Abstract:
A power supply device for inverting power to be supplied to a motor and a method of controlling the power supply device. The power supply device includes an inrush protection (IP) circuit, a power factor correction (PFC) circuit and an overvoltage protection (OP) circuit. A controller and a pair of relays selectively connect predetermined components so that at least one component is selectively changed from operation in one of the IP, PFC and OP circuits to operation in another of the IP, PFC and OP circuits in response to a detected value of an inverter input voltage. The inrush protection circuit operates in a start up mode; the PFC circuit operates while normally driving the motor; and the overvoltage protection circuit operates where the inverter input voltage increases due to regeneration by the motor.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application claims the benefit of Korean Patent Application No. 2003-1365, filed Jan. 9, 2003, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a power supply device and a method of controlling the power supply device, and more particularly, to a power supply device having an inrush current protection circuit, a power factor correction (PFC) circuit and an overvoltage protection circuit and a method of controlling the inrush current protection circuit, the PFC circuit and the overvoltage protection circuit. 
   2. Description of the Related Art 
   A three-phase motor is a motor having a plurality of windings which are arranged around a rotor and which receive energy from a three phase voltage to rotate the motor. As shown in  FIG. 1 , a power supply device which obtains a three-phase voltage necessary for driving a motor  200  via input terminals U, V and W of the motor  200 , comprises an AC power supply  100  which supplies a commercial AC power, such as for example, (AC 110/220V), a rectifier  300  which rectifies the AC power output from the AC power supply  100 , a capacitor C DC  which smoothes a voltage rectified by the rectifier  300 , an inverter  120  which inverts a DC power output from the capacitor C DC  to an AC power having various frequencies and outputs a three-phase voltage. The power supply device may further comprise an inrush current protection circuit  140  which prevents an inrush current into the capacitor C DC  during an initial supply of power, a power factor correction (PFC) circuit  150  which maintains an output voltage from the capacitor C DC  at a constant value, and an overvoltage protection circuit  130  which protects the capacitor C DC  from an overvoltage. 
   In the inverter  120 , a pulse width modulation (PWM) part (not shown) generates a PWM control signal and a plurality of transistors are turned on/off according to a square wave signal of the PWM part. The power supply device comprises a controller (not shown) which controls the output frequency thereof so as to control a rotation speed of the motor  200  and turns on/off an output of the inverter  120  by turning on/off the transistors according to the PWM control signal. 
   The inrush current protection circuit  140  comprises an inrush current protection resistor Rs provided between the rectifier  300  and the capacitor C DC  and connected to the capacitor C DC . A relay part  142  comprises first, second and third contacting points  142   a,    142   b  and  142   c.  When the relay part  142  connects the first contacting point  142   a  with the third contacting point  142   b,  the inrush current protection resistor Rs connects the capacitor C DC  with the rectifier  300 , which allows power rectified by the rectifier  300  and charged to the capacitor C DC  to be limited by the resistor Rs, to prevent the capacitor C DC  from being broken down by excessive inrush current in an initial supply of power. 
   The PFC circuit  150  comprises a PFC switching unit S PFC  such as a field effect transistor, a PFC diode D PFC  provided with a cathode connected to the capacitor C DC  and an anode connected to a node  151  of the PFC switching unit S PFC , and a PFC inductor L PFC  provided between the node  151  and the rectifier  300 . Herein, the PFC inductor L PFC  is disconnected from the rectifier  300  when the relay part  142  connects the first contacting point  142   a  with the third contacting point  142   c,  and connected to the rectifier  300  when the relay part  142  connects the second contacting point  142   b  with the third contacting point  142   c.  The PFC circuit  150  maintains a voltage applied across the capacitor C DC  at a constant value by turning on/off the PFC switching unit S PFC  in driving the motor  200 , and improves a power factor by making an input current input to the PFC circuit  150  have a same phase as a phase of an input voltage. 
   The overvoltage protection circuit  130  is connected in parallel with the capacitor C DC , and provided with an overvoltage protection switching unit S OV  connected in series with a parallel combination of an overvoltage protection diode D OV  and an overvoltage protection resistor R OV . As to the overvoltage protection circuit  130 , if the voltage applied across the capacitor C DC  is increased and reaches a predetermined overvoltage region due to a voltage regenerated through the inverter  120  from the motor  200  in driving the motor  200 , the overvoltage protection switching unit Sov is turned On, to thereby prevent the capacitor C DC  from being broken down by an overvoltage. 
   In the conventional power supply device shown in  FIG. 1 , the inrush current protection circuit  140  functions until a voltage charged in the capacitor C DC  reaches a reference charging voltage after power is initially applied from the AC power supply  100 . The inrush current protection circuit  140  becomes unnecessary after a voltage charged in the capacitor C DC  reaches the reference charging voltage. 
   Since the PFC circuit  150  operates after the voltage applied across the capacitor C DC  is stabilized (i.e. sufficiently charged), operation of the PFC circuit  150  is not necessary while the inrush current protection circuit  140  operates. 
   Since the overvoltage protection circuit  130  operates only while the voltage applied across the capacitor C DC  is increased by the voltage regenerated from the motor  200 , operation of the overvoltage protection circuit  130  is not necessary while the inrush current protection circuit  140  operates (i.e., in an initial charging period), or while the PFC circuit  150  operates after the voltage applied across the capacitor C DC  is stabilized. 
   Since large capacity components are used in the inrush current protection circuit  140 , the overvoltage protection circuit  120  and the PFC circuit  150 , a size of a product including the conventional power supply device shown in  FIG. 1  is increased. Eliminating one or more of the large capacity components would result in a reduction in the product size and a decrease in manufacturing cost. 
   SUMMARY OF THE INVENTION 
   Accordingly, it is an aspect of the present invention to provide a power supply device and a control method thereof which allows a number of parts of the power supply device to be reduced, a size of the power to be reduced, a size of a product incorporating the power supply to be reduced, and manufacturing costs of the power supply device and the product to be reduced. 
   Additional and/or other aspects and advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious form the description, or may be learned by practice of the invention. 
   The above and/or other aspects of the present invention are achieved by providing a power supply device having an AC power supply, a rectifier which rectifies power supplied from the AC power supply, and a capacitor which smoothes power rectified by the rectifier, comprising: a switching unit; a diode having a cathode connected to the capacitor and an anode connected to the switching unit; an inductor having a first end connectable to the rectifier and a second end connectable to a node between the switching unit and the anode of the diode; a resistor having a first end connected to the capacitor and a second end; a relay operable in a first position to connect the node between the switching unit and the anode of the diode to the inductor, and operable in a second position to connect the node between the switching unit and the diode to the second end of the resistor; and a controller which controls the relay to be in the second position if a voltage applied across the capacitor exceeds a predetermined PFC voltage limit. 
   In an aspect of the present invention, the power supply device further comprises a capacitor voltage detector which detects the voltage applied across the capacitor, wherein the controller controls the relay to be in the second position if the voltage applied across the capacitor and detected by the capacitor voltage detector exceeds the predetermined PFC voltage limit. 
   In an aspect of the present invention, the controller turns on/off the switching unit if the voltage applied across the capacitor and detected by the capacitor voltage detector reaches a predetermined overvoltage region and the relay is in the second position. 
   In an aspect of the present invention, the controller controls the relay to be in the first position if the voltage applied across the capacitor and detected by the capacitor voltage detector becomes lower than the predetermined PFC voltage limit. 
   In an aspect of the present invention, the power supply device further comprises a second relay operable in a first position to connect the rectifier and the second end of the resistor, and operable in a second position to connect the rectifier and the first end of the inductor. 
   In an aspect of the invention, the controller controls the second relay to be in the first position so that power rectified by the rectifier is supplied to the capacitor through the resistor when power is initially supplied. 
   In an aspect of the invention, the controller controls the second relay to transfer to the second position if the voltage applied across the capacitor exceeds a predetermined reference charging voltage in a state that the second relay is in the first position. 
   The foregoing and/or other aspects of the present invention are also achieved by providing a method of controlling a power supply device having an AC power supply, a rectifier which rectifies power supplied from the AC power supply, a capacitor which smoothes power rectified by the rectifier, a switching unit, a diode having a cathode connected to the capacitor and an anode connected to the switching unit, and an inductor provided between the rectifier and a node between the switching device and the diode, the method comprising: providing a resistor connectable in parallel with the diode; detecting a voltage applied across the capacitor; and disconnecting the inductor and the node between the switching unit and the diode and connecting the resistor and the node between the switching unit and the diode, if a detected voltage applied across the capacitor exceeds a predetermined PFC voltage limit. 
   In an aspect of the invention, the method of controlling the power supply device further comprises turning on/off the switching unit if the detected voltage applied across the capacitor reaches a predetermined overvoltage region in a state that the resistor and the node between the switching unit and the diode are connected. 
   In an aspect of the invention, the method of controlling the power supply device further comprises disconnecting the resistor and the node between the switching unit and the diode and connecting the inductor and the node between the switching unit and the diode, if the detected voltage applied across the capacitor becomes lower than the predetermined PFC voltage limit. 
   In an aspect of the invention, the method of controlling the power supply device further comprises connecting the rectifier and the resistor and disconnecting the rectifier and the inductor so that power rectified by the rectifier is supplied to the capacitor through the resistor, when power is initially supplied. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and/or other aspects and advantages of the present invention will become apparent and more readily appreciated from the following description of the embodiments, taken in conjunction with the accompany drawings of which: 
       FIG. 1  is a view illustrating a circuit of a conventional power supply device; 
       FIG. 2  is a view illustrating a state for performing an inrush current protection function in a power supply device circuit according to the present invention; 
       FIGS. 3A–3D  are views illustrating waveforms of the power supply device circuit of the present invention in the state shown in  FIG. 2 ; 
       FIG. 4  is a view illustrating a state for performing a PFC function in the power supply device circuit according to the present invention; 
       FIGS. 5A–5F  are views illustrating waveforms of the power supply device circuit of the present invention in the state shown in  FIG. 4 ; 
       FIG. 6  is a view illustrating a state for performing an overvoltage protection function in the power supply device circuit according to the present invention; and 
       FIGS. 7A–7E  are views illustrating waveforms of the power supply device circuit of the present invention in the state shown in  FIG. 6 . 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Reference will now be made in detail to the embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to like elements throughout. 
     FIG. 2  illustrates a circuit of a power supply device circuit for a three-phase motor, according to an embodiment of the present invention. The power supply device shown in  FIG. 2 , comprises an AC power supply  1  which supplies a commercial AC power, such as for example, AC 110/220V; a rectifier  3  which rectifies the AC power; a capacitor  13  which smoothes power rectified by the rectifier  3 ; and a inverter  12  which inverts DC power outputted from the capacitor  13  to an AC power having a variable frequency and outputs the AC power as a three-phase voltage to terminals U, V and W of the motor  2 . 
   The power supply device shown in  FIG. 2  further comprises a switching unit  4 ; a diode  5  having a cathode connected to an end  15  of the capacitor  13  and an anode connected to the switching unit  4 ; an inductor  6  selectively connectable between the rectifier  3  and a node  17  between the switching unit  4  and the diode  5 ; a resistor  7  selectively connectable to the diode  5  in parallel; a first relay  8  having first second and third contacting points  8   a,    8   b  and  8   c,  respectively, the relay  8  selectively connecting the node  17  and the inductor  6  via the first contacting point  8   a  and the third contacting point  8   c  and selectively connecting the node  17  and the resistor  7  via the second contacting point  8   b  and the third contacting point  8   c;  and a controller  11  which controls the first relay  8  to connect the second contacting point  8   b  and the third contacting point  8   c  if a voltage applied across the capacitor  13  exceeds a predetermined PFC voltage limit. 
   The power supply device according to the present invention may further comprise a capacitor voltage detector  10  which detects the voltage applied across the capacitor  13 . The controller  11  may control the first relay  8  to connect the second contacting point  8   b  and the third contacting point  8   c  if the voltage applied across the capacitor  13  detected by the capacitor voltage detector  10  exceeds the predetermined PFC voltage limit. 
   The switching unit  4 , the diode  5 , and the inductor  6  according to the present invention, function as a PFC circuit. That is, in a state that the first relay  8  connects the first contacting point  8   a  and the third contacting point  8   c,  the switching unit  4 , the diode  5 , and the inductor  6  maintain the voltage applied across the capacitor  13  at a constant value by being connected to the rectifier  3  and the capacitor  13 , and function as the PFC circuit to improve a power factor by controlling an input current input from the rectifier  3  to have a same phase as of an input voltage input from the rectifier  3 . 
   The switching unit  4 , such as a MOS transistor, or a Field effect transistor, is switched according to a signal input to a gate of the transistor. The controller  11  turns on/off the switching unit  4  by controlling the signal input to the gate of the switching unit  4 . 
   The switching unit  4 , the diode  5 , and the resistor  7  function an overvoltage circuit. That is, while a function of the PFC circuit is performed with the first relay  8  connecting the first contacting point  8   a  and the third contacting point  8   c,  the voltage applied across the capacitor  13  may be increased by a voltage regenerated through the inverter  12  from a motor  2 . If the voltage across the capacitor  13  continues to increase and exceeds the predetermined PFC voltage limit, the node  17  between the switching unit  4  and the diode  5  is cut off from the inductor  6  and the resistor  7  and the diode  5  are connected in parallel by the relay  8  connecting the second contacting point  8   b  and the third contacting point  8   c.  Herein, the controller  11  prevents the voltage across the capacitor  13  from being increased into an overvoltage region by turning on/off the switching unit  4  to reduce the voltage across the capacitor  13 . 
   If the voltage across the capacitor  13  is decreased to the predetermined PFC voltage limit or lower, due to reduction of the voltage regenerated from the motor  2  by the overvoltage protection circuit, the controller  11  makes the first relay  8  to connect the first contacting point  8   a  and the third contacting point  8   c.  Thus, the switching unit  4 , the diode  5 , and the inductor  6  again function as the PFC circuit. 
   The power supply according to the present invention may further comprise a second relay  9  having a first contacting point  9   a,  a second contacting point  9   b  and a third contacting point  9   c.  The second relay  9  selectively connects the rectifier  3  and the resistor  7  via the first contacting point  9   a  and the third contacting point  9   c,  and selectively connects the rectifier  3  and the inductor  6  via the second contacting point  9   b  and the third contacting point  9   c.  The controller  11  makes the second relay  9  connect the contacting point  9   a  and the contacting point  9   c  so that power rectified from the rectifier  3  is supplied to the capacitor  13  through the resistor  7  when power is initially supplied from the AC power supply  1 . Thus, the capacitor  13  is prevented from being broken down by an excessive inrush current by limiting current supplied to the capacitor  13  with the resistor  7 . 
   The controller  11  makes the second relay  9  connect the second contacting point  9   b  and the third contacting point  9   c  if the voltage across the capacitor  13  exceeds a predetermined reference charging voltage. Thus, the rectifier  3  is connected to the capacitor  13  through the inductor  6 , and the switching unit  4 , the inductor  6  and the diode  5  perform the PFC function. 
   A process that performs functions of an inrush current protection, phase factor correction and overvoltage protection using the apparatus shown in  FIG. 2  will be described will be described with reference to  FIGS. 3A–3D . 
   When power is initially supplied from the AC power supply  1 , the controller  11  makes the first relay  8  connect the first contacting point  8   a  and the third connecting point  8   c,  and makes the second relay  9  connect the first contacting point  9   a  and the third contacting point  9   c.  Referring now to  FIG. 3B , an AC voltage V(L 1 –L 2 ) supplied from the AC power supply  1  is rectified by the rectifier  3  to obtain a voltage VD 1 . The voltage VD 1  is charged to the capacitor  13  through the resistor  7 . That is, in a state that the first relay  8  connects the first contacting point  8   a  and the third contacting point  8   c  and the second relay  9  connects the first contacting point  9   a  and the third contacting point  9   c,  the resistor  7  performs an inrush current protection function. While performing the inrush current protection function, the voltage V PN  applied across the capacitor  13  is gradually increased as the capacitor  13  is charged as shown in  FIG. 3B . If the voltage V PN  applied across the capacitor  13  exceeds a reference charging voltage V1, the controller  11  controls the second relay  9  to connect the second contacting point  9   b  and the third contacting point  9   c.    FIG. 3C  illustrates a waveform of a current flowing from the rectifier  3  to the resistor  7 , and  FIG. 3D  illustrates a point of time in which the second relay  9  operates to connect the second contacting point  9   b  and the third contacting point  9   c.    
   In a state that the second relay  9  connects the second contacting point  9   b  and the third contacting point  9   c  and the first relay  8  connects the first contacting point  8   a  and the third contacting point  8   c,  the PFC function performed by the switching unit  4 , the inductor  6 , and the diode  5  will be described as follows, with reference to FIGS.  4  and  5 A– 5 F. 
   In a state that the second relay  9  connects the contacting point  9   b  and the contacting point  9   c,  the controller  11  turns on/off the switching unit  4  so that the voltage applied V PN  across the capacitor  13  may be maintained constant at a value V DC.  That is, the controller  11  stores energy in the inductor  6  by turning on the switching unit  4 , and transmits the energy stored in the inductor  6  to the capacitor  13  through the diode  5  by turning off the switching unit  4 . Thus, the voltage V PN  applied across the capacitor  13  is maintained constant at a value V DC,  and an input current I D1  as shown in  FIG. 5F  input from the rectifier  3  has a same phase as a phase of an input voltage V D1  as shown in  FIG. 5B , to thereby increase the power factor. In a state that the voltage V PN  applied across the capacitor  13  is maintained constant at V DC  by the PFC circuit, the motor  2  is driven according to a current I INV  as shown in  FIG. 5E .  FIG. 5A  is a view illustrating a waveform of an AC voltage supplied to the rectifier  3  from the AC power supply  1 .  FIG. 5C  is a view illustrating a time when contact of the second relay  9  is switched from connecting the contacting point  9   a  and the contacting point  9   c  (A) to connecting the contacting point  9   b  and the contacting point  9   c  (B).  FIG. 5D  is a view illustrating a time when the PFC circuit starts to perform the power factor correction function. 
   While the motor  2  is driving, energy stored in the motor  2  by rotation of the motor  2  may be regenerated to the capacitor  13  through the inverter  12  under certain conditions. For example, energy stored while the motor  2  rotates regularly, is regenerated to the capacitor  13  through the inverter  12  when the motor  2  reverses a direction of rotation. Herein, energy regenerated through the inverter  12 , that is, a regenerated voltage increases the voltage V PN  applied across the capacitor  13  above the value V DC . 
   When the voltage applied across the capacitor  13  is increased by the regenerated voltage regenerated through the inverter  12  from the motor  2 , the overvoltage protection function of the power supply device according to the present invention will be described with reference to FIGS.  6  and  7 A– 7 E. 
   At first, if the voltage V PN  across the capacitor  13  is increased by the regenerated voltage of the motor  2  at a time t 1  shown in  FIG. 7B  and accordingly exceeds a PFC voltage limit (V 2 ), the controller  11  controls the first relay  8  to connect the second contacting point  8   b  and the third contacting point  8   c  at a time t 2  shown in  FIG. 7C  (refer to (C) of  FIG. 7 ). The PFC voltage limit V 2  means the voltage applied across the capacitor  13  at a moment when current does not flow from the rectifier  3  to the capacitor  13  as the voltage V PN  is increased by the regenerated voltage. 
   Even when the first relay  8  is connecting the second contacting point  8   b  and the third contacting point  8   c,  the regenerated voltage from the motor  2  increases the voltage V PN  applied across the capacitor  13 . The controller  11  turns on/off the switching unit  4  when the voltage V PN  applied across the capacitor  13  reaches an overvoltage region (hysteresis region, V H1 –V H2 ). 
   That is, if the voltage V PN  applied across the capacitor  13  is increased and reaches an overvoltage upper limit V H2 , the controller  11  allows the regenerated voltage from the motor  2  through the resistor  7  to be consumed by turning on the switching unit  4  as shown in  FIG. 7D . Thus, the voltage V PN  applied across the capacitor  13  is decreased. If the regenerated voltage from the motor  2  is consumed through the resistor  7 , so that the voltage V PN  applied across the capacitor  13  reaches an overvoltage lower limit V H1 , the controller  11  prevents the voltage V PN  from becoming lower than the overvoltage region (V H1 –V H2 ) by turning off the switching unit  4 , to maintain the voltage V PN  within the overvoltage region (V H1 –V H2 ). Thus, the controller  11  controls consumption of the regenerated voltage from the motor  2  by turning on/off the switching unit  4 . 
   Subsequently, if the regenerated voltage of the motor  2  is all consumed, the voltage V PN  applied across the capacitor  13  is not increased even though the switching unit  4  is off. Also, because the capacitor  13  is cut off from the AC power supply  1 , the voltage V PN  applied across the capacitor  13  is decreased by power consumed to drive the motor  2 . If the voltage V PN  applied across the capacitor  13  is decreased and becomes lower than the PFC voltage limit V 2 , the controller  11  connects the capacitor  13  and the AC power supply  1  by operating the first relay  8  to connect the first contacting point  8   a  and the third contacting point  8   c  at a time t 3  as shown in  FIG. 7C . Herein, the capacitor  13  and the rectifier  3  are connected in the PFC circuit, and the voltage V PN  applied across the capacitor  13  is maintained constant by the PFC circuit. 
     FIG. 7A  is a waveform of the input voltage (V L1-L2 ) input from the AC power supply  1  to the rectifier  3 .  FIG. 7C  is a view illustrating a time when the first relay  8  connects the first contacting point  8   a  and the third contacting point  8   c  (time before t 2 ), the time t 2  when the first relay  8  connects the second contacting point  8   b  and the third contacting point  8   c  and the time t 3  when the first relay  8  again connects the first contacting point  8   a  and the third contacting point  8   c  during operation of the overvoltage protection circuit.  FIG. 7D  is a view illustrating times when the switching unit  4  is turned on/off to perform the overvoltage protection function. 
   In the above embodiment, the power supply device according to the present invention is illustrated by reference to a three-phase motor. However, a configuration of the inverter  12  may be changed in order to supply power to a single-phase motor or other poly-phase motors, and the power supply device according to the present invention may be applied to other devices as well as a motor. 
   Also, in the above embodiment, the resistor is used in common in the overvoltage protection circuit and the inrush current protection circuit. However, a separate inrush current protection resistor can be provided. 
   With the above configuration, in the power supply device, a number of parts may be reduced and a size and a manufacturing cost of a product may be decreased by using the resistor  7 , the switching unit  4 , and the diode  5  necessary for implementing functions of the inrush current protection circuit, the PFC circuit, and the overvoltage protection circuit in common. 
   As described above, according to the present invention, a power supply device and a control method thereof the number of parts thereof to be reduced, and also the size of a product and manufacturing cost to be decreased. 
   Although a few embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that changes may be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the appended claims and their equivalents.