Capacitor degradation evaluation method, capacitor degradation evaluation device, inverter degradation evaluation method and inverter degradation evaluation device

Abstract

To provide a degradation evaluation method and degradation evaluation device for evaluating a degree of degradation of a capacitor without a sensor, in an inverter having the capacitor on an input side and inputting a direct current to output a single-phase or three-phase alternating current.SOLUTION: A capacitor degradation evaluation method for evaluating a degree of degradation of a capacitor C of an inverter 10 having the capacitor C on the input side and inputting a direct current to output a single-phase or three-phase alternating current, includes: generating an instantaneous output power signal using an output voltage signal and an output current signal of the inverter 10; generating a ripple current signal by dividing the instantaneous output power signal by a capacitor voltage signal, the voltage signal between both ends of the capacitor; and evaluating the degree of degradation of the capacitor C by using the ripple current signal.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a method for evaluating the deterioration of a capacitor provided on the input side of an inverter, a device for evaluating the deterioration of the capacitor, and further to a method for evaluating the deterioration of an inverter and a device for evaluating the deterioration of the inverter.

Background Art

[0002] In recent years, solar power generation and wind power generation have been carried out on a large scale as measures against global warming. In these power generation systems, power conditioners, reactive power compensation devices, etc. are used, and they are composed of various inverters. Also, in electric vehicles whose use is expanding, a motor drive system is required, and various inverters are also used in this motor drive system.

[0003] These inverters are configured by combining switching elements such as transistors, diodes of rectifying elements, and capacitors provided for smoothing. It is known that capacitors are most likely to deteriorate due to repeated charging and discharging, and the performance of the inverter is maintained by replacing the capacitor that has reached the specified replacement conditions.

[0004] However, it is known that unexpected deterioration occurs in capacitors and they fail relatively frequently. In order to prevent the occurrence of such failures before replacement, it is considered necessary to monitor the deterioration of the capacitor. As a method for monitoring the deterioration of the capacitor, a method of monitoring the current flowing through the capacitor using a current sensor or the like is known. In this method, the degree of deterioration of the capacitor is evaluated by evaluating the equivalent series resistance and capacitance from the current value detected by the current sensor.

[0005] When constantly monitoring with this current sensor, it is necessary to provide a current sensor in the circuit constituting the inverter. However, providing a current sensor in the circuit constituting the inverter requires a complete overhaul of the existing inverter circuit and incurs cost increases, so it has rarely been implemented from the perspective of cost-effectiveness.

[0006] Under such circumstances, the inventor invented a method of obtaining desired current information without using a current sensor, identifying the equivalent series resistance and capacitance of a capacitor, and diagnosing the life of the capacitor (see, for example, Patent Document 1). Here, the inverter is an inverter for driving a motor used in industrial machines, various robots, etc., which rectifies the AC power input from a three-phase input power supply into DC power by a rectifier in the inverter, and then converts this DC power into AC power by an inverter circuit in the inverter. In order to smooth the fluctuations in the voltage rectified by the rectifier, a capacitor is provided between the rectifier and the inverter circuit, and the life of this capacitor is monitored. Also, a filter inductor is provided between this capacitor and the rectifier to suppress harmonics.

[0007] In such an inverter, the ripple current flowing through the capacitor can be calculated from the rectifier voltage and the impedance of the filter inductor in the inverter. Note that the rectifier voltage utilizes the fact that it can be calculated from the power supply voltage of the input power supply and the output power of the inverter.

[0008] The inventor has invented a method of evaluating the equivalent series resistance and capacitance of a capacitor using this ripple current and the capacitor voltage, which is the voltage across both ends of the capacitor.

Prior Art Documents

Patent Documents

[0009]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0010] However, in an inverter that does not have a filter inductor, there is a problem that the ripple current cannot be calculated and its use is limited. The inventor conducted research and development to evaluate the degree of deterioration of the capacitor sensorless in other types of inverters as well, and as a result, it became possible to calculate the ripple current in an inverter that inputs direct current and outputs single-phase alternating current or three-phase alternating current, leading to the present invention.

[0011] That is, the present invention provides a deterioration evaluation method and a deterioration evaluation device for a capacitor that evaluate the degree of deterioration of the capacitor sensorless in an inverter that inputs direct current and outputs single-phase alternating current or three-phase alternating current.

Means for Solving the Problems

[0012] The capacitor deterioration evaluation method of the present invention is a capacitor deterioration evaluation method for evaluating the degree of deterioration of a capacitor in an inverter that has a capacitor on the input side and inputs direct current and outputs single-phase alternating current or three-phase alternating current. It includes an instantaneous output power signal generation step of generating an instantaneous output power signal using the output voltage signal and the output current signal of the inverter, and a ripple current signal generation step of dividing the instantaneous output power signal by the capacitor voltage signal, which is the voltage signal across the capacitor, to generate a ripple current signal.

[0013] Furthermore, the capacitor deterioration evaluation method of the present invention is also characterized by the following points. (1) An impedance signal generation step of generating an impedance signal by dividing a high-speed Fourier-transformed capacitor voltage signal by a high-speed Fourier-transformed ripple current signal; an equivalent series resistance and capacitance identification step of identifying an equivalent series resistance and a capacitance from a curve of the frequency characteristics of the impedance signal; and a degradation evaluation step of comparing the initially detected initial equivalent series resistance with the identified equivalent series resistance to evaluate degradation, or comparing the initially detected initial capacitance with the identified capacitance to evaluate the degree of degradation. (2) In the degradation evaluation step, when degradation of the capacitor is detected, execute a switching element degradation evaluation step of evaluating the degree of degradation of the switching element and diode in the inverter.

[0014] Further, the capacitor degradation evaluation device of the present invention is a capacitor degradation evaluation device for evaluating the degree of degradation of a capacitor of an inverter that has a capacitor on the input side and inputs direct current and outputs single-phase alternating current or three-phase alternating current, and includes an instantaneous output power signal generation unit that generates an instantaneous output power signal using the output voltage signal and output current signal of the inverter, and a ripple current signal generation unit that generates a ripple current signal by dividing the instantaneous output power signal by a capacitor voltage signal that is the voltage signal across the capacitor.

[0015] Furthermore, the capacitor degradation evaluation device of the present invention is also characterized by the following points. (1) An impedance signal generation unit that generates an impedance signal by dividing a high-speed Fourier-transformed capacitor voltage signal by a high-speed Fourier-transformed ripple current signal; an equivalent series resistance and capacitance identification unit that identifies an equivalent series resistance and a capacitance from a curve of the frequency characteristics of the impedance signal; and an evaluation unit that compares the initially detected initial equivalent series resistance with the identified equivalent series resistance to evaluate degradation, or compares the initially detected initial capacitance with the identified capacitance to evaluate degradation. (2) When the evaluation unit detects the deterioration of the capacitor, it has a switching element deterioration evaluation unit that evaluates the degree of deterioration of the switching element and diode in the inverter.

[0016] Further, the inverter deterioration evaluation method of the present invention is an inverter deterioration evaluation method for evaluating the degree of deterioration of an inverter that has a capacitor on the input side, inputs direct current, and outputs single-phase alternating current or three-phase alternating current. In this method, from the amplitude of the output voltage signal of the inverter obtained by inputting a test voltage smaller than the operating voltage to the inverter, it has a switching element evaluation step of evaluating the degree of deterioration of the switching element and diode in the inverter. Furthermore, the input of the test voltage to the inverter is characterized in that it is input in the startup mode executed when the inverter is started, and after the end of the startup mode, the operating voltage is input to the inverter as the operating mode.

[0017] Also, the inverter deterioration evaluation device of the present invention is an inverter deterioration evaluation device for evaluating the degree of deterioration of an inverter that has a capacitor on the input side, inputs direct current, and outputs single-phase alternating current or three-phase alternating current. In this device, from the amplitude of the output voltage signal of the inverter obtained by inputting a test voltage smaller than the operating voltage to the inverter, it has a switching element evaluation unit that evaluates the degree of deterioration of the switching element and diode in the inverter. Furthermore, the input of the test voltage to the inverter is characterized in that it is input in the startup mode executed when the inverter is started, and after the end of the startup mode, the operating voltage is input to the inverter as the operating mode.

Advantages of the Invention

[0018] According to the present invention, it is possible to calculate the ripple current even in an inverter that inputs direct current and outputs single-phase alternating current or three-phase alternating current, and thus it is possible to provide a deterioration evaluation method and a deterioration evaluation device that can evaluate the degree of deterioration of the capacitor as sensorless.

Brief Description of the Drawings

[0019]

Figure 1

Figure 2

Figure 3

Figure 4

Mode for Carrying Out the Invention

[0020] The capacitor deterioration evaluation method and the capacitor deterioration evaluation device of the present invention evaluate the degree of deterioration of a capacitor provided on the input side of an inverter that inputs direct current and outputs single-phase alternating current or three-phase alternating current.

[0021] In particular, the instantaneous output power is calculated using the output voltage and output current output from the inverter, and the ripple current can be calculated by dividing this instantaneous output power by the capacitor voltage, which is the voltage across the capacitor. The degree of deterioration of the capacitor is evaluated using this ripple current.

[0022] Hereinafter, based on the drawings, the capacitor deterioration evaluation device and the capacitor deterioration evaluation method according to the present invention will be described in detail.

[0023] As shown in FIG. 1, the capacitor C deterioration evaluation device 20 has an output voltage signal and an output current signal output from the inverter 10 having the capacitor C on the input side input thereto, and a capacitor voltage signal, which is the voltage across the capacitor C, input thereto, thereby evaluating the degree of deterioration of the capacitor C.

[0024] The inverter 10 has an inverter circuit 11 composed of first to sixth switching elements S1, S2, S3, S4, S5, and S6 to which first to sixth diodes D1, D2, D3, D4, D5, and D6 are respectively connected in anti-parallel. That is, in the inverter circuit 11, the first switching element S1 and the second switching element S2 form a U-phase leg 12, and a U-phase output line Lu is provided between the first switching element S1 and the second switching element S2. Also, in the inverter circuit 11, the third switching element S3 and the fourth switching element S4 form a V-phase leg 13, and a V-phase output line Lv is provided between the third switching element S3 and the fourth switching element S5. Further, in the inverter circuit 11, the fifth switching element S5 and the sixth switching element S6 form a W-phase leg 14, and a W-phase output line Lw is provided between the fifth switching element S5 and the sixth switching element S6. The capacitor C is connected in parallel with the U-phase leg 12, the V-phase leg 13, and the W-phase leg 14, respectively. In the present embodiment, the inverter 10 that inputs direct current and outputs three-phase alternating current will be described. However, when single-phase alternating current is output, the above-described V-phase leg 13 and W-phase leg 14 are not present, and the description of the case of outputting single-phase alternating current will be omitted. Although not shown, the inverter 10 is provided with a drive control unit that appropriately drives the inverter circuit 11.

[0025] The deterioration evaluation device 20 is provided with a capacitor voltage signal generation unit 21, a voltage-current signal generation unit 22, an instantaneous output power signal generation unit 23, a ripple current signal generation unit 24, a first fast Fourier transform unit 25, a second fast Fourier transform unit 26, an impedance signal generation unit 27, an equivalent series resistance-capacitance specifying unit 28, and an evaluation unit 29.

[0026] The capacitor voltage signal generation unit 21 inputs the voltage signal at both ends of the capacitor C of the inverter 10 to generate a capacitor voltage signal Vc(t). The generated capacitor voltage signal Vc(t) is input to the first fast Fourier transform unit 25 and also input to the ripple current signal generation unit 24.

[0027] The voltage and current signal generation unit 22 receives signals from the U-phase output line Lu, V-phase output line Lv, and W-phase output line Lw of the inverter 10, generates a U-phase output voltage signal Vu(t), a U-phase output current signal iu(t), a V-phase output voltage signal Vv(t), a V-phase output current signal iv(t), a W-phase output voltage signal Vw(t), and a W-phase output current signal iw(t), and inputs them to the instantaneous output power signal generation unit 23.

[0028] The instantaneous output power signal generation unit 23 generates an instantaneous output power signal Po(t) using the input U-phase output voltage signal Vu(t), U-phase output current signal iu(t), V-phase output voltage signal Vv(t), V-phase output current signal iv(t), W-phase output voltage signal Vw(t), and W-phase output current signal iw(t). That is, the instantaneous output power signal Po(t) is Po(t) = Vu(t)·iu(t)+Vv(t)·iv(t)+Vw(t)·iw(t) and is. The generated instantaneous output power signal Po(t) is input to the ripple current signal generation unit 24.

[0029] In the ripple current signal generation unit 24, the instantaneous output power signal Po(t) input from the instantaneous output power signal generation unit 23 is divided by the capacitor voltage signal Vc(t) input from the capacitor voltage signal generation unit 21 to generate a ripple current signal ic(t). That is, ic(t) = Po(t) / Vc(t) is set. The generated ripple current signal ic(t) is input to the second fast Fourier transform unit 26.

[0030] The first fast Fourier transform unit 25 performs a fast Fourier transform on the capacitor voltage signal Vc(t) input from the voltage and current signal generation unit 22 to generate a transformed capacitor voltage signal Vc(f). The generated transformed capacitor voltage signal Vc(f) is input to the impedance signal generation unit 27.

[0031] The second fast Fourier transform unit 26 performs a fast Fourier transform on the ripple current signal ic(t) input from the ripple current signal generation unit 24 to generate a transformed ripple current signal ic(f). The generated transformed ripple current signal ic(f) is also input to the impedance signal generation unit 27.

[0032] The impedance signal generation unit 27 generates an impedance signal Zc(f) by dividing the transformed capacitor voltage signal Vc(f) input from the first fast Fourier transform unit 25 by the transformed ripple current signal ic(f) input from the second fast Fourier transform unit 26. That is, Zc(f) = Vc(f) / ic(f) is set. The generated impedance signal Zc(f) is input to the equivalent series resistance and capacitance specifying unit 28.

[0033] The equivalent series resistance and capacitance specifying unit 28 uses the impedance signal Zc(f) input from the impedance signal generation unit 27 to specify the equivalent series resistance and capacitance of the capacitor C. The specified equivalent series resistance and capacitance are input to the evaluation unit 29.

[0034] The equivalent series resistance and capacitance specifying unit 28 specifically specifies the equivalent series resistance and capacitance of the capacitor C using the least squares method. That is, in the equivalent series resistance and capacitance specifying unit 28, first, a virtual curve of the frequency characteristics of the series impedance with an arbitrary equivalent series resistance and an arbitrary capacitance is set. Next, the equivalent series resistance and capacitance specifying unit 28 calculates an evaluation value by the least squares method between the curve of the frequency characteristics of the impedance signal Zc(f) and the virtual curve. The equivalent series resistance and capacitance specifying unit 28 specifies the equivalent series resistance and capacitance at which this evaluation value becomes the minimum while changing the values of the equivalent series resistance and capacitance. In the case of the equivalent series resistance and capacitance at which the evaluation value becomes the minimum, the virtual curve becomes the curve that most closely approximates the curve of the frequency characteristics of the impedance signal Zc(f), and the equivalent series resistance and capacitance in this case are specified as the equivalent series resistance and capacitance of the capacitor C.

[0035] The evaluation unit 29 compares the equivalent series resistance and capacitance input from the equivalent series resistance and capacitance specifying unit 28 with the initial equivalent series resistance and initial capacitance stored in advance in the storage unit 31 provided in the degradation evaluation device 20, and evaluates the degree of degradation. Note that when the capacitor C degrades, the equivalent series resistance increases and the capacitance decreases. The equivalent series resistance is clearly abnormal when it becomes twice or more the initial equivalent series resistance, and the capacitance is clearly abnormal when it falls below 80% of the initial capacitance, and these can be used as the threshold values for abnormality detection.

[0036] The evaluation unit 29 sequentially stores the equivalent series resistance and capacitance input from the equivalent series resistance and capacitance identification unit 28 in the storage unit 31, and can use the oldest stored equivalent series resistance and capacitance as the initial equivalent series resistance and initial capacitance. When the capacitor C is replaced, it is desirable to delete the data of the equivalent series resistance and capacitance stored in the storage unit 31 and store the equivalent series resistance and capacitance immediately after the replacement in the initialization operation after the replacement of the capacitor C. The evaluation of the degree of deterioration can be performed using the increase rate of the equivalent series resistance and the decrease rate of the capacitance.

[0037] In the evaluation unit 29, even when it is considered that the capacitor C is deteriorated by detecting a change in the equivalent series resistance or capacitance, this may not necessarily be the case. That is, it is also conceivable that any of the first to sixth switching elements S1, S2, S3, S4, S5, S6 and the first to sixth diodes D1, D2, D3, D4, D5, D6 of the inverter circuit 11 is faulty or deteriorated.

[0038] Therefore, in the evaluation unit 29, when the deterioration of the capacitor C is detected, the degree of deterioration of the first to sixth switching elements S1, S2, S3, S4, S5, S6 and the first to sixth diodes D1, D2, D3, D4, D5, D6 of the inverter circuit 11 is also evaluated.

[0039] In addition, it is desirable to lower the voltage on the input side of the inverter 10 below the normal operating voltage of the inverter 10 to perform this evaluation. Therefore, in this embodiment, when the deterioration of the capacitor C is detected, a flag for executing the evaluation of the deterioration of the device of the inverter circuit 11 is set, and when the inverter 10 is started, the drive control unit of the inverter 10 detects the flag and executes the evaluation of the deterioration of the device of the inverter circuit 11. Note that the evaluation of the deterioration of the device of the inverter circuit 11 may always be performed when the inverter 10 is started.

[0040] When evaluating the degradation of the devices in the inverter circuit 11, a voltage approximately one tenth to one fortieth of the operating voltage is input to the inverter circuit 11 to generate an output voltage signal.

[0041] This output voltage signal is generated by the voltage-current signal generation unit 22 and input to the switching element evaluation unit 32.

[0042] The switching element evaluation unit 32 compares the magnitude of the amplitude of the input output voltage signal with the magnitude of the amplitude of the initial output voltage signal stored in the storage unit 31 to determine whether degradation has occurred in the devices of the inverter circuit 11. In this case, the amplitude of the output voltage signal sequentially stored in the storage unit 31 can also be used as the initial output voltage signal.

[0043] The switching element evaluation unit 32 cannot determine which devices of the first to sixth switching elements S1, S2, S3, S4, S5, S6 and the first to sixth diodes D1, D2, D3, D4, D5, D6 in the inverter circuit 11 have deteriorated, but can detect the occurrence of degradation in units of the U-phase leg 12, V-phase leg 13, and W-phase leg 14.

[0044] When the switching element evaluation unit 32 determines that there is no degradation in the devices of the inverter circuit 11, the evaluation unit 29 evaluates that the capacitor C has deteriorated. This can suppress the occurrence of misevaluation.

[0045] The above-described degradation evaluation device 20 can be configured by creating a dedicated evaluation circuit or by using a personal computer. When configured using a personal computer, the output voltage, output current, and capacitor voltage output from the inverter 10 can be input to the personal computer via appropriate input connectors.

[0046] Hereinafter, based on the flowchart of FIG. 2, the case where a personal computer is used as a degradation evaluation device will be described. In the memory of the personal computer, various programs for executing functions necessary as a degradation evaluation device, the initial equivalent series resistance and initial capacitance, or the amplitude of the initial output voltage signal, etc. are stored. For convenience of explanation, hereinafter, the personal computer functioning as a degradation evaluation device will simply be referred to as the degradation evaluation device. Also, it is assumed that the degradation evaluation device has acquired data on the amplitude of the output voltage signal used for determining the degradation of the devices in the inverter circuit 11 when the inverter 10 is started up.

[0047] When the inverter 10 is operating normally, the output voltage, output current, and capacitor voltage output from the inverter 10 are input to the degradation evaluation device (step T1: YES), and the degradation evaluation device generates an output voltage signal, an output current signal, and a capacitor voltage signal (step T2). When there is no input from the inverter 10 to the degradation evaluation device (step T1: NO), since the inverter 10 is not operating, the degradation evaluation device is stopped.

[0048] The degradation evaluation device starts the instantaneous output power signal generation program and generates an instantaneous output power signal using the output voltage signal and the output current signal (step T3). This is the instantaneous output power signal generation step.

[0049] Next, the degradation evaluation device starts the ripple current signal generation program and divides the instantaneous output power signal by the capacitor voltage signal to generate a ripple current signal (step T4). This is the ripple current signal generation step.

[0050] Next, the degradation evaluation device starts the fast Fourier transform program and performs fast Fourier transform on the capacitor voltage signal and the ripple current signal respectively to generate a transformed capacitor voltage signal and a transformed ripple current signal (step T5).

[0051] Next, the deterioration evaluation device activates an impedance signal generation program, divides the converted capacitor voltage signal by the converted ripple current signal to generate an impedance signal (step T6). This is the impedance signal generation step.

[0052] Next, the deterioration evaluation device activates an equivalent series resistance and capacitance identification program, and identifies the equivalent series resistance and capacitance from the curve of the frequency characteristics of the impedance signal (step T7). This is the equivalent series resistance and capacitance identification step. The equivalent series resistance and capacitance identification program executed in this equivalent series resistance and capacitance identification step is a program for identifying the equivalent series resistance and capacitance by the least squares method. A virtual curve of the frequency characteristics of the series impedance with an arbitrary equivalent series resistance and an arbitrary capacitance is set, and the equivalent series resistance and capacitance are identified when this virtual curve is most approximated to the curve of the frequency characteristics of the impedance signal.

[0053] Next, the deterioration evaluation device activates an evaluation program, compares the equivalent series resistance and capacitance identified in the equivalent series resistance and capacitance identification step with the initial equivalent series resistance and initial capacitance stored in advance in the storage unit, and evaluates the degree of deterioration (step T8). This is the deterioration evaluation step.

[0054] When the deterioration evaluation device detects the deterioration of the capacitor C in the deterioration evaluation step (step T8: YES), it activates a switching element deterioration evaluation program to evaluate the degree of deterioration of devices such as the switching elements and diodes in the inverter 10 (step T9). This is the switching element deterioration evaluation step. On the other hand, when the deterioration of the capacitor C is not detected in the deterioration evaluation step (step T8: NO), the deterioration evaluation device returns to step T1 to receive the signal input from the inverter 10.

[0055] As described above, for the degradation evaluation of the switching element and the diode, it is necessary to input a voltage about one-tenth to one-fortieth of the operating voltage to generate an output voltage signal, rather than the input voltage in the normal operating state of the inverter 10. In the present embodiment, when the inverter 10 is started, a predetermined voltage is input, and data on the amplitude of the output voltage signal used for the degradation determination of the devices in the inverter circuit 11 is acquired in advance.

[0056] In the switching element degradation evaluation step in step T9, the amplitude of the output voltage signal acquired in advance is compared with the amplitude of the initial output voltage signal stored in the memory to determine whether degradation has occurred in the devices of the inverter circuit 11. When degradation has occurred in the devices of the inverter circuit 11, since the amplitude of the output voltage signal decreases, the degree of degradation can be evaluated from the decrease rate of the amplitude of the output voltage signal.

[0057] In the switching element degradation evaluation step in step T9, when it is determined that the switching elements and diodes constituting the inverter circuit 11 are degraded (step T9: YES), the degradation evaluation device sets a flag to prompt inspection of the inverter circuit 11 (step T10). Thereafter, the degradation evaluation device returns to step T1 and accepts signal input from the inverter 10. Based on this flag, the degradation evaluation device notifies the administrator of the degradation evaluation device of a warning.

[0058] On the other hand, when it is determined that the switching elements and diodes constituting the inverter circuit 11 are not degraded (step T9: NO), the degradation evaluation device determines whether the degradation of the capacitor is such that replacement is necessary (step T11).

[0059] If it is determined in step T11 that the capacitor does not need to be replaced (step T11: NO), the degradation evaluation device returns to step T1 and accepts signal input from the inverter 10.

[0060] On the other hand, in step T11, when it is determined that the capacitor C needs to be replaced (step T11: YES), the degradation evaluation device sets a flag to prompt the replacement of the capacitor C (step T12). After that, the degradation evaluation device returns to step T1 and is configured to receive a signal input from the inverter 10. Based on this flag, the degradation evaluation device is configured to send a warning notification to the administrator of the degradation evaluation device.

[0061] In the determination of the necessity of replacing the capacitor C in step T11, by setting the determination criteria in consideration of the margin until the replacement work is carried out, it is desirable to be able to replace the capacitor C at the timing when the operation of the inverter stops.

[0062] In this way, by being able to evaluate the degree of degradation of the capacitor C without using a sensor, it is possible to eliminate the risk of the inverter 10 stopping due to a sudden failure of the capacitor C.

[0063] As described above, in the inverter 10, the first to sixth switching elements S1, S2, S3, S4, S5, S6 and the first to sixth diodes D1, D2, D3, D4, D5, D6 that make up the inverter circuit 11 may fail or deteriorate earlier than the capacitor C. As a method for detecting the deterioration of the switching element, Japanese Patent Laid-Open No. 08-275586 also proposes managing by counting the number of switching operations of the switching element.

[0064] In the present invention, separately from the detection of the deterioration of the capacitor C described above, the deterioration of the switching elements and diodes that make up the inverter circuit 11 is detected from the amplitude of the output voltage signal of the inverter 10. In addition, due to the circuit configuration, it is difficult to specify whether a failure or deterioration has occurred in the switching element or the diode in the series connection state, and it is evaluated that a failure or deterioration has occurred in at least one of them.

[0065] In the present invention, as a method for evaluating the degree of deterioration of an inverter 10 that has a capacitor C on the input side and inputs direct current and outputs single-phase alternating current or three-phase alternating current, from the amplitude of the output voltage signal of the inverter 10 obtained by inputting a test voltage that is smaller than the operating voltage to the inverter 10, it is configured to have a switching element evaluation step for evaluating the degree of deterioration of the switching elements and diodes in the inverter 10. Further, the input of the test voltage to the inverter 10 is characterized in that it is input in a test mode executed when the inverter 10 is started, and after the end of this test mode, the operating voltage is input to the inverter 10 in the operating mode.

[0066] Furthermore, in the case of an inverter deterioration evaluation device, it is configured to have a switching element evaluation unit for evaluating the degree of deterioration of the switching elements and diodes in the inverter 10 from the amplitude of the output voltage signal of the inverter 10 obtained by inputting a test voltage that is smaller than the operating voltage to the inverter 10. Also, the input of the test voltage to the inverter 10 is characterized in that it is input in a test mode executed when the inverter 10 is started, and after the end of this test mode, the operating voltage is input to the inverter 10 in the operating mode.

[0067] By inputting a test voltage that is smaller than the operating voltage to the inverter, it is possible to detect a decrease in the amplitude of the output voltage signal of the inverter 10 that does not appear during operation in the normal operating mode, and by using this decrease in amplitude for the evaluation of deterioration, it is possible to evaluate the degree of deterioration of the inverter 10.

[0068] The deterioration evaluation device for the inverter 10 of the present invention uses the voltage-current signal generation unit 22 in the deterioration evaluation device 20 for the capacitor C described above as a voltage signal generation unit, and inputs the voltage signal generated by this voltage signal generation unit into the switching element evaluation unit 32 to evaluate the degree of deterioration of the inverter 10. Hereinafter, the deterioration evaluation device for the inverter 10 of the present invention will be described with reference to FIG. 3. Note that the inverter 10 itself is the same as that in the case of the deterioration evaluation device 20 for the capacitor C in FIG. 1, and the same reference numerals are used for the same components.

[0069] As shown in FIG. 3, the inverter 10 has an inverter circuit 11 composed of first to sixth switching elements S1, S2, S3, S4, S5, and S6 to which first to sixth diodes D1, D2, D3, D4, D5, and D6 are respectively connected in antiparallel. That is, in the inverter circuit 11, the first switching element S1 and the second switching element S2 form a U-phase leg 12, and a U-phase output line Lu is provided between the first switching element S1 and the second switching element S2. Also, in the inverter circuit 11, the third switching element S3 and the fourth switching element S4 form a V-phase leg 13, and a V-phase output line Lv is provided between the third switching element S3 and the fourth switching element S5. Further, in the inverter circuit 11, the fifth switching element S5 and the sixth switching element S6 form a W-phase leg 14, and a W-phase output line Lw is provided between the fifth switching element S5 and the sixth switching element S6. The capacitor C is connected in parallel with the U-phase leg 12, the V-phase leg 13, and the W-phase leg 14, respectively. In the present embodiment, the inverter 10 that inputs DC and outputs three-phase AC will be described. However, when single-phase AC is output, the above-described V-phase leg 13 and W-phase leg 14 are not present, and the description of the case of outputting single-phase AC will be omitted. Although not shown, the inverter 10 is provided with a drive control unit for appropriately driving the inverter circuit 11.

[0070] The deterioration evaluation device 20' for the inverter 10 is provided with a voltage signal generation unit 22' and a switching element evaluation unit 32'.

[0071] The voltage signal generation unit 22' receives signals from the U-phase output line Lu, the V-phase output line Lv, and the W-phase output line Lw of the inverter 10, generates a U-phase output voltage signal Vu(t), a V-phase output voltage signal Vv(t), and a W-phase output voltage signal Vw(t), and inputs them to the switching element evaluation unit 32'. The voltage signal generation unit 22' may use the voltage current signal generation unit 22 described above as it is, or may input the U-phase output voltage signal Vu(t), the V-phase output voltage signal Vv(t), and the W-phase output voltage signal Vw(t) output from the voltage current signal generation unit 22 to the switching element evaluation unit 32'.

[0072] The switching element evaluation unit 32' compares the magnitude of the amplitude of the input output voltage signal with the magnitude of the amplitude of the initial output voltage signal stored in the storage unit 31' to determine whether the device of the inverter circuit 11 has deteriorated.

[0073] Here, the input signal input to the inverter circuit 11 to generate the output voltage signal is a test voltage that is smaller than the operating voltage input when the inverter circuit 11 is in a normal operating state.

[0074] That is, at a relatively high operating voltage, even if the switching element or diode deteriorates, the influence of the deterioration is less likely to appear. However, when a test voltage smaller than the operating voltage is input, it is found that the influence of the deterioration is more likely to appear, and moreover, it is found that it can be evaluated by using the magnitude of the amplitude of the output voltage signal. Here, the test voltage is desirably 1 / 5 or less of the operating voltage, preferably 1 / 10 or less.

[0075] The input of the test voltage to the inverter circuit 11 is controlled by the drive control unit of the inverter circuit 11. In particular, the input of the test voltage is performed in the startup mode executed by the drive control unit when the inverter 10 is started. The evaluation of the degradation of the inverter 10 is performed by calculating the amount of decrease in the magnitude of the amplitude from the difference value between the magnitude of the output voltage signal when the test voltage is input and the magnitude of the amplitude of the initial output voltage signal stored in advance in the storage unit 31' of the degradation evaluation device 20'. When the amount of decrease in the magnitude of the amplitude becomes larger than a preset reference value, the drive control unit sets a flag and prompts the confirmation operation of the inverter circuit 11. As described above, in the inverter circuit 11, when an operating voltage higher than the test voltage is input, the influence of degradation is less likely to appear. Therefore, even if the degradation of the inverter circuit 11 is detected in the startup mode, it is often not necessary to immediately replace the inverter circuit 11.

[0076] The magnitude of the amplitude of the output voltage signal detected in the startup mode may be sequentially stored in the storage unit 31', and the magnitude of the amplitude of the initial output voltage signal may be the magnitude of the amplitude of the oldest stored output voltage signal.

[0077] After evaluating the degradation of the inverter 10 in the startup mode, the drive control unit of the inverter circuit 11 ends the startup mode and inputs an operating voltage to the inverter circuit 11 as the operating mode.

[0078] The above-described degradation evaluation device 20' can be configured by creating a dedicated evaluation circuit or can be configured using a personal computer. When configured using a personal computer, the output voltage output from the inverter 10 can be input to the personal computer via an appropriate input connector.

[0079] Hereinafter, based on the flowchart of FIG. 4, the case where a personal computer is used as a degradation evaluation device will be described. In the memory of the personal computer, various programs for executing functions necessary for the degradation evaluation device and the amplitude of the initial output voltage signal, etc. are stored. For convenience of explanation, hereinafter, the personal computer functioning as the degradation evaluation device will simply be referred to as the degradation evaluation device.

[0080] When the main power supply is turned on, the inverter 10 activates the drive control unit of the inverter circuit 11 and executes the startup mode. At this time, the startup mode signal is also input to the degradation evaluation device, and the startup mode is executed (step t1). That is, the signal input from the inverter circuit 11 to the degradation evaluation device is regarded as a signal generated by the inspection voltage.

[0081] In the startup mode, the drive control unit inputs an inspection voltage that is smaller than the operating voltage to the inverter circuit 11. Specifically, the voltage dividing circuit is activated to appropriately divide the drive voltage and input it.

[0082] The inverter circuit 11 to which the inspection voltage is input outputs a predetermined voltage from the U-phase output line Lu, the V-phase output line Lv, and the W-phase output line Lw, respectively, and inputs them to the degradation evaluation device. In the degradation evaluation device, the output voltage signal generation program is activated to generate a U-phase output voltage signal Vu(t), a V-phase output voltage signal Vv(t), and a W-phase output voltage signal Vw(t) (step t2).

[0083] Next, the degradation evaluation device activates the switching element evaluation program, and uses the generated U-phase output voltage signal Vu(t), V-phase output voltage signal Vv(t), and W-phase output voltage signal Vw(t) to compare with the amplitude of the initial output voltage signal stored in advance in the storage unit to evaluate the degree of degradation (step t3). This is the switching element evaluation step.

[0084] When the deterioration evaluation device detects the deterioration of devices such as switching elements and diodes in the inverter 10 because the amplitude of the output voltage signal has become small in the switching element evaluation step (step t3: YES), it sets a flag indicating that the deterioration of the devices such as switching elements and diodes has been detected (step t4).

[0085] After that, the deterioration evaluation device decides to end the startup mode (step t5). On the other hand, when the amplitude of the output voltage signal has not become small in the deterioration evaluation step (step t3: NO), it decides to end the startup mode as it is (step t5).

[0086] When ending the startup mode, the deterioration evaluation device may store the data of the amplitudes of the U-phase output voltage signal Vu(t), the V-phase output voltage signal Vv(t), and the W-phase output voltage signal Vw(t) in the storage unit.

[0087] Receiving the signal indicating the end of the startup mode from the deterioration evaluation device, the drive control unit enters the operation mode and inputs a predetermined operating voltage to the inverter circuit 11.

[0088] In this way, by being able to evaluate the degree of deterioration of the switching elements and diodes constituting the inverter circuit 11 without a sensor, it is possible to detect abnormalities in the inverter circuit 11 at an early stage.

Explanation of symbols

[0089] C Capacitor D1 First diode D2 Second diode D3 Third diode D4 Fourth diode D5 Fifth diode D6 Sixth diode S1 First switching element S2 Second switching element S3 Third switching element S4 Fourth switching element S5 Fifth switching element S6 Sixth switching element Lu U-phase output line Lv V-phase output line Lw W-phase output line 10 Inverter 11 Inverter circuit 12 U-phase leg 13 V-phase leg 14 W-phase leg 20 Deterioration evaluation device 21 Capacitor voltage signal generation unit 22 Voltage-current signal generation unit 23 Instantaneous output power signal generation unit 24 Ripple current signal generation unit 25 First fast Fourier transform unit 26 Second fast Fourier transform unit 27 Impedance signal generation unit 28 Equivalent series resistance and capacitance identification unit 29 Evaluation unit 31 Memory unit 32 Switching element evaluation unit

Claims

1. In a method for evaluating the degree of deterioration of a capacitor in an inverter that has a capacitor on the input side and inputs direct current to output single-phase alternating current or three-phase alternating current, an instantaneous output power signal generation step of generating an instantaneous output power signal using the output voltage signal and the output current signal of the inverter; a ripple current signal generation step of dividing the instantaneous output power signal by a capacitor voltage signal that is a signal of the voltage across both ends of the capacitor to generate a ripple current signal A method for evaluating the deterioration of a capacitor having the above steps.

2. an impedance signal generation step of dividing the capacitor voltage signal subjected to fast Fourier transform by the ripple current signal subjected to fast Fourier transform to generate an impedance signal; an equivalent series resistance and capacitance identification step of identifying an equivalent series resistance and a capacitance from a curve of the frequency characteristics of the impedance signal; a deterioration evaluation step of comparing the initially detected initial equivalent series resistance with the equivalent series resistance to evaluate deterioration, or comparing the initially detected initial capacitance with the capacitance to evaluate the degree of deterioration The method for evaluating the deterioration of a capacitor according to claim 1, having the above steps.

3. The method for evaluating the deterioration of a capacitor according to claim 2, wherein in the deterioration evaluation step, when deterioration of the capacitor is detected, a switching element deterioration evaluation step of evaluating the degree of deterioration of the switching element and the diode in the inverter is executed.

4. In a capacitor deterioration evaluation device for evaluating the degree of deterioration of a capacitor in an inverter that has a capacitor on the input side and inputs direct current to output single-phase alternating current or three-phase alternating current, an instantaneous output power signal generation unit that generates an instantaneous output power signal using the output voltage signal and the output current signal of the inverter; a ripple current signal generation unit that divides the instantaneous output power signal by a capacitor voltage signal that is a signal of the voltage across both ends of the capacitor to generate a ripple current signal A capacitor deterioration evaluation device having the above steps.

5. an impedance signal generation unit that divides the capacitor voltage signal subjected to fast Fourier transform by the ripple current signal subjected to fast Fourier transform to generate an impedance signal; an equivalent series resistance and capacitance identification unit that identifies an equivalent series resistance and a capacitance from a curve of the frequency characteristics of the impedance signal; An evaluation unit that compares the initially detected initial equivalent series resistance with the equivalent series resistance to evaluate degradation, or compares the initially detected initial capacitance with the capacitance to evaluate degradation, and The capacitor degradation evaluation device according to claim 4, which has the above.

6. The capacitor degradation evaluation device according to claim 5, further comprising a switching element degradation evaluation unit that evaluates the degree of degradation of the switching element and diode in the inverter when the degradation of the capacitor is detected by the evaluation unit.

7. In an inverter degradation evaluation method for evaluating the degree of degradation of an inverter that has a capacitor on the input side and inputs direct current to output single-phase alternating current or three-phase alternating current, A switching element evaluation step for evaluating the degree of degradation of the switching element and diode in the inverter from the amplitude of the output voltage signal of the inverter obtained by inputting a test voltage smaller than the operating voltage to the inverter. The inverter degradation evaluation method.

8. The method for evaluating the degradation of an inverter according to claim 7, wherein the input of the test voltage to the inverter is an input in a startup mode executed when the inverter is started, and after the end of the startup mode, the operating voltage is input to the inverter as an operating mode.

9. In an inverter degradation evaluation device for evaluating the degree of degradation of an inverter that has a capacitor on the input side and inputs direct current to output single-phase alternating current or three-phase alternating current, A switching element evaluation unit that evaluates the degree of degradation of the switching element and diode in the inverter from the amplitude of the output voltage signal of the inverter obtained by inputting a test voltage smaller than the operating voltage to the inverter. The inverter degradation evaluation device.

10. The inverter degradation evaluation device according to claim 7, wherein the input of the test voltage to the inverter is an input in a startup mode executed when the inverter is started, and after the end of the startup mode, the operating voltage is input to the inverter as an operating mode.

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