JP2006042498A - Power conversion apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a power conversion apparatus that produces low loss during operation and is thus excellent in conversion efficiency, is short in heat radiation time until its voltage drops to a safe voltage after its operation is stopped, and is small is size. <P>SOLUTION: The power conversion apparatus is constructed of: a power converter 25 that is placed between a direct-current power source 10 and an alternating-current load 15 and includes a switching element subjected to switching for power conversion; a smoothing capacitor 30 that is placed on the direct current side of the power converter and suppresses power supply ripples due to switching; and a discharging resistor 35 that is connected with the smoothing capacitor for discharging the electric charges in the smoothing capacitor and has a resistance value that is low when applied voltage is low and is increased with increase in applied voltage. When high voltage is applied to the discharging resistor, its resistance value is increased and loss is suppressed. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a power conversion device, and more particularly, to an improved discharge resistance for discharging a charge of a smoothing capacitor that suppresses power supply ripple.

  One type of power converter is an inverter device. As shown in FIG. 17, the inverter device is arranged between a DC power supply 180 and an AC load 182 and converts DC power into AC power. An inverter 185 including a switching element 184 that converts DC power into AC power; And a smoothing capacitor 186 that is disposed on the input side thereof and suppresses power supply ripple during switching.

Further, a discharge resistor 188 is provided for safety when an operator performs maintenance when the inverter 185 is stopped. In order to prevent the operator from receiving an electric shock due to the high charge stored in the smoothing capacitor 185 during the operation of the inverter 185, the discharge resistor 188 discharges it within a certain time before work. As the discharge resistor 188, a resistor having a constant resistance value is used.
JP 2003-333859 A

  The above conventional example has the following problems. First, the loss of the discharge resistor 188 during the operation of the inverter 185 is large, which hinders power conversion with high efficiency. Further, since the loss (heat generation) is large, it is necessary to increase the size of the discharge resistance in order to keep the temperature of the discharge resistance below its allowable value. Since the loss is inversely proportional to the resistance value, the loss can be reduced by increasing the resistance value of the discharge resistor 188. However, when the resistance value is increased, the time (discharge time) until the smoothing capacitor 186 is lowered to a work-safe voltage after the inverter 185 is switched off or the like is increased. If the operator touches the same potential portion of the smoothing capacitor 186 while the voltage does not drop sufficiently, there is a risk of electric shock.

  Second, the heat generated during operation of the inverter 185 restricts the arrangement of peripheral components. If peripheral components are arranged in consideration of heat generation, downsizing of the inverter is hindered, and the overall size of the inverter device is increased.

  The present invention has been made in view of the above circumstances, and since the loss during operation is small, the conversion efficiency is good, and the heat dissipation time until the voltage drops to a safe voltage after the operation is stopped is short, and the power conversion is small in size. An object is to provide an apparatus.

  The inventor of the present application has earnestly researched a method for satisfying the above three requirements which are not compatible with each other, that is, the loss is minimized as much as possible during operation, the discharge time is reduced to a safe voltage after stopping, and the size is small. . As a result, the inventors have come up with the idea of changing the resistance value in accordance with the voltage applied to the discharge resistance, thereby completing the present invention.

  The power conversion device according to the present invention comprises, as described in claim 1, at least one power converter including a switching element disposed between a power source and a load and switched for power conversion, and power ripple caused by switching And at least one smoothing capacitor that is connected to the smoothing capacitor in order to discharge the electric charge of the smoothing capacitor, and at least one discharge resistor that has a resistance value that increases as the applied voltage decreases with a low applied voltage. In this power conversion device, when a high voltage is applied to the discharge resistor, its own resistance value increases and the loss is suppressed.

  According to the power conversion device of the present invention, when a high voltage is applied, the resistance value of the discharge resistor is high and the amount of heat generated is small, so that loss is suppressed and the efficiency of power conversion increases. In addition, since the resistance value of the discharge resistor is low when a low voltage is applied, the amount of heat radiation is large and heat is dissipated quickly, and the time until the smoothing capacitor falls to a safe voltage is shortened. Furthermore, since a large resistance can be obtained when a high voltage is applied without increasing the size of the discharge resistance, the size of the power converter can be reduced.

  According to the power conversion device of the second aspect, the above effect can be obtained in a power conversion device including one power converter, such as a DC-DC converter. According to the power converter of the third aspect, the above effect can be obtained in a power converter including two power converters such as a DC-DC converter and a DC-AC converter.

  According to the power converter of claim 4, the power source is a DC power source, the upstream first power converter is a DC-DC converter, the downstream second power converter is a DC-AC converter, and the load is AC. In the case of a load, the conversion efficiency can be increased, the discharge time can be shortened, and the discharge resistance and thus the power converter can be downsized. According to the power converter of claim 5, the power source is a DC power source, the upstream first power converter is a DC-AC converter, the downstream second power converter is an AC-DC converter, and a transformer is provided therebetween. When the load is a DC load, the conversion efficiency can be increased, the discharge time can be shortened, and the discharge resistance and thus the power converter can be downsized.

  According to the power conversion device of the sixth aspect, since the smoothing capacitor is arranged on the DC side of the power converter that is easily affected by the power supply ripple at the time of switching, the power supply ripple can be effectively suppressed. According to the power conversion device of the seventh aspect, since the heat radiation resistor is composed of a general-purpose PTC thermistor, a predetermined temperature resistance value characteristic can be realized at low cost. According to the power converter of the eighth aspect, since the discharge resistor is disposed in the vicinity of the smoothing capacitor, the electric charge of the smoothing capacitor is easily and reliably discharged.

  According to the power conversion device of the ninth aspect, since the discharge resistance is composed of two or more PTC thermistors connected in series, even if one fails, if the other is normal, it does not fail as a whole and is safe.

  According to the power conversion device of the tenth aspect, the high frequency removing capacitor absorbs the high frequency voltage of the switching element, and the action of the discharge resistance is stabilized. According to the power converters of the eleventh and twelfth aspects, when the PTC thermistor fails, the power converter is stopped to prevent the influence of the PTC thermistor failure from affecting the entire power converter.

<Power conversion device>
The power conversion device of the present invention is arranged between a power source and a load, and can be roughly divided into two types according to the type of power source and load, the type and number of power converters, and the second type further includes a plurality of types. Can be classified into types. Note that power conversion means changing electrical characteristics such as current and voltage, and the magnitude of power is ideally unchanged.

(B) First Type A first type of power conversion device includes any one of a DC-DC converter, a DC-AC converter (reverse converter), or an AC-DC converter (forward converter). 2). Specific examples include a DC-DC converter (DC chopper, type a) that boosts or decreases DC power, an inverter (b type) that converts DC to AC, and a rectifier (c type) that converts AC to DC. .

(B) Second type The second type power converter is a case where any two or more of a DC-DC converter, a DC-AC converter, and an AC-DC converter are connected (see claim 3). ). For example, the upstream first power converter is a DC-DC converter, the downstream second power converter is a DC-AC converter (e-type, see claim 4), and the upstream first power converter. Is a DC-AC converter, the downstream second power converter is an AC-DC converter (f type), the first power converter is an AC-DC converter, and the second power converter is DC-AC. A converter (g-type) is included. The power source is a DC power source for the e type and the f type, and an AC power source for the g type. The load is an AC load for the e-type and the g-type, and a DC load for the f-type.

  In some cases, the two power converters are connected via a device other than the power converter (h-type). For example, this corresponds to a DC-DC converter in which an upstream DC-AC converter and a downstream AC-DC converter are connected by a transformer (see claim 5). In this case, the power source is a DC power source, the load is a DC load, and is accompanied by step-up / step-down in the transformer.

<Smoothing capacitor>
The smoothing capacitor suppresses power supply ripple generated when the switching element of the power converter is switched, and is disposed on the DC side of the power converter. The direct current side includes the input side and the output side of the power converter. Specifically, the first type a-type (DC-DC converter) is arranged on the input side and output side, the b-type (DC-AC converter) is arranged on the input side, and c-type (AC-DC conversion). Device) on the output side.

  The smoothing capacitor is the input side of the DC-DC converter or between the DC-DC converter and the DC-AC converter in the second type e type, and the input side of the DC-AC converter or the AC-DC type in the f type. On the output side of the converter, in the g type, it is arranged between the AC-DC converter and the DC-AC converter. In h type, it is arranged on the input side of the DC-AC converter or on the outlet side of the AC-DC converter.

<Discharge resistance>
(B) General The discharge resistor discharges the electric charge of the smoothing capacitor. In any of the above types, it is desirable to reduce the loss of the discharge resistance as much as possible during the operation of the power converter and as much as possible after the stop. Since the magnitude of the resistance value and the loss are inversely proportional (W = V ² / R), in the present invention, the resistance value of the discharge resistance is increased at a high applied voltage and decreased at a low applied voltage.

As a discharge resistor having such characteristics, for example, a PTC (positive temperature coefficient) thermistor can be used (see claim 6). In the PTC thermistor, Y ₂ 0 ₃ or the like is added to BaTiO ₃ and a part of Ba is replaced with Sr or Pb so as to have a specific Curie temperature. It has the characteristic that itself generates heat and changes its resistance value when voltage is applied.

(B) Location of Discharge The discharge resistor is disposed at a position where the charge of the smoothing capacitor is discharged, that is, generally in the vicinity of the smoothing capacitor (refer to claim 8), and one end and the other end of the smoothing capacitor are disposed on one electrode plate side and the other electrode. Connected to the board side. Specifically, if the withstand voltage varies depending on the applied high frequency, the discharge resistor may be placed at a position that is equal to or lower than the high frequency withstand voltage. For this purpose, a smoothing capacitor is placed upstream of the power converter. In addition, even in the case of being arranged on the downstream side, it is desirable to arrange it near the smoothing capacitor and closer to the smoothing capacitor than the switching element of the power converter.

For example, when the smoothing capacitor is arranged on the upstream side of the power converter, the distance between the discharge resistance and the upstream smoothing capacitor is L ₁ when the distance between the discharge resistance and the downstream power converter or the like is L _1. is the L _1/5 or less. This is because it is easily affected by a surge voltage (high frequency voltage) generated in the power converter at the time of switching, and the characteristic changes as the frequency increases, and the resistance value tends to decrease. Incidentally, if the smoothing capacitor is disposed on the downstream side of the power converter, discharge resistance when the distance between the upstream side of the smoothing capacitor and L _2, the discharge resistor and smoothing capacitor upstream of the power converter or the like The distance is 5L ₂ or more.

(C) Number and failure detection One PTC thermistor may be used as a heat dissipation resistor, but two PTC thermistors may be connected in series between a pair of plates of a smoothing capacitor (see claim 9). In this way, even if the first heat radiation resistor on the high-level wiring side fails (short circuit), the second heat radiation resistor on the low-level wiring side is present, so that the short circuit as a whole is safe. Moreover, when the 1st heat radiation resistor fails, the presence or absence of a failure can be determined by detecting the applied voltage with the second heat radiation resistor, a failure signal can be output as necessary, and the power converter can be stopped ( (See claims 11 and 12).

<High frequency rejection capacitors and relays>
A high frequency removing capacitor can be connected in parallel with one or more PTC thermistors (refer to claim 10). This capacitor removes (absorbs) the high-frequency voltage generated in the switching element, and stabilizes the action of the discharge resistance.

  In general, a relay (electromagnetic switch) is provided between the power source and the smoothing capacitor. For example, in the high-level wiring extending between the positive terminal of the DC power supply and the power converter, the power converter is turned on and off by being arranged upstream of the smoothing capacitor and the heat radiation resistor.

  Embodiments of the present invention will be described below with reference to the accompanying drawings.

<First embodiment>
This is a case where the present invention is applied to an inverter device including an inverter.

(Constitution)
As shown in FIG. 1, an inverter device 20 is arranged between a vehicle-mounted battery (DC power supply) 10 and a three-phase AC motor (AC load) 15. This inverter device 20 includes an inverter 25 and a smoothing capacitor 30 and a PTC thermistor 35 arranged on the input side thereof. As is well known, the power conversion unit 25 is configured by arranging three pairs (six in total) of a pair of switching elements (not shown) arranged in series between the high level wiring 21 and the low level wiring 22. Switching elements (for example, IGBTs) are controlled and controlled by a control circuit (not shown), and feedback diodes are connected in antiparallel to each switching element.

  As shown in FIGS. 2, 3, and 4, the smoothing capacitor 30 includes a pair of electrode plates 32a and 32b and a pair of bus bars 31a and 31b. One electrode plate 32a is connected to the high level wiring 21 and the other electrode plate 32b is connected to the low level wiring 22 via the bus bars 31a and 31b.

  A PTC thermistor (hereinafter referred to as “thermistor” in the embodiment) 35 disposed on the downstream side of the smoothing capacitor 30 is accommodated in a case 37, and one electrode plate 32 a and the other electrode of the capacitor 30 are connected by a pair of lead wires 36 a and 36 b. It is connected to the plate 32b. In FIG. 1, the distance between the capacitor 30 and the inverter 25 is about 150 mm, and the distance between the capacitor 30 and the thermistor 35 is about 10 mm.

  Next, the characteristics of the thermistor 35 will be described with reference to FIGS. As shown in FIG. 5, the thermistor 35 changes its own temperature by the voltage applied thereto, and the resistance value changes according to the change in temperature. As shown by the curve a in FIG. 6, in the case of 0 Hz (direct current), when the temperature is lower than 150 ° C., the resistance value is relatively small and the magnitude thereof does not vary much, but when the temperature exceeds 200 ° C., it suddenly increases. To rise.

  Further, the resistance value of the thermistor 35 changes according to the frequency of the voltage applied thereto. In FIG. 6 showing the relationship between the temperature and the resistance component using the frequency as a parameter, the direct current is a curve a, the curve is 1 kHz, the curve b is 10 kHz, the curve c is 100 kHz, and the curve d is 100 kHz. The case of 1 MHz is indicated by a curve e.

  In the case of direct current, the resistance value is large, and the resistance value decreases as the frequency increases. It can be seen that the resistance value decreases as a high-frequency voltage is applied. Since the high frequency voltage is generated by the switching element, the distance from the inverter 25 to the thermistor 35 becomes a problem.

  In FIG. 7, the waveform of the switching voltage applied to the discharge resistor 35 was examined when the discharge resistor 35 was disposed at the intersection m between the high-level wiring 21 and the wiring 23a and when it was disposed halfway through the high-level wiring 21. As a result, as shown in FIG. 8A, the generated surge voltage V1 is relatively low in the former case. On the other hand, as shown in FIG. 8B, it was found that the surge voltage V2 generated in the latter case was relatively high.

  It can be seen that the surge voltage generated in the discharge resistor 35 due to the switching of the switching element is less affected when it is far from the inverter 25, in other words, closer to the smoothing capacitor 30. This is considered because the surge voltage is absorbed by the high-level wiring 21 and the low-level wiring 22 and the parasitic inductance I existing in the wirings 23a and 23b of the smoothing capacitor 30 in FIG.

(Function)
Next, the operation of this embodiment will be described.

a. During operation When the inverter 25 is operated by the control circuit, the switching element is switched to convert the DC power of the in-vehicle battery 10 into AC power and drive the three-phase AC motor 15. At that time, the smoothing capacitor 30 smoothes the power supply ripple generated in the switching element.

  At this time, a voltage is also applied to the thermistor 35 disposed in the vicinity of the smoothing capacitor 30, and the temperature rises. Accordingly, the resistance value of the thermistor 35 increases (see FIG. 5), the current consumption is reduced, and the loss is suppressed.

b. After the stop, when the operation of the inverter 25 is stopped by the control circuit, the charge stored in the smoothing capacitor 30 is discharged from the thermistor 35. As the discharge progresses, the voltage applied to the thermistor 35 decreases and the temperature decreases. Along with this, the resistance value decreases (see FIG. 5) and discharges more rapidly than a conventional constant resistor (a resistor having a constant resistance value even when the voltage changes).

(effect)
According to this embodiment, the following effects can be obtained. First, the conversion efficiency of direct current power into alternating current power during operation in which a high voltage is applied to the inverter 25 increases. This is because the resistance value of the thermistor 35 increases and the loss of the thermistor 35 during the operation of the inverter 25 decreases. In relation to the first effect, secondly, since the thermal influence on the peripheral device during operation of the inverter 25 is reduced, peripheral components can be arranged near the inverter 25, and the size of the entire inverter device is reduced.

  Third, after the operation of the inverter 25 stops, the time (discharge time) until the smoothing capacitor 30 drops to a safe voltage is shortened. As a result, the time until the smoothing capacitor 30 is discharged to a safe voltage is shortened. This is because the resistance value of the thermistor 35 after stopping is small and discharges in a short time.

  Fourth, the first to third effects are obtained by the thermistor 35 having a small size, and the inverter device can be miniaturized. This is because the resistance value of the thermistor 35 increases as the temperature rises, so it is not necessary to increase the discharge resistance in order to increase the resistance value and suppress the amount of heat generation.

<Modification>
FIG. 9 shows a first modification of the first embodiment. In the first modification, a relay 45 is inserted between the DC power supply 10 and the smoothing capacitor 30 in the high-level wiring 21 extending from the DC power supply 10 to the inverter 25.

  In the second modification of the first embodiment shown in FIG. 10, a high frequency removing capacitor 48 is connected in parallel with the PTC thermistor 35. The high frequency removing capacitor 48 removes (absorbs) the high frequency voltage generated by the switching element, and stabilizes the operation of the PTC thermistor 35.

<Second embodiment>
The power conversion apparatus of the second embodiment shown in FIG. 11 includes an upstream DC-DC converter (DC chopper) 50 connected to a DC power supply 51 and a downstream DC-AC conversion connected to an AC load 54. Device (inverter) 53. The DC chopper 50 boosts or lowers the direct current power, and the inverter 53 converts the stepped up / down direct current into alternating current and outputs it to the alternating current load 54. A smoothing capacitor 56 is disposed between the DC chopper 50 and the inverter 53, and one PTC thermistor 58 is inserted in the vicinity of the smoothing capacitor 56.

  In the second embodiment, the smoothing capacitor 56 smoothes the power ripple generated in the DC chopper 50 and the switching elements in the inverter 53, and the PTC thermistor 58 increases its own resistance value and suppresses the loss. According to the second embodiment, in the power converter including the DC chopper 50 and the inverter 53, basically the same effects as the first to fourth effects of the first embodiment can be obtained.

<Modification>
In the modification of the second embodiment shown in FIG. 12, a relay 63 is inserted between high-level wirings 61 extending from the DC power source 51 to the DC-DC converter 50. This relay 63 has the same function as the relay 45 of the modified example of the first embodiment.

<Third embodiment>
The power converter of the third embodiment shown in FIG. 13 includes an upstream inverter 70 connected to a DC power supply 71, a downstream rectifier 72 connected to a DC load 73, and a transformer 75 therebetween. . The inverter 70 converts direct current into alternating current, and the rectifier 72 converts alternating current into direct current. The transformer 75 boosts or steps down AC power. A smoothing capacitor 77 is disposed on the outlet side of the rectifier 73, and one PTC thermistor 78 is inserted in the vicinity of the smoothing capacitor 77.

  In this third embodiment, the smoothing capacitor 77 smoothes the power ripple generated after rectification by the rectifier 72, and the PTC thermistor 78 increases its own resistance value and suppresses the loss. According to the third embodiment, in the power conversion device (DC-DC converter) including the inverter 70, the transformer 75, and the rectifier 72, basically the same effects as the first to fourth effects of the first embodiment. Is obtained.

<Modification>
In the modification of the third embodiment shown in FIG. 14, two PTC thermistors 82 and 84 connected in series instead of the PTC thermistor 78 constitute a discharge resistor. In the first embodiment and the second embodiment, the discharge resistance can be configured by two PTC thermistors connected in series.

  Since the resistance value R1 of the first PTC thermistor 82 and the resistance value R2 of the second PTC thermistor 84 are equal, the voltage V2 at both ends of the second PTC thermistor 84 is 1 of the potential V1 between the high level wiring 86 and the low level wiring 87 in the normal state. / 2. FIG. 16A shows the open failure of the first PTC thermistor 82, where V2 = V1. Therefore, if the upper threshold value Vb = V1 × 3/4 and the lower threshold value Va = V1 × 1/4, the voltage V2 across the second PTC thermistor 84 is larger than Vb as indicated by S1 in FIG. An open failure of the first PTC thermistor 82 can be detected at S2. In this case, a failure signal is output in S2. When the first PTC thermistor 82 is short-circuited, V2 is smaller than Va as shown in FIG. 16B, so that the failure can be detected. In any case, malfunction can be prevented by stopping the power conversion device based on the failure signal as necessary.

It is circuit explanatory drawing which shows the Example (inverter apparatus) of this invention. It is a perspective view which shows the smoothing capacitor and PTC thermistor of an Example. It is connection explanatory drawing of a smoothing capacitor and discharge resistance. It is a detailed view of a PTC thermistor. It is a graph which shows the temperature-resistance characteristic of a PTC thermistor. It is a graph which shows the frequency characteristic of a PTC thermistor. It is explanatory drawing of the parasitic inductance which exists in wiring. (A) And (b) is a graph which shows the relationship between the switching voltage which generate | occur | produces in the specific part on wiring, and time. It is circuit explanatory drawing which shows the 1st modification of 1st Example. It is explanatory drawing which shows the 2nd modification of 1st Example. It is explanatory drawing which shows 2nd Example of this invention. It is circuit explanatory drawing which shows the modification of 2nd Example. It is circuit explanatory drawing which shows 3rd Example of this invention. It is circuit explanatory drawing which shows the modification of 3rd Example. It is operation | movement explanatory drawing of the modification of 3rd Example. (A) And (b) is operation | movement explanatory drawing of the modification of 3rd Example. It is circuit explanatory drawing which shows a prior art example.

Explanation of symbols

10: DC power supply 15: AC load 20: Power converter 25: Power converter 30: Smoothing capacitor 35: Discharge resistance

Claims (12)

At least one power converter including a switching element disposed between the power source and the load and switched for power conversion;
At least one smoothing capacitor that suppresses power ripple caused by switching;
At least one discharge resistor connected to the smoothing capacitor for discharging the charge of the smoothing capacitor and having a resistance value that increases with decreasing applied voltage and increasing applied voltage;
A power conversion device comprising:   The power converter according to claim 1, wherein the power converter is any one of a DC-DC converter, a DC-AC converter, and an AC-DC converter. The power converter according to claim 1, wherein the power converter is two or more of a DC-DC converter, a DC-AC converter, or an AC-DC converter.   The power converter according to claim 3, wherein the first power converter on the upstream side is a DC-DC converter, and the second power converter on the downstream side is a DC-AC converter.   The power converter according to claim 3, wherein the first power converter on the upstream side is a DC-AC converter, the second power converter on the downstream side is an AC-DC converter, and a transformer is disposed in the middle.   The power converter according to claim 2, 3, 4, or 5, wherein the smoothing capacitor is disposed on a direct current side of the power converter.   The power converter according to claim 6, wherein the discharge resistor is a PTC thermistor.   The power converter according to claim 7, wherein the discharge resistor is disposed in the vicinity of the smoothing capacitor.   The power converter according to claim 6, wherein the discharge resistor includes at least two PTC thermistors connected in series arranged in the vicinity of the smoothing capacitor.   The power converter according to claim 8 or 9, wherein a high frequency removing capacitor is connected in parallel with the PTC thermistor.   The power converter according to claim 10, wherein an applied voltage of the PTC thermistor is extracted as a signal, and whether or not there is a failure of the PTC thermistor is determined based on the signal.   The power conversion device according to claim 11, wherein a failure signal is output at the time of the failure determination, and the power conversion device is stopped as necessary.

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