conversion device 1A according to an aspect of the present disclosure further includes a diode D2 connected in parallel to the capacitor C1. [Industrial Applicability]

[0057] A power conversion device according to each aspect of the present disclosure is applicable to an electric device that operates on DC power supplied from a DC power source. [Explanation of symbols]

[0058] 1,1A,1B Power conversion device 2 DC power supply 3 Load device 11 Relay 12 Comparator 13 Drive circuit 14 Rectifier circuit C1~C3 capacitors D1~D3 Diodes E1 Reference voltage source R1~R5 Resistors T1, T2 transformer TR1~TR3 switching elements

Claims

1. A power conversion device that converts an input voltage supplied from a DC power source into a predetermined output voltage, At least one switching element; a first diode connected between the DC power supply and the switching element, the first diode having a forward direction from the DC power supply to the switching element; a relay connected in parallel with the first diode; a relay control circuit that controls the relay so that the relay is turned off when application of the input voltage to the power conversion device begins and so that the relay is turned on when a forward voltage is applied to the first diode, Power conversion equipment.

2. The relay control circuit turns on the relay when a voltage at a node between the switching element and the relay exceeds a predetermined threshold. The power converter according to claim 1 .

3. The power conversion device further includes a transformer having a primary winding connected to the switching element, a secondary winding, and an auxiliary winding electromagnetically coupled to the primary winding and the secondary winding, The relay control circuit turns on the relay when a voltage generated in the auxiliary winding exceeds a predetermined threshold value. The power converter according to claim 1 .

4. The power conversion device is a capacitor connected so that the input voltage is applied from the DC power supply via the first diode or the relay; a resistor connected in series with the first diode; the relay is connected in parallel with the first diode and the resistor; A power conversion device according to any one of claims 1 to 3.

5. a second diode connected in parallel with the capacitor; The power converter according to claim 4.

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