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1. (WO2019065472) POWER SUPPLY APPARATUS
Document

Description

Title of Invention POWER SUPPLY APPARATUS

Technical Field

0001  

Background Art

0002   0003   0004   0005  

Summary

0006   0007  

Brief Description of Drawings

0008  

Description of Embodiments

0009   0010   0011   0012   0013   0014   0015   0016   0017   0018   0019   0020   0021   0022   0023   0024   0025   0026   0027   0028   0029   0030   0031   0032   0033   0034   0035   0036   0037   0038   0039   0040   0041   0042   0043   0044   0045   0046   0047   0048   0049   0050   0051   0052   0053   0054  

Claims

1   2   3   4   5   6   7   8   9  

Drawings

1   2   3   4   5   6  

Description

Title of Invention : POWER SUPPLY APPARATUS

Technical Field

[0001]
The present invention relates to a power supply apparatus.

Background Art

[0002]
A related art inverter device generates a DC power supply from an AC power supply, acquires an AC output from a DC output through a smoothing circuit composed of a reactor and a smoothing capacitor by controlling turn-on/off of a switching device of an inverter circuit, and applies high-frequency AC power to a heating coil for induction heating. In the inverter device, a discharge resistor for discharging the smoothing capacitor with a predetermined discharge time constant is connected in parallel to the smoothing capacitor (see, e.g., JP3419641B2).
[0003]
When the discharge resistor is connected in parallel to the smoothing capacitor, power is always consumed by the discharge resistor. When the resistance value of the discharge resistor is increased to reduce the power consumed by the discharge resistor, the discharge time constant is increased, and quite a long time is required for discharging the smoothing capacitor. When charge is left in the smoothing capacitor, the charge may serve as an obstacle to checking or repairing the circuit. Thus, when an abnormality occurs in the apparatus, the smoothing capacitor is required to be rapidly discharged (e.g., within 10 seconds).
[0004]
The related art inverter device is used for induction heating of a cooking utensil such as a pan, and has a relatively small output, and the smoothing capacitor also has a relatively low capacitance. Therefore, although the resistance value of the discharge resistor is increased to raise the discharge time constant, the influence is slight. As an example, when the smoothing capacitor has a capacitance of 9 μF and the discharge resistor has a resistance value of 240 kΩ, the discharge time constant is set to about 2 seconds.
[0005]
However, in a power supply apparatus having relatively high output which is used for a heat treatment for a steel material or a welding operation for an electric resistance welded tube, a smoothing capacitor also has a high capacitance. In particular, the power supply apparatus used for welding an electric resistance welded tube is required to have a low ripple, and the smoothing capacitor used for this kind of power supply apparatus has an extremely high capacitance of tens of thousands of μF. When the capacitance of the smoothing capacitor is as high as the above value, the increase in resistance value of the discharge resistor significantly raises the discharge time constant. On the other hand, when the resistance value of the discharge resistor is decreased, the amount of power consumed by the discharge resistor is increased. Furthermore, a plurality of resistors may be needed in the relationship between the power consumption and the rating of the resistor. In this case, the manufacturing cost and operation cost of the power supply apparatus may be increased while the size of the power supply apparatus is increased.

Summary

[0006]
Illustrative aspects of the present invention provide a power supply apparatus which can rapidly discharge a capacitor included in a smoothing unit in case of an abnormality, and reduce a loss at normal times.
[0007]
According to an illustrative aspect of the invention, a power supply apparatus includes a rectifier configured to convert AC power into DC power, the AC power being supplied from an AC power supply, a smoothing unit configured to smooth the DC power output from the rectifier, the DC power containing a ripple, an inverter configured to convert the DC power smoothed by the smoothing unit into the AC power, a casing in which the rectifier, the smoothing unit and the inverter are accommodated, and an abnormality detection unit configured to detect an abnormality of at least one of the rectifier, the inverter and the casing. The smoothing unit includes at least one capacitor connected in parallel to an output of the rectifier, a first discharge resistor configured to discharge the capacitor, and a switching device connected in series to the first discharge resistor. The switching device is closed by the abnormality detection unit when an abnormality is detected by the abnormality detection unit, and the capacitor is discharged by the first discharge resistor when the switching device is closed.

Brief Description of Drawings

[0008]
[fig. 1] Fig. 1 is a block diagram illustrating a power supply apparatus according to an embodiment.
[fig. 2] Fig. 2 is a circuit diagram illustrating a smoothing unit of the power supply apparatus of Fig. 1.
[fig. 3] Fig. 3 is a circuit diagram illustrating a modification of a smoothing unit of the power supply apparatus of Fig. 1.
[fig. 4] Fig. 4 is a block diagram illustrating a power supply apparatus according to another embodiment.
[fig. 5] Fig. 5 is a circuit diagram illustrating a control unit of the power supply apparatus of Fig. 4.
[fig. 6] Fig. 6 is a circuit diagram illustrating the control unit of the power supply apparatus of Fig. 4.

Description of Embodiments

[0009]
Fig. 1 illustrates an example of a power supply apparatus according to an embodiment. Fig. 2 illustrates an example of a smoothing unit.
[0010]
A power supply apparatus 1 includes a rectifier 3 for converting AC power supplied from an AC power supply 2 into DC power, a smoothing unit 4 for smoothing the DC power having a ripple and output from the rectifier 3, and an inverter 5 for converting the DC power smoothed by the smoothing unit 4 into the AC power. In the present embodiment, the power supply apparatus 1 further includes a breaker 6 for cutting off the power supply to the rectifier 3 when an over-current flows to the rectifier 3 from the AC power supply 2, and the rectifier 3, the smoothing unit 4, the inverter 5 and the breaker 6 are housed in a casing 7.
[0011]
The rectifier 3 may perform rectification using a diode bridge, or variably rectify a smoothed DC voltage, using a semiconductor device such as a thyristor capable of controlling conduction based on an external signal. When the semiconductor device is used, the conduction of the semiconductor device is controlled by a control unit 8.
[0012]
The inverter 5 includes a full bridge circuit including, for example, four power semiconductor devices each capable of performing a switching operation, and generates high-frequency AC power through predetermined switching operations of the four power semiconductor devices. The high-frequency output may be set to a three-phase output through six power semiconductor devices. The switching operation of the power semiconductor device is controlled by the control unit 8.
[0013]
At this time, various types of power semiconductor devices capable of performing a switching operation, such as an insulated gate bipolar transistor (IGBT) and a metal-oxide-semiconductor field-effect transistor (MOSFET) can be used as the power semiconductor device, and silicon (Si) or silicon carbide (SiC) may be used as the semiconductor material.
[0014]
A load 9 including a heating coil is connected to an output of the inverter 5, and the high-frequency AC power generated by the inverter 5 is applied to the heating coil. Furthermore, a heating target is induction-heated by the heating coil. The heating target and the heating purpose are not specifically limited, but a heat treatment (quenching or the like) for a steel material and a welding operation for an electric resistance welded tube can be exemplified.
[0015]
As illustrated in Fig. 2, the smoothing unit 4 includes a capacitor 10, a reactor 11, a first discharge resistor 12, a second discharge resistor 13 and a switching device 14.
[0016]
The capacitor 10 is connected in parallel to the output of the rectifier 3, and removes or reduces a ripple included in the DC power of the rectifier 3. The capacitance of the capacitor 10 is properly set depending on an output of the power supply apparatus 1. For example, when the output of the power supply apparatus 1 is set to about 300 kW, the capacitance of the capacitor 10 can be set to about 20,000 μF (however, the capacitance is a value of a power supply apparatus with a significantly low ripple). At this time, an electrolytic capacitor whose capacitance can be easily increased may be used as the capacitor 10, but the capacitor 10 is not limited to the electrolytic capacitor.
[0017]
In the present embodiment, the reactor 11 is interposed between a positive electrode of the output of the rectifier 3 and a terminal of the capacitor 10 connected to the positive electrode side. The reactor 11 forms a low-pass filter in cooperation with the capacitor 10, and raises the ripple removing ability.
[0018]
The first discharge resistor 12 and the switching device 14 are connected in series to each other, and the first discharge resistor 12 and the switching device 14 connected in series are connected in parallel to the output of the rectifier 3. The switching device 14 can be opened/closed by the control unit 8, based on an external signal. When the switching device 14 is closed (electricity is conducted), the capacitor 10 is discharged through the first discharge resistor 12 and the switching device 14.
[0019]
An element having a mechanical contact, such as a magnet switch, which is opened/closed by attracting moving iron using an electromagnet, or a semiconductor device such as a thyristor is used as the switching device 14. However, the semiconductor device having a long lifetime may be preferably used rather than the element having a mechanical contact.
[0020]
The second discharge resistor 13 is connected in parallel to the first discharge resistor 12, and the capacitor 10 is always discharged through the second discharge resistor 13. The second discharge resistor 13 has a larger resistance value than the first discharge resistor 12. For example, the resistance value of the first discharge resistor 12 is several hundreds of Ω, and the resistance value of the second discharge resistor 13 ranges from several tens of kΩ to several hundreds of kΩ.
[0021]
The breaker 6 cuts off power supply to the rectifier 3 when an over-current flows from the AC power supply 2 to the rectifier 3, and transmits an abnormality signal indicating an abnormality of the rectifier 3 to the control unit 8 when cutting off the power supply to the rectifier 3.
[0022]
The control unit 8 includes a processor as a main part, for example. The control unit 8 controls a switching operation of the power semiconductor device of the inverter 5, and controls the conduction of a semiconductor device such as a thyristor when the semiconductor device is used in the rectifier 3. The control unit 8 closes the switching device 14 when the abnormality signal is input from the breaker 6.
[0023]
When the switching device 14 is closed, the capacitor 10 is discharged through the first discharge resistor 12 in addition to the second discharge resistor 13. The resistance value (e.g., several hundreds of Ω) of the first discharge resistor 12 is smaller than the resistance value (e.g., several tens of kΩ to several hundreds of kΩ) of the second discharge resistor 13, and a most portion of charge stored in the capacitor 10 flows to the first discharge resistor 12. As the discharge resistor has a smaller resistance value with respect to an inter-terminal voltage of the capacitor 10, the current flowing through the discharge resistor increases. When an abnormality of the rectifier 3 is detected by the breaker 6 and the control unit 8, the capacitor 10 can be rapidly discharged by the first discharge resistor 12 having a small resistance value. For example, when the capacitor 10 has a capacitance of 20,000 μF and the first discharge resistor 12 has a resistance value of 300 Ω, a discharge time constant is set to about six seconds.
[0024]
From the viewpoint of stability against heat generation, a resistor to which electricity is conducted at all times is operated at about 1/4 of the rated power. However, when the switching device 14 is closed in case of an abnormality, the charge stored in the capacitor 10 only flows to the first discharge resistor 12, and heat generation associated with the conduction of the first discharge resistor 12 is temporary. Therefore, the first discharge resistor 12 can be operated at or around the upper limit of the rated power. Accordingly, the number of resistors constituting the first discharge resistor 12 can be reduced, the manufacturing cost of the power supply apparatus 1 can be lowered, and the size of the power supply apparatus 1 can be reduced. For example, when the output voltage of the AC power supply 2 is 440 V and the rectifier 3 performs rectification through the diode bridge, the output voltage of the rectifier 3 becomes about 600 V. Moreover, when the resistance value of the first discharge resistor 12 is 300 Ω, a current flowing through the first discharge resistor 12 is a maximum of 2 A, and the power consumption of the first discharge resistor 12 is a maximum of 1,200 W. In this case, when a resistor having relatively high rated power, such as an enameled resistor, is used, the first discharge resistor 12 can be implemented by one resistor. That is because the first discharge resistor 12 is only used during discharging and used by a method of which the use rate is significantly low.
[0025]
When the power supply apparatus 1 is normally operated and stopped at normal times, that is, without detecting an abnormality, electricity is not conducted to the first discharge resistor 12, and power is not consumed by the first discharge resistor 12. Accordingly, the operation cost of the power supply apparatus 1 can be reduced.
[0026]
In order to rapidly discharge the capacitor 10 in case of an abnormality, the second discharge resistor 13 may be omitted. Preferably, however, when the second discharge resistor 13 is provided and the power supply apparatus 1 is normally operated and stopped, the capacitor 10 is always discharged through the second discharge resistor 13. The inter-terminal voltage of the capacitor 10 may temporarily rise in a transient state, for example, when the charging of the capacitor 10 is started. However, as the capacitor 10 is discharged through the second discharge resistor 13, an excessive voltage can be suppressed from being applied to the inverter 5, and the power semiconductor device of the inverter 5 can be protected.
[0027]
Since the resistance value of the second discharge resistor 13 is much higher than the resistance value of the first discharge resistor 12, for example, the resistance value ranges from several tens of kΩ to several hundreds of kΩ, the current flowing through the second discharge resistor 13 is extremely low, for example, the current ranges from several mA to several tens of mA. Therefore, although power is always consumed by the second discharge resistor 13, the power consumption is significantly low.
[0028]
Fig. 3 illustrates a modification of a smoothing unit 4.
[0029]
In an example illustrated in Fig. 3, the smoothing unit 4 includes a first capacitor 21 and a second capacitor 22 as capacitors connected in parallel to the output of the rectifier 3. The first capacitor 21 is connected through a diode 20, and the second capacitor 22 is directly connected. The smoothing unit 4 further includes a first discharge resistor 23, a second discharge resistor 24, a third discharge resistor 25 and a switching device 26.
[0030]
The first discharge resistor 23 and the switching device 26 are connected in series to each other, and the first discharge resistor 23 and the switching device 26 connected in series are connected in parallel to the first capacitor 21. The switching device 26 can be opened/closed by the control unit 8, based on an external signal.
[0031]
The second discharge resistor 24 is connected in parallel to the first discharge resistor 23, and the first capacitor 21 is always discharged through the second discharge resistor 24. In order to reduce the power consumption of the second discharge resistor 24, the resistance value of the second discharge resistor 24 may be set to a larger resistance value than that of the first discharge resistor 23. For example, the resistance value of the first discharge resistor 23 is several hundreds of Ω, and the resistance value of the second discharge resistor 24 ranges from several tens of kΩ to several hundreds of kΩ.
[0032]
The third discharge resistor 25 is connected in parallel to the second capacitor 22, and the second capacitor 22 is always discharged through the third discharge resistor 25. In order to reduce the power consumption of the third discharge resistor 25, the resistance value of the third discharge resistor 25 may be set to a larger resistance value than that of the first discharge resistor 23. For example, the resistance value of the first discharge resistor 23 is several hundreds of Ω, and the resistance value of the third discharge resistor 25 ranges from several tens of kΩ to several hundreds of kΩ.
[0033]
The first capacitor 21 connected in parallel to the output of the rectifier 3 through the diode 20 is charged when the inter-terminal voltage of the first capacitor 21 is lower than that of the second capacitor 22. Therefore, a ripple contained in the output of the rectifier 3 is basically removed or reduced by the second capacitor 22. Like the capacitor 10 of the smoothing unit 4 illustrated in Fig. 2, the second capacitor 22 is always discharged through the third discharge resistor 25, which makes it possible to suppress a rise in inter-terminal voltage of the second capacitor 22 in a transient state while protecting the power semiconductor device of the inverter 5. The first capacitor 21 forms a transient voltage suppression circuit in cooperation with the diode 20 and the second discharge resistor 24, and further suppresses a rise in inter-terminal voltage of the second capacitor 22 in a transient state. Since a rise in inter-terminal voltage of the second capacitor 22 in a transient state is suppressed by the transient voltage suppression circuit, the third discharge resistor 25 may be omitted.
[0034]
Preferably, the first capacitor 21 may have a lower capacitance than the second capacitor 22, and a film capacitor having a longer lifetime than an electrolytic capacitor, for example, may be suitably used as the first capacitor 21 having relatively low capacitance.
[0035]
In the embodiment illustrated in Fig. 3, when an over-current flows to the rectifier 3 from the AC power supply 2, the breaker 6 cuts off power supply to the rectifier 3 and an abnormal signal is transmitted from the breaker 6 to the control unit 8 such that the switching device 26 is closed by the control unit 8. When the switching device 26 is closed, the first capacitor 21 is first discharged through the first discharge resistor 23 in addition to the second discharge resistor 24. The resistance value (e.g., several hundreds of Ω) of the first discharge resistor 23 is smaller than the resistance value (e.g., several tens of kΩ to several hundreds of kΩ) of the second discharge resistor 24, and a most portion of charge stored in the first capacitor 21 flows to the first discharge resistor 23 such that the first capacitor 21 is rapidly discharged through the first discharge resistor 23. When the first capacitor 21 is discharged so that the inter-terminal voltage of the first capacitor 21 becomes lower than the inter-terminal voltage of the second capacitor 22, the second capacitor 22 is also rapidly discharged through the first discharge resistor 23. For example, when the first capacitor 21 has a capacitance of 7,000 μF, the second capacitor 22 has a capacitance of 20,000 μF, and the first discharge resistor 23 has a resistance value of 300 Ω, the discharge time constant is set to about eight seconds.
[0036]
In the present invention, it has been described that an abnormality is determined to occur in the power supply apparatus 1 when an over-current flows from the AC power supply 2 to the rectifier 3, and an abnormality of the rectifier 3 is detected by the breaker 6 and the control unit 8. However, door opening of the casing 7 may be detected as an abnormality of the power supply apparatus 1. For example, a door opening detection unit including an appropriate switch or sensor is installed at a door or door frame of the casing 7, and turned on or off depending on door opening of the casing 7, and door opening of the casing 7 is detected by the control unit 8, based on the on/off state of the door opening detection unit. When door opening of the casing 7 is detected, the switching device 14 in the smoothing unit 4 illustrated in Fig. 2 is closed by the control unit 8, and the capacitor 10 is rapidly discharged through the first discharge resistor 12. Furthermore, the switching device 26 in the smoothing unit 4 illustrated in Fig. 3 is closed by the control unit 8, and the first capacitor 21 and the second capacitor 22 are rapidly discharged through the first discharge resistor 23.
[0037]
As for an abnormality of the power supply apparatus 1, an abnormality of the inverter 5 may be detected. Referring to Figs. 4 to 6, an abnormality of the inverter 5 and a detection method thereof will be described. Furthermore, the same elements as those of the above-described power supply apparatus 1 are represented by the same reference numerals, and the detailed descriptions thereof are omitted or simplified.
[0038]
The control unit 8 includes a phase locked loop circuit (hereinafter, abbreviated to “PLL circuit”) 30 and an abnormality detection circuit 31. The PLL circuit 30 controls the frequency of AC power output from the inverter 5 such that the frequency of the AC power becomes the resonance frequency of the load 9 connected to the inverter 5. The inverter 5 includes a current transformer 32 for detecting a current I1 supplied to the load 9 and a voltage transformer 33 for detecting a voltage V1 applied to the load 9.
[0039]
As illustrated in Fig. 5, the PLL circuit 30 includes a phase comparison circuit 40, an analog adder/subtractor 41, a voltage control oscillator 42, and a control signal circuit 43. The phase comparison circuit 40 detects the phase of the current I1 detected by the current transformer 32 and the phase of the voltage V1 detected by the voltage transformer 33. The analog adder/subtractor 41 adds/subtracts a preset frequency setting value depending on the phase detected by the phase comparison circuit 40. The voltage control oscillator 42 outputs a signal at a frequency corresponding to the voltage output from the analog adder/subtractor 41. The control signal circuit 43 transmits a control signal to control terminals g1 to g4 of power semiconductor devices M1 to M4 of the inverter 5, according to the frequency of the signal output from the voltage control oscillator 42.
[0040]
The PLL circuit 30 controls the operating frequency of the inverter 5 to remove a phase shift between the current I1 supplied to the load 9 and the voltage V1 applied to the load 9, and the frequency of the AC power output from the inverter 5 coincides with the resonance frequency of the load 9 including an inductance component L and a capacitance component C. Therefore, the efficiency of the power supply apparatus 101 can be improved.
[0041]
However, when a part of the circuit on the load 9 side is shorted or an abnormality such as opening occurs, the impedance of the load 9 is rapidly changed, and the resonance frequency is significantly varied. Then, the PLL circuit 30 adjusts the operating frequency of the inverter 5 such that the operating frequency follows the resonance frequency of the load 9. In a transient state, a high current or voltage may be instantaneously generated in the inverter 5, and destroy the power semiconductor devices M1 to M4. In particular, when the phase of the current I1 advances to the phase of the voltage V1 due to the change of the impedance of the load 9, a high surge voltage may be generated, and the power semiconductor devices M1 to M4 may be destroyed by the surge voltage. The abnormality detection circuit 31 constitutes a phase shift detection unit in cooperation with the current transformer 32 and the voltage transformer 33, and detects a phase shift between the current I1 detected by the current transformer 32 and the voltage V1 detected by the voltage transformer 33.
[0042]
The current I1 detected by the current transformer 32 and the voltage V1 detected by the voltage transformer 33 are input to the abnormality detection circuit 31. As illustrated in Fig. 6, the abnormality detection circuit 31 includes a waveform shaper 50, a waveform shaper 51, a data flip-flop 52, a flip-flop 53, a comparator 54 and an inversion unit 55. The waveform shaper 50 adjusts the waveform of the input voltage V1 to a predetermined square wave. The waveform shaper 51 adjusts the waveform of the input current I1 to a predetermined square wave. The data flip-flop 52 serves as a phase shift detection unit for detecting a phase shift between the voltage V1 and the current I1. The flip-flop 53 serves as a latch for holding an output of the data flip-flop 52. The comparator 54 detects whether the magnitude of the current I1 has reached a reference value. The inversion unit 55 inverts an output signal of the comparator 54.
[0043]
The waveform shaper 50 includes a resistor 50A having a DC resistance value corresponding to a voltage input to the data flip-flop 52 and a capacitor 50B for cutting an unnecessary harmonic component contained in the waveform of the voltage V1. The waveform shaper 51 includes a resistor 51A having a DC resistance value corresponding to the voltage input to the data flip-flop 52 and a capacitor 51B for cutting an unnecessary harmonic component contained in the waveform of the current I1, like the waveform shaper 50.
[0044]
The data flip-flop 52 includes a clock input port CL for receiving a clock signal, a data input port D for receiving a data signal, a set input port S for receiving a set signal, a reset input port R for receiving a reset signal, and a set signal port Q for transmitting the set signal in a set state. When the clock signal and the data signal are input at the same time, the data flip-flop 52 is set in the set state, and transmits the set signal from the set signal port Q.
[0045]
The comparator 54 serves to compare the magnitudes of AC signals input to two input ports, respectively. One input port of the comparator 54 receives an AC signal indicating the value of the current I1 supplied to the load 9. The other input port of the comparator 54 receives an AC signal as a preset reference value, the AC signal being obtained by dividing a predetermined AC voltage V2 through a variable resistor 56. When the current I1 becomes higher than the reference value, the comparator 54 outputs a normal operation signal. The normal operation signal is inverted by the inversion unit 55 and sent to the reset input port R of the data flip-flop 52. The comparator 54, the inversion unit 55 and the variable resistor 56 form a mask unit 57 that continuously outputs the reset signal to the data flip-flop 52 until the value of the current I1 becomes higher than the reference value.
[0046]
In the above-described configuration, until the operation of the power supply apparatus 1 reaches the normal state after the power supply apparatus 1 has been activated, or specifically until the operating frequency of the inverter 5 coincides with the resonance frequency of the load 9 and the current I1 supplied to the load 9 becomes higher than the reference value, the mask unit 57 continuously outputs the reset signal to the data flip-flop 52, and the phase shift detection operation by the abnormality detection circuit 31 is paused. Accordingly, it is possible to remove failures which may occur when the current I1 supplied to the load 9 is destabilized and the power supply apparatus 1 in which the phase does not coincide with the voltage is forcibly stopped immediately after being activated. Furthermore, when the operation of the power supply apparatus 1 reaches the normal state, the phase shift detection operation by the abnormality detection circuit 31 is started.
[0047]
When the resonance frequency of the load 9 coincides with the operating frequency of the inverter 5 and the phases of the voltage V1 and the current I1 coincide with each other, the data flip-flop 52 is maintained in the reset state and does not transition to the set state, the set signal is not transmitted from the set signal port Q, and the operation of the power supply apparatus 1 is continued without any change.
[0048]
On the other hand, when an abnormality occurs in the load 9 and the resonance frequency of the load 9 is shifted from the operating frequency of the inverter 5, the phase of the voltage V1 and the phase of the current I1 do not coincide with each other, but the phase shift becomes an abnormality of the inverter 5. In such a state, the data flip-flop 52 transitions to the set state, and the set signal is transmitted from the set signal port Q. The set signal is input as an abnormality signal to the PLL circuit 30 through the flip-flop 53, the abnormality signal indicating the abnormality of the inverter 5.
[0049]
The PLL circuit 30 receiving the abnormality signal properly turns off the power semiconductor devices M1 to M4 and stops power supply to the load 9, and thus the power semiconductor devices M1 to M4 are protected. The abnormality signal is continuously output until the flip-flop 53 is reset. The switching device 14 in the smoothing unit 4 illustrated in Fig. 2 is closed by the control unit 8 which transmits and receives the abnormality signal between the PLL circuit 30 and the abnormality detection circuit 31 thereinside, and the capacitor 10 is rapidly discharged through the first discharge resistor 12. Furthermore, the switching device 26 in the smoothing unit 4 illustrated in Fig. 3 is closed, and the first capacitor 21 and the second capacitor 22 are rapidly discharged through the first discharge resistor 23.
[0050]
According to the above-described abnormality detection method of the inverter 5, an abnormality of the inverter 5 can be rapidly detected from a phase shift between the current I1 and the voltage V1, which is caused by a variation in resonance frequency of the load 9. Thus, the abnormality of the inverter 5 can be reliably detected before the operation of the PLL circuit 30 of controlling the operating frequency of the inverter 5 to follow the resonance frequency of the load 9 is ended. Furthermore, when the abnormality of the inverter 5 is detected, the power semiconductor devices M1 to M4 of the inverter 5 can be properly turned off, and thus a breakdown of the power semiconductor devices M1 to M4 is prevented in advance.
[0051]
The abnormality detection circuit 31 for detecting a phase shift between the current I1 and the voltage V1 is set in the set state by the data signal input at the same time as the clock signal, and the data flip-flop 52 transmits a set output as a signal in the set state. Only when the phases of the current I1 and the voltage V1 are shifted, the set signal (abnormality signal) is output from the data flip-flop 52. Therefore, the phase shift between the current I1 and the voltage V1 can be detected through the simple circuit configuration.
[0052]
The abnormality detection circuit 31 includes the mask unit 57 which compares the current value of the current I1 supplied to the load 9 to the preset reference value, and continuously outputs the reset signal to the data flip-flop 52 until the value of the current I1 becomes higher than the reference value. During the activation process of the power supply apparatus 1 in which the current I1 is destabilized and the phase of the current I1 and the phase of the voltage V1 do not coincide with each other, the phase shift detection operation of the abnormality detection circuit 31 is temporarily paused, which makes it possible to prevent the power supply apparatus 1 from being forcibly stopped immediately after the power supply apparatus 1 has been activated.
[0053]
The abnormality detection unit which is constituted by the breaker 6 and the control unit 8 and detects an abnormality of the rectifier 3, the abnormality detection unit which is constituted by the door opening detection unit and the control unit 8 and detects an abnormality of the casing 7, and the abnormality detection unit which is constituted by the current transformer 32, the voltage transformer 33 and the control unit 8 including the abnormality detection circuit 31 and detects an abnormality of the inverter 5 may be independently used or combined and used.
[0054]
This application claims priority to Japanese Patent Application No. 2017-185140 filed on September 26, 2017, the entire content of which is incorporated herein by reference.

Claims

[Claim 1]
A power supply apparatus comprising:
a rectifier configured to convert AC power into DC power, the AC power being supplied from an AC power supply;
a smoothing unit configured to smooth the DC power output from the rectifier, the DC power containing a ripple;
an inverter configured to convert the DC power smoothed by the smoothing unit into the AC power;
a casing in which the rectifier, the smoothing unit and the inverter are accommodated; and
an abnormality detection unit configured to detect an abnormality of at least one of the rectifier, the inverter and the casing,
wherein the smoothing unit includes:
at least one capacitor connected in parallel to an output of the rectifier;
a first discharge resistor configured to discharge the capacitor; and
a switching device connected in series to the first discharge resistor, and
wherein the switching device is closed by the abnormality detection unit when an abnormality is detected by the abnormality detection unit, and the capacitor is discharged by the first discharge resistor when the switching device is closed.
[Claim 2]
The power supply apparatus according to claim 1, wherein the smoothing unit further includes a second discharge resistor connected in parallel to the first discharge resistor, and is configured to always discharge the capacitor, and
wherein the second discharge resistor has a larger resistance value than the first discharge resistor.
[Claim 3]
The power supply apparatus according to claim 1, wherein the smoothing unit includes a first capacitor connected to the output of the rectifier through a diode and a second capacitor connected in series to the output of the rectifier and having a larger capacitance than the first capacitor, as the capacitor, and
wherein the first discharge resistor is connected in parallel to the first capacitor.
[Claim 4]
The power supply apparatus according to claim 3, wherein the smoothing unit further includes a third discharge resistor connected in parallel to the second capacitor, and configured to always discharge the second capacitor, and
wherein the third discharge resistor has a larger resistance value than the first discharge resistor.
[Claim 5]
The power supply apparatus according to claim 1, wherein the switching device has a mechanical contact.
[Claim 6]
The power supply apparatus according to claim 1, wherein the switching device is a semiconductor device.
[Claim 7]
The power supply apparatus according to any one of claims 1 to 6, wherein the abnormality detection unit includes a breaker configured to cut off power supply to the rectifier when an over-current flows from the AC power supply to the rectifier, and closes the switching device when the power supply to the rectifier is cut off by the breaker.
[Claim 8]
The power supply apparatus according to any one of claims 1 to 6, wherein the abnormality detection unit includes a door opening detection unit configured to detect door opening when the casing is opened, and closes the switching device when door opening is detected by the door opening detection unit.
[Claim 9]
The power supply apparatus according to any one of claims 1 to 6, wherein the inverter is controlled to have an output frequency corresponding to a resonance frequency of a load connected to the power supply apparatus, and
wherein the abnormality detection unit includes a phase shift detection unit configured to detect a phase shift between an output current and an output voltage of the inverter, and closes the switching device when a phase shift is detected by the phase shift detection unit.

Drawings

[ Fig. 1]

[ Fig. 2]

[ Fig. 3]

[ Fig. 4]

[ Fig. 5]

[ Fig. 6]