Abstract:
An uninterruptible power supply (UPS) system with energy feedback to chargers and sinusoidal output charges a battery pack through a first charger under a mains mode. Under a battery mode, the UPS boosts DC voltage outputted from the battery pack to a higher voltage level through a DC-to-DC conversion module, converts the DC voltage to a sinusoidal AC voltage through a DC-to-AC conversion module, and supplies the sinusoidal AC voltage to a load. When the load has energy storage elements and discharged energy occurs in a power supply loop, a micro-controller unit can control the discharged power to charge the battery pack through a second charger, thereby solving the issue of the discharged power from the energy storage elements of the load and enhancing the operational efficiency of the UPS.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to an uninterruptible power supply (UPS) and more particularly to a UPS with dual chargers and sinusoidal output. 
         [0003]    2. Description of the Related Art 
         [0004]    With reference to  FIG. 4 , a conventional UPS has an output filter  71 , a charger  72 , a transfer switch  73 , a DC-to-DC controller  74 , a battery pack  75 , a DC-to-DC conversion module  76  and an inverter  77 . An input terminal of the output filter  71  is connected to an AC mains. The charger  72  and the transfer switch  73  are connected to an output terminal of the output filter  71 . The transfer switch  73  has a first contact, a second contact and a common contact. The second contact is connected to the output terminal of the output filter  71 . The common contact serves as a power output terminal connected to a load. When the mains power is normal, the charger  72  is controlled by the DC-to-DC controller  74  to charge the battery pack  75 . An input terminal of the DC-to-DC conversion module  76  is connected to the battery pack  75 . An input terminal of the inverter  77  is connected to the output terminal of the DC-to-DC conversion module  76 , and an output terminal of the inverter  77  is connected to the second contact of the transfer switch  73 . 
         [0005]    When the mains power is normal, the mains power passes through the output filter  71 , the first contact and the common contact of the transfer switch  73  to supply power to the load. When the mains power is abnormal, the transfer switch is switched to disconnect the first contact from the common contact, and to connect the second contact with the common contact so as to enter a battery mode. Under the battery mode, the DC-to-DC conversion module  76  boosts the DC voltage of the battery pack  75  and outputs the DC voltage to the inverter  77  for the inverter  77  to convert the DC voltage into an AC voltage and supply power to the load through the transfer switch  73 . 
         [0006]    Although the foregoing off-line UPS can supply backup power when the mains power is abnormal, its application is limited to the resistive loads or current loads because of its square wave output. In the case of inductive loads or mixed loads, the load equipment connected to the off-line UPS may be damaged. On the other hand, as the output of on-line UPSs has a sinusoidal waveform identical to that of the mains power, the on-line UPSs are applicable to inductive loads, purely capacitive loads, and mixed loads. In this regard, the applicant files a China Patent Application CN 20120138935.7, entitled “Method for controlling output waveform of uninterruptible power supplies”, which discloses a UPS providing multiple output waveforms for users to selectively switch to one of the output waveforms of the UPS after the UPS enters a battery mode. The output waveforms include a square waveform and a sinusoidal waveform. Accordingly, the output waveforms can be selectable based on the type of load, thereby avoiding damage to the load equipment and enhancing the operation efficiency. 
         [0007]    Despite the feasibility of sinusoidal output, if the on-line and off-line UPSs are practically applied to inductive loads, capacitive loads or mixed loads having energy storage elements, those energy storage elements discharge its stored energy in the form of voltage or current to the DC-to-DC conversion modules of the UPSs after the loads are switched off. The energy discharged by the energy storage elements after the loads are switched off is called a “phantom power”. Even when the DC-to-DC conversion modules are not operating, the “phantom power” is stored in the circuit loops of the DC-to-DC conversion modules. After the DC-to-DC conversion modules are operating, the “phantom power” is then added to pulsating DC voltage outputted from the DC-to-DC conversion modules to further distort the sinusoidal waves outputted from the inverters. The current approach used to tackle such issue is to consume the “phantom power” by converting it into heat and dissipating the heat. However, such approach results in temperature rise of the UPS and energy waste. 
       SUMMARY OF THE INVENTION 
       [0008]    An objective of the present invention is to provide a UPS system with energy feedback to chargers and sinusoidal output capable of feeding energy discharged from energy storage elements of a load back to an independent charger to charge a battery pack. 
         [0009]    To achieve the foregoing objective, the UPS system with energy feedback to chargers and sinusoidal output has a first charger, a battery pack, a DC-to-DC conversion module, a DC-to-AC conversion module, a second charger, a feedback circuit, and a micro-controller unit (MCU). 
         [0010]    The first charger has a first power input terminal and a first power output terminal. The first power input terminal is adapted to connect to an AC mains. 
         [0011]    The battery pack is connected to the first power output terminal of the first charger. 
         [0012]    The DC-to-DC conversion module has an input terminal and an output terminal. The input terminal connected to the battery pack. 
         [0013]    The DC-to-AC conversion module has a DC power input terminal and an AC power output terminal. The DC power input terminal is connected to the output terminal of the DC-to-DC conversion module. 
         [0014]    The second charger has a second power input terminal, a second power output terminal, and a control terminal. The second power input terminal is connected to the output terminal of the DC-to-DC conversion module. The second power output terminal is connected to the battery pack. 
         [0015]    The feedback circuit has at least one signal input terminal and at least one feedback signal output terminal. The at least one signal input terminal is connected to the AC power output terminal of the DC-to-AC conversion module. 
         [0016]    The MCU has at least one feedback terminal, multiple driving signal output terminals, and a charging control terminal. The at least one feedback terminal is respectively connected to the at least one feedback signal output terminal. The driving signal output terminals are each respectively connected to the DC-to-DC conversion module and the DC-to-AC conversion module. The charging control terminal is connected to the control terminal of the second charger. 
         [0017]    Given the foregoing UPS, the first charger charges the battery pack when the mains power is normal, and the DC-to-DC conversion module boosts DC voltage outputted from the battery pack to a higher voltage level and the DC-to-AC conversion module converts the DC voltage to a sinusoidal AC power and supplies the AC power to a load when the mains power is abnormal. When the load has energy storage elements, the energy storage elements discharge energy to the input terminal of the DC-to-DC conversion module. The MCU detects a load condition from the AC power output terminal of the DC-to-AC conversion module through the feedback circuit to determine the charging timing and the duty cycle value of the second charger. 
         [0018]    Accordingly, the benefits of the present invention resides in that the energy discharged by the energy storage elements of the load can be fed back to charge the battery pack through the second charger, thereby solving the issue of the discharged power from the energy storage elements of the load and enhancing the operational efficiency of the UPS. 
         [0019]    Other objectives, advantages and novel features of the invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0020]      FIG. 1  is a functional block diagram of a basic architecture of a UPS system with energy feedback to chargers and sinusoidal output in accordance with the present invention; 
           [0021]      FIG. 2  is a functional block diagram of an embodiment of a UPS system with energy feedback to chargers and sinusoidal output; 
           [0022]      FIG. 3  is a partial circuit diagram of the UPS system in  FIG. 2 ; and 
           [0023]      FIG. 4  is a functional block diagram of a conventional off-line UPS. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0024]    With reference to  FIG. 1 , a basic architecture of a UPS system with energy feedback to chargers and sinusoidal output in accordance with the present invention is shown. The UPS has a first charger  11 , a DC-to-DC controller  13 , a DC-to-DC conversion module  20 , a DC-to-AC conversion module  30 , a second charger  12 , a feedback circuit  14 , a micro-controller unit (MCU)  10  and a battery pack  40 . 
         [0025]    The first charger  11  has a first power input terminal, a first power output terminal, and a control terminal. The first power input terminal is connected to an AC mains. 
         [0026]    The DC-to-DC controller  13  has an output terminal connected to the control terminal of the first charger  11 . 
         [0027]    The DC-to-DC conversion module  20  has an input terminal, an output terminal, and at least one control terminal. The output terminal is connected to the control terminal of the first charger  11 . 
         [0028]    The DC-to-AC conversion module  30  has a DC power input terminal, an AC power output terminal, and at least one control terminal. The DC power input terminal is connected to the output terminal of the DC-to-DC conversion module  20 . 
         [0029]    The second charger  12  has a second power input terminal, a second power output terminal, and a control terminal. The second power input terminal is connected to the output terminal of the DC-to-DC conversion module  20 . 
         [0030]    The feedback circuit  14  has at least one signal input terminal and at least one feedback signal output terminal. The signal input terminal is connected to the AC power output terminal of the DC-to-AC conversion module  30 . 
         [0031]    The MCU  10  has at least one feedback terminal, multiple driving signal output terminals, and a charging control terminal. The at least one feedback terminal is respectively connected to the at least one feedback signal output terminal of the feedback circuit  14 . The driving signal output terminals are each respectively connected to the at least one control terminal of the DC-to-DC conversion module  20  and the at least one control terminal of the DC-to-AC conversion module  30 . The charging control terminal is connected to the control terminal of the second charger  12 . 
         [0032]    The battery pack  40  is connected to the first power output terminal of the first charger  11 , the input terminal of the DC-to-DC conversion module  20 , and the second power output terminal of the second charger  12 , and is charged by the first charger  11  under the control of the DC-to-DC controller  13  when the mains power is normal. 
         [0033]    Under the foregoing system architecture, when the mains power is abnormal, the first charger  11  stops charging the battery pack  40  and the battery pack  40  starts supplying DC power. The DC power is boosted to a higher voltage level by the DC-to-DC conversion module  20  in generation of a pulsating DC voltage. The pulsating DC voltage is transmitted to the DC-to-AC conversion module  30  and is converted into a sinusoidal AC power by the DC-to-AC conversion module  30  to be supplied to a load. If the load has energy storage elements, the energy storage elements discharge their stored energy in the form of voltage or current to the output terminal of the DC-to-DC conversion module  20  when the load is switched off. The MCU  10  acquires a load condition from the AC power output terminal of the DC-to-AC conversion module  30  through the feedback circuit  14  as a basis for the control over the charging timing and the duty cycle value of the second charger  12  so that the discharged energy to the DC-to-DC conversion module  20  can be outputted from the output terminal of the DC-to-DC conversion module  20  to charge the battery pack  40 . 
         [0034]    With reference to  FIG. 2 , an embodiment of a UPS system with energy feedback to chargers and sinusoidal output in accordance with the present invention, which is an off-line UPS, is shown. The UPS also inherits the basic architecture of the UPS in  FIG. 1 , and further has an input filter  15  and a transfer switch  16 . The input filter  15  has an input terminal and an output terminal. The input terminal is connected to an AC mains. The output terminal is connected to the first AC power input terminal of the first charger  11  to filter the inputted mains power. The transfer switch  16  has a first contact  161 , a second contact  162  and a common contact  163 . The common contact  163  serves as a power output terminal switchably connected to the first contact  161  or the second contact  162 . In the present embodiment, the first contact  161  is connected to the output terminal of the input filter  15 , and the second contact  162  is connected to the AC power output terminal of the DC-to-AC conversion module  30 . 
         [0035]    When the mains power is normal, besides power supplied to the load through the first contact  161  and the common contact  163  of the transfer switch  16 , the mains power charges the battery pack  40  through the first charger  11 . When the mains power is abnormal, the common contact  163  of the transfer switch  16  is switched to connect with the second contact  162 , and the battery pack  40  starts supplying DC power. The DC power is converted into a pulsating DC power by the DC-to-DC conversion module  20 , the pulsating DC power is converted into a sinusoidal AC power by the DC-to-AC conversion module  30 , and the sinusoidal AC power is supplied to the load through the second contact  162  and the common contact  163  of the transfer switch  16 . 
         [0036]    With reference to  FIG. 3 , the first charger  11  has a rectification circuit  111  and a flyback converter  112 . An input terminal of the rectification circuit  111  is connected to an AC mains. An input terminal of the flyback converter  112  is connected to the output terminal of the rectification circuit  111 , and an output terminal thereof is connected to the battery pack  40 . The flyback converter  112  has a power switch having a control terminal connected to the DC-to-DC controller  13  and is controlled by the DC-to-DC controller  13 . 
         [0037]    The DC-to-DC conversion module  20  has a push-pull converter. The push-pull converter has two power switches GA, GB connected to two corresponding driving signal output terminals of the MCU  10  for the MCU  10  to control the power switches GA, GB and duty cycles thereof using pulse width modulation (PWM) signals. Hence, the DC-to-DC conversion module  20  can convert the DC power outputted from the battery pack  40  into pulsating DC voltage. 
         [0038]    The DC-to-AC conversion module  30  has four power switches GD, GE, GF, GG connected to four corresponding driving signal output terminals of the MCU  10  for the MCU  10  to selectively turn on two pairs of the power switches GD, GE, GF, GG to convert the pulsating DC voltage outputted from the DC-to-DC conversion module  20  into sinusoidal AC power. 
         [0039]    The second charger  12  may has a DC-to-DC converter or a flyback converter. In the present embodiment, the second charger  12  has a flyback converter, which has a power switch GC. The power switch GC may be a MOSFET (Metal oxide semiconductor field effect transistor) having a gate as a control terminal connected to a corresponding driving signal output terminal of the MCU  10 . It should be stressed that the second charger  12  differs from the first charger  11  in that the first charger  11  is controlled by the DC-to-DC controller  13  and the second charger  12  is controlled by the MCU  10 . 
         [0040]    The feedback circuit  14  has multiple operational power amplifiers (OPA)  141 ˜ 143 . An output terminal of each OPA  141 ˜ 143  is connected to a corresponding feedback terminal of the MCU  10 . An input terminal of one of the OPAs  141  is connected to the AC power output terminal of the DC-to-AC conversion module  30  through a current transformer  144 . An input terminal of another one of the OPAs  142  is directly connected to the AC power output terminal of the DC-to-AC conversion module  30 . An input terminal of yet another one of the OPAs  143  is connected to the first power input terminal of the first charger  11  to detect a condition of the mains power. Accordingly, the MCU  10  can determine operation timing and duty cycle of the second charger  12  according to the mains power and the voltage and current of the AC power outputted from the UPS. 
         [0041]    Even though numerous characteristics and advantages of the present invention have been set forth in the foregoing description, together with details of the structure and function of the invention, the disclosure is illustrative only. Changes may be made in detail, especially in matters of shape, size, and arrangement of parts within the principles of the invention to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed.