Abstract:
An uninterruptible power supply and a control method therefor. The uninterruptible power supply includes: an alternating current input end ( 20 ) and an alternating current output end ( 30 ); a rectification voltage regulating circuit ( 10 ), including a first diode (D 1 ) and a first switching tube (Q 1 ) that are connected in series, a second diode (D 2 ) and a second switching tube (Q 2 ) that are connected in series, and a third diode (D 5 ) and a fourth diode (D 6 ); an inverter voltage regulating circuit ( 40 ) including a third switching tube (Q 3 ) and a fifth diode (D 1 ′) that are connected in series, a fourth switching tube (Q 4 ) and a sixth diode (D 2 ′) that are connected in series, and a fifth switching tube (Q 5 ) and a sixth switching tube (Q 6 ); an inductor (L); a capacitor (C); a chargeable/dischargeable device for providing a direct current; a seventh switching tube (Q 7 ) connected in series to an output end of the chargeable/dischargeable device; a safety diode (D 7 ) connected in series to the seventh transistor (Q 7 ); a charger ( 14 ); and a switch (S). The uninterruptible power supply can provide a stable alternating current, and does not have an automatic voltage regulator.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a power supply device, and in particular, to an uninterruptible power supply and a control method therefor. 
       BACKGROUND 
       [0002]    Uninterruptible power supplies can continuously supply power to electric equipment, and have been widely applied in various fields. 
         [0003]    For an online interactive uninterruptible power supply, a load is powered directly by the mains supply when the mains supply is normal. The load is powered by batteries when the mains supply is interrupted. When the mains supply has a high or low voltage, to enable the online interactive uninterruptible power supply to have a stable output voltage, an automatic voltage regulator (AVR) is generally connected to an input end of the mains supply and used for regulating the voltage at an output end of the uninterruptible power supply. The automatic voltage regulator has high reliability and can regulate the voltage at the input end in a wide range. 
         [0004]    However, the automatic voltage regulator has large volume, heavy weight, high costs, and high energy consumption, which directly cause decrease of power utilization rate and increase of costs of the uninterruptible power supply. Therefore, an uninterruptible power supply not having an automatic voltage regulator and capable of providing a stable alternating-current voltage is urgently needed at present. 
       SUMMARY 
       [0005]    In view of the aforementioned problem, an embodiment of the present invention provides an uninterruptible power supply, which includes: 
         [0006]    an alternating current input end and an alternating current output end; 
         [0007]    a rectification voltage regulating circuit, including a positive output end, a negative output end, and a first input end and a second input end that are electrically connected to the alternating current input end, and further including a first diode and a first switching tube that are connected in series between the first input end and the positive output end, a second diode and a second switching tube that are connected in series between the second input end and the positive output end, a third diode electrically connected between the negative output end and the first input end, and a fourth diode electrically connected between the negative output end and the second input end; 
         [0008]    an inversion voltage regulating circuit, including a positive input end, a negative input end, a first output end, and a second output end, and further including a third switching tube and a fifth diode that are connected in series between the positive input end and the first output end, a fourth switching tube and a sixth diode that are connected in series between the positive input end and the second output end, a fifth switching tube electrically connected between the negative input end and the first output end, and a sixth switching tube electrically connected between the input end and the second output end; 
         [0009]    an inductor electrically connected between the positive output end and the positive input end; 
         [0010]    a capacitor electrically connected between the first output end and the second output end; 
         [0011]    a chargeable/dischargeable device for providing a direct current; 
         [0012]    a seventh switching tube, connected in series to an output end of the chargeable/dischargeable device between the negative output end and the positive output end; 
         [0013]    a safety diode connected in series to the seventh switching tube, for preventing a current from flowing to the negative output end from the positive output end through the chargeable/dischargeable device; 
         [0014]    a charger, for charging the chargeable/dischargeable device using an alternating current of the alternating current output end; and 
         [0015]    a switch, for selectively electrically connecting the alternating current input end or one of the first output end and the second output end of the inversion voltage regulating circuit to the alternating current output end. 
         [0016]    Preferably, the fifth switching tube and the sixth switching tube are thyristors. 
         [0017]    Preferably, the chargeable/dischargeable device includes a rechargeable battery and a boost-type DC/DC converter, two ends of the rechargeable battery and an input end of the boost-type DC/DC converter are all electrically connected to an output end of the charger, and an output end of the boost-type DC/DC converter is the output end of the chargeable/dischargeable device. 
         [0018]    An embodiment of the present invention provides a method for controlling an uninterruptible power supply. When a voltage of an alternating current of the alternating current input end is in a first predetermined range, the switch is controlled so that the first output end and the second output end of the inversion voltage regulating circuit are electrically connected to the alternating current output end, the seventh switching tube is controlled to be off, the first switching tube and the second switching tube are controlled to obtain a bucked pulsating direct-current voltage between the positive input end and the negative input end, and the inversion voltage regulating circuit is controlled to convert the pulsating direct-current voltage into a required alternating current. 
         [0019]    Preferably, in a positive half cycle of the alternating current, the third switching tube and the sixth switching tube are controlled to be on, and complementary pulse-width modulation signals are provided to the first switching tube and the second switching tube; and in a negative half cycle of the alternating current, the fourth switching tube and the fifth switching tube are controlled to be on, and complementary pulse-width modulation signals are provided to the first switching tube and the second switching tube. 
         [0020]    An embodiment of the present invention provides a method for controlling an uninterruptible power supply. When a voltage of an alternating current of the alternating current input end is in a second predetermined range, the switch is controlled so that the first output end and the second output end of the inversion voltage regulating circuit are electrically connected to the alternating current output end, the seventh switching tube is controlled to be off, the first switching tube and the second switching tube are controlled to obtain a pulsating direct-current voltage between the positive input end and the negative input end, and the inversion voltage regulating circuit is controlled to boost and convert the pulsating direct-current voltage into a required alternating current. 
         [0021]    Preferably, in a positive half cycle of the alternating current, the first switching tube and the sixth switching tube are controlled to be on, and complementary pulse-width modulation signals are provided to the third switching tube and the fourth switching tube; and in a negative half cycle of the alternating current, the second switching tube and the fifth switching tube are controlled to be on, and complementary pulse-width modulation signals are provided to the third switching tube and the fourth switching tube. 
         [0022]    An embodiment of the present invention provides a method for controlling an uninterruptible power supply. When a voltage of an alternating current of the alternating current input end is larger than a first threshold voltage or smaller than a second threshold voltage, the switch is controlled so that the first output end and the second output end of the inversion voltage regulating circuit are electrically connected to the alternating current output end, the first switching tube and/or the second switching tube is controlled so that a free-wheeling path is formed between the negative output end and the positive output end, the seventh switching tube is controlled to work so that a pulsating direct-current voltage is obtained between the positive input end and the negative input end, and the inversion voltage regulating circuit is controlled to convert the pulsating direct-current voltage into a required alternating current, where the first threshold voltage is larger than the second threshold voltage. 
         [0023]    Preferably, when a direct-current voltage provided by the chargeable/dischargeable device is not smaller than a peak voltage of the alternating current required by the alternating current output end, the seventh switching tube is controlled to work in a pulse-width modulation mode, and the inversion voltage regulating circuit is controlled to alternately perform the following two steps: 
         [0024]    1) in a positive half cycle of the required alternating current starting from a moment when the pulsating direct-current voltage is zero, controlling the third switching tube and the sixth switching tube to be on; and 
         [0025]    2) in a negative half cycle of the required alternating current starting from a moment when the pulsating direct-current voltage is zero, controlling the fourth switching tube and the fifth switching tube to be on. 
         [0026]    Preferably, when a direct-current voltage provided by the chargeable/dischargeable device is smaller than a peak voltage of the alternating current required by the alternating current output end, the control method includes periodically performing the following steps: 
         [0027]    1) in a positive half cycle of the alternating current of the alternating current output end: 
         [0028]    11) in a period of time in which a voltage value of the alternating current output end rises from zero to the direct-current voltage provided by the chargeable/dischargeable device, controlling the seventh switching tube to work in a pulse-width modulation mode, and meanwhile controlling the third switching tube and the sixth switching tube to be on; 
         [0029]    12) in a period of time in which the voltage value of the alternating current output end is greater than the direct-current voltage provided by the chargeable/dischargeable device, controlling the seventh switching tube to be on, and meanwhile controlling the sixth switching tube to be on, and providing complementary pulse-width modulation signals to the third switching tube and the fourth switching tube; and 
         [0030]    13) in a period of time in which the voltage value of the alternating current output end drops from the direct-current voltage provided by the chargeable/dischargeable device to zero, controlling the seventh switching tube to work in a pulse-width modulation mode, and meanwhile controlling the third switching tube and the sixth switching tube to be on; and 
         [0031]    2) in a negative half cycle of the alternating current of the alternating current output end: 
         [0032]    24) in a period of time in which the voltage value of the alternating current output end rises from zero to the direct-current voltage provided by the chargeable/dischargeable device, controlling the seventh switching tube to work in a pulse-width modulation mode, and meanwhile controlling the fourth switching tube and the fifth switching tube to be on; 
         [0033]    25) in a period of time in which the voltage value of the alternating current output end is greater than the direct-current voltage provided by the chargeable/dischargeable device, controlling the seventh switching tube to be on, controlling the fifth switching tube to be on, and providing complementary pulse-width modulation signals to the third switching tube and the fourth switching tube; and 
         [0034]    26) in a period of time in which the voltage value of the alternating current output end drops from the direct-current voltage provided by the chargeable/dischargeable device to zero, controlling the seventh switching tube to work in a pulse-width modulation mode, and meanwhile controlling the fourth switching tube and the fifth switching tube to be on. 
         [0035]    Another embodiment of the present invention provides a method for controlling an uninterruptible power supply. When an alternating current of the alternating current input end is interrupted, the switch is controlled so that the first output end and the second output end of the inversion voltage regulating circuit are electrically connected to the alternating current output end, the first switching tube and/or the second switching tube is controlled so that a free-wheeling path is formed between the negative output end and the positive output end, and when a direct-current voltage provided by the rechargeable battery is smaller than a peak voltage of an alternating current required by the alternating current output end, the boost-type DC/DC converter and the seventh switching tube are controlled to work so that a pulsating direct-current voltage is obtained between the positive input end and the negative input end, and the inversion voltage regulating circuit is controlled to convert the pulsating direct-current voltage into the required alternating current. 
         [0036]    Preferably, the boost-type DC/DC converter is controlled to work in a pulse-width modulation mode and output a direct current not smaller than the peak voltage of the required alternating current, the seventh switching tube is controlled to work in a pulse-width modulation mode, and meanwhile the following two steps are alternately performed: 
         [0037]    1) in a first half cycle of the required alternating current starting from a moment when the pulsating direct-current voltage is zero, controlling the third switching tube and the sixth switching tube to be on; and 
         [0038]    2) in a second half cycle of the required alternating current starting from a moment when the pulsating direct-current voltage is zero, controlling the fourth switching tube and the fifth switching tube to be on. 
         [0039]    Preferably, the seventh switching tube is controlled to be on, the boost-type DC/DC converter is controlled to work in a pulse-width modulation mode and output a pulsating direct-current voltage, and meanwhile the following two steps are alternately performed: 
         [0040]    1) in a first half cycle of the required alternating current starting from a moment when the pulsating direct-current voltage is zero, controlling the third switching tube and the sixth switching tube to be on; and 
         [0041]    2) in a second half cycle of the required alternating current starting from a moment when the pulsating direct-current voltage is zero, controlling the fourth switching tube and the fifth switching tube to be on. 
         [0042]    Another embodiment of the present invention provides a method for controlling an uninterruptible power supply. When an alternating current of the alternating current input end is in a predetermined range, the first switching tube, the second switching tube, the inversion voltage regulating circuit, and the seventh switching tube are controlled to stop working, and the switch is controlled so that the alternating current input end is electrically connected to the alternating current output end. 
         [0043]    Another embodiment of the present invention provides a method for controlling an uninterruptible power supply. When an alternating current of the alternating current input end is in a predetermined range, the switch is controlled so that the first output end and the second output end of the inversion voltage regulating circuit are electrically connected to the alternating current output end, the first switching tube and the second switching tube are controlled to be on, the third switching tube and the sixth switching tube are controlled to be on in a positive half cycle of the alternating current, and the fourth switching tube and the fifth switching tube are controlled to be on in a negative half cycle of the alternating current. 
         [0044]    The uninterruptible power supply of the present invention can provide a stable alternating current, does not have an automatic voltage regulator, uses few components and has low costs, and meanwhile has improved power utilization efficiency. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0045]    The embodiments of the present invention are further described below with reference to the accompanying drawings, in which: 
           [0046]      FIG. 1  is a circuit diagram of an uninterruptible power supply according to a first embodiment of the present invention; 
           [0047]      FIG. 2  is an equivalent circuit diagram of the uninterruptible power supply shown in  FIG. 1  in an online mode; 
           [0048]      FIG. 3  is a sequence diagram of pulse-width modulation signals realizing voltage bucking in the online mode; 
           [0049]      FIG. 4  is a sequence diagram of pulse-width modulation signals realizing voltage boosting in the online mode; 
           [0050]      FIG. 5  is an equivalent circuit diagram of the uninterruptible power supply shown in  FIG. 1  in a backup mode; 
           [0051]      FIG. 6  is an equivalent circuit diagram of the uninterruptible power supply shown in  FIG. 1  in a first bypass mode; 
           [0052]      FIG. 7  is an equivalent circuit diagram of the uninterruptible power supply shown in  FIG. 1  in a second bypass mode; 
           [0053]      FIG. 8  is a circuit diagram of an uninterruptible power supply according to a second embodiment of the present invention; and 
           [0054]      FIG. 9  is an equivalent circuit diagram of the uninterruptible power supply shown in  FIG. 8  in a backup mode. 
       
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0055]    In order to make the objectives, technical solutions and advantages of the present invention more clear, the present invention is further described in detail below through specific embodiments with reference to the accompanying drawings. 
         [0056]      FIG. 1  is a circuit diagram of an uninterruptible power supply according to a first embodiment of the present invention. As shown in  FIG. 1 , the uninterruptible power supply  100  includes an alternating current input end  20 , a switch S, an alternating current output end  30 , a rectification voltage regulating circuit  10 , an inversion voltage regulating circuit  40 , an insulated gate bipolar transistor Q 7 , a diode D 7 , an inductor L, a capacitor C, a rechargeable battery  13 , and a charger  14 . 
         [0057]    The rectification voltage regulating circuit  10  includes diodes D 1 , D 2 , D 5 , and D 6 , insulated gate bipolar transistors Q 1  and Q 2 , input ends N 11  and N 12  electrically connected to the alternating current input end  20 , and a positive output end N 1  and a negative output end N 2  used for providing direct current output. The diode D 1  and the insulated gate bipolar transistor Q 1  are connected in series between the input end N 11  and the positive output end N 1 , that is, a collector of the insulated gate bipolar transistor Q 1  is connected to a cathode of the diode D 1 , or an emitter of the insulated gate bipolar transistor Q 1  is connected to an anode of the diode D 1 . The diode D 2  and the insulated gate bipolar transistor Q 2  are connected in series between the input end N 12  and the positive output end N 1 , that is, a collector of the insulated gate bipolar transistor Q 2  is connected to a cathode of the diode D 2 , or an emitter of the insulated gate bipolar transistor Q 2  is connected to an anode of the diode D 2 . An anode of the diode D 5  is electrically connected to the negative output end N 2 , and a cathode of the diode D 5  is connected to the input end N 11 . An anode of the diode D 6  is electrically connected to the negative output end N 2 , and a cathode of the diode D 6  is connected to the input end N 12 . 
         [0058]    The inversion voltage regulating circuit  40  includes insulated gate bipolar transistors Q 3 , Q 4 , Q 5 , and Q 6 , and diodes D 1 ′ and D 2 ′, and further includes a positive input end N 3 , a negative input end N 4 , and an output end N 41  and an output end N 42  used for providing alternating current output. The insulated gate bipolar transistor Q 3  and the diode D 1 ′ are connected in series between the positive input end N 3  and the output end N 41 , that is, a cathode of the diode D 1 ′ is connected to a collector of the insulated gate bipolar transistor Q 3 , or an anode of the diode D 1 ′ is connected to an emitter of the insulated gate bipolar transistor Q 3 . The insulated gate bipolar transistor Q 4  and the diode D 2 ′ are connected in series between the positive input end N 3  and the output end N 42 , that is, a cathode of the diode D 2 ′ is connected to a collector of the insulated gate bipolar transistor Q 4 , or an anode of the diode D 2 ′ is connected to an emitter of the insulated gate bipolar transistor Q 4 . Emitters of the insulated gate bipolar transistors Q 5  and Q 6  are connected to the negative input end N 4 , and collectors of the insulated gate bipolar transistors Q 5  and Q 6  are respectively connected to the output end N 41  and the output end N 42 . That is, the insulated gate bipolar transistor Q 5  is electrically connected between the negative input end N 4  and the output end N 41 , and the insulated gate bipolar transistor Q 6  is electrically connected between the negative input end N 4  and the output end N 42 . 
         [0059]    The capacitor C is connected to output ends (namely, the output ends N 41  and N 42 ) of the inversion voltage regulating circuit  40 . The inductor L is connected between the positive output end N 1  and the positive input end N 3  (that is, electrically connected to the positive output end N 1  and the positive input end N 3 ). The negative output end N 2  is electrically connected to the negative input end N 4 . 
         [0060]    The rechargeable battery  13 , the diode D 7 , and the insulated gate bipolar transistor Q 7  are sequentially connected in series, and a cathode of the rechargeable battery  13  is electrically connected to the negative output end N 2 , an anode of the rechargeable battery  13  is connected to an anode of the diode D 7 , a cathode of the diode D 7  is connected to a collector of the insulated gate bipolar transistor Q 7 , and an emitter of the insulated gate bipolar transistor Q 7  is electrically connected to the positive output end N 1 . An input end of the charger  14  is electrically connected to the alternating current output end  30 , and an output end of the charger  14  is electrically connected to two ends of the rechargeable battery  13  for charging the rechargeable battery  13 . The switch S selectively electrically connects the alternating current input end  20  or the output ends of the inversion voltage regulating circuit  40  to the alternating current output end  30 . 
         [0061]      FIG. 2  is an equivalent circuit diagram of the uninterruptible power supply shown in  FIG. 1  in an online mode. When a voltage of an alternating current provided by the alternating current input end  20  is in a first predetermined range or a second predetermined range, the switch S is controlled so that the output ends of the inversion voltage regulating circuit  40  are electrically connected to the alternating current output end  30  and the insulated gate bipolar transistor Q 7  (not shown in  FIG. 2 ) turns off. At this time, the uninterruptible power supply  100  is in an online mode. A voltage in the first predetermined range is slightly higher than a voltage required by the alternating current output end  30 , and a voltage in the second predetermined range is slightly lower than the voltage required by the alternating current output end  30 . The first predetermined range and the second predetermined range may be selected according to the actual application, and the specific ranges are not limited herein. 
         [0062]    Voltage bucking may be realized in the following manner based on the equivalent circuit shown in  FIG. 2  and the basic principle of a buck conversion circuit (for example, a Buck circuit). For example, in a positive half cycle of an alternating current, a pulse-width modulation signal is provided to the insulated gate bipolar transistor Q 1  so that the insulated gate bipolar transistor Q 1  is equivalent to a switching tube in the Buck circuit, and the insulated gate bipolar transistor Q 2  is controlled to be on so that it forms, together with the diodes D 6  and D 2 , part of a free-wheeling path (that is, equivalent to a diode in the Buck circuit), and the insulated gate bipolar transistors Q 3  and Q 6  are controlled to be on to realize a bucked-voltage output. 
         [0063]      FIG. 3  is a sequence diagram of pulse-width modulation signals realizing voltage bucking in the online mode. Pulse-width modulation signals (denoted by black filled lines in  FIG. 3 ) of the insulated gate bipolar transistors Q 1  and Q 2  are complementary, and the frequencies thereof are not limited herein. The working state of the uninterruptible power supply in one cycle of an alternating current having a frequency of 50 Hz will be described in detail below with reference to  FIG. 3 . In a positive half cycle of the alternating current, the following two control processes are alternately performed: 1) controlling the insulated gate bipolar transistors Q 1 , Q 3 , and Q 6  to be on; and 2) controlling the insulated gate bipolar transistors Q 2 , Q 3 , and Q 6  to be on. In a negative half cycle of the alternating current, the following two control processes are alternately performed: 1) controlling the insulated gate bipolar transistors Q 2 , Q 4 , and Q 5  to be on; and 2) controlling the insulated gate bipolar transistors Q 1 , Q 4 , and Q 5  to be on. A bucked pulsating direct-current voltage can be obtained between the positive input end N 3  and the negative input end N 4  through the aforementioned control process, and the cycle of the pulsating direct-current voltage is half (0.01 second) of the cycle of the alternating current, and a required sine-wave voltage is obtained at the alternating current output end  30 . 
         [0064]    Voltage boosting may be realized in the following manner based on the equivalent circuit shown in  FIG. 2  and the basic principle of a boost conversion circuit (for example, a Boost circuit). For example, in a positive half cycle of an alternating current, the insulated gate bipolar transistors Q 1  and Q 6  are controlled to be on to form part of a free-wheeling path, and complementary pulse-width modulation signals are provided to the insulated gate bipolar transistors Q 3  and Q 4  so that the insulated gate bipolar transistor Q 4  is equivalent to a switching tube in the Boost circuit. When the insulated gate bipolar transistor Q 4  turns on, the inductor L charges; when the insulated gate bipolar transistor Q 3  turns on, the inductor L discharges, thereby realizing voltage boosting. In a negative half cycle of the alternating current, the insulated gate bipolar transistors Q 2  and Q 5  are controlled to be on to form part of a free-wheeling path, and complementary pulse-width modulation signals are provided to the insulated gate bipolar transistors Q 3  and Q 4  so that the insulated gate bipolar transistor Q 3  is equivalent to a switching tube in the Boost circuit. When the insulated gate bipolar transistor Q 3  turns on, the inductor L charges; when the insulated gate bipolar transistor Q 4  turns on, the inductor L discharges, thereby realizing voltage boosting. 
         [0065]      FIG. 4  is a sequence diagram of pulse-width modulation signals realizing voltage boosting in the online mode. Pulse-width modulation signals (denoted by black filled lines in  FIG. 4 ) of the insulated gate bipolar transistors Q 3  and Q 4  are complementary, and the frequencies thereof are not limited herein. The working state of the uninterruptible power supply in one cycle of an alternating current having a frequency of 50 Hz will be described in detail below with reference to  FIG. 4 . In a positive half cycle of the alternating current, the following two control processes are alternately performed: 1) controlling the insulated gate bipolar transistors Q 1 , Q 4 , and Q 6  to be on; and 2) controlling the insulated gate bipolar transistors Q 1 , Q 3 , and Q 6  to be on. In a negative half cycle of the alternating current, the following two control processes are alternately performed: 1) controlling the insulated gate bipolar transistors Q 2 , Q 3 , and Q 5  to be on; and 2) controlling the insulated gate bipolar transistors Q 2 , Q 4 , and Q 5  to be on. A rectified pulsating direct-current voltage can be obtained between the positive input end N 3  and the negative input end N 4  through the aforementioned control process, and a boosted sine-wave voltage is obtained at the alternating current output end  30 . 
         [0066]      FIG. 5  is an equivalent circuit diagram of the uninterruptible power supply shown in  FIG. 1  in a backup mode. When a voltage of an alternating current is less than a lower limit value (namely, a second threshold voltage) of the second predetermined range or greater than an upper limit value (namely, a first threshold voltage) of the first predetermined range, the switch S is controlled so that the output ends of the inversion voltage regulating circuit  40  are electrically connected to the alternating current output end  30 , and the insulated gate bipolar transistor Q 1  and/or the insulated gate bipolar transistor Q 2  is controlled to be on or alternately on. As shown in  FIG. 5 , a free-wheeling diode D 1  between the positive output end N 1  and the negative output end N 2  is an equivalent diode between the positive output end N 1  and the negative output end N 2  when the insulated gate bipolar transistor Q 1  and/or the insulated gate bipolar transistor Q 2  turns on. It can be seen from  FIG. 5  that the free-wheeling diode D′, the insulated gate bipolar transistor Q 7 , and the inductor L constitute a Buck circuit  50 . The insulated gate bipolar transistor Q 7  is controlled to work in a pulse-width modulation mode, so that a pulsating direct-current voltage is obtained between the positive input end N 3  and the negative input end N 4  and has a cycle being half of the cycle of an alternating current required by the alternating current output end  30 . 
         [0067]    Control is performed in the following two situations depending on the direct-current voltage of the rechargeable battery  13 . In the first situation, if the direct current of the rechargeable battery  13  is not smaller than a peak voltage of the alternating current required by the alternating current output end  30 , the insulated gate bipolar transistor Q 7  is controlled to work in a pulse-width modulation mode, so that a peak value of the pulsating direct-current voltage obtained between the positive input end N 3  and the negative input end N 4  is equal to or approximately equal to a peak value of the voltage required by the alternating current output end  30 . Gate driving signals respectively provided to the insulated gate bipolar transistors Q 3 , Q 4 , Q 5 , and Q 6  are the same as gate driving signals of the insulated gate bipolar transistors Q 3 , Q 4 , Q 5 , and Q 6  in  FIG. 3 , so as to invert the pulsating direct-current voltage into a sine-wave voltage and output the sine-wave voltage. That is, the following two processes are alternately performed: 1) in a positive half cycle of the required alternating current starting from a moment when the pulsating direct-current voltage is zero, controlling the insulated gate bipolar transistors Q 3  and Q 6  to be on; and 2) in a negative half cycle of the required alternating current starting from a moment when the pulsating direct-current voltage is zero, controlling the insulated gate bipolar transistors Q 4  and Q 5  to be on. 
         [0068]    In the second situation, if the direct-current voltage of the rechargeable battery  13  is smaller than the peak voltage of the required alternating current, the insulated gate bipolar transistor Q 7  is controlled to work, so that a pulsating direct-current voltage is obtained between the positive input end N 3  and the negative input end N 4 , and the inversion voltage regulating circuit  40  is controlled to work so as to obtain the alternating current having the required amplitude at the alternating current output end  30 . In one cycle of the alternating current of the alternating current output end  30 , the specific control process is as follows: in a positive half cycle of alternating current output, 11) in a period of time in which a voltage value of the alternating current output end  30  rises from zero to a direct-current voltage value of the rechargeable battery  13 , controlling the insulated gate bipolar transistor Q 7  to work in a pulse-width modulation mode so that it is equivalent to a switching tube in the Buck circuit, and meanwhile controlling the insulated gate bipolar transistors Q 3  and Q 6  to be on; 12) in a period of time in which the voltage value of the alternating current output end  30  is greater than the direct-current voltage value of the rechargeable battery  13 , controlling the insulated gate bipolar transistor Q 7  to be on, and meanwhile controlling the insulated gate bipolar transistor Q 6  to be on, and providing complementary pulse-width modulation signals to the insulated gate bipolar transistors Q 3  and Q 4 , so that the insulated gate bipolar transistor Q 4  is equivalent to a switching tube in the Boost circuit; and 13) in a period of time in which the voltage value of the alternating current output end  30  drops from the direct-current voltage value of the rechargeable battery  13  to zero, controlling the insulated gate bipolar transistor Q 7  to work in a pulse-width modulation mode so that it is equivalent to a switching tube in the Buck circuit, and meanwhile controlling the insulated gate bipolar transistors Q 3  and Q 6  to be on; and in a negative half cycle of the alternating current output, 21) in a period of time in which the voltage value of the alternating current output end  30  rises from zero to the direct-current voltage value of the rechargeable battery  13 , controlling the insulated gate bipolar transistor Q 7  to work in a pulse-width modulation mode so that it is equivalent to a switching tube in the Buck circuit, and meanwhile controlling the insulated gate bipolar transistors Q 4  and Q 5  to be on; 22) in a period of time in which the voltage value of the alternating current output end  30  is greater than the direct-current voltage value of the rechargeable battery  13 , controlling the insulated gate bipolar transistor Q 7  to be on, controlling the insulated gate bipolar transistor Q 5  to be on, and providing complementary pulse-width modulation signals to the insulated gate bipolar transistor Q 3  and the insulated gate bipolar transistor Q 4 , so that the insulated gate bipolar transistor Q 4  is equivalent to a switching tube in the Boost circuit; and 23) in a period of time in which the voltage value of the alternating current output end  30  drops from the direct-current voltage value of the rechargeable battery  13  to zero, controlling the insulated gate bipolar transistor Q 7  to work in a pulse-width modulation mode so that it is equivalent to a switching tube in the Buck circuit, and meanwhile controlling the insulated gate bipolar transistors Q 4  and Q 5  to be on. 
         [0069]      FIG. 6  is an equivalent circuit diagram of the uninterruptible power supply shown in  FIG. 1  in a first bypass mode. When an alternating current provided by the alternating current input end  20  satisfies a voltage range required by the alternating current output end  30 , the insulated gate bipolar transistors Q 1 -Q 7  (not shown in  FIG. 6 ) are made off, and the switch S is controlled to electrically connect the alternating current input end  20  to the alternating current output end  30 . The alternating current input end  20  supplies power to the alternating current output end  30 , and meanwhile the charger  14  selects to charge or not charge the rechargeable battery  13  depending on the electric quantity of the rechargeable battery  13 . 
         [0070]      FIG. 7  is an equivalent circuit diagram of the uninterruptible power supply shown in  FIG. 1  in a second bypass mode. The switch S is controlled so that the alternating current output end  30  is connected to output ends of the inversion voltage regulating circuit  40 , the insulated gate bipolar transistors Q 1  and Q 2  are controlled to be on (the insulated gate bipolar transistors Q 1  and Q 2  are equivalent to wires in  FIG. 7 ), and the pulse-width modulation signals of the insulated gate bipolar transistors Q 3 , Q 4 , Q 5 , and Q 6  in  FIG. 3  are respectively provided to the insulated gate bipolar transistors Q 3 , Q 4 , Q 5 , and Q 6 , that is, the inversion voltage regulating circuit  40  is controlled to invert a pulsating direct-current voltage between the positive input end N 3  and the negative input end N 4  into a sinusoidal alternating-current voltage. Meanwhile, the charger  14  selects to charge or not charge the rechargeable battery  13  depending on the electric quantity of the rechargeable battery  13 . 
         [0071]      FIG. 8  is a circuit diagram of an uninterruptible power supply according to a second embodiment of the present invention.  FIG. 8  is substantially the same as  FIG. 1 , and the difference lies in that: the uninterruptible power supply  200  further includes a boost-type DC/DC converter  15 , the boost-type DC/DC converter  15  has input ends connected to two ends of the rechargeable battery  13  and constitutes, together with the rechargeable battery  13 , a chargeable/dischargeable device  13 ′ for providing a direct current. The chargeable/dischargeable device  13 ′, the diode D 7 , and the insulated gate bipolar transistor Q 7  are connected in series, and one output terminal of the chargeable/dischargeable device  13 ′ (namely, one output terminal of the boost-type DC/DC converter  15 ) is connected to the negative output end N 2 . The online mode and bypass mode of the uninterruptible power supply  200  are the same as those of the uninterruptible power supply  100  in  FIG. 1 , and will not be described herein again. 
         [0072]    The uninterruptible power supply  200  is mainly used in the situation that the voltage of the rechargeable battery  13  is smaller than the peak voltage required by the alternating current output end  30 . In a backup mode, the switch S is controlled so that the output ends of the inversion voltage regulating circuit  40  are electrically connected to the alternating current output end  30 , and the insulated gate bipolar transistor Q 1  and/or the insulated gate bipolar transistor Q 2  is controlled so that a free-wheeling path is formed between the negative output end N 2  and the positive output end N 1 . An equivalent circuit diagram of the uninterruptible power supply  200  in the backup mode is shown in  FIG. 9 , where the free-wheeling diode D′, the insulated gate bipolar transistor Q 7 , and the inductor L constitute a Buck circuit  50 . The boost-type DC/DC converter  15  and the insulated gate bipolar transistor Q 7  are controlled so that the cycle of a pulsating direct-current voltage obtained between the positive input end N 3  and the negative input end N 4  is half of the cycle of an alternating current required by the alternating current output end  30 , and a peak value of the pulsating direct-current voltage is equal to or substantially equal to a peak voltage of the required alternating current, and the inversion voltage regulating circuit  40  is controlled to invert the pulsating direct-current voltage into an alternating current and output the alternating current to the alternating current output end  30 . The uninterruptible power supply  200  may specifically work in the following two manners: 
         [0073]    (1) The boost-type DC/DC converter  15  is controlled to work in a pulse-width modulation mode and output a direct current (having a substantially unchanged amplitude) not smaller than the peak voltage required by the alternating current output end  30 , the insulated gate bipolar transistor Q 7  is controlled to work in a pulse-width modulation mode, so as to obtain a pulsating direct-current voltage between the positive input end N 3  and the negative input end N 4 , and the inversion voltage regulating circuit  40  is controlled to convert the pulsating direct-current voltage between the positive input end N 3  and the negative input end N 4  into an alternating current and output the alternating current to the alternating current output end  30 . 
         [0074]    (2) The insulated gate bipolar transistor Q 7  is controlled to be on all the time, the boost-type DC/DC converter  15  is controlled to work in a pulse-width modulation mode and obtain a pulsating direct-current voltage between the positive input end N 3  and the negative input end N 4 , and the inversion voltage regulating circuit  40  is controlled to convert the pulsating direct-current voltage between the positive input end N 3  and the negative input end N 4  into an alternating current and output the alternating current to the alternating current output end  30 . The boost-type DC/DC converter  15  in this embodiment may be any boost-type, for example, isolated or non-isolated, DC/DC conversion circuit. 
         [0075]    The advantage of the uninterruptible power supply  200  having the boost-type DC/DC converter  15  is: once the alternating current of the alternating current input end  20  is normal, since the pulse-width modulation signals of the insulated gate bipolar transistors Q 3 , Q 4 , Q 5 , and Q 6  in a battery power supply mode are the same as the pulse-width modulation signals in the bypass mode, the uninterruptible power supply  200  can conveniently and rapidly switch to the bypass mode. 
         [0076]    The diode D 7  in the aforementioned embodiments can prevent the current from flowing to the negative output end N 2  from the positive output end N 1  through the rechargeable battery  13 . In other embodiments of the present invention, when the voltage between the positive output end N 1  and the negative output end N 2  is smaller than the voltage of the rechargeable battery  13 , the insulated gate bipolar transistor Q 7  may not be connected in series to the diode D 7  (that is, not have the diode D 7 .) 
         [0077]    In other embodiments of the present invention, metal-oxide-semiconductor field effect transistors may be used to replace the insulated gate bipolar transistors Q 1 , Q 2 , Q 3 , Q 4 , Q 5 , Q 6 , and Q 7 . In other embodiments of the present invention, thyristors may be used to replace the insulated gate bipolar transistors Q 5  and Q 6 . The insulated gate bipolar transistors Q 1 , Q 2 , Q 7 , Q 3 , and Q 4  in the uninterruptible power supply of the present invention may be any fully-controlled switching devices. 
         [0078]    A person skilled in the art knows that an equivalent circuit of a reverse blocking insulated gate bipolar transistor (RBIGBT) is a circuit formed by an insulated gate bipolar transistor and a diode connected in series, and therefore, in other embodiments of the present invention, a reverse blocking insulated gate bipolar transistor may be used to replace the diode D 1  and the insulated gate bipolar transistor Q 1  that are connected in series, the diode D 2  and the insulated gate bipolar transistor Q 2  that are connected in series, the diode D 1 ′ and the insulated gate bipolar transistor Q 3  that are connected in series, the diode D 2 ′ and the insulated gate bipolar transistor Q 4  that are connected in series, or the diode D 7  and the insulated gate bipolar transistor Q 7  that are connected in series in the aforementioned embodiments. 
         [0079]    The uninterruptible power supply of the present invention can provide a stable alternating current, does not have an automatic voltage regulator, uses few components and has low costs, and meanwhile has improved power utilization efficiency. 
         [0080]    Although the present invention has been described through preferred embodiments, the present invention is not limited to the embodiments described herein and further includes various changes and variations made without departing from the scope of the present invention.