WO2010098084A1

WO2010098084A1 - Power factor correction circuit with overcurrent protection

Info

Publication number: WO2010098084A1
Application number: PCT/JP2010/001227
Authority: WO
Inventors: Akihiro Kyogoku; Yoshiaki Doyama; Hidehisa Tanaka; Tomohiro Kawasaki
Original assignee: Panasonic Corporation
Priority date: 2009-02-26
Filing date: 2010-02-24
Publication date: 2010-09-02
Also published as: CN102334269B; JP2010226941A; CN102334269A; JP5549187B2

Abstract

The invention relates to a circuit for switching a DC power supply apparatus. The circuit short-circuits and opens an AC voltage supplied from an AC voltage source (1) through an inductive element (2) using a switching means (4), at least once in a half-cycle period of the AC voltage, in order to convert the AC voltage supplied from the AC voltage source (1) to a DC voltage. The switching means (4) is short-circuited for a predetermined time period prior to the switching means (4) commencing a switching operation after switching on, and a current detecting means (3) detects a current flowing through one of the inductive element (2) and the switching means (4). The switching operation is not commenced if a magnitude of the detected current value is greater than a predetermined current level, thereby protecting an apparatus when the inductive element (2) is in an abnormal short-circuiting state.

Description

CIRCUIT FOR SWITCHING A DC POWER SUPPLY APPARATUS

The present invention relates to a circuit for switching a DC power supply according to claim 1, a DC power supply apparatus for converting an AC voltage supplied from an AC voltage source to a DC voltage according to claim 13 and a corresponding method according to claim 14.

A DC power supply apparatus is known in which an AC voltage which is supplied from an AC voltage source through an inductive element is short-circuited and opened, by using a switching device, at least once in a half-cycle period of the AC voltage, wherein the AC voltage supplied from the AC voltage source is converted to a DC voltage. In the DC power supply apparatus, when an inductance value of the inductive element or circuit is substantially reduced, for example due to an inductive winding being subjected to short-circuiting between loops or layers of the inductive element, an increase in a peak value of a current flowing through the switching device and/or an increase in a ripple current flowing through the inductive element causes an increase in heat generation. Therefore, it is necessary to use a switching device providing a sufficient design margin, or to detect an abnormal state in some way so as to prevent the switching device and/or the inductive element (for example, an inductive coil) from being in an abnormal overheating state.
Japanese Laid-Open Patent Publication No. 2007-300697 discloses a method for avoiding abnormal overheating occurring when an inductive element is in an abnormal short-circuiting state. According to this prior art, a power supply circuit controller as shown in FIG. 10 is known which includes: a signal output section 101 for outputting a PAM (pulse amplitude modulation) control signal for controlling a switching means 106; an overcurrent detecting section for detecting a current flowing through the switching means 106 and outputting an overcurrent detection signal when an instantaneous value of the detected current is greater than a predetermined level; and a short-circuit determination section 104 for determining, when the number of times the overcurrent detection signal is detected is greater than a predetermined number of times (for example, X = 100 times) during a predetermined time period (for example, T = 3s), that an inductive element 2 is short-circuited; and wherein the power supply circuit controller corrects an input current and controls an input current value when the short-circuit determination section 104 determines that the inductive element 2 is short-circuited, thereby suppressing an increase in an input current flowing through a DC power supply apparatus such as an AC-DC converter.

Unexamined Japanese Patent Publication No. 2007-300697

However, the conventional DC power supply apparatus as described above can only detect whether or not the inductive element is short-circuited after a switching operation for power factor correction is actually commenced.
Therefore, it is necessary to allow for a state in which a peak value of a current flowing through the switching device is temporarily increased, such that it is necessary to use a switching device in which a value of a maximum rated current is greater than a value of a current which actually flows when the inductive element has a normal inductance value, so as to provide a sufficient margin.
The present invention deals with the aforementioned problems at least to some extent, and an object of the present invention is in particular to realize a simplified configuration in which short-circuiting is detected for an inductive element prior to a switching operation for power factor correction which is commenced after switching on. When an abnormal short-circuiting state is detected, a protecting operation is performed such that the switching operation is prevented from being performed. Therefore, an excessive current is prevented from flowing through the switching device even when the inductive element is short-circuited, thereby securely preventing an overheating state. Accordingly, it is possible to realize the protecting operation for protecting an apparatus in a simplified configuration, by using a switching device having a reduced maximum rated current.

In order to at least partly solve the aforementioned problems of the conventional art, a circuit according to claim 1 is proposed. In addition, a DC power supply apparatus according to claim 13 and a corresponding method according to claim 14 are proposed. The circuit of the present invention is particularly useful in a DC power supply apparatus, wherein the DC power supply apparatus short-circuits and opens an AC voltage which is supplied from an AC voltage source through an inductive element by using a switching means, at least once in a half-cycle period of the AC voltage, to convert the AC voltage supplied from the AC voltage source to a DC voltage. The DC power supply apparatus includes: a phase detecting means for the AC voltage source; and a current detecting means for detecting a current flowing through one of the inductive element and the switching means; wherein a short-circuiting operation for short-circuiting the switching means is performed for a predetermined period prior to a switching operation which is commenced by the switching means after switching on. If a magnitude of a value of a current which flows through one of the inductive element and the switching means in the short-circuiting operation is greater than a predetermined current level, the switching operation is not performed.
In the following, the circuit according to the invention is described within the technical environment of a DC power supply apparatus. However, it is clear that the circuit of the invention can be configured as a stand-alone circuit which can be assembled with other components to form a DC power supply.
Furthermore, in the DC power supply apparatus according to the present invention, the short-circuiting operation for short-circuiting the switching means is also performed after the switching operation is commenced, for a predetermined short-circuiting period, at predetermined time intervals and in a predetermined voltage phase of an AC voltage supplied from the AC voltage source, and a value of a current flowing through said one of the inductive element and the switching means during the short-circuiting operation is detected, and the switching operation is stopped when a magnitude of the detected value of the current is greater than the predetermined current level.
One special advantageous effect of the present invention is that in the DC power supply apparatus according to the present invention, a switching device in which a maximum rated current is reduced can be used. Thus, even when the inductive element is short-circuited, a protecting stop operation can be performed without allowing a high current to flow through the switching means, before a switching operation is commenced after switching on. It is thus possible to prevent an overheating state from being caused by the switching operation and to prevent thermal stress from being applied to the switching means. It is thus possible to protect an apparatus by using a simple and low-price configuration.

Fig. 1 is a diagram illustrating a configuration of a DC power supply apparatus according to a first embodiment of the present invention. Fig. 2A is a diagram illustrating an example configuration of a phase detecting means for use in the DC power supply apparatus, and phase detection as performed by the phase detecting means, according to the present invention. Fig. 2B is a diagram illustrating an example of phase detection as performed by the phase detecting means, according to the present invention. Fig. 3 is a diagram illustrating an input current waveform detected in a normal operating state, according to the first embodiment of the present invention. Fig. 4A is a diagram illustrating waveforms at respective portions which are detected when short-circuiting is detected for an inductive element in a normal state according to the first embodiment of the present invention. Fig. 4B is a diagram illustrating waveforms at the respective portions which are detected when short-circuiting is detected for the inductive element, wherein an inductance value is less than a normal value, according to the first embodiment of the present invention. Fig. 5 is a diagram illustrating a configuration of a DC power supply apparatus according to a second embodiment of the present invention. Fig. 6 is a diagram illustrating an input current waveform detected in a normal operating state, according to the second embodiment of the present invention. Fig. 7A is diagram illustrating waveforms at respective portions which are detected when short-circuiting is detected for an inductive element in a normal state according to the second embodiment of the present invention. Fig. 7B is a diagram illustrating waveforms at the respective portions which are detected when short-circuiting is detected for the inductive element, wherein an inductance value is less than a normal value, according to the second embodiment of the present invention. Fig. 8 is a diagram illustrating a configuration of a DC power supply apparatus according to a third embodiment of the present invention. Fig. 9 is a diagram illustrating waveforms at respective portions which are detected when short-circuiting is detected for an inductive element, according to the third embodiment of the present invention. Fig. 10 is a diagram illustrating a configuration of a conventional DC power supply apparatus.

A first embodiment of the invention is directed to a DC power supply apparatus that short-circuits and opens an AC voltage which is supplied from an AC voltage source through an inductive element (referred to in the following as a coil) by using a switching means, at least once in a half-cycle period of the AC voltage, to convert the AC voltage supplied from the AC voltage source to a DC voltage. The DC power supply apparatus includes: a phase detecting means for the AC voltage source; and a current detecting means for detecting a current flowing through one of the coil and the switching means; wherein a short-circuiting operation for short-circuiting the switching means is performed for a predetermined period prior to a switching operation which is commenced by the switching means after switching on. If a magnitude of a current value which is detected by the current detecting means during the short-circuiting operation is greater than a predetermined current level, the switching operation is not performed or is interrupted.
It is thus possible to detect whether or not an inductance value of the coil is reduced, prior to the switching operation being actually commenced. Accordingly, it is possible to detect whether or not the coil is in an abnormal short-circuiting state, without allowing an excessive current to flow through the switching means.
When the current detecting means detects a current flowing through the switching means, it is unnecessary to determine whether or not the current detected by the current detecting means is a current detected when the switching means is short-circuited (ON). It is thus possible to detect short-circuiting of the coil using a simplified configuration as compared to a scenario in which a current flowing through the coil is detected.
According to a second embodiment of the invention based on the first embodiment of the invention, the short-circuiting operation is performed multiple times. Therefore, when instantaneous power failure occurs during one of the short-circuiting operations, it is possible to reduce the risk that abnormal short-circuiting cannot be detected.
According to a third embodiment of the invention based on the second embodiment, when the current value detected by the current detecting means becomes greater than the predetermined current level for at least a predetermined and/or preadjustable number of times, for example twice, during the short-circuiting operation, the switching operation is not performed. It is thus possible to reduce the risk that abnormal short-circuiting is erroneously detected due to noise generated in a circuit.
According to a fourth embodiment which is based on one of the second and third embodiments, a voltage phase in which the short-circuiting operation is performed is determined such that the greater the number of times the short-circuiting operation is performed, the greater an absolute value of an instantaneous voltage supplied from the AC voltage source. Therefore, the smaller an inductance value of the coil, the smaller the number of times the short-circuiting operation is performed in order to detect an abnormal state, and the same effect as that of the second or third embodiments is realized by substantially reducing a current which flows through the switching means when the coil is abnormally short-circuited.
According to a fifth embodiment based on one of the second and third embodiments, the short-circuiting operation is performed such that the greater the number of times the short-circuiting operation is performed, the longer the predetermined short-circuiting period. Therefore, in a similar way to the fourth embodiment, the same effect as that of the second or third embodiments is realized by substantially reducing a current which flows through the switching means when the coil is abnormally short-circuited.
In a sixth embodiment based on one of the second and third embodiments, the short-circuiting operation is performed at least once at each of a positive polarity and a negative polarity which are represented by the AC voltage supplied from the AC voltage source. Therefore, even if the DC power supply apparatus has an asymmetrical circuit configuration or a circuit symmetrical performance is unbalanced between a positive polarity and a negative polarity of the AC voltage source, for example due to one of two switching devices of the DC power supply apparatus being in an abnormal state, it is possible to detect an abnormal short-circuiting state of the coil (or transformer).
In a seventh embodiment based on the fifth embodiment, the greater the number of times the short-circuiting operation is performed, the higher the predetermined current level. It is thus possible to detect whether or not the coil has an abnormal inductance value, in a phase in which an absolute value of an instantaneous voltage supplied from the AC voltage source is reduced, thereby substantially reducing a current flowing through the switching means when the coil is in an abnormal short-circuiting state.
In an eighth embodiment based on the sixth embodiment, the greater the number of times the short-circuiting operation is performed, the higher the predetermined current level. It is thus possible to detect whether or not the coil has an abnormal inductance value, by performing the short-circuiting operation in a reduced short-circuiting period, thereby substantially reducing a current flowing through the switching means when the coil is in an abnormal short-circuiting state.
A ninth embodiment, which is based on one of the second and third embodiments, features a voltage detecting means for the AC voltage source, and the greater an absolute value of an instantaneous voltage of an AC voltage during the short-circuiting operation, the higher the predetermined current level. Therefore, an influence of variation in the AC voltage can be alleviated or decreased, thereby enhancing the accuracy of detecting an inductance value of the coil (or transformer).
According to a tenth embodiment of the invention which is based on any one of the first to third embodiments, the predetermined short-circuiting period used for at least the short-circuiting operation when performed for the first time is set so as to be less than or equal to a time period corresponding to a short-circuit capability of a switching device of the switching means. Therefore, even when the coil is in a dead short state, the switching means is reliably prevented from being damaged, even if an overcurrent protecting circuit capable of operating at a high speed is not used.
In an eleventh embodiment based on any one of the first to third embodiments, the phase detecting means is formed by using a photocoupler. A low-price configuration is thus realized.
In a twelfth embodiment of the invention, based on any one of the first to third embodiments, the predetermined current level is set so as to be lower than a maximum value of a current which flows through the switching means in a normal operating state. Therefore, a current which flows through the switching means for detecting a short-circuit in the coil is reduced so as to be within a range of values detected in a normal operating state, thereby realizing the switching means by using a device in which a necessary maximum rated current is minimized.
According to a thirteenth embodiment of the invention based on any one of the first to third embodiments, a current is detected during the short-circuiting operation by performing AD conversion once during the predetermined short-circuiting period. Therefore, the load on the AD conversion and control means can be suppressed, thereby realizing a simplified and low-price configuration.
The DC power supply apparatus for controlling an input current in the PWM (pulse width modulation) control in a normal operating state also exerts the effect that synchronization can easily be achieved by the short-circuiting operation, such that the AD conversion is performed in synchronization with a carrier cycle period of the PWM control.
In a fourteenth embodiment based on any one of the second and third embodiments, an absolute value of an instantaneous voltage which is supplied from the AC voltage source when the short-circuiting operation is commenced is the same, and the predetermined short-circuiting period is the same, in some or all of the process steps of the short-circuiting operation. Therefore, even if due to instantaneous power failure or noise, it is detected once during some of the process steps that the coil is not in an abnormal short-circuiting state although the coil is actually in an abnormal short-circuiting state, it is unnecessary to increase a voltage phase of an AC voltage from the AC voltage source in which the short-circuiting operation is commenced or to lengthen a short-circuiting period. Accordingly, it is possible to reduce a value of a current which flows through the switching means when the coil is in an abnormal short-circuiting state.
Furthermore, in a fifteenth embodiment of the invention which is based on any one of the first to third embodiments, after the switching operation is commenced after the short-circuiting operation is ended, the short-circuiting operation for short-circuiting the switching means is performed for a predetermined period, at least once in a predetermined period, in a predetermined voltage phase of an AC voltage supplied from the AC voltage source or in a voltage phase in which an instantaneous voltage supplied from the AC voltage source indicates a predetermined absolute value, and the switching operation is stopped when a magnitude of a value of a current which is detected by the current detecting means in the short-circuiting operation becomes greater than the predetermined current level. Therefore, during a normal operation, it is detected whether or not an inductance value of the coil (or transformer) is reduced, thereby enabling the switching operation to be immediately stopped for protection purposes.
In a sixteenth embodiment based on the fifteenth embodiment, the short-circuiting operation is performed near a zero-cross point of an AC voltage supplied from the AC voltage source. It is thus possible to substantially decrease the distortion of an input current waveform and/or an influence on a power factor in a normal operating state.
Embodiments of the present invention are described below with reference to the drawings. It should be noted that the present invention is not limited to the embodiments described below. Furthermore, corresponding electrical and/or electronic elements or parts or functional arrangements of the different embodiments can be combined with those of other embodiments in order to realize comparable effects or circuits which at least partly solve at least one of the objects of the invention. It is in particular possible to replace elements in one embodiment with corresponding elements of other embodiments having the same reference numbers.

Figure 1 is a diagram illustrating a configuration of a DC power supply apparatus according to a first embodiment of the present invention.
As shown in Figure 1, the DC (direct current) power supply apparatus according to the present embodiment includes: an inductive element, for example a coil or coil arrangement, referred to in the following as a coil 2 connected to one of the AC lines from an AC (alternating current) voltage source 1; a current detecting means 3 for detecting a current flowing through the coil 2; a bidirectional-type switching means 4 which short-circuits and opens an AC voltage which is supplied from the AC voltage source 1 through the coil 2; a rectifier circuit 5 in which one of the AC input terminals is connected to a connection portion between the switching means 4 and the coil 2; a smoothing capacitor 6 connected between DC output terminals of the rectifier circuit 5; and

capacitors

7a and 7b which are connected between the DC output terminals and the other of the AC input terminals, respectively, thereby forming a voltage-doubler rectifier circuit. A DC voltage is supplied to a load 8.
The DC power supply apparatus according to the present embodiment also includes: a phase detecting means 9 connected to both of the AC lines from the AC voltage source 1, for detecting a voltage phase of an AC voltage supplied from the AC voltage source 1; and a control means 10 for controlling the ON and OFF states of the bidirectional-type switching means 4 which is formed by a combination of a diode bridge and one IGBT (insulated gate bipolar transistor) or by two Power MOSFETs which are connected so as to be oriented in opposite directions, such that an input current supplied from the AC voltage source 1 represents an almost sinusoidal current waveform.
Figure 2 is a diagram illustrating an example configuration of the phase detecting means 9.
Although the phase detecting means 9 may be formed by using a voltage transformer (PT) for detecting a voltage, the phase detecting means 9 is preferably formed as a circuit including a photocoupler, a resistor and the like as shown in Figure 2A. In this case, as shown in Figure 2B, the phase detecting means 9 detects a zero-cross point of an AC voltage supplied from the AC voltage source 1 and estimates a voltage phase of the AC voltage supplied from the AC voltage source 1, based on the detected zero-cross point. A low-price configuration can thus be realized.
Figure 3 is a diagram illustrating an input current waveform which is detected when the DC power supply apparatus according to the present embodiment is in a normal operating state.
As shown in Figure 3, the control means 10 of the DC power supply apparatus according to the present embodiment controls the ON and OFF states of the switching means 4 based on PWM (pulse width modulation) control using, as a carrier frequency, about 20 kHz which corresponds to a non-audible frequency range, and rectifies an input current waveform to an almost sinusoidal waveform, in order to step-up the voltage and perform PFC (power factor correction).
The DC power supply apparatus according to the present embodiment detects short-circuiting in the coil or coil arrangement 2 prior to a switching operation which is commenced after switching on, based on the PWM control for power factor correction. When it is determined that an inductance value is less than a normal value, a protecting operation is performed such that the subsequent switching operation is not performed.
According to the present embodiment, the current detecting means 3 is connected in series with the coil 2. The current detecting means 3 is provided for detecting a current flowing through the coil 2. Therefore, the current detecting means 3 may be connected to the other AC line which is opposite to the AC line to which the coil 2 is connected, instead of the current detecting means 3 being connected in series with the coil 2 as shown in Figure 1.
The short-circuiting detection for the coil 2 will now be described in detail.
Figure 4A and Figure 4B are diagrams illustrating waveforms, at respective portions, which are detected when short-circuiting is detected for the coil 2 of the DC power supply apparatus according to the present embodiment.
Figure 4A shows an AC voltage from the AC voltage source 1, a current flowing through the coil 2 and a short-circuiting signal from a control section, which are detected when the coil or arrangement of windings is in a normal state.
As shown in Figure 4A, a control signal generating section 10a in the control means 10 generates a control signal in order to force the switching means 4 to be short-circuited, for a short-circuiting period (for example, 5 micro sec) and in predetermined short-circuiting phases (for example, A1 ( = 10 deg) and A2 ( = 190 deg) as shown in Figure 4A) of an AC voltage supplied from the AC voltage source 1, in order to force the switching means 4 to be short-circuited, and the current detecting means 3 detects a current flowing through the coil 2 in a short-circuiting operation. It should be noted that the short-circuiting period and the predetermined short-circuiting phases described above are stored beforehand in the storage section 10c.
Using a coil short-circuit detecting section 10b, the control means 10 compares a magnitude of a detected current value with a determined current level which is stored beforehand in the storage section 10c, and when the detected current value is greater than the determined current level, the control means 10 determines that the coil 2 is in an abnormal state in which an inductance value of the coil 2 is less than a normal value, and the protecting operation is performed, such that the switching means 4 is then maintained in the OFF state, and the switching operation for power factor correction is not performed, thereby preventing a high current from flowing through the switching means 4.
The determined current level is set in sufficient consideration of the variation in the current value which is determined based on a product of a forced short-circuiting period and a gradient dI/dt. The gradient dI/dt represents an increase in current and is obtained by dividing a magnitude of an AC voltage supplied from the AC voltage source 1 by a normal inductance value of the coil 2. Therefore, the determined current level corresponds to a value which is less than or equal to about 1/2 of the normal inductance value of the coil 2.
The current is detected by using a current sensor such as a CT (current transformer) and an AD (analog-digital) converter in a microcomputer. However, the current may be detected by using a peak hold circuit which detects a maximum value, or by using a maximum value among values of a plurality of detected currents.
The short-circuiting operation and the AD conversion may also be performed in synchronization with a carrier cycle period of the PWM control, and a result of the AD conversion based on only the center value detected in the short-circuiting period may be used, and the determined current level may be set to a value which is less than a current value determined on the basis of a product of the forced short-circuiting period and the gradient dI/dt, thereby synchronizing the short-circuiting operation and the current detection by using a simplified configuration,.
Furthermore, when a photocoupler is used for the phase detecting means 9, a time period which is longer than or equal to at least one cycle period of an AC voltage supplied from the AC voltage source 1 is necessary after switching on in order to accurately estimate a voltage phase of the AC voltage supplied from the AC voltage source 1. Therefore, short-circuiting is detected for the coil 2 when a few cycle periods of the AC voltage supplied from the AC voltage source 1 have elapsed after switching on, thereby enabling a voltage phase of the AC voltage supplied from the AC voltage source 1 to be reliably estimated.
In an example of Figure 4A, in order to perform short-circuiting detection for the coil 2, the switching means 4 is forced to be short-circuited once at a positive polarity represented by the AC voltage supplied from the AC voltage source 1, and once at a negative polarity represented by the AC voltage supplied from the AC voltage source 1. However, in either case, the detected current value is less than the determined current level, such that the coil 2 is determined as being in a normal state.
Consequently, the control means 10 commences the switching operation for power factor correction (not shown) and performs the switching operation for obtaining an input current waveform as shown in Figure 3, thereby continuing the operation.
As shown in Figure 4A, since the determination is made when the AC voltage supplied from the AC voltage source 1 represents the positive polarity, and when the AC voltage supplied from the AC voltage source 1 represents the negative polarity, the symmetrical property represented by the circuit can be checked, in addition to the short-circuiting detection being performed for the coil 2.
That is to say, when the diodes and switching devices included in the switching means 4 are partially in abnormal states, currents detected in the short-circuiting operation are different between the scenario in which the AC voltage supplied from the AC voltage source 1 represents a positive polarity and the scenario in which the AC voltage supplied from the AC voltage source 1 represents a negative polarity. Therefore, when a degree of imbalance is checked, it is also possible to check for the abnormal state as described above, prior to the switching operation.
Furthermore, when currents are detected, the short-circuiting operation is performed multiple times, and the short-circuiting operation is performed for the same short-circuiting period each time, thereby suppressing influences of an instantaneous power failure and noise.
Figure 4B shows waveforms, at respective portions, which are detected when an inductance value of the coil 2 is less than a normal value.
In an example shown in Figure 4B, currents which each indicate a value greater than the determined current level stored in the storage section 10c are detected in both of the forced short-circuiting operations performed twice (B1 and B2 in Figure 4B), and it is thus determined that the coil 2 is in an abnormal short-circuiting state, such that no subsequent switching operation is performed.
As shown in Figure 4, since the short-circuiting operation is performed multiple times, it is possible to reduce the risk that a current cannot be detected and therefore that an abnormal short-circuiting state of the coil cannot be detected, even if an instantaneous power failure occurs in the forced short-circuiting operation.
Furthermore, when the currents detected in some of the multiple short-circuiting operations which are performed for the same short-circuiting period indicate values which are greater than the determined current level, the current detection is likely to be influenced by noise (not shown). Therefore, only when detected currents indicate values which are greater than the determined current level for a predetermined number of times which is at least two is it determined that the coil 2 is in an abnormal short-circuiting state, and the protecting operation is performed, such that the switching operation is stopped, thereby enabling the risk of an erroneous detection caused by the noise to be reduced.
The determined current level used for detecting an abnormal state is set as a value which is less than a maximum value of a current which flows through the switching means 4 in a normal operating state. The short-circuiting period is set to a reduced time period so as to keep a magnitude of a value of a current flowing through the switching means 4 from reaching the determined current level when an inductance value of the coil 2 is within a normal range.
Consequently, the protecting operation is performed such that an operation for power factor correction is not performed in the subsequent switching operation, thereby preventing an excessive current from flowing through the switching means 4 even when an inductance value of the coil or coil arrangement 2 is abnormally small.
Furthermore, the short-circuiting period is set as a time period which is shorter than or equal to a time period corresponding to a short-circuit capability ( i.e. shorter than a permissible short-circuit time) of the switching device of the switching means 4.
In general, when the coil 2 is almost in a dead short state, the gradient dI/dt representing an increase in a current flowing through the switching means 4 is substantially increased. Therefore, it is necessary to provide an overcurrent protecting circuit operating at a high response speed while controlling the gradient dI/dt, such that dI/dt in the OFF state is not increased, in order to reliably protect the switching device of the switching means 4 so as to prevent the switching device from being damaged.
However, in the DC power supply apparatus according to the present embodiment, the short-circuiting period is set so as to be shorter than or equal to a time period corresponding to a short-circuit capability of the switching device. Therefore, the device cannot be damaged, and overcurrent protection performed at a high response speed is not required in order to protect the switching means 4, even if the coil 2 is almost in a dead short state.
As described above, the DC power supply apparatus according to the present embodiment forces the AC voltage which is supplied from the AC voltage source 1 through the coil 2 to be short-circuited for a short time period prior to the switching operation for power factor correction, and when a flowing current indicates a value which is greater than the determined current level, the protecting operation is performed such that the switching operation for the power factor correction is not performed. Therefore, an excessive current is prevented from flowing through the switching means 4 even if the coil 2 is in an abnormal state, such as in a layer short state, and it is thus possible to form the switching means 4 using a switching device in which a maximum rated current is reduced.
Furthermore, in the DC power supply apparatus according to the present embodiment, the forced short-circuiting operation is also performed, in a predetermined voltage phase of the AC voltage supplied from the AC voltage source 1, after the switching means 4 commences the switching operation for power factor correction, and the detected current value is compared with the determined current level in the short-circuiting detection, whereby it is also possible to detect whether or not the coil 2 has an abnormal inductance value during operation (not shown).
That is to say, the detection control as described above is performed at least once in a predetermined time period which ranges from about a half-cycle period of the AC voltage supplied from the AC voltage source 1 to about several tens of seconds. It is thus possible to immediately stop the apparatus for protection purposes without continuing, for a time period longer than or equal to the predetermined time period described above, an abnormal state in which a lot of ripple currents occur, even when an inductance value of the coil 2 is reduced during operation.
Moreover, the forced short-circuiting operation described above is performed near the zero-cross point of the AC voltage supplied from the AC voltage source 1. Therefore, influences of distortion in the input current and the reduction of the power factor can be almost disregarded, as can be seen from the current waveforms shown in Figure 3 and Figure 4. It is possible to continue the operation while the short-circuiting detection is constantly performed for the coil, thereby immediately and reliably stopping the apparatus for protection purposes, even when an inductance value of the coil is reduced during operation.

Figure 5 is a diagram illustrating a configuration of a DC power supply apparatus according to another embodiment of the present invention.
As shown in Figure 5, the DC power supply apparatus according to the present embodiment includes: a coil 2 connected to one of the AC lines from an AC voltage source 1; a bidirectional-type switching means 4 which short-circuits and opens an AC voltage which is supplied from the AC voltage source 1 through the coil 2; a current detecting means 3 for detecting a current flowing through the switching means 4; a rectifier circuit 5 in which one of the AC input terminals is connected to a connection portion between the switching means 4 and the coil 2; and a smoothing capacitor 6 which is connected between DC output terminals of the rectifier circuit 5. A DC voltage is supplied to a load 8.
The DC power supply apparatus according to the present embodiment also includes: a phase detecting means 9 connected to both of the AC lines of the AC voltage source 1, for detecting a voltage phase of an AC voltage supplied from the AC voltage source 1; and a control means 10 for controlling the ON and OFF states of the bidirectional-type switching means 4 which is formed for example by two IGBTs which are connected so as to be opposite to each other and oriented in opposite directions. These electric elements can for example also be used instead of the corresponding parts in the other embodiments.
Figure 6 shows an example input current waveform which is detected when the DC power supply apparatus according to the present embodiment is in a normal operating state.
As shown in Figure 6, the control means 10 in the DC power supply apparatus according to the present embodiment short -circuits and opens the switching means 4 once or several times in a half-cycle period of an AC voltage supplied from the AC voltage source 1, in order to convert the AC voltage supplied from the AC voltage source 1 to a DC voltage and to perform power factor correction.
Figure 7A and Figure 7B show waveforms, at respective portions, which are detected when short-circuiting is detected for the coil in the DC power supply apparatus according to the present embodiment.
Figure 7A shows waveforms, at the respective portions, which are detected when the coil is in a normal state.
As shown in Figure 7A, the control means 10 in the DC power supply apparatus according to the present embodiment forces the switching means 4 to be short-circuited, for a short time period which is stored beforehand in the storage section 10c, and in a voltage phase which is stored beforehand in the storage section 10c, of an AC voltage supplied from the AC voltage source 1, after detection of a voltage phase of an AC voltage supplied from the AC voltage source 1 is enabled after switching on.
Furthermore , a value of a current flowing through the switching means 4 is detected in the forced short-circuiting operation, and when the detected value of the current is greater than a determined current level stored in the storage section 10c, the protecting operation is performed, such that the subsequent switching operation is not performed.
Furthermore, in the configuration of the first embodiment, even when the switching means 4 is OFF, an input current flows through the load 8 in a voltage phase in which an instantaneous voltage of an AC voltage supplied from the AC voltage source 1 is higher than a DC voltage of the smoothing capacitor 6, and a current thus flows through the current detecting means 3 for a certain time period, even if the switching means 4 is OFF. However, in the configuration of the present embodiment, as shown in Figure 7A, a current only flows through the current detecting means 3 when the switching means 4 is ON.
Therefore, in the DC power supply apparatus of the first embodiment, when the determined current level used for detecting an abnormal state cannot be set, for the short-circuiting detection, so as to be sufficiently higher than a generally estimated input current value, it is necessary to check whether or not a current detected by the current detecting means 3 is a current detected when the switching means 4 is short-circuited (ON), based for example on voltage phase information of an AC voltage supplied from the AC voltage source 1 and/or information from the control means 10 indicating whether the switching means 4 is ON or OFF. However, in the DC power supply apparatus according to the present embodiment, it is unnecessary to determine whether or not a current detected by the current detecting means 3 is a current detected when the switching means 4 is short-circuited (ON).
That is to say, according to the present embodiment, it is possible to perform the forced short-circuiting in any voltage phase, enabling the apparatus to be more freely designed, and short-circuiting can be detected in the coil 2 by using a simplified configuration.
In Figure 7A, the forced short-circuiting operation is performed twice (A1 and A2 as shown in Figure 7A) in voltage phases in which absolute values of instantaneous voltages of an AC voltage supplied from the AC voltage source 1 are the same. However, the short-circuiting period for the second detection is longer than the short-circuiting period for the first detection, thereby gradually increasing a current value.
However, a current flowing through the switching means 4 indicates a sufficiently small value at either time point, and it is thus determined that the coil 2 is in a normal state, and the switching operation for power factor correction is commenced (not shown), thereby continuing the operation so as to obtain the input current waveform shown in Figure 6.
Figure 7B shows waveforms, at respective portions, which are detected when an inductance value of the coil is lower than a normal value.
The forced short-circuiting operation is performed twice (B1 and B2 as shown in Figure 7B) in voltage phases in which absolute values of instantaneous voltages of an AC voltage supplied from the AC voltage source 1 are the same. However, the short-circuiting period for the second detection is longer than the short-circuiting period for the first detection, thereby gradually increasing a current value. Furthermore, in the second detection, the detected current indicates a value greater than the determined current level. Accordingly, it is determined that the coil 2 has a reduced inductance value, and the protecting stop operation is performed, such that the subsequent switching operation is not performed (not shown).
Furthermore, in the forced short-circuiting operation which is performed twice, the short-circuiting period for the first detection is set so as to be shorter than or equal to a time period corresponding to the short-circuit capability of the switching means 4. Therefore, the switching means 4 is not damaged even if the coil 2 is in a dead short state.
Furthermore, when a ratio of the short-circuiting period for the second detection to the short-circuiting period for the first detection is for example set to be smaller than or equal to a ratio of a maximum current value Ipmax of a peak current which can flow through the switching means 4 to a magnitude of a current value detected by the current detecting means 3, a magnitude of a current flowing through the switching means 4 can be suppressed so as to be smaller than or equal to Ipmax. The short-circuiting period for the second detection can thus be set to a time period which is longer than or equal to a time period corresponding to the short-circuit capability of the switching means 4.
As described above, when the forced short-circuiting operation is performed multiple times in the DC power supply apparatus according to the present embodiment, the short-circuiting period is gradually increased. Therefore, the closer the coil 2 to a completely short-circuiting state, the shorter the short-circuiting period can be for detecting whether or not the coil has an abnormal inductance value. Accordingly, the protecting operation can be performed in such a way that an excessive current is prevented from flowing through the switching means 4. Consequently, the switching means 4 can be a switching device in which a maximum rated current is substantially reduced.
Moreover, in a similar way to the DC power supply apparatus according to the first embodiment, the forced short-circuiting operation is also performed in the DC power supply apparatus according to the present embodiment after the switching means 4 commences the switching operation for power factor correction, in a predetermined voltage phase of an AC voltage supplied from the AC voltage source 1 and at predetermined time intervals, and the detected current value is compared with the determined current level in the short-circuiting detection, whereby it is possible to continue to detect whether or not the coil 2 has an abnormal inductance value during operation.

Figure 8 is a diagram illustrating a configuration of a DC power supply apparatus according to a third embodiment of the present invention.
As shown in Figure 8, the DC power supply apparatus according to the present embodiment includes: a rectifier circuit 5 connected in series with an AC voltage source 1; a coil 2 connected to a DC output terminal of the rectifier circuit 5 representing a positive polarity; a switching means 4, connected between the other end of the coil 2 and a DC output terminal of the rectifier circuit 5 representing a negative polarity, for short-circuiting and opening an AC voltage which is supplied from the AC voltage source 1 through the coil or coil arrangement (for example, transformer) 2; a current detecting means 3 for detecting a current flowing through the switching means 4; an AC voltage detecting means 13, connected between the DC output terminals of the rectifier circuit 5, for detecting an instantaneous voltage supplied from the AC voltage source 1; a diode 12 in which an anode is connected to the other end of the coil 2; and a smoothing capacitor 6 connected between a cathode of the diode 12 and the DC output terminal of the rectifier circuit 5 representing the negative polarity. A DC voltage is supplied to a load 8.
Figure 9 shows waveforms, at respective portions, which are detected when short-circuiting is detected for the coil 2 in the DC power supply apparatus according to the present embodiment.
As shown in Figure 9, the control means 10 in the DC power supply apparatus according to the present embodiment forces the switching means 4 to be short-circuited for a predetermined time period in a plurality of voltage phases of an AC voltage supplied from the AC voltage source 1, prior to the switching operation for power factor correction which is performed by the switching means 4 after switching on, and causes the current detecting means 3 to detect a current flowing through the switching means 4, thereby detecting a state of the coil 2. It should be noted that the predetermined time period and the plurality of voltage phases described above are stored beforehand in the storage section 10c.
Figure 9 shows an example scenario in which an inductance value of the coil 2 is less than a normal value, and a current value which is greater than a determined current level is detected in the third forced short-circuiting detection (A3 as shown in Figure 9). Therefore, the forced short-circuiting operation is stopped, and the protecting operation is performed, such that the switching operation for power factor correction is not commenced.
The determined current level is corrected depending on a voltage supplied from the AC voltage source 1.
The determined current level is for example adjusted so as to be proportional to a source voltage supplied from the AC voltage source 1, such that when an AC voltage corresponding to an effective value of 110V is detected in an article having an AC maximum rated voltage of 100V, a value obtained by multiplying the determined current level stored in the storage section 10c by 1.1 is used as the corrected determined current level.
Using the control described above, the influence of variation in the voltage supplied from the AC voltage source 1 can be cancelled when a current is detected in the forced short-circuiting operation for the coil 2, thereby enhancing the accuracy with which short-circuiting is detected for the coil 2.
According to the present embodiment, the determined current level is constant, regardless of the AC voltage phases in the short-circuiting operation. However, the voltage phase is determined such that the smaller an absolute value of an instantaneous voltage supplied from the AC voltage source 1, the lower the determined current level, and the greater an absolute value of the instantaneous voltage supplied from the AC voltage source 1, the higher the determined current level. It is thus possible to detect whether or not the coil 2 has an abnormal inductance value, in a voltage phase in which an instantaneous voltage supplied from the AC voltage source 1 has a reduced absolute value, such that a value of a current flowing through the switching means 4 can be suppressed when a layer short occurs in the coil 2.
As described above, when the switching means 4 is forced to be short-circuited multiple times in the DC power supply apparatus according to the present embodiment, a voltage phase in which the switching means 4 is forced to be short-circuited is determined such that the greater the number of times the switching means 4 is forced to be short-circuited, the greater an absolute value of an instantaneous voltage supplied from the AC voltage source 1. Therefore, a current which flows through the switching means 4 when the coil 2 has an abnormal inductance value can be substantially suppressed, thereby protecting the apparatus.
Furthermore, in a similar way to the DC power supply apparatus according to each of the first and second embodiments, the forced short-circuiting operation is also performed in the DC power supply apparatus according to the present embodiment after the switching means 4 commences the switching operation for power factor correction, in a predetermined voltage phase of an AC voltage supplied from the AC voltage source 1 and at predetermined time intervals, and the detected current value is compared with the determined current level in the short-circuiting detection, whereby it is possible to continue to detect whether or not the coil 2 has an abnormal inductance value during operation.

As described above, the DC power supply apparatus according to the present invention is capable of detecting whether or not the inductive element has an abnormal inductance value due to a layer short, prior to the switching operation which is performed after switching on, and is capable of stopping the apparatus for protection purposes without imposing a load on the switching means, even after the switching operation has been commenced, using a simplified configuration. The DC power supply apparatus according to the present invention is applicable to almost all electrical appliances, such as for example air conditioners, refrigerators and laundry machines, which use power supplied from an AC voltage source.

1 AC voltage source
2 inductive element, referred to in the examples as a coil
3 current detecting means
4 switching means
5 rectifier circuit
6 smoothing capacitor
7 capacitor
8 load
9 AC phase detecting means
10 control section
10a control signal generating section
10b short-circuit detecting section for the inductive element
10c storage section

Claims

A circuit for switching a DC power supply apparatus by means of a switching means of the circuit which short-circuits and opens an AC voltage supplied through an inductive element , which is switched at least once in a half-cycle period of the AC voltage for conversion to a DC voltage, said circuit being configured for power factor correction and comprising:
a first input for receiving a phase signal from a detecting means for detecting a phase of the AC voltage;
a second input for receiving a current-related signal from a detecting means for detecting a current flowing through one of the inductive element and the switching means,
wherein said circuit is configured such that at least one short-circuiting operation for short-circuiting the switching means is performed for a predetermined short-circuiting period prior to a switching operation for the conversion of the AC voltage to the DC voltage which is commenced by the switching means after switching on, and such that the switching operation for the conversion of the AC voltage to the DC voltage is not performed if a magnitude of the current-related signal is greater than a predetermined current level at least once, and wherein the switching operation for the conversion of the AC voltage to the DC voltage is performed if the current-related signal is smaller than and/or equal to the predetermined current level.
The circuit according to claim 1, wherein said circuit being configured so that the switching operation is not performed if the magnitude of the current-related signal is greater than the predetermined current level for a predetermined number of times n larger than one and wherein the switching operation is performed if the current-related signal is smaller than and/or equal to the predetermined current level for less than the predetermined number of times n.
The circuit according to any one of claims 1 or 2, wherein the circuit is also configured such that the short-circuiting operation is performed at least once at each of a positive polarity and a negative polarity which are represented by the AC voltage supplied from the AC voltage source.
The circuit according to any one of claims 2 or 3, wherein the circuit is also configured such that the greater the number of times the short-circuiting operation is performed, the higher is the predetermined current level.
The circuit according to any one of claims 1 to 4, further comprising a voltage detecting means for the AC voltage source, wherein the circuit is also configured such that the greater an absolute value of an instantaneous voltage of an AC voltage during the short-circuiting operation, the higher the predetermined current level.
The circuit according to any one of claims 1 to 5, wherein the circuit is also configured such that the predetermined short-circuiting period used for at least the short-circuiting operation when performed for the first time is set so as to be less than or equal to a time period corresponding to a short-circuit capability of a switching device of the switching means.
The circuit according to any one of claims 1 to 6, wherein the circuit is also configured such that the phase detecting means is formed by using a photocoupler.
The circuit according to any one of claims 1 to 7, wherein the circuit is also configured such that the predetermined current level is set so as to be lower than a maximum value of a current which flows through the switching means in a normal operating state.
The circuit according to any one of claims 1 to 8, wherein the circuit is also configured such that a current is detected during the short-circuiting operation by performing AD conversion once during the predetermined short-circuiting period.
The circuit according to claim 2 or 3, wherein the circuit is also configured such that an absolute value of an instantaneous voltage which is supplied from the AC voltage source when the short-circuiting operation is commenced is the same, and the predetermined short-circuiting period is the same, in some or all of the process steps of the short-circuiting operation.
The circuit according to any one of claims 1 to 10, wherein the circuit is also configured such that after the switching operation is commenced after the short-circuiting operation is ended, the short-circuiting operation for short-circuiting the switching means is performed for a predetermined short-circuiting period, at least once in a predetermined period, in a predetermined voltage phase of an AC voltage supplied from the AC voltage source or in a voltage phase in which an instantaneous voltage supplied from the AC voltage source indicates a predetermined absolute value, and the switching operation is stopped when a magnitude of a value of a current which is detected by the current detecting means in the short-circuiting operation becomes greater than the predetermined current level.
The circuit according to claim 1, wherein the circuit is also configured such that the short-circuiting operation is performed near a zero-cross point of an AC voltage supplied from the AC voltage source.
A DC power supply apparatus for short-circuiting and opening an AC voltage which is supplied from an AC voltage source through an inductive element, comprising:
a phase detecting means for the AC voltage source, wherein the circuit is also configured to generate a phase signal;
a current detecting means which generates a current-related signal; and
a circuit according to at least one of claims 1 to 12.
A method for generating a DC voltage on the basis of an AC voltage supplied from an AC voltage source through an inductive element for accomplishing a power factor correction, comprising the following steps:
a) switching the AC voltage at least once in a half-cycle period of the AC voltage source, by means of a switching means;
b) generating a phase detection signal related to the AC phase of the AC voltage;
c) generating a current-related signal related to a current flowing through one of the inductive element and the switching means;
d) short-circuiting the AC voltage by means of the switching means, prior to commencing a switching operation after switching on the AC voltage;
e) the switching operation is not performed if a magnitude of the current-related signal detected is greater than a predetermined current level, and
f) the switching operation is performed if the current-related signal is smaller than and/or equal to the predetermined current level.