Abstract:
A method of controlling an uninterruptible power supply apparatus (UPS) is provided. The UPS apparatus includes at least an AC input voltage, a DC input voltage and a single-phase AC/AC converter. The single-phase AC/AC converter includes an AC inductor, a bus capacitor, a boost arm, a common arm and a buck arm. The method includes steps of: controlling the bus voltage to have a DC component and full-wave rectifying component, and setting a bus voltage parameter K so that the bus voltage approaches to a full-wave rectifying voltage when K approaches to 1, wherein 0≦K≦1.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates to a method of controlling an uninterruptible power supply apparatus, particularly to an uninterruptible power supply of a simple-phase AC/AC converter having three arms.  
       BACKGROUND OF THE INVENTION  
       [0002]     Please refer to  FIG. 1  which is a circuit diagram of a conventional line-interactive uninterruptible power supply. In  FIG. 1 , the conventional line-interactive uninterruptible power supply contains an AC input voltage AC, a switch containing two diodes D 1  and D 2 , a single-phase AC/AC converter  11 , an AC filter  12  containing a filter inductor Lo and a filter capacitor Co, and a load R.  
         [0003]     The single-phase AC/AC converter  11  contains an AC inductor Li, a bus capacitor Cs and three arms. The three arms are respectively a boost arm consisted of a switch S 1  and a switch S 2 , a common arm consisted of a switch S 3  and a switch S 4  and a buck arm consisted of a switch S 5  and S 6 .  
         [0004]     An AC input voltage AC directly provides energy to the load R by the line-interactive uninterruptible power supply  1  of  FIG. 1  when the AC input voltage AC (mains electricity) is operated normally. The boost arm and the common arm execute a rectifying function. When the AC input voltage functions abnormally, a storing battery (not shown) provides energy to the load R. At this time, the common arm and the buck arm execute a inverting function.  
         [0005]     In fact, two switches S 3  and S 4  of the common arm are controlled by network frequency. The switching frequency is low-frequency switching. Therefore, the boost arm is used as a rectifying device and the buck arm is used as an inverting device.  
         [0006]     In the prior arts, in order to implement regulation of the AC input voltage, several controlling methods could be used. The difference between the controlling methods was to generate bus voltages having different waveforms. The following explanations show two kinds of common methods of controlling the bus voltages having different waveforms.  
         [0007]     Please refer to FIGS.  2 ( a ) and  2 ( b ) which were waveform diagrams of bus voltages of an uninterruptible power supply of  FIG. 1  for different controlling methods. The FIGS.  2 ( a ) and  2 ( b ) showed respectively waveforms of different bus voltages. The bus voltage of  FIG. 2 ( a ) had a DC voltage waveform while the bus voltage of  FIG. 2 ( b ) had a full-wave rectifying voltage waveform. Certainly, the different bus voltages generated under different controlling methods had advantages and drawbacks.  
         [0008]     In order to obtain the DC bus voltage shown in  FIG. 2 ( a ), the buck arm and the boost arm must be operated under a high frequency pulse-width-modulation mode and the common arm must be operated at low frequency switch state. When the AC input voltage AC was a positive half-wave, the switch S 4  turned off. When the AC input voltage AC was a negative half-wave, the switch S 3  turned off. An unit input power factor was obtained by using a method of calculating an input current and an input voltage so as to obtain a duty cycle of the buck arm of a single-phase AC/AC converter  11 . Therefore, a DC voltage was controlled by controlling an increasing amount of an input reference current.  
         [0009]     A main advantage of this controlling method was that the input current could be controlled to be a sine-wave so as to obtain an unit input power factor. An output voltage could be accurately regulated. A no-load current would decrease. On the contrary, a main drawback was that a switch loss was large and a efficiency was poor (especially under full-load).  
         [0010]     In order to obtain a full-wave bus voltage shown in  FIG. 2 ( b ), when the AC input voltage AC was abnormal, a converter  11  was operated at a boost state, the switches S 1  and S 2  of the boost arm were operated under high frequency pulse-width-modulation mode. When the converter  11  was operated at a buck state, only the switches S 5  and S 6  of the buck arm were operated high frequency pulse-width-modulation mode. Besides, a capacitance of a bus capacitor Cs was small, then a bus voltage having full-wave rectifying voltage waveform shown in  FIG. 2 ( b ) was obtained.  
         [0011]     A main advantage of this controlling method was that the volume could be decreased, reliability of the circuit was enhanced and usage life of the circuit was lengthen by using a high frequency film capacitor as the bus capacitor Cs. Besides, a loss of the switches was small when a design of the controlling unit was simplified.  
         [0012]     A main drawback of this controlling method was a poor dynamic performance, a large reactive current of input, and a large ripple current of the bus capacitor Cs. Because a current flowing through the load R during light-load and no-load periods was small, in order to maintain the full-wave rectifying voltage waveform of the bus capacitor Cs, an inefficient charging and discharging on the bus capacitor Cs was carried out. But, a large loss of the converter  11  was generated during light-load or no-load period.  
       SUMMARY OF THE INVENTION  
       [0013]     It is an object of the present invention to provide a method of controlling an uninterruptible power supply apparatus for use in a single-phase AC/AC converter of the uninterruptible power supply apparatus having three arms. In prior arts, there were mentioned two kinds of conventional controlling modes, the first was (1) a DC voltage controlling mode for a voltage waveform on a bus line, and the second was (2) a full-wave rectifying waveform controlling mode for a voltage waveform on the bus line. The controlling method of the present invention tries to sustain the advantages of the two conventional controlling modes and to overcome the drawbacks of them in order to obtain better effects.  
         [0014]     According to a main aspect of the present invention, there is provided a method of controlling an uninterruptible power supply apparatus for use in the single-phase AC/AC converter of the uninterruptible power supply apparatus having three arms. According to an analysis of an operation of the AC/AC converter, waveforms on a bus capacitor are controlled by segment division in order to decrease a reactive current generated by the bus capacitor and to decrease a high frequency ripple current through the bus capacitor and, at the same time, to obtain high efficiency under all-input range no matter when the system (the uninterruptible power supply apparatus) is operated in light-load or heavy-load state, when the system can maintain operation under high efficiency.  
         [0015]     According to one aspect of the present invention, there is provided a method of controlling an uninterruptible power supply apparatus having a bus voltage, an AC input voltage, a DC input voltage and a single-phase AC/AC converter including an AC inductor, a bus capacitor, a boost arm, a common arm and a buck arm, the method comprising steps of: 
    (a) controlling the bus voltage to have a DC voltage and a full-wave rectifying voltage; and     (b) setting a bus voltage parameter K where 0≦K≦1, so that the bus voltage approaches to the DC voltage when K approaches to 0 and the bus voltage approaches to the full-wave rectifying voltage when K approaches to 1; 
 
 wherein when the AC input voltage is normal, the bus voltage is rectified via the single-phase AC/AC converter to output, and when the AC input voltage is abnormal, the DC input voltage is inverted via the single-phase AC/AC converter to output. 
   
 
         [0018]     Preferably, the uninterruptible power supply apparatus includes a switch set, an AC filter and a load.  
         [0019]     Preferably, in step (b) when the load is light-load, the bus voltage parameter K is increased to approach to 1, and when the load is heavy-load, the bus voltage parameter K is decreased to approach to 0.  
         [0020]     In accordance with the present invention, the method further comprises a step of (c) setting a duty cycle d 3  of the buck arm, a duty cycle d 1  of the boost arm and a voltage gain M of the single-phase AC/AC converter to meet an equation of d 3 =M(1−d 1 ).  
         [0021]     In accordance with the present invention, the method further comprises a step of (d) defining a wave function F of the bus voltage to meet the following condition: when |sin(wt)|&lt;K, F=|sin(wt)|; and when |sin(wt)|≧K, F=K, wherein w is an angular velocity, and t is a passing time.  
         [0022]     In accordance with the present invention, the duty cycle d 1  of the boost arm, the voltage gain M of the single-phase AC/AC converter, the bus voltage parameter K and the wave function of the bus voltage F meet an equation d 1 =(2−M)KF.  
         [0023]     In accordance with the present invention, the method further comprises a step of (d) controlling one of boost arm and the buck arm to operate under a pulse-width-modulation mode when sin(wt)&gt;1/K, and controlling both of the boost arm and the buck arm to operate under pulse-width-modulation mode when sin(wt)&lt;1/K.  
         [0024]     According to another aspect of the present invention, there is provided a method of controlling an uninterruptible power supply apparatus having a bus voltage, an AC input voltage, a DC input voltage and a single-phase AC/AC converter comprising an AC inductor, a bus capacitor, a boost arm, a common arm and a buck arm, the method comprising steps of: (a) controlling the bus voltage and making the bus voltage have a waveform including a low slope segment and a full-wave rectifying segment; (b) setting a bus voltage parameter K representing an amount of an output power, wherein 0≦K≦1; and (c) regulating a proportion of the low slope segment and the full-wave rectifying segment within a full cycle based on a variation of the bus voltage parameter K, the waveform of the bus voltage during the low slope segment having a slope lower than a further slope of the waveform of the bus voltage during the full-wave rectifying segment; wherein, when the AC input voltage is normal, the bus voltage is rectified via the single-phase AC/AC converter to output, and when the AC input voltage is abnormal, the DC input voltage is inverted via the single-phase AC/AC converter to output.  
         [0025]     Preferably, an average voltage value during the full-wave rectifying segment is larger than that during the low slope segment.  
         [0026]     In accordance with the present invention, the method further comprises a step of (d) increasing a duration of the low slope segment and decreasing a duration of the full-wave rectifying segment when the output power decreases.  
         [0027]     In accordance with the present invention, the waveform of the bus voltage is obtained by regulating duty cycles of the boost arm and the buck arm.  
         [0028]     According to another aspect of the present invention, there is provided a method of controlling an uninterruptible power supply apparatus having a bus voltage, an AC input voltage, a DC voltage and an AC/AC converter, comprising steps of: (a) controlling the bus voltage to provide one of a DC voltage and a full-wave rectifying voltage; and (b) setting a bus voltage parameter K, where 0≦K≦1, so that the bus voltage approaches to the DC voltage when K approaches to 0 and the bus voltage approaches to the full-wave rectifying voltage when K approaches to 1.  
         [0029]     The foregoing and other features and advantages of the present invention will be more clearly understood through the following descriptions with reference to the drawings, wherein: 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0030]      FIG. 1  is a circuit diagram of a conventional line-interactive uninterruptible power supply;  
         [0031]     FIGS.  2 ( a ) and  2 ( b ) are diagrams showing waveforms of the bus voltage under different controlling methods for the conventional line-interactive uninterruptible power supply shown in  FIG. 1 ;  
         [0032]      FIG. 2 ( c ) is a diagram showing a waveform of the bus voltage applied by using the controlling method for an uninterruptible power supply of the present invention;  
         [0033]      FIG. 3 ( a ) is a circuit diagram showing an line-interactive uninterruptible power supply of the present invention;  
         [0034]      FIG. 3 ( b ) is a switch status table showing each main switch is operated under different operational modes in  FIG. 3 ( a ) according to the present invention;  
         [0035]      FIG. 4 ( a ) is a timing diagram showing a duty cycle of a boost arm under a boost mode according to the controlling method of the present invention;  
         [0036]      FIG. 4 ( b ) is a timing diagram showing a duty cycle of a buck arm under a boost mode according to the controlling method of the present invention;  
         [0037]      FIG. 5 ( a ) is a timing diagram showing a duty cycle of a boost arm under a buck mode according to the controlling method of the present invention; and  
         [0038]      FIG. 5 ( b ) is a timing diagram showing a duty cycle of a buck arm under a buck mode according to the controlling method of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0039]     The present invention will now described more specifically with reference to the following embodiments. Please refer to  FIG. 3 ( a ) which is a circuit diagram of a line-interactive uninterruptible power supply apparatus on which the controlling method of the present invention is applied. The numerals of  FIG. 3 ( a ) are similar to those of  FIG. 1  for the same components. The line-interactive uninterruptible power supply apparatus  3  contains a DC input voltage DC, an AC input voltage AC, a switch set containing diodes D 1  and D 2 , a single-phase AC/AC converter  31 , an AC filter  32  containing a filter inductor Lo and a filter capacitor Co, and a load R.  
         [0040]     The single-phase AC/AC converter  31  contains an AC inductor Li, a bus capacitor Cs and three arms. A arm containing switches S 1  and S 2  is called as a boost arm. A arm containing switches S 3  and S 4  is called as a common arm. A arm containing switches S 5  and S 6  is called as a buck arm. Switches SW 1 , SW 2  and SW 3  are respectively used to control three operations of the AC input voltage AC, the DC input voltage DC and a bypass mode.  
         [0041]     Please refer to  FIG. 3 ( b ) which is a switch status table of different operation modes by the main switches in  FIG. 3 ( a ). According to  FIG. 3 ( b ), it is known that for the line-interactive uninterruptible power supply apparatus  3  under operation of the AC input voltage AC (mains electricity), the switch SW 1  is turned on and the switches SW 2  and SW 3  are switched to be turned off so that the bus voltage is rectified by the simple-phase AC/AC converter  31  and output to the load R. When the performance of the AC input voltage AC is abnormal, the switch SW 2  is turned on and the switches SW 1  and SW 3  are switched to be turned off, and the DC input voltage is inverted through the single-phase AC/AC converter to output. When the line-interactive uninterruptible power supply apparatus  3  does not function, the switch SW 3  is turned on and the switches SW 1  and SW 2  are switched to be turned off to let technicians maintain the device.  
         [0042]     A main object of the controlling method of the present invention is to obtain the bus voltage shown in  FIG. 2 ( c ). Similar to the conventional techniques, the bus capacitor Cs has such a small capacitance that a voltage having a full-wave rectifying voltage waveform is obtained. The method of controlling the bus voltage of the present invention which has a DC voltage and a full-wave rectifying voltage is explained as follows.  
         [0043]     As shown in  FIG. 2 ( c ), firstly, a bus voltage parameter K is set between 0 and 1. When the K value approaches to 0, the full-wave rectifying voltage of the bus voltage becomes larger and the waveform of the bus voltage approaches to a waveform of full-wave rectifying voltage. When the K value approaches to 1, the DC voltage of the bus voltage becomes larger and the waveform the bus voltage approaches to a waveform of a DC voltage.  
         [0044]     When the line-interactive uninterruptible power supply apparatus  3  is running and the load R is a light-load, the reactive current of the converter  31  occupies a large proportion of the current. Then, the K value is correspondently increased to decrease the reactive current. On the other hand, when the load R become larger, the main concern is the efficiency of the converter  31 . Then, the K value is correspondently decreased to decrease the loss of each switch and to increase the whole efficiency of the converter  31 .  
         [0045]     In the above controlling method, the mode of the variation of the K value is irrelevant to a load current. A voltage gain determines a duty cycle d 3  of each switch of the buck arm and a duty cycle d 1  of each switch of the boost arm. Furthermore, the switches S 3  and S 4  of the common arm are relevant to a polarity of the AC input voltage AC. When the voltage gain M is smaller than 1, the converter  31  is operated under a buck mode. When the voltage gain M is larger than 1, the converter  31  is operated under a boost mode.  
         [0046]     A wave function F of the bus voltage for the controlling method of the present invention is defined to meet the following condition:
 
when |sin( wt )|&lt; K,F= sin( wt )|; and
 
when |sin( wt )|≧ K,F=K;    (1)
 
 wherein w is an angular velocity, and t is a passing time. 
 
         [0047]     The duty cycle d 3  of the buck arm, the duty cycle d 1  of the boost arm, the voltage gain M of the simple-phase AC/AC converter, the bus voltage parameter K and the wave function of the bus voltage F meet equations:
 
 d 3= M (1− d 1);   (2)
 
 d 1=(2− M ) KF    (3)
 
         [0048]     When the voltage input from mains electricity (the AC input voltage AC) is lower than the required value, it is necessary to increase the input voltage and the system is under boost mode and the voltage gain M is between 1 to 1.3. It can be known from equations (2)-(3) that it is necessary to control the duty cycle of the switches of the buck arm as shown in  FIG. 4 ( b ) while a duty cycle of the switches of the boost arm at the same time is shown in  FIG. 4 ( a ).  
         [0049]     When the voltage input from mains electricity is higher than the required value, it is necessary to decrease the input voltage and the system is under the buck mode and the voltage gain M is between 0.7 to 1. It can be known from equations (2)-(3) that it is necessary to control the duty cycle of the switches of the boost arm as shown in  FIG. 5 ( a ) while a duty cycle of the switches of the buck arm at the same time is shown in  FIG. 5 ( b ).  
         [0050]     It shall be noted that in view of timing, during a same cycle when sin(wt)&gt;1/k, one of the boost arm and the buck arm is operated under the pulse-width-modulation mode. When sin(wt)&lt;1/k, both of the boost arm and the buck arm are operated under the pulse-width-modulation mode.  
         [0051]     It shall be noted that the examples shown above in the present invention are relevant to a combination of a DC waveform and a full-wave rectifying waveform. But, as to the object of the present invention, a decrease in the slope of the voltage waveform variation during a light-load period can increase the efficiency compared to the original full-wave rectifying waveform.  
         [0052]     Accordingly, the present invention provides a method of controlling an uninterruptible power supply apparatus having three arms for use in the single-phase AC/AC converter. By controlling the voltage waveform on the bus capacitor by segment method, waveforms on a bus capacitor are controlled by segment division in order to decrease a reactive current generated by the bus capacitor and to decrease a high frequency ripple current through the bus capacitor and, at the same time, to obtain high efficiency under all-input voltage range no matter when the system (the uninterruptible power supply apparatus) is operated in light-load or heavy-load state, the system can maintain operation under high efficiency.  
         [0053]     While the invention has been described in terms of what is presently considered to be the most practical and preferred embodiments, it is to be understood that the invention needs not be limited to the disclosed embodiments. On the contrary, it is intended to cover various modifications and similar arrangements included within the spirit and scope of the appended claims which are to be accorded with the broadest interpretation so as to encompass all such modifications and similar structures.