CN115589164A - Power conversion device and power conversion method - Google Patents

Abstract

The invention detects the temperature difference between the power conversion units connected in parallel with high precision. The power conversion apparatus includes: a plurality of power conversion units (14, 15) connected in parallel, each having a first switching element (24, 34) and a second switching element (25, 35) connected in series; temperature sensors (41, 42) that detect the internal temperature of each power conversion unit (14, 15); and a signal generation unit (120) that generates, for each power conversion unit (14, 15), an ON/OFF command signal for the control electrodes of the first switching elements (24, 34) and the second switching elements (25, 35) on the basis of the detection result of the temperature sensors (41, 42). A signal generation unit (120) detects the temperature of each power conversion unit when the power conversion device (1) outputs a DC current, using temperature sensors (41, 42).

Description

Power conversion device and power conversion method

Technical Field

The present invention relates to a power conversion device and a power conversion method for converting power between input and output.

Background

In order to reduce the amount of energy used in the world, power conversion devices using semiconductor switching elements, such as inverters for driving electric motors, converters for supplying power to inverters, and charge/discharge devices for electric vehicles, are required to have high efficiency. In these power conversion devices, a plurality of power conversion units having switching elements may be configured to be connected in parallel.

For example, patent document 1 describes that "when IGBT modules are connected in parallel, temperature variations occur in the IGBT chips due to differences in characteristics and structure, and if the temperature is suppressed to an absolute maximum temperature, the size of the device increases, and the cost also increases. Each module in which a temperature detection sensor is embedded is provided with a temperature detector, the magnitude of these temperature differences is obtained by a comparator, and the on timing of the module having a high temperature is delayed by an integration circuit of a resistor and a capacitor, thereby reducing the temperature.

Documents of the prior art

Patent document

Patent document 1: japanese patent laid-open No. 2009-159662

Disclosure of Invention

Technical problem to be solved by the invention

Generally, a power conversion unit includes switching elements called an upper arm and a lower arm. The technique described in patent document 1 can suppress temperature imbalance between the switching elements connected in parallel. However, since there is little temperature imbalance when the alternating current is output between the power conversion units connected in parallel, there is a problem that the detection accuracy of the temperature difference between the power conversion units is low.

In light of the above, a method capable of detecting the temperature difference between the power conversion units connected in parallel with high accuracy is required.

Means for solving the problems

In order to solve the above problem, a power conversion device according to an aspect of the present invention includes: a plurality of power conversion units connected in parallel, each having a first switching element and a second switching element connected in series; a temperature sensor that detects an internal temperature for each power conversion unit; and a signal generation unit that generates an on/off command signal for the control electrodes of the first switching element and the second switching element for each power conversion unit based on a detection result of the temperature sensor, wherein the signal generation unit detects the temperature of each power conversion unit when the power conversion device outputs a direct current using the temperature sensor.

Effects of the invention

According to at least one aspect of the present invention, the temperature difference between the power conversion units can be detected with high accuracy by detecting the temperatures of the power conversion units connected in parallel when the power conversion device outputs the direct current.

Technical problems, configurations, and effects other than those described above will be further apparent from the following description of the embodiments.

Drawings

Fig. 1 is a diagram showing an example of an overall configuration of an elevator system according to an embodiment of the present invention.

Fig. 2 is a block diagram showing an example of a conventional power conversion device (inverter system) and a drive circuit thereof.

Fig. 3 is a timing chart showing an example of waveforms of signals measured by each unit when there is no switching operation delay in the switching elements between the power conversion units connected in parallel.

Fig. 4 is a timing chart showing an example of waveforms of signals measured by each unit when the switching elements between the power conversion units connected in parallel have on-delay time variations.

Fig. 5 is a timing chart showing an example of waveforms of signals measured by each unit when switching elements between power conversion units connected in parallel have off delay time variations.

Fig. 6 is a diagram showing an example of the speed versus time characteristics in each operation period of the elevator system according to the embodiment of the present invention.

Fig. 7 is a configuration diagram showing an example of a power conversion device (inverter system) and a drive circuit thereof according to an embodiment of the present invention.

Fig. 8 is a diagram showing an example of the dc current output to the motor by the three-phase inverter system during the start compensation period.

Fig. 9 is a graph showing a characteristic of a temperature detected in the inverter system with respect to an output current.

Fig. 10 is a flowchart showing an example of the procedure of the process of reducing the temperature difference between the power conversion units connected in parallel according to the embodiment of the present invention.

Detailed Description

An example of a mode for carrying out the present invention will be described below with reference to the drawings. In the present specification and the drawings, components having substantially the same function or configuration are denoted by the same reference numerals, and redundant description thereof is omitted.

The power conversion device can convert power from direct current to alternating current by switching operation of the semiconductor element or vice versa, and is suitable for use in a variety of fields such as elevators, railways, and automobiles. As an example of the power conversion device, the inverter device is required to have a high output density, and the power conversion device is being downsized and lightened. With the miniaturization of power conversion units (part of power conversion devices) in which components such as power semiconductor modules, capacitors, and buses, on which power semiconductor elements are mounted, are integrated, there is an increasing demand for miniaturization and cost reduction of drive circuits for driving the power semiconductor elements.

Further, by mounting a plurality of power conversion units in which components such as a power semiconductor module, a capacitor, a bus line, and a gate circuit are integrated, the components are shared and the output capacity is improved, thereby reducing the cost of the power conversion device. By increasing the number of parallel power conversion units, the capacity of the power conversion device can be increased.

When power semiconductor modules are connected in parallel, the values of currents flowing through the power semiconductor elements become unbalanced due to variations in characteristics inherent to the power semiconductor elements, such as on delay times and off delay times of the power semiconductor elements. Therefore, current is concentrated in a part of the power semiconductor elements, and switching loss and conduction loss become large, which causes temperature imbalance.

In the related art, when power semiconductor elements, that is, power conversion units are connected in parallel, the power semiconductor elements need to be designed with a current value smaller than the rated current of each power semiconductor element in consideration of current imbalance. Therefore, the performance of the power semiconductor element cannot be utilized to the maximum.

As a method of detecting a current imbalance, there is a method of measuring a current of each power semiconductor element by a current sensor, but the same number of current sensors as the number of power semiconductor elements are required. Therefore, the cost corresponding to the number of current sensors added increases. Here, a method is known which utilizes a case where a temperature imbalance occurs when the current of the power semiconductor element is in an unbalanced state, using a temperature sensor of lower cost than the current sensor instead of the current sensor. However, in the elevator system, since the dc current output and the ac current output are switched according to the operating state, the detection result changes according to the timing of temperature detection. Therefore, the method of detecting the temperature is a problem. Hereinafter, a power conversion device according to an embodiment of the present invention in which a temperature sensor is provided in a power conversion unit will be described.

< one embodiment >

Fig. 1 is a diagram showing an example of an overall configuration of an elevator system according to an embodiment of the present invention. In the illustrated elevator system 1, ac power supplied from a system 2 is input to a three-phase converter system 10 in which a plurality of power conversion units 12 and 13 are connected in parallel via a filter circuit 3. The alternating current input to the converter system 10 is converted from alternating current to direct current in the converter system 10 via the power conversion units 12 and 13. Then, the three-phase inverter system 11 in which the plurality of power conversion units 14 and 15 are connected in parallel drives the motor 5 via the filter circuit 4. The filter circuits 3 and 4 remove harmonic components from the input sine wave (square wave).

As the load of the motor 5, there are a car 7 of the elevator connected to the rope 6 and a counterweight 8 for balancing the car 7. The power supplied to the motor 5 is consumed for winding up the rope 6 to move the car 6 of the elevator up and down.

The converter system 10 and the inverter system 11 are controlled by the control circuit section 9. The control circuit unit 9 controls on/off of the switching elements included in the power conversion units 14 and 15, and controls the current output to the load side.

[ Structure of conventional Power conversion device ]

Fig. 2 is a block diagram showing an example of a conventional power conversion device and a drive circuit thereof. To prevent the drawing from becoming complicated, only one phase of the bus bar is shown, and the other phases are omitted. As shown in fig. 2, in an inverter system 100 as a power conversion apparatus, power conversion units 14 and 15 are connected in parallel. The input sides of the power conversion units 14 and 15 are connected in parallel to a dc power supply 102 (corresponding to the converter system 10), and the output sides are connected to a resistive load 104 and an inductive load 105 of the inverter system 100. A resistive load 104 and an inductive load 105 are provided as output loads. The current sensor 106 is mounted on the wiring between the output of the inverter system 100 and the load.

The power conversion unit 14 includes a capacitor 21, an upper arm gate circuit 22, a lower arm gate circuit 23, an upper arm switching element 24, a lower arm switching element 25, an upper arm switching freewheel diode 26, and a lower arm switching freewheel diode 27. The upper arm switching element 24 and the lower arm switching element 25 are connected in antiparallel with an upper arm switching freewheel diode 26 and a lower arm switching freewheel diode 27, respectively. A switching branch composed of an upper arm switching element 24 and a lower arm switching element 25 connected in series is connected in parallel to the capacitor 21.

The connection midpoint between the upper arm switching element 24 and the lower arm switching element 25 is connected to the output terminal T1 via a resistive load 28 and an inductive load 29 connected in series. Output terminals of the upper arm gate circuit 22 and the lower arm gate circuit 23 are connected to gate terminals (control electrodes) of an upper arm switching element 24 and a lower arm switching element 25, respectively.

The power conversion unit 15 includes a capacitor 31, an upper arm gate circuit 32, a lower arm gate circuit 33, an upper arm switching element 34, a lower arm switching element 35, an upper arm switching flywheel diode 36, and a lower arm switching flywheel diode 37. The upper arm switching element 34 and the lower arm switching element 35 are connected in anti-parallel with an upper arm switching freewheel diode 36 and a lower arm switching freewheel diode 37, respectively. A switching branch composed of an upper arm switching element 34 and a lower arm switching element 35 connected in series is connected in parallel to the capacitor 31.

The connection midpoint between the upper arm switching element 34 and the lower arm switching element 35 is connected to the output terminal T2 via a resistive load 38 and an inductive load 39 connected in series. Output terminals of the upper arm gate circuit 32 and the lower arm gate circuit 33 are connected to gate terminals (control electrodes) of an upper arm switching element 34 and a lower arm switching element 35, respectively.

In the following description, the upper arm switching element 24, the lower arm switching element 25, the upper arm switching element 34, and the lower arm switching element 35 are sometimes simply referred to as "switching elements". In addition, the upper arm gate circuit 22, the lower arm gate circuit 23, the upper arm gate circuit 32, and the lower arm gate circuit 33 are sometimes simply referred to as "gate circuits".

The switching elements constituting the power conversion units 14 and 15 are, for example, IGBTs (Insulated Gate Bipolar transistors) or MOSFETs (Metal Oxide Semiconductor field effect transistors). The same applies to the switching elements of the power conversion units 12, 13.

One end of the capacitor 21 of the power conversion unit 14 is connected to one electrode (for example, a positive electrode) of the dc power supply 102, and the other end of the capacitor 21 is connected to the other electrode (for example, a negative electrode) of the dc power supply 102. The other electrode of the dc power supply 102 is connected to the ground 103. The same applies to the capacitor 31 of the power conversion unit 15. The output terminals T1 and T2 are connected to the output terminal T3 (load side) via the resistive load 104 and the inductive load 105. A current sensor 106 for detecting an output current is connected to a wiring for connecting the resistive load 104 and the inductive load 105 to the output terminal T3.

In addition, when the inductance of the inductive load 105 of the inverter system 100 can be replaced with the inductance of the wiring, the inductive load 105 may be omitted. In addition, when the load connected to the output terminal T3 is the motor 5 or the like having a sufficiently large inductance or having a characteristic regarded as a current source, the inductive load 105 may be omitted.

The control circuit unit 9 shown in fig. 1 controls on/off of the switching elements 24, 25, 34, and 35 included in the power conversion units 14 and 15, and controls the output current Itotal detected by the current sensor 106. The output current Itotal is the sum of the output current I1 of the power conversion unit 14 and the output current I2 of the power conversion unit 15. Then, the control circuit unit 9 controls on/off of the switching elements 24, 25, 34, and 35 based on the output current Itotal detected by the current sensor 106. The power conversion units 14, 15 comprise gate circuits 22, 23, 32, 33 providing gate signals to each switching element 24, 25, 34, 35. The control circuit unit 9 outputs a control command to the gate circuits corresponding to the switching elements 24, 25, 34, and 35, and controls the switching operation (on/off) of the switching elements 24, 25, 34, and 35.

The control circuit unit 9 is a controller composed of a microcomputer or the like, for example. The control circuit unit 9 includes an analog/digital (a/D) conversion circuit 9a, a processor 9b, a memory 9c, and the like, and the analog/digital (a/D) conversion circuit 9a converts the output current Itotal detected by the current sensor 106 into a digital signal. The processor 9b is a Processing device such as a CPU (Central Processing Unit). As the Processing device, an MPU (Micro-Processing Unit) may be used instead of the CPU. The memory 9c is a storage device such as a semiconductor memory in which a program code (control program) of software for realizing each function of the present embodiment is stored. The Control circuit Unit 9 has a network interface (not shown) and receives a target value of an output current (load current) from, for example, an ECU (Electronic Control Unit) of the system to be controlled. The processor 9b reads out a control program from the memory 9c, executes the control program, and outputs a control command (input signal 101) to the gate circuits corresponding to the switching elements 24, 25, 34, and 35 based on the current detection value of the current sensor 106 input from the a/D conversion circuit 9a and the target value.

An input signal 101 is output from the control circuit unit 9 as a control command, and the input signal 101 is input to the gate circuits 22, 23, 32, and 33. The gate circuits 22, 23, 32, and 33 generate gate signals (gate voltage pulses) for driving the switching elements 24, 25, 34, and 35 based on the input signal 101, respectively, and input the gate signals to the gate terminals of the upper arm switching elements 24 and 34 and the lower arm switching elements 25 and 35. The gate signal is a signal (on/off command signal) for giving an on/off command to the switching element.

When the gate signal is switched from high level to low level (on), the upper arm switching elements 24 and 34 and the lower arm switching elements 25 and 35 are turned on and brought into an on state, and a current flows. On the other hand, when the gate signal is switched from low level to high level (off), the upper arm switching elements 24 and 34 and the lower arm switching elements 25 and 35 are turned off without conduction between the source terminal and the drain terminal, and no current flows.

[ operation waveform without a shift operation delay time deviation ]

Fig. 3 is a timing chart showing an example of waveforms of signals measured by the respective sections when there is no switching operation delay time deviation in the switching elements between the power conversion units 14 and 15 connected in parallel. The horizontal axis of fig. 3 represents time [ s ]. The vertical axis of fig. 3 is, in order from the top, the gate signal of the power conversion unit 14, the gate signal of the power conversion unit 15, the output voltage of the power conversion unit 14, the output voltage of the power conversion unit 15, the output current of the power conversion unit 14, the output current of the power conversion unit 15, the temperature of the power conversion unit 14, and the temperature of the power conversion unit 15. In the present specification, the description is given assuming that the inductance of the inductive load 105 or the load side is sufficiently large and the current Itotal of the inductive load 105 is regarded as constant. In addition, the voltage applied to the capacitor 21 and the capacitor 31 is equal to the voltage of the dc power supply 102.

When gate signals of the same pulse waveform are input to the switching elements 24, 25, 34, 35 of the power conversion units 14, 15, the on delay times Ton1, ton2 of the output voltages of the power conversion units 14, 15 are equal when there is no delay time deviation in these switching elements. Similarly, the turn-off delay times Toff1, toff2 are also equal. As a result, the output currents of the power conversion units 14 and 15 become equal. In addition, the temperatures of the power conversion units 14, 15 also become equal.

[ operating waveform when there is a variation in ON delay time ]

Fig. 4 is a timing chart showing an example of waveforms of signals measured by each unit when there is a variation in on delay time of the switching elements between the power conversion units 14 and 15 connected in parallel. The relationship between the horizontal axis and the vertical axis in fig. 4 is the same as that in fig. 3.

When gate signals of the same pulse waveform are input to the switching elements 24, 25, 34, 35 of the power conversion units 14, 15, the on delay times Ton1, ton2 of these switching elements are deviated (Ton 1 < Ton 2), and therefore the pulse width of the output voltage of the power conversion unit 15 becomes narrower than that of the power conversion unit 14. As a result, the output current of the power conversion unit 15 becomes smaller, and the output current of the power conversion unit 14 becomes larger than that of the power conversion unit 15. Therefore, the temperature of the power conversion unit 14 becomes higher than that of the power conversion unit 15.

[ operating waveform when there is a variation in the off delay time ]

Fig. 5 is a timing chart showing an example of waveforms of signals measured by each unit when there is a variation in off delay time of the switching elements between the power conversion units 14 and 15 connected in parallel. The relationship between the horizontal axis and the vertical axis in fig. 5 is the same as that in fig. 3.

When gate signals of the same pulse waveform are input to the switching elements 24, 25, 34, 35 of the power conversion units 14, 15, the off delay times Toff1, toff2 of these switching elements are deviated (Toff 1 < Toff 2), and therefore, the pulse width of the output voltage of the power conversion unit 15 becomes wider compared to the power conversion unit 14. As a result, the output current of the power conversion unit 15 increases, and the output current of the power conversion unit 14 decreases compared to the power conversion unit 15. Thereby, the temperature of the power conversion unit 14 becomes lower than that of the power conversion unit 15.

When the output currents between the power conversion units 14, 15 connected in parallel are unbalanced, the currents concentrate on a part of the switching elements, and the switching loss and the conduction loss become large, thereby generating a temperature imbalance of the switching elements (between the power conversion units 14, 15).

Therefore, a method which is inexpensive compared to the method using the current sensor 106 and which can detect the occurrence of imbalance in the output current between the power conversion units 14, 15 with high accuracy even in the case of using a temperature sensor is a problem.

[ speed characteristics of Elevator System ]

Fig. 6 is a graph in which the horizontal axis of fig. 6 represents time [ s ] and the vertical axis represents speed [ m/s ] showing an example of the speed versus time characteristics in each operation period of the elevator system 1. As shown, the elevator system 1 includes a start-up compensation period 150, an acceleration period 151, a constant speed period 152, and a deceleration period 153 in one operation period.

In the start-up compensation period 150, the elevator system 1 fixes the motor 5, and causes the motor 5 to generate torque by flowing a direct current. At this stage, the motor 5 is stopped and the car 7 does not move. In the acceleration period 151, the elevator system 1 outputs an ac current from the power conversion device, and increases the frequency of the output current to increase the rotation speed of the motor 5, thereby accelerating the car 6. In the constant speed period 152, the elevator system 1 makes the frequency of the output current constant and the rotation speed of the motor 5 constant. In the deceleration period 153, the elevator system 1 reduces the frequency of the output current to slow down the rotation speed of the motor 5 and decelerate the car 6.

Between the parallel connected power conversion units 14, 15 there are resistive loads 28, 38 with a resistive component and inductive loads 29, 39 with an inductive component. Since the load at the time of dc current output is not an inductive component but only a resistive component, a cross current flowing between the power conversion cells 14 and 15 connected in parallel increases, and imbalance of the output currents of the power conversion cells 14 and 15 becomes maximum. Here, the larger the imbalance of the output currents of the power conversion units 14, 15, the larger the temperature difference (temperature imbalance) between the power conversion units 14, 15, and the more significant the temperature difference.

Therefore, the start-up compensation period 150 in which the dc current is output generates a significant temperature difference between the power conversion units 14 and 15 as compared with the acceleration period 151, the constant speed period 152, and the deceleration period 153 in which the other ac currents are output. Therefore, the detection of the temperature difference between the power conversion units 14, 15 can be performed with high accuracy during the startup compensation period 150. Therefore, during the start-up compensation period 150 of the output cross current, the temperature difference between the power conversion cells 14 and 15 is detected, whereby the imbalance of the output currents between the power conversion cells 14 and 15 can be detected with high accuracy.

[ configuration of Power conversion device of one embodiment ]

Next, a power conversion device and a drive circuit thereof according to an embodiment of the present invention will be described with reference to fig. 7.

Fig. 7 is a configuration diagram showing an example of a power conversion device and a driving circuit thereof according to an embodiment of the present invention. The inverter system 11 as a power conversion device is similar to the conventional inverter system 100 (fig. 2) in that it includes the power conversion units 14 and 15, but differs in the control signals (gate voltage pulse widths) supplied to the gate terminals of the gate circuits 22 to 33.

As shown in fig. 7, the input sides of the power conversion units 14 and 15 are connected in parallel to the dc power supply 102, and the output sides are connected in parallel to the resistive load 104 and the inductive load 105 of the inverter system 11. A current sensor 106 is mounted on a wiring on the output side of the inverter system 11. The internal configuration of the power conversion units 14 and 15 is the same as that shown in fig. 2, and therefore the description will be given with a focus on the difference.

In the power conversion unit 14, the temperature sensor 41 is disposed in the vicinity of the upper arm switching element 24 and the lower arm switching element 25. The distances between the upper arm switching element 24 and the lower arm switching element 25 and the temperature sensor 41 are designed to be appropriate distances for measuring the temperatures of the switching elements 24 and 25 by experiments or the like. In the power conversion unit 15, the temperature sensor 42 is disposed in the vicinity of the upper arm switching element 34 and the lower arm switching element 35. The temperature sensor 41 detects the temperature in the power conversion unit 14, which is the switching elements 24 and 25 of the power conversion unit 14, and the temperature sensor 41 detects the temperature in the power conversion unit 15, which is the switching elements 34 and 35 of the power conversion unit 15. The detected temperature information is input to the temperature storage unit 121.

The control circuit section 9 includes a signal generation section 120, and the signal generation section 120 generates control signals to be supplied to the gate circuits 22, 23, 32, and 33. The signal generating section 120 includes a temperature storage section 121 and an on/off time adjusting section 122. The temperature storage unit 121 is configured by the processor 9b and the memory 9c, and stores temperature information measured by the temperature sensors 41 and 42. The temperature information and the input signal 101 stored in the temperature storage section 121 are input to the on/off time adjustment section 122. The on/off time adjustment section 122 adjusts the pulse width of the input signal 101 (gate voltage pulse) based on the temperature information and the input signal 101, and supplies the adjusted input signal 101 to the respective gate circuits 22, 23, 32, and 33 as an on/off instruction signal. The input signal 101 may be input to the on/off time adjustment unit 122 via the temperature storage unit 121.

Fig. 8 shows an example of the dc current output from the three-phase inverter system 11 to the motor 5 during the start-up compensation period 150. The phase difference of each phase with respect to the reference axis is determined by the position of the motor 5 (the position of the rotation axis). The motor position at the time of start compensation is the motor position at the time when the motor 5 is stopped in the previous operation mode, and the motor position is irregular. Therefore, during the startup compensation period 150, the output currents of the power conversion units 14, 15 become irregular.

[ temperature vs. output Current characteristics ]

Fig. 9 is a graph showing the characteristic (rate of change) of the temperature detected in the inverter system 11 with respect to the output current. In fig. 9, the horizontal axis represents the magnitude (absolute value) of the output current Itotal of the power conversion device (inverter system 11) [ a ], and the vertical axis represents the temperature difference Δ T [ ° c ] between the power conversion units 14, 15 connected in parallel.

Hereinafter, in the present specification, the characteristic of the temperature of the inverter system 11 with respect to the output current is referred to as a change rate. When the elevator is running, a direct current is output only during the start-up compensation period 150. Since the output current imbalance becomes maximum when the dc current is output, the temperature difference can be detected with high accuracy. Therefore, it is preferable to perform detection at the time of start-up compensation of the output dc current. However, as described in fig. 8, at the time of the dc current output, a different dc output current is obtained every detection depending on the motor position (position of the rotating shaft).

When comparing the temperature difference between the power conversion units 14, 15, it is necessary to perform comparison with the same dc output current, but since the dc output current is irregular depending on the motor position, it is difficult to perform comparison of the temperature difference based on the same dc output current. Therefore, the temperatures of the power conversion units 14, 15 are detected a plurality of times, and temperature information with respect to the direct current is stored. From the stored information, the rate of change of the temperature difference between the power conversion units 14, 15 with respect to the dc output current can be calculated. By using the rate of change of the temperature difference, it is possible to detect a temperature imbalance that occurs between the power conversion units 14, 15 connected in parallel.

In the inverter system 11, the temperatures of the power conversion units 14 and 15 are detected at the time of dc current output. The temperature difference between the power conversion units 14, 15 connected in parallel is calculated from the detected temperature, and information of the output current and the temperature difference is stored. The information of the output current and the temperature difference is stored for at least two times, and the change rate 200 of the temperature difference relative to the output current is calculated according to the detection result.

When the change rate 200 is large, the temperature imbalance is large, and the loss is concentrated on a part of the switching elements, so that it is necessary to eliminate the imbalance. Therefore, the control for eliminating the unbalance according to the change rate of the temperature difference will be described next.

The imbalance in the output currents or the temperatures of the power conversion units 14 and 15 depends on the pulse width deviation of the output voltages of the power conversion units 14 and 15 caused by the delay time deviation of the switching operation of the switching elements. Therefore, in order to eliminate the imbalance of the output current, it is necessary to adjust the gate signals supplied to the respective gate circuits in accordance with the relationship between the rate of change of the temperature difference and the threshold value.

In addition, as a control method for eliminating the imbalance according to the change rate of the temperature difference, for example, when the change rate 200 exceeds a threshold value, the on/off time adjustment unit 122 performs control for reducing the imbalance by delaying the on time of the power conversion cell on the high temperature side to narrow the pulse width. After this control, the temperature of the power conversion units 14 and 15 is detected and stored again, and the rate of change 201 is obtained by calculating the rate of change in the temperature difference between the power conversion units 14 and 15.

The controlled rate of change 201 is lower than the rate of change 200, and the change in temperature difference is smaller than the output current of the inverter system 11, so the temperatures of the power conversion units 14 and 15 are equalized. This reduces the temperature imbalance of the power conversion units 14 and 15, and thus can suppress an increase in the switching loss and the conduction loss of some of the switching elements. And when the change rate of the temperature difference is less than or equal to the threshold value, judging that no temperature imbalance exists, and not adjusting.

In addition, when the change rate 200 exceeds the threshold value, the off time of the power conversion unit on the low temperature side is delayed, so that the pulse width is widened and the change rate 200 is reduced. This may be a method of equalizing the temperatures between the power conversion units 14 and 15.

In this way, the signal generating unit 120 has a function of correcting at least one of the on time and the off time of the on/off command signal in accordance with the detected temperature imbalance between the power conversion units 14 and 15.

[ example of procedure for temperature difference lowering treatment ]

Next, a step example of a process for reducing the temperature difference between the power conversion units 14, 15 connected in parallel according to an embodiment of the present invention will be described with reference to fig. 10.

Fig. 10 is a flowchart showing an example of the procedure of the process for reducing the temperature difference between the power conversion units 14, 15 connected in parallel. The signal generation unit 120 repeats the processing of steps S2 to S4 until the count value of the number of detections reaches a predetermined number (S1). First, the signal generation unit 120 determines whether or not the start compensation period 150 is currently present (S2), and proceeds to step S3 if the start compensation period 150 is present (yes determination in S2), and executes the determination process in step S2 again if the start compensation period 150 is not present (no determination in S2).

Next, the signal generation unit 120 detects the temperatures of the power conversion units 14 and 15 and the output current of the inverter system 11 using the temperature sensors 41 and 42 and the current sensor 106 during the start-up compensation period 150, and stores information on the detected temperatures and output currents in the temperature storage unit 121 (S3). Next, the signal generation unit 120 increments the count value of the number of times of detection of the temperature and the output current by "1" (S4).

Next, the signal generation unit 120 calculates a rate of change α (for example, the rate of change 200 in fig. 9) of the temperature difference between the power conversion units 14 and 15 with respect to the output current, based on the stored information of the temperature and the output current (S5). When the change rate α is larger than the threshold value (yes in S6), the signal generation unit 120 adjusts the gate voltage pulse width (S7). For example, the signal generation unit 120 delays the on time of the switching element included in the high-temperature-side power conversion unit by using the on/off time adjustment unit 122, and reduces the rate of change α of the temperature difference between the power conversion units 14 and 15. By reducing the rate of change α, the temperatures of the power conversion units 14 and 15 can be controlled in the equalization direction.

On the other hand, when the change rate α is equal to or less than the threshold value (no in S6), it is determined that there is no temperature imbalance or a slight difference in the power conversion units 14 and 15, and the gate voltage pulse width is not adjusted. If it is determined to be "no" after the process of step S7 or in step S6, the process of the present flowchart is ended.

According to the power conversion device according to the embodiment of the present invention, the inverter system 11 detects the temperatures of the power conversion units 14 and 15 connected in parallel a plurality of times when outputting the dc current, and stores the temperatures in the temperature storage unit 121. Then, in the inverter system 11, when the rate of change α of the temperature difference between the power conversion units 14 and 15 with respect to the output current exceeds a threshold value, the pulse width of the gate signal of each switching element is adjusted. As a result, the inverter system 11 according to the present embodiment can detect the temperature difference between the power conversion units 14 and 15 with higher accuracy than in the conventional art.

[ adjustment of Upper and lower arms according to output Current ]

In addition, it is necessary to switch the upper arm switching elements 24, 34 and the lower arm switching elements 25, 35 according to the direction of the output current of the inverter system 11 and adjust the gate signals, respectively. Therefore, a method of adjusting the upper and lower arms in accordance with the output current of the inverter system 11 will be described next.

Since a current flows to the upper arm switching devices 24 and 34 when a current is output from the inverter system 11 and a current flows to the lower arm switching devices 25 and 35 when a current is drawn into the inverter system 11, a method of changing the arm for adjusting the gate signal in accordance with the direction of the output current becomes a problem.

Therefore, the current sensor 106 is used to detect whether a current is output from the inverter system 11 or introduced into the inverter system 11, and to switch the arm that adjusts the gate signal. This makes it possible to suppress variation in the pulse width of the gate voltage for each of the upper and lower arms. It is determined whether the current is output from the inverter system 11 or introduced into the inverter system 11 based on the detected current of the current sensor 106.

As described above, the signal generation unit 120 has the following functions: the on/off time adjustment unit 122 switches the upper arm switching elements 24 and 25 and the lower arm switching elements 25 and 35 in accordance with the output current Itotal of the inverter system 11, thereby correcting at least one of the on time and the off time of the on/off command signal.

That is, the signal generating unit 120 corrects at least one of the on time and the off time of the switching elements 24 and 34 corresponding to the upper arm among the upper arm switching elements 24 and 34 and the lower arm switching elements 25 and 35 when the current is output from the inverter system 11. When a current is introduced into the inverter system 11, the signal generating unit 120 corrects at least one of the on time and the off time of the switching elements 25 and 35 corresponding to the lower arm among the upper arm switching elements 24 and 34 and the lower arm switching elements 25 and 35.

The signal generating unit 120 has such a correction function that it is possible to select an appropriate arm from the lower arm and the upper arm and adjust the delay time of the switching operation at the time of current output and current introduction of the inverter system 11.

As described above, the power conversion device (inverter system 11) according to the present embodiment includes: a plurality of power conversion units connected in parallel, each having a first switching element (upper arm switching element 24, 34) and a second switching element (upper arm switching element 25, 35) connected in series at each power conversion unit (power conversion unit 14, 15); temperature sensors (temperature sensors 41, 42) that detect the internal temperature for each power conversion unit; and a signal generation unit (signal generation unit 120) that generates an on/off command signal (gate signal) for the control electrodes of the first switching element and the second switching element for each power conversion unit based on the detection result of the temperature sensor. The signal generation unit detects the temperature of each power conversion unit when the power conversion device outputs a direct current, using a temperature sensor.

In the power converter (inverter system 11) according to the present embodiment, the dc output time is a start compensation period of the motor connected to the power converter.

In the power conversion device (inverter system 11) according to the present embodiment, the signal generation unit includes a storage device (temperature storage unit 121), and the storage device (temperature storage unit 121) stores the detected temperature information of each power conversion cell. Then, the power conversion apparatus stores the output current of the power conversion apparatus and temperature information of each power conversion cell detected by the temperature sensor, calculates a change rate of a temperature difference between the power conversion cells with respect to the output current from the detection results of a plurality of times, and compares the change rate of the temperature difference with a threshold value, thereby detecting a temperature imbalance between the power conversion cells.

According to the power conversion device of the present embodiment, the temperature difference between the power conversion units can be detected with higher accuracy than in the conventional technology by detecting and storing the temperatures of the power conversion units connected in parallel when the power conversion device outputs the dc current a plurality of times.

[ modified examples ]

In the above-described embodiment, the start-up compensation period 150 of the electric motor 5 is used as the dc current output of the inverter system 11, but other methods are also possible. For example, in a system such as the elevator system 1, a dc output mode may be prepared in the power conversion device (the inverter system 11), and when the dc output mode is selected, the temperature of each power conversion cell at the time when the power conversion device outputs dc can be detected.

In the present description, the configuration of the power conversion device (inverter system 11) in which two power conversion units are connected in parallel has been described, but the number of power conversion units connected in parallel may be 3 or more. In this case, for example, for a combination of a plurality of types of power conversion units, the rate of change in the temperature difference between the power conversion units may be determined for all the combinations, or the rate of change in the temperature difference may be determined only for a combination of one or more power conversion units specified in advance.

Although the power conversion device of the present invention is applied to a three-phase inverter system, the power conversion device of the present invention can be applied to a three-phase inverter system including power conversion units connected in parallel. The power conversion device of the present invention can also be applied to a single-phase inverter system, a single-phase converter system, a boost converter system, a buck converter system, or the like, which includes power conversion units connected in parallel.

The present invention is not limited to the above-described embodiment, and various other application examples and modifications can be made without departing from the technical idea of the present invention described in the claims. For example, although the above-described embodiment describes the configuration of the inverter system as the power conversion device in detail and specifically for the purpose of easily understanding the present invention, the present invention is not necessarily limited to the configuration including all the components described. Further, other components may be added to, replaced with, or deleted from a part of the configurations of the embodiments.

Some or all of the above-described structures, functions, processing units, and the like may be implemented in hardware by being designed, for example, in an integrated circuit or the like. As the hardware, a general processor device such as an FPGA (Field Programmable Gate Array) or an ASIC (Application Specific Integrated Circuit) may be used.

In the above embodiment, the control lines and the information lines necessary for the description are shown, but the present invention is not limited to the control lines and the information lines shown in the drawings. In practice, it is also possible to consider that almost all structural elements are connected to each other.

Description of the reference symbols

1. Elevator system

2. System

3. 4 filter circuit

5. Motor (load)

6. Rope

7. Car

8. Counterweight

9. Control circuit part

9a A/D conversion circuit

9b processor

9c memory

10. Converter system

11. Inverter system

12-15 power conversion unit

21. 31 capacitor

22. 23, 32, 33 gate circuit

24. 34 upper arm switching element

25. 35 lower arm switching element

26. 36 upper arm switching freewheeling diode

27. 37 lower arm switch freewheeling diode

14. 15 power conversion unit

28. 38 resistive load

29. 39 inductive load

101. Input signal

102. Direct current power supply

103 GND

104. Resistance load (output load)

105. Inductive load (output load)

106. Current sensor

120. Signal generating part (control circuit part)

121. Temperature storage part

122. On/off time adjustment unit

150. During startup compensation

151. During acceleration

152. During constant speed

153. During deceleration

200. 201 rate of change.

Claims (8)

1. A power conversion apparatus comprising:

a plurality of the power conversion units connected in parallel, each having a first switching element and a second switching element connected in series; a temperature sensor that detects an internal temperature for each of the power conversion units; and a signal generating unit that generates an on/off command signal for the control electrodes of the first switching element and the second switching element for each of the power conversion units based on a detection result of the temperature sensor,

the signal generation unit detects the temperature of each power conversion unit when the power conversion device outputs a direct current, using the temperature sensor.

2. The power conversion apparatus according to claim 1,

the output is during start-up compensation of a motor connected to the power conversion device.

3. The power conversion apparatus of claim 2,

the signal generating unit includes a storage device for storing the detected temperature information of each power conversion unit,

the temperature imbalance between the power conversion units is detected by storing the output current of the power conversion device and the temperature information of each power conversion unit detected by the temperature sensor, calculating the rate of change of the temperature difference between the power conversion units with respect to the output current from the results of the detection a plurality of times, and comparing the rate of change of the temperature difference with a threshold value.

4. The power conversion apparatus according to claim 3,

the signal generation unit has the following functions:

at least one of the on-time and the off-time of the on/off command signal is corrected in accordance with the detected temperature imbalance between the power conversion units.

5. The power conversion apparatus of claim 4,

the signal generation unit has the following functions:

the first switching element and the second switching element are switched according to an output current of the power conversion device and at least one of an on time and an off time of the on/off command signal is corrected.

6. The power conversion apparatus of claim 5,

the signal generation unit has the following functions:

at least one of on-time and off-time of a switching element corresponding to an upper arm of the first switching element and the second switching element is corrected when a current is output from the power conversion device, and at least one of on-time and off-time of a switching element corresponding to a lower arm of the first switching element and the second switching element is corrected when a current is introduced into the power conversion device.

7. The power conversion apparatus of claim 2,

the motor is a winding motor for winding up a car of an elevator by using an output of the power conversion device,

the output is that the winding motor is in a stop process.

8. A power conversion method that is a power conversion method of a power conversion apparatus, the power conversion apparatus including:

a plurality of the power conversion units connected in parallel having a first switching element and a second switching element connected in series at each power conversion unit; a temperature sensor that detects an internal temperature of each of the power conversion units; and a signal generating unit that generates an on/off command signal for the control electrodes of the first switching element and the second switching element for each of the power conversion units based on a detection result of the temperature sensor, the power conversion method being characterized in that,

the signal generation unit detects the temperature of each power conversion unit when the power conversion device outputs a direct current, using the temperature sensor.

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