Power conversion device, remote monitoring system for power conversion device, and life estimation method for power conversion device

Abstract

There is a problem in that the accuracy of a calculated loss and the accuracy of subsequent calculations of temperature and degree of degradation are low. A power conversion device includes: a junction-fin temperature calculator capable of calculating a junction-fin temperature; and a fin temperature sensor capable of detecting a fin temperature. A junction temperature is calculated from the sum of the junction-fin temperature and the fin temperature. A loss characteristic based on the junction temperature at that time is called from the calculated junction temperature, and a more accurate loss is calculated. The temperature is estimated from the calculated loss and a transient thermal characteristics table, and then the degree of degradation is calculated.

Description

Power conversion device, remote monitoring system for power conversion device, and method for estimating life span of power conversion device

[0001] The present invention relates to a power conversion device, a remote monitoring system for the power conversion device, and a method for estimating the life span of the power conversion device.

[0002] Inverters, a type of power conversion device, are widely used in industry as motor drive devices in manufacturing equipment, elevators, transport equipment, etc. In these various applications, inverters are required to operate stably. If an inverter were to fail, it would cause factory production to stop and equipment operation to stop, resulting in a huge impact.

[0003] Inverters use power semiconductor devices such as IGBTs and diodes to control the flow and interruption of current and perform the desired power conversion. The power semiconductor devices are joined by wire bonding or soldering to copper foil patterns formed on an insulating substrate, which electrically connects them to external circuits. The insulating substrate is mounted on a metal base, and the power semiconductor devices are cooled via the metal base. A component that incorporates power semiconductor devices in a housing equipped with a cooling structure and electrical connection structure with external circuits is called a power module.

[0004] When current flows through or is cut off in a power semiconductor device, the power semiconductor device generates heat, and a temperature difference (hereinafter referred to as ΔT) occurs between the junctions of the power semiconductor device (the junctions between the device and wire bonding, and the junctions between the device and copper foil pattern) and the fins (metal bases with cooling structures).When the inverter is stopped, heat generation ceases and ΔT becomes smaller.

[0005] The junctions of the above-mentioned power semiconductor devices are made of materials with different thermal expansion coefficients, so fluctuations in ΔT cause thermal stress at the junctions. Repeated fluctuations in ΔT can cause separation or cracks in the junctions, leading to failure. The time it takes for such failures to occur depends on the magnitude and frequency of ΔT. The magnitude and frequency of ΔT vary depending on how the power conversion device is used and the device driven by the power conversion device.

[0006] Furthermore, the ratio of the load on the IGBTs and the diodes varies depending on the usage conditions of the device. Therefore, in order to prevent such failures, measures must be taken to understand the degree of the load on the IGBTs and the diodes depending on the usage conditions of the power conversion device.

[0007] Patent Document 1 is a prior art in this technical field. In Patent Document 1, a power conversion device equipped with a switching element is disclosed, and the loss of the switching element is calculated from the current flowing through the switching element and a loss data table. The temperature change of the switching element (junction) is calculated from the calculated temperature change and transient thermal resistance characteristics. The degree of deterioration of the switching element is estimated from the relationship between the calculated temperature change and the number of power cycles lifespan.

[0008] International Publication No. 2021 / 106175

[0009] In Patent Document 1, a certain loss data table is used to calculate the loss of the switching element, but the degree of damage to the switching element varies greatly depending on the junction temperature of the switching element.

[0010] In other words, the method of Patent Document 1 has a problem in that the accuracy of the calculated loss, as well as the accuracy of the subsequent calculation of temperature and degradation level, is low due to differences between the on-site junction temperature and the loss data table.

[0011] Therefore, the present invention is equipped with a junction-fin temperature calculator capable of calculating the junction-fin temperature and a fin temperature sensor capable of detecting the fin temperature. The junction temperature is calculated from the sum of the junction-fin temperature and the fin temperature. From the calculated junction temperature, loss characteristics based on the junction temperature at that time are retrieved to calculate more accurate loss. The temperature is estimated from the calculated loss and a transient thermal characteristic table, and then the degree of degradation is calculated.

[0012] The power conversion device according to the present invention performs loss calculations with higher accuracy than conventional ones based on real-time junction temperatures, thereby improving the accuracy of estimating the degree of degradation.

[0013] 1 is a configuration diagram of a power conversion device according to an embodiment of the present invention. FIG. 2 is a circuit diagram of an inverter according to an embodiment of the power conversion device according to the present invention. FIG. 3 is a perspective view of a power module of a power conversion device according to an embodiment of the present invention. FIG. 4 is a cross-sectional view of a power module of a power conversion device according to an embodiment of the present invention. FIG. 5 is a graph showing the collector-emitter voltage-collector current characteristics of an IGBT of a power conversion device according to an embodiment of the present invention. FIG. 6 is a graph showing the single-pulse switching loss-collector current characteristics of an IGBT of a power conversion device according to an embodiment of the present invention. FIG. 7 is a graph showing the forward voltage-forward current characteristics of a diode of a power conversion device according to an embodiment of the present invention. FIG. 8 is a graph showing the single-pulse recovery loss-forward current characteristics of an IGBT of a power conversion device according to an embodiment of the present invention. FIG. 9 is a graph showing the thermal impedance-time characteristics of an IGBT of a power conversion device according to an embodiment of the present invention. FIG. 10 is a graph showing the relationship between a junction temperature threshold and an electrical characteristic table according to an embodiment of the present invention. FIG. 11 is a flowchart showing processing in a temperature history calculator according to an embodiment of the present invention. FIG. 12 is an example of an electrical characteristic table according to an embodiment of the present invention. FIG. 13 is a graph showing the output of a lifespan calculation result of a power conversion device according to an embodiment of the present invention. FIG. 14 is a graph showing the life cycle-Tjc characteristics of a power semiconductor element of a power conversion device according to an embodiment of the present invention. FIG. 15 is an example of a remote monitoring system using a power conversion device according to the present invention.

[0014] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0015] 1 is a block diagram of a power conversion device according to an embodiment of the present invention. The power conversion device 100 according to the embodiment of the present invention includes a main circuit 200, a lifespan estimation device 300, and an interface device 400.

[0016] The main circuit 200 is composed of a diode rectifier 201 that rectifies AC power sent from the AC power source 101, a smoothing capacitor 202, IGBTs 203 (a, b, c, d, e, f) that are power semiconductor switching elements, and an inverter 205 that includes diodes 204 (a, b, c, d, e, f) that are connected in anti-parallel to the IGBTs.

[0017] 2 is a circuit diagram of an inverter in an embodiment of the power conversion device of the present invention. In this embodiment, the inverter 205 is a three-phase, two-level inverter. The inverter 205 is controlled by a motor control unit 206. Specifically, the motor control unit 206 calculates a gate signal at a set carrier frequency f_C based on the current value detected by current sensors 207 (a, b) and a speed command.

[0018] The calculated gate signal is amplified by the gate driver 208 and input as gate voltage to the IGBTs 203 (a, b, c, d, e, f). The ratio of the carrier period to the gate on-period is called on-duty D. This outputs a voltage so that the motor 102 operates at the commanded speed. In both the IGBTs 203 and diodes 204, the junction temperature rises due to Joule loss when on, switching loss when current is cut off, and recovery loss, and the junction temperature drops when off.

[0019] Fig. 3 is a perspective view of a power module of a power conversion device according to an embodiment of the present invention. A perspective view of a power module 220 incorporating an IGBT 203 and a diode 204 is shown in Fig. 4, and a cross-sectional view taken along line A-A' in Fig. 3 is shown. In Fig. 3, a plurality of power semiconductor elements 222, such as the IGBT 203 and the diode 204, and a temperature sensor 223 are arranged on a surface inside a housing 221 (only one semiconductor element is shown in Figs. 3 and 4).

[0020] 4 is a cross-sectional view of a power module for a power converter according to an embodiment of the present invention. A power semiconductor element 222, under-chip solder 224, copper foil 225, insulating substrate 226, under-substrate solder 227, and metal base 228 are stacked in this order, with the under-chip solder 224 and under-substrate solder 227 joining adjacent layers. The other side of the semiconductor element is joined with a metal wire 229.

[0021] Since the power semiconductor element 222 is bonded with materials having different thermal expansion coefficients, stress is applied to the bonded portion when the temperature of the power semiconductor element rises and falls. The ability to withstand this stress is called power cycle capability, and is expressed as the number of cycles that can be used at a given temperature amplitude, called a life cycle.

[0022] Therefore, if the temperature history of a semiconductor element is known, it is possible to estimate its lifespan.

[0023] The on-duty is determined by any modulation method, for example, by the ratio of the DC voltage vd to the motor voltage vo (vo / vd).

[0024] The losses of the IGBT 203 and the diode 204 can be calculated using Equations 2 and 3, respectively.

[0025]

[0026] FIG. 5 is a diagram showing the collector-emitter voltage-collector current characteristics of the IGBT of the power conversion device according to the embodiment of the present invention.

[0027] Here, rq and vq are the slope and intercept of a linear approximation curve of the collector-emitter voltage-collector current characteristics of an IGBT as shown in FIG.

[0028] The collector-emitter voltage-collector current characteristics of an IGBT are temperature dependent. FIG. 5 shows a characteristic 331 at low temperature, its approximate curve 332, a characteristic 331' at high temperature, and an approximate curve 332' at high temperature. In this example, the slope rq' of the approximate curve 332' at high temperature is smaller than the slope rq at low temperature. The intercept vq' of the approximate curve 332' at high temperature is larger than the slope vq at low temperature. FIG. 6 is a diagram showing the single-pulse switching loss-collector current characteristics of an IGBT in a power conversion device according to an embodiment of the present invention.

[0029] As shown in FIG. 6, aq and bq are the slope and intercept of the linear approximation curve of the switching loss-collector current characteristics per single pulse of the IGBT when the DC voltage is vdb.

[0030] The switching loss per pulse vs. collector current characteristic is temperature dependent. Figure 6 shows a characteristic 338 at low temperature, its linear approximation curve 337, a characteristic 338' at high temperature, and a linear approximation curve 337' at high temperature. In this example, the slope aq' of the approximation curve 338' at high temperature is smaller than the slope aq at low temperature. The intercept bq' of the approximation curve 332' at high temperature is larger than the slope vq at low temperature.

[0031] FIG. 7 is a diagram showing the forward voltage-forward current characteristics of the diode of the power conversion device according to the embodiment of the present invention.

[0032] rd and vd are the slope and intercept of a linear approximation curve 342 of the forward voltage-forward current characteristic 341 of the diode shown in FIG.

[0033] The forward voltage-forward current characteristics of a diode are temperature dependent. Figure 7 shows a characteristic 341 at low temperature, its linear approximation curve 342, a characteristic 341' at high temperature, and a linear approximation curve 342' at high temperature. In this example, the slope rd' of the linear approximation curve 342' at high temperature is smaller than the slope rd at low temperature. The intercept vd' of the linear approximation curve 342' at high temperature is larger than the slope vd at low temperature.

[0034] FIG. 8 is a diagram showing the single pulse recovery loss vs. forward current characteristics of the IGBT of the power conversion device according to the embodiment of the present invention.

[0035] ad and bd are the slope and intercept of a linear approximation curve 347 of the diode recovery loss per single pulse vs. forward current characteristic 346 when the DC voltage is Vdb, as shown in FIG.

[0036] The recovery loss per pulse vs. forward current characteristic is temperature dependent. Figure 8 shows a characteristic 346 at low temperature, its linear approximation curve 347, a characteristic 346' at high temperature, and a linear approximation curve 347' at high temperature. In this example, the slope ad' of the linear approximation curve 347' at high temperature is smaller than the slope ad at low temperature. The intercept bd' of the linear approximation curve 347' at high temperature is larger than the slope bd at low temperature.

[0037] Next, the temperatures of the IGBT and diode are calculated from the loss obtained above and the thermal characteristics of the IGBT and diode.

[0038]

[0039] The calculation is performed as follows.

[0040] 9 is a diagram showing the thermal impedance-time characteristics of the IGBT of the power conversion device according to the embodiment of the present invention, where τthq and rthq are variables used when the thermal impedance-time characteristics of the IGBT are approximated by Equation 11.

[0041] 10 is a diagram showing the thermal impedance-time characteristics of the diode of the power conversion device according to the embodiment of the present invention, where τthd and rthd are variables when the thermal impedance-time characteristics of the IGBT are approximated by Equation 11.

[0042] Next, the junction temperature is calculated using Equations 6 and 7.

[0043]

[0044] Tf is the temperature of the heat sink on which the power module shown in FIG.

[0045] The temperature of the heat sink is acquired using a temperature sensor and input to a temperature calculator. The temperature sensor may be, for example, built into the power module and installed on the heat sink near the power module. For example, a thermocouple, a thermistor, or the like may be used as the temperature sensor.

[0046] Next, based on the calculation results of the junction temperature based on the above, the variables used in the calculations of Equations 2 and 3 are reset.

[0047] 11 is a diagram showing the relationship between the junction temperature threshold and the electrical characteristics table in an embodiment of the present invention. A temperature region is determined in which the junction temperature 361 is bounded by thresholds 3621 and 3622. In section 3631, the junction temperature is determined to be equal to or lower than threshold 3621. In section 3632, the junction temperature is determined to be equal to or higher than threshold 3621 and equal to or lower than threshold 3622.

[0048] In section 3633, the junction temperature is determined to be equal to or greater than threshold 3622. The thresholds may be set within a typical operating range of a power semiconductor, for example, threshold 3621 may be set to 50°C, and threshold 3622 may be set to 100°C. Here, an example has been described in which there are two types of thresholds, but the number of thresholds may be one or more. Based on the above determination, the electrical characteristics table 302 shown in FIG. 13 , which is displayed for each temperature range, is referenced, and the set of variables rq, vq, aq, bq, rd, vd, ad, and bd for the temperature range to which the junction temperature belongs is selected.

[0049] For example, in the electrical characteristics table, in the collector-emitter voltage-collector current characteristics of an IGBT shown in FIG. 5, in the region where junction temperature 361 is low, the characteristics become like characteristic 331, but as junction temperature 361 becomes high, the characteristics become like characteristic 331', and therefore, it is common for the slope rq (rq') and intercept vq (vq') of the linear approximation curve of the collector-emitter voltage-collector current characteristics to also have different characteristics.

[0050] Next, the temperatures of the IGBT and the diode are calculated again using the electrical characteristics table 302 according to the junction temperature 361, using the formulas 2, 3, 4, and 5.

[0051] As shown in FIG. 12, the above flow first estimates the junction temperature, measures the fin temperature, calculates the junction temperature, and then selects a variable value corresponding to the junction temperature from the electrical characteristics table, and calculates the temperatures of the IGBT and diode, as shown in FIG. 13.

[0052] Here, the junction temperature 361 is estimated by calculating the sum of the junction temperature and the heat sink temperature, but a temperature sensor may be provided to measure the junction temperature. The junction temperature can also be estimated by referring to variables that have correlations with the ambient temperature, inverter load factor, operating time, etc.

[0053] The thresholds 3621 and 3622 that divide the temperature ranges may be one or more. If there are two or more thresholds, the intervals between the thresholds may be equal or unequal. Furthermore, the values ​​and temperature ranges in the electrical characteristics table may be arbitrarily set externally via an appropriate interface, such as the display 402 shown in FIG. 14.

[0054] This example shows that 36% of the life of the power semiconductor device remains during normal operation.

[0055] The above procedure is repeated until the tasks essential for maintaining the functionality of the power converter, such as inverter PWM calculation, are completed, and the microcomputer has spare processing capacity. This state is called the standby state shown in FIG. 12, and the process moves to the next flow, which is degradation evaluation.

[0056] Since the temperature change is stored for a certain period of time, the frequency of occurrence of temperature fluctuations is counted using a counting method such as the rainflow method. From this result, the damage d[1] of the entire temperature history is calculated using, for example, Equation 8.

[0057] Here, R[j] is the j-th temperature amplitude, and n[j] represents the number of occurrences of R[j].

[0058] 15 is a diagram showing the life cycle-Tjc characteristics of the power semiconductor element of the power conversion device according to the embodiment of the present invention, where alx and blx are coefficients of the life cycle characteristic curve that represents the relationship between temperature amplitude and life.

[0059] The calculation result d[1] is sent to the cumulative damage calculation unit 307 shown in Figure 1 and added to the cumulative damage d[0] read from the past cumulative damage storage device 308. That is, the new cumulative damage d[0] is calculated using Equation 9.

[0060] d[0] is initially 0, increases as damage accumulates, and when it reaches 1, it is determined that the life has expired. The result of this calculation d[0] is sent to the cumulative damage storage device and saved. d[0] is sent to the life estimator 309, which calculates the life L using Equation 10.

[0061] L is initially 100, decreases as damage accumulates, and reaches 0, indicating the end of the service life. With the above configuration, the service life estimation device 300 can calculate the service life of the IGBT 203 and the diode 204 in accordance with the power cycle.

[0062] 12 is a flowchart showing the processing in the temperature history calculator in the embodiment of the present invention. First, it is determined whether the inverter has started operating (S2). Once operation is confirmed, the switching frequency and on-duty are obtained from the motor control unit (S3).

[0063] In addition to this information, the loss is estimated based on the output current and DC voltage (S4) acquired from the sensor, the parameters in the electrical characteristics table, and Equation 2 and Equation 3 (S5). Next, the temperature difference between the junction and the case is estimated (S7) from the estimated loss, the thermal characteristics table, and Equation 4 and Equation 5 (S6). Next, the junction temperature is calculated from the temperature difference between the junction and the case, the temperature of the heat sink, and Equation 6 and Equation 7 (S8).

[0064] The obtained junction temperature is compared to see if it is within the temperature range of the electrical characteristics table (S9).

[0065] If the temperature is not within the temperature range, the electrical characteristics table that is within the temperature range is referenced and the parameters are reselected. After the parameters in the electrical characteristics table converge to within the range of the estimated junction temperature, the temperature amplitude is calculated based on Equations 4 and 5 (S10) and stored in the temperature history storage device (S11).

[0066] If the temperature is not within the temperature range and the computing device has spare processing capacity (S12), the damage level of the power semiconductor (Equation 8) (S13), the cumulative damage level (Equation 9) (S14), and the remaining life of the power semiconductor (Equation 10) (S15) are estimated from the temperature history.

[0067] Next, a remote monitoring system for the power conversion device 100 will be described with reference to Fig. 1 and Fig. 16. The power conversion device 100 includes a communication device 501 and a monitoring device 503 that monitors a plurality of inverters via a communication network 502.

[0068] 16 shows an example of a remote monitoring system using the power conversion device of the present invention. A temperature history calculator 301 sends the temperature history calculation results and the alarm determination results to a communication device 501. The communication device 501 sends this information to a monitoring device 503 via a communication network 502.

[0069] Each power electronics device 100 is connected to a communication network 502 via a communication device provided therein. A monitoring device 503 is also connected to the communication network 502 and monitors the plurality of power electronics devices 100.

[0070] The monitoring device 503 periodically receives the identifier and remaining life of the inverter from each power conversion device 100 in association with each other, and when the remaining life becomes shorter than a predetermined remaining life, outputs the identifier and remaining life of the inverter in association with each other to the output device.

[0071] At this time, the contact information associated with the manager of the inverter may also be output.

[0072] With the above configuration, the monitoring device 503 can monitor a plurality of power conversion devices 100. Furthermore, by equipping the monitoring device 503 with a display device such as a more detailed display than the display 402 and a high-performance arithmetic device, integrated management and analysis can be performed, such as comparing the operating conditions of a plurality of power conversion devices 100 and detecting abnormal operation.

[0073] For example, the system can manage daily operating status even from a location far from the power conversion equipment, such as an office, thereby streamlining management tasks. Furthermore, by accumulating data, it is possible to continuously update the information needed to formulate maintenance and operation plans. In addition, when an abnormality occurs, the system can share objective operating status information with related departments, thereby reducing downtime.

[0074] 100: Power conversion device 101: AC power supply 102: Motor 200: Main circuit 201: Diode rectifier 202: Smoothing capacitor 203 (a, b, c, d, e, f): IGBT 204 (a, b, c, d, e, f): Diode 205: Inverter 206: Motor control unit 207 (a, b): Current sensor 208: Gate driver 220: Power module 221: Housing 222: Power semiconductor element 223: Temperature sensor 224: Solder under chip 225: Copper foil 226: Insulating substrate 227: Solder under substrate 228: Metal base 229: Metal wire 300: Life estimation device 301: Temperature history calculator 302: Electrical characteristics table 303: Thermal characteristics table 304: Temperature history storage device 305: Damage calculation unit 306: Withstand characteristics table 307: Accumulative damage calculation unit 308: Accumulative damage storage device 309: Lifetime estimator 321: DC voltage 322: Reference voltage 336: Switching loss - collector current characteristics 337: Linear approximation curve 341: Diode forward voltage - forward current characteristics 342: Linear approximation curve 346: Recovery loss - forward current characteristics 347: Linear approximation curve 351: IGBT thermal impedance - time characteristics 356: Diode thermal impedance - time characteristics 361: Junction temperature 362: Lifecycle - Tjc characteristic curve 400: Interface device 401: Alarm determination device 402: Display 421: Lifetime estimation result 422: Reference value 501: Communication device 502: Communication network 503: Monitoring device

Claims

1. A power conversion device comprising: an inverter equipped with a temperature sensor that supplies power to drive a motor; a main circuit equipped with a motor control unit that controls the motor; a damage calculation unit that calculates the degree of damage to an element based on the inverter drive period received from the motor control unit and historical information of temperature changes obtained from the temperature sensor; a life estimation device equipped with a life estimation unit that calculates the remaining life of the element based on the degree of damage obtained from the damage calculation unit; and an interface device that outputs the remaining life calculated by the life estimation unit.

2. A power conversion device as claimed in claim 1, wherein the temperature sensor is installed in a heat sink of the inverter, and the damage calculation unit converts the temperature change of the heat sink obtained from the temperature sensor into the temperature change of the junction of the element, thereby determining the degree of damage to the element.

3. A power conversion device as claimed in claim 1, wherein the life estimation device comprises a temperature history calculation unit which calculates the cumulative number of temperature changes from the drive cycle of the inverter, calculates the temperature rise from the temperature sensor, and calculates temperature change history information from the cumulative number of temperature changes and the temperature rise, and a damage calculation unit which calculates the degree of damage to the elements from the temperature change history information calculated by the temperature history calculation unit.

4. A power conversion device as claimed in claim 1, wherein the lifespan estimation device comprises a cumulative damage calculation section which calculates the cumulative damage of the element from the degree of damage to the element obtained from the damage calculation section, and the lifespan estimation section calculates the remaining lifespan of the element from the cumulative damage of the element calculated by the cumulative damage calculation section.

5. A power conversion device as claimed in claim 3, wherein the life estimation device comprises a thermal characteristics table storing the correspondence between the temperature of the heat sink of the inverter and the temperature of the elements, and the temperature history calculation unit refers to the thermal characteristics table to obtain historical information on temperature changes of the elements.

6. A method for estimating a lifetime of a power conversion device, in which a main circuit supplies power to drive a motor, a temperature sensor attached to the inverter outputs the inverter temperature, a motor control unit outputs the inverter drive period, a damage calculation unit provided in a lifetime estimation device calculates the degree of damage to an element based on the inverter drive period received from the motor control unit and historical information of temperature changes obtained from the temperature sensor, a lifetime estimation unit calculates the remaining lifetime of the element based on the degree of damage obtained from the damage calculation unit, and an interface device outputs the remaining lifetime calculated by the lifetime estimation unit.

7. A remote monitoring system for power conversion devices comprising: a main circuit including an inverter having a temperature sensor for supplying power to drive the motor, and a motor control unit for controlling the motor; a damage calculation unit for determining the degree of damage to an element based on the inverter drive cycle received from the motor control unit and historical information of temperature changes obtained from the temperature sensor; a life estimation device including a life estimation unit for determining the remaining life of the element based on the degree of damage obtained from the damage calculation unit; and an interface unit for outputting the remaining life determined by the life estimation unit; and a monitoring device connected via a network, wherein the monitoring device receives the remaining life of the inverter sent from the power conversion devices and outputs the received remaining life of the inverter in association with an identifier of the inverter.

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