JP2013207986A - Power conversion device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a power conversion device that allows reducing the operation load of a computer and estimating the temperatures of semiconductor elements with a high degree of accuracy.SOLUTION: A power conversion device 10 detects an output current Iout of a power conversion circuit 1, generates a voltage command value Ec for controlling a voltage, and calculates loss of switching elements 11 to 14 on the basis of the output current Iout, the voltage command value Ec, and predetermined constants k1 and k2 to estimate the element temperatures of the switching elements 11 to 14.

Description

  The present invention relates to a power conversion device for protecting a semiconductor element.

  Generally, in a power converter, it is known to estimate the temperature of a semiconductor element in order to protect the semiconductor element from a failure due to a temperature rise.

  For example, it is disclosed that the temperature is estimated by detecting the load current and the ambient temperature of the semiconductor switching element (see, for example, Patent Document 1). Further, it is disclosed that a temperature difference between temperatures measured by a semiconductor element and a temperature sensor is calculated using a plurality of first-order lag transfer functions having different thermal time constants in order to estimate the temperature of the semiconductor element. (For example, refer to Patent Document 2).

JP 2010-268614 A JP 2011-036095 A

  However, in order to accurately estimate the temperature of the semiconductor element, the turn-on loss, the turn-off loss, and the conduction loss are individually calculated, and the total element loss is calculated. However, if such calculation is performed during operation of the power converter, a large calculation load is applied to the computer.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a power converter that can reduce the computational load of a computer and can estimate the temperature of a semiconductor element with high accuracy.

  A power conversion device according to an aspect of the present invention includes a power conversion circuit configured by a switching element, current detection means for detecting a current including a current flowing through the switching element, and a voltage output from the power conversion circuit. Voltage command value calculation means for calculating a voltage command value for control, current detected by the current detection means, voltage command value calculated by the voltage command value calculation means, detected by the current detection means A first preset value for taking a product with the current and a second preset value for taking the product with the voltage command value calculated by the voltage command value calculating means. Based on the loss calculation means for calculating the loss of the switching element, and based on the loss of the switching element calculated by the loss calculation means And a device temperature estimation means for estimating the element temperature of the element.

  ADVANTAGE OF THE INVENTION According to this invention, the power converter device which can reduce the calculation load of a computer and can estimate the temperature of a semiconductor element with high precision can be provided.

The block diagram which shows the structure to which the power converter device which concerns on embodiment of this invention was applied. The block diagram which shows the structure of the control apparatus which concerns on embodiment. The wave form diagram which shows the production | generation method of the gate pulse signal by the gate pulse production | generation part which concerns on embodiment.

  Embodiments of the present invention will be described below with reference to the drawings.

(Embodiment)
FIG. 1 is a configuration diagram illustrating a configuration to which a power conversion device 10 according to an embodiment of the present invention is applied. In addition, the same code | symbol is attached | subjected to the same part in drawing, the detailed description is abbreviate | omitted, and a different part is mainly described.

  The power conversion device 10 converts DC power supplied from the DC power supply 5 into AC power and supplies the AC power to the load 6.

  The power conversion device 10 includes a power conversion circuit 1, a control device 2, a smoothing capacitor 3, and a current detector 4.

  The power conversion circuit 1 is a circuit that converts DC power supplied from the DC power supply 5 into AC power. The power conversion circuit 1 includes four switching elements 11, 12, 13, and 14. Antiparallel diodes are connected to the switching elements 11 to 14, respectively.

  The four switching elements 11 and 12 constitute two arms. One arm is a circuit in which two switching elements 11 and 12 are connected in series. The other arm is a circuit in which the remaining two switching elements 13 and 14 are connected in series. The switching elements 11 to 14 are driven (switched) by a gate pulse signal Gp output from the control device 2. The switching elements 11 to 14 are, for example, IGBTs (insulated gate bipolar transistors).

  The smoothing capacitor 3 smoothes the DC voltage applied to the power conversion circuit 1.

  The current detector 4 detects an alternating current (output current) Iout output from the power conversion circuit 1. The current detector 4 outputs the detected output current Iout to the control device 2.

  The control device 2 is a device that performs arithmetic processing by a computer. The control device 2 controls the power conversion circuit 1. Specifically, the control device 2 performs control for supplying power to the load 6 by outputting the gate pulse signal Gp to the power conversion circuit 1 based on the detected output current Iout. Further, the control device 2 monitors the temperatures of the switching elements 11 to 14 based on the output current Iout detected by the current detector 4.

  FIG. 2 is a configuration diagram showing the configuration of the control device 2 according to the present embodiment.

  The control device 2 includes a current control unit 21, a temperature monitoring unit 22, and a gate pulse generation unit 23.

  The current controller 21 receives the current command value Ir and the output current Iout detected by the current detector 4. The current command value Ir is input from, for example, a higher control system. The current control unit 21 generates the voltage command value Ec so that the output current Iout follows the current command value Ir. The voltage command value Ec is determined by a modulation rate (a value between 0 and 1). The current control unit 21 outputs the generated voltage command value Ec to the temperature monitoring unit 22 and the gate pulse generation unit 23.

  The temperature monitoring unit 22 receives the output current Iout detected by the current detector 4 and the voltage command value Ec generated by the current control unit 21. The temperature monitoring unit 22 performs a calculation for estimating the element temperature (junction temperature or channel temperature) of each of the switching elements 11 to 14 based on the output current Iout and the voltage command value Ec. The temperature monitoring unit 22 performs switching when the estimated element temperature is not within a predetermined allowable range (for example, when there is one switching element 11 to 14 whose element temperature exceeds a preset allowable temperature). Control is performed to protect against a failure due to a temperature rise of the elements 11 to 14. Specifically, the temperature monitoring unit 22 outputs a stop signal St for gate-blocking the switching elements 11 to 14 to the gate pulse generation unit 23.

  The gate pulse generator 23 generates a gate pulse signal Gp based on the voltage command value Ec calculated by the current controller 21. The gate pulse generator 23 outputs the generated gate pulse signal Gp to the gate drive circuits of the switching elements 11 to 14. In this way, the gate pulse generator 23 controls the driving of the switching elements 11 to 14 by pulse width modulation.

  FIG. 3 is a waveform diagram showing a method for generating the gate pulse signal Gp by the gate pulse generator 23. Note that the gate pulse signal Gp shown in FIG. 3 drives the switching element 11 shown in FIG. 1, and the illustration of the gate pulse signal Gp that drives the other switching elements 11 is omitted.

  The gate pulse generator 23 generates a carrier wave Cr. Here, the carrier wave Cr is a triangular wave with a constant period, but the carrier wave Cr may not be a constant frequency or a triangular wave.

  First, a method for generating the gate pulse signal Gp for driving the switching element 11 will be described.

  The gate pulse generator 23 compares the carrier wave Cr with a voltage command value Ec that is a sine wave. When the voltage command value Ec is larger than the carrier wave Cr, the gate pulse generator 23 sets the gate pulse signal Gp to “1”. The gate pulse generator 23 sets the gate pulse signal Gp to “0” when the voltage command value Ec is equal to or less than the carrier wave Cr. In this way, the gate pulse generator 23 generates the gate pulse signal Gp for driving the switching element 11.

  The gate pulse signal Gp for driving the switching element 12 is a signal obtained by inverting the gate pulse signal Gp for driving the switching element 11. Similarly, the gate pulse signal Gp for driving the switching elements 13 and 14 is a signal generated by inverting the voltage command value Ec (or carrier wave Cr) and performing carrier comparison.

  The switching elements 11 to 14 are driven by the respective gate pulse signals Gp determined in this way, and the output current Iout of the power conversion circuit 1 is controlled.

  Next, a method for estimating the element temperature by the temperature monitoring unit 22 will be described.

  The temperature monitoring unit 22 calculates the element loss P from the output current Iout and the voltage command value Ec according to the following equation.

P = k1 × Iout × (1 + k2 × Ec) (1)
Here, 'k1' and 'k2' are preset constants. The constants k1 and k2 vary depending on the type of semiconductor element. 'Iout' is an instantaneous value.

  The element loss P calculated from the equation (1) is a value per unit time (for example, every calculation cycle of the microcomputer).

  The temperature monitoring unit 22 estimates the element temperature by processing the calculated element loss P per unit time using a thermal resistance model. Here, the heat resistance model may be a conventionally used one.

  A method for obtaining the two constants k1 and k2 of Expression (1) will be described.

  First, before operating the power converter 10, data for ascertaining the correspondence between the element loss and the output current Iout and the correspondence between the element loss and the voltage command value Ec are obtained.

  The element loss grasped here is a total loss obtained by individually calculating the turn-on loss, the turn-off loss, and the conduction loss. From the gate pulse signal Gp and the output current Iout, the device current at turn-on (IGBT current) and the device current at turn-off are obtained. The device current at turn-on is' Ion ', the device current at turn-off is' Ioff', the device current at conduction is' I ', the turn-on loss is' Eon', the turn-on loss is' Eoff ', and the conduction loss is' Assuming EVce ′, it is expressed as follows.

Eon = fEon (Ion) (I> 0) (2)
Eoff = fEoff (Ioff) (I> 0) Equation (3)
EVce = f (I) (I> 0) Formula (4)
Here, 'Ion', 'Ioff', and 'I' are instantaneous values. FEon (Ion), fEoff (Ioff), and f (I) are functions of 'Ion', 'Ioff', and 'I', respectively.

  Based on the measured data, the correspondence relationship between the element loss and the output current Iout and the correspondence relationship between the element loss and the voltage command value Ec are respectively shown in graphs. The two constants k1 and k2 are determined so that the graph represented by the equation (1) is proportionally approximated with the graph representing the two correspondences.

  According to this embodiment, the following effects can be obtained.

  If the loss is to be obtained in a straightforward manner, the microcomputer must carry out a calculation for individually obtaining and summing the turn-on loss Eon, the turn-on loss Eoff, and the conduction loss EVce. However, if such calculation is always performed during operation of the power converter 10, a large calculation load is applied to the microcomputer.

  Therefore, as in the present embodiment, the element loss P can be calculated based on the output current Iout and the voltage command value Ec with one arithmetic expression shown in the expression (1) obtained in advance. Calculation load can be reduced.

  In addition, since the element temperature can be estimated without using a temperature sensor, it is possible to reduce the size and the manufacturing cost.

  Note that the switching elements 11 to 14 are not limited to IGBTs. Any switching element may be used as long as it is a semiconductor element. By changing the two constants k1 and k2 in Expression (1) in accordance with the characteristics of the switching element to be monitored, the power converter 10 can be configured to match the characteristics of the switching element.

  Further, the power conversion circuit 1 may have any configuration as long as it is configured by a semiconductor element. For example, the power conversion circuit 1 is a circuit that converts to single-phase AC power, a circuit that converts to three-phase AC power, a converter circuit that converts AC power to DC power, a half-bridge circuit, a full-bridge circuit, a two-level inverter circuit, Any circuit such as a multi-level inverter circuit may be used.

  Further, the DC power source 5 may be any device as long as it is a device that outputs DC power. For example, the DC power supply 5 may be a converter that converts AC power into DC power.

  In the embodiment, the power conversion device 10 is a device that converts DC power supplied from the DC power source 5 into AC power and supplies the AC power to the load 6, but is not limited thereto. The power conversion device 10 may be used as a converter that converts AC power into DC power, or may be used as a device that converts AC power and DC power to each other.

  Furthermore, in the embodiment, the element loss P is calculated using the output current Iout. However, as long as the current flowing through the switching elements 11 to 14 to be monitored is included, the current at other places may be used. For example, instead of the output current Iout, an element current flowing through the switching elements 11 to 14 or an arm current flowing through an arm constituted by the switching elements 11 to 14 may be measured and used.

  In addition, the arithmetic expression for calculating the element loss P is a linear expression as shown in Expression (1), but may be expressed by a secondary or higher expression if the calculation load can be reduced.

  Furthermore, in the embodiment, when the temperature of the switching elements 11 to 14 is not within the allowable range, the gate block of the switching elements 11 to 14 is configured as a control for protecting from a failure due to a temperature rise. Not limited to. Any operation may be performed as long as the device temperature can be prevented from rising further. For example, such control may be operation stop of the power conversion circuit 1 or suppression of load current.

  In addition, the method of obtaining the two constants k1 and k2 in Expression (2) is not limited to the embodiment. The constants k1 and k2 may be determined while operating the power conversion apparatus 10, or may be determined using empirical rules.

  Note that the present invention is not limited to the above-described embodiment as it is, and can be embodied by modifying the constituent elements without departing from the scope of the invention in the implementation stage. Moreover, various inventions can be formed by appropriately combining a plurality of constituent elements disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, constituent elements over different embodiments may be appropriately combined.

  DESCRIPTION OF SYMBOLS 1 ... Power converter circuit, 2 ... Control apparatus, 3 ... Smoothing capacitor, 4 ... Current detector, 5 ... DC power supply, 6 ... Load, 10 ... Power converter, 11-14 ... Switching element.

Claims (6)

A power conversion circuit composed of switching elements;
Current detection means for detecting a current including a current flowing through the switching element;
Voltage command value calculating means for calculating a voltage command value for controlling the voltage output from the power conversion circuit;
A preset first set value for taking the product of the current detected by the current detection means, the voltage command value calculated by the voltage command value calculation means, and the current detected by the current detection means Loss calculating means for calculating the loss of the switching element based on a second preset value for taking a product of the voltage command value calculated by the voltage command value calculating means;
An element temperature estimating means for estimating an element temperature of the switching element based on the loss of the switching element calculated by the loss calculating means. 2. The apparatus according to claim 1, further comprising a failure prevention unit that performs control to prevent a failure due to a temperature rise of the switching element when the element temperature estimated by the element temperature estimation unit is not within an allowable range. The power converter device described in 1. The power conversion device according to claim 1, wherein the current detection unit detects an output current of the power conversion circuit. The power conversion device according to claim 1, wherein the current detection unit detects a current flowing through the switching element. The power conversion device according to claim 1, wherein the current detection unit detects a current flowing in an arm configured by the switching element. A method for controlling a power conversion device including a power conversion circuit configured by a switching element,
Detecting a current including a current flowing through the switching element;
A voltage command value for controlling the voltage output from the power conversion circuit is calculated,
Based on the detected current and the calculated voltage command value, calculate the loss of the switching element,
A control method for a power converter, comprising estimating an element temperature of the switching element based on the calculated loss of the switching element.

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