Abstract:
An uninterruptible power supply includes an isolation transformer having dual primary windings. The secondary winding generates an output voltage based on the magnetic field generated in one of the dual primary windings. A first primary winding is coupled to an inverter circuit that receives an alternating current input voltage and applies a clean and filter alternating current to the first primary winding. A second primary winding is coupled to a bypass circuit that applies a bypass voltage when the inverter circuit is in a failure state. The power supply also includes a compensation circuit to maintain the output voltage at a desired level.

Description:
BACKGROUND 
     1. Field of the Invention 
     The present invention relates to power supplies for electronic devices. More particularly, the present invention relates to an uninterruptible power supply to provide power to critical equipment. 
     2. Discussion of the Related Art 
     Uninterruptible power supplies (UPSs) provide power to critical equipment that cannot experience any break in service. In other words, even a short duration brownout or blackout is unacceptable. Examples of such equipment include computer servers, computer networks, telecommunication electronics, medical devices, security networks, and the like. Regulated power is available no matter the status of the power supply. 
     Isolated power is important for these devices so that the input power is isolated from the output power. In short, UPSs use an isolation transformer to provide clean power to the device. An isolation transformer may have the same output voltage as input voltage. Isolation of the input and output power also prevents mutual interference, and may be required under certain conditions. 
     A device or equipment using a conventional UPS may include two modes of operation. First is an online mode using alternating current (AC) power applied to the primary winding. The online mode converts DC power that is rectified from an AC power input. The output power from the UPS may be reduced because of loss in the converting process. 
     The other mode may be called a bypass mode. If the online inverter circuit fails to provide power to the secondary winding, or load side, then a bypass circuit ensures power is provided from the power supply. The bypass mode can be implemented in two ways. One bypass mode configures the bypass power directly to the output power, thereby “bypassing” the transformer entirely. This mode does not isolate the input bypass power from the output power. If the bypass power is connected directly to the output, then any power spikes will be transferred to the output side of the power supply because the bypass is not isolated. 
     The other mode for providing bypass power uses a switch to apply the power to the primary winding of the transformer. Drawbacks of this configuration include a voltage interruption during the switchover of power, the output of the inverter circuit needs to be the same voltage as the input, and pulse-width modulation limitations that raise the possibility of distortion, which makes it difficult to compensate the voltage to keep the output of the inverter circuit the same. In terms of supplying uninterrupted power, a transient timing issue exists as the power supply switches from online inverter mode to bypass mode. Further, the bypass and online inverter circuits are connected to the same winding. Thus, the bypass voltage needs to be the same as the output voltage. This aspect results in unregulated voltage going to the primary winding and no adjustment available for the output voltage. 
     In summary, measures exist to provide uninterruptible power to devices and equipment. These measures, however, reduce the effectiveness of the power supply to provide isolated power, or result in temporary loss of power when switching to a bypass mode. Thus, these approaches fail to provide totally isolated output power in an uninterrupted manner. 
     SUMMARY 
     Accordingly, the disclosed embodiments of the present invention improve upon existing UPS technology and alleviate the drawbacks of conventional power supplies discussed above. The disclosed embodiments allow for greater control over the voltage applied to the primary windings and reduce any potential lapse in power during transition from online inverter mode to bypass mode. The disclosed embodiments perform these tasks while keeping the input power isolated from the output power. 
     The disclosed embodiments incorporate a double primary winding configuration for each mode. The primary windings fit each side&#39;s requirements. The configuration for the bypass mode may not be the same as one for the AC online inverter mode. Thus, any switchover from one mode to the other occurs continuously and without any interruption in service. Further, the disclosed embodiments include a circuit to control the output voltage in the online inverter mode based on the load condition. 
     As discussed above, a UPS device usually includes an online inverter circuit and a bypass circuit. The UPS device also may have a battery backup circuit. The online inverter circuit includes an AC-DC-AC converter that provides better quality power to the primary winding. The online inverter circuit takes an AC input and converts it to direct current (DC) power. The DC power is reconverted to AC power to supply “good” quality power. AC power is desirable to utilize the transformer in the power supply. 
     According to the disclosed embodiments, the output voltage is totally isolated from the AC input and bypass side of the power supply. The output voltage provided by the secondary winding while in the AC online inverter mode will be compensated output voltage by using the feedback of load current information. The disclosed embodiments also keep the desired sine waveforms for the alternating current by adjusting the switching pattern. 
     During the bypass mode, the disclosed embodiments isolate the output voltage from the AC input. Any surge voltage experienced within the power supply is isolated. Further, when in bypass mode, the voltage source differs from the source in the AC input side, which results in a different voltage level coming to the primary windings. The disclosed embodiments, however, provides the same output voltage via the secondary winding despite these differences. 
     According to the disclosed embodiments, an uninterruptible power supply is disclosed. The uninterruptible power supply includes an isolation transformer having dual primary windings and a secondary winding to supply an output voltage. A first winding of the dual primary windings is coupled to an inverter circuit that receives an alternating current input voltage. A second winding of the dual primary windings is coupled to a bypass circuit that receives a bypass voltage. Voltage is applied to the second winding upon failure of the inverter circuit to generate the output voltage without interruption. 
     Further according to the disclosed embodiments, an uninterruptible power supply includes an isolation transformer. The isolation transformer includes a first primary winding coupled to an inverter circuit that receives an alternating current input voltage, a second winding coupled to a bypass circuit that receives a bypass voltage, and a secondary winding. The inverter circuit includes a diode to generate a direct current voltage and an inverter to convert the direct current voltage to an alternating current voltage that receives a compensation voltage before being applied to the first primary winding. The alternating current voltage is cleaner than the alternating current input voltage. The uninterruptible power supply also includes a compensation circuit to detect a load current to the first primary winding and to generate the compensation voltage based on the load current. The uninterruptible power supply also includes an output coupled to the secondary winding to provide an output voltage corresponding to the bypass voltage or the alternating current voltage. 
     Further according to the disclosed embodiments, an isolation transformer is disclosed. The isolation transformer includes a first primary winding coupled to an inverter circuit. The inverter circuit provides an alternating current voltage to the first primary winding based on an alternating current input voltage. The isolation transformer also includes a second primary winding coupled to a bypass circuit to provide a bypass voltage. The isolation transformer also includes a secondary winding to generate an output voltage without interruption according to the first primary winding or the second primary winding. The second primary winding is used upon failure of the first primary winding. 
     Further according to the disclosed embodiments, a method for supplying power without interruption is disclosed. The method includes determining whether an inverter circuit is in a failure state. The method also includes applying an alternating current voltage using the inverter circuit to a first primary winding of an isolation transformer if the inverter circuit is not in the failure state. The method also includes applying a bypass voltage to a second primary winding of the isolation transformer if the inverter circuit is in the failure state. The method also includes generating an output voltage using a secondary winding of the isolation transformer based on the alternating current voltage or the bypass voltage. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings are included to provide further understanding of the invention and constitute a part of the specification. The drawings listed below illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention, as disclosed in the claims. 
         FIG. 1  illustrates a block diagram of a power supply to provide power without interruption according to the disclosed embodiments. 
         FIG. 2  illustrates a graph showing the relationship between voltages within the inverter circuit and the load current according to the disclosed embodiments. 
         FIG. 3  illustrates a flowchart for providing power via an uninterruptible power supply according to the disclosed embodiments. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Reference will now be made in detail to the preferred embodiments of the present invention. Examples of the preferred embodiments are illustrated in the accompanying drawings. The preferred embodiments may include those variations readily available to one skilled in the art. 
       FIG. 1  depicts a power supply  100  according to the disclosed embodiments. Power supply  100  includes two circuits that supply power to isolation transformer  101 . Isolation transformer  101  separates the power applied in the primary windings from the power generated in the secondary winding. Isolation transformer  101  also may not include a wire or coupling to the ground so that one must come across both terminals to receive a shock. The primary circuit to supply voltage to a primary winding is inverter circuit  102 . If inverter circuit  102  fails or is off-line, then bypass circuit  104  applies voltage. Other circuits, such as a battery or backup circuit, also may be used, but or not shown. By using circuit  102  or  104 , output voltage Vout is generated at output  150  of power supply  100 . 
     AC power supply  108  provides input voltage Vin to circuit  102 . Diode  110  converts input voltage Vin into rectified DC voltage Vdc. Rectified DC voltage Vdc is applied to inverter  112  to generate AC voltage Vo. This process of going through diode  110  and inverter  112  results in a cleaner waveform for voltage Vo, which means cleaner power will be applied to primary winding  118 . The level of voltage Vo may be adjusted by a voltage Vc, disclosed in greater detail below. 
     Voltage Vo is filtered by a filter circuit comprising inductor  114  and capacitor  116  to generate voltage Va. Voltage Va creates load current I L  that flows through primary winding  118 . Current I L  creates a magnetic field in primary winding  118  that causes a magnetic field to bleed over to secondary winding  120  within transformer  101 . The magnetic field then generates current that results in output voltage Vout. 
     If circuit  102  fails or becomes unavailable, then bypass circuit  104  takes over. Bypass power supply  106  provides voltage Vb through circuit  104 . Voltage Vb generates current Ib that flows through primary winding  105 . Like winding  118 , winding  105  generates a magnetic field that bleeds over onto secondary winding  120 . The magnetic field applied to secondary winding  120  then creates a current that causes output voltage Vout at output  150 . 
     The disclosed embodiments may switch over from circuit  102  to bypass circuit  104  without the need of a switch that delays or interrupts the availability of output voltage Vout at output  150 . Further, primary windings  105  and  118  of transformer  101  isolate output  150  from the inputs, whether it is the regular AC voltage input or a bypass one, as bypass circuit  104  is not attached directly to secondary winding  120 . 
     Inductor  114  and capacitor  116  may serve as a filter circuit to filter voltage Vo and generate voltage Va. The filter circuit cleans up the waveform of the voltage in circuit  102  before load current I L  enters primary winding  118 . Inductor  114  and capacitor  116  also reduce the ripple that results from rectification of the alternating current coming from inverter  112 . Cleaner power then may be provided to output  150  through transformer  101 . As shown in  FIG. 1 , capacitor  116  is connected to a common line, or between phases, while inductor  114  is in line with inverter  112  and winding  118 . Values for inductor  114  and capacitor  116  may be adjustable depending on the specifications for power supply  100 . Moreover, other filter circuits may be provided along circuit  102 , as readily available to those skilled in the art. Other circuitry and devices also may be included within circuit  102  that provides a clean waveform for voltage Va. 
     Circuit  102  also includes a compensation component that serves to keep voltage Va at levels able to provide a constant output voltage Vout. The compensation component may include a current transformer  130  and a voltage compensator  132 . Voltage compensator  132  provides a compensation voltage Vc based on load current I L  detected by current transformer, or detector,  130  as it flows to primary winding  118 . Current transformer  130  may be any detector known in the art. 
     Based on detected load current I L , voltage compensator  132  outputs voltage Vc to adjust the level of voltage Vo coming from inverter  112 . Thus, circuit  102  seeks to provide a constant output voltage Vout by adjusting Vo. Over time, load current I L  increases as it flows into inductor  114 . As a result, voltage Va may decrease as well which cause a lower voltage to be applied to secondary winding  120 , and voltage Vout also will decrease due to the impedence of the transformer. To keep the output voltage constant, voltage compensator  132  provides voltage Vc to compensate for those voltage drops due to load current. 
     Alternatively, the voltage level applied by AC power supply  108  may drop as it is converted to DC and then back to AC voltage in circuit  102 . Voltage Vc also may be used to adjust the voltage applied to primary winding  118  to remain constant by adjusting the voltage for any drops experienced in circuit  102 . 
     Referring to  FIG. 2 , a graph  200  depicts the relationship between voltages Vo and Vout, and load current I L  in this application. The horizontal axis represents the increasing value of load current I L  as it flows into primary winding  118 . As load current I L  increases, the value of voltage Vo increases as well as the output voltage remains substantially the same during operations. 
     The disclosed embodiments employ voltage compensator  132  to adjust voltage Vo to the level shown by the line for voltage Vo. As shown, voltage Vout remains the same even as load current I L  increases. The difference between voltages Va and Vo may be shown by voltage Vc, provided by voltage compensator  132 , as disclosed above. Thus, according to the disclosed embodiments, a constant output voltage Vout is provided by power supply  100  because the voltage applied to primary winding  118  remains constant. 
       FIG. 3  depicts a flowchart  300  for providing power via an uninterruptible power supply according to the disclosed embodiments. For simplicity, reference will be made to the features of the disclosed embodiments shown in  FIG. 1  by power supply  100 . 
     Step  302  executes by activating power supply  100  to provide voltage Vout at output  150 . Voltage Vout preferably is provided without interruption and at an approximately constant level. Step  304  executes by determining whether the circuit for providing the power has failed, such as inverter circuit  102 . Inverter circuit  102  may be determined to be in a failure state if it is not capable of receiving the alternating current input voltage, or if any of its components are inoperable. Moreover, the failure state may exist is a spike occurred that shuts down inverter circuit  102 . Thus, the primary circuit for providing power to the secondary side of the isolation transformer has failed. 
     If step  304  is no, then step  306  executes by receiving the AC input voltage, or voltage Vac. Step  308  executes by converting the AC input voltage to DC voltage, or voltage Vdc. Step  310  executes by converting the DC voltage back to AC voltage, or voltage Vo. This process serves to clean up and rectify the waveform of the voltage applied to primary winding  118  of transformer  101 . 
     Step  312  executes by filtering the waveform of voltage Vo to generate voltage Va. The flowchart may then proceed to step  320  directly or, after a set period of time, certain conditions and the like, proceed to step  314  to determine if the load current flowing into primary winding  118  is acceptable. Thus, step  314  executes by detecting the load current that is used to generate the magnetic field in transformer  101 . Step  316  executes by determining whether the load current is acceptable. The load current may be unacceptable if it results in the voltage generated at output  150  being too high or low. In other words, if output voltage Vout fluctuates beyond the level desired, then the load current is unacceptable. 
     If step  316  is yes, then flowchart  300  proceeds to step  320 , as disclosed below. If step  316  is no, then step  318  executes by adjusting voltage applied to primary winding  118  to remain constant. Compensation voltage Vc is applied to adjust voltage Vo to the acceptable level for constant output, or voltage Va. 
     Step  320  executes by applying voltage Va to primary winding  118  using the load current. Step  320  may be executed directly after filtering the waveform, or after any adjustments are made to the voltage level. Flowchart  300  then proceeds to step  326 , as disclosed below. 
     Referring back to step  304 , if inverter circuit  102  fails, then bypass circuit  104  is used to supply the power at output  150  of power supply  100 . Thus, step  304  determines a “yes” condition. Step  322  executes by receiving bypass voltage Vb at circuit  104 . Step  324  executes by applying voltage Vb to primary winding  105  within transformer  101 . Step  324  and step  320  are shown separately because the voltages are not applied to the same winding, but to one of two independent windings within transformer  101 . Thus, transformer  101  uses two separate, isolated primary windings  105  and  118 . 
     After execution of step  320  or step  324 , step  326  executes by generating a magnetic field within transformer  101 . Current flows through the applicable winding to create the magnetic field. The magnetic field bleeds over to secondary winding  118  to generate a current within the winding. As a load is applied to secondary winding  118 , voltage Vout is generated, as executed in step  328 . 
     For example, an output voltage Vout of 480 volts may be desired. Thus, the AC input voltage and bypass voltage may be 480 volts at 60 Hertz. Further, voltage Va applied to primary winding  118  may be an AC voltage of 480 volts. Alternatively, transformer  101  may step up or step down voltage levels as desired. Thus, if the input voltage to power supply is 480 volts but the desired output voltage is 208 volts, then the number of windings within primary windings  105  and  118  and secondary winding  120  may be adjusted accordingly. 
     Further, primary windings  105  and  118  may differ as the voltages available in inverter circuit  102  and bypass circuit  104  differ. For example, the voltage applied to primary winding  118 , or voltage Va, may be 300 volts while the bypass voltage is 480 volts. Transformer  101  may step up the voltage to result in an output voltage of 480 volts. Thus, inverter circuit  102  may stay at more manageable or safer levels during normal operations of power supply  100 . 
     It will be apparent to those skilled in the art that various modifications and variations can be made in the disclosed embodiments of the present invention without departing from the spirit or scope of the invention. Thus, it is intended that the present invention covers the modifications and variations of the embodiments disclosed above provided that they come within the scope of any claims and their equivalents.