JP2009060691A - Inverter apparatus and its design method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inverter apparatus in which a ceramic capacitor is used as a smoothing capacitor and which cannot easily results in thermal runaway. <P>SOLUTION: A switching circuit 3 for switching DC current to AC current is connected between a DC power supply 2 and a load 5 connected to the DC power supply 2. The DC power supply 2 is connected to the smoothing ceramic capacitor 4 in parallel for suppressing ripple current caused with switching in the switching circuit 3. A frequency of AC current in the switching circuit 3, electrostatic capacity of the smoothing ceramic capacitor 4 and an inductance component of an inductance 6 are set in the inverter apparatus 1 so that a resonance frequency f0 decided by electrostatic capacity and inductance I of the smoothing ceramic capacitor 4 becomes higher than a frequency f1 of ripple current in an assumed use temperature range of the inverter apparatus 1 in which inductance 6 by wiring between the DC power supply 2 and the smoothing ceramic capacitor 4 exists. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an inverter device to which a large load such as a motor of a hybrid vehicle is connected, and more particularly, to suppress a ripple caused by switching in a switching means for switching a direct current to an alternating current. The present invention relates to an inverter device provided with a capacitor and a design method thereof.

  Inverter circuits are widely used to switch direct current to alternating current. Among inverter circuits, inverter circuits to which a large load such as a motor of a hybrid vehicle is connected have a high rated voltage of 100 V or higher, a large ripple current of 10 Arms or more, and a use temperature range from room temperature to 125 ° C. or higher. It reaches the area.

  FIG. 7 is a circuit diagram showing a conventional inverter device. In the inverter device 101, a switching circuit 103 for switching a direct current supplied from the direct current power source 102 to an alternating current is connected to the direct current power source 102. A load 105 is connected to the switching circuit 103. A smoothing capacitor 104 is connected in parallel to the DC power supply 102 in order to suppress ripples that occur as the switching circuit 103 switches from DC to AC. The inductance 106 is an inductance component due to wiring.

  When the load connected to the inverter circuit is large like the motor of the hybrid vehicle described above, an aluminum electrolytic capacitor or a film capacitor is used as the smoothing capacitor, for example, as described in Patent Document 1 below. It has been.

On the other hand, multilayer ceramic capacitors have been widely used as capacitors in order to reduce the size of electronic devices and circuits. In the multilayer ceramic capacitor, since the allowable ripple current per unit volume is large, the miniaturization can be promoted. In addition, as described in Patent Document 2 below, since it is excellent in heat resistance, maintainability, and surge suppression effect, it is said that the multilayer ceramic capacitor can meet the market demand for the inverter system. ing.
JP 2004-21533 A JP 2002-335688 A

  In the aluminum electrolytic capacitor and the film capacitor described in Patent Document 1, since the allowable ripple current per unit volume is small, there is a problem that the occupied volume of the capacitor in the system including the inverter device is increased. In general, these capacitors are not sufficiently high in heat resistance and surge suppression effect.

  On the other hand, in the multilayer ceramic capacitor, since the allowable ripple current per unit volume is large, the size can be reduced. The multilayer ceramic capacitor is also excellent in heat resistance and surge suppression effect.

  However, in the multilayer ceramic capacitor, when the temperature rises, the capacitance decreases, and the capacitance reduction ratio varies depending on the magnitude of the DC bias voltage. For this reason, it is not a problem when the current used is small, but in applications where a large current flows, the multilayer ceramic capacitor compared to the aluminum electrolytic capacitor or film capacitor, such as the change of the resonance frequency accompanying the change of the circuit constant, etc. It was necessary to pay attention to the overcurrent generation requirement.

  The object of the present invention is suitable for applications in which a large current flows in view of the above-described state of the prior art, and has a large capacitance and permissible ripple current per unit volume. An object of the present invention is to provide a highly reliable inverter device and a method for designing the same that are unlikely to cause thermal runaway even when the temperature of the capacitor rises.

  DC power source, a load connected to the DC power source so that power is supplied by the DC power source, and a DC current supplied from the DC power source, connected between the DC power source and the load. Switching means for switching to an alternating current, a smoothing ceramic capacitor connected in parallel to the direct current power source, the direct current power source, And an inductance component existing between the smoothing ceramic capacitor and an electrostatic capacity and the inductance of the smoothing ceramic capacitor based on a frequency of the ripple current in an assumed operating temperature range of the inverter device. The LC resonance frequency determined by the inductance of the component will be higher , The frequency of the alternating current in said switching means, characterized in that the inductance of the capacitance and the inductance component of the ceramic capacitor wherein smoothing is set, the inverter device is provided.

  According to the second invention of the present application, the DC power source, the load connected to the DC power source, and the DC power source and the load are connected so that electric power is supplied from the DC power source. A switching means for switching a direct current supplied from the direct current power supply to an alternating current, and a smoothing device connected in parallel to the direct current power supply in order to suppress a ripple current generated by the switching in the switching means. An inverter device comprising a ceramic capacitor, the DC power source, and an inductance component existing between the smoothing ceramic capacitor, wherein the smoothing is performed from the ripple current frequency in an assumed operating temperature range of the inverter device. L determined by the capacitance of the ceramic capacitor and the inductance of the inductance component The frequency of the alternating current in the switching means so that the resonance frequency is lowered and the time differential value of the temperature rise is negative and the absolute value thereof gradually decreases in the time course of the temperature rise of the ceramic capacitor. An inverter device is provided in which an electrostatic capacitance of the smoothing ceramic capacitor and an inductance of the inductance component are set.

  Moreover, 3rd invention of this application is connected between the direct-current power supply, the load connected to the direct-current power supply, and the direct-current power supply and the load so that electric power may be supplied by the direct-current power supply. A switching means for switching a direct current supplied from the direct current power supply to an alternating current, and a smoothing device connected in parallel to the direct current power supply in order to suppress a ripple current generated by the switching in the switching means. A design method for an inverter device comprising a ceramic capacitor, the DC power supply, and an inductance component existing between the smoothing ceramic capacitor, wherein the frequency of the ripple current is within an assumed operating temperature range of the inverter device. The capacitance of the smoothing ceramic capacitor and the inductance of the inductance component A method for designing an inverter device, wherein the frequency of the alternating current in the switching means, the capacitance of the smoothing ceramic capacitor, and the inductance of the inductance component are determined so that a fixed LC resonance frequency is increased. It is.

  4th invention of this application is connected between the direct-current power supply, the load connected to the direct-current power supply, and the direct-current power supply and the load so that electric power may be supplied by the direct-current power supply, Switching means for switching a direct current supplied from a direct current power supply to an alternating current, and a smoothing ceramic capacitor connected in parallel to the direct current power supply in order to suppress a ripple current generated by the switching in the switching means And an inverter device design method comprising an inductance component present between the DC power source and the smoothing ceramic capacitor, in the assumed operating temperature range of the inverter device, from the frequency of the ripple current, Determined by the capacitance of the smoothing ceramic capacitor and the inductance of the inductance component The alternating current in the switching means is such that the LC resonance frequency becomes lower and the time differential value of the temperature rise is negative and its absolute value gradually decreases in the time course of the temperature rise of the ceramic capacitor. The design method of the inverter device is characterized in that the frequency of the smoothing ceramic capacitor and the inductance of the inductance component are determined.

  In the present invention (the first to fourth inventions are collectively referred to as the present invention hereinafter), a motor for an automobile is used as the load. In that case, a relatively large current flows through the inverter device, or Even in this case, the inverter device can be reduced in size according to the present invention, and failure due to thermal runaway is unlikely to occur.

  According to the first and third inventions of the present application, the frequency of the alternating current in the switching means, the capacitance of the smoothing ceramic capacitor, and the inductance of the inductance component are adjusted, and in the assumed operating temperature range of the inverter device, the above The LC resonance frequency determined by the capacitance of the smoothing ceramic capacitor and the inductance of the inductance component is set higher than the frequency of the ripple current. Therefore, when the temperature of the smoothing ceramic capacitor rises, the absolute value of the impedance Z in the closed loop circuit composed of the DC power source and the smoothing ceramic capacitor connected in parallel to the DC power source increases, The current that flows through the ceramic capacitor is reduced. As a result, the temperature rise of the smoothing ceramic capacitor is moderated and thermal runaway is unlikely to occur. That is, the temperature of the smoothing ceramic capacitor converges to a certain temperature, and the magnitude of the current flowing through the smoothing ceramic capacitor is also stabilized.

  In the second and fourth inventions of the present application, the frequency of the alternating current in the switching means, the capacitance of the smoothing ceramic capacitor, and the inductance of the inductance component are adjusted, and the frequency of the ripple current in the assumed operating temperature range is adjusted. However, the LC resonance frequency determined by the capacitance of the smoothing ceramic capacitor and the inductance of the inductance component is lowered, and the time differential value of the temperature rise is negative in the time course of the temperature rise of the smoothing ceramic capacitor. The absolute value is set to gradually decrease. Accordingly, the magnitude of the impedance of the closed loop circuit composed of the DC power source and the smoothing ceramic capacitor connected in parallel to the DC power source becomes smaller as the temperature of the smoothing ceramic capacitor rises. As a result, the current flowing through the smoothing ceramic capacitor increases, and the temperature of the smoothing ceramic capacitor rises.

  However, since the time differential value of the temperature rise is negative and its absolute value gradually decreases, the temperature rise of the smoothing ceramic capacitor is saturated over time, and the temperature of the smoothing ceramic capacitor is almost stabilized. It becomes. Accordingly, in the second invention as well, since the temperature of the smoothing ceramic capacitor is stabilized, the current flowing through the smoothing ceramic capacitor is also stabilized, and thermal runaway does not occur.

  As described above, in any of the first, third, and second and fourth inventions, for example, a motor for a hybrid vehicle is connected as a load, and even if a large current flows, smoothing is performed. Thermal runaway due to ceramic capacitor temperature rise is unlikely to occur. Therefore, the reliability and safety of the inverter device can be improved.

  In addition, in the present invention, since the smoothing ceramic capacitor is used as the smoothing capacitor, the allowable ripple current per unit volume is large and the capacitance per unit volume is large. Therefore, it is possible to reduce the size of the system including the inverter device. Furthermore, since the smoothing ceramic capacitor is made of ceramics which are inorganic materials, it is excellent in heat resistance and has a small equivalent series resistance ESR.

  Therefore, according to the present invention, it is possible to improve the reliability of an inverter device suitable for an application used under a large current and high temperature, and to further reduce the size of a system including the inverter device.

  Hereinafter, the present invention will be clarified by describing specific embodiments of the present invention with reference to the drawings.

(First embodiment)
FIG. 1 is a circuit diagram of an inverter device according to a first embodiment of the present invention.

  The inverter device 1 has a DC power supply 2. The DC power source 2 is not particularly limited, but in this embodiment, a lead storage battery is used. This lead storage battery has a structure in which ten 12V cells are connected in series. The 5-hour rate current value is 105 Ah, and the supplied DC voltage is 128V.

  As the DC power supply 2, in addition to the lead storage battery, a DC power supply such as another storage battery, a DC / DC converter other than the storage battery, and a power converter such as a step-up / step-down chopper can be used.

  A switching circuit 3 as a switching means is connected to the DC power source 2. The switching circuit 3 is provided for switching a direct current supplied from the direct current power source 2 to an alternating current.

  The switching circuit 3 has a plurality of switching circuit portions SW. Each switching circuit portion SW includes transistors Tr1 and Tr2 that are complementarily connected between the positive electrode and the anode of the DC power supply 2, and diodes D1 and D2 that are connected between the collector electrodes of the transistors Tr1 and Tr2. . Note that another semiconductor switching element may be used instead of the transistor. A connection point between the emitter electrode of one transistor Tr1 of each switching circuit portion SW and the collector electrode of the other transistor Tr2 is connected to a motor 5 as a load, and an AC current is applied to the motor 5.

  Although the switching circuit 3 includes three sets of switching circuit portions SW, the number is not particularly limited. In the present embodiment, the maximum rated voltage of Vcs, which is the voltage between the emitter electrode and the collector electrode in the switching circuit 3, is 600 V, the collector current ± Ic is 300 A, and the collector loss Pc is 781 W at 25 ° C. The temperature Tj was −20 ° C. to + 150 ° C. However, the specification of the switching circuit 3 is not limited to this.

  A smoothing ceramic capacitor 4 is connected in parallel with the DC power source 2. In the present embodiment, the smoothing ceramic capacitor 2 is a multilayer ceramic capacitor having a rated voltage = 200 V and a capacitance = 52 μF (value measured at 25 ° C. without applying a bias voltage). That is, as the smoothing ceramic capacitor 4, a large capacity multilayer ceramic capacitor for high withstand voltage was used.

  The motor 5 is a motor of a hybrid vehicle. The circuit wiring portion between the smoothing ceramic capacitor 4 and the DC power source 2 forms an inductance component in the present invention. In FIG. 1, the inductance component due to this wiring portion is schematically indicated as inductance 6.

  The feature of the inverter device 1 of the present embodiment is that the capacitance of the smoothing ceramic capacitor 4 and the inductance described above are higher than the frequency of the ripple current generated by switching in the switching circuit 3 at the assumed operating temperature of the inverter device 1. That is, the AC frequency, the capacitance of the smoothing ceramic capacitor 4 and the magnitude of the inductance I are set so that the LC resonance frequency determined by the inductance of I is increased. Thereby, in the inverter device 1, it is possible to reliably prevent the thermal runaway accompanying the temperature rise of the smoothing ceramic capacitor 4.

  As shown in FIG. 7, in the conventional inverter device, the LC resonance frequency due to the inductance 106 of the circuit wiring from the DC power source 102 to the smoothing capacitor 104 and the capacitance of the smoothing capacitor 104 is the frequency of the ripple current of the inverter. If the two values coincide with each other, an overcurrent due to the resonance occurs. Therefore, a large current flows through the smoothing capacitor, which may cause thermal runaway. In particular, when a ceramic capacitor having a low equivalent series resistance ESR is used as the smoothing capacitor 104, an overcurrent due to resonance tends to be significant.

  On the other hand, in the inverter apparatus 1 of this embodiment, it is hard to produce the failure by the above thermal runaway. This will be specifically described with reference to FIGS.

  FIG. 2 is a diagram showing a capacitance temperature characteristic of the smoothing ceramic capacitor 4 used in the above embodiment. FIG. 2 shows capacitance temperature characteristics when the bias voltage applied to the smoothing ceramic capacitor 4 is 0V, 125V, 150V and 200V.

  As is apparent from FIG. 2, when the bias voltage is applied, the capacitance becomes smaller as the temperature is higher than when the bias voltage is 0 V, that is, when no bias voltage is applied. That is, in general, it can be seen that the effective capacitance value tends to decrease as the capacitor temperature increases.

  On the other hand, FIG. 3 is a diagram showing impedance-frequency characteristics of an LC resonance circuit constituted by the capacitance of the smoothing ceramic capacitor 4 and the inductance 6. The solid line shows the result when the capacitance of the smoothing ceramic capacitor 4 at 50 ° C. is 48 μF. Here, the resonance frequency f0 of the LC resonance appears at about 32.5 kHz. In this case, in this embodiment, the resonance frequency f0 is set higher than the ripple frequency f1 = 30 kHz in the entire range of the assumed operating temperature range of the inverter device 1.

  In FIG. 3, when the temperature of the capacitor reaches 85 ° C., the capacitance of the smoothing ceramic capacitor is as low as 42 μF, and the resonance frequency f0 of the LC resonance changes to 35 kHz. That is, when the inverter device 1 is driven and the temperature of the smoothing ceramic capacitor 4 made of a multilayer ceramic capacitor is increased, the effective capacitance is decreased, and the LC resonance frequency is shifted to the high frequency side.

  In this case, for example, when the LC resonance frequency f0 is 32.5 kHz and is lower than the ripple frequency f1 = 35 kHz in the entire operating temperature range, the DC power supply 2 and the smoothing ceramic capacitor 4 are configured as the temperature rises. The absolute value of the impedance Z of the closed loop circuit to be performed becomes smaller. As a result, as shown in FIG. 5, the current flowing through the smoothing ceramic capacitor 4 increases, and the temperature of the smoothing ceramic capacitor 4 further increases. This process is repeated, leading to thermal runaway.

  On the other hand, in this embodiment, since f0> f1, the absolute value of the impedance Z of the closed loop circuit increases as the temperature rises, and the current flowing through the smoothing ceramic capacitor 4 decreases. It will be. As a result, as shown in FIG. 4, with the passage of time, the current flowing through the smoothing ceramic capacitor 4 decreases, and the temperature of the smoothing ceramic capacitor 4 rises gradually. The temperature of the smoothing ceramic capacitor 4 is almost stabilized at a certain temperature. Therefore, the magnitude of the current flowing through the smoothing ceramic capacitor 4 is also stabilized, and thermal runaway does not occur.

  Therefore, according to the present embodiment, since the resonance frequency f0 of the LC resonance is higher than the ripple frequency f1 over the entire operating temperature range, even if the inverter device 1 is driven, a failure due to thermal runaway occurs. Not likely to occur.

  Therefore, it is possible to provide an inverter device 1 with excellent reliability, which has the advantage of a multilayer ceramic capacitor that has a low equivalent series resistance ESR, excellent heat resistance, and can be reduced in size, and is less prone to failure due to thermal runaway. It becomes possible.

(Second Embodiment)
The circuit configuration itself of the inverter device of the second embodiment is the same as that of the first embodiment. Therefore, the second embodiment will also be described with reference to the circuit diagram of FIG.

  The difference between the second embodiment and the first embodiment is that, based on the ripple frequency f1, the capacitance of the smoothing ceramic capacitor and the inductance I of the inductance I are in the entire range of the assumed operating temperature range of the inverter device 1. Further, the switching circuit 3 is configured so that the time differential value of the temperature rise is negative and the absolute value thereof gradually decreases with the lapse of time of the temperature rise of the smoothing ceramic capacitor 4 so that the determined LC resonance frequency f0 is lowered. The frequency of the alternating current at, the capacitance of the smoothing ceramic capacitor 4 and the inductance component of the inductance 6 are set. It will be described with reference to FIG. 6 that such a configuration can prevent thermal runaway.

  In the present embodiment, the LC resonance frequency f0 is 32.5 kHz, which is sufficiently lower than the ripple frequency f1 = 40 kHz. Therefore, as the temperature of the smoothing ceramic capacitor 4 rises, the absolute value of the impedance Z of the closed loop circuit having the DC power supply 2 and the smoothing ceramic capacitor 4 gradually decreases, and the current flowing through the smoothing ceramic capacitor 4 increases. To go. However, as shown in FIG. 6, in the present embodiment, the time differential value d (ΔT) / dt of the temperature rise ΔT is a negative value and the absolute value thereof in the temporal change of the temperature rise in the smoothing ceramic capacitor 4. The value | d (ΔT) / dt | becomes smaller with time, that is, approaches 0. Therefore, as shown by the broken line in FIG. 6, the temperature rise amount of the smoothing ceramic capacitor 4 becomes smaller with time, and the temperature gradually stabilizes. Therefore, the current flowing through the smoothing ceramic capacitor 4 becomes stable, and thermal runaway does not occur. As described above, when the LC resonance frequency f0 is set lower than the ripple frequency f1, the degree of decrease is set so that d (ΔT) / dt <0 and | d (ΔT) / dt | If it is set to approach, thermal runaway can be reliably prevented as in the first embodiment, and the reliability of the inverter device 1 can be improved.

  Therefore, the second invention also has the advantage of the multilayer ceramic capacitor, that is, the low equivalent series resistance ESR, excellent heat resistance, and the ability to promote downsizing, and is less likely to cause a failure due to thermal runaway. An inverter device with excellent reliability can be provided.

  In the first and second embodiments, the smoothing ceramic capacitor 4 is formed of a multilayer ceramic capacitor, but other ceramic capacitors may be formed.

  Further, the load in the inverter device of the present invention is not limited to the motor of the hybrid vehicle, and other loads through which a high voltage of a large current flows may be used.

It is a circuit diagram of the inverter apparatus which concerns on one Embodiment of this invention. In one Embodiment of this invention, it is a figure which shows the electrostatic capacitance temperature characteristic of the ceramic capacitor for smoothing. In one Embodiment of this invention, it is a figure which shows the change of LC resonant frequency at the time of the temperature rise of the smoothing ceramic capacitor. It is a figure which shows the temperature rise of a capacitor | condenser with time, and the change of the electric current which flows through a capacitor | condenser in case the LC resonance frequency is higher than a ripple frequency in the inverter apparatus of one Embodiment of this invention. It is a figure which shows the temperature rise of the smoothing ceramic capacitor with the passage of time, and the change of the electric current which flows into this smoothing ceramic capacitor for demonstrating reaching a thermal runaway when LC resonance frequency is lower than a ripple frequency. It is a figure which shows the temperature rise with time in the ceramic capacitor for smoothing, and the electric current change with time in the 2nd Embodiment of this invention. It is a circuit diagram which shows the circuit structure of the conventional inverter apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Inverter apparatus 2 ... DC power supply 3 ... Switching circuit 4 ... Smoothing ceramic capacitor 5 ... Load Tr, Tr2 ... Transistor D1, D2 ... Diode

Claims (6)

DC power supply,
A load connected to the DC power supply so that power is supplied by the DC power supply;
A switching means connected between the DC power supply and the load, for switching a DC current supplied from the DC power supply to an AC current;
A smoothing ceramic capacitor connected in parallel to the DC power source in order to suppress a ripple current generated with switching in the switching means,
An inverter device comprising an inductance component existing between the DC power source and the smoothing ceramic capacitor,
In the assumed operating temperature range of the inverter device, the alternating current in the switching means is higher than the frequency of the ripple current so that the LC resonance frequency determined by the capacitance of the smoothing ceramic capacitor and the inductance of the inductance component is higher. The inverter device is characterized in that a frequency of the smoothing ceramic capacitor and an inductance of the inductance component are set. DC power supply,
A load connected to the DC power supply so that power is supplied by the DC power supply;
Switching means connected between the DC power supply and the load, and for switching a DC current supplied from the DC power supply to an AC current;
A smoothing ceramic capacitor connected in parallel to the DC power source in order to suppress a ripple current generated with switching in the switching means,
An inverter device comprising an inductance component existing between the DC power source and the smoothing ceramic capacitor,
In the assumed operating temperature range of the inverter device, the LC resonance frequency determined by the capacitance of the smoothing ceramic capacitor and the inductance of the inductance component is lower than the ripple current frequency, and the temperature rise of the ceramic capacitor The time differential value of the temperature rise is negative over time, and the frequency of the alternating current in the switching means, the capacitance of the smoothing ceramic capacitor, and the inductance of the inductance component so that the absolute value gradually decreases. An inverter device characterized in that is set.   The inverter device according to claim 1, wherein the load is a motor for an automobile. DC power supply,
A load connected to the DC power supply so that power is supplied by the DC power supply;
Switching means connected between the DC power supply and the load, and for switching a DC current supplied from the DC power supply to an AC current;
A smoothing ceramic capacitor connected in parallel to the DC power source in order to suppress a ripple current generated with switching in the switching means,
An inverter device design method comprising an inductance component present between the DC power source and the smoothing ceramic capacitor,
In the assumed operating temperature range of the inverter device, the alternating current in the switching means is higher than the frequency of the ripple current so that the LC resonance frequency determined by the capacitance of the smoothing ceramic capacitor and the inductance of the inductance component is higher. And determining the frequency of the smoothing ceramic capacitor and the inductance of the inductance component. DC power supply,
A load connected to the DC power supply so that power is supplied by the DC power supply;
A switching means connected between the DC power supply and the load, for switching a DC current supplied from the DC power supply to an AC current;
A smoothing ceramic capacitor connected in parallel to the DC power source in order to suppress a ripple current generated with switching in the switching means,
An inverter device design method comprising an inductance component present between the DC power source and the smoothing ceramic capacitor,
In the assumed operating temperature range of the inverter device, the LC resonance frequency determined by the capacitance of the smoothing ceramic capacitor and the inductance of the inductance component is lower than the frequency of the ripple current, and the temperature of the ceramic capacitor is increased. Of the AC current in the switching means, the capacitance of the smoothing ceramic capacitor, and the inductance component so that the time differential value of the temperature rise is negative and the absolute value thereof gradually decreases. A method for designing an inverter device, wherein the inductance is determined. The inverter device design method according to claim 4, wherein an automobile motor is connected as the load.

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