Deterioration estimation device and deterioration estimation program for power conversion device

Provided is a deterioration estimation device and a deterioration estimation program for a power conversion device that can estimate the deterioration of a switching element without providing a special sensor. A deterioration estimation device includes a calculating device calculating the variation of the characteristics of an IGBT in an inverter from a voltage command treated as a target of the output voltage of the power conversion device and the output voltage value of the power conversion device, a determining device determining whether the variation of the characteristics calculated by the calculating device has changed from an initial state by a threshold value or greater, and a notifying device issuing a warning when the determining device has determined that the change in the variation of the characteristics is equal to or greater than the threshold value.

TECHNICAL FIELD

The present invention relates to a deterioration estimation device and a deterioration estimation program that estimate the deterioration of a switching element used in a power conversion device such as an inverter or a converter.

BACKGROUND ART

In a power conversion device such as a motor drive inverter or a converter for power transmission, power is controlled by controlling the switching width of a switching element for power conversion. The switching element is a key component of a power conversion device, and trouble occurring in the switching element has a large impact, such as causing a device that obtains power from the power conversion device to stop, or causing the entire system to stop.

To prevent trouble from occurring, measures such as replacing semiconductor switching elements for power conversion in an aging device with new switching elements are taken, but there are problems of not only heavy maintenance costs but also a shortage of maintenance personnel. Consequently, it is desirable to provide means for detecting the signs of trouble in a switching element for power conversion in advance and issuing an alarm before the trouble occurs.

In relation to detecting the signs of trouble in advance, the technology disclosed in, for example, Patent Literature 1 is known. The power conversion device disclosed in Patent Literature 1 is provided with leakage current detecting means for detecting a gate leakage current in a semiconductor switching element for power conversion, and element abnormality detecting means for outputting an element abnormality detection signal indicating signs of abnormality when the magnitude of the leakage current changes by a fixed value or greater with reference to the leakage current when the device began to be used.

CITATION LIST

Patent Literature

SUMMARY OF INVENTION

Technical Problem

However, the power conversion device disclosed in Patent Literature 1 is newly provided with, as the leakage current detecting means between the gate and the emitter of the semiconductor switching element, a VGE detection circuit that detects the gate voltage applied between an interconnection point between the gate resistor and the gate of the semiconductor switching element, and the emitter of the semiconductor switching element.

In a power conversion device, even if means for measuring the input voltage and input current, the output voltage and output current, and the like is provided for conversion control, means for measuring the characteristics of a switching element and providing feedback is not usually provided. Consequently, with the power conversion device disclosed in Patent Literature 1, it is necessary to provide a new, special sensor for the switching element.

There is also a simple method of connecting a resistor and measuring the voltage to measure the leakage current between the gate and the emitter, but if a current flows from the gate control signal, the conditions change between when a switching element is on and when the switching element is off. In this case, the only option is to use special measuring means such as a clamp-on ammeter.

Accordingly, an objective of the present invention is to provide a deterioration estimation device and a deterioration estimation program for a power conversion device that can estimate the deterioration of a switching element without providing a special sensor.

Solution to Problem

A deterioration estimation device for a power conversion device of the present invention includes: calculating means for calculating a variation of characteristics of a switching element for power conversion in the power conversion device from a voltage command treated as a target for an output voltage of the power conversion device and an output voltage value of the power conversion device; determining means for determining whether the variation of the characteristics calculated by the calculating means has changed from an initial state by a threshold value or greater; and notifying means for issuing a warning when the determining means has determined that the change in the variation of the characteristics is equal to or greater than the threshold value, wherein the calculating means includes polarity determining means for determining a polarity of current according to an output current from the power conversion device formed from an upper arm and a lower arm by the switching element, and switching means for switching the variation of the characteristics according to a switching signal from the polarity determining means, and the determining means is provided in a pair for respectively determining the variation of the characteristics switched by the switching means.

Also, a deterioration estimation program for a power conversion device of the present invention causes a computer to function as: calculating means for calculating a variation of characteristics of a switching element for power conversion in the power conversion device from a voltage command treated as a target for an output voltage of the power conversion device and an output voltage value of the power conversion device; determining means for determining whether the variation of the characteristics calculated by the calculating means has changed from an initial state by a threshold value or greater; and notifying means for issuing a warning when the determining means has determined that the change in the variation of the characteristics is equal to or greater than the threshold value, wherein the calculating means includes polarity determining means for determining a polarity of current according to an output current from the power conversion device formed from an upper arm and a lower arm by the switching element, and switching means for switching the variation of the characteristics according to a switching signal from the polarity determining means, and the determining means is provided in a pair for respectively determining the variation of the characteristics switched by the switching means.

According to the present invention, by having the calculating means calculate the variation of the characteristics of the switching element from the voltage command for the power conversion device and the output voltage value of the power conversion device, and by having the determining means determine whether the change in the variation of the characteristics is equal to or greater than a threshold value, the notifying means issues a warning when the determining means has determined that the change in the variation of the characteristics is equal to or greater than the threshold value. The voltage command for the power conversion device and the output voltage value or output current of the power conversion device can be acquired from DC voltage measuring means provided in an inverter and output voltage measuring means or output current measuring means, and therefore it is not necessary to provide a special sensor.

Furthermore, since the switching means can switch between a pair of integrating means depending on the polarity of current determined by the polarity determining means, the change in the variation of the characteristics of each of the upper arm and the lower arm can be calculated. Consequently, signs of trouble in the upper arm and the lower arm can be estimated by the pair of determining means.

The determining means may store and treat the variation of the characteristics corresponding to the output current of the power conversion device as an initial state, and determine the threshold value on the basis of the initial state. With this configuration, the threshold value for the variation of the characteristics can be determined according to the output current, and therefore the deterioration of a switching element can be estimated accurately.

The calculating means may include subtracting means for calculating a difference between the voltage command and the output voltage value, and integrating means for outputting, to the determining means, a differential integral value obtained by integrating the difference calculated by the subtracting means. Since the difference between the voltage command and the output voltage value calculated by the subtracting means is integrated by the integrating means, tiny fluctuations or the like in the voltage value can be ignored, and since the difference is accumulated, signs of deterioration can be magnified.

The integrating means may output an integral value from a definite integral over a predetermined interval as the differential integral value. By calculating the differential integral value with a definite integral over an interval, divergent integral values can be suppressed.

The calculating means may include first averaging means for calculating an average value of an input voltage value into the power conversion device at respective time intervals synchronized with a carrier signal, multiplying means for multiplying the average value of the input voltage value from the first averaging means by a modulation ratio to calculate and output the voltage command to the subtracting means, and second averaging means for calculating and outputting, to the subtracting means, an average value of the output voltage value of the power conversion device at respective time intervals synchronized with the carrier signal. By averaging the input voltage value with the first averaging means and averaging the output voltage value with the second averaging means, during maintenance, a worker can observe the waveforms to grasp the operating state of the power conversion device.

Advantageous Effect of Invention

According to the present invention, the deterioration of a switching element can be estimated without providing a special sensor.

DESCRIPTION OF EMBODIMENTS

A deterioration estimation device for a power conversion device according to Embodiment 1 of the present invention will be described on the basis of the drawings.

In Embodiment 1, the power conversion device is an inverter10, as illustrated inFIG.1. First, the configuration of the inverter10will be described.

The inverter10according to Embodiment 1 accepts direct current and outputs three-phase alternating current. As illustrated inFIG.1, a three-phase AC motor M is connected to the inverter10.

The inverter10includes a first arm11to a third arm13, in which upper arms111,121,131and lower arms112,122,132are respectively connected in series.

The upper arms111to131are connected to a positive power line P by first wiring lines141ato141c. The lower arms112to132are connected to a negative power line N by second wiring lines142ato142c. The upper arms111to131and the lower arms112to132are connected to each other by third wiring lines143ato143c.

The upper arms111to131and the lower arms112to132are configured by a switching element and a freewheeling diode. The switching element is formed from a semiconductor device. For example, a bipolar transistor, a metal-oxide-semiconductor field-effect transistor (MOSFET), an insulated-gate bipolar transistor (IGBT), or the like can be used as the switching element. In Embodiment 1, an IGBT which allows large currents to flow through and which has a fast switching speed is used as the switching element.

The inverter10is provided with controlling means for controlling the switching of the upper arms111to131and the lower arms112to132through pulse-width modulation (PWM).

The controlling means is provided with voltage commanding means15for outputting a voltage command as a target voltage for the U to W phases, modulation ratio calculating means16for outputting a modulation ratio signal from the voltage command from the voltage commanding means15and an input voltage value indicated by an input voltage value signal, oscillating means17for outputting a carrier signal, comparing means18for comparing the modulation ratio signal to a triangle wave signal and outputting a switching signal (gate signal), and inverting means19for inverting the switching signals to the upper arms111to131for the lower arms112to132.

The voltage commanding means15is provided with U-phase voltage commanding means151for the U phase, V-phase voltage commanding means152for the V phase, and W-phase voltage commanding means153for the W phase.

From the U-phase voltage commanding means151, V-phase voltage commanding means152, and W-phase voltage commanding means153, a U-phase voltage command, V-phase voltage command, and W-phase voltage command are outputted.

The modulation ratio calculating means16is a divider that outputs the modulation ratio by dividing the voltage command from the voltage commanding means15by an input voltage value indicated by an input voltage value signal measured by DC voltage measuring means described later. The modulation ratio can be set from −1.0 to 1.0.

The modulation ratio calculating means16is provided with U-phase modulation ratio calculating means161for the U phase, V-phase modulation ratio calculating means162for the V phase, and W-phase modulation ratio calculating means163for the W phase.

From the U-phase modulation ratio calculating means161, V-phase modulation ratio calculating means162, and W-phase modulation ratio calculating means163, voltage commands (U-phase voltage command, V-phase voltage command, W-phase voltage command) are outputted to the comparing means18, and in addition, modulation ratios are outputted through a U-phase modulation ratio signal, a V-phase modulation ratio signal, and a W-phase modulation ratio signal.

The oscillating means17outputs a triangle wave signal as a carrier signal.

The comparing means18is provided with U-phase comparing means181for the U phase, V-phase comparing means182for the V phase, and W-phase comparing means183for the W phase.

The inverting means19is provided with U-phase inverting means191for the U phase, V-phase inverting means192for the V phase, and W-phase inverting means193for the W phase.

Additionally, the inverter10is provided with DC voltage measuring means21for measuring the input voltage value, a voltage divider22for acquiring the reference potentials of the output voltages (U-phase voltage, V-phase voltage, W-phase voltage) from a connection point between a resistor22aand a resistor22bconnected in series between the positive power line P and the negative power line N, output voltage measuring means23for measuring the output voltage of the inverter10, and output current measuring means24for measuring the output current of the inverter10.

The DC voltage measuring means21illustrated inFIG.1outputs the voltage value of the input voltage as the input voltage value signal.

The resistors22aand22bin the voltage divider22are set to the same resistance value for treating a medium voltage of the input voltage as a reference potential.

The output voltage measuring means23measures the output voltage of each phase. The output voltage measuring means23is provided with U-phase output voltage measuring means231for the U phase, V-phase output voltage measuring means232for the V phase, and W-phase output voltage measuring means233for the W phase.

From the U-phase output voltage measuring means231, V-phase output voltage measuring means232, and W-phase output voltage measuring means233, output voltage values are outputted through a U-phase output voltage value signal, a V-phase output voltage value signal, and a W-phase output voltage value signal.

The output current measuring means24measures the output current of each phase. Any of various types of current sensors can be used as the output current measuring means24. For example, various types of sensors such as a CT sensor, a Hall effect sensor, or a Rogowski coil sensor can be used as the output current measuring means24. The output current measuring means24is provided with U-phase output current measuring means241for the U phase, V-phase output current measuring means242for the V phase, and W-phase output current measuring means243for the W phase. From the U-phase output current measuring means241, V-phase output current measuring means242, and W-phase output current measuring means243, output current values are outputted through a U-phase output current signal, a V-phase output current signal, and a W-phase output current signal.

Next, the configuration of the deterioration estimation device that estimates the deterioration of the IGBTs (upper arms111to131and lower arms112to132of the first arm11to the third arm13) which are the switching elements in the inverter10will be described on the basis of the drawings.

The deterioration estimation device30illustrated inFIG.2is achieved by causing a computer to run a deterioration estimation program.

In addition, the deterioration estimation device30is provided with calculating means31, determining means32, and notifying means33.

The calculating means31calculates the delay, which is one example of a variation of the characteristics of a switching element, from a voltage command treated as a target for the output voltage of the inverter10illustrated inFIG.1and an output voltage value from the inverter10.

The calculating means31is provided with U-phase calculating means311for the U phase, V-phase calculating means312for the V phase, and W-phase calculating means313for the W phase. The U-phase calculating means311, the V-phase calculating means312, and the W-phase calculating means313have the same configuration.

The first averaging means31aaverages the input voltage value when the first arm11to the third arm13are on and off at respective time intervals synchronized with a triangle wave signal (carrier signal).

The second averaging means31baverages the voltage value indicated by the output voltage value signals (U-phase output voltage value signal, V-phase output voltage value signal, W-phase output voltage value signal) when the first arm11to the third arm13are on and off at respective time intervals synchronized with the triangle wave signal (carrier signal).

The multiplying means31cmultiplies the voltage value from the first averaging means31aby the modulation ratio signals (U-phase modulation ratio signal, V-phase modulation ratio signal, W-phase modulation ratio signal) from the voltage commanding means15(U-phase voltage commanding means151, V-phase voltage commanding means152, W-phase voltage commanding means153).

The subtracting means31dsubtracts the voltage value from the second averaging means31bfrom the voltage value from the multiplying means31c.

The integrating means31eoutputs the differential integral value obtained by integrating the voltage value from the subtracting means31d, and is provided in a pair.

The polarity determining means31fdetermines the polarity of current according to the output current indicated by the output current signal from the output current measuring means24(seeFIG.1) for each phase.

The switching means31gswitches the signal from the subtracting means31dto one of the integrating means31eor the other of the integrating means31eaccording to a switching signal from the polarity determining means31f.

The determining means32detects whether the voltage value from the calculating means31has changed from the initial state by a threshold value or greater, and thereby detects a delay abnormality of the upper arms111to131and the lower arms112to132in the first arm11to the third arm13which are the switching elements. The threshold value can be set to any value according to the individual characteristics, individual differences, and loads of the switching elements.

The determining means32is provided with U-phase determining means321for the U phase, V-phase determining means322for the V phase, and W-phase determining means323for the W phase.

The U-phase determining means321for the U phase, V-phase determining means322for the V phase, and W-phase determining means323for the W phase are provided in pairs for each phase to determine the differential integral value from each of one of the integrating means31eand the other of the integrating means31e.

The notifying means33notifies a user, a worker, or a person in charge of maintenance about the detection of an abnormality from the determining means32.

The operations of the deterioration estimation device30according to Embodiment 1 of the present invention configured as above will be described on the basis of the drawings. Note that a description of the U phase will be represented for the description of Embodiment 1.

Description of Operations of Inverter10

First, the operations of the inverter10illustrated inFIG.1will be described.

A voltage command signal is outputted from the U-phase voltage commanding means151. On the basis of the voltage command designated by the voltage command signal, the U-phase modulation ratio calculating means161outputs a U-phase modulation ratio signal indicating the modulation ratio.

The U-phase comparing means181compares the voltage according to the triangle wave signal from the oscillating means17to the U-phase voltage command from the U-phase voltage commanding means151(U-phase modulation ratio calculating means161), and in the period in which the U-phase voltage command is higher than the triangle wave signal, outputs an upper-arm PWM signal for turning on the upper arm111of the first arm11. Also, in the period in which the U-phase command voltage is lower than the triangle wave signal, the U-phase inverting means191outputs a lower-arm PWM signal for turning on the lower arm112of the first arm11. By repeating the above operations, the three-phase AC motor M can obtain alternating current as the U-phase output.

Description of Operations of Deterioration Estimation Device30

As an advance sign of trouble in an IGBT (switching element), it is anticipated that the output voltage of the inverter10will no longer follow the voltage command (the error will be larger than normal).

Accordingly, first, as illustrated inFIG.2, the deterioration estimation device30uses the first averaging means31ato average the input voltage value indicated by the input voltage value signal from the DC voltage measuring means21(seeFIG.1) in a half cycle of the triangle wave signal from the oscillating means17. Additionally, the multiplying means31cmultiplies the average value of the input voltage value from the first averaging means31aby the modulation ratio indicated by the U-phase modulation ratio signal from the U-phase voltage commanding means151. Through the multiplication by the multiplying means31c, the average value of the U-phase voltage command is calculated.

Also, on the basis of the triangle wave signal from the oscillating means17, the second averaging means31baverages the output voltage value indicated by the U-phase output voltage value signal from the U-phase output voltage measuring means231(seeFIG.1) in a half cycle of the triangle wave signal.

In Embodiment 1, the first averaging means31aand the second averaging means31buse a half cycle of the triangle wave signal, but it is sufficient for the timing to be synchronized with the triangle wave signal, and therefore a full cycle may also be used.

FIG.3(a)illustrates the average value of the U-phase voltage command from the multiplying means31cand the average value of the output voltage value from the second averaging means31b. In this way, by averaging the U-phase voltage command and averaging the output voltage value, the respective waveforms of the voltage command and the output voltage value can be easily understood visually.

Next, the subtracting means31dcalculates the difference by subtracting the average value of the U-phase output voltage value from the second averaging means31bfrom the average value of the U-phase voltage command from the multiplying means31c, and thereby calculates the delay of the upper arm111of the first arm11which is a switching element.

Thereafter, the polarity determining means31fdetermines the polarity of current according to the output current indicated by the U-phase output current signal, and switches the switching means31gaccording to the switching signal.

According to the switching signal, when the polarity of the output current is positive, the difference from the subtracting means31dis integrated by one of the integrating means31e(inFIG.2, the integrating means31eon the top). Also, when the polarity of the output current is negative, the difference from the subtracting means31dis integrated by the other of the integrating means31e(inFIG.2, the integrating means31eon the bottom).

Here,FIG.3(a)illustrates the average value of the U-phase voltage command from the multiplying means31cand the average value of the output voltage value from the second averaging means31bwhen the polarity of the output current is positive.

Also,FIG.3(b)illustrates the average value of the U-phase voltage command from the multiplying means31cand the average value of the output voltage value from the second averaging means31bwhen the polarity of the output current is negative.

In addition, the output (variation of characteristics) from one of the integrating means31e(inFIG.2, refer to the integrating means31eon the top) when the off-delays of the upper arm111and the lower arm112are in an initial state (4 μs) is illustrated inFIG.4(a).

Moreover, the output from the other of the integrating means31e(inFIG.2, refer to the integrating means31eon the bottom) when the delay is the same as the delay state inFIG.4(a)is illustrated inFIG.4(b).

The waveforms illustrated inFIGS.4(a) and4(b)are obtained in a state in which the three-phase AC motor M (seeFIG.1) has a fixed number of revolutions and a fixed load, and are obtained by starting the integrations by the integrating means31e,31efrom the time 10 s.

AsFIGS.4(a) and4(b)demonstrate, the outputs from the integrating means31e,31erise or fall on a prescribed slope.

For example, if both the upper arms111to131and the lower arms112to132illustrated inFIG.1deteriorate, the characteristics change, and the off-delay increases, the slopes of both waveforms illustrated inFIGS.4(a) and4(b)will be gentle. At this time, if there is no switching means31gand the difference from the subtracting means31dis integrated by singular integrating means31e, the positive and negative values will be added together and cancel each other out, and consequently, signs of abnormality cannot be detected.

However, in the deterioration estimation device30, it is determined whether the upper arms111to131or the lower arms112to132have deteriorated on the basis of the direction of the current outputted from the first arm11to the third arm13.

As an example of a change in the characteristics of the upper arm111, assume that the delay when being switched off has increased from 4 μs to 8 μs. Note that the off-delay of the lower arm112is still in the initial state (a delay of 4 μs).

The output from one of the integrating means31eat this time is illustrated inFIG.5(a). Also, the output from the other of the integrating means31eis illustrated inFIG.5(b).

The waveforms illustrated inFIGS.5(a) and5(b), similarly toFIG.4, are also obtained in a state in which the three-phase AC motor M (seeFIG.1) has a fixed number of revolutions and a fixed load, and are obtained by starting the integrations by the integrating means31e,31efrom the time 10 s.

InFIG.5(b), there is no change fromFIG.4(b), but inFIG.5(a)it can be seen that the slope of the off-delay has become gentler from the initial state.

Consequently, the variation of the characteristics is such that the difference from the initial state is larger, and one of the U-phase determining means321can determine that the upper arm111has deteriorated by detecting that the change from the initial state is equal to or greater than a threshold value. Moreover, one of the U-phase determining means321can inform the notifying means33of a U-phase first alarm signal.

Next, assume that, for example, the off-delay of the upper arm111is still in the initial state (a delay of 4 μs), but the delay of the lower arm112when being switched off has increased from 4 μs to 8 μs. The output from one of the integrating means31eat this time is illustrated inFIG.6(a). Also, the output from the other of the integrating means31eis illustrated inFIG.6(b).

The waveforms illustrated inFIGS.6(a) and6(b), similarly toFIG.4, are also obtained in a state in which the three-phase AC motor M (seeFIG.1) has a fixed number of revolutions and a fixed load, and are obtained by starting the integrations by the integrating means31e,31efrom the time 10 s.

InFIG.6(a), there is no change fromFIG.4(a), but inFIG.6(b)it can be seen that the slope of the delay has become gentler from the initial state.

Consequently, the difference from the initial state is larger, and the other of the U-phase determining means321can determine that the lower arm112has deteriorated by detecting that the change from the initial state is equal to or greater than a threshold value. Moreover, the other of the U-phase determining means321can inform the notifying means33of a U-phase second alarm signal.

Furthermore, in the case where both off-delays of the upper arm111and the lower arm112have increased from 4 μs to 8 μs, the output voltage of the upper arm111for which the current is a positive value becomes the waveform illustrated byFIG.5(a), and the output voltage of the lower arm112for which the current has a negative value becomes the waveform illustrated byFIG.6(b).

Consequently, since it is understood that a change has occurred from the waveforms illustrated inFIG.5(b)andFIG.6(a)which illustrate the normal state, by detecting that the change has become equal to or greater than a threshold value, the notifying means33can be informed of a U-phase first alarm signal with which the deterioration of both the upper arm111and the lower arm112can be estimated.

Also, by using the integrating means31e,31eillustrated inFIG.2to integrate the on-delays and off-delays (difference) from the subtracting means31d, tiny fluctuations or the like in the voltage value can be ignored, and since the difference is accumulated, signs of deterioration can be magnified.

In addition, by informing the notifying means33of the abnormality, a user, an administrator, a person in charge of maintenance, or the like can be informed of the possibility of trouble in the inverter10(seeFIG.1). The notification can be issued according to various methods, such as with light from a lamp or the like, with sound from a speaker, or through email over the Internet.

As above, according to the deterioration estimation device30according to Embodiment 1, by having the calculating means31calculate the variation of the characteristics of an IGBT from the voltage command treated as a target for the output voltage of the inverter10and the output voltage value from the inverter10, and by having the determining means32determine whether the change in the variation of the characteristics is equal to or greater than a threshold value, the notifying means33can issue a warning when the determining means32has determined that the change is equal to or greater than the threshold value.

The voltage command with respect to the inverter10and the output voltage value and output current of the inverter10can be acquired from the DC voltage measuring means21, the output voltage measuring means23, and the output current measuring means24provided in the inverter10, and therefore the deterioration estimation device30can estimate the deterioration of an IGBT which is a switching element without providing a special sensor.

Also, by switching the integrating means31eand making respective determinations when the polarity of the output current is positive and when the polarity is negative, it is possible to determine whether the upper arm111, the lower arm112, or both have deteriorated.

Furthermore, since the calculating means31and the determining means32are provided respectively for each of the U, V, and W phases, the deterioration in each of the phases can be detected.

In the above description, an example of an increase in the off-delay is described in regard to detecting the variation of the characteristics through subtraction of the voltage command to the inverter10, which is one example of a power conversion device, and the output voltage value from the inverter10. However, it is also possible to detect the on-delay, the off-delay, the on-voltage, the on-resistance, dv/dt (rate of voltage change), or the like as a change in the characteristics of a switching element.

In Embodiment 1, the calculating means31uses the first averaging means31ato average the input voltage value indicated by the input voltage value signal, and also uses the second averaging means31bto average the output voltage value. With this configuration, the waveforms illustrated inFIGS.3(a) and3(b)can be obtained, and therefore a worker can observe the waveforms during maintenance or the like and easily grasp the operating state of the inverter10.

However, if it is not necessary to obtain the waveforms illustrated inFIGS.3(a) and3(b), the first averaging means31aand the second averaging means31bcan be omitted since the difference is integrated by the integrating means31edownstream from the subtracting means31d.

Next, a deterioration estimation device according to Embodiment 2 of the present invention will be described.

In the pair of integrating means31eillustrated inFIG.2, since the difference is integrated, the differential integral value increasingly diverges over time.

Accordingly, in the integration by the integrating means31e, a definite integral over a predetermined interval (interval integral) is evaluated to obtain the differential integral value. Hereinafter, this operation is referred to as the interval integral.

The interval integral can be found by the following expression (1) when the interval is set to 5 s, for example.

[Expression 1]
∫T−5Te(t)dt  (1)
Here, T is any time and e(t) is the integral value from the integrating means31e.

FIGS.7to9illustrate waveforms when the three-phase AC motor M illustrated inFIG.1is driven by the inverter10and the differential integral value from the integrating means31eis calculated by setting the predetermined interval to 5 s, for example.

The waveforms illustrated inFIGS.7(a) and7(b)correspond toFIG.4which illustrates the waveforms when the off-delay of the upper arm111and the off-delay of the lower arm112are in the initial state (4 μs), and illustrate the case where the integral of the difference is replaced by the interval integral.

Also, the waveforms illustrated inFIGS.8(a) and8(b)correspond toFIGS.5(a) and5(b)which illustrate the waveforms when the off-delay of the upper arm111is increased from 4 μs to 8 μs and the off-delay of the lower arm112is in the initial state (4 μs), and illustrate the case where the integral of the difference is replaced by the interval integral.

Moreover, the waveforms illustrated inFIGS.9(a) and9(b)correspond toFIGS.6(a) and6(b)which illustrate the waveforms when the off-delay of the upper arm111is in the initial state (4 μs) and the off-delay of the lower arm112is increased from 4 μs to 8 μs, and illustrate the case where the integral of the difference is replaced by the interval integral.

In Embodiment 2, the integral is over a 5 s interval and therefore becomes a constant value 5 s after the integral start (time 10 s) as illustrated inFIGS.7to9.

In bothFIGS.8and9, the slopes of the waveforms become gentler with increasing delay, similarly to the waveforms illustrated inFIGS.4to6, and therefore by detecting that the change from the initial state is equal to or greater than a threshold value, the deterioration of the delay characteristics of a switching element can be detected.

Also, as illustrated inFIGS.8and9, by having the integrating means31eevaluate an interval integral to obtain the differential integral value, divergent integral values can be suppressed.

Next, a deterioration estimation device according to Embodiment 3 of the present invention will be described.

The delay of the IGBTs constituting the first arm11to the third arm13in the inverter10illustrated inFIG.1is calculated by the differential integral value from the pair of integrating means31eillustrated inFIG.2. However, the differential integral value is influenced by the load current. For example, the delay of the IGBTs constituting the first arm11to the third arm13is different between the unloaded state and the state in which a predetermined current is flowing as the output current.

Accordingly, in the determining means32, the output voltage from the first arm11to the third arm13of each phase is inputted, the differential integral value indicating the delay corresponding to the output voltage is stored and treated as an initial state, and a threshold value is determined on the basis of the initial state. With this configuration, the threshold value for the variation of the characteristics can be determined according to the load current (output current), and therefore the deterioration of a switching element (IGBT) can be estimated accurately.

Note that Embodiments 1 to 4 describe an example of a two-level inverter10including upper arms111to131and lower arms112to132, as illustrated inFIG.1, but the deterioration estimation device of the present invention can also be applied to a three-level inverter.

Also, in the embodiments, as illustrated inFIG.1, the output voltage measuring means23including the U-phase output voltage measuring means231for the U phase, the V-phase output voltage measuring means232for the V phase, and the W-phase output voltage measuring means233for the W phase measures and outputs the output voltage of each phase as a U-phase output voltage value signal, a V-phase output voltage value signal, and a W-phase output voltage value signal.

However, the output voltage may not only be treated as a phase voltage but also as a line voltage.

For example, that which outputs the output voltage to the U-phase calculating means311illustrated inFIG.2can be configured to be a U-V output voltage value signal from U-V output voltage measuring means251as illustrated inFIG.10instead of the U-phase output voltage value signal. In this case, a signal of “U-phase modulation ratio signal-V-phase modulation ratio signal” is used instead of the U-phase modulation ratio signal of the U-phase calculating means311.

For example, that which outputs the output voltage to the V-phase calculating means312illustrated inFIG.2can be configured to be a V-W output voltage value signal from V-W output voltage measuring means252as illustrated inFIG.10instead of the V-phase output voltage value signal. In this case, a signal of “V-phase modulation ratio signal-W-phase modulation ratio signal” is used instead of the V-phase modulation ratio signal of the V-phase calculating means312.

Moreover, that which outputs the output voltage to the W-phase calculating means313illustrated inFIG.2can be configured to be a W-U output voltage value signal from W-U output voltage measuring means253as illustrated inFIG.10instead of the W-phase output voltage value signal. In this case, a signal of “W-phase modulation ratio signal-U-phase modulation ratio signal” is used instead of the W-phase modulation ratio signal of the W-phase calculating means313.

Even if such output voltage measuring means25(U-V output voltage measuring means251, V-W output voltage measuring means252, W-U output voltage measuring means253) for measuring line voltages is used, the output voltage can be measured and the calculating means31can calculate the delay which is one example of a variation of the characteristics of a switching element.

INDUSTRIAL APPLICABILITY

The present invention can estimate the deterioration of a power conversion device and is therefore suitable for a power supply that supplies power to a mission-critical system from a simple power supply or the like.

REFERENCE SIGNS LIST