Power conversion device and power conversion method

Abstract

This invention provides a high-precision method for detecting the temperature difference between power conversion units connected in parallel. The power conversion device includes: multiple 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) for detecting the internal temperature of each power conversion unit (14, 15); and a signal generation unit (120) for generating on / off command signals for the control electrodes of the first switching element (24, 34) and the second switching element (25, 35) of each power conversion unit (14, 15) based on the detection results of the temperature sensors (41, 42). The signal generation unit (120) uses the temperature sensors (41, 42) to detect the temperature of each power conversion unit when the power conversion device (1) outputs DC current.

Description

Technical Field

[0001] This invention relates to a power conversion device and a power conversion method for converting power between input and output. Background Technology

[0002] To reduce global energy consumption, there is a growing demand for high efficiency in power conversion devices that utilize semiconductor switching elements, such as inverters for driving electric motors, converters supplying power to inverters, and charging / discharging devices for electric vehicles. In these power conversion devices, multiple power conversion units with switching elements are sometimes configured to be connected in parallel.

[0003] For example, Patent Document 1 describes that "when IGBT modules are connected in parallel, the IGBT chips will have temperature deviations due to differences in characteristics or structure. If the absolute maximum temperature is suppressed, it will lead to larger devices and increased costs. Temperature detectors are set in each module that embeds temperature detection sensors, the magnitude of these temperature differences is determined by a comparator, and the conduction timing of the module with higher temperature is delayed by an integrating circuit of resistors and capacitors, thereby reducing the temperature."

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: Japanese Patent Application Publication No. 2009-159662 Summary of the Invention

[0007] The technical problem that the invention aims to solve

[0008] Generally, a power conversion unit includes switching elements referred to as the upper arm and the lower arm. The technology described in Patent Document 1 can suppress temperature imbalance between parallel switching elements. However, since there is less temperature imbalance during AC current output between power conversion units connected in parallel, there is a problem of low detection accuracy of temperature difference between power conversion units.

[0009] Based on the above, a method is needed that can accurately detect the temperature difference between power conversion units connected in parallel.

[0010] Technical means for solving technical problems

[0011] To address the aforementioned problems, one aspect of the power conversion device 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 for detecting the internal temperature of each power conversion unit; and a signal generation unit for generating on / off command signals for the control electrodes of the first and second switching elements of each power conversion unit based on the detection results of the temperature sensor, wherein the signal generation unit uses the temperature sensor to detect the temperature of each power conversion unit when the power conversion device outputs DC current.

[0012] Invention Effects

[0013] According to at least one aspect of the present invention, by detecting the temperature of the power conversion units connected in parallel when the power conversion device outputs DC current, the temperature difference between the power conversion units can be detected with high precision.

[0014] Other technical issues, structures, and effects not mentioned above will be further clarified through the following description of the implementation methods. Attached Figure Description

[0015] Figure 1 This is a diagram illustrating an example of the overall structure of an elevator system according to an embodiment of the present invention.

[0016] Figure 2 This is a block diagram showing an example of an existing power conversion device (inverter system) and its drive circuit.

[0017] Figure 3 This is a timing diagram showing an example of the waveform of the signal measured by each part when there is no switching delay between the switching elements of the power conversion units connected in parallel.

[0018] Figure 4 This is a timing diagram showing an example of the waveform of the signal measured by each part when the switching elements between power conversion units connected in parallel have a turn-on delay time deviation.

[0019] Figure 5 This is a timing diagram showing an example of the waveform of the signal measured by each part when the switching elements between power conversion units connected in parallel have a turn-off delay time deviation.

[0020] Figure 6 This is a diagram illustrating an example of the speed-time characteristics of an elevator system according to an embodiment of the present invention during each operation period.

[0021] Figure 7 This is a structural diagram illustrating an example of a power conversion device (inverter system) and its drive circuit according to an embodiment of the present invention.

[0022] Figure 8 This is a diagram illustrating an example of the DC current output by the three-phase inverter system to the motor during the start-up compensation period.

[0023] Figure 9 It is a graph representing the characteristics of the detected temperature in the inverter system relative to the output current.

[0024] Figure 10 This is a flowchart illustrating an example of a process for reducing the temperature difference between parallel-connected power conversion units according to an embodiment of the present invention. Detailed Implementation

[0025] Hereinafter, examples of embodiments for carrying out the present invention will be described with reference to the accompanying drawings. In this specification and the drawings, constituent elements having substantially the same function or structure are labeled with the same reference numerals, and repeated descriptions are omitted.

[0026] Power conversion devices can convert direct current (DC) to alternating current (AC) or vice versa through the switching action of semiconductor elements, and are applicable to various fields such as elevators, railways, and automobiles. As an example of power conversion devices, there is a demand for high output density in inverter devices, and miniaturization and weight reduction of power conversion devices are underway. With the miniaturization of power conversion units (part of the power conversion device) that integrate power semiconductor modules, capacitors, buses, and other components containing power semiconductor elements, the demand for miniaturization and cost reduction of the drive circuits used to drive the power semiconductor elements is increasing.

[0027] Furthermore, by incorporating multiple power conversion units that integrate power semiconductor modules, capacitors, buses, gate circuits, and other components, the aim is to achieve component commonality and increase output capacity, thereby reducing the cost of the power conversion device. Increasing the number of power conversion units in parallel allows for a larger capacity power conversion device.

[0028] When power semiconductor modules are connected in parallel, the inherent characteristic deviations of power semiconductor elements, such as their turn-on and turn-off delay times, cause an imbalance in the current flowing through each element. Consequently, current concentrates on a portion of the power semiconductor elements, increasing switching and conduction losses and resulting in temperature imbalances.

[0029] In existing technologies, considering current imbalance, when power semiconductor elements, i.e., power conversion units, are connected in parallel, a current value smaller than the rated current of each power semiconductor element needs to be used in the design. Therefore, the performance of the power semiconductor elements cannot be maximized.

[0030] One method for detecting current imbalance is to measure the current of each power semiconductor element using current sensors. However, this requires a number of current sensors equal to the number of power semiconductor elements, thus increasing the cost associated with the additional number of current sensors. A known method utilizes the temperature imbalance that occurs when the current of the power semiconductor elements is unbalanced, using a temperature sensor, which is less expensive than a current sensor, instead of a current sensor. However, in elevator systems, since the DC current output and AC current output are switched according to the operating state, the detection result changes depending on the timing of temperature detection. Therefore, the method for detecting temperature is problematic. Hereinafter, a power conversion device according to an embodiment of the present invention, in which a temperature sensor is installed within the power conversion unit, will be described.

[0031] <One Implementation Method>

[0032] Figure 1 This diagram illustrates an example of the overall structure of an elevator system according to an embodiment of the present invention. In the illustrated elevator system 1, alternating current (AC) supplied from system 2 is input via filter circuit 3 to a three-phase converter system 10, which is formed by multiple power conversion units 12 and 13 connected in parallel. The AC input to the converter system 10 is converted from AC to DC by power conversion units 12 and 13. Then, a three-phase inverter system 11, which is formed by multiple power conversion units 14 and 15 connected in parallel, drives a motor 5 via filter circuit 4. Filter circuits 3 and 4 remove harmonic components from the input sine wave (square wave).

[0033] As a load on the motor 5, there is an elevator car 7 connected to the rope 6 and a counterweight 8 for balancing the car 7. The power supplied to the motor 5 is consumed to wind up the rope 6 to move the elevator car 6 up and down.

[0034] The converter system 10 and the inverter system 11 are controlled by the control circuit section 9. The control circuit section 9 controls the on / off state of the switching elements provided in the power conversion units 14 and 15, and controls the current output to the load side.

[0035] [Structure of existing power conversion devices]

[0036] Figure 2 This is a structural diagram illustrating an example of an existing power conversion device and its drive circuit. To avoid complicating the diagram, only one phase of the bus is shown, omitting the other phases. (Example) Figure 2As shown, in the inverter system 100, which serves as a power conversion device, power conversion units 14 and 15 are connected in parallel. The input sides of power conversion units 14 and 15 are connected in parallel to the DC power supply 102 (equivalent to converter system 10), and the output sides are connected to the resistive load 104 and the inductive load 105 of the inverter system 100. The resistive load 104 and the inductive load 105 are configured as output loads. A current sensor 106 is mounted on the wiring between the output terminal of the inverter system 100 and the load.

[0037] 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 freewheeling diode 26, and a lower arm freewheeling diode 27. The upper arm switching element 24 and the lower arm switching element 25 are connected in reverse parallel with the upper arm freewheeling diode 26 and the lower arm freewheeling diode 27, respectively. The switching branch formed by the series-connected upper arm switching element 24 and the lower arm switching element 25 is connected in parallel with the capacitor 21.

[0038] The midpoint of the connection between the upper arm switching element 24 and the lower arm switching element 25 is connected to the output terminal T1 via a series-connected resistive load 28 and an inductive load 29. The output terminals of the upper arm gate circuit 22 and the lower arm gate circuit 23 are respectively connected to the gate terminals (control electrodes) of the upper arm switching element 24 and the lower arm switching element 25.

[0039] 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 freewheeling diode 36, and a lower arm freewheeling diode 37. The upper arm switching element 34 and the lower arm switching element 35 are connected in reverse parallel with the upper arm freewheeling diode 36 and the lower arm freewheeling diode 37, respectively. The switching branch formed by the series-connected upper arm switching element 34 and the lower arm switching element 35 is connected in parallel with the capacitor 31.

[0040] The midpoint between the upper arm switching element 34 and the lower arm switching element 35 is connected to the output terminal T2 via a series-connected resistive load 38 and an inductive load 39. The output terminals of the upper arm gate circuit 32 and the lower arm gate circuit 33 are respectively connected to the gate terminals (control electrodes) of the upper arm switching element 34 and the lower arm switching element 35.

[0041] Additionally, in the following description, upper arm switching element 24, lower arm switching element 25, upper arm switching element 34, and lower arm switching element 35 are sometimes simply referred to as "switching elements". Furthermore, upper arm gate circuit 22, lower arm gate circuit 23, upper arm gate circuit 32, and lower arm gate circuit 33 are sometimes simply referred to as "gate circuits".

[0042] The switching elements constituting power conversion units 14 and 15 are, for example, IGBTs (Insulated Gate Bipolar Transistors) or MOSFETs (Metal Oxide Semiconductors). The same applies to the switching elements of power conversion units 12 and 13.

[0043] One end of capacitor 21 in power conversion unit 14 is connected to one electrode (e.g., positive terminal) of DC power supply 102, and the other end of capacitor 21 is connected to the other electrode (e.g., negative terminal) of DC power supply 102. The other electrode of DC power supply 102 is connected to ground 103. The same applies to capacitor 31 in power conversion unit 15. Output terminals T1 and T2 are connected to output terminal T3 (load side) via resistive load 104 and inductive load 105. A current sensor 106 for detecting output current is connected to wiring for connecting resistive load 104 and inductive load 105 to output terminal T3.

[0044] Furthermore, if the inductance of the inductor load 105 in the inverter system 100 can be replaced by the inductance of the wiring, the inductor load 105 can also be omitted. Additionally, if the load connected to the output terminal T3 is a motor 5 or the like with a sufficiently large inductance, or has characteristics that can be considered as a current source, the inductor load 105 can also be omitted.

[0045] Figure 1 The control circuit unit 9 shown controls the on / off state of the switching elements 24, 25, 34, 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 the on / off state of each switching element 24, 25, 34, 35 based on the output current Itotal detected by the current sensor 106. The power conversion units 14 and 15 include gate circuits 22, 23, 32, 33 that provide gate signals to each switching element 24, 25, 34, 35. The control circuit unit 9 outputs control commands to the gate circuits corresponding to each switching element 24, 25, 34, 35 to control the switching operation (on / off) of the switching elements 24, 25, 34, 35.

[0046] The control circuit unit 9 is, for example, a controller composed of a microcomputer. The control circuit unit 9 includes an analog-to-digital (A / D) conversion circuit 9a, a processor 9b, and a memory 9c. The analog-to-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, for example, a processing device such as a CPU (Central Processing Unit). Alternatively, an MPU (Micro-Processing Unit) can be used instead of a CPU. The memory 9c is a storage device such as a semiconductor memory that stores the program code (control program) of the software implementing the various functions of this embodiment. The control circuit unit 9 has a network interface (not shown) to receive, for example, the target value of the output current (load current) from the ECU (Electronic Control Unit) of the controlled system. The processor 9b reads the control program from the memory 9c and executes it. Based on the current detection value of the current sensor 106 input from the A / D conversion circuit 9a and the aforementioned target value, it outputs control commands (input signals 101) to the gate circuits corresponding to each switching element 24, 25, 34, 35.

[0047] The control circuit section 9 outputs an input signal 101 as a control command, which is then input to gate circuits 22, 23, 32, and 33. Gate circuits 22, 23, 32, and 33 generate gate signals (gate voltage pulses) based on the input signal 101 to drive switching elements 24, 25, 34, and 35, respectively, and input these 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 that issues a command to the switching elements to turn on or off (turn-on / off command signal).

[0048] When the gate signal switches from high to low (on), the source and drain terminals of the upper arm switching elements 24 and 34 and the lower arm switching elements 25 and 35 are switched on, and current flows. Conversely, when the gate signal switches from low to high (off), the source and drain terminals of the upper arm switching elements 24 and 34 and the lower arm switching elements 25 and 35 are switched off, and no current flows.

[0049] [Motion waveform without transition delay time deviation]

[0050] Figure 3 This is a timing diagram showing an example of the waveform of the signal measured by each part when there is no switching delay time deviation between the switching elements of the power conversion units 14 and 15 connected in parallel. Figure 3 The horizontal axis represents time [s]. Figure 3The vertical axis, from top to bottom, represents the gate signal of power conversion unit 14, the gate signal of power conversion unit 15, the output voltage of power conversion unit 14, the output voltage of power conversion unit 15, the output current of power conversion unit 14, the output current of power conversion unit 15, the temperature of power conversion unit 14, and the temperature of power conversion unit 15. Furthermore, in this specification, it is assumed that the inductive load 105 or the inductance on the load side is sufficiently large, and the current Itotal of the inductive load 105 is considered constant. Additionally, the voltage applied to capacitors 21 and 31 is equal to the voltage of the DC power supply 102.

[0051] When gate signals with the same pulse waveform are input to the switching elements 24, 25, 34, and 35 of power conversion units 14 and 15, the turn-on delay times Ton1 and Ton2 of the output voltage of power conversion units 14 and 15 are equal, assuming no time delay deviation among these switching elements. Similarly, the turn-off delay times Toff1 and Toff2 are also equal. As a result, the output currents of power conversion units 14 and 15 become equal. In addition, the temperatures of power conversion units 14 and 15 also become equal.

[0052] [Action waveform when there is a conduction delay time deviation]

[0053] Figure 4 This is a timing diagram showing an example of the waveform of the signal measured by each part when there is a conduction delay time deviation between the switching elements of the power conversion units 14 and 15 connected in parallel. Figure 4 The relationship between the horizontal and vertical axes and Figure 3 same.

[0054] When gate signals with the same pulse waveform are input to the switching elements 24, 25, 34, and 35 of power conversion units 14 and 15, the turn-on delay times Ton1 and Ton2 of these switching elements deviate (Ton1 < Ton2). Therefore, the pulse width of the output voltage of power conversion unit 15 is narrower compared to that of power conversion unit 14. As a result, the output current of power conversion unit 15 is smaller, while the output current of power conversion unit 14 is larger than that of power conversion unit 15. Consequently, the temperature of power conversion unit 14 is higher than that of power conversion unit 15.

[0055] [Action waveform when there is a shutdown delay time deviation]

[0056] Figure 5 This is a timing diagram showing an example of the waveform of the signal measured by each part when there is a turn-off delay time deviation between the switching elements of the power conversion units 14 and 15 connected in parallel. Figure 5 The relationship between the horizontal and vertical axes and Figure 3 same.

[0057] When gate signals with the same pulse waveform are input to the switching elements 24, 25, 34, and 35 of power conversion units 14 and 15, the turn-off delay times Toff1 and Toff2 of these switching elements deviate (Toff1 < Toff2). Therefore, the pulse width of the output voltage of power conversion unit 15 is wider than that of power conversion unit 14. As a result, the output current of power conversion unit 15 increases, while the output current of power conversion unit 14 decreases compared to power conversion unit 15. Consequently, the temperature of power conversion unit 14 is lower than that of power conversion unit 15.

[0058] When the output current between the parallel-connected power conversion units 14 and 15 is unbalanced, the current concentrates on a portion of the switching elements, increasing the switching losses and conduction losses, thereby causing temperature imbalance between the switching elements (power conversion units 14 and 15).

[0059] Therefore, a method that is cheaper than using a current sensor 106 and can detect the imbalance of output current between power conversion units 14 and 15 with high accuracy even when using a temperature sensor is a problem.

[0060] [Speed ​​characteristics of elevator systems]

[0061] Figure 6 This is a diagram illustrating an example of the speed versus time characteristics during each operation of elevator system 1. Figure 6 The horizontal axis represents time [s], and the vertical axis represents speed [m / s]. As shown in the figure, elevator system 1 includes a start-up compensation period 150, an acceleration period 151, a constant speed period 152, and a deceleration period 153 during one operation.

[0062] During the initial compensation period 150, the elevator system 1 fixes the motor 5 and generates torque by flowing direct current through the motor 5. During this phase, the motor 5 stops, and the car 7 does not move. During the acceleration period 151, the elevator system 1 outputs alternating current from the power conversion device and increases the rotational speed of the motor 5 by increasing the frequency of the output current, thus accelerating the car 6. During the constant speed period 152, the elevator system 1 keeps the frequency of the output current constant and maintains a constant rotational speed of the motor 5. During the deceleration period 153, the elevator system 1 slows down the rotational speed of the motor 5 by decreasing the frequency of the output current, thus decelerating the car 6.

[0063] Between the parallel-connected power conversion units 14 and 15 are resistive loads 28 and 38 with resistive components and inductive loads 29 and 39 with inductive components. Since the loads at DC current output have no inductive component and only a resistive component, the cross-current flowing between the parallel-connected power conversion units 14 and 15 increases, and the imbalance of the output current of the power conversion units 14 and 15 becomes maximum. Here, the greater the imbalance of the output current of the power conversion units 14 and 15, the greater the temperature difference (temperature imbalance) between the power conversion units 14 and 15, and the more significant the temperature difference becomes.

[0064] Therefore, during the DC current startup compensation period 150, a significant temperature difference occurs between the power conversion units 14 and 15 compared to the acceleration period 151, constant speed period 152, and deceleration period 153 of the AC current output. Thus, the temperature difference between the power conversion units 14 and 15 can be detected with high precision during the startup compensation period 150. Therefore, by detecting the temperature difference between the power conversion units 14 and 15 during the DC current startup compensation period 150, the output current imbalance between the power conversion units 14 and 15 can be detected with high precision.

[0065] [Structure of a power conversion device according to one embodiment]

[0066] Next, refer to Figure 7 This invention describes a power conversion device and its driving circuit according to an embodiment of the present invention.

[0067] Figure 7 This is a structural diagram illustrating an example of a power conversion device and its drive circuit according to an embodiment of the present invention. The inverter system 11, as a power conversion device, differs from the conventional inverter system 100 ( Figure 2 In comparison, they are similar in that they have power conversion units 14 and 15, but the control signals (gate voltage pulse widths) provided to the gate terminals of the gate circuits 22 to 33 are different.

[0068] like Figure 7 As shown, the input sides of power conversion units 14 and 15 are connected in parallel with the DC power supply 102, and the output sides are connected in parallel with the resistive load 104 and the inductive load 105 of the inverter system 11. A current sensor 106 is installed on the wiring on the output side of the inverter system 11. The internal structure of power conversion units 14 and 15 is similar to... Figure 2 Since the structures shown are the same, the explanation will focus on the differences.

[0069] In power conversion unit 14, temperature sensor 41 is disposed near upper arm switching element 24 and lower arm switching element 25. The distance between upper arm switching element 24 and lower arm switching element 25 and temperature sensor 41 is designed to be an appropriate distance for measuring the temperature of switching elements 24 and 25 through experiments, etc. In power conversion unit 15, temperature sensor 42 is disposed near upper arm switching element 34 and lower arm switching element 35. Temperature sensor 42 detects the temperature of switching elements 24 and 25 (i.e., within power conversion unit 14) in power conversion unit 14, and temperature sensor 42 detects the temperature of switching elements 34 and 35 (i.e., within power conversion unit 15) in power conversion unit 15. The detected temperature information is input to temperature storage unit 121.

[0070] The control circuit unit 9 includes a signal generation unit 120, which generates control signals to be supplied to the gate circuits 22, 23, 32, and 33. The signal generation unit 120 has a temperature storage unit 121 and an on / off time adjustment unit 122. The temperature storage unit 121 is composed of a processor 9b and a memory 9c, and stores temperature information measured by temperature sensors 41 and 42. The temperature information stored in the temperature storage unit 121 and the input signal 101 are input to the on / off time adjustment unit 122. The on / off time adjustment unit 122 adjusts the pulse width of the input signal 101 (gate voltage pulse) based on the temperature information and the input signal 101, and provides the adjusted input signal 101 as an on / off command signal to each of the gate circuits 22, 23, 32, and 33. Alternatively, the input signal 101 can also be input to the on / off time adjustment unit 122 via the temperature storage unit 121.

[0071] Figure 8 This represents an example of the DC current output by the three-phase inverter system 11 to the motor 5 during startup compensation period 150. The phase difference of each phase relative to the reference axis is determined by the position of the motor 5 (position of the rotating shaft). The motor position during startup compensation is the same as the motor position when the motor 5 was stopped in the previous operating mode, and the motor position is irregular. Therefore, during startup compensation period 150, the output current of the power conversion units 14 and 15 becomes irregular.

[0072] [Temperature characteristics relative to output current]

[0073] Figure 9 This is a graph showing the characteristic (rate of change) of the temperature detected in inverter system 11 relative to the output current. Figure 9 In the figure, 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 ΔT [°C] between the parallel-connected power conversion units 14 and 15.

[0074] Hereinafter, in this specification, the temperature characteristic of the inverter system 11 relative to the output current will be referred to as the rate of change. During elevator operation, DC current is output only during the start-up compensation period. Since the imbalance of the output current becomes maximum during the output of DC current, temperature difference can be detected with high accuracy. Therefore, it is preferable to perform detection during the start-up compensation of the output DC current. However, as... Figure 8 As described above, when outputting DC current, a different DC output current is obtained for each detection depending on the position of the motor (position of the rotating shaft).

[0075] When comparing the temperature difference between power conversion units 14 and 15, it is necessary to use the same DC output current for comparison. However, since the DC output current is irregular depending on the motor position, it is difficult to compare the temperature difference based on the same DC output current. Therefore, the temperature of power conversion units 14 and 15 is measured multiple times, and the temperature information relative to the DC current is stored. Based on the stored information, the rate of change of the temperature difference between power conversion units 14 and 15 with respect to the DC output current can be calculated. By using the rate of change of the temperature difference, the temperature imbalance generated between the parallel-connected power conversion units 14 and 15 can be detected.

[0076] In inverter system 11, the temperatures of power conversion units 14 and 15 are detected during DC current output. The temperature difference between the parallel-connected power conversion units 14 and 15 is calculated based on the detected temperatures, and the output current and temperature difference information are stored. The output current and temperature difference information are stored at least twice, and the rate of change of the temperature difference relative to the output current (200%) is calculated based on the detection results.

[0077] When the rate of change is large (200), the temperature imbalance is significant, and losses are concentrated on a portion of the switching elements, thus requiring the elimination of this imbalance. Therefore, the following section explains how to eliminate imbalance based on the rate of change of temperature difference.

[0078] The imbalance in output current or temperature of power conversion units 14 and 15 depends on the pulse width deviation of the output voltage of power conversion units 14 and 15 caused by the time delay deviation of the switching action of the switching elements. Therefore, in order to eliminate the imbalance in output current, it is necessary to adjust the gate signal supplied to each gate circuit according to the relationship between the rate of change of temperature difference and the threshold.

[0079] Furthermore, as a control method to eliminate imbalance based on the rate of change of temperature difference, for example, if the rate of change 200 exceeds a threshold, the on / off time adjustment unit 122 narrows the pulse width and reduces imbalance by delaying the on-time of the power conversion unit on the high-temperature side. After this control, the temperatures of the power conversion units 14 and 15 are detected and stored again, and the rate of change 201 is calculated by calculating the rate of change of the temperature difference between the power conversion units 14 and 15.

[0080] The controlled rate of change 201 is lower than the rate of change 200, and the temperature difference change is less relative to the output current of the inverter system 11, thus equalizing the temperatures of power conversion units 14 and 15. This reduces the temperature imbalance in power conversion units 14 and 15, thereby suppressing the increase in switching and conduction losses of some switching elements. When the rate of change of temperature difference is less than or equal to the threshold, it is determined that there is no temperature imbalance, and no adjustment is made.

[0081] Furthermore, when the rate of change 200 exceeds the threshold, the pulse width is widened and the rate of change 200 is reduced by delaying the turn-off time of the power conversion unit on the low-temperature side. This can also be a method to equalize the temperature between power conversion units 14 and 15.

[0082] Thus, the signal generation unit 120 has the function of correcting at least one of the turn-on time and turn-off time of the turn-on / turn-off command signal based on the detected temperature imbalance between the power conversion units 14 and 15.

[0083] [Example of steps for reducing temperature difference]

[0084] Next, we will refer to Figure 10 An example of the steps for reducing the temperature difference between power conversion units 14 and 15 connected in parallel, according to an embodiment of the present invention, is described.

[0085] Figure 10 This is a flowchart illustrating an example of the steps for reducing the temperature difference between the parallel-connected power conversion units 14 and 15. The signal generation unit 120 repeats the following steps S2 to S4 until the count of the number of detections reaches a predetermined number (multiple times) (S1). First, the signal generation unit 120 determines whether the current period is the start-up compensation period 150 (S2). If it is the start-up compensation period 150 (S2 "Yes" determination), it proceeds to step S3. If it is not the start-up compensation period 150 (S2 "No" determination), it executes the determination process of step S2 again.

[0086] Next, during the compensation start-up period 150, the signal generation unit 120 uses temperature sensors 41 and 42 and current sensor 106 to detect the temperature of power conversion units 14 and 15 and the output current of inverter system 11, and stores the detected temperature and output current information in the temperature storage unit 121 (S3). Then, the signal generation unit 120 increments the count of the number of temperature and output current detections by "1" (S4).

[0087] Next, the signal generation unit 120, based on the stored temperature and output current information, calculates the rate of change α of the temperature difference between the power conversion units 14 and 15 relative to the output current (e.g., ...). Figure 9 The rate of change α is calculated (S5). If the rate of change α is greater than a threshold (S6 "Yes" determination), the signal generation unit 120 adjusts the gate voltage pulse width (S7). For example, the signal generation unit 120 uses the on / off time adjustment unit 122 to delay the turn-on time of the switching element in the power conversion unit on the high-temperature side and reduce 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 temperature of the power conversion units 14 and 15 can be controlled in the direction of equalization.

[0088] On the other hand, if the rate of change α is below the threshold (the "No" determination in S6), it is determined that there is no temperature imbalance or slight difference in the power conversion units 14 and 15, and therefore no adjustment of the gate voltage pulse width is performed. After the processing in step S7 or if the determination in step S6 is "No", the processing of this flowchart ends.

[0089] According to the power conversion device according to one embodiment of the present invention described above, the inverter system 11 repeatedly detects the temperature of the parallel-connected power conversion units 14 and 15 when outputting DC current, and stores the temperature data in the temperature storage unit 121. Then, in the inverter system 11, if 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, the pulse width of the gate signal of each switching element is adjusted. Therefore, the inverter system 11 according to this embodiment can detect the temperature difference between the power conversion units 14 and 15 with high precision compared to the prior art.

[0090] [Adjust the upper and lower arms according to the output current]

[0091] Furthermore, the upper arm switching elements 24 and 34 and the lower arm switching elements 25 and 35 need to be switched according to the direction of the output current of the inverter system 11, and the gate signals need to be adjusted accordingly. Therefore, the method for adjusting the upper and lower arms according to the output current of the inverter system 11 will be explained next.

[0092] When current is output from inverter system 11, current flows to upper arm switching elements 24 and 34, and when current is introduced into inverter system 11, current flows to lower arm switching elements 25 and 35. Therefore, the method of changing the arm that adjusts the gate signal according to the direction of the output current becomes a problem.

[0093] Therefore, current sensor 106 is used to detect whether the current is output from inverter system 11 or introduced into inverter system 11, and the arm for adjusting the gate signal is switched. This allows for suppression of pulse width deviation of the gate voltage on both the upper and lower arms. The current is determined based on the current detected by current sensor 106 to determine whether the current is output from inverter system 11 or introduced into inverter system 11.

[0094] As described above, the signal generation unit 120 has the following function: by switching the upper arm switching elements 24, 25 and the lower arm switching elements 25, 35 according to the output current Itotal of the inverter system 11 through the on / off time adjustment unit 122, at least one of the on-time and off-time of the on / off command signal is corrected.

[0095] That is, when the signal generation unit 120 outputs current from the inverter system 11, it corrects at least one of the turn-on time and turn-off time of the upper arm switching elements 24 and 34 and the lower arm switching elements 25 and 35 corresponding to the upper arm switching elements 24 and 34. Furthermore, when the signal generation unit 120 introduces current into the inverter system 11, it corrects at least one of the turn-on time or turn-off time of the lower arm switching elements 25 and 35.

[0096] The signal generation unit 120 has such a correction function that it can select the appropriate arm from the lower arm and the upper arm and adjust the delay time of the switching action when the inverter system 11 outputs current and when it introduces current.

[0097] As described above, the power conversion device (inverter system 11) according to this embodiment includes: a plurality of power conversion units connected in parallel, each power conversion unit (power conversion unit 14, 15) 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; temperature sensors (temperature sensors 41, 42) for detecting the internal temperature of each power conversion unit; and a signal generation unit (signal generation unit 120) for generating on / off command signals (gate signals) for the control electrodes of the first and second switching elements for each power conversion unit based on the detection results of the temperature sensors. The signal generation unit uses the temperature sensors to detect the temperature of each power conversion unit when the power conversion device outputs DC current.

[0098] Furthermore, in the power conversion device (inverter system 11) involved in this embodiment, the aforementioned DC current output refers to the starting compensation period of the motor connected to the power conversion device.

[0099] Furthermore, in the power conversion device (inverter system 11) according to this embodiment, the signal generation unit includes a storage device (temperature storage unit 121) that stores the detected temperature information of each power conversion unit. Then, the power conversion device stores the output current of the power conversion device and the temperature information of each power conversion unit detected by the temperature sensor. Based on multiple detection results, it calculates the rate of change of the temperature difference between the power conversion units relative to the output current, and compares this rate of change of temperature difference with a threshold value to detect temperature imbalance between the power conversion units.

[0100] According to the power conversion device described in this embodiment, by repeatedly detecting and storing the temperature of the power conversion units connected in parallel when the power conversion device outputs DC current, the temperature difference between the power conversion units can be detected with high precision compared to the prior art.

[0101] [Variation Example]

[0102] Furthermore, in the above embodiment, the start-up compensation period 150 of the motor 5 is utilized when the DC current output of the inverter system 11 is provided, but other methods may also be used. For example, in systems such as elevator system 1, a DC current output mode can be prepared in the power conversion device (inverter system 11), and when the DC current output mode is selected, the temperature of each power conversion unit can be detected when the power conversion device outputs DC current.

[0103] Furthermore, this specification describes the structure of a power conversion device (inverter system 11) obtained by connecting two power conversion units in parallel, but the number of power conversion units connected in parallel can also be three or more. In this case, for example, for a combination of multiple power conversion units, the rate of change of temperature difference between the power conversion units can be calculated for all combinations, or the rate of change of temperature difference can be calculated only for a combination of one or more pre-specified power conversion units.

[0104] Furthermore, although an example of applying the power conversion device of the present invention to a three-phase inverter system has been described, the power conversion device of the present invention can of course also be applied to a three-phase converter system having power conversion units connected in parallel. Additionally, the power conversion device of the present invention can also be applied to single-phase inverter systems, single-phase converter systems, boost converter systems, or buck converter systems having power conversion units connected in parallel.

[0105] Furthermore, the present invention is not limited to the above-described embodiment. Undoubtedly, various other applications and modifications can be obtained without departing from the technical concept of the invention as described in the claims. For example, the above-described embodiment provides a detailed and specific description of the structure of the inverter system as a power conversion device for ease of understanding of the present invention, but it is not necessarily limited to possessing all the structural elements described. Additionally, it is possible to add, replace, or delete other constituent elements from a portion of the structure of each embodiment.

[0106] Furthermore, some or all of the aforementioned structures, functions, and processing units can be implemented in hardware, for example, by designing them into integrated circuits. As hardware, broader processor devices such as FPGAs (Field Programmable Gate Arrays) or ASICs (Application Specific Integrated Circuits) can also be used.

[0107] Furthermore, in the above embodiments, control lines and information lines necessary for the description are shown, but it is not limited to showing all the control lines and information lines necessary for the product. In fact, it can be considered that almost all structural elements are interconnected.

[0108] Label Explanation

[0109] 1. Elevator System

[0110] 2 System

[0111] 3 and 4 filter circuits

[0112] 5. Electric motor (load)

[0113] 6 ropes

[0114] 7. Car

[0115] 8 pairs of weights

[0116] 9. Control Circuit Section

[0117] 9a A / D conversion circuit

[0118] 9b processor

[0119] 9c memory

[0120] 10 Converter System

[0121] 11 Inverter System

[0122] 12-15 Power conversion units

[0123] 21, 31 capacitors

[0124] Gate circuits 22, 23, 32, 33

[0125] 24, 34 Upper arm switching elements

[0126] 25, 35 Lower arm switching elements

[0127] 26, 36 Upper arm switching freewheeling diodes

[0128] 27, 37 Lower arm switching freewheeling diode

[0129] 14 and 15 Power conversion units

[0130] 28 and 38Ω resistive loads

[0131] 29, 39 Inductive load

[0132] 101 Input Signal

[0133] 102 DC power supply

[0134] 103 GND

[0135] 104 Resistive Load (Output Load)

[0136] 105 Inductive load (output load)

[0137] 106 Current Sensor

[0138] 120 Signal Generation Unit (Control Circuit Unit)

[0139] 121 Temperature Storage Section

[0140] 122 On / Off Time Adjustment Section

[0141] 150 During the compensation period

[0142] 151 During acceleration

[0143] 152 During constant speed period

[0144] 153 During deceleration

[0145] 200, 201 rate of change

Claims

1. A power conversion device, comprising: Multiple power conversion units connected in parallel, each power conversion unit having a first switching element and a second switching element connected in series; The power conversion device is characterized by a temperature sensor for detecting the internal temperature of each power conversion unit, and a signal generation unit for generating on / off command signals for the control electrodes of the first and second switching elements for each power conversion unit based on the detection results of the temperature sensors. The signal generation unit includes a storage device. The signal generation unit uses the temperature sensor to detect the temperature of each power conversion unit when the power conversion device outputs DC current. By storing the output current information of the power conversion device and the temperature information of each power conversion unit detected by the temperature sensor in the storage device, the unit calculates the rate of change of the temperature difference between the power conversion units relative to the output current based on multiple detection results, and compares the rate of change of the temperature difference with a threshold, thereby detecting the temperature imbalance between the power conversion units.

2. The power conversion device as described in claim 1, characterized in that, The output DC current is during the start-up compensation period of the motor connected to the power conversion device.

3. The power conversion device as described in claim 1, characterized in that, The signal generation unit has the following functions: The on / off time of the turn-on command signal is corrected based on the detected temperature imbalance between the power conversion units.

4. The power conversion device as described in claim 3, characterized in that, The signal generation unit has the following functions: The first switching element and the second switching element are switched according to the output current of the power conversion device, and at least one of the on-time and off-time of the on / off command signal is corrected.

5. The power conversion device as described in claim 4, characterized in that, The signal generation unit has the following functions: When current is output from the power conversion device, at least one of the on-time and off-time of the upper arm of the first and second switching elements is corrected; when current is introduced into the power conversion device, at least one of the on-time and off-time of the lower arm of the first and second switching elements is corrected.

6. The power conversion device as described in claim 2, characterized in that, The electric motor is a hoisting motor that uses the output of the power conversion device to hoist the elevator car. The output DC current occurs when the winding motor is in a stopped state.

7. A power conversion method, which is a power conversion method using a power conversion device, the power conversion device comprising: Multiple power conversion units connected in parallel, each power conversion unit having a first switching element and a second switching element connected in series; The power conversion method is characterized by a temperature sensor for detecting the internal temperature of each power conversion unit, and a signal generation unit for generating on / off command signals for the control electrodes of the first and second switching elements for each power conversion unit based on the detection results of the temperature sensor. The signal generation unit uses the temperature sensor to detect the temperature of each power conversion unit when the power conversion device outputs DC current. By storing the output current information of the power conversion device and the temperature information of each power conversion unit detected by the temperature sensor in the storage device included in the signal generation unit, the unit calculates the rate of change of the temperature difference between the power conversion units relative to the output current based on multiple detection results, and compares the rate of change of the temperature difference with a threshold, thereby detecting the temperature imbalance between the power conversion units.

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