JP2022078591A - Voltage smoothing circuit and power conversion device - Google Patents

Abstract

To provide a voltage smoothing circuit capable of lowering loss of resistors connected in parallel to capacitors and being downsized.SOLUTION: A voltage smoothing circuit comprises a plurality of capacitors connected in series between a pair of wirings, a plurality of resistors connected in series between the pair of wirings, a detection circuit detecting imbalance of a voltage applied to each of the plurality of capacitors, and a switching circuit. The plurality of capacitors include a first capacitor and a second capacitor. The plurality of resistors include a first resistor, a second resistor, and a third resistor. The switching circuit switches a middle point connection destination between the first capacitor and the second capacitor to a first connection point between the first resistor and the second resistor or to a second connection point between the second resistor and the third resistor according to detection results of the imbalance.SELECTED DRAWING: Figure 1

Description

The present disclosure relates to voltage smoothing circuits and power converters.

The DC voltage between a pair of wires may be smoothed by a plurality of electrolytic capacitors connected in series between the pair of wires. On the other hand, when a voltage is applied to the electrolytic capacitor, a leakage current flows through the electrolytic capacitor. Therefore, the electrolytic capacitor can be considered as an equivalent circuit in which an internal capacitance component and an internal resistance component are connected in parallel.

However, there are individual differences in the internal resistance component of the electrolytic capacitor. Therefore, when a plurality of electrolytic capacitors are connected in series and used, the individual shared voltage of the plurality of electrolytic capacitors connected in series may become unbalanced due to the deviation of the internal resistance component. If there is no margin in the withstand voltage of the electrolytic capacitor with respect to the voltage applied to the electrolytic capacitor, this imbalance becomes a problem.

Therefore, it is possible to suppress the imbalance of the shared voltage by connecting resistors in parallel to each of a plurality of electrolytic capacitors connected in series so that the voltage applied to the electrolytic capacitor does not exceed the withstand voltage. May be done.

Japanese Unexamined Patent Publication No. 10-295081

However, in order to suppress the imbalance of the shared voltage, if the resistance value of the resistor connected in parallel with the electrolytic capacitor is reduced to reduce the influence of the deviation of the internal resistance component of the electrolytic capacitor, the loss in the resistor is large. Become. As a result, the loss of the voltage smoothing circuit is increased. In addition, since the loss in the resistor becomes large, if a large resistor having a large rated power is used, the voltage smoothing circuit becomes large.

The present disclosure provides a voltage smoothing circuit capable of reducing loss and miniaturization of a resistor connected in parallel to a capacitor, and a power conversion device including the voltage smoothing circuit.

In one aspect of the disclosure,
A voltage smoothing circuit that smoothes the DC voltage between the first wiring and the second wiring having a lower potential than the first wiring.
A plurality of capacitors connected in series between the first wiring and the second wiring,
A plurality of resistors connected in parallel to the plurality of capacitors and connected in series between the first wiring and the second wiring, and
A detection circuit that detects the imbalance of the voltage applied to each of the plurality of capacitors, and
With a switching circuit,
The plurality of capacitors include a first capacitor and a second capacitor connected in series on the side of the second wiring of the first capacitor.
The plurality of resistors are on the side of the first resistor, the second resistor connected in series to the side of the second wiring of the first resistor, and the second wiring of the second resistor. Including a third resistor connected in series
In the switching circuit, the connection destination of the midpoint between the first capacitor and the second capacitor is set between the first resistor and the second resistor according to the detection result of the imbalance. A voltage smoothing circuit is provided that switches between a first connection point and a second connection point between the second resistor and the third resistor.

According to one aspect of the present disclosure, it is possible to reduce the loss and size of the resistor connected in parallel with the capacitor.

It is a figure which shows the structural example of the voltage smoothing circuit in 1st Embodiment. It is a figure for demonstrating the operation state when the 1st unbalanced state of the voltage smoothing circuit in 1st Embodiment is detected. It is a figure for demonstrating the operation state when the 2nd unbalanced state of the voltage smoothing circuit in 1st Embodiment is detected. It is a figure which shows the structural example of the voltage smoothing circuit in one comparative form. It is a figure which shows an example of the simulation result which calculated the variation range of the voltage applied to the 1st capacitor in each voltage smoothing circuit of one comparative form and 1st Embodiment. It is a figure which shows the specific 1st structural example of the voltage smoothing circuit in 1st Embodiment. It is a figure which shows the specific 2nd structural example of the voltage smoothing circuit in 1st Embodiment. It is a figure which shows the specific 3rd structural example of the voltage smoothing circuit in 1st Embodiment. It is a figure which shows an example of the operation waveform of the 3rd configuration example. It is a figure which shows the specific structural example of the voltage smoothing circuit in 2nd Embodiment. It is a figure which shows the structural example of the power conversion apparatus in one Embodiment.

Hereinafter, embodiments according to the present disclosure will be described with reference to the drawings. In addition, "greater than or equal to" and "greater than or equal to" may be read interchangeably, and "less than or equal to" and "less than" may be read interchangeably.

FIG. 1 is a diagram showing a configuration example of a voltage smoothing circuit according to the first embodiment. The voltage smoothing circuit 100 shown in FIG. 1 is a circuit that smoothes the DC voltage Edc between the pair of wirings 91 and 92. The second wiring 92 is a wiring having a lower potential than the first wiring 91. The DC voltage Edc corresponds to the potential difference between the pair of wires 91, 92. The voltage smoothing circuit 100 suppresses fluctuations in the DC voltage Edc by, for example, smoothing the DC voltage Edc supplied to the pair of wirings 91 and 92 from a voltage source (not shown). For example, when the pair of wirings 91 and 92 is a power supply line for supplying a DC voltage Edc which is a DC power supply voltage, the first wiring 91 corresponds to a positive electrode line and the second wiring 92 is a negative electrode line (ground line). ).

The voltage smoothing circuit 100 includes a plurality of capacitors (first capacitor 11 and second capacitor 12 in this example) and a plurality of resistors (first resistor 21, second resistor 22 and third resistor in this example). 23), the detection circuit 30 and the switching circuit 60 are provided. The first capacitor 11 and the second capacitor 12 may be collectively referred to as capacitors 11 and 12. The first resistor 21, the second resistor 22, and the third resistor 23 may be collectively referred to as resistors 21, 22, 23.

Capacitors 11 and 12 are capacitive elements connected in series between a pair of wires 91 and 92. The second capacitor 12 is connected in series on the side of the second wiring 92 of the first capacitor 11. The first capacitor 11 has a first end connected to the first wiring 91 and a second end connected to the first end of the second capacitor 12. The second capacitor 12 has a first end connected to the second end of the first capacitor 11 and a second end connected to the second wiring 92. The DC voltage Edc is applied to both ends of the capacitors 11 and 12 connected in series.

The midpoint 40 is a connection node between the first capacitor 11 and the second capacitor 12, and the second end of the first capacitor 11 and the first end of the second capacitor 12 are connected to each other.

The first capacitor 11 can be represented by an equivalent circuit in which the internal capacitance component 11a and the internal resistance component 11b are connected in parallel. Similarly, the second capacitor 12 can be represented by an equivalent circuit in which the internal capacitance component 12a and the internal resistance component 12b are connected in parallel. Specific examples of the capacitors 11 and 12 include electrolytic capacitors.

The resistors 21, 22 and 23 are resistance elements connected in parallel to the capacitors 11 and 12 connected in series and connected in series between the pair of wirings 91 and 92. The second resistor 22 is connected in series to the side of the second wiring 92 of the first resistor 21. The third resistor 23 is connected in series to the side of the second wiring 92 of the second resistor 22. The DC voltage Edc is applied to both ends of the resistors 21, 22, 23 connected in series.

The first connection point 51 is a connection node between the first resistor 21 and the second resistor 22. The second connection point 52 is a connection node between the second resistor 22 and the third resistor 23.

The detection circuit 30 detects an imbalance in the voltage (shared voltage) applied to each of the capacitors 11 and 12. The detection circuit 30 detects the imbalance of the shared voltage by detecting the circuit state representing the imbalance of the shared voltage from the voltage smoothing circuit 100. Some configuration examples of the detection circuit 30 will be described later.

The switching circuit 60 switches the connection destination of the midpoint 40 to one of the first connection point 51 and the second connection point 52 according to the detection result of the imbalance of the shared voltage obtained by the detection circuit 30. It is a circuit. The switching circuit 60 switches the connection destination of the midpoint 40 to one of the first connection point 51 and the second connection point 52, so that the voltage applied individually to the capacitors 11 and 12 (in other words, the internal voltage). The voltage applied to each of the capacitance components 11a and 12a) can be switched.

The resistance value of the internal resistance component 11b of the first capacitor 11 is R11b, and the resistance value of the internal resistance component 12b of the second capacitor 12 is R12b. The resistance values of the resistors 21, 22, and 23 are R21, R22, and R23, respectively.

In the first switching state in which the connection destination of the middle point 40 is switched to the second connection point 52, the series resistor of the first resistor 21 and the second resistor 22 (hereinafter referred to as the first series resistor) is It is connected in parallel to the first capacitor 11 and the third resistor 23 is connected in parallel to the second capacitor 12. Therefore, in the first switching state, the parallel combined resistance of the internal resistance component 11b and the first series resistor (hereinafter referred to as the first parallel combined resistance) is connected in parallel to the internal capacitance component 11a and becomes the internal resistance component 12b. The parallel combined resistance with the third resistor 23 (hereinafter referred to as the second parallel combined resistance) is connected in parallel to the internal capacitance component 12a. Therefore, assuming that the resistance value of the first parallel combined resistance is Rp1 and the resistance value of the second parallel combined resistance is Rp2, in the first switching state, the individually applied voltages of the capacitors 11 and 12 are Rp1 and Rp2. Determined by the ratio.

Specifically, in the first switching state, the voltage Vc1 applied to the capacitor 11 and the voltage Vc2 applied to the capacitor 12 are
Vc1 = Rp1 / (Rp1 + Rp2) × Edc ・ ・ ・ Equation 1
Vc2 = Rp2 / (Rp1 + Rp2) × Edc ・ ・ ・ Equation 2
It is decided by.

The resistance value Rp1 of the first parallel combined resistance and the resistance value Rp2 of the second parallel combined resistance are
Rp1 = R11b × (R21 + R22) / (R11b + R21 + R22)
... Equation 3
Rp2 = R12b × R23 / (R12b + R23)
... Equation 4
It is represented by.

On the other hand, in the second switching state in which the connection destination of the middle point 40 is switched to the first connection point 51, a series resistor of the third resistor 23 and the second resistor 22 (hereinafter referred to as a second series resistor). ) Is connected in parallel to the second capacitor 12, and the first resistor 21 is connected in parallel to the first capacitor 11. Therefore, in the second switching state, the parallel combined resistance of the internal resistance component 12b and the second series resistor (hereinafter referred to as the third parallel combined resistance) is connected in parallel to the internal capacitance component 12a and becomes the internal resistance component 11b. The parallel combined resistance with the first resistor 21 (hereinafter referred to as the fourth parallel combined resistance) is connected in parallel with the internal capacitance component 11a. Therefore, assuming that the resistance value of the third parallel combined resistance is Rp3 and the resistance value of the fourth parallel combined resistance is Rp4, in the second switching state, the individually applied voltages of the capacitors 11 and 12 are Rp3 and Rp4. Determined by the ratio.

Specifically, in the second switching state, the voltage Vc1 applied to the capacitor 11 and the voltage Vc2 applied to the capacitor 12 are
Vc1 = Rp4 / (Rp3 + Rp4) × Edc ・ ・ ・ Equation 5
Vc2 = Rp3 / (Rp3 + Rp4) × Edc ・ ・ ・ Equation 6
It is decided by.

The resistance value Rp3 of the third parallel combined resistance and the resistance value Rp4 of the fourth parallel combined resistance are
Rp3 = R12b × (R22 + R23) / (R12b + R22 + R23)
・ ・ ・ Equation 7
Rp4 = R11b × R21 / (R11b + R21)
... Equation 8
It is represented by.

The switching circuit 60, for example, turns on or off the connection between the first switch 61, which turns on or off the connection between the midpoint 40 and the first connection point 51, and the connection between the midpoint 40 and the second connection point 52. It has a second switch 62 to turn off. The changeover circuit 60 sets one of the first switch 61 and the second switch 62 in the on state and the other switch in the off state. That is, when the first switch 61 is in the on state, the second switch 62 is in the off state, and when the first switch 61 is in the off state, the second switch 62 is in the on state.

Next, an operation example of the first embodiment will be described.

Ileak1 represents the leakage current of the first capacitor 11, Ileak2 represents the leakage current of the second capacitor 12, and Ileak represents the current flowing into or out of the midpoint 40. Vc1 represents the voltage applied to the first capacitor 11, and Vc2 represents the voltage applied to the second capacitor 12.

When there is a variation between Ileak1 and Ileak2, the voltage difference between Vc1 and Vc2 widens.

As a first example, consider a case where Ileak2 is larger than Ileak1 in the first switching state in which the connection destination of the midpoint 40 is switched to the second connection point 52. When Ileak2 is larger than Ileak1, the Ileak flows in the direction of flowing into the midpoint 40. Further, when Ileak2 is larger than Ileak1, the speed at which the discharge of the second capacitor 12 proceeds is faster than the speed at which the discharge of the first capacitor 11 proceeds, so that Vc1 gradually increases and Vc2 gradually decreases. When the detection circuit 30 detects a first unbalanced state in which the voltage difference obtained by subtracting Vc2 from Vc1 is larger than the first deviation, the switching circuit 60 connects the midpoint 40 to the first connection point 52 to the first. Switch to the connection point 51 (see FIG. 2). As a result, the element connected in parallel to the first capacitor 11 is switched from the first series resistor (R21 + R22) to the first resistor 21 (R21), and the element connected in parallel to the second capacitor 12 is the first. 3 The resistor 23 (R23) is switched to the second series resistor (R22 + R23). As a result, the voltage applied to the first capacitor 11 decreases and the voltage applied to the second capacitor 12 increases, so that Vc1 can be changed from gradual increase to gradual decrease, and Vc2 can be changed from gradual decrease to gradual increase. be able to.

As a second example, consider a case where Ileak1 is larger than Ileak2 in the second switching state in which the connection destination of the midpoint 40 is switched to the first connection point 51. When Ileak1 is larger than Ileak2, Ileak flows in the direction of outflow from the midpoint 40. Further, when Ileak1 is larger than Ileak2, the speed at which the discharge of the first capacitor 11 proceeds is faster than the speed at which the discharge of the second capacitor 12 proceeds, so that Vc1 gradually decreases and Vc2 gradually increases. When the detection circuit 30 detects a second unbalanced state in which the voltage difference obtained by subtracting Vc1 from Vc2 is larger than the second deviation, the switching circuit 60 connects the midpoint 40 to the second connection point 51 to the second. Switch to the connection point 52 (see FIG. 3). As a result, the element connected in parallel to the first capacitor 11 is switched from the first resistor 21 (R21) to the first series resistor (R21 + R22), and the element connected in parallel to the second capacitor 12 is the first. The 2 series resistor (R22 + R23) is switched to the 3rd resistor 23 (R23). As a result, the voltage applied to the first capacitor 11 increases and the voltage applied to the second capacitor 12 decreases, so that Vc1 can be changed from gradual decrease to gradual increase, and Vc2 can be changed from gradual increase to gradual decrease. be able to. The second deviation may be the same as or different from the first deviation.

In this way, the switching circuit 60 switches the connection destination of the midpoint 40 to one of the first connection point 51 and the second connection point 52 according to the imbalance detection result by the detection circuit 30. The voltages Vc1 and Vc2 applied to each of the capacitors 11 and 12 can be reduced. If the voltages Vc1 and Vc2 applied to each of the capacitors 11 and 12 can be reduced, the series combined resistance value of the resistors 21 and 22 and 23 can be increased, so that the series combined resistance of the resistors 21 and 22 and 23 can be used. The power consumed can be reduced, and a small resistor with a small rated power can be used. Therefore, the resistors 21, 22, and 23 can be miniaturized and the loss can be reduced, and as a result, for example, the voltage smoothing circuit 100 can be miniaturized. For example, a large resistor such as an enamel resistor or a metal clad resistor can be replaced with a small resistor such as a chip resistor.

FIG. 4 is a diagram showing a configuration example of a voltage smoothing circuit in one comparative mode. The voltage smoothing circuit 200 shown in FIG. 4 is applied to each of the capacitors 11 and 12 by the resistor R1 connected in parallel to the first capacitor 11 and the resistor R2 connected in parallel to the second capacitor 12. It is a circuit that suppresses voltage imbalance.

FIG. 5 shows a simulation result of calculating the variation range of the voltage Vc1 applied to the first capacitor 11 in the voltage smoothing circuit 200 (FIG. 4) in one comparative embodiment and the voltage smoothing circuit 100 (FIG. 1) in the first embodiment. It is a figure which shows an example. The horizontal axis represents the current Ileak that flows in or out of the midpoint 40. Negative Ileak represents the current flowing into midpoint 40 when Ileak2 is greater than Ileak1, and positive Ileak represents the current flowing out of midpoint 40 when Ileak1 is greater than Ileak2. The DC voltage Edc between the pair of wires 91 and 92 is 600 V.

The data of the one comparative form shown in FIG. 5 shows the simulation result when each resistance value of the resistors R1 and R2 is 43 kΩ. In one comparative form, Vc1 varies within a certain range as shown in the figure due to fluctuations in Ileak. On the other hand, the data of the first embodiment shown in FIG. 5 shows the simulation results when the resistance values of the resistors 21, 22, and 23 are set so that the variation range of Vc1 is the same as that of the comparative embodiment. The resistance values of the first resistor 21 and the third resistor 23 are 60 kΩ, and the resistance value of the second resistor 22 is 40 kΩ. In the case of FIG. 5, in the first embodiment, when Ileak crosses a positive threshold value slightly larger than zero in the increasing direction, the connection destination of the midpoint 40 is switched from the first connection point 51 to the second connection point 52. Therefore, Vc1 is changed to a large voltage so that Vc1 does not drop too much. On the contrary, when Ileak crosses a positive threshold value slightly larger than zero in the decreasing direction, the connection destination of the midpoint 40 switches from the second connection point 52 to the first connection point 51, so that Vc1 rises too much. Change Vc1 to a small voltage so that it does not exist.

In one comparative mode shown in FIG. 5, the series combined resistance value of the resistors R1 and R2 is 86 kΩ (= 43 kΩ + 43 kΩ), so that the power consumption of the resistors R1 and R2 in the series combined resistance is 4.19 W (=). 600V x 600V ÷ 86kΩ). On the other hand, in the first embodiment shown in FIG. 5, the series combined resistance value of the resistors 21, 22, 23 is 160 kΩ (= 60 kΩ + 40 kΩ + 60 kΩ), so that the series combined resistance of the resistors 21, 22, 23 is used. The power consumption is 2.25 W (= 600 V × 600 V ÷ 160 kΩ). That is, when the variation range of Vc1 is comparable between the one comparative embodiment and the first embodiment, the first embodiment is a series synthesis of the resistors 21, 22, 23 as compared with the one comparative embodiment. Since the power consumed by the resistor can be reduced, a small resistor with a small rated power can be used. Therefore, the resistors 21, 22, and 23 can be miniaturized and the loss can be reduced.

In FIG. 1, in the first switch 61 and the second switch 62, when one switch is in the on state, the other switch is in the off state. Therefore, the voltage applied to the switching circuit 60 (more specifically, the voltage applied across each of the first switch 61 and the second switch 62) is the voltage across the second resistor 22 (= Edc). × (R22 / (R21 + R22 + R23))). Therefore, the voltage applied to the switching circuit 60 by making the resistance value R22 of the second resistor 22 smaller than the resistance value R21 of the first resistor 21 and smaller than the resistance value R23 of the third resistor 23. (Voltage applied to both ends of the first switch 61 and the second switch 62) can be reduced. As a result, since the low withstand voltage switching circuit 60 (first switch 61 and second switch 62) can be adopted, the switching circuit 60 (first switch 61 and second switch 62) can be miniaturized, and eventually the voltage smoothing can be achieved. The circuit 100 can be downsized.

The resistance value R23 of the third resistor 23 is preferably equal to the resistance value R21 of the first resistor 21. Thereby, the variation range of Vc1 and the variation range of Vc2 can be adjusted to the same extent.

FIG. 6 is a diagram showing a specific first configuration example of the voltage smoothing circuit according to the first embodiment. The voltage smoothing circuit 101 shown in FIG. 6 shows a first specific example of the voltage smoothing circuit 100 described above. The switching circuit 60A is the first specific example of the switching circuit 60 described above. The detection circuit 30A is a first specific example of the above-mentioned detection circuit 30.

The switching circuit 60A sets the connection destination of the midpoint 40 to either the first connection point 51 or the second connection point 52 according to the imbalance detection result by the detection circuit 30A, and the first switch 61 and the second. It is switched by the switch 62. The first switch 61 and the second switch 62 are, for example, electrolytic effect transistors (FETs), in this example, the first switch 61 is a P-type MOSFET, and the second switch 62 is an N-type MOSFET. be. A specific example of the switching circuit 60A having such a configuration is a photomos relay.

The switching circuit 60A has a drive control circuit that turns on one of the first switch 61 and the second switch 62 and turns off the other according to the imbalance detection result by the detection circuit 30A. The drive control circuit is, for example, an insulating element having a photodiode 64 and a drive circuit 63. A specific example of an insulating element is a photocoupler. The drive circuit 63 turns on one of the first switch 61 and the second switch 62 and turns off the other, depending on the presence or absence of a current flowing through the photodiode 64.

The detection circuit 30A detects the imbalance of the voltage applied to each of the capacitors 11 and 12 by detecting the current Ileak that flows in or out of the midpoint 40.

As described above, when the leakage current Ileak2 of the second capacitor 12 is larger than the leakage current Ileak1 of the first capacitor 11, the current Ileak flows in the direction of flowing into the midpoint 40. Therefore, the detection circuit 30A detects the current Ileak flowing into the midpoint 40, so that the voltage Vc1 applied to the first capacitor 11 is higher than the voltage Vc2 applied to the second capacitor 12 in the first unbalanced state. Can be detected. For example, the detection circuit 30A can detect a first unbalanced state in which the voltage difference obtained by subtracting Vc2 from Vc1 is larger than the first deviation by detecting the current Ileak exceeding the first current threshold value flowing into the midpoint 40. ..

On the other hand, as described above, when the leakage current Ileak1 of the first capacitor 11 is larger than the leakage current Ileak2 of the second capacitor 12, the current Ileak flows in the direction of flowing out from the midpoint 40. Therefore, the detection circuit 30A detects the current Ileak flowing out from the midpoint 40, so that the voltage Vc2 applied to the second capacitor 12 is higher than the voltage Vc1 applied to the first capacitor 11 in the second unbalanced state. Can be detected. For example, the detection circuit 30A can detect a second unbalanced state in which the voltage difference obtained by subtracting Vc1 from Vc2 is larger than the second deviation by detecting the current Ileak exceeding the second current threshold value flowing out from the midpoint 40. .. The second current threshold value may be the same as or different from the first current threshold value.

The detection circuit 30A includes, for example, a current detector 31, a direction detection circuit 32, and a determination circuit 33. The current detector 31 detects the current Ileak that flows into or out of the midpoint 40. Specific examples of the current detector 31 include CT (Current Transformer) and shunt resistance. The direction detection circuit 32 uses the operational amplifier 32a to detect whether the direction in which the current Ileak detected by the current detector 31 flows is the direction in which the current Ileak flows into the midpoint 40 or the direction in which the current Ileak flows out from the midpoint 40.

The determination circuit 33 uses the comparator 33a to determine whether or not the current value of the current Ileak flowing into the midpoint 40 detected by the direction detection circuit 32 is equal to or greater than the first current threshold value.

When the determination circuit 33 determines that the current value of the current Ileak flowing into the midpoint 40 detected by the direction detection circuit 32 is less than the first current threshold value, the determination circuit 33 determines that the capacitors 11 and 12 are not in the first unbalanced state. .. In this case, the determination circuit 33 does not output the control signal If that switches the connection destination of the midpoint 40 from the second connection point 52 to the first connection point 51 to the photodiode 64 of the switching circuit 60A. As a result, the drive circuit 63 of the changeover circuit 60A maintains the first changeover state in which the first switch 61 is in the off state and the second switch 62 is in the on state. The control signal If f corresponds to, for example, the forward current of the photodiode 64.

On the other hand, when the determination circuit 33 determines that the current value of the current Ileak flowing into the midpoint 40 detected by the direction detection circuit 32 is equal to or higher than the first current threshold value, the capacitors 11 and 12 are in the first unbalanced state. judge. In this case, the determination circuit 33 outputs the control signal If that switches the connection destination of the midpoint 40 from the second connection point 52 to the first connection point 51 to the photodiode 64 of the switching circuit 60A. As a result, in the drive circuit 63 of the switching circuit 60A, the first switching state in which the first switch 61 is in the off state and the second switch 62 is in the on state, the first switch 61 is in the on state, and the second switch 62 is in the off state. Change to the second switching state of the state. As a result, since the connection destination of the midpoint 40 is switched from the second connection point 52 to the first connection point 51, Vc1 can be changed from gradual increase to gradual decrease, and Vc2 can be changed from gradual decrease to gradual increase.

The determination circuit 33 may determine whether or not the current value of the current Ileak flowing out from the midpoint 40 detected by the direction detection circuit 32 is equal to or greater than the second current threshold value by using the comparator 33a.

When the determination circuit 33 determines that the current value of the current Ileak flowing out from the midpoint 40 detected by the direction detection circuit 32 is less than the second current threshold value, the determination circuit 33 determines that the capacitors 11 and 12 are not in the second unbalanced state. .. In this case, the determination circuit 33 does not output the control signal If that switches the connection destination of the midpoint 40 from the first connection point 51 to the second connection point 52 to the photodiode 64 of the switching circuit 60A. As a result, the drive circuit 63 of the changeover circuit 60A maintains the second changeover state in which the first switch 61 is on and the second switch 62 is off.

On the other hand, when the determination circuit 33 determines that the current value of the current Ileak flowing out from the midpoint 40 detected by the direction detection circuit 32 is equal to or higher than the second current threshold value, the capacitors 11 and 12 are in the second unbalanced state. judge. In this case, the determination circuit 33 outputs the control signal If that switches the connection destination of the midpoint 40 from the first connection point 51 to the second connection point 52 to the photodiode 64 of the switching circuit 60A. As a result, the drive circuit 63 of the changeover circuit 60A has a second changeover state in which the first switch 61 is on and the second switch 62 is off, and the first switch 61 is in the off state and the second switch 62 is on. Change to the first switching state of the state. As a result, since the connection destination of the midpoint 40 is switched from the first connection point 51 to the second connection point 52, Vc1 can be changed from gradual decrease to gradual increase, and Vc2 can be changed from gradual increase to gradual decrease.

FIG. 7 is a diagram showing a specific second configuration example of the voltage smoothing circuit according to the first embodiment. The voltage smoothing circuit 102 shown in FIG. 7 shows a second specific example of the voltage smoothing circuit 100 described above. The detection circuit 30B is a second specific example of the above-mentioned detection circuit 30.

The detection circuit 30B detects the imbalance of the voltage applied to each of the capacitors 11 and 12 by comparing the magnitude of the voltage Vc1 applied to the first capacitor 11 and the voltage Vc2 applied to the second capacitor 12. do.

As described above, when the leakage current Ileak2 of the second capacitor 12 is larger than the leakage current Ileak1 of the first capacitor 11, Vc1 gradually increases and Vc2 gradually decreases. Therefore, in the detection circuit 30B, the voltage Vc1 applied to the first capacitor 11 is higher than the voltage Vc2 applied to the second capacitor 12 by comparing the detected value of Vc1 and the detected value of Vc2. Unbalanced state can be detected. For example, the detection circuit 30B can detect the first unbalanced state by detecting that the voltage difference obtained by subtracting Vc2 from Vc1 is larger than the first deviation.

On the other hand, as described above, when the leakage current Ileak1 of the first capacitor 11 is larger than the leakage current Ileak2 of the second capacitor 12, Vc1 gradually decreases and Vc2 gradually increases. Therefore, the detection circuit 30B can detect the second unbalanced state in which the voltage difference obtained by subtracting Vc1 from Vc2 is larger than the second deviation by comparing the detected value of Vc1 and the detected value of Vc2. For example, the detection circuit 30B can detect the second unbalanced state by detecting that the voltage difference obtained by subtracting Vc1 from Vc2 is larger than the second deviation.

The detection circuit 30B includes, for example, a voltage detection circuit 34, an amplifier circuit 35, and a determination circuit 36. The voltage detection circuit 34 includes a voltage divider circuit 34a that outputs a detected value of the voltage Vc1 applied to the first capacitor 11 and a voltage divider circuit 34b that outputs a detected value of the voltage Vc2 applied to the second capacitor 12. Have. The voltage detection circuit 34 transfers the detected value of the voltage Vc1 obtained by the voltage dividing circuit 34a to the amplifier circuit 35 and the insulating element 34c that transfers the detected value of the voltage Vc1 to the amplifier circuit 35. It has an insulating element 34d and the like.

The amplifier circuit 35 amplifies the detected value of the voltage Vc1 transferred by the insulating element 34c by using the operational amplifier 35a, and amplifies the detected value of the voltage Vc2 transferred by the insulating element 34d by using the operational amplifier 35b.

The determination circuit 36 determines the magnitude relationship between the detected values of Vc1 and Vc2 obtained by the voltage detection circuit 34 and the amplifier circuit 35 by using the comparator 36a.

When the determination circuit 36 determines that the capacitors 11 and 12 are not in the first unbalanced state, the determination circuit 36 switches the control signal If that switches the connection destination of the midpoint 40 from the second connection point 52 to the first connection point 51 of the switching circuit 60A. Do not output to the photodiode 64. As a result, the drive circuit 63 of the switching circuit 60A maintains the connection destination of the midpoint 40 at the second connection point 52. On the other hand, when the determination circuit 36 determines that the capacitors 11 and 12 are in the first unbalanced state, the determination circuit 36 switches the control signal If that switches the connection destination of the midpoint 40 from the second connection point 52 to the first connection point 51. It outputs to the photodiode 64 of 60A. As a result, since the connection destination of the midpoint 40 is switched from the second connection point 52 to the first connection point 51, Vc1 can be changed from gradual increase to gradual decrease, and Vc2 can be changed from gradual decrease to gradual increase.

On the other hand, when the determination circuit 36 determines that the capacitors 11 and 12 are not in the second unbalanced state, the determination circuit 36 switches the control signal If that switches the connection destination of the midpoint 40 from the first connection point 51 to the second connection point 52. It does not output to the photodiode 64 of 60A. As a result, the drive circuit 63 of the switching circuit 60A maintains the connection destination of the midpoint 40 at the first connection point 51. On the other hand, when the determination circuit 36 determines that the capacitors 11 and 12 are in the second unbalanced state, the determination circuit 36 switches the control signal If that switches the connection destination of the midpoint 40 from the first connection point 51 to the second connection point 52. It outputs to the photodiode 64 of 60A. As a result, the connection destination of the midpoint 40 is switched from the first connection point 51 to the second connection point 52, so that Vc1 can be changed from gradual decrease to gradual increase, and Vc2 can be changed from gradual increase to gradual decrease.

FIG. 8 is a diagram showing a specific third configuration example of the voltage smoothing circuit according to the first embodiment. The voltage smoothing circuit 103 shown in FIG. 8 shows a third specific example of the voltage smoothing circuit 100 described above. The detection circuit 30C is a third specific example of the above-mentioned detection circuit 30.

The detection circuit 30C includes a voltage dividing circuit 37 that divides and outputs a DC voltage Edc, and a resistor 38 having one end connected to a second connection point 52. The detection circuit 30C detects the imbalance of the voltage applied to each of the capacitors 11 and 12 by comparing the output voltage of the voltage dividing circuit 37 with the voltage VR3 of the second connection point 52. The voltages VR1, VR2, and VR3 correspond to the voltages across the resistors 21, 22, and 23, respectively.

The resistance value of the first resistor 21 is R21, the resistance value of the second resistor 22 is R22, and the resistance value of the third resistor 23 is R23. At this time, the voltage dividing circuit 37 divides the DC voltage Edc into a voltage higher than (Edc × R23 / (R21 + R22 + R23)) and outputs the voltage. In this example, the voltage divider circuit 37 outputs a voltage (Edc / 2) that is half the DC voltage Edc.

When the voltage VR3 is larger than (Edc / 2), the forward current If does not flow from the detection circuit 30C to the photodiode 64, so that the drive circuit 63 of the switching circuit 60A connects the connection destination of the midpoint 40 to the second connection point. Keep at 52. On the other hand, when the voltage VR3 is smaller than (Edc / 2), the forward current If flows from the detection circuit 30C to the photodiode 64, so that the drive circuit 63 of the switching circuit 60A connects the connection destination of the midpoint 40 to the second connection destination. The point 52 is switched to the first connection point 51. Thereby, Vc1 can be changed from gradual increase to gradual decrease, and Vc2 can be changed from gradual decrease to gradual increase.

FIG. 9 is a diagram showing an example of the operation waveform of the third configuration example shown in FIG. FIG. 9 illustrates a case where the leakage currents of the capacitors 11 and 12 vary (Ileak1 <Ileak2). When the DC voltage Edc is 600V, the deviations of the respective voltages Vc1 and Vc2 of the capacitors 11 and 12 increase around the initial value of 300V.

For example, assuming that the first switch 61 is off and the second switch 62 is on in the initial state, a series resistor (R21 + R22) is connected in parallel to the first capacitor 11 and a second capacitor 12 is connected to the second capacitor 12. Three resistors (R23) are connected in parallel. In this connected state, the discharge of the second capacitor 12 becomes large, so that Vc1 rises and Vc2 falls (see period P1).

When the voltage difference obtained by subtracting Vc2 from Vc1 exceeds the first deviation, the switch to be turned on is switched from the second switch 62 to the first switch 61. As a result, the first resistor (R21) is connected in parallel to the first capacitor 11 and the series resistor (R22 + R23) is connected in parallel to the second capacitor 12, so that Vc1 changes from rising to falling. Vc2 changes from a decrease to an increase (see period P2).

The discharge currents including the leakage currents of the capacitors 11 and 12 are balanced, and Vc1 and Vc2 are balanced with a constant deviation (see period P3). After that, if the characteristics of the capacitors 11 and 12 do not change due to a temperature change or the like, the first switch 61 is always on. In the above-mentioned comparative embodiment (FIG. 4), the voltage difference between Vc1 and Vc2 widens, whereas in the present embodiment, the connection destination of the midpoint 40 is only switched, so that the voltage difference between Vc1 and Vc2 remains. , The spread of the voltage difference can be suppressed.

Further, in the process of the periods P1, P2, and P3, the voltage applied to each of the first switch 61 and the second switch 62 is the voltage VR2 across the second resistor 22. Therefore, by adjusting the resistance value of the second resistor 22, a relatively small and inexpensive low withstand voltage switch can be used for the first switch 61 and the second switch 62.

FIG. 10 is a diagram showing a specific configuration example of the voltage smoothing circuit according to the second embodiment. In the second embodiment, the description of the same configuration as that of the first embodiment will be omitted by referring to the above description. The number of capacitors connected in series between the pair of wirings 91 and 92 is not limited to two, and may be three or more. The voltage smoothing circuit 104 shown in FIG. 10 includes three capacitors 11, 12, and 13 and five resistors 21 to 25. It includes two switching circuits 60A and 60B.

The switching circuit 60A connects the connection destination of the midpoint 40 between the capacitors 11 and 12 to the first connection point 51 and the second connection point according to the detection result of the imbalance of the voltage applied to each of the capacitors 11 and 12. This is a circuit for switching to one of the points 52. The switching circuit 60B connects the connection destination of the midpoint 41 between the capacitors 12 and 13 to the third connection point 53 and the fourth connection according to the detection result of the imbalance of the voltage applied to each of the capacitors 12 and 13. This is a circuit for switching to one of the points 54. The switching circuit 60B has the same function as the switching circuit 60A. The third switch 66, the fourth switch 67, and the drive circuit 68 correspond to the first switch 61, the second switch 62, and the drive circuit 63, respectively.

Also in the second embodiment shown in FIG. 10, by operating in the same manner as in the first embodiment, the resistors 21 to 25 can be miniaturized and the loss can be reduced, and as a result, for example, the voltage smoothing circuit 104 can be miniaturized. It becomes possible to change.

FIG. 11 is a diagram showing a configuration example of a power conversion device according to an embodiment including a voltage smoothing circuit. The power conversion device 1 shown in FIG. 11 is a device that converts the input power supplied from the power supply 2 into the output power supplied to the load 3. The power conversion device 1 includes a voltage smoothing circuit 100 according to the present disclosure, and a conversion circuit 300 that converts direct current output from the voltage smoothing circuit 100 into direct current or alternating current.

The power conversion device 1 is, for example, a device that converts the DC power supplied from the power supply 2 into the DC power supplied to the load 3. In this case, the voltage smoothing circuit 100 smoothes the DC voltage supplied from the power supply 2. The conversion circuit 300 converts the DC voltage smoothed by the voltage smoothing circuit 100 into a DC voltage applied to the load 3. Specific examples of the conversion circuit 300 in this case include a chopper circuit, an isolated DC / DC converter circuit, and the like.

The power conversion device 1 may be a device that converts the DC power supplied from the power supply 2 into AC power supplied to the load 3. In this case, the voltage smoothing circuit 100 smoothes the DC voltage supplied from the power supply 2. The conversion circuit 300 converts the DC voltage smoothed by the voltage smoothing circuit 100 into an AC voltage applied to the load 3 of the motor or the like. Specific examples of the conversion circuit 300 in this case include an inverter circuit and the like.

The power conversion device 1 may be a device that converts AC power supplied from the power source 2 into AC power or DC power supplied to the load 3. In this case, the power conversion device 1 includes a rectifier circuit (not shown) that converts alternating current supplied from the power supply 2 into direct current between the power supply 2 and the voltage smoothing circuit 100.

Although the voltage smoothing circuit and the power conversion device have been described above by the embodiment, the present invention is not limited to the above embodiment. Various modifications and improvements, such as combinations and substitutions with some or all of the other embodiments, are possible within the scope of the present invention.

For example, the pair of wirings that supply the DC voltage is not limited to the power supply line, and may be wirings used for other purposes such as a voltage monitor line for monitoring the DC voltage. The capacitor is not limited to the electrolytic capacitor, and may be another type of capacitor.

1 Power converter 11 1st capacitor 12 2nd capacitor 21 1st resistor 22 2nd resistor 23 3rd resistor 30 Detection circuit 40 Midpoint 51 1st connection point 52 2nd connection point 60 Switching circuit 61 1st switch 62 2nd switch 91 1st wiring 92 2nd wiring 100, 101, 102, 103, 104, 200 Voltage smoothing circuit 300 Conversion circuit

Claims (12)

A voltage smoothing circuit that smoothes the DC voltage between the first wiring and the second wiring having a lower potential than the first wiring.
A plurality of capacitors connected in series between the first wiring and the second wiring,
A plurality of resistors connected in parallel to the plurality of capacitors and connected in series between the first wiring and the second wiring, and
A detection circuit that detects the imbalance of the voltage applied to each of the plurality of capacitors, and
With a switching circuit,
The plurality of capacitors include a first capacitor and a second capacitor connected in series on the side of the second wiring of the first capacitor.
The plurality of resistors are on the side of the first resistor, the second resistor connected in series to the side of the second wiring of the first resistor, and the second wiring of the second resistor. Including a third resistor connected in series
In the switching circuit, the connection destination of the midpoint between the first capacitor and the second capacitor is set between the first resistor and the second resistor according to the detection result of the imbalance. A voltage smoothing circuit that switches between a first connection point and a second connection point between the second resistor and the third resistor. When the switching circuit detects a first unbalanced state in which the voltage applied to the first capacitor is higher than the voltage applied to the second capacitor, the connection destination of the midpoint is changed to the second connection point. The voltage smoothing circuit according to claim 1, wherein the voltage smoothing circuit is switched from the first connection point to the first connection point. The first unbalanced state is a state in which the voltage difference obtained by subtracting the voltage applied to the second capacitor from the voltage applied to the first capacitor is larger than the first deviation.
The switching circuit claims that when the first unbalanced state is detected in a state where the connection destination of the midpoint is switched to the second connection point, the connection destination of the midpoint is switched to the first connection point. Item 2. The voltage smoothing circuit according to Item 2. When the switching circuit detects a second unbalanced state in which the voltage applied to the second capacitor is larger than the voltage applied to the first capacitor, the connection destination of the midpoint is changed to the first connection point. The voltage smoothing circuit according to any one of claims 1 to 3, which switches from the second connection point to the second connection point. The second unbalanced state is a state in which the voltage difference obtained by subtracting the voltage applied to the first capacitor from the voltage applied to the second capacitor is larger than the second deviation.
The switching circuit claims that when the second unbalanced state is detected in a state where the connection destination of the midpoint is switched to the first connection point, the connection destination of the midpoint is switched to the second connection point. Item 4. The voltage smoothing circuit according to Item 4. The voltage smoothing circuit according to any one of claims 1 to 5, wherein the resistance value of the second resistor is smaller than the resistance value of the first resistor and smaller than the resistance value of the third resistor. .. The voltage smoothing circuit according to claim 6, wherein the resistance value of the third resistor is equal to the resistance value of the first resistor. The voltage smoothing circuit according to any one of claims 1 to 7, wherein the detection circuit detects the imbalance by detecting a current flowing into or out of the midpoint. The detection circuit detects the imbalance by comparing the voltage applied to the first capacitor with the voltage applied to the second capacitor, according to any one of claims 1 to 7. The voltage smoothing circuit described. When the DC voltage is Edc, the resistance value of the first resistor is R21, the resistance value of the second resistor is R22, and the resistance value of the third resistor is R23.
It is provided with a voltage dividing circuit that divides the DC voltage into a voltage higher than (Edc × R23 / (R21 + R22 + R23)) and outputs the voltage.
The voltage smoothing circuit according to any one of claims 1 to 7, wherein the detection circuit detects the imbalance by comparing the output voltage of the voltage dividing circuit with the voltage of the second connection point. .. The voltage smoothing circuit according to claim 10, wherein the output voltage of the voltage divider circuit is half the voltage of the DC voltage. A power conversion device comprising the voltage smoothing circuit according to any one of claims 1 to 11 and a conversion circuit for converting direct current output from the voltage smoothing circuit into direct current or alternating current.

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