Power conversion device and control method for power conversion device

Abstract

To provide a power conversion device and a control method for the same that can prevent an output current from becoming large while preventing a circuit configuration from becoming more complex.SOLUTION: A power conversion device 100 includes a chopper section 40 that converts input DC power and outputs it and inverter sections 50, 60 that convert the DC power output by the chopper section 40 into AC power and output it to induction heating coils 10, 20. Furthermore, the power conversion device 100 includes a control section 70 that controls the duty ratio D of a chopper drive signal GCHO that is input to a switching element 41 of the chopper section 40. The control section 70 is configured to reduce the duty ratio D of the chopper drive signal GCHO by a predetermined first percentage when a current abnormal condition is detected.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a power conversion device including a chopper unit and a method for controlling the power conversion device. [Background technology]

[0002] BACKGROUND ART Conventionally, a power conversion device having a power conversion circuit including a chopper section is known (see, for example, Patent Document 1).

[0003] The above-mentioned Patent Document 1 discloses a step-down chopper type power conversion circuit equipped with a switching element. In this step-down chopper type power conversion circuit, the input voltage is reduced by the switching operation of the switching element. In this power conversion circuit, the output voltage applied to the load is controlled to a constant value by controlling the duty ratio, which is the proportion of the switching element that is in an on state.

[0004] Here, when constant voltage control is being performed to maintain the output voltage constant, if the load suddenly decreases due to a wire breakage or switching of operation, the constant voltage control may not be able to suppress the increase in output voltage, resulting in an overcurrent. Therefore, the power conversion circuit described in Patent Document 1 above is provided with a discharge switching element for suppressing the occurrence of an overcurrent, separate from the switching element that performs the power conversion operation. This discharge switching element turns on its switching operation to suppress the increase in output voltage when the load suddenly decreases. As a result, the power conversion circuit described in Patent Document 1 forms a discharge circuit that releases power separately from the load, thereby suppressing the increase in output voltage. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 4-54864 Summary of the Invention [Problem to be solved by the invention]

[0006] However, in the power conversion circuit described in Patent Document 1, a discharging switching element is provided separately from the switching element that performs power conversion operation in order to prevent the output voltage from increasing and causing an overcurrent, which complicates the circuit configuration by providing the discharging switching element. Therefore, it is desired to suppress an increase in output current while suppressing the circuit configuration from becoming more complicated.

[0007] The present invention has been made to solve the above-mentioned problems, and one object of the present invention is to provide a power conversion device and a control method for a power conversion device that can suppress an increase in output current while suppressing an increase in the complexity of the circuit configuration. [Means for solving the problem]

[0008] In order to achieve the above object, a power conversion device according to a first aspect of the present invention includes a chopper unit including a switching element that converts input DC power and outputs the converted power; an inverter unit that converts the DC power output by the chopper unit into AC power and outputs the AC power to an induction heating coil; and a control unit that controls a duty ratio that is a ratio of an on state of a chopper drive signal input to the switching element of the chopper unit, wherein the control unit: a constant power control unit that performs constant power control based on an input power command value and a power feedback value of the output power output from the chopper unit, and a constant current control unit that performs constant current control based on the output of the constant power control by the constant power control unit and a current feedback value of the output current output from the chopper unit, When an abnormal current state is detected, the abnormal current state includes at least one of a case where the current of the chopper unit is larger than a predetermined chopper current judgment value and a case where the current of the inverter unit is larger than a predetermined inverter current judgment value. Set based on the output of the constant current control The duty ratio of the chopper drive signal is configured to be reduced by a predetermined first ratio.

[0009] In the power conversion device according to the first aspect of the present invention, as described above, the control unit is configured to reduce the duty ratio of the chopper drive signal by a predetermined first percentage when an abnormal current state is detected, including at least one of a state where the current of the chopper unit is greater than a predetermined chopper current determination value and a state where the current of the inverter unit is greater than a predetermined inverter current determination value. Thus, when an abnormal current state is detected while AC power is being output to the induction heating coil by controlling the duty ratio of the chopper unit, the control unit can further reduce the output from the chopper unit by the first percentage from the magnitude set by normal control. Therefore, when an abnormal current state is detected, the control unit can further reduce the output from the chopper unit from the magnitude set by normal control without increasing the number of components. As a result, even when an overcurrent occurs under normal control due to a sudden load decrease, the output current can be prevented from increasing while preventing the circuit configuration from becoming complicated.

[0010] In the aforementioned power conversion device according to the first aspect, preferably, the control unit , fixed Duty ratio setting that sets the duty ratio of the chopper drive signal based on the output of the constant current control by the current control section FurtherThe control circuit includes a constant power control unit that controls the duty ratio of the chopper drive signal, which is set by the duty ratio setting unit based on the output of the constant current control, by a first percentage when an abnormal current state is detected. Here, if only constant power control is performed to maintain a constant output level for the induction heating coil, control of the current output from the chopper unit is not performed, and an increase in the current cannot be prevented. In contrast, in the present invention, the control unit is configured to include both a constant power control unit that performs constant power control and a constant current control unit that performs constant current control, thereby enabling constant current control in addition to constant power control, thereby controlling the output current from the chopper unit to be constant. Therefore, an increase in the output current from the chopper unit can be prevented. Furthermore, when an abnormal current state is detected while the current output from the chopper unit is being controlled to be constant by performing constant current control in addition to constant power control, the duty ratio can be further reduced by a first percentage. As a result, if an abnormal current state is detected while the output current is being controlled to a constant value by constant current control, the output current from the chopper section can be further reduced in addition to the constant current control, so that the output current can be effectively prevented from increasing even when the load suddenly decreases.

[0011] In this case, the constant current control unit is preferably configured to output a first output value by constant current control and to reduce the output first output value by a first percentage when an abnormal current state is detected. With this configuration, when an abnormal current state is detected, the duty ratio of the chopper drive signal set by the duty ratio setting unit can be reduced by the first percentage by reducing the first output value from the constant current control unit input to the duty ratio setting unit by the first percentage. Therefore, even if the command value and feedback value input to the constant current control unit are the same as those at the time of the abnormal current state, the duty ratio set by the duty ratio setting unit can be reduced by the first percentage from the value at the time of the abnormal current state by reducing the first output value output from the constant current control unit by the first percentage. As a result, an increase in the output current can be suppressed while suppressing a complex circuit configuration.

[0012] In the power conversion device configured with a constant current control unit to reduce the first output value by a first percentage when an abnormal current state is detected, the constant current control unit is preferably configured to output the first output value by performing constant current control, which is feedback control including an integral operation that calculates a time integral of the deviation between the output of the constant power control by the constant power control unit and a current feedback value, and is configured to reduce the output first output value by the first percentage and reduce the value of the time integral calculated by the integral operation in the constant current control when an abnormal current state is detected. Here, even when the first output value output from the constant current control unit is reduced by the first percentage, if the value of the time integral in the integral operation of the feedback control of the constant current control unit remains the same as when the abnormal current state was detected, the output first output value will return to the value at the time the abnormal current state was detected through feedback control by the constant current control unit. In contrast, in the present invention, when an abnormal current state is detected, the first output value output from the constant current control unit is reduced by the first percentage and the value of the time integral calculated by the integral operation in the constant current control is reduced, thereby preventing the first output value, once reduced by the first percentage, from returning to the value at the time the abnormal current state was detected. Therefore, it is possible to prevent the output from the chopper unit from returning to the output at the time when the current abnormality state was detected, and therefore it is possible to prevent the detection of the current abnormality state from being repeated, and as a result, it is possible to stably prevent the output current output from the chopper unit from increasing.

[0013] In the power conversion device configured with a constant current control unit that reduces the first output value by a first percentage when an abnormal current state is detected, the constant power control unit is preferably configured to output the second output value by constant power control and to reduce the second output value by a predetermined second percentage when an abnormal current state is detected. With this configuration, when an abnormal current state is detected, in addition to reducing the first output value output from the constant current control unit by the first percentage, the second output value input from the constant power control unit to the constant current control unit is also reduced by the second percentage, thereby preventing the output first output value from returning to the value at the time when the abnormal current state was detected through feedback control by the constant current control unit. As a result, by reducing the input to the constant current control unit in addition to the output from the constant current control unit, it is possible to more stably prevent the output current from the chopper unit from increasing when an abnormal current state is detected.

[0014] In this case, the constant power control unit is preferably configured to output the second output value by performing constant power control, which is feedback control including an integral operation that calculates a time integral of the deviation between the input power command value and the power feedback value, and is configured to reduce the output second output value by the second percentage and reduce the value of the time integral calculated by the integral operation in the constant power control when an abnormal current state is detected. With this configuration, as with the feedback control of the constant current control unit, by reducing the value of the time integral in the integral operation of the feedback control by the constant power control unit, it is possible to prevent the second output value reduced by the second percentage from returning to the value at the time when the abnormal current state was detected. Therefore, it is possible to further prevent repeated detection of the abnormal current state, and it is possible to more stably prevent the output current output from the chopper unit from increasing.

[0015] In the power conversion device configured with the constant current control unit to reduce the first output value by a first percentage when an abnormal current state is detected, the duty ratio setting unit is preferably configured to reduce the duty ratio of the chopper drive signal by the first percentage before the first output value output by the constant current control unit is reduced by the first percentage when an abnormal current state is detected. With this configuration, the duty ratio of the chopper drive signal set by the duty ratio setting unit can be reduced by the first percentage before one calculation cycle of the feedback control calculation of the constant current control unit has elapsed. Therefore, when an abnormal current state is detected, the output current output from the chopper unit can be reduced more quickly, thereby more effectively preventing the output current from the chopper unit from increasing.

[0016] In the power conversion device according to the first aspect, preferably, a plurality of inverter units are provided to output AC power to the plurality of induction heating coils, respectively, and the control unit is configured to reduce the duty ratio of the chopper drive signal by a first percentage when an abnormal current state is detected, including at least one of a state where the current of the chopper unit is greater than a predetermined chopper current determination value and a state where the current in at least one of the plurality of inverter units is greater than an inverter current determination value. With this configuration, even when AC power is output to each of the plurality of induction heating coils by the plurality of inverter units, when an abnormal current state is detected, the control unit can suppress an increase in the output current from the chopper unit through control processing while suppressing an increase in the circuit configuration. Furthermore, since an increase in the output current can be suppressed by controlling the switching operation of the switching element of the chopper unit without controlling the operation of each of the plurality of inverter units, an increase in the processing load for control processing to suppress an increase in the output current can be suppressed, unlike when the operation of each of the plurality of inverter units is controlled.

[0017] In the power conversion device according to the first aspect, the inverter unit preferably includes a first inverter unit and a second inverter unit that output AC power to each of a pair of induction heating coils provided for heating and welding the welding objects, the first inverter unit and the second inverter unit are configured to stop operation of either one of them based on an input operation to the operation unit, and the control unit is configured to reduce the duty ratio of the chopper drive signal by a first percentage when an abnormal current state is detected, the abnormal current state including at least one of a case where the current of the chopper unit is greater than a predetermined chopper current determination value, a case where the current of the first inverter unit is greater than a predetermined first inverter current determination value, and a case where the current of the second inverter unit is greater than a predetermined second inverter current determination value. Here, when the operation of one of the first and second inverter units is stopped from a state in which both the first and second inverter units are operating, the output current from the chopper unit may increase due to a sudden change (decrease) in the load. In contrast, in the present invention, the control unit is configured to reduce the duty ratio of the chopper drive signal by a first percentage when an abnormal current state is detected, the abnormal current state including at least one of a case where the current of the chopper unit is greater than a predetermined chopper current determination value, a case where the current of the first inverter unit is greater than a predetermined first inverter current determination value, and a case where the current of the second inverter unit is greater than a predetermined second inverter current determination value. With this configuration, even if the output current increases when the operation of either the first inverter unit or the second inverter unit is stopped, by reducing the duty ratio of the chopper drive signal by the first percentage, it is possible to effectively prevent the output current from increasing while preventing the circuit configuration from becoming complicated.

[0018] In the power conversion device according to the first aspect, the control unit is preferably configured to reduce the duty ratio of the chopper drive signal by the first percentage when an abnormal current state is detected, without changing the inverter drive signal input to the inverter unit. With this configuration, it is possible to prevent the processing load of the control process from increasing compared to when both the chopper drive signal input to the chopper unit and the inverter drive signal input to the inverter unit are controlled to prevent the output current from increasing.

[0019] In order to achieve the above object, a second aspect of the present invention provides a control method for a power conversion device including a chopper unit including a switching element that converts input DC power and outputs the converted power, and an inverter unit that converts the DC power output by the chopper unit into AC power and outputs the AC power to an induction heating coil, the control method comprising: controlling a duty ratio, which is a ratio of an on state of a chopper drive signal input to the switching element of the chopper unit; a step of performing constant power control based on an input power command value and a power feedback value of the output power output from the chopper unit; and a step of performing constant current control based on the output of the constant power control and a current feedback value of the output current output from the chopper unit. detecting an abnormal current state including at least one of a case where the current of the chopper unit is larger than a predetermined chopper current determination value and a case where the current of the inverter unit is larger than a predetermined inverter current determination value; and when the abnormal current state is detected, Set based on the output of the constant current control The duty ratio of the chopper drive signal is predetermined and reducing the first ratio.

[0020] In a control method for a power conversion device according to a second aspect of the present invention, as described above, an abnormal current state is detected, including at least one of a state in which the current of the chopper unit is greater than a predetermined chopper current determination value and a state in which the current of the inverter unit is greater than a predetermined inverter current determination value. When an abnormal current state is detected, the duty ratio of the chopper drive signal is reduced by a predetermined first percentage. Thus, when an abnormal current state is detected while AC power is being output to the induction heating coil by controlling the duty ratio of the chopper unit, the output from the chopper unit can be further reduced by the first percentage from the magnitude set by normal control. Therefore, when an abnormal current state is detected, the output from the chopper unit can be further reduced from the magnitude set by normal control through control processing by the control unit without increasing the number of components. As a result, a control method for a power conversion device can be provided that can suppress an increase in output current while suppressing a complex circuit configuration, even when an overcurrent occurs under normal control due to a sudden load decrease.

[0021] In the control method for a power conversion device according to the second aspect, preferably, fixed Steps for setting the duty ratio of the chopper drive signal based on the output of the current control PThe step of reducing the duty ratio of the chopper drive signal by a first percentage includes, when an abnormal current state is detected, reducing the duty ratio of the chopper drive signal, which is set based on the output of constant current control, by the first percentage. Here, if only constant power control is performed to maintain a constant output to the induction heating coil, control of the current output from the chopper unit is not performed, and an increase in the current cannot be prevented. In contrast, the present invention includes a step of performing constant power control and a step of performing constant current control, which allows constant current control in addition to constant power control, thereby suppressing the output current from the chopper unit to be constant. Therefore, an increase in the output current from the chopper unit can be prevented. Furthermore, when an abnormal current state is detected while the current output from the chopper unit is being controlled to be constant by performing constant current control in addition to constant power control, the duty ratio can be further reduced by the first percentage. As a result, if an abnormal current state is detected while the output current is being controlled to a constant value by constant current control, the output current from the chopper section can be further reduced in addition to the constant current control, so that the output current can be effectively prevented from increasing even when the load suddenly decreases. [Effects of the Invention]

[0022] According to the present invention, as described above, it is possible to prevent the output current from increasing while preventing the circuit configuration from becoming complicated. [Brief explanation of the drawings]

[0023] [Figure 1] 1 is a block diagram showing the overall configuration of a welding device provided with a power conversion device according to an embodiment of the present invention. [Figure 2] 1 is a circuit diagram showing a configuration of a power conversion device according to an embodiment of the present invention. [Figure 3]FIG. 2 is a diagram showing functional blocks of a control unit of a power conversion device according to an embodiment of the present invention. [Figure 4] FIG. 2 is a flowchart illustrating a method for controlling a power conversion device by constant power control and constant current control according to an embodiment of the present invention. [Figure 5] FIG. 4 is a flowchart illustrating a method for controlling a power conversion device when an abnormal current state is detected according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0024] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, specific embodiments of the present invention will be described with reference to the accompanying drawings.

[0025] The configuration of a power conversion device 100 according to one embodiment of the present invention will be described with reference to FIGS.

[0026] As shown in FIG. 1, a power conversion device 100 of this embodiment is configured to convert AC power input from an AC power source 101 and supply the converted power to induction heating coils 10 and 20. In this embodiment, the pair of induction heating coils 10 and 20 is provided for heat-welding plastic or other materials to be welded. That is, the power conversion device 100 of this embodiment is used in a welding device 102 that heat-welds plastic or other materials. Specifically, the welding device 102 includes a pair of metal members 102a and 102b that sandwich the plastic or other materials (the materials to be welded) in order to heat-weld the materials to be welded. The induction heating coil 10 and the induction heating coil 20 are configured in the welding device 102 to heat the pair of metal members 102a and 102b by receiving AC power from the power conversion device 100. The induction heating coil 10 and the induction heating coil 20 have, for example, the same inductance as each other.

[0027] The welding device 102 also includes an operation unit 102c. The operation unit 102c accepts an input operation to stop the flow of electricity to one of the pair of induction heating coils 10 and 20 of the power conversion device 100. For example, the operation unit 102c is configured to accept an input operation to stop the flow of electricity to the induction heating coil 20 when both induction heating coils 10 and 20 are energized.

[0028] (Configuration of power conversion device) As shown in Fig. 1, the power conversion device 100 includes a converter unit 30, a chopper unit 40, an inverter unit 50, an inverter unit 60, and a control unit 70. The inverter unit 50 is an example of a "first inverter unit" in the claims. The inverter unit 60 is an example of a "second inverter unit" in the claims.

[0029] As shown in Fig. 2, converter unit 30 converts AC voltage input from AC power supply 101 into DC voltage and outputs it. Specifically, converter unit 30 includes rectifier unit 31 and smoothing capacitor 32. In rectifier unit 31, a rectifier circuit is formed by six diodes that are full-bridge connected so as to convert the input three-phase AC power into DC power. Then, smoothing capacitor 32 smoothes the DC power from rectifier unit 31.

[0030] The chopper unit 40 converts and outputs the DC power input from the converter unit 30. Specifically, the chopper unit 40 includes a switching element 41, a diode 42, an inductor 43, and a resistor 44.

[0031] The switching element 41 and the inductor 43 are connected in series in this order on the positive electrode side of the DC power output from the converter unit 30. The diode 42 has an anode connected to the resistor 44 and a cathode connected between the switching element 41 and the inductor 43 on the positive electrode side of the DC power output from the converter unit 30. The resistor 44 is connected between the negative electrode side of the DC power output from the converter unit 30 and the diode 42. With the above configuration, a step-down chopper circuit is formed that steps down and outputs the DC power from the converter unit 30 by the switching operation of the switching element 41. The switching operation of the switching element 41 of the chopper unit 40 is controlled by the control unit 70. The switching element 41 is, for example, a MOSFET (metal-oxide-semiconductor field-effect transistor). The resistor 44 is a shunt resistor provided to measure the current output from the chopper unit 40.

[0032] In this embodiment, inverter unit 50 and inverter unit 60 convert the DC power output by chopper unit 40 into AC power. Then, inverter unit 50 and inverter unit 60 output the AC power to each of the pair of induction heating coils 10 and 20. Inverter unit 50 and inverter unit 60 are connected in parallel on the output side of chopper unit 40. That is, the output from chopper unit 40 is configured to be output in parallel to inverter unit 50 and inverter unit 60.

[0033] The inverter unit 50 includes a smoothing capacitor 51, a switching element 52, a switching element 53, a matching capacitor 54, a matching capacitor 55, and a resistor 56. The smoothing capacitor 51 smoothes the DC power output from the chopper unit 40. The switching elements 52 and 53 form a half-bridge inverter circuit. The switching elements 52 and 53 are, for example, MOSFETs. In the inverter unit 50, the switching operations of the switching elements 52 and 53 are controlled by control processing of the control unit 70. The matching capacitors 54 and 55 form a resonant circuit together with the induction heating coil 10, which is the output destination. The resistor 56 is a shunt resistor provided to measure the current output from the inverter unit 50 to the induction heating coil 10.

[0034] Inverter unit 60 has the same configuration as inverter unit 50. That is, inverter unit 60 includes smoothing capacitor 61, switching element 62, switching element 63, matching capacitor 64, matching capacitor 65, and resistor 66. Smoothing capacitor 61, switching element 62, switching element 63, matching capacitor 64, and matching capacitor 65 of inverter unit 60 have the same configurations as smoothing capacitor 51, switching element 52, switching element 53, matching capacitor 54, and matching capacitor 55 of inverter unit 50, respectively. Resistor 66, like resistor 56, is a shunt resistor provided to measure the current output from inverter unit 60 to induction heating coil 20.

[0035] The control unit 70 controls each unit of the power conversion device 100. The control unit 70 is, for example, a microcomputer (microcontroller) having a CPU (Central Processing Unit) and a storage device such as a flash memory. Specifically, the control unit 70 is configured to control the power conversion operations of the chopper unit 40, the inverter unit 50, and the inverter unit 60.

[0036] Furthermore, the control unit 70 calculates a chopper current I , which is a measurement value of the current flowing through the resistor 44, based on the voltage across the resistor 44 of the chopper unit 40 and the resistance value of the resistor 44. C The control unit 70 also acquires the intermediate voltage V measured by a voltage measurement unit (not shown) based on the potential difference between the positive and negative sides of the output of the chopper unit 40. dc Furthermore, the control unit 70 obtains a measurement value of the current flowing through the resistor 56 based on the voltage across the resistor 56 of the inverter unit 50 and the resistance value of the resistor 56, and converts the measured value of the current flowing through the resistor 56 into the output current I of the inverter unit 50 that is output to the induction heating coil 10. L1 Furthermore, the control unit 70 obtains the measured value of the current flowing through the resistor 66 based on the voltage across the resistor 66 of the inverter unit 60 and the resistance value of the resistor 66 as the output current I of the inverter unit 60 output to the induction heating coil 20. L2 Obtain as.

[0037] (Controlled by the control unit) The control unit 70 controls the operation of the inverter units 50 and 60 based on an input operation to the operation unit 102c. In this embodiment, in order to stop the supply of current to one of the induction heating coils 10 and 20, the inverter units 50 and 60 are configured to stop the operation of one of them based on an input operation to the operation unit 102c. For example, based on an input operation received by the operation unit 102c, the control unit 70 is configured to switch between operating both the inverter units 50 and 60 and operating only the inverter unit 50.

[0038] Here, the power conversion device 100 includes a gate drive unit 81 (hereinafter referred to as GDU 81) and a gate drive unit 82 (hereinafter referred to as GDU 82). When operating the inverter unit 50, the control unit 70 outputs a signal indicating a predetermined frequency and duty ratio (pulse width) to the GDU 81, thereby driving the inverter drive signal G to each of the switching elements 52 and 53 of the inverter unit 50. INVSimilarly, when the control unit 70 operates the inverter unit 60, the control unit 70 outputs a signal indicating a predetermined frequency and duty ratio (pulse width) to the GDU 81, thereby transmitting the inverter drive signal G to each of the switching elements 62 and 63 of the inverter unit 60. INV When the control unit 70 stops the operation of the inverter unit 50, the control unit 70 outputs the inverter drive signal G INV Similarly, when the control unit 70 stops the operation of the inverter unit 60, the control unit 70 turns off the inverter drive signal G input to the switching elements 62 and 63. INV By stopping the operation, the switching elements 62 and 63 are turned off.

[0039] Here, the control unit 70 outputs the same inverter drive signal G INV The inverter drive signal G input to the inverter unit 50 and the inverter unit 60 is INV is a pulse signal with a constant frequency and a constant duty ratio (pulse width). For example, the inverter drive signal G INV The frequency of the inverter drive signal G is higher than the resonant frequency of the resonant circuit formed by the induction heating coil 10 and the matching capacitors 54 and 55. INV The frequency of the inverter drive signal G is also higher than the resonant frequency of the resonant circuit formed by the induction heating coil 20 and the matching capacitors 64 and 65. INV The duty ratio is 50%.

[0040] <Details of Chopper Control> In this embodiment, the control unit 70 controls the chopper drive signal G CHOThe control unit 70 is configured to control the outputs of the induction heating coils 10 and 20 by controlling a gate signal (gate signal) between the switching elements 41 of the chopper unit 40 and the control unit 70 by outputting a predetermined signal to the GDU 82. CHO In this embodiment, the control unit 70 outputs a chopper drive signal G (gate signal) to be input to the switching element 41 of the chopper unit 40. CHO The chopper driving signal G is configured to control the duty ratio D, which is the ratio of the ON state of the chopper driving signal G. CHO The frequency of is a constant magnitude.

[0041] 3, the control unit 70 includes, as functional components, a chopper-coil current calculation unit 71, a power calculation unit 72, a constant power control unit 73, a constant current control unit 74, a duty ratio setting unit 75, and a current determination unit 76. Specifically, the control unit 70 as hardware is configured to include, as software (program) functional blocks, the chopper-coil current calculation unit 71, the power calculation unit 72, the constant power control unit 73, the constant current control unit 74, the duty ratio setting unit 75, and the current determination unit 76.

[0042] The chopper coil current calculation unit 71 (control unit 70) calculates the output current value I FB Specifically, the chopper coil current calculation unit 71 calculates the chopper current I, which is a measurement value of the current flowing through the resistor 44 of the chopper unit 40. C Then, the chopper coil current calculation unit 71 calculates the chopper current I C and a duty ratio D output from a duty ratio setting unit 75, which will be described later, the output current value I FB The output current value I FB is an example of a "current feedback value" in the claims.

[0043] The power calculation unit 72 (control unit 70) calculates the output current value I FB and the measured intermediate voltage V dc Based on this, the output power value P from the chopper unit 40 is calculated. FB The power calculation unit 72 calculates the measured intermediate voltage V dc and the output current value I FB By integrating these, the output power value P from the chopper unit 40 is obtained. FB The output power value P FB is an example of a "power feedback value" in the claims.

[0044] In this embodiment, the constant power control unit 73 (control unit 70) calculates the input power command value P Ctrl and the output power value P, which is a feedback value of the output power output from the chopper unit 40 calculated by the power calculation unit 72. FB Based on this, constant power control (APR: Auto Power Regulator) is performed so that the power output from the chopper unit 40 becomes constant. Specifically, the constant power control unit 73 executes feedback control of PI control (Proportional-Integral control) including proportional action and integral action as the constant power control. That is, the constant power control unit 73 performs feedback control of the input power command value P Ctrl and the output power value P FB The proportional action multiplies the deviation between the input power command value P Ctrl and the output power value P FB The constant power control unit 73 performs constant power control, which is feedback control (PI control) including an integral action in which the time integral of the deviation from the current is calculated and the calculated time integral value is multiplied by a predetermined integral gain. The constant power control unit 73 then outputs the sum of the value of the proportional term of the proportional action and the value of the integral term of the integral action as the output value A. In this way, the constant power control unit 73 is configured to output the output value A by constant power control, which is PI control. The output value A is a command value (target value) of the current controlled by the constant current control unit 74, which will be described later. The output value A is also an example of a "second output value" in the claims.

[0045] In this embodiment, the constant current control unit 74 (control unit 70) calculates the output (output value A) of the constant power control by the constant power control unit 73 and the output current value I, which is a feedback value of the output current output from the chopper unit 40 calculated by the chopper coil current calculation unit 71. FB Based on this, constant current control (ACR: Auto Current Regulator) is performed so that the current output from the chopper unit 40 becomes constant. Specifically, the constant current control unit 74 performs feedback control of PI control including proportional action and integral action as constant current control, similar to the constant power control by the constant power control unit 73. That is, the constant current control unit 74 performs feedback control of PI control including proportional action and integral action as constant current control based on the output value A and the output current value I FB The proportional action multiplies the deviation between the output value A and the output current value I by a predetermined proportional gain. FB The constant current control unit 74 performs constant current control, which is feedback control (PI control) including an integral action in which the time integral of the deviation between the current and the pulse width is calculated and the calculated time integral value is multiplied by a predetermined integral gain. The constant current control unit 74 then outputs the sum of the value of the proportional term of the proportional action and the value of the integral term of the integral action as the output value B. In this way, the constant current control unit 74 is configured to output the output value B by constant current control, which is PI control, similar to the constant power control by the constant power control unit 73. The output value B is an amount of operation for the duty ratio D (pulse width) set by the duty ratio setting unit 75, which will be described later. The output value B is also an example of a "first output value" in the claims.

[0046] The duty ratio setting unit 75 (control unit 70) determines the chopper drive signal G based on the output (output value B) of the constant current control by the constant current control unit 74. CHO Specifically, the duty ratio setting unit 75 sets the duty ratio D of the chopper drive signal G input to the switching element 41 of the chopper unit 40. CHOThe duty ratio D of the chopper is set to be corrected from the current value based on the output value B from the constant current control unit 74. A signal indicating the duty ratio D set by the duty ratio setting unit 75 is output to the GDU 82 (see FIG. 2), and thus the chopper drive signal G having the set duty ratio D is generated. CHO is output to the switching element 41 of the chopper section 40. Furthermore, the duty ratio setting section 75 outputs the set duty ratio D to the chopper coil current calculation section 71.

[0047] As described above, the control unit 70 of the power conversion device 100 of this embodiment calculates the chopper current I C and intermediate voltage V dc and obtains the preset power command value P Ctrl The chopper drive signal G input to the switching element 41 of the chopper unit 40 is generated by performing constant power control and constant current control based on the CHO The duty ratio D of the power command value P Ctrl is stored in advance in a storage device such as a flash memory of the control unit 70. When stopping only the operation of the inverter unit 60 from a state in which both the inverter unit 50 and the inverter unit 60 are driven based on an input operation to the operation unit 102c, the control unit 70 Ctrl It is configured to change the size of the image to half (50%).

[0048] The current determination unit 76 (control unit 70) detects an abnormal current state (overcurrent state). The abnormal current state is detected by detecting the current of the chopper unit 40 (chopper current I C ) is the preset chopper current judgment value T C When the current of the inverter unit 50 (output current I L1 ) is the preset inverter current judgment value T L1 When the current of the inverter unit 60 (output current I L2 ) is the preset inverter current judgment value T L2 The chopper current determination value TC , inverter current judgment value T L1 , and inverter current judgment value T L2 is stored in advance in a storage device such as a flash memory of the control unit 70. L1 is an example of the "first inverter current determination value" in the claims. L2 is an example of a "second inverter current determination value."

[0049] Specifically, the current determination unit 76 determines the chopper current I at each predetermined determination period while the chopper unit 40 and at least one of the inverter unit 50 and the inverter unit 60 are operating. C is obtained as the current of the chopper unit 40, and the output current I L1 is obtained as the current of the inverter unit 50, and the output current I L2 is acquired as the current of the inverter unit 60. Then, the current determination unit 76 determines the acquired chopper current I C is the preset chopper current judgment value T C The current determination unit 76 determines whether a current abnormality greater than the acquired output current I L1 is the preset inverter current judgment value T L1 Similarly, the current determination unit 76 determines whether a current abnormality greater than the acquired output current I L2 is the preset inverter current judgment value T L2 Then, the current determination unit 76 determines whether a current abnormality greater than the chopper current I C , output current I L1 , and the output current I L2 If it is determined that a current abnormality has occurred in at least one of the above, a current abnormality state in which a current abnormality with a large current (overcurrent) has occurred is detected. Note that since the inverter unit 50 and the inverter unit 60 have the same configuration, the inverter current determination value T L1 and inverter current judgment value T L2 are set to be equal to each other.C The value may be updated when the operation of either inverter unit 50 or 60 is stopped.

[0050] In this embodiment, when the current determination unit 76 (control unit 70) detects an abnormal current state, the control unit 70 determines whether the chopper drive signal G is set by the duty ratio setting unit 75 based on the output (output value B) of the constant current control unit 74. CHO The duty ratio D is reduced by a predetermined first ratio. The predetermined first ratio is a constant value set in advance, for example, 50%.

[0051] Specifically, in this embodiment, the constant power control unit 73 (control unit 70) is configured to reduce the output value A by a predetermined second rate (50%) and reduce the value of the time integral calculated by the integral operation in the constant power control when an abnormal current state is detected. Also, in this embodiment, the constant current control unit 74 (control unit 70) is configured to reduce the output value B by a predetermined first rate (50%) and reduce the value of the time integral calculated by the integral operation in the constant power control when an abnormal current state is detected. Also, in this embodiment, the duty ratio setting unit 75 (control unit 70) is configured to set the chopper drive signal G before the output value B output by the constant current control unit 74 is reduced by 50% when an abnormal current state is detected. CHO The duty ratio D is set to be 50% smaller. The control process method when an abnormal current state is detected will be described later in detail.

[0052] In this embodiment, the control unit 70 controls the outputs from the inverter units 50 and 60 to be constant (constant frequency and constant duty ratio). Therefore, when a current abnormality state is detected, the inverter drive signal G input to the inverter units 50 and 60 is INV Without changing the chopper drive signal G CHOThe control unit 70 is configured to reduce the duty ratio D of the chopper unit 40 by 50%. For example, if an abnormal current state is detected when the duty ratio of the inverter units 50 and 60 is 50% and the duty ratio of the chopper unit 40 is 40%, the control unit 70 reduces the duty ratio of the chopper unit 40 to 20% while maintaining the duty ratio of the inverter units 50 and 60 at 50%.

[0053] (Control method of power conversion device according to this embodiment) Next, a processing flow of the control method for the power conversion device 100 of this embodiment will be described with reference to Fig. 4 and Fig. 5. The control method for the power conversion device 100 of this embodiment is executed by control processing by the control unit 70. The control processing in steps S11 to S17 is feedback control processing in a normal state that is executed constantly (every calculation cycle) while the power conversion device 100 is operating (while the chopper unit 40 is operating). The control processing in steps S21 to S24 is control processing when an abnormal current state is detected by the current determination unit 76 (control unit 70).

[0054] Feedback Control Processing in Normal State As shown in FIG. 4, first, in step S11, the chopper current I C and intermediate voltage V dc Then, in step S12, the chopper coil current calculation unit 71 calculates the acquired chopper current I C and the duty ratio D currently output from the duty ratio setting unit 75, the output current value I output from the chopper unit 40 is calculated. FB Then, in step S13, the power calculation unit 72 calculates the output current value I FB and the intermediate voltage V dc Based on this, the output power value P from the chopper unit 40 is calculated. FB (power feedback value) is calculated.

[0055] Next, in step S14, the constant power control unit 73 sets the preset power command value P Ctrl and the output power value P calculated in step S13. FB Based on this, constant power control (PI control) is performed, and an output value A is output.

[0056] Then, in step S15, the constant current control unit 74 calculates the output value A output in step S14 and the output current value I calculated in step S12. FB Based on this, constant current control (PI control) is performed to output an output value B.

[0057] Then, in step S16, the duty ratio setting unit 75 sets the chopper drive signal G based on the output value B output in step S15. CHO That is, the duty ratio D currently being output is corrected by feedback control and reset.

[0058] Then, in step S17, the chopper unit 40 is operated with the duty ratio D set in step S16. Specifically, the chopper drive signal G CHO is input to the switching element 41 of the chopper unit 40. That is, the output from the chopper unit 40 is reset based on the duty ratio D set in step S16. The control processing in steps S11 to S17 is executed at predetermined calculation intervals.

[0059] <Control process when an abnormal current state is detected> Next, a control process when an abnormal current state is detected as shown in FIG. 5 will be described.

[0060] First, in step S21, it is determined whether or not an abnormal current state has been detected. If it is determined that an abnormal current state has been detected, the process proceeds to step S22. If it is not determined that an abnormal current state has been detected, the control process is terminated. The control process in step S21 is executed at every predetermined determination cycle. That is, the acquired chopper current I C , output current I L1 , and the output current I L2 It is determined whether or not a current abnormality has occurred in each of the above.

[0061] Next, in step S22, if a current abnormality state is detected, the chopper drive signal G CHO That is, the duty ratio D of the chopper drive signal G is reduced by a predetermined first ratio (50%). CHO The duty ratio D is set to be reduced from the current value by 50%, which is a preset ratio for suppressing the current. Note that the "50% ratio for suppressing the current" mentioned here is an example of the "predetermined first ratio" in the claims.

[0062] Specifically, the signal indicating the duty ratio D outputted to the GDU 82 by the duty ratio setting unit 75 is a chopper drive signal G CHO The duty ratio D is updated to be reduced by 50% from the current value. Then, a signal set to reduce the current duty ratio D by 50% is output to the GDU 82. That is, regardless of the feedback control output by the constant power control unit 73 and the constant current control unit 74 (separate from the outputs of the constant power control and constant current control), if an abnormal current state is detected, the duty ratio setting unit 75 reduces the duty ratio D by 50%.

[0063] Next, in step S23, in this embodiment, when an abnormal current state is detected, the output value B output by the constant current control unit 74 is reduced by 50% (first ratio), and the value of the time integral calculated by the integral operation in the constant current control is reduced.

[0064] That is, when an abnormal current state is detected, the duty ratio D set by the duty ratio setting unit 75 is reduced by 50%, and the output value B output from the constant current control unit 74 and input to the duty ratio setting unit 75 is reduced by 50%. Therefore, when an abnormal current state is detected, the output value B output separately from the calculation of the constant current control (feedback control) by the constant current control unit 74 is reduced by 50% so that the duty ratio D once set to be 50% smaller by the duty ratio setting unit 75 does not return to its original value by the output (output value B) of the constant current control in the next calculation cycle.

[0065] Also, at this time, the value of the integral term (I term) of the integral action of the proportional and integral actions in the feedback control (PI control) of the constant current control is reduced by 50%, just like the output value B. In other words, the value of the time integral of the integral term in the constant current control is reduced by 50%. Therefore, not only is the output value B by constant current control reduced by 50%, but the value of the time integral of the deviation used to calculate the output value B is also reduced by 50%, so that when an abnormal current state is detected, the output value B, which was once reduced, is prevented from being immediately returned to its original size by feedback control in the constant current control calculation at each calculation cycle.

[0066] Then, in step S24, similar to the constant current control in step S23, in this embodiment, when an abnormal current state is detected, the output value A output by the constant power control unit 73 is reduced by a predetermined 50% (second rate), and the value of the time integral calculated by the integral operation in the constant power control is reduced. Note that the rate of 50% by which the output value A in the constant power control is reduced is an example of the "second rate" in the claims.

[0067] That is, output value B output by constant current control unit 74 is reduced by 50%, and output value A output by constant power control unit 73 and input to constant current control unit 74 is reduced by 50%. Also, as in constant current control, the value of the integral term (I term) of the integral action in the feedback control (PI control) of constant power control by constant power control unit 73 is reduced by 50%, similar to output value A. Therefore, as in constant current control, in constant power control as well, output value A calculated by calculation is reduced by 50%, and the value of the time integral of the deviation used to calculate output value A is also reduced by 50%.

[0068] Note that either step S23, in which the output of the constant current control (output value B) is reduced and the value of the integral term of the constant current control is reduced, or step S24, in which the output of the constant power control (output value A) is reduced and the value of the integral term of the constant power control is reduced, may be executed first. Also, steps S23 and S24 may be executed substantially simultaneously.

[0069] As described above, when an abnormal current state is detected, the duty ratio D is reduced, and the feedback control parameters of the constant power control and the constant current control are adjusted to be smaller so that the reduced duty ratio D does not immediately return to its original value. In other words, the sensitivity of the feedback control is reduced.

[0070] Note that even when an abnormal current state is detected, the control processing by constant current control and constant power control is executed at every predetermined calculation period. On the other hand, when an abnormal current state is detected, the resetting operation by the duty ratio setting unit 75 to reduce the duty ratio D is executed at every predetermined judgment period that is separate from the predetermined calculation period for controlling the setting of the duty ratio D by executing constant power control and constant current control. This predetermined judgment period is shorter than the calculation period for the constant current control and constant power control. In other words, the detection of the abnormal current state at step S21 and the processing to reduce the duty ratio D by 50% at step S22 are executed at every judgment period that is shorter than the calculation period for the normal control of constant current control and constant power control at steps S11 to S16. In other words, the chopper drive signal G by the duty ratio setting unit 75 is reset at every predetermined judgment period that is separate from the predetermined calculation period for controlling the setting of the duty ratio D by executing constant power control and constant current control. This predetermined judgment period is shorter than the calculation period for the normal control of constant current control and constant power control at steps S11 to S16. CHO The operation of reducing the duty ratio D by 50% is executed at the time when an abnormal current state is detected (determined) before the timing of the calculation cycle of the constant current control and the constant power control. The process of reducing the output value B and the integral term of the constant current control by 50% in step S23 and the process of reducing the output value A and the integral term of the constant power control by 50% in step S24 are executed at the timing of the calculation cycle next to the time when an abnormal current state is detected. Therefore, in this embodiment, when an abnormal current state is detected, the duty ratio setting unit 75 reduces the chopper drive signal G by 50% before the output value B output by the constant current control is reduced by 50% and the output value A output by the constant power control is reduced by 50%. CHO The duty ratio D is reduced by 50%.

[0071] (Effects of the embodiment) In this embodiment, the following effects can be obtained.

[0072] In this embodiment, as described above, the control unit 70 controls the current of the chopper unit 40 (chopper current I C ) is the preset chopper current judgment value T C When the current of the inverter units 50 and 60 (output current I L1 and IL2 ) is the preset inverter current judgment value T L1 and T L2 When a current abnormality state including at least one of a current abnormality state where the chopper drive signal G CHO The control unit 70 is configured to reduce the duty ratio D of the chopper unit 40 by 50% (a predetermined first ratio). As a result, if an abnormal current state is detected while AC power is being output to the induction heating coils 10 and 20 by controlling the duty ratio D of the chopper unit 40, the output from the chopper unit 40 can be reduced by an additional 50% (first ratio) from the magnitude set by normal control. Therefore, if an abnormal current state is detected, the control unit 70 can further reduce the output from the chopper unit 40 from the magnitude set by normal control through control processing without increasing the number of components. As a result, even if an overcurrent occurs under normal control due to a sudden decrease in load, the output current can be prevented from increasing while preventing the circuit configuration from becoming complicated.

[0073] Furthermore, in this embodiment, further effects can be obtained by configuring as follows.

[0074] That is, in this embodiment, as described above, the control unit 70 calculates the input power command value P Ctrl and the output power value P of the output power output from the chopper unit 40. FB a constant power control unit 73 (control unit 70) that performs constant power control based on the power feedback value, an output of the constant power control by the constant power control unit 73 (output value A), and an output current value I of the output current output from the chopper unit 40. FB A constant current control unit 74 (control unit 70) performs constant current control based on the current feedback value (current feedback value), and a chopper drive signal G based on the output (output value B) of the constant current control by the constant current control unit 74. CHOand a duty ratio setting unit 75 (control unit 70) that sets a duty ratio D of the chopper drive signal G, which is set by the duty ratio setting unit 75 based on the output (output value B) of the constant current control when an abnormal current state is detected. CHO In this embodiment, the control unit 70 is configured to reduce the duty ratio D of the chopper unit 40 by 50% (first ratio). Here, if only constant power control is performed to maintain the output of the induction heating coils 10 and 20 at a constant magnitude, the magnitude of the current output from the chopper unit 40 is not controlled, and therefore an increase in the current cannot be prevented. In contrast, in this embodiment, the control unit 70 is configured to include both a constant power control unit 73 that performs constant power control and a constant current control unit 74 that performs constant current control, thereby enabling constant current control in addition to constant power control, and thereby controlling the output current from the chopper unit 40 to be constant. Therefore, an increase in the output current from the chopper unit 40 can be prevented. Furthermore, if an abnormal current state is detected while the magnitude of the current output from the chopper unit 40 is being controlled to be constant by performing constant current control in addition to constant power control, the duty ratio D can be further reduced by 50% (first ratio). As a result, when an abnormal current state is detected while the output current is being controlled to a constant value by constant current control, the output current from the chopper unit 40 can be further reduced in addition to the constant current control, so that the output current can be effectively prevented from increasing even when the load suddenly decreases.

[0075] Furthermore, in this embodiment, as described above, the constant current control section 74 (control section 70) is configured to output the output value B (first output value) by constant current control, and is configured to reduce the output value B by 50% (first ratio) when an abnormal current state is detected. As a result, when an abnormal current state is detected, the output value B from the constant current control section 74 input to the duty ratio setting section 75 (control section 70) is reduced by 50% (first ratio), thereby reducing the chopper drive signal G set by the duty ratio setting section 75. CHOTherefore, the command value (output value A) and the feedback value (output current value I) input to the constant current control unit 74 can be reduced by 50% (first ratio). FB ) is the same as the magnitude at the time when the current abnormality state occurred, by reducing the output value B output from the constant current control unit 74 by 50% (first ratio), the duty ratio D set by the duty ratio setting unit 75 can be reduced by 50% (first ratio) from the magnitude at the time when the current abnormality state was detected. As a result, it is possible to prevent the output current from increasing while preventing the circuit configuration from becoming complicated.

[0076] In this embodiment, as described above, the constant current control unit 74 (control unit 70) controls the constant power control output (output value A) by the constant power control unit 73 (control unit 70) and the output current value I FBThe constant current control unit 74 is configured to output an output value B (first output value) by performing constant current control, which is feedback control including an integral operation that calculates a time integral of a deviation from the current (current feedback value). When an abnormal current state is detected, the constant current control unit 74 reduces the output value B by 50% (first ratio) and reduces the value of the time integral calculated by the integral operation in the constant current control. Here, even when the output value B output from the constant current control unit 74 is reduced by 50% (first ratio), if the time integral in the integral operation of the feedback control of the constant current control unit 74 remains the same as when the abnormal current state was detected, the feedback control by the constant current control unit 74 will cause the output value B to return to the magnitude at the time when the abnormal current state was detected. In contrast, in this embodiment, when an abnormal current state is detected, the output value B output from the constant current control unit 74 is reduced by 50% (first ratio) and the value of the time integral calculated by the integral operation in the constant current control is reduced, thereby preventing the output value B, which was once reduced by 50% (first ratio), from returning to the magnitude at the time when the abnormal current state was detected. Therefore, it is possible to prevent the output from the chopper unit 40 from returning to the output at the time when the current abnormality state was detected, and therefore it is possible to prevent the detection of the current abnormality state from being repeated. As a result, it is possible to stably prevent the output current output from the chopper unit 40 from increasing.

[0077] Furthermore, in this embodiment, as described above, the constant power control unit 73 (control unit 70) is configured to output the output value A (second output value) through constant power control, and is configured to reduce the output value A by 50% (a predetermined second rate) when an abnormal current state is detected. As a result, when an abnormal current state is detected, in addition to reducing the output value B (first output value) output from the constant current control unit 74 (control unit 70) by 50% (first rate), the output value A from the constant power control unit 73 input to the constant current control unit 74 is also reduced by 50% (second rate), thereby preventing the output value B from returning to the magnitude at the time when the abnormal current state was detected through feedback control by the constant current control unit 74. As a result, by reducing the input to the constant current control unit 74 in addition to the output from the constant current control unit 74, it is possible to more stably prevent the output current from the chopper unit 40 from increasing when an abnormal current state is detected.

[0078] In this embodiment, as described above, the constant power control unit 73 (control unit 70) determines the input power command value P Ctrl and the output power value P FB The constant power control unit 73 is configured to output an output value A (second output value) by performing constant power control, which is feedback control including an integral operation that calculates a time integral of a deviation from the current value (power feedback value). When an abnormal current state is detected, the constant power control unit 73 reduces the output value A to be output by 50% (second rate) and also reduces the value of the time integral calculated by the integral operation in the constant power control. As a result, similar to the feedback control of the constant current control unit 74 (control unit 70), by reducing the value of the time integral in the integral operation of the feedback control by the constant power control unit 73, it is possible to prevent the output value A reduced by 50% (second rate) from returning to the value at the time when the abnormal current state was detected. This further reduces the repetition of detection of the abnormal current state, thereby more stably preventing the output current output from the chopper unit 40 from increasing.

[0079] In addition, in this embodiment, as described above, when an abnormal current state is detected, the duty ratio setting unit 75 (control unit 70) reduces the chopper drive signal G before the output value B (first output value) output by the constant current control unit 74 (control unit 70) is reduced by 50% (first ratio). CHO The duty ratio D of the chopper drive signal G set by the duty ratio setting unit 75 is set to be 50% (first ratio) smaller than the first ratio. This allows the chopper drive signal G to be set by the duty ratio setting unit 75 before the time equivalent to one calculation cycle for calculating the feedback control of the constant current control unit 74 has elapsed. CHO The duty ratio D can be reduced by 50% (first ratio). Therefore, when an abnormal current state is detected, the output current output from the chopper unit 40 can be reduced more quickly, and the output current from the chopper unit 40 can be more effectively prevented from increasing.

[0080] In this embodiment, as described above, the inverter units 50 and 60 are provided in plural (two) so as to output AC power to each of the plural (two) induction heating coils 10 and 20, and the control unit 70 controls the current of the chopper unit 40 to be equal to or higher than the preset chopper current judgment value T C and when the current in at least one of the inverter units 50 and 60 is greater than the inverter current determination value T L1 and T L2 When a current abnormality state including at least one of a current abnormality state where the chopper drive signal G CHOThe duty ratio D is reduced by 50% (first ratio). As a result, even when AC power is output to each of the multiple (two) induction heating coils 10 and 20 by the multiple (two) inverter units 50 and 60, if an abnormal current state is detected, the control processing by the control unit 70 can prevent the output current from increasing by controlling the chopper unit 40 while preventing the circuit configuration from becoming complicated. Furthermore, since the output current can be prevented from increasing by controlling the switching operation of the switching element 41 of the chopper unit 40 without controlling the operation of each of the multiple inverter units 50 and 60, unlike when the operation of each of the multiple inverter units 50 and 60 is controlled, the processing burden of the control processing for preventing the output current from increasing can be prevented from increasing.

[0081] In addition, in this embodiment, as described above, the inverter unit 50 (first inverter unit) and the inverter unit 60 (second inverter unit) are included, which output AC power to the pair of induction heating coils 10 and 20 provided for heating and welding plastics or the like (welding objects), and the inverter unit 50 and the inverter unit 60 are configured to stop the operation of either one of them based on an input operation to the operation unit 102c, and the control unit 70 is configured to stop the operation of either one of the inverter unit 50 and the inverter unit 60 based on an input operation to the operation unit 102c, and the control unit 70 is configured to stop the operation of either the inverter unit 50 or the inverter unit 60 based on an input operation to the operation unit 102c, and ... C When the current of the inverter unit 50 is greater than the predetermined inverter current judgment value T L1 (first inverter current determination value), or when the current of the inverter unit 60 is greater than a preset inverter current determination value T L2 When a current abnormality state is detected, including at least one of the cases where the current is greater than the second inverter current judgment value, the chopper drive signal G CHOThe duty ratio D of the inverter unit 50 is reduced by 50% (first ratio). When the operation of one of the inverter units 50 and 60 is stopped from a state in which both inverter units 50 and 60 are operating, the output current from the chopper unit 40 may increase due to a sudden change (sudden decrease) in the load. In response to this, in this embodiment, the control unit 70 is configured to adjust the current of the chopper unit 40 to a predetermined chopper current determination value T C When the current of the inverter unit 50 is greater than the predetermined inverter current judgment value T L1 When the current of the inverter unit 60 is greater than the predetermined inverter current judgment value T L2 When a current abnormality state is detected, the chopper drive signal G CHO In this way, even if the output current increases when the operation of either the inverter unit 50 or the inverter unit 60 is stopped, the duty ratio D of the chopper drive signal G CHO By reducing the duty ratio D by 50% (first ratio), it is possible to effectively prevent the output current from increasing while preventing the circuit configuration from becoming complicated.

[0082] In this embodiment, as described above, when a current abnormality state is detected, the control unit 70 controls the inverter drive signal G INV Without changing the chopper drive signal G CHO The chopper driving signal G input to the chopper unit 40 is configured to be reduced by 50% (first ratio) in order to prevent the output current from increasing. CHO and the inverter drive signal G input to the inverter units 50 and 60. INV In comparison with the case where both of the above are controlled, the processing load of the control process can be prevented from increasing.

[0083] (Effects of the power conversion device control method according to this embodiment) The control method for the power conversion device 100 of this embodiment can provide the following effects.

[0084] In the control method of the power conversion device 100 of this embodiment, as described above, the current of the chopper unit 40 is set to a predetermined chopper current judgment value T C When the current of the inverter units 50 and 60 is greater than the predetermined inverter current judgment value T L1 and T L2 When the current abnormality state is detected, the chopper drive signal G CHO The duty ratio D of the chopper unit 40 is reduced by 50% (a predetermined first ratio). As a result, when an abnormal current state is detected while AC power is being output to the induction heating coils 10 and 20 by controlling the duty ratio D of the chopper unit 40, the output from the chopper unit 40 can be reduced by a further 50% (a first ratio) from the magnitude set by normal control (constant power control and constant current control). Therefore, when an abnormal current state is detected, the output from the chopper unit 40 can be further reduced from the magnitude set by normal control through control processing by the control unit 70 without increasing the number of components. As a result, it is possible to provide a control method for the power conversion device 100 that can prevent the output current from increasing while suppressing the complexity of the circuit configuration, even when an overcurrent occurs under normal control due to a sudden decrease in load.

[0085] Furthermore, in the control method for the power conversion device 100 of this embodiment, as described above, the input power command value P Ctrl and the output power value P of the output power output from the chopper unit 40. FB Step S14: performing constant power control based on the power feedback value, and outputting the constant power control output and the output current value I of the output current output from the chopper unit 40. FB Step S15: performing constant current control based on the current feedback value; and step S16: performing constant current control based on the output of the constant current control. CHOand step S16 of setting the duty ratio D of the chopper drive signal G. CHO In steps S22 to S24, the duty ratio D of the chopper drive signal G, which is set based on the output of the constant current control, is reduced by 50% (first ratio) when an abnormal current state is detected. CHO In this case, the duty ratio D of the chopper unit 40 is reduced by 50% (first ratio). Here, if only constant power control is performed to maintain the output of the induction heating coils 10 and 20 at a constant magnitude, the magnitude of the current output from the chopper unit 40 is not controlled, and therefore an increase in the current cannot be prevented. In contrast, in this embodiment, by including step S14 of performing constant power control and step S15 of performing constant current control, constant current control can be performed in addition to constant power control, and the output current from the chopper unit 40 can be suppressed to be constant. Therefore, an increase in the output current from the chopper unit 40 can be prevented. Furthermore, if an abnormal current state is detected in a state in which the magnitude of the current output from the chopper unit 40 is controlled to be constant by performing constant current control in addition to constant power control, in addition to controlling the duty ratio D by constant current control, the duty ratio D can be further reduced by 50% (first ratio). As a result, when an abnormal current state is detected while the output current is being controlled to a constant value by constant current control, the output current from the chopper unit 40 can be further reduced in addition to the constant current control, so that the output current can be effectively prevented from increasing even when the load suddenly decreases.

[0086] [Variations] The embodiments disclosed herein should be considered to be illustrative and not restrictive in all respects. The scope of the present invention is defined by the claims rather than the description of the above embodiments, and further includes all modifications (variations) within the meaning and scope of the claims.

[0087] For example, in the above embodiment, the control unit 70 performs constant power control and constant current control to control the chopper drive signal GCHO The chopper drive signal G is set based on the output of the constant current control (output value B) when an abnormal current state is detected. CHO In the example shown, the duty ratio D is reduced by 50% (first ratio), but the present invention is not limited to this. In the present invention, the control unit 70 performs only constant power control, and the chopper drive signal G is controlled by feedback control. CHO The chopper drive signal G is set based on the output (output value A) of the constant power control when an abnormal current state is detected. CHO Alternatively, the duty ratio D may be reduced by a predetermined percentage (for example, 50%).

[0088] Furthermore, in the above embodiment, when an abnormal current state is detected, the duty ratio setting unit 75 (control unit 70) sets the duty ratio D to be 50% (first ratio) smaller, and the output value B (first output value) output by constant current control is reduced by 50% (first ratio). However, the present invention is not limited to this. In the present invention, when an abnormal current state is detected, the output value B output by constant current control does not have to be reduced. Furthermore, when an abnormal current state is detected, the output value B output by constant current control may be reduced by a ratio different from the first ratio (50%) by which the duty ratio D is reduced.

[0089] In addition, in the above embodiment, an example was shown in which the value of the time integral (I term) calculated by the integral operation in constant current control (PI control) was reduced by 50% when an abnormal current state was detected, but the present invention is not limited to this. In the present invention, the value of the time integral calculated by the integral operation in constant current control may not be reduced when an abnormal current state is detected. Furthermore, when an abnormal current state is detected, the value of the time integral calculated by the integral operation in current control may be reduced by a percentage different from the percentage by which output value B (first output value) output by constant current control was reduced.

[0090] Furthermore, in the above embodiment, an example was shown in which the output value A (second output value) output by constant power control was reduced by 50% (second rate) when an abnormal current state was detected, but the present invention is not limited to this. In the present invention, the output value A output by constant power control does not have to be reduced when an abnormal current state is detected. Furthermore, when an abnormal current state is detected, the duty ratio setting unit 75 (control unit 70) may reduce the output value A output by constant power control by a rate different from the first rate (50%) by which the duty ratio D is reduced. Furthermore, the output value A output by constant power control may be reduced by a rate different from the first rate (50%) by which the output value B (first output value) output by constant current control is reduced.

[0091] In addition, in the above embodiment, an example was shown in which the value of the time integral (I term) calculated by the integral action in constant power control (PI control) was reduced by 50% when an abnormal current state was detected, but the present invention is not limited to this. In the present invention, the value of the time integral calculated by the integral action in constant power control may not be reduced when an abnormal current state is detected. Furthermore, when an abnormal current state is detected, the value of the time integral calculated by the integral action in constant power control may be reduced by a percentage different from the percentage by which the output value A output by constant power control was reduced.

[0092] In the above embodiment, when an abnormal current state is detected, the duty ratio D is reduced by 50%, and the output value A and the time integral value (I term) in constant power control and the output value B and the time integral value (I term) in constant current control are reduced by 50%. However, the present invention is not limited to this. When an abnormal current state is detected, the duty ratio D, the output value A and the time integral value (I term) in constant power control, and the output value B and the time integral value (I term) in constant current control may be reduced by a percentage other than 50% (for example, 10% or more but less than 50%). In this case, the percentages by which the duty ratio D, the output value A and the time integral value (I term) in constant power control, and the output value B and the time integral value (I term) in constant current control are reduced may be equal to or different from each other.

[0093] In the above embodiment, when an abnormal current state is detected, the chopper drive signal G is generated before the output value B (first output value) output by the constant current control is reduced by 50% (predetermined first ratio). CHO In the example shown, the duty ratio D of the chopper drive signal G is set (reset) to be 50% (first ratio) smaller, but the present invention is not limited to this. In the present invention, before the output value B (first output value) output by the constant current control is reduced by 50% (first ratio), the chopper drive signal G CHO It is not necessary to set the duty ratio D to be 50% (first ratio) smaller. That is, instead of resetting the duty ratio D to be smaller by the duty ratio setting unit 75 (control unit 70) at the time when the abnormal current state is detected, the output value B (first output value) output by the constant current control may be reduced at the timing of the next calculation process of the constant current control, thereby changing (resetting) the duty ratio D to be smaller by a predetermined first ratio.

[0094] Furthermore, in the above embodiment, an example was shown in which two inverter units 50 and 60 were provided to output AC power to each of the pair of induction heating coils 10 and 20, but the present invention is not limited to this. In the present invention, a configuration in which only one inverter unit is provided may also be used. Alternatively, three or more inverter units may be provided. In this case, power may be supplied (output) from one inverter unit to multiple induction heating coils.

[0095] In the above embodiment, the power converter 100 is used in the welding device 102 that heats and welds plastics or the like (welding objects), but the present invention is not limited to this. In the present invention, the power converter 100 may be provided in an induction heating (IH) heater device for cooking. In other words, the power converter 100 may be configured to supply power to an induction heating coil of the IH heater device for cooking.

[0096] In the above embodiment, when an abnormal current state is detected, the inverter drive signal G INV Without changing the chopper drive signal G CHO In the example shown, the duty ratio D of the chopper drive signal G is reduced by 50% (first ratio), but the present invention is not limited to this. CHO In addition to reducing the duty ratio D by 50% (first ratio), the inverter drive signal G input to the inverter units 50 and 60 INV The duty ratio may be reduced.

[0097] In the above embodiment, the resistors 44, 56, and 66 are used to measure (detect) the currents of the chopper unit 40, the inverter unit 50, and the inverter unit 60, but the present invention is not limited to this. In the present invention, the configuration for detecting the currents is not limited to shunt resistors. For example, the currents may be measured using a current transformer (CT) as the current measuring unit. Furthermore, the current measuring units for measuring the currents of the chopper unit 40, the inverter unit 50, and the inverter unit 60 may be connected at different positions from those in the above embodiment.

[0098] In the above embodiment, the inverter unit 50 and the inverter unit 60 are configured to output AC power using half-bridge inverter circuits, but the present invention is not limited to this. For example, the inverter unit 50 and the inverter unit 60 may be configured to include full-bridge inverter circuits.

[0099] In the above embodiment, the inverter unit 50 and the inverter unit 60 have the same configuration, but the present invention is not limited to this. For example, when the impedances of the output induction heating coils 10 and 20 are different from each other, the inverter unit 50 and the inverter unit 60 may have different configurations from each other. In this case, the inverter current determination value T L1 (first inverter current determination value) and inverter current determination value T L2 The (second inverter current determination value) is set to be a different value from the first inverter current determination value. That is, when a plurality of inverter units are provided, a plurality of inverter current determination values ​​that are different from each other are set to correspond to each of the plurality of inverter units. Furthermore, the drive signals input to each of the plurality of inverter units may be of different types.

[0100] In the above embodiment, the switching element 41 of the chopper unit 40, the switching elements 52 and 53 of the inverter unit 50, and the switching elements 62 and 63 of the inverter unit 60 are MOSFETs, but the present invention is not limited to this. For example, the switching elements included in each of the chopper unit 40 and the inverter units 50 and 60 may be IGBTs (Insulated Gate Bipolar Transistors). Furthermore, different types of switching elements may be used in the chopper unit 40 and the inverter units 50 and 60.

[0101] In the above embodiment, the chopper unit 40 is configured to form a step-down chopper circuit, but the present invention is not limited to this. For example, the chopper unit 40 may be configured to form a step-up chopper circuit.

[0102] In the above embodiment, the current determination unit 76 of the control unit 70 determines whether there is a current abnormality in the chopper unit 40, the inverter unit 50, and the inverter unit 60, but the present invention is not limited to this. For example, a hardware configuration including a comparison circuit such as a comparator may be used to detect whether the current in each of the chopper unit 40, the inverter unit 50, and the inverter unit 60 is greater than a predetermined threshold value, thereby detecting a current abnormality state. [Explanation of symbols]

[0103] 10 induction heating coil 20 induction heating coil 40 Chopper section 41 Switching element 50 Inverter section (first inverter section) 60 Inverter section (second inverter section) 70 Control Unit 73 Constant power control section 74 Constant current control section 75 Duty ratio setting section 100 Power conversion device 102c Operations Unit

Claims

1. a chopper unit including a switching element for converting input DC power and outputting the converted power; an inverter unit that converts the DC power output by the chopper unit into AC power and outputs the AC power to an induction heating coil; a control unit that controls a duty ratio, which is a ratio of an on-state of a chopper drive signal input to the switching element of the chopper unit, The control unit a constant power control unit that performs constant power control based on an input power command value and a power feedback value of the output power output from the chopper unit; a constant current control unit that performs constant current control based on an output of the constant power control by the constant power control unit and a current feedback value of the output current output from the chopper unit, a power conversion device configured to reduce, by a predetermined first percentage, a duty ratio of the chopper drive signal, which is set based on an output of the constant current control, when an abnormal current state is detected, the duty ratio being set based on an output of the constant current control, the duty ratio being set based on an output of the constant current control, the first percentage being reduced when an abnormal current state is detected, the duty ratio being set based on an output of the constant current control

2. The control unit a duty ratio setting unit that sets a duty ratio of the chopper drive signal based on an output of the constant current control by the constant current control unit, 2. The power conversion device according to claim 1, wherein, when the abnormal current state is detected, the duty ratio of the chopper drive signal, which is set by the duty ratio setting unit based on the output of the constant current control, is reduced by the first ratio.

3. 3. The power conversion device according to claim 2, wherein the constant current control unit is configured to output a first output value by the constant current control, and is configured to reduce the first output value to be output by the first percentage when the current abnormality state is detected.

4. The constant current control unit the constant current control is a feedback control including an integral operation of calculating a time integral of a deviation between an output of the constant power control by the constant power control unit and the current feedback value, thereby outputting the first output value, 4. The power conversion device according to claim 3, wherein when the current abnormality state is detected, the first output value to be output is reduced by the first percentage, and a value of a time integral calculated by an integral operation in the constant current control is reduced.

5. 5. The power conversion device according to claim 3, wherein the constant power control unit is configured to output a second output value through the constant power control, and is configured to reduce the second output value to be output by a predetermined second percentage when the current abnormality state is detected.

6. The constant power control unit the second output value is output by performing the constant power control, which is feedback control including an integral operation of calculating a time integral of a deviation between the input power command value and the power feedback value, 6. The power conversion device according to claim 5, wherein, when the current abnormality state is detected, the second output value to be output is reduced by the second percentage, and a value of a time integral calculated by an integral operation in the constant power control is reduced.

7. 7. The power conversion device according to claim 3, wherein, when the abnormal current state is detected, the duty ratio setting unit sets the duty ratio of the chopper drive signal to be smaller by the first percentage before the first output value output by the constant current control unit is reduced by the first percentage.

8. a plurality of inverter units are provided to output AC power to the plurality of induction heating coils, The power conversion device according to any one of claims 1 to 7, wherein the control unit is configured to reduce the duty ratio of the chopper drive signal by the first percentage when the abnormal current state is detected, the abnormal current state including at least one of a case where the current of the chopper unit is greater than the predetermined chopper current determination value and a case where the current in at least one of the plurality of inverter units is greater than the inverter current determination value.

9. the inverter unit includes a first inverter unit and a second inverter unit that output AC power to each of the pair of induction heating coils provided for heating and welding the welding object, the first inverter unit and the second inverter unit are configured to stop operation of either one of them based on an input operation to an operation unit, The power conversion device according to any one of claims 1 to 8, wherein the control unit is configured to reduce the duty ratio of the chopper drive signal by the first percentage when an abnormal current state is detected, the abnormal current state including at least one of a case where the current of the chopper unit is greater than a predetermined chopper current judgment value, a case where the current of the first inverter unit is greater than a predetermined first inverter current judgment value, and a case where the current of the second inverter unit is greater than a predetermined second inverter current judgment value.

10. The power conversion device according to any one of claims 1 to 9, wherein the control unit is configured to reduce the duty ratio of the chopper drive signal by the first ratio without changing the inverter drive signal input to the inverter unit when the current abnormal state is detected.

11. A power conversion device including a chopper unit including a switching element that converts input DC power and outputs the converted power, and an inverter unit that converts the DC power output by the chopper unit into AC power and outputs the AC power to an induction heating coil, the power conversion device control method controlling a duty ratio that is a ratio of an on state of a chopper drive signal input to the switching element of the chopper unit, comprising: performing constant power control based on the input power command value and a power feedback value of the output power output from the chopper unit; performing constant current control based on an output of the constant power control and a current feedback value of the output current output from the chopper unit; detecting an abnormal current state including at least one of a case where the current of the chopper unit is larger than a predetermined chopper current determination value and a case where the current of the inverter unit is larger than a predetermined inverter current determination value; and when the abnormal current state is detected, reducing the duty ratio of the chopper drive signal, which is set based on the output of the constant current control, by a predetermined first ratio.

12. The inverter further comprises a step of setting a duty ratio of the chopper drive signal based on an output of the constant current control; 12. The control method for a power conversion device according to claim 11, wherein the step of reducing the duty ratio of the chopper drive signal by the first percentage includes the step of reducing, by the first percentage, a duty ratio of the chopper drive signal that is set based on an output of the constant current control when the current abnormal state is detected.

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