Inverter circuit fault detection device and kitchen equipment equipped therewith

Abstract

This system detects short-circuit failures in switching elements without increasing product costs. [Solution] The inverter circuit fault detection device comprises a resistor 46 with one end connected to the high-potential side VH of IGBTs 41 and 43; a resistor 47 with one end connected to the low-potential side of IGBT 41 and the high-potential side of IGBT 42, and the other end connected to the other end of resistor 46; a resistor 48 with one end connected to the low-potential side of IGBT 43 and the high-potential side of IGBT 44, and the other end connected to the other end of resistor 46; a resistor 49 with one end connected to the other end of each of the resistors 46 to 48; an I / V conversion circuit 50 connected to the other end of resistor 49 that operates as a constant voltage source Vcnt and converts the current Ir4 input from resistor 49 into a voltage with the voltage of the constant voltage source Vcnt as its maximum value and outputs it; and a controller 37 connected to the I / V conversion circuit 50 that detects faults in each of the IGBTs 41 to 44 based on the input voltage.

Description

Technical Field

[0005] ,

[0004] , , ,

[0001] The present invention relates to a failure detection device for an inverter circuit having a plurality of semiconductor switching elements and a kitchen appliance including the same.

Background Art

[0002] In kitchen appliances, an inverter circuit is used for heating control such as an IH cooker or a steam convection oven, and rotation control such as a compressor of a refrigerator or a freezer. The electromagnetic induction heating device disclosed in Patent Document 1 below is an example thereof. Generally, in this type of inverter circuit, a switching circuit composed of semiconductor switching elements for power control applications such as IGBTs and power MOSFETs (hereinafter referred to as "switching elements"), that is, a semiconductor switching circuit for power is used. In the electromagnetic induction heating device of Patent Document 1, the first switching circuit 16 and the second switching circuit 18 correspond to this.

[0003] By the way, due to the characteristics of kitchen appliances being used in cooking facilities that provide food and drink, water is often used inside and outside the appliances. Therefore, although waterproof measures are taken for a machine room or the like that houses an inverter circuit or a control circuit including such switching elements by means of a sealing member such as a rubber packing, there is still a possibility that water may enter from the outside or condensation may occur inside compared to other equipment used indoors.

[0004] For example, in the case of an IH cooker, a liquid such as soup or water spilled from the pan may enter a machine room or the like through an unexpected gap and reach the package of the switching element or the like (hereinafter referred to as "water ingress"), or dust or dirt attached to the package of the switching element or the like may absorb the moisture condensed due to the temperature difference between the outside and inside of the appliance and water droplets may occur. Also, it cannot be said that insects do not enter from the outside.

[0005] Such exposure to water, condensation, and invading insects can cause malfunctions and failures in electronic circuits. In particular, power switching elements are subjected to high voltages and large currents during operation. Therefore, exposure to water, condensation, and insects can cause short-circuit failures or deterioration of switching elements. Furthermore, such short-circuit failures of power switching elements can occur in applications other than kitchen equipment. Accordingly, for example, Patent Document 2 below discloses a technology for detecting short-circuit failures of switching elements, and Patent Document 3 below discloses a technology for determining the deterioration state of switching elements. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2009-158366 [Patent Document 2] Japanese Patent Publication No. 2016-213977 [Patent Document 3] International Publication No. 2022 / 153520 [Overview of the project] [Problems that the invention aims to solve]

[0007] However, in the transport vehicle disclosed in Patent Document 2, a current sensing resistor is connected in series with the wiring that supplies power to the motor, and a short-circuit fault is detected based on the magnitude of the motor current flowing through it. Therefore, because a considerable amount of heat is generated when a large current flows through the current sensing resistor, it was necessary to use a special component that is large in size or has heat dissipation measures. Furthermore, even if a short-circuit fault in the switching element is detected, if, for example, the user is able to restart the transport vehicle before the fault is fixed, it could lead to secondary failures as described later, potentially causing significant damage to the switching element itself and the electronic components of its surrounding circuitry.

[0008] Furthermore, although the function of determining the degradation state of switching elements in the power converter disclosed in Patent Document 3 is theoretically possible, the output destination of the power converter is typically a drive system requiring high power, as described above. Therefore, the inverter circuit that constitutes the device is often a high-voltage circuit. Consequently, in realizing this function, it would be necessary to use special components such as photocouplers and isolation transformers in various places at the connection point between the control circuit, such as a microcontroller driven by a low voltage of about 5V, and the high-voltage circuit of several hundred volts, and to ensure a predetermined creepage distance, which could lead to a significant increase in product costs.

[0009] The present invention aims to detect short-circuit failures in switching elements without significantly increasing product costs. Another objective of the present invention is to prevent secondary failures in inverter circuits and their surrounding circuits caused by short-circuit failures in switching elements. [Means for solving the problem]

[0010] To solve the above problems, the present invention provides a fault detection device for an inverter circuit having a plurality of switching elements (semiconductor switching elements) connected in a full bridge configuration, wherein the first switching element constitutes one upper arm, the second switching element constitutes one lower arm, the third switching element constitutes the other upper arm, and the fourth switching element constitutes the other lower arm, comprising: a first resistor with one end connected to the high potential side of the first and third switching elements; and a second resistor with one end connected to the low potential side of the first switching element and the high potential side of the second switching element, and the other end connected to the other end of the first resistor. The present invention provides a fault detection device for an inverter circuit, comprising: a resistor; a third resistor, one end of which is connected to the low-potential side of the third switching element and the high-potential side of the fourth switching element, and the other end of which is connected to the other end of the first resistor; a fourth resistor, one end of which is connected to the other end of each of the first, second, and third resistors; a conversion unit connected to the other end of the fourth resistor, which operates as a constant voltage source and converts the current input from the fourth resistor into a voltage with the voltage of the constant voltage source as its maximum value and outputs it; and a detection unit connected to the conversion unit, which detects the fault of each of the first to fourth switching elements based on the voltage input from the conversion unit.

[0011] In the fault detection device for the inverter circuit configured as described above, the first to fourth resistors are connected in the following relationships [A] to [Ke] according to the on / off states of the first to fourth switching elements. For example, the connection relationships correspond to those shown in the circuit diagram in Figure 7. In the circuit diagram in Figure 7, VH corresponds to the high potential side of the first and third switching elements, and VL corresponds to the low potential side of the second and fourth switching elements. Also, R1 to R4 correspond to the first to fourth resistors, respectively. Furthermore, Vcnt corresponds to a constant voltage source.

[0012] [a] When all of the first to fourth switching elements are in the off state ("all off state"), the first resistor, the fourth resistor, and a constant voltage source are connected in series between the high-potential side of the first and third switching elements and the low-potential side of the second and fourth switching elements (hereinafter referred to as "between the high-potential side and the low-potential side") (Figure 7(a)). [b] When the first switching element is on and the second to fourth switching elements are off, the first resistor, the second resistor, the fourth resistor, and a constant voltage source are connected in parallel in series between the high-potential side and the low-potential side (Figure 7(b)). [c] When the third switching element is on and the first, second, and fourth switching elements are off, the first resistor, the third resistor, the fourth resistor, and a constant voltage source are connected in parallel in series between the high-potential side and the low-potential side (in parentheses in Figure 7(b)). [E] When the first and third switching elements are ON and the second and fourth switching elements are OFF, the first resistor, second resistor, third resistor, fourth resistor, and constant voltage source are connected in series in parallel between the high potential side and the low potential side (Figure 7(c)). [O] When the second switching element is ON and the first, third, and fourth switching elements are OFF, the first resistor, the fourth resistor and constant voltage source connected in series, and the second resistor connected in parallel with these are connected in series between the high potential side and the low potential side (Figure 7(d)). [Ka] When the fourth switching element is ON and the first to third switching elements are OFF, the first resistor, the fourth resistor and constant voltage source connected in series, and the third resistor connected in parallel with these are connected in series between the high potential side and the low potential side (in parentheses in Figure 7(d)). [Ki] When the second and fourth switching elements are ON and the first and third switching elements are OFF, the first resistor, the fourth resistor connected in series with a constant voltage source, and the second and third resistors connected in parallel with these are connected in series between the high potential side and the low potential side (Figure 7(e)). [Ku] When the first and fourth switching elements are ON and the second and third switching elements are OFF, the first and second resistors connected in parallel, the fourth resistor connected in series with a constant voltage source, and the third resistor connected in parallel with these are connected in series between the high potential side and the low potential side (Figure 7(f)).[Ke] When the second and third switching elements are ON and the first and fourth switching elements are OFF, the first and third resistors connected in parallel, the fourth resistor and constant voltage source connected in series, and the second resistor connected in parallel with them are connected in series between the high potential side and the low potential side (in parentheses in Figure 7(f)).

[0013] As a result, if the first to fourth resistors are in the connection relationship [I] to [Ke] even though the first to fourth switching elements are not intentionally controlled to be ON, there is a possibility that one of the first to fourth switching elements has a short circuit failure. That is, compared to the current flowing through the fourth resistor (the current flowing through R4 in Figure 7(a)) when none of the first to fourth switching elements have a short circuit failure, the current flowing through the fourth resistor (the current flowing through R4 in Figure 7(b)) increases when the first or third switching element has a short circuit failure, and the current flowing through the fourth resistor (the current flowing through R4 in Figure 7(c)) increases further when both the first and third switching elements have short circuit failures. Also, if the second or fourth switching element has a short circuit failure, the current flowing through the fourth resistor (the current flowing through R4 in Figure 7(d)) ​​decreases, and the current flowing through the fourth resistor (the current flowing through R4 in Figure 7(e)) decreases further when both the second and fourth switching elements have short circuit failures. Therefore, the conversion unit converts the current flowing through the fourth resistor into a voltage and outputs it to the detection unit, which in turn enables the detection unit to detect failures in each of the first to fourth switching elements based on the voltage input from the conversion unit.

[0014] Furthermore, the voltage output by the conversion unit is a voltage with the voltage of the constant voltage source as its maximum value. Therefore, by setting the voltage of the constant voltage source to a low voltage of, for example, 5V, analog information of the current flowing through the fourth resistor can be output in a voltage range of 0 to 5V. For example, the conversion unit can be configured as a voltage-to-current conversion circuit (transimpedance amplifier) ​​using an operational amplifier, and the detection unit can use a microcontroller that controls the on / off state of the first to fourth switching elements. This makes it possible to connect, for example, a high-voltage inverter circuit with a high potential side set to 280V and a low potential side to 0V, and a detection unit consisting of a microcontroller driven by a low voltage of 5V, using a conversion unit configured with inexpensive general-purpose components such as resistors and operational amplifiers. Consequently, there is no need to use special components such as photocouplers and isolation transformers in various places, so it was possible to detect short-circuit failures of switching elements without significantly increasing product costs.

[0015] Furthermore, in order to solve the above problems, the present invention provides a fault detection device for an inverter circuit having a plurality of switching elements (semiconductor switching elements) connected in a half-bridge configuration, wherein the first switching element constitutes an upper arm and the second switching element constitutes a lower arm, and the device comprises: a first resistor with one end connected to the high potential side of the first switching element; a second resistor with one end connected to the low potential side of the first switching element and the high potential side of the second switching element, and the other end connected to the other end of the first resistor; a fourth resistor with one end connected to the other ends of the first and second resistors; a conversion unit connected to the other end of the fourth resistor that operates as a constant voltage source and converts the current input from the fourth resistor into a voltage with the voltage of the constant voltage source as its maximum value and outputs it; and a detection unit connected to the conversion unit that detects faults in the first and second switching elements based on the voltage input from the conversion unit.

[0016] In the fault detection device for the inverter circuit configured as described above, the first, second, and fourth resistors are connected in the following [S]~[S] relationship according to the on / off states of the first and second switching elements, respectively. For example, the connection relationship corresponds to the circuit diagram shown in Figure 7. In the circuit diagram of Figure 7, VH corresponds to the high potential side of the first and third switching elements, and VL corresponds to the low potential side of the second and fourth switching elements. Also, R1~R4 correspond to the first to fourth resistors, respectively. Furthermore, Vcnt corresponds to a constant voltage source.

[0017] [Sa] When both the first and second switching elements are in the off state, the first resistor, the fourth resistor, and the constant voltage source are connected in series between the high-potential side of the first switching element and the low-potential side of the second switching element (hereinafter referred to as "between the high-potential side and the low-potential side") (Figure 7(a)). [Shi] When the first switching element is in the on state and the second switching element is in the off state, the first resistor and the second resistor, the fourth resistor, and the constant voltage source are connected in parallel between the high-potential side and the low-potential side (Figure 7(b)). [Su] When the second switching element is in the on state and the first switching element is in the off state, the first resistor, the fourth resistor and constant voltage source connected in series, and the second resistor connected in parallel with them are connected in series between the high-potential side and the low-potential side (Figure 7(d)). As a result, when the first switching element experiences a short-circuit failure, the current flowing through the fourth resistor (the current flowing through R4 in Figure 7(b)) increases compared to when neither the first nor the second switching element experiences a short-circuit failure (the current flowing through R4 in Figure 7(a)). Conversely, when the second switching element experiences a short-circuit failure, the current flowing through the fourth resistor (the current flowing through R4 in Figure 7(d)) ​​decreases. Therefore, by having the conversion unit convert the current flowing through the fourth resistor into a voltage and output it to the detection unit, the detection unit can detect failures in the first and second switching elements based on the voltage input from the conversion unit.

[0018] Furthermore, the voltage output by the conversion unit is a voltage with the voltage of the constant voltage source as its maximum value. Therefore, by setting the voltage of the constant voltage source to a low voltage of, for example, 5V, analog information of the current flowing through the fourth resistor can be output in a voltage range of 0 to 5V. For example, the conversion unit can be configured as a voltage-to-current conversion circuit (transimpedance amplifier) ​​using an operational amplifier, and the detection unit can use a microcontroller that controls the on / off state of the first to fourth switching elements. This makes it possible to connect, for example, a high-voltage inverter circuit with a high potential side set to 280V and a low potential side to 0V, and a detection unit consisting of a microcontroller driven by a low voltage of 5V, using a conversion unit configured with inexpensive general-purpose components such as resistors and operational amplifiers. Consequently, there is no need to use special components such as photocouplers and isolation transformers in various places, so it was possible to detect short-circuit failures of switching elements without increasing product costs.

[0019] Furthermore, in order to solve the above problems, the present invention provides a kitchen appliance equipped with an inverter circuit fault detection device as described in claim 1 or 2, wherein the inverter circuit has a plurality of switching elements (semiconductor switching elements) and is housed in a predetermined space, and the detection unit prohibits the startup of the inverter circuit when it detects that any of the plurality of switching elements has a short-circuit failure.

[0020] In the kitchen appliance configured as described above, an inverter circuit is housed within a predetermined space. And when the detection unit detects that any one of a plurality of switching elements included in the inverter circuit has short-circuited, the detection unit prohibits the activation of the inverter circuit. Thereby, based on the voltage input from the conversion unit, when the detection unit detects a failure of each of the first to fourth switching elements connected in a full bridge or a failure of each of the first and second switching elements connected in a half bridge, for example, even if the kitchen appliance is restarted, at least the subsequent activation activation of the inverter circuit is prohibited from being activated. Therefore, even if it is possible for the user to restart the kitchen appliance before the failure is resolved, when a short-circuit failure of the switching element is detected, the activation of the inverter circuit is prohibited, so that, as will be described later, the possibility of significant damage to the switching element itself and the electronic components of its peripheral circuit is extremely low. Also, the restart itself may be prohibited. Thus, it is possible to prevent the occurrence of secondary failures in the inverter circuit and its peripheral circuit due to the short-circuit failure of the switching element.

Brief Description of the Drawings

[0021] [Figure 1] It is a front view of a cooking appliance which is an embodiment of the kitchen appliance of the present invention. [Figure 2] It is a cross-sectional view taken along line A-A of FIG. 1. [Figure 3] It is a side view (a) and a plan view (b) of a steam generator. [Figure 4] It is a block diagram of an electric control system. [Figure 5] It is a block diagram of a steam generator. [Figure 6] It is a circuit diagram showing a circuit and its failure detection circuit when the induction heating circuit is a full bridge inverter (a), and a circuit diagram when the parts of each IGBT and the failure detection circuit are taken out (b). [Figure 7] It is an equivalent circuit diagram of a failure detection circuit corresponding to the on / off states of each IGBT constituting a full bridge inverter circuit. [Figure 8](a) is a circuit diagram showing the circuit and its fault detection circuit when the induction heating circuit is a half-bridge inverter, and (b) is a circuit diagram showing the individual IGBTs and fault detection circuits separately. [Figure 9] This is a flowchart of the fault detection program. [Figure 10] This is a flowchart of the program for detecting short-circuit faults in the upper arm. [Figure 11] This is a flowchart of the program for detecting short-circuit faults in the lower arm. [Best Mode for Carrying Out the Invention]

[0022] Below, an embodiment of the kitchen equipment of the present invention applied to a cooking appliance will be described with reference to the attached drawings. The cooking appliance in this embodiment is called a steam convection oven, and it generates steam using a steam generator that utilizes electromagnetic induction heating, and cooks food by circulating the hot air containing the steam.

[0023] As shown in Figures 1 and 2, the heating appliance 10 includes a cooking chamber 14 for heating food in the part of the housing 11 excluding the left side, a door 12 that allows the front of the cooking chamber 14 to be opened and closed, a machine room 15 in the space on the left side of the housing 11, and an operation panel 13 that covers the front of the machine room 15.

[0024] As shown in Figure 2, the left side of the cooking chamber 14 is designated as the heating space 14a, and is equipped with a heater 16 for heating the inside of the cooking chamber 14 and a blower fan 17 for circulating (convection) the air inside the cooking chamber 14. The area excluding the heating space 14a is designated as the storage space 14b for storing food ingredients. The blower fan 17 is a centrifugal fan such as a Sirocco fan, which draws in air from the center and sends it outwards in the centrifugal direction. When the blower fan 17 is driven, air is drawn in from the storage space 14b as shown by the arrow in Figure 2, and the air sent outwards in the centrifugal direction is heated by the heater 16 to become hot air, which is then sent back to the storage space 14b along the peripheral walls (front wall, rear wall, top wall, and bottom wall) of the cooking chamber 14.

[0025] Rack frames 18 are provided on both the left and right sides of the storage space 14b of the cooking chamber 14 to support trays (not shown) for receiving ingredients, called hotel pans, in a multi-tiered vertical arrangement. A steam generator 20 for supplying steam into the cooking chamber 14 is provided at the rear of the machine room 15. A control device 60 for controlling the heater 16, blower fan 17, steam generator 20, etc., is provided on the back of the operation panel 13 at the front of the machine room 15. The control device 60 is configured by mounting electronic components such as a microcomputer on a printed circuit board 61, as will be described later. Reference numeral 70 indicates a cooling fan that cools the heatsink to which the IGBT of the induction heating circuit, which will be described later, is attached.

[0026] As shown in Figures 3 to 5, the steam generator 20 comprises a steam generating container 21 that stores water at a predetermined level, a steam outlet pipe 22 connected to the upper part of the steam generating container 21 to send steam into the cooking chamber 14, a water level detection tank 23 connected to the lower part of the steam generating container 21 to detect the water level inside the steam generating container 21, a water level sensor 24 provided in the water level detection tank 23 to detect the water level inside the steam generating container 21, and a heating unit 30 that heats the water inside the steam generating container 21, and is controlled by a control device 60.

[0027] The steam generating container 21 has a cylindrical shape with openings at the top and bottom. The top opening serves as a steam outlet, and the bottom opening serves as a drain. A drain pipe is connected to the bottom of the steam generating container 21, and water inside the steam generating container 21 is drained by opening a drain valve provided in the drain pipe. A temperature sensor 39 capable of detecting the overheating state of the heating element 31 (described later) is provided on the upper part of the circumferential surface of the steam generating container 21.

[0028] A water level detection tank 23 is erected adjacent to the steam generation vessel 21, and the lower part of the water level detection tank 23 is connected in communication with the lower part of the steam generation vessel 21. A water level sensor 24 is attached to the water level detection tank 23. The water level sensor 24 detects the water level in the steam generation vessel 21 by detecting the water level in the water level detection tank 23. A water supply pipe 25, which leads from a water supply source such as a water tap, is connected to the upper part of the water level detection tank 23. By opening a water supply valve 27 interposed in the water supply pipe 25, water is supplied into the water level detection tank 23. Excess water in the water level detection tank 23 is discharged to a drain tank (not shown) that receives wastewater from the cooking area 14 via a drain pipe 26 connected to the lower part.

[0029] The heating unit 30 includes a heating element 31 inside a steam generating container 21, an induction heating coil 34 wound around the outer circumference of the steam generating container 21 from the middle to the bottom in the vertical direction, an induction heating circuit 40 including the induction heating coil 34, a fault detection device including an I / V conversion circuit 50, a rectifier circuit 36 ​​that supplies DC power to the induction heating circuit 40, a controller 37 that controls the induction heating circuit 40, a voltage sensor 38a for detecting the input voltage of an AC power supply 90 which is an external power supply, and a current sensor 38b for detecting the input current of the AC power supply 90.

[0030] Of these, the voltage sensor 38a, current sensor 38b, controller 37, I / V conversion circuit 50, and fault detection device including it are located on a printed circuit board 61 on the back of the operation panel 13, similar to the control device 60, away from the heating element 31 and induction heating coil 34. In addition, the IGBTs 41-44 (see Figure 6) of the rectifier circuit 36 ​​and induction heating circuit 40 are mounted on a heat sink (not shown) located physically away from the printed circuit board 61, and can be cooled by a cooling fan 70. The voltage and current values ​​of the AC power supply 90 detected by the voltage sensor 38a and current sensor 38b, and the current information, which is converted to voltage and output by the I / V conversion circuit 50 (described later), are configured to be output to the controller 37.

[0031] The heating element 31 comprises a substantially annular holder 32 supported at the top of the steam generating container 21, and a plurality of heating rods 33 arranged in an annular shape with their upper ends fixed to the holder 32. In this embodiment, the heating rods 33 have a circular radial cross-sectional shape. For example, the holder 32 is made of austenitic stainless steel (non-magnetic material), while the heating rods 33 are made of ferritic stainless steel (magnetic material).

[0032] An induction heating coil 34 is wound around the outer circumference of the steam generating container 21 that houses the heating element 31 configured in this way, approximately coaxially with a ring-shaped arrangement of multiple heating rods 33. For example, the induction heating coil 34 can be made of Litz wire (stranded wire) made by twisting together multiple enameled copper wires, or a single enameled copper wire. As a result, as will be described later, magnetic field lines repeatedly generated as a high-frequency current flows through the induction heating coil 34 pass through the multiple heating rods 33, causing eddy currents to flow within the heating rods 33. This generates Joule heat due to the electrical resistance of the heating rods 33, causing the heating rods 33 themselves to heat up.

[0033] The rectifier circuit 36 ​​is a bridge circuit consisting of silicon diodes that rectify an AC voltage into a DC voltage. In this embodiment, it is configured to rectify the voltage according to each phase of the AC power supply 90 that supplies a three-phase AC 200V, and then output a DC 280V (for example, a maximum of 200A) to the induction heating circuit 40. In this embodiment, the positive side of the DC voltage output from the rectifier circuit 36 ​​is called the high-potential power line 35H, and the negative side of the same DC voltage is called the low-potential power line 35L. The rectifier circuit 36 ​​generates heat during operation, and is therefore attached to a heat sink as described above.

[0034] The controller 37 includes a one-chip microcontroller (not shown) that controls the induction heating circuit 40 based on control information input from the control device 60. The one-chip microcontroller is a microcomputer having a CPU, RAM, EEPROM, timer, ADC (analog-to-digital converter), and input / output interfaces (all not shown) connected via a bus. The EEPROM stores a switching control program for switching the IGBTs 41-44 that constitute the induction heating circuit 40, and a fault detection program for detecting short-circuit failures of the IGBTs 41-44, etc.

[0035] The I / V conversion circuit 50 is a current-voltage converter (conversion unit) that converts the current flowing through the resistor 49 (described later) into a voltage and outputs it to the controller 37. The other end of the resistor 49 is connected to the input side, and the analog input port (ADC input side) of the controller 37 is connected to the output side. The I / V conversion circuit 50 is, for example, a transimpedance amplifier composed of an operational amplifier. In this embodiment, it is composed of an operational amplifier whose inverting input is connected to the resistor 49 (described later), a feedback resistor connected between the inverting input and output of the operational amplifier, and a constant voltage source connected between the non-inverting input of the operational amplifier and a reference potential. As a result, the I / V conversion circuit 50 can output the voltage obtained by the product of the current Ir4 input from the resistor 49 and the feedback resistor Rf, shifted by the voltage Vcnt of the constant voltage source, as the output voltage Vout (=Vcnt-Ir4×Rf).

[0036] In this embodiment, the I / V conversion circuit 50 is composed of an operational amplifier and a resistor, and a constant voltage source that outputs a predetermined voltage Vcnt is connected to its non-inverting input. Due to its characteristics, the operational amplifier has a very high input impedance at the inverting input, and the non-inverting input and the inverting input are at almost the same potential. Therefore, from the perspective of the resistor 49 connected to the inverting input, the I / V conversion circuit 50 appears as a constant voltage source that generates a predetermined voltage Vcnt relative to a reference potential. Note that when the I / V conversion circuit 50 operates as a constant voltage source of a predetermined voltage Vcnt, the constant voltage source may be denoted as Vcnt and indicated as "constant voltage source Vcnt" in the specification and drawings.

[0037] The fault detection device consists of resistors 46-49, an I / V conversion circuit 50, and a controller 37. Resistors 46-49 will be explained along with the configuration of the induction heating circuit 40 with reference to Figure 6. The controller 37 also functions as part of the fault detection device by performing fault detection processing (Figure 9), upper arm short-circuit fault detection processing (Figure 10), and lower arm short-circuit fault detection processing (Figure 11), respectively, as will be described later.

[0038] As shown in Figure 6(a), the induction heating circuit 40 consists of IGBTs 41 and 43, whose collectors are connected to the high-potential power line 35H; IGBT 42, whose collector is connected to the emitter of IGBT 41 and whose emitter is connected to the low-potential power line 35L of the circuit 40; IGBT 44, whose collector is connected to the emitter of IGBT 43 and whose emitter is connected to the low-potential power line 35L of the circuit 40; and an induction heating coil 34 and a capacitor 45 connected in series between the connection points of IGBTs 41 and 42 and IGBTs 43 and 44. A current sensor (not shown) is also provided to detect the current flowing through the induction heating coil 34 and the capacitor 45, and the current value is output to the controller 37. Although not shown, freewheeling diodes are connected in antiparallel between the collectors and emitters of each of the IGBTs 41 to 44. IGBTs 41-44 are configured to allow currents of, for example, 150A to flow between the input and output (collector-emitter).

[0039] In other words, the induction heating circuit 40 shown in Figure 6(a) is an inverter circuit capable of supplying high-frequency current (AC power) to the induction heating coil 34 and capacitor 45 connected in series, and is called a full-bridge inverter circuit or full-bridge circuit. IGBTs 41 and 43 constitute the upper arm, and IGBTs 42 and 44 constitute the lower arm. The correspondence with the claims (in quotation marks) is as follows: The collector of IGBT 41 may correspond to the "high-potential side of the first switching element", the collector of IGBT 42 to the "high-potential side of the second switching element", the collector of IGBT 43 to the "high-potential side of the third switching element", and the collector of IGBT 44 to the "high-potential side of the fourth switching element". The emitter of IGBT 41 may correspond to the "low-potential side of the first switching element", and the emitter of IGBT 43 to the "low-potential side of the third switching element".

[0040] In the induction heating circuit 40 configured in this way, AC current flows to the induction heating coil 34 by the controller 37 alternately switching on and off the IGBT 41, 44 pair (right bridge) and the IGBT 42, 43 pair (left bridge). That is, at the moment when both IGBT 41 and 44 are controlled to be ON and both IGBT 42 and 43 are controlled to be OFF, current flows through the path IGBT 41 → capacitor 45 → induction heating coil 34 → IGBT 44. At the moment when both IGBT 42 and 43 are controlled to be ON and both IGBT 41 and 44 are controlled to be OFF, current flows through the path IGBT 43 → induction heating coil 34 → capacitor 45 → IGBT 42. By performing this switching of IGBTs 41 to 44 on the order of microseconds, for example, it becomes possible to supply high-frequency current (AC power) to the induction heating coil 34.

[0041] In this embodiment, the induction heating circuit 40 is equipped with resistors 46-49, an I / V conversion circuit 50, and a controller 37 as fault detection devices for IGBTs 41-44. As mentioned above, the controller 37 has the function of switching control IGBTs 41-44 using a switching control program, but in this embodiment, it also has the function of detecting short-circuit faults of IGBTs 41-44 using a fault detection program. Figure 6(b) shows a circuit diagram obtained by extracting IGBTs 41-44, resistors 46-49, and the I / V conversion circuit 50 from the circuit diagram shown in Figure 6(a), so the explanation from here on will also refer to this figure.

[0042] Resistor 46(R1), connected to both the upper arms of one and the other, has one end connected to the collectors (high potential side) of IGBT41(Q1) and IGBT43(Q3), and the other end connected to the other end of resistors 47,48(R2,3) and one end of resistor 49(R4). Resistor 47(R2), connected to the midpoint of one upper and lower arm, has one end connected to the emitter (low potential side) of IGBT41(Q1) and the collector (high potential side) of IGBT42(Q2), and the other end connected to the other end of resistor 46(R1). Resistor 48(R3), connected to the midpoint of the other upper and lower arm, has one end connected to the emitter (low potential side) of IGBT43(Q3) and the collector (high potential side) of IGBT44(Q4), and the other end connected to the other end of resistor 46(R1). The resistor 49 (R4), which is connected to these resistors 46-48 (R1-3), has one end connected to the other end of each of the resistors 46-48 (R1-3), and the other end connected to the input side of the I / V conversion circuit 50. In Figure 6(b), the I / V conversion circuit 50 is represented as a constant voltage source Vcnt.

[0043] By connecting resistors 46 to 49 to the induction heating circuit 40 in this manner, the resistors 46 to 49 and the constant voltage source Vcnt that constitute the fault detection device form the equivalent circuit shown in Figures 7(a) to (f) according to the on / off state of IGBTs 41 to 44. The resistors 46 to 49 are set to a resistance value such that, for example, resistor 46 > resistor 49 > resistor 47 = resistor 48, and the current flowing through resistor 49 is on the order of microamperes. This is just one example, and the resistance values ​​of resistors 46 to 49 can be arbitrarily set within a range that does not interfere with the switching operation of IGBTs 41 to 44 or the supply of high-frequency current (AC power) to the induction heating coil 34. Here, we will use the symbols (R1 to 4, VH, VL, Vcnt) shown in each circuit diagram in Figures 7(a) to (f) for explanation. Also, here, unless a fault is explicitly stated, it is assumed that all IGBTs 41 to 44 are normal (no faults).

[0044] [A] When all IGBTs 41-44 (Q1-4) are in the off state, a circuit is formed in which R1 (resistor 46), R4 (resistor 49), and a constant voltage source Vcnt are connected in series between the high-potential side VH of IGBTs 41 and 43 (Q1 and 3) and the low-potential side VL of IGBTs 42 and 44 (Q2 and 4) (Figure 7(a)). In this circuit, the current Ir4a flowing through R4 (resistor 49) is expressed as (Vh-Vcnt) / (R1+R4). Vh is the potential difference between VH and VL, and in this embodiment, VH is 280V and VL is 0V, so Vh is 280V.

[0045] [i] When IGBT41(Q1) is ON and IGBTs42~44(Q2~4) are OFF, a circuit is formed between the high-potential side VH and the low-potential side VL, with R1 (resistor 46) and R2 (resistor 47) connected in parallel, and R4 (resistor 49) and a constant voltage source Vcnt connected in series (Figure 7(b)). In this circuit, the current Ir4b flowing through R4 (resistor 49) is expressed as (Vh-Vcnt) / (R1∥R2+R4). The symbol ∥ indicates that the resistors before and after this symbol are connected in parallel (the same applies below).

[0046] [U] When IGBT43(Q3) is ON and IGBTs41,42,44(Q1,2,4) are OFF, a circuit is formed between the high-potential side VH and the low-potential side VL, with R1 (resistor 46) and R3 (resistor 48) connected in parallel, and R4 (resistor 49) and a constant voltage source Vcnt connected in series (in parentheses in Figure 7(b)). In this circuit, the current Ir4b' flowing through R4 (resistor 49) is expressed as (Vh-Vcnt) / (R1∥R3+R4).

[0047] [E] When IGBTs 41 and 43 (Q1 and 3) are ON and IGBTs 42 and 44 (Q2 and 4) are OFF, a circuit is formed between the high-potential side VH and the low-potential side VL, with R1 (resistor 46), R2 (resistor 47), and R3 (resistor 48) connected in parallel, and R4 (resistor 49) connected in series with a constant voltage source Vcnt (Figure 7(c)). In this circuit, the current Ir4c flowing through R4 (resistor 49) is expressed as (Vh - Vcnt) / (R1∥R2∥R3 + R4).

[0048] [O] When IGBT42(Q2) is ON and IGBT41,43,44(Q1,3,4) are OFF, a circuit is formed between the high-potential side VH and the low-potential side VL, with R1 (resistor 46), R4 (resistor 49) connected in series with it, a constant voltage source Vcnt, and R2 (resistor 47) connected in parallel with them, all connected in series (Figure 7(d)). The current Ir4d flowing through R4 (resistor 49) in this circuit is expressed as (Vh-Vcnt) / (R1+R4)-Ir2d, which is obtained by subtracting the current Ir2d that branches off to the R2 (resistor 47) side and flows to the low-potential side VL from the current Ir4a flowing through R4 (resistor 49) in the circuit [A].

[0049] [K] When IGBT44(Q4) is ON and IGBT41~43(Q1~3) are OFF, a circuit is formed between the high-potential side VH and the low-potential side VL, in which R1 (resistor 46), R4 (resistor 49) connected in series with a constant voltage source Vcnt, and R3 (resistor 48) connected in parallel with these are connected in series (in parentheses in Figure 7(d)). In this circuit, the current Ir4d' flowing through R4 (resistor 49) is expressed as (Vh-Vcnt) / (R1+R4)-Ir3d, using the same approach as in [O].

[0050] [Ki] When IGBTs 42 and 44 (Q2 and 4) are ON and IGBTs 41 and 43 (Q1 and 3) are OFF, a circuit is formed between the high-potential side VH and the low-potential side VL, in which R1 (resistor 46), R4 (resistor 49) connected in series with a constant voltage source Vcnt, and R2 (resistor 47) and R3 (resistor 48) connected in parallel with these are connected in series (Figure 7(e)). In this circuit, the current Ir4e flowing through R4 (resistor 49) is expressed as (Vh - Vcnt) / (R1 + R4) - Ir2e - Ir3e) using the same approach as in [O].

[0051] [K] When IGBTs 41 and 44 (Q1 and 4) are ON and IGBTs 42 and 43 (Q2 and 3) are OFF, R1 (resistor 46) and R2 (resistor 47) are connected in parallel, R4 (resistor 49) and the constant voltage source Vcnt are connected in series, and R3 (resistor 48) is connected in parallel with these resistors between the high-potential side VH and the low-potential side VL (Figure 7(f)). The current Ir4f flowing through R4 (resistor 49) in this circuit is expressed as (Vh-Vcnt) / (R1∥R2+R4)-Ir3f, which is obtained by subtracting the current Ir3f that branches off to the R3 (resistor 48) side and flows to the low-potential side VL from the current Ir4b flowing through R4 (resistor 49) in the circuit [I].

[0052] [Ke] When IGBTs 42 and 43 (Q2 and 3) are ON and IGBTs 41 and 44 (Q1 and 4) are OFF, R1 (resistor 46) and R3 (resistor 48) are connected in parallel, R4 (resistor 49) and the constant voltage source Vcnt are connected in series, and R2 (resistor 47) is connected in parallel with these resistors between the high-potential side VH and the low-potential side VL (in parentheses in Figure 7(f)). In this circuit, the current Ir4f' flowing through R4 (resistor 49) is expressed as (Vh - Vcnt) / (R1∥R2 + R4) - Ir2f, using the same approach as in [Ku].

[0053] As described above, the current Ir4 flowing through R4 (resistor 49) will be a specific current value (Ir4a, Ir4b, Ir4b', Ir4c, Ir4d, Ir4d', Ir4e, Ir4f, Ir4f') depending on the on / off state of IGBTs 41-44 (Q1-4). However, if R1-4 (resistors 46-49) are in the connection relationship [I]-[Ke] even though the controller 37 is not controlling IGBTs 41-44 (Q1-4) to be in the on state, there is a high probability that one of IGBTs 41-44 (Q1-4) has a short circuit failure. Also, if R1-4 (resistors 46-49) are not in the intended connection relationship due to IGBTs 41-44 (Q1-4) being controlled by the controller 37, there is a high probability that one of IGBTs 41-44 (Q1-4) has a short circuit failure or an open circuit failure.

[0054] For example, when one or both of IGBTs 41 and 43 (Q1 and 3, upper arms) are turned on, R2 (resistor 47) and R3 (resistor 48) are connected in parallel to R1 (resistor 46), and current flows to R4 (resistor 49) through these resistors. As a result, the current flowing through R4 (resistor 49) increases by the same amount as the current Ir4a when all IGBTs 41 to 44 (Q1 to 4) are turned on (referred to as the "all-on state"). Also, when one or both of IGBTs 42 and 44 (Q2 and 4, lower arms) are turned on, R2 (resistor 47) and R3 (resistor 48) are connected to the low-potential side VL, and current flows to the low-potential side VL through these resistors. As a result, the current flowing through R4 (resistor 49) decreases by the same amount as the current Ir4a when all are turned on. Therefore, it becomes possible to detect when IGBTs 41-44 (Q1-4) are ON when they should be OFF (i.e., a short circuit fault) or OFF when they should be ON (i.e., an open circuit fault).

[0055] As shown in Figure 8(a), the induction heating circuit 40' may be configured using a half-bridge inverter circuit or a half-bridge circuit. In this case, the circuit consists of an IGBT 41 with its collector connected to the high-potential power line 35H, an IGBT 42 with its collector connected to the emitter of the IGBT 41 and its emitter connected to the low-potential power line 35L of the same circuit 40', two capacitors 45a and 45b of the same capacitance connected in series between these power lines 35H and 35L, and an induction heating coil 34 with both ends connected between the connection points of the IGBTs 41 and 42 and the connection points of the capacitors 45a and 45b. A current sensor (not shown) is also provided to detect the current flowing through the induction heating coil 34 and the capacitors 45a and 45b, and the current value is output to the controller 37.

[0056] When the induction heating circuit 40' is configured as a half-bridge inverter circuit, the controller 37 alternately switches IGBT 41 and IGBT 42 on and off, causing alternating current to flow through the induction heating coil 34. Specifically, at the moment IGBT 41 is switched on and IGBT 42 is switched off, current flows through the path IGBT 41 → induction heating coil 34 → capacitor 45b. At the moment IGBT 42 is switched on and IGBT 41 is switched off, current flows through the path capacitor 45a → induction heating coil 34 → IGBT 42. By performing this switching of IGBT 41 and 42 on the order of microseconds, for example, it becomes possible to supply high-frequency current (alternating current power) to the induction heating coil 34.

[0057] When the induction heating circuit 40' is composed of IGBTs 41 and 42 connected in a half-bridge configuration, resistors 46, 47, and 49, an I / V conversion circuit 50, and a controller 37 are provided as fault detection devices for the IGBTs 41 and 42. The I / V conversion circuit 50 and controller 37 are almost the same as those in the induction heating circuit 40 which is configured in a full bridge configuration. Figure 8(b) shows a circuit diagram taken from the circuit diagram shown in Figure 8(a) and including the IGBTs 41 and 42, resistors 46, 47, and 49, and the I / V conversion circuit 50. From here on, we will explain the resistors 46, 47, and 49 while referring to this figure.

[0058] Resistor 46(R1), connected to the upper arm, has one end connected to the collector (high potential side) of IGBT41(Q1), and the other end connected to the other end of resistor 47(R2) and one end of resistor 49(R4). Resistor 47(R2), connected at the midpoint between the upper and lower arms, has one end connected to the emitter (low potential side) of IGBT41(Q1) and the collector (high potential side) of IGBT42(Q2), and the other end connected to the other end of resistor 46(R1). Resistor 49(R4), connected to these resistors 46 and 47(R1,2), has one end connected to the other ends of resistors 46 and 47(R1,2), and the other end connected to the input side of the I / V conversion circuit 50. In Figure 8(b), the I / V conversion circuit 50 is represented as a constant voltage source Vcnt.

[0059] By connecting resistors 46, 47, and 49 to the half-bridge type induction heating circuit 40' in this manner, the resistors 46, 47, and 49 and the constant voltage source Vcnt that constitute the fault detection device form an equivalent circuit as shown in Figures 7(a), (b), and (d), according to the on / off state of the IGBTs 41 and 42. The resistors 46, 47, and 49 have a magnitude relationship such as resistor 46 > resistor 49 > resistor 47, and their resistance values ​​are set such that the current flowing through resistor 49 is on the order of microamperes. This is just one example, and the resistance values ​​of resistors 46, 47, and 49 can be arbitrarily set within a range that does not interfere with the switching operation of the IGBTs 41 and 42 or the supply of high-frequency current (AC power) to the induction heating coil 34. In other words, it can be explained in much the same way as [A], [B], and [E] in the case of the full-bridge type induction heating circuit 40 described above ([S] ≈ [A], [C] ≈ [B], [S] ≈ [E]).

[0060] [S] When IGBTs 41 and 42 (Q1 and 2) are all in the off state, a circuit is formed in which R1 (resistor 46), R4 (resistor 49), and a constant voltage source Vcnt are connected in series between the high-potential side VH of IGBT 41 (Q1) and the low-potential side VL of IGBT 42 (Q2) (Figure 7(a)). In this circuit, the current Ir4a flowing through R4 (resistor 49) is expressed as (Vh - Vcnt) / (R1 + R4). In this embodiment, Vh is 280V.

[0061] [C] When IGBT41(Q1) is ON and IGBT42(Q2) is OFF, a circuit is formed between the high-potential side VH and the low-potential side VL, with R1 (resistor 46) and R2 (resistor 47) connected in parallel, and R4 (resistor 49) and a constant voltage source Vcnt connected in series (Figure 7(b)). In this circuit, the current Ir4b flowing through R4 (resistor 49) is expressed as (Vh-Vcnt) / (R1∥R2+R4).

[0062] [S] When IGBT42(Q2) is ON and IGBT41(Q1) is OFF, a circuit is formed between the high-potential side VH and the low-potential side VL, with R1 (resistor 46), R4 (resistor 49) connected in series with it, a constant voltage source Vcnt, and R2 (resistor 47) connected in parallel with them, all connected in series (Figure 7(d)). The current Ir4d flowing through R4 (resistor 49) in this circuit is expressed as (Vh-Vcnt) / (R1+R4)-Ir2d, which is obtained by subtracting the current Ir2d that branches off to the R2 (resistor 47) side and flows to the low-potential side VL from the current Ir4a flowing through R4 (resistor 49) in the circuit [S].

[0063] In this half-bridge type induction heating circuit 40', the current Ir4 flowing through R4 (resistor 49) becomes a specific current value (Ir4a, Ir4b, Ir4d) depending on the on / off state of IGBTs 41 and 42 (Q1 and 2). When IGBT 41 (Q1, upper arm) is turned on, the current Ir4 increases compared to the current Ir4a flowing through R4 (resistor 49) when IGBTs 41 and 42 (Q1 and 2) are both turned on. Also, when IGBT 42 (Q2, lower arm) is turned on, the current Ir4 decreases compared to the current Ir4a when all are turned on. Therefore, it becomes possible to detect when IGBTs 41 and 42 (Q1 and 2) are turned on when they should be off (i.e., a short circuit fault) or off when they should be on (i.e., an open circuit fault).

[0064] In this embodiment, in the induction heating circuits 40, 40' which can be configured as a full-bridge inverter circuit or a half-bridge inverter circuit, resistors 46~49 (R1~4) and an I / V conversion circuit 50 are provided in the case of a full-bridge inverter circuit, and resistors 46, 47, 49 (R1,2,4) and an I / V conversion circuit 50 are provided in the case of a half-bridge inverter circuit. This point differs from typical full-bridge inverter circuits and half-bridge inverter circuits.

[0065] As shown in Figures 2 and 4, the control device 60 is located on the back of the operation panel 13 and is connected to the liquid crystal touch panel 13a, start button 13b, heater 16, blower fan 17, controller 37 of the heating unit 30 of the steam generator 20, water level sensor 24, water supply valve 27, and temperature sensor 39. The control device 60 has a microcomputer (not shown), which includes a CPU, RAM, EEPROM, timer, and input / output interface (all not shown) connected via a bus. The EEPROM stores cooking programs for heating and cooking food in the cooking chamber 14.

[0066] The heating appliance 10 operates, for example, the heater 16 and blower fan 17 to circulate hot air inside the cooking chamber 14, and the steam generator 20 to supply steam inside the cooking chamber 14, according to the cooking program of the cooking mode selected by the user via the liquid crystal touch panel 13a. As a result, steam and hot air circulate inside the cooking chamber 14, and the food inside the cooking chamber 14 is heated and cooked by this steam-infused hot air.

[0067] By the way, as mentioned in the section on [Problems the invention aims to solve], the heating appliance 10 is used in cooking facilities that serve food and beverages, and therefore water is often used inside and outside the appliance. For this reason, although the machine room 15, which houses the induction heating circuits 40 and 40', is waterproofed by sealing members (not shown), there is still a possibility that water may enter the machine room 15 from the outside or that condensation may form inside. Furthermore, it is difficult to say that insects cannot enter from the outside.

[0068] According to the inventor's knowledge, failures of IGBTs 41-44 caused by water exposure, condensation, or invading insects often result from short-circuit failures caused by current exceeding the absolute maximum rated current flowing between the collector and emitter of IGBT 41, etc. Therefore, even if the current sensor 38b detects that an input current exceeding the allowable upper limit has flowed to the AC power supply 90 and the control device 60 displays failure information for the induction heating circuits 40 and 40' on the operation panel 13 of the cooking appliance 10 based on that information, if the user does not understand the importance of that failure information, it may develop into a serious failure. For example, if the user attempts to turn the power switch off and on (re-energizing after power cut-off) expecting the cooking appliance 10 to immediately return to normal operation, there is a possibility that significant damage may be inflicted on the IGBTs 41-44 themselves, as well as their surrounding circuits such as the rectifier circuit 36, controller 37, and their electronic components.

[0069] For example, if the cooking appliance 10 is restarted while either the IGBTs 41, 43 on the upper arm or the IGBTs 42, 44 on the lower arm (or IGBT 41 on the upper arm or IGBT 42 on the lower arm) are short-circuited, the controller 37 will control the induction heating circuits 40, 40' on and off, causing the upper and lower arms to turn on simultaneously the moment the other, undamaged IGBT turns on. As a result, IGBTs 41, 42 and IGBTs 43, 44 (or IGBT 41 and IGBT 42) will be short-circuited between power lines 35H and 35L. This will cause a current exceeding the absolute maximum rated current of the rectifier circuit 36 ​​to flow from the rectifier circuit 36 ​​between their collectors and emitters, resulting in short-circuit failure of both IGBTs 41, 42 and IGBTs 43, 44, including the other, which was not previously faulty. The rectifier circuit 36 ​​may also fail if a current exceeding its absolute maximum rated current flows through it. Furthermore, the controller 37 may also experience failures in its drive circuits, such as those for the IGBT41, due to short-circuit failures in the IGBT41, etc.

[0070] Therefore, in this embodiment, as described above, resistors 46 and the like and an I / V conversion circuit 50 are provided in the induction heating circuits 40 and 40', and the controller 37 performs the fault detection process described below, thereby making it possible to prevent secondary failures of the induction heating circuits 40 and 40', as well as their peripheral circuits such as the rectifier circuit 36 ​​and the controller 37, caused by short-circuit failures of IGBTs 41-44 and IGBTs 41 and 42. This fault detection process is performed when the controller 37, which has received control information from the control device 60, executes a fault detection program stored in the EEPROM.

[0071] When the power switch of the heating cooker 10 is turned on via software control, the control device 60 first starts up and performs a series of preparatory processes to initialize the operation panel 13, steam generator 20, etc., to a predetermined state. After that, it executes the aforementioned cooking program, etc., and according to the cooking program etc. of the cooking mode selected by the user, it operates the heater 16 and blower fan 17 so that hot air circulates in the cooking chamber 14, and also operates the steam generator 20 so that steam is supplied to the cooking chamber 14. The controller 37, for example, before operating the steam generator 20 (before operating the steam generator 20 at the start of cooking or during cooking), receives control information from the control device 60, executes a fault detection program, and starts fault detection processing. In other words, the fault detection processing is performed in the stage before transitioning from the heating stopped state to the heating started state by the steam generator 20.

[0072] Here, we will explain using the full-bridge type induction heating circuit 40 as an example, but in the case of the half-bridge type induction heating circuit 40', the explanation can be almost the same by omitting the IGBT 43 (Q3) and IGBT 44 (Q4) parts. For example, the "Q1-Q4 off processing" in step 12 becomes the "Q1, Q2 off processing". Also, the fault detection processing may be performed during the preparation processing after power-on.

[0073] As shown in Figure 9, when the fault detection process is started, the initialization process in step 11 first sets the work area and flags reserved in RAM to predetermined initial values. In this embodiment, for example, the fault flags (Q1 fault flag to Q4 fault flag) associated with each of the IGBTs 41 to 44 constituting the induction heating circuit 40, which have fault information, are set to "00" to represent "no fault". Note that "01" is set for "short circuit fault". Furthermore, "10" is set for "open circuit fault", which will be described later, and "11" is set for "abnormality outside of fault".

[0074] In step 12, the Q1-Q4 off process controls the IGBTs 41-44 to be completely turned off. In the next step, step 13, the charge release process waits for a predetermined time (for example, several tens of milliseconds) to allow any remaining charge in the off IGBTs 41-44 to move to a reference potential such as ground. Then, in step 14, the current information acquisition process acquires the current information of the current Ir4 flowing through resistor 49 (R4) from the I / V conversion circuit 50.

[0075] In this embodiment, as described above, the I / V conversion circuit 50 is a transimpedance amplifier using an operational amplifier, etc., so the current information is converted to a voltage value (analog value) and input to the controller 37. For this reason, the controller 37 uses the voltage value converted to a digital value by its built-in ADC for information processing, but here the current information of the current Ir4 flowing through resistor 49 (R4) will be explained as information representing the current value.

[0076] The current information obtained in step 14 is the current value of Ir4 when IGBTs 41-44 are controlled to the completely off state (current value when Q1-Q4 are off). Therefore, if this current value of Ir4 matches the current value of Ir4a (=(Vh-Vcnt) / (R1+R4)) flowing through resistor 49 (R4) when all IGBTs 41-44 are normal (no faults) as described in [A] above, it can be determined that all IGBTs 41-44 are currently normal (no faults). (Note that in the case of a half-bridge type induction heating circuit 40', [A] above becomes [S] above.)

[0077] However, there is a certain range of error in the potential of the high-potential side VH, the constant voltage source Vcnt, and the resistance values ​​of resistors 46 (R1) and 49 (R4), and there is also a certain variation in the on-resistance (resistance between the collector and emitter when the IGBTs 41 to 44 are on). Therefore, it is necessary to have a predetermined margin (safety margin) in the current reference value (judgment reference current value) for determining a short-circuit fault. In this embodiment, the upper limit (upper limit current value) and lower limit (lower limit current value) of the judgment reference current value are stored as predetermined values ​​in the EEPROM of the controller 37 or the like.

[0078] In the determination process of step 15, it is determined whether the Q1-Q4 off-state current value obtained in step 14 (the current value when all IGBTs 41-44 are off) exceeds the upper limit of the judgment criterion current value (upper limit current value) for determining a short-circuit failure in IGBTs 41 and 43 (upper arms). When IGBTs 41 and 43 (upper arms) are short-circuited, current flows through the paths of resistors 47 (R2) and 48 (R3), increasing the current Ir4 compared to the current Ir4a when all IGBTs 41-44 are off. Therefore, if it is determined that the Q1-Q4 off-state current value exceeds this upper limit current value (S15; YES), there is a high probability that the upper arm IGBTs 41 and 43, which should be in the off state, are in the on state, i.e., short-circuited (Note that in the case of a half-bridge type induction heating circuit 40', the above [I] and [U] become the above [Shi]). In this case, the process proceeds to step 16, the upper arm short-circuit fault device detection process (S30 in Figure 10).

[0079] In contrast, if it is determined that the current value when Q1 to Q4 are off does not exceed the upper limit current value (i.e., it is determined to be below the upper limit current value) (S15; NO), then there is a high probability that no current is flowing to the low-potential side VL through the paths of resistors 47 (R2) and 48 (R3), and that IGBTs 41 and 43 are in the off state, meaning that there is no short-circuit fault. Therefore, in this case, step 16 is skipped and the process proceeds to the next step 17, which is the determination process. The upper arm short-circuit fault device determination process S30 will be described later with reference to Figure 10.

[0080] In the determination process of step 17, it is determined whether the current value when Q1 to Q4 are off is below the lower limit of the judgment criterion current value (lower limit current value) for determining a short-circuit failure in IGBTs 42 and 44 (lower arms). When IGBTs 42 and 44 (lower arms) are short-circuited, the current Ir4 decreases as current flows through the low-potential side VL via the paths of resistors 47 (R2) and 48 (R3), compared to the current Ir4a when all IGBTs 41 to 44 are off. Therefore, if it is determined that the current value when Q1 to Q4 are off is less than this lower limit current value (S17; YES), there is a high probability that IGBTs 42 and 44 of the lower arms, which should be in the off state, are in the on state, i.e., they are short-circuited, as explained in [O] and [Ka] above (Note that in the case of a half-bridge type induction heating circuit 40', [O] and [Ka] above become [Su] above). In this case, the process proceeds to step 18, the lower arm short-circuit fault device detection process (S50 in Figure 11).

[0081] In contrast, if it is determined that the current value when Q1 to Q4 are off is not less than the lower limit current value (i.e., it is determined to be greater than or equal to the lower limit current value) (S17; NO), then there is a high probability that no current is flowing to the low-potential side VL through the paths of resistors 47 (R2) and 48 (R3), and that IGBTs 42 and 44 are in the off state, meaning that there is no short-circuit fault. Therefore, in this case, step 18 is skipped and the process proceeds to the next step 19, which is the determination process. The lower arm short-circuit fault device determination process S50 will be described later with reference to Figure 11.

[0082] Step 19 determines whether any of IGBTs 41 to 44 are faulty. As described later, the upper arm short-circuit fault device detection process S30 and the lower arm short-circuit fault device detection process S50 determine and identify if any of IGBTs 41 to 44 are short-circuit faulty, and set the "short-circuit fault present" information "01" to the fault flag (Q1 fault flag to Q4 fault flag). Therefore, in the determination process of step 19, the status of the Q1 fault flag to Q4 fault flag is checked, and if a fault flag set to "01" exists and it is determined that any of IGBTs 41 to 44 (Q1 to Q4) are faulty (S19; YES), the process proceeds to step 20.

[0083] In contrast, if no fault flag is set to "01" and it is determined that there are no short-circuit faults in any of the IGBTs 41-44 (Q1-Q4) (S19; NO), then the fault detection process is terminated normally (end 1) because none of the IGBTs 41-44 in the induction heating circuit 40 have short-circuit faults. Subsequently, the induction heating circuit 40 transitions to steady-state operation (switching control of IGBTs 41-44) according to the control of the control device 60.

[0084] In the error display processing in step 20, information on devices (IGBTs 41-44) that are highly likely to have short-circuit failures is obtained from the Q1 failure flag to the Q4 failure flag. Therefore, this failure information is sent to the control device 60, and the start of the induction heating circuit 40 (start of switching control) is prohibited so that the induction heating circuit 40 does not start (switching control of IGBTs 41-44). Then, this fault detection processing is terminated abnormally (end 2). The control device 60 may also terminate the preparation processing at this point and interrupt the start of the cooking appliance 10. This makes it possible to prevent secondary failures of the induction heating circuit 40 and its surrounding rectifier circuit 36 ​​and controller 37 caused by the short-circuit failure of IGBTs 41-44.

[0085] Upon receiving information about a faulty device, the control device 60 may, for example, display on the liquid crystal touch panel 13a of the operation panel 13 that IGBT 41 or the like is short-circuited as fault information for the induction heating circuit 40, record information about IGBT 41 or the like which is highly likely to be short-circuited in the operation information log, or prohibit operations such as selecting a cooking mode using the liquid crystal touch panel 13a. As a result, even if the user could restart the cooking appliance 10 before the short-circuited IGBTs 41-44 are repaired, the induction heating circuit 40 will not be started. Therefore, it is possible to prevent secondary failures of the induction heating circuit 40 and its surrounding rectifier circuit 36 ​​and controller 37 caused by the short-circuit failure of IGBTs 41-44.

[0086] Next, the upper arm short-circuit fault device detection process S30 and the lower arm short-circuit fault device detection process S50 will be explained with reference to Figures 10 and 11. These processes S30 and S50 assume that one of the IGBTs 41 to 44 is short-circuited. These processes are also performed by executing the fault detection program.

[0087] As shown in Figure 10, in the upper arm short-circuit fault device detection process S30, in order to first detect a short-circuit fault in one of the upper arm IGBTs 41, the Q1 ON process in step 31 controls IGBT 41 to be turned ON. IGBTs 42-44 have already been controlled to be OFF by step 12 of the fault detection process (Figure 9) described above. Therefore, no switching control is performed on IGBTs 42-44 here, but control to turn them OFF again may be performed.

[0088] In the next step 32, the waiting process waits for a predetermined time (for example, several tens of milliseconds) for the ON state of IGBT41 to stabilize. Then, in the current information acquisition process of step 33, the current information of the current Ir4 flowing through resistor 49 (R4) is acquired from the I / V conversion circuit 50.

[0089] The current information obtained in step 33 is the current value of Ir4 (current value when Q1 is ON) when IGBT41 is controlled to the ON state and IGBTs42-44 are controlled to the OFF state. Therefore, if this current value of Ir4 matches the current value of Ir4b (=(Vh-Vcnt) / (R1∥R2+R4)) flowing through resistor 49 (R4) when all IGBTs41-44 are normal (no faults) as described in [a] above, it can be determined that IGBT41 is currently normal (no faults). (Note that in the case of a half-bridge type induction heating circuit 40', [a] above becomes [shi] above.)

[0090] However, as mentioned above, there is a certain range of error in the potential of the high-potential side VH, etc., and the resistance of resistor 46 (R1), etc., and there is also a certain variation in the on-resistance of the IGBT41. Therefore, the current reference value used to determine a short-circuit fault of the IGBT41 also needs to have a predetermined margin. However, if the current reference value has a predetermined margin, judgment processing is required for its upper and lower limits, which complicates information processing.

[0091] Therefore, the current values ​​when Q1 to Q4 are off, which have already been acquired by the current information acquisition process (S14) of the fault detection process (Figure 9) described above, and which indicate a high probability that either IGBT 41 or 43 (upper arm) is short-circuited, are compared with the current when Q1 is on, which was acquired in step 33. If the difference between the two current values ​​is smaller than a predetermined first reference current value, then the difference in current values ​​(< first reference current value) is not caused by IGBT 41 transitioning from the off state to the on state, but rather indicates a high probability that IGBT 41 was already on, i.e., short-circuited, before being controlled in step 31. Therefore, in this case, it is determined that IGBT 41 is short-circuited. The predetermined first reference current value is the current Ir4 flowing through resistor 49 (R4), which is a current value that can increase when IGBT 41 is turned on.

[0092] Therefore, in this embodiment, in the determination process of step 34, it is determined whether the value obtained by subtracting the Q1-Q4 off current values ​​obtained in the current information acquisition process (S14) from the Q1 on current value obtained in step 33 (Q1 on current value - Q1-Q4 off current value) is less than a predetermined first reference current value. If it is determined that this difference in current values ​​is less than the first reference current value (S34; YES), there is a high probability that IGBT41 (Q1) is short-circuited. Therefore, the process proceeds to step 35, where the Q1 failure flag is set to "01" by the Q1 failure flag setting process, and then the process proceeds to step 36.

[0093] On the other hand, if it is determined that the difference in current values ​​(current value when Q1 is ON - current values ​​when Q1 to Q4 are OFF) is not less than the first reference current value (it is determined to be greater than or equal to the first reference current value) (S34; NO), the process proceeds to the next step 36 to perform the Q1 to Q4 OFF process. However, if the determination process in step 34 determines that the difference in current values ​​(current value when Q1 is ON - current values ​​when Q1 to Q4 are OFF) is less than the first reference current value (S34; YES), the main arm short-circuit fault device detection process may be forcibly terminated without proceeding to step 35, and the startup of the cooking appliance 10 may be interrupted. This makes it possible to prevent secondary failures of the induction heating circuit 40, and the surrounding rectifier circuit 36 ​​and controller 37, etc., caused by short-circuit failures of IGBTs 41 to 44.

[0094] In step 36, the Q1-Q4 off process controls all IGBTs 41-44 to be turned off. In the next step, step 37, the charge discharge process waits for a predetermined time (e.g., several tens of milliseconds) to allow any remaining charge on the off IGBTs 41, etc., to move to a reference potential such as earth. Once step 37 is complete, the system is ready to detect the next short-circuit fault in IGBT 43.

[0095] In step 38, to detect a short-circuit fault in the other IGBT43 of the upper arm, the Q3 ON process is used to turn on the IGBT43. In the next step 39, the waiting process waits for a predetermined time (for example, several tens of milliseconds) to allow the ON state of the IGBT43 to stabilize. Then, in the current information acquisition process of step 40, the current information of the current Ir4 flowing through resistor 49 (R4) is acquired from the I / V conversion circuit 50.

[0096] The current information obtained in step 40 is the current value of Ir4 (current value when Q3 is ON) when IGBT43 is controlled to the ON state and IGBTs41,42, and44 are controlled to the OFF state. Therefore, if this current value of Ir4 matches the current value of Ir4b' (=(Vh-Vcnt) / (R1∥R3+R4)) flowing through resistor 49 (R4) when IGBTs41~44 are all normal (no faults) as described in [c] above, it can be determined that IGBT43 is currently normal (no faults).

[0097] However, as mentioned above, there is a certain range of error in the potential of the high-potential side VH, etc., and the resistance of resistor 46 (R1), etc., and there is also a certain variation in the on-resistance of the IGBT43. Therefore, the current reference value used to determine a short-circuit fault of the IGBT43 also needs to have a predetermined margin. However, if the current reference value has a predetermined margin, judgment processing is required for its upper and lower limits, which complicates information processing.

[0098] Therefore, the current values ​​of Q1 to Q4 when they are off, which have already been acquired by the current information acquisition process (S14) of the fault detection process (Figure 9) described above, are compared with the current values ​​of Q3 when it is on, which indicate a high probability that either IGBT 41 or 43 (upper arm) is short-circuited. If the difference between the two current values ​​is smaller than a predetermined second reference current value, then the difference in current values ​​(< second reference current value) is not caused by IGBT 43 transitioning from the off state to the on state, but rather indicates a high probability that IGBT 43 was already on, i.e., short-circuited, before being controlled in step 40. Therefore, in this case, it is determined that IGBT 43 is short-circuited. The predetermined second reference current value is the current Ir4 flowing through resistor 49 (R4), which is the current value that can increase when IGBT 43 is turned on.

[0099] Therefore, in this embodiment, in the determination process of step 41, it is determined whether the value obtained by subtracting the Q1~Q4 off current values ​​obtained in the current information acquisition process (S14) from the Q3 on current value obtained in step 40 (Q3 on current value - Q1~Q4 off current value) is less than a predetermined second reference current value. If it is determined that this difference in current values ​​is less than the second reference current value (S41; YES), there is a high probability that IGBT43 (Q3) has a short-circuit failure. Therefore, the process moves to step 42 and the Q3 failure flag is set to "01" by the Q3 failure flag setting process. With this, all failure detection for IGBT41,43 (Q1,3) constituting the upper arm is completed, and the upper arm short-circuit failure device detection process S30 is terminated (return). Then, the process returns to the failure detection process shown in Figure 9 and moves to the determination process of step 17.

[0100] Furthermore, if it is determined that the difference in current values ​​(current value when Q3 is ON - current values ​​when Q1~Q4 are OFF) is not less than the second reference current value (it is determined to be greater than or equal to the second reference current value) (S41; NO), the fault detection for the upper arm IGBTs 41 and 43 (Q1 and 3) is complete, so the upper arm short-circuit fault device detection process S30 is terminated (return), and the process returns to the fault detection process shown in Figure 9 and proceeds to the determination process in step 17. Note that if the determination process in step 41 determines that the difference in current values ​​(current value when Q3 is ON - current values ​​when Q1~Q4 are OFF) is less than the second reference current value (S41; YES), the upper arm short-circuit fault device detection process may be forcibly terminated without proceeding to step 42, and the startup of the cooking appliance 10 may be interrupted. This makes it possible to prevent secondary failures of the induction heating circuit 40 and its surrounding rectifier circuit 36 ​​and controller 37 caused by short-circuit failures of IGBTs 41~44.

[0101] As shown in Figure 11, in the lower arm short-circuit fault device detection process S50, in order to first detect a short-circuit fault in one of the lower arm IGBTs 42, the Q2 ON process in step 51 controls the IGBT 42 to be turned ON. IGBTs 41, 43, and 44 have already been controlled to be OFF by step 12 of the fault detection process (Figure 9) described above. Therefore, no switching control is performed on IGBTs 41, 43, and 44 here, but control to turn them OFF again may be performed.

[0102] In the next step 52, the waiting process waits for a predetermined time (for example, several tens of milliseconds) for the ON state of the IGBT 42 to stabilize. Then, in the current information acquisition process of step 53, the current information of the current Ir4 flowing through resistor 49 (R4) is acquired from the I / V conversion circuit 50.

[0103] The current information obtained in step 53 is the current value of Ir4 (current value when Q2 is ON) when IGBT42 is controlled to the ON state and IGBTs41,43, and44 are controlled to the OFF state. Therefore, if this current value of Ir4 matches the current value of Ir4d (=(Vh-Vcnt) / (R1+R4)-Ir2d) flowing through resistor 49 (R4) when all IGBTs41~44 mentioned above are normal (no faults), it can be determined that IGBT42 is currently normal (no faults). (Note that in the case of a half-bridge type induction heating circuit 40', the aforementioned [O] becomes the aforementioned [S].)

[0104] However, as mentioned above, there is a certain range of error in the potential of the high-potential side VH, etc., and the resistance of resistor 46 (R1), etc., and there is also a certain variation in the on-resistance of the IGBT42. Therefore, the current reference value used to determine a short-circuit fault of the IGBT42 also needs to have a predetermined margin. However, if the current reference value has a predetermined margin, judgment processing is required for its upper and lower limits, which complicates information processing.

[0105] Therefore, the current values ​​of Q1 to Q4 when they are off, which have already been acquired by the current information acquisition process (S14) of the fault detection process (Figure 9) described above, are compared with the current values ​​of Q2 when it is on, which indicate a high probability that either IGBT42 or 44 (lower arm) is short-circuited. If the difference between the two current values ​​is smaller than a predetermined third reference current value, then the difference in current values ​​(< third reference current value) is not caused by IGBT42 transitioning from the off state to the on state, but rather indicates a high probability that IGBT42 was already on, i.e., short-circuited, before being controlled in step 51. Therefore, in this case, it is determined that IGBT42 is short-circuited. The predetermined third reference current value is the current Ir4 flowing through resistor 49 (R4), which is a current value that can decrease when IGBT42 is on.

[0106] In this embodiment, in the determination process of step 54, it is determined whether the value obtained by subtracting the Q2 ON current value obtained in step 52 from the Q1~Q4 OFF current value obtained in the current information acquisition process (S14) (Q1~Q4 OFF current value - Q2 ON current value) is less than a predetermined third reference current value. If it is determined that this difference in current values ​​is less than the third reference current value (S54; YES), there is a high probability that IGBT42 (Q2) is short-circuited. Therefore, the process proceeds to step 55, where the Q2 fault flag is set to "01" by the Q2 fault flag setting process, and then the process proceeds to step 56.

[0107] On the other hand, if it is determined that the difference in current values ​​(current values ​​when Q1~Q4 are off - current value when Q2 is on) is not less than the third reference current value (it is determined to be greater than or equal to the third reference current value) (S54; NO), the process proceeds to the next step 56 to perform the Q1~Q4 off process. However, if the determination process in step 54 determines that the difference in current values ​​(current values ​​when Q1~Q4 are off - current value when Q2 is on) is less than the third reference current value (S54; YES), the lower arm short-circuit fault device detection process may be forcibly terminated without proceeding to step 55, and the startup of the cooking appliance 10 may be interrupted. This makes it possible to prevent secondary failures of the induction heating circuit 40, and the surrounding rectifier circuit 36 ​​and controller 37, etc., caused by short-circuit failures of IGBTs 41~44.

[0108] In step 56, the Q1-Q4 off process controls all IGBTs 41-44 to be turned off. In the next step, step 57, the charge discharge process waits for a predetermined time (e.g., several tens of milliseconds) to allow any remaining charge on the off IGBTs 41, etc., to move to a reference potential such as earth. Once step 57 is complete, the system is ready to detect the next short-circuit fault in IGBT 44.

[0109] In step 58, to detect a short-circuit fault in the other IGBT44 of the lower arm, control is performed to turn on IGBT44 by Q4 ON ​​processing. In the next step 59, the waiting process waits for a predetermined time (for example, several tens of milliseconds) to allow the ON state of IGBT44 to stabilize. Then, in the current information acquisition process of step 60, the current information of the current Ir4 flowing through resistor 49 (R4) is acquired from the I / V conversion circuit 50.

[0110] The current information obtained in step 60 is the current value of Ir4 (current value when Q4 is ON) when IGBT44 is controlled to the ON state and IGBTs41-43 are controlled to the OFF state. Therefore, if this current value of Ir4 matches the current value of Ir4d' (=(Vh-Vcnt) / (R1+R4)-Ir3d) flowing through resistor 49 (R4) when all IGBTs41-44 as described in [K] above are normal (no faults), it can be determined that IGBT44 is currently normal (no faults).

[0111] However, as mentioned above, there is a certain range of error in the potential of the high-potential side VH, etc., and the resistance of resistor 46 (R1), etc., and there is also a certain variation in the on-resistance of the IGBT44. Therefore, the current reference value used to determine a short-circuit fault of the IGBT44 also needs to have a predetermined margin. However, if the current reference value has a predetermined margin, it becomes necessary to perform judgment processing for its upper and lower limits, which complicates information processing.

[0112] Therefore, the current values ​​of Q1 to Q4 when they are off, which have already been acquired by the current information acquisition process (S14) of the fault detection process (Figure 9) described above, are compared with the current values ​​of Q4 when they are on, which indicate a high probability that either IGBT 42 or 44 (lower arm) is short-circuited. If the difference between the two current values ​​is smaller than a predetermined fourth reference current value, then the difference in current values ​​(< fourth reference current value) is not caused by IGBT 44 transitioning from the off state to the on state, but rather indicates a high probability that IGBT 44 was already on, i.e., short-circuited, before being controlled in step 60. Therefore, in this case, it is determined that IGBT 44 is short-circuited. The predetermined fourth reference current value is the current Ir4 flowing through resistor 49 (R4), which is a current value that can decrease when IGBT 44 is on.

[0113] In this embodiment, in the determination process of step 61, it is determined whether the value obtained by subtracting the Q4 ON ​​current value obtained in step 60 from the Q1~Q4 OFF current value obtained in the current information acquisition process (S14) (Q1~Q4 OFF current value - Q4 ON ​​current value) is less than a predetermined fourth reference current value. If it is determined that this difference in current values ​​is less than the fourth reference current value (S61; YES), there is a high probability that IGBT44 (Q4) has a short-circuit failure. Therefore, the process proceeds to step 62 and the Q4 failure flag is set to "01" by the Q4 failure flag setting process. With this, all failure detection for IGBT42,44 (Q2,4) constituting the lower arm is completed, and the lower arm short-circuit failure device detection process S50 is terminated (return). Then, the process returns to the failure detection process shown in Figure 9 and proceeds to the determination process of step 19.

[0114] Furthermore, if it is determined that the difference in current values ​​(current values ​​when Q1~Q4 are off - current value when Q4 is on) is not less than the fourth reference current value (it is determined to be greater than or equal to the fourth reference current value) (S61; NO), the fault detection for the lower arm IGBTs 42 and 44 (Q2 and 4) is complete, so the lower arm short-circuit fault device detection process S50 is terminated (return), and the process returns to the fault detection process shown in Figure 9 and proceeds to the determination process in step 19. Note that if it is determined in the determination process in step 61 that the difference in current values ​​(current values ​​when Q1~Q4 are off - current value when Q4 is on) is less than the fourth reference current value (S61; YES), the lower arm short-circuit fault device detection process may be forcibly terminated without proceeding to step 62, and the startup of the cooking appliance 10 may be interrupted. This makes it possible to prevent secondary failures of the induction heating circuit 40 and its surrounding rectifier circuit 36 ​​and controller 37 caused by short-circuit failures of IGBTs 41~44.

[0115] Furthermore, in the determination process of step 19 of the fault detection process shown in Figure 9, if it is determined that there is no fault in any of the IGBTs 41-44 (Q1-Q4) (S19; NO), the algorithm may be configured so that instead of immediately terminating the fault detection process normally (end 1), it proceeds to an open fault detection process that detects open faults other than short-circuit faults, and then terminates normally (end 1). An example of an open fault detection process is shown below. Note that this process assumes that none of the IGBTs 41-44 are short-circuit faults. This process is implemented, for example, as an optional function of the fault detection process described above, and can be executed by the controller 37 by setting the optional function to active (enabled).

[0116] <1> Open-circuit fault detection for IGBT41 and 43 In detecting open-circuit faults in IGBTs 41 and 43, first, to determine if an open-circuit fault exists in one of the upper arm's IGBTs, IGBT 41 is turned ON and IGBTs 42-44 are turned OFF. Then, the system waits for a predetermined time (e.g., several tens of milliseconds) for the ON / OFF states of IGBTs 41-44 to stabilize. After that, the current information Ir4 flowing through resistor 49 (R4) is obtained from the I / V conversion circuit 50. Then, it is determined whether the value obtained by subtracting the Q1-Q4 OFF current values ​​obtained in the current information acquisition process (S14) of the fault detection process (Figure 9) from the obtained Q1 ON current value (Q1 ON current value - Q1-Q4 OFF current value) is less than a predetermined 1' reference current value. The predetermined first' reference current value is the current Ir4 flowing through resistor 49 (R4) that is 3 to 5 times greater than the aforementioned first reference current value, and is the current value that flows when IGBT41 is not in the off state (i.e., when it is in the on state). If the difference in these current values ​​(current value when Q1 is on - current values ​​when Q1 to Q4 are off) is greater than or equal to the first' reference current value, then IGBT41 is in the on state, and it is determined that there is no open-circuit fault. On the other hand, if the difference in these current values ​​is less than the first' reference current value, then IGBT41 will not turn on even if controlled to the on state, and it is determined that there is a high probability of an open-circuit fault.

[0117] Next, in order to determine if the other IGBT43 on the upper arm has an open circuit fault, control is performed to turn on IGBT41 and IGBT43, and then the system waits for a predetermined time (for example, several tens of milliseconds) for the ON state of IGBT41 and IGBT43 to stabilize. After that, the current information Ir4 flowing through resistor 49 (R4) is obtained from the I / V conversion circuit 50. Then, it is determined whether the value obtained by subtracting the previously obtained Q1 ON current value from the obtained Q1+Q3 ON current value (Q1+Q3 ON current value - Q1 ON current value) is less than a predetermined second reference current value. The predetermined second reference current value is the same as that explained in the determination process of step 41 of the upper arm short circuit fault device determination process shown in Figure 10. If this difference in current values ​​(Q1+Q3 ON current value - Q1 ON current value) is greater than or equal to the second reference current value, then it is determined that the IGBT43 is in the ON state and there is no open circuit fault. Conversely, if the difference in current values ​​is less than the second reference current value, the IGBT43 will not turn on even if controlled to the ON state, and therefore it is determined that there is a high probability of an open circuit fault.

[0118] These determination results, for example, are passed to the fault detection process in Figure 9 by setting the aforementioned Q1 fault flag and Q3 fault flag associated with IGBT41 and IGBT43 to "10," which indicates "open fault present." The fault detection process then sends this fault information to the control device 60, which, upon receiving it, displays on the liquid crystal touch panel 13a of the operation panel 13 that IGBT41 and 43 have an open fault as fault information for the induction heating circuit 40, or records information about IGBT41 and 43 that are highly likely to have an open fault in the operation information log.

[0119] <2> Open-circuit fault detection for IGBT42 and 44 In detecting open-circuit faults in IGBT42 and 44, information processing is performed using an algorithm almost identical to that used for detecting open-circuit faults in IGBT41 and 43 as described above. Therefore, here we will explain the differences and omit the explanation of the similarities. In detecting open-circuit faults in IGBT41 and 43, IGBT41 is replaced with IGBT42, IGBT43 is replaced with IGBT44, Q1 is replaced with Q2, and Q3 is replaced with Q4. Also, the upper arm is replaced with the lower arm. A predetermined first' reference current value is replaced with a predetermined third' reference current value, and the predetermined third' reference current value is the current Ir4 flowing through resistor 49 (R4), which is 5 to 10 times greater than the aforementioned third reference current value, and is the current value that flows when IGBT42 is not in the off state (it is in the on state). Furthermore, the second reference current value is replaced by the fourth' reference current value, which is almost the same as the one described in the determination process of step 61 of the lower arm short-circuit fault device determination process shown in Figure 11. In IGBTs 42 and 44, it is determined whether the value obtained by subtracting the Q2 ON current value obtained from the I / V conversion circuit 50 from the Q1~Q4 OFF current values ​​obtained in the current information acquisition process (S14) of the fault detection process (Figure 9) is less than a predetermined third' reference current value. The difference in current values ​​is also (Q1~Q4 OFF current value - Q2 ON current value). This also allows for the explanation of open-circuit fault detection in IGBTs 42 and 44.

[0120] <3> Non-fault anomaly detection for IGBT41-44 In the non-fault abnormality detection for IGBT41-44, an abnormal state is detected in the electrical function of IGBT41-44 that is neither a short-circuit nor an open-circuit fault, i.e., an abnormal state. First, in order to determine the abnormal state of IGBT41 and 44 that constitute the right bridge, control is performed to turn IGBT41 and 44 to the ON state and IGBT42 and 43 to the OFF state, and then a predetermined time (for example, several tens of milliseconds) is waited for the ON / OFF state of IGBT41-44 to stabilize. After that, current information of the current Ir4 flowing through resistor 49 (R4) is obtained from the I / V conversion circuit 50. Then, it is determined whether the value obtained by subtracting the Q1-Q4 OFF current value obtained in the current information acquisition process (S14) of the fault detection process (Figure 9) from this obtained right bridge ON current value (right bridge ON current value - Q1-Q4 OFF current value) is less than a predetermined right bridge reference current value. The predetermined right bridge reference current value is the current Ir4 flowing through resistor 49 (R4), which is the current value when IGBT 41 and IGBT 44 are sufficiently ON. If the difference between these current values ​​(right bridge ON current value - Q1~Q4 OFF current value) is greater than or equal to the right bridge reference current value, the right bridge (IGBT 41, 44) is sufficiently ON, and therefore no abnormal condition is determined. On the other hand, if the difference between these current values ​​is less than the right bridge reference current value, even if the right bridge (IGBT 41, 44) is controlled to be ON, it is not OFF, but it is not sufficiently ON either, and therefore there is a high probability that an abnormal condition exists.

[0121] Next, the abnormal state of IGBTs 42 and 43, which constitute the left bridge, is determined. Before that, control is performed to turn off all IGBTs 41 to 44, and then the system waits for a predetermined time (e.g., several tens of milliseconds) to allow any remaining charge in IGBTs 41 to 44 to move to a reference potential such as ground. After this, information processing is performed using the same algorithm as described for the right bridge. Therefore, here we will explain the differences and omit the explanation of the common points. IGBT 41 is replaced with IGBT 42, and IGBT 44 is replaced with IGBT 43, and the right bridge is replaced with the left bridge. This also allows us to explain the detection of abnormalities other than faults in IGBTs 41 to 44.

[0122] These judgment results, for example, are passed to the fault detection process in Figure 9 by setting "11" to indicate "non-fault abnormality" for the aforementioned Q1 fault flags ~ Q4 fault flags associated with the right bridge (IGBT 41, 44) and left bridge (IGBT 42, 43). The fault detection process then sends this fault information to the control device 60, which, upon receiving it, displays, for example, on the liquid crystal touch panel 13a of the operation panel 13 that the IGBTs 41, 44 of the right bridge and IGBTs 42, 43 of the left bridge are non-fault abnormalities as fault information for the induction heating circuit 40, or records information such as IGBT 41 which has a high probability of being a non-fault abnormality in the operation information log.

[0123] The cooking appliance 10 configured as described above has an induction heating circuit 40 (full-bridge inverter circuit) in which IGBT 41 (Q1) constitutes one upper arm, IGBT 42 (Q2) constitutes one lower arm, IGBT 43 (Q3) constitutes the other upper arm, and IGBT 44 (Q4) constitutes the other lower arm, and is equipped with a fault detection device. This fault detection device includes a resistor 46(R1) whose one end is connected to the high-potential side VH of IGBT41(Q1) and IGBT43(Q3), a resistor 47(R2) whose one end is connected to the low-potential side of IGBT41(Q1) and the high-potential side of IGBT42(Q2), and whose other end is connected to the other end of resistor 46(R1), and a resistor 48(R3) whose one end is connected to the low-potential side of IGBT43(Q3) and the high-potential side of IGBT44(Q4), and whose other end is connected to the other end of resistor 46(R1), and resistors 46(R1), 47( The system includes a resistor 49 (R4) with one end connected to the other end of resistors R2) and 48 (R3), an I / V conversion circuit 50 connected to the other end of resistor 49 (R4) which operates as a constant voltage source Vcnt and converts the current Ir4 input from resistor 49 (R4) into a voltage with the voltage of the constant voltage source Vcnt as its maximum value and outputs it, and a controller 37 connected to the I / V conversion circuit 50 which detects faults in each of the IGBTs 41~44 (Q1~4) based on the voltage input from the I / V conversion circuit 50.

[0124] In the fault detection device for the induction heating circuit 40 configured as described above, resistors 46 to 49 (R1 to 4) have the relationship described in [A] to [Ke] above, according to the on / off state of each IGBT 41 to 44 (Q1 to 4). However, Vh is the potential difference between the high-potential side VH and the low-potential side VL, Ir2d, Ir2e, Ir2f are the currents flowing through resistor 47 (R2), and Ir3d, Ir3e, Ir3f are the currents flowing through resistor 48 (R3).

[0125] That is, [A] When IGBTs 41-44 (Q1-4) are all in the off state, the current Ir4a flowing through resistor 49 (R4) is expressed as (Vh-Vcnt) / (R1+R4). [B] When IGBT 41 (Q1) is on and IGBTs 42-44 (Q2-4) are off, the current Ir4b flowing through resistor 49 (R4) is expressed as (Vh-Vcnt) / (R1∥R2+R4). [C] When IGBT 43 (Q3) is on and IGBTs 41, 42, 44 (Q1, 2, 4) are off, the current Ir4b' flowing through resistor 49 (R4) is expressed as (Vh-Vcnt) / (R1∥R3+R4). [E] When IGBTs 41 and 43 (Q1 and 3) are ON and IGBTs 42 and 44 (Q2 and 4) are OFF, the current Ir4c flowing through resistor 49 (R4) is expressed as (Vh - Vcnt) / (R1 || R2 || R3 + R4). [O] When IGBT 42 (Q2) is ON and IGBTs 41, 43, and 44 (Q1, 3, and 4) are OFF, the current Ir4d flowing through resistor 49 (R4) is expressed as (Vh - Vcnt) / (R1 + R4) - Ir2d. [Ka] When IGBT 44 (Q4) is ON and IGBTs 41 to 43 (Q1 to 3) are OFF, the current Ir4d' flowing through resistor 49 (R4) is expressed as (Vh - Vcnt) / (R1 + R4) - Ir3d. [Ki] When IGBTs 42 and 44 (Q2 and 4) are ON and IGBTs 41 and 43 (Q1 and 3) are OFF, the current Ir4e flowing through resistor 49 (R4) is expressed as (Vh - Vcnt) / (R1 + R4) - Ir2e - Ir3e. [Ku] When IGBTs 41 and 44 (Q1 and 44) ​​are ON and IGBTs 42 and 43 (Q2 and 3) are OFF, the current Ir4f flowing through resistor 49 (R4) is expressed as (Vh - Vcnt) / (R1 || R2 + R4) - Ir3f. [Ke] When IGBTs 42 and 43 (Q2 and 3) are ON and IGBTs 41 and 44 (Q1 and 4) are OFF, the current Ir4f' flowing through resistor 49 (R4) is expressed as (Vh - Vcnt) / (R1 || R2 + R4) - Ir2f.

[0126] Therefore, even though controller 37 is not controlling IGBTs 41-44 to be ON, if the current Ir4 flowing through resistor 49 (R4) is not the current Ir4a when all are OFF (=(Vh-Vcnt) / (R1+R4)) but a current with a different value from Ir4a (Ir4b, Ir4b', Ir4c, Ir4d, Ir4d', Ir4e, Ir4f, Ir4f'), then there is a high probability that resistors 46-49 (R1-4) have the connection relationship [I]-[Ke] and that one of IGBTs 41-44 (Q1-4) is short-circuited.

[0127] In other words, compared to the current Ir4a (=(Vh-Vcnt) / (R1+R4)) flowing through resistor 49(R4) when none of IGBT41~44(Q1~4) are short-circuited, if IGBT41(Q1) or IGBT43(Q3) is short-circuited, the current Ir4b or Ir4b' (=(Vh-Vcnt) / (R1∥R2+R4) or (Vh-Vcnt) / (R1∥R3+R4)) flowing through resistor 49(R4) increases, and if both IGBT41(Q1) and IGBT43(Q3) are short-circuited, the current Ir4c (=(Vh-Vcnt) / (R1∥R2∥R3+R4)) flowing through resistor 49(R4) increases further.

[0128] Furthermore, compared to the current Ir4a flowing through resistor 49(R4) when none of IGBT41~44(Q1~4) are short-circuited, the current Ir4d or Ir4d' (=(Vh-Vcnt) / (R1+R4)-Ir2d or (Vh-Vcnt) / (R1+R4)-Ir3d) flowing through resistor 49(R4) decreases when IGBT42(Q2) or IGBT44(Q4) are short-circuited, and the current Ir4e (=(Vh-Vcnt) / (R1+R4)-Ir2e-Ir3e) flowing through resistor 49(R4) decreases even further when both IGBT42(Q2) and IGBT44(Q4) are short-circuited.

[0129] Therefore, the I / V conversion circuit 50 converts the current flowing through resistor 49 (R4) into a voltage and outputs it to the controller 37, which enables the controller 37 to detect each of the IGBTs 41-44 (Q1-4) based on the voltage input from the I / V conversion circuit 50.

[0130] Furthermore, the cooking appliance 10 configured as described above may also have an induction heating circuit 40' (half-bridge inverter circuit) in which IGBT 41 (Q1) constitutes the upper arm and IGBT 42 (Q2) constitutes the lower arm, and in that case as well, it is equipped with a fault detection device. This fault detection device comprises a resistor 46(R1) with one end connected to the high-potential side VH of IGBT41(Q1), a resistor 47(R2) with one end connected to the low-potential side of IGBT41(Q1) and the high-potential side of IGBT42(Q2), and the other end connected to the other end of resistor 46(R1), a resistor 49(R4) with one end connected to the other ends of resistors 46(R1) and 47(R2), an I / V conversion circuit 50 connected to the other end of resistor 49(R4) that operates as a constant voltage source Vcnt and converts the current Ir4 input from resistor 49(R4) into a voltage with the voltage of the constant voltage source Vcnt as its maximum value and outputs it, and a controller 37 connected to the I / V conversion circuit 50 that detects faults in IGBT41 and 42 based on the voltage input from the I / V conversion circuit 50.

[0131] In the fault detection device for the induction heating circuit 40' configured as described above, resistors 46, 47, and 49 (R1, 2, 4) have the aforementioned [S]~[S] relationship according to the on / off state of IGBTs 41 and 42 (Q1, 2). Here, Vh is the potential difference between the high-potential side VH and the low-potential side VL, and Ir2d is the current flowing through resistor 47 (R2).

[0132] That is, [Sa] When IGBT41,42(Q1,2) are all in the off state, the current Ir4a flowing through resistor 49(R4) is expressed as (Vh-Vcnt) / (R1+R4). [Shi] When IGBT41(Q1) is on and IGBT42(Q2) is off, the current Ir4b flowing through resistor 49(R4) is expressed as (Vh-Vcnt) / (R1∥R2+R4). [Su] When IGBT42(Q2) is on and IGBT41(Q1) is off, the current Ir4d flowing through resistor 49(R4) is expressed as (Vh-Vcnt) / (R1+R4)-Ir2d.

[0133] As a result, when neither IGBT41 nor IGBT42(Q1,2) is short-circuited, the current Ir4a (=(Vh-Vcnt) / (R1+R4)) flowing through resistor 49(R4) increases compared to when IGBT41(Q1) is short-circuited, resulting in an increase in the current Ir4b (=(Vh-Vcnt) / (R1∥R2+R4)) flowing through resistor 49(R4), while when IGBT42(Q2) is short-circuited, the current Ir4d (=(Vh-Vcnt) / (R1+R4)-Ir2d) flowing through resistor 49(R4) decreases. Therefore, when the I / V conversion circuit 50 converts the current flowing through resistor 49(R4) into a voltage and outputs it to the controller 37, the controller 37 can detect the failures of IGBT41 and IGBT42(Q1,2) based on the voltage input from the I / V conversion circuit 50.

[0134] In these fault detection devices, the voltage output by the I / V conversion circuit 50 is a voltage with the voltage of the constant voltage source Vcnt as its maximum value. Therefore, by setting the voltage of the constant voltage source Vcnt to a low voltage of, for example, 5V, analog information of the current flowing through the resistor 49 (R4) can be output in a voltage range of 0 to 5V. For example, the I / V conversion circuit 50 can be configured as a transimpedance amplifier using an operational amplifier, and the controller 37 can be a microcontroller that controls the on / off state of IGBTs 41 to 44 (Q1 to 4). This makes it possible to connect, for example, the induction heating circuits 40, 40' of a high-voltage circuit where the high-potential side VH is set to 280V and the low-potential side VL is set to 0V, with the controller 37 which is configured as a microcontroller that drives at a low voltage of 5V, using an I / V conversion circuit 50 configured with inexpensive general-purpose components such as resistors and operational amplifiers. Therefore, since there is no need to use special components such as photocouplers and isolation transformers in various places, it was possible to detect short-circuit faults in IGBT41~44 (Q1~4) and IGBT41,42 (Q1,2) without significantly increasing product costs.

[0135] Furthermore, in the cooking appliance 10 configured as described above, the induction heating circuits 40 and 40' are housed in the machine room 15. When the controller 37 detects that any of the IGBTs 41 to 44 (or IGBTs 41 and 42) in the induction heating circuits 40 and 40' have short-circuited, it prohibits the activation of the induction heating circuits 40 and 40', for example, as described in the fault detection process explained with reference to Figures 9 to 11. As a result, if the controller 37 detects a fault in any of the fully bridged IGBTs 41-44 or a fault in any of the half-bridged IGBTs 41, 42 based on the voltage input from the I / V conversion circuit 50 (S19; YES, S34; YES, S41; YES, S54; YES, S61; YES), it will, for example, prohibit the subsequent startup of the induction heating circuits 40, 40' even if the cooking appliance 10 is restarted (S20, or S34 or S41 or S54 or S61; YES and forced termination). Therefore, even if, for example, the user can restart the cooking appliance 10 before the fault is fixed, if a short-circuit fault in IGBT 41, etc. is detected, the startup of the induction heating circuits 40, 40' will be prohibited, making it extremely unlikely that the IGBT 41, etc. itself or the electronic components of its surrounding circuit, the rectifier circuit 36, will suffer significant damage. Alternatively, the restart of the cooking appliance 10 itself may also be prohibited. Therefore, it was possible to prevent secondary failures of the induction heating circuits 40, 40' and surrounding rectifier circuits 36 and controllers 37 caused by short-circuit failures of IGBTs 41-44 and 41, 42.

[0136] In the fault detection device described above, the controller 37 is shown as the detection unit that performs fault detection processing by executing a fault detection program. However, for example, the current information of the resistor 49 (R4) obtained from the I / V conversion circuit 50 may be sent to the control device 60, and the control device 60 that receives this information may perform judgment processing (e.g., S15, S17, S19, S34, S41, S54, S61) or prohibition processing (e.g., S20, or S34 or S41 or S54 or S61; YES and forced termination) in the fault detection process. As a result, the controller 37 performs the control processing for the induction heating circuits 40, 40', and the control device 60 performs other judgment processing, etc., thereby reducing the information processing burden on the controller 37.

[0137] Furthermore, as an example of a detection unit constituting the fault detection device, a window comparator may be provided with voltage values ​​corresponding to the aforementioned upper and lower current limits, and configured to accept input to it a voltage value (analog signal) corresponding to the current information of resistor 49 (R4) obtained from the I / V conversion circuit 50. This makes it possible to implement the fault detection processing performed by the controller 37 and control device 60 in hardware (electronic circuitry).

[0138] In the fault detection device described above, resistors 46, 47, 48, and 49 are provided as an example of the first, second, third, and fourth resistors that constitute the fault detection device. The relative sizes of these resistors are set to be 46 > 49 > 47 = 48, and the resistance values ​​are set so that the current flowing through resistor 49 is on the order of microamperes. However, the resistance values ​​of resistors 47 and 48 may be set so that one is larger and the other is smaller.

[0139] In the fault detection device described above, the example shown was that the conversion section of the fault detection device is configured with a transimpedance amplifier using an operational amplifier or the like in the I / V conversion circuit 50. However, it may also be configured with an inverting amplifier circuit using an operational amplifier or the like, for example.

[0140] In the above-described heating appliance 10, the induction heating circuit 40 was composed of IGBTs 41-44 or the induction heating circuit 40' was composed of IGBTs 41 and 42 as multiple semiconductor switching elements connected in a full-bridge or half-bridge configuration. However, for example, power MOSFETs may be used instead of IGBTs. In this case, the collectors of IGBTs 41-44 are replaced by the drains of the power MOSFETs, the emitters of IGBTs 41-44 are replaced by the sources of the power MOSFETs, and the gates of IGBTs 41-44 are replaced by the gates of the power MOSFETs. Alternatively, GTO thyristors or the like may be used.

[0141] Furthermore, in the above-described heating appliance 10, the IGBTs 41 to 44, which are multiple semiconductor switching elements connected in a full-bridge or half-bridge configuration, are configured to be mounted on a heat sink (not shown) located at a position physically separate from the printed circuit board 61 on which the control device 60 is mounted. However, the invention is not limited to this configuration, and for example, the IGBTs 41 to 44 may be assembled on the printed circuit board 61 on which the control device 60 is mounted.

[0142] Furthermore, in the above-described heating cooker 10, the induction heating circuits 40, 40' of the steam generator 20 utilizing electromagnetic induction heating were configured as an inverter circuit in which multiple semiconductor switching elements are connected in a full-bridge or half-bridge configuration, but the invention is not limited to this. For example, induction heating circuits (inverter circuits) such as those of IH cooktops and IH plates may be configured as heating devices utilizing electromagnetic induction heating. In addition, an inverter circuit may be configured to control the rotation of a multiphase AC motor that drives a compressor in a refrigerator or freezer, or other rotating mechanism. In addition, an inverter circuit may be configured to control the rotation of a multiphase AC motor used as a driving force source for transport vehicles or conveyor vehicles. [Explanation of symbols]

[0143] 10... Cooking appliance (kitchen equipment), 11... Housing, 12... Door, 13... Control panel, 14... Cooking cabinet, 15... Machine room (designated space), 20... Steam generator, 21... Steam generating container, 30... Heating unit, 31... Heating element, 33... Heating rod, 34... Induction heating coil, 35H... Power line, 35L... Power line, 36... Rectifier circuit, 37... Controller (detection unit), 40, 40'... Induction heating circuit (inverter circuit), 41... IGBT (first switching element, one upper arm), 42... IGBT (second switching element, one lower arm), 43... IGBT (third switching element, the other upper arm) 44...IGBT (fourth switching element, other lower arm), 46...Resistor (first resistor), 47...Resistor (second resistor), 48...Resistor (third resistor), 49...Resistor (fourth resistor), 50...I / V conversion circuit (conversion section), Q1...IGBT (first switching element), Q2...IGBT (second switching element), Q3...IGBT (third switching element), Q4...IGBT (fourth switching element), R1...Resistor (first resistor), R2...Resistor (second resistor), R3...Resistor (third resistor), R4...Resistor (fourth resistor), Vcnt...Constant voltage source, VH...High potential side, VL...Low potential side (reference potential).

Claims

1. A fault detection device for an inverter circuit having a plurality of semiconductor switching elements (hereinafter referred to as "switching elements" in this claim) that are connected in a full bridge configuration, wherein the first switching element constitutes one upper arm, the second switching element constitutes one lower arm, the third switching element constitutes the other upper arm, and the fourth switching element constitutes the other lower arm, A first resistor, one end of which is connected to the high-potential side of the first switching element and the third switching element, A second resistor, one end of which is connected to the low-potential side of the first switching element and the high-potential side of the second switching element, and the other end of which is connected to the other end of the first resistor, A third resistor, one end of which is connected to the low-potential side of the third switching element and the high-potential side of the fourth switching element, and the other end of which is connected to the other end of the first resistor, A fourth resistor, one end of which is connected to the other end of each of the first resistor, the second resistor, and the third resistor, A conversion unit connected to the other end of the fourth resistor and operating as a constant voltage source, which converts the current input from the fourth resistor into a voltage with the voltage of the constant voltage source as its maximum value and outputs it, A detection unit connected to the conversion unit detects failures in each of the first to fourth switching elements based on the voltage input from the conversion unit, An inverter circuit fault detection device characterized by comprising the following:

2. A fault detection device for an inverter circuit having a plurality of semiconductor switching elements (hereinafter referred to as "switching elements" in this claim) connected in a half-bridge configuration, wherein the first switching element constitutes an upper arm and the second switching element constitutes a lower arm, A first resistor, one end of which is connected to the high-potential side of the first switching element, A second resistor, one end of which is connected to the low-potential side of the first switching element and the high-potential side of the second switching element, and the other end of which is connected to the other end of the first resistor, A fourth resistor, one end of which is connected to the other ends of the first and second resistors, A conversion unit connected to the other end of the fourth resistor and operating as a constant voltage source, which converts the current input from the fourth resistor into a voltage with the voltage of the constant voltage source as its maximum value and outputs it, A detection unit connected to the conversion unit detects failures in the first and second switching elements based on the voltage input from the conversion unit, An inverter circuit fault detection device characterized by comprising the following:

3. A kitchen appliance comprising a fault detection device for an inverter circuit as described in claim 1 or 2, The inverter circuit has a plurality of semiconductor switching elements and is housed within a predetermined space. The kitchen appliance is characterized in that the detection unit prohibits the startup of the inverter circuit when it detects that any of the plurality of semiconductor switching elements has short-circuited.

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