Title of Invention	'AN IMPROVED UNINTERRUPTED POWER SUPPLY (UPS) SYSTEM'
Abstract	This invention relates to an improved uninterruptible power supply (UPS) system comprises at least two inverters, one of which is connected to mains and the other is connected to load.

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FIELD OF INVENTION This invention relates to an improved uninterrupted Power supply (UPS) system with efficient digital control scheme incorporating a new technology called Dynamic Power Manager (DPM). Specifically but without implying any limitation thereto, the invention relates to a lOKva UPS. The system is specifically useful for mission critical servers, main frame computers, data centers, critical medical/ life support systems. PRIOR ART With the proliferation of sophisticated digital electronics and increasing dependence on high performance computing and networked systems all over the world, the need for high quality and eliable power supply, has become of paramount importance. The commercial grid supply is generally not capable of providing clear and consistent electric power which is required for sensitive equipment and systems. For critical applications, we need highly reliable uninterrupted Power Supply (UPS) that can protect the load against power failure as well as other disturbances like voltage sags, surges and power outages in the grid supply. UPS presently known in the art are double conversion on-line UPS and single conversion OFF-line UPS. The schematic of double conversion online UPS system known in the art is shown in ig. 1. A front-end rectifier converts the grid supply into DC power, which services as input to the inverter. The load is fed from the inverter. When the power grid is within the specified limit, the rectifier converts the available grid AC power into DC power and also charges the battery, if it is required. The power available at the DC bus is again converted into AC power and supplied to the load. If the grid is not present, the inverter takes the power from the battery and supplies to the load. A disadvantage of the above type of UPS is that because of twice conversion in the rectifier/inverter combination, the energy loss of this system is very high. Another disadvantage of the above UPS is that power factor of the grid is low since there is not control over it. Still another disadvantage of the above UPS is that heavily distorted grid current, distorts the grid voltage severely. Further disadvantage of the above UPS is that it introduces harmonic currents into the grid supply since most of them have thyristor controlled front-end converter. The harmonies together with low power factor cause additional heating of cabling switch gear and distribution transformers in addition to high electricity bills. In the case of single conversion off-line UPS system shown in fig. 2, the load is fed directly form the grid supply and when the supply fails, it is fed from the battery through the main inverter. During normal operating condition, static switch is closed and the power to the load is taken from the grid via choke. The advantage in this case is that power to the load is taken from the grid via choke. The advantage in this case is that power is not converted twice as in the case of Double Conversion Scheme. So the energy loss is very low when compared to the Double Conversion scheme. The input voltage to the load is sinusoidal there are no grid harmonic currents from this technique. A limitation of the above UPS is that load voltage is not regulated and the load is not protected from the transient distarbances on the grid. Another limitation of the above UPS is that power factor is low and it changes with grid voltage variations and the type of load. OBJECTS OF PRESENT INVENTION An object of the present invention is to provide an improved Uninterrupted Power Supply (UPS) system for sensitive equipment and systems. Another object of the present invention is to provide an improved UPS system with Dynamic Power Manager (DPM). Still another object of the present invention is to provide an improved UPS system which enables high reduction in energy waste involved in the UPS system known in the art. Further object of the present invention is to provided an improved UPS system which reduces harmonic currents thereby minimizing the heating of cables. Still further object of the present invention is to provide an improved UPS system which enables optimum utilization of installed capacity. Even further object of the present invention is to provide an improved UPS system which maintains grid power factor as unity, irrespective of the type of load. Yet further object of the present invention is to provide an improved UPS system which has low conversion loss and therefore high efficiency of 95% for 20% load to full load which makes it superior to UPS systems known in art that provide high efficiency only near full load. Even further object of the present invention is to provide an improved UPS system which has built-in-battery charging any additional hardware. Still further object of the present invention is to provide an improved UPS system with excellent control of active and reactive power which makes it capable of paralleling similar systems for redundancy/load sharing. STATEMENT OF INVENTION According to this invention there is provided an improved uninterruptible power supply (UPS) system characterized in that at least two inverters, one of which is connected to mains and the other is connected to load wherein one inverter is main inverter and the other is dynamic voltage restorer (DVR) inverter and the main inverter is connected to the mains through a static switch and the DVR inverter is connected with the supplying the load via a transformerin series, wherein the dynamic voltage restorer inverter and the main inverter are connected to a common battery/DC bus, which enables high reduction in energy waste, reduces harmonic currents thereby minimizing the heating of cables, maintains grid power factor as unity irrespective of the type of load and has low conversion loss with high efficiency. BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS: Further objects and advantages of this invention will be more apparent from the ensuing description when read in conjunction with the accompanying drawings and wherein: Fig. 1 : shows the schematic diagram of double conversion on-line UPS; Fig. 2 : shows the schematic diagram of single conversion off-line UPS; Fig. 3 :. shows Block diagram of UPS of present invention; Fig. 4 : shows main voltage and current waveforms of a grid interactive UPS system; Fig. 5 : shows the input grid voltage and grid current weave forms of the UPS of present invention; Fig. 6 : shows power flow control under nominal voltage condition; Fig. 7 : shows power flow control of UPS of present invention under low voltage condition; Fig. 8 : shows power flow control of UPS of present invention under high voltage condition; Fig. 9 : shows power flow control of UPS oi present invention under normal condition except battery is being charged; Fig. 9A: shows paralleling of two AC Voltage Sources; Fig. 9B: shows estimation block diagram ofDPM UPS system; Fig. 10 : shows Estimation block diagram of DPM UPS system; Fig. 11 : shows overall system control algorithm; Fig. 12 : shows stand alone operation; Fig. 13: shows normal operation; Fig .14 : shows stand alone operation salve node Fig. 15 : shows normal operation-slave mode. DESCRITPION OF THE INVENTION WITH REFERENCE TO ACCOMPANYING DRAWINGS There is provided an improved UPS system, which is called a Dynamic Power Manager UPS system overcomes the drawbacks of double conversion an single conversion and single co iversion UPS system. The block diagram of DPM UPS system is shown in Fig. 3. The scheme has two inverters connected to a common battery/DC bus. DVR Inverter is rated at 30% of rated output power of the UPS and it is connected via a transformer in series with the mains supplying the load. The main Inverter is a fully rated inverter. The voltage fluctuations in the supply are compensated by the DVR inverter (1) and thus the load voltage is regulated. The power factor and the current harmonics are compensated by the main inverter during normal operation. During grid failure, the main inyerter (2) supplies power to the load by taking power from the battery. The energy losses are less than half that of the Double conversion on-line UPS system. There is no need to oversize the main inverter to supply the inrush current of the load since the same will be supplied directly from the grid. The DPM UPS system controls the input power to the UPS and also the input power factor to almost unity. When the mains is present, the DVR inverter regulates the output voltage and the main inverter controls the power factor and charges the battery. The static switch is used to prevent back feed into the mains when supply is not pfesent. The mains voltage and current waveforms are shown in Fig. 4. Under normal mode of operation, when the grid is within the specified limit of ±15%, the static switch (5) is closed and the DVR inverter regulates the output voltage, the main inverter controls the power factor and charges the battery. The input grid voltage and current waveforms are shown in fig. 5. From this it is evident that there is no distortion in the grid current and hence the quality of grid voltage is not at all affected. The grid voltage and rid current are in phase meaning that the grid power factor is maintained to unity power factor whatever may be the type of load and grid voltage variations. In stand-alone mode, when the grid fails or is not within the specified limit of ±15%, the main inverter supplies the required power to the lo; d from the battery, static switch (5) is opened to isolate the grid and to prevent back-feed into the grid. The operation of the DPM UPS system can be easily understood by the following different operating conditions. Reference is made to fig .6. In this case the mains voltage is equal to output voltage, batteries are fully charged and the load is 100%. The main current in this case is equal to the load current and the voltage across the transformer is zero. Hence the net power from or to the DVR Inverter is zero. The main Inverter is idling since its output is exactly equal to the mains voltage. Hence no conversion is taking place in any stage hence losses are negligible in this technique. Reference is made to fig. 7. In this case under voltage (-10%) on the main side is assumed i.e. voltage =90% and current =110%. In order to compensate the 10% of under voltage, the DVR inverter add this 10% of voltage to the main voltage. This 10% power is taken from the mains by the main Inverter. The DC voltage available on the input of the DVR Inverter is converted into AC and fed to the transformer. This is a double conversion process with related losses, but only the difference in input and output is converted. If we assume that the total losses in a traditional double conversion to be 10%, losses would be only 1% in this case. So, this technique has very low energy losses. Reference is made to fig. 8. In this case over voltage (+10%) on the main side is assumed i.e. voltage =110% and current =90%. In order to compensate the 10% of over voltage, the DVR inverter absorbs this 10% of voltage. In this case 10% of the total power is passed the DVR inverter, DC link and the main inverter to load. Again a double conversion process, where the same loss consi( eration as in the previous case apply. Reference is made to fig. 9. In this case the nominal conditions are assumed except that the battery is being charg ,d. In this case 110% of power being taken from the mains and since the load is not taking more than 10%, the remain ing 10% power is passed backwards through the main inverter and al sorbed in the battery as charging current. The power flow control along with the schematic model for four operating conditions are shown. Reference is made to fig. 9A. The performance of an UPS system are strongly dependent on its control. Digital Signal Processor (DSP) controllers enable enhanced real time control algorithm design and implementation. Space vector theory based gate pulse generation is playing an important role to switch the 3-phase inverters because of its easier implementation methodology role and maximum output voltage generation with less harmonic content as compared to the other sinusoidal method of PWM generation. One such Space Vector Pulse Width control performance. An appropriate Signal scaling is necessary when digital controllers are used in real time control applications. In order to support a dynamic range of signals and control parameters as wide as possible, the sensor gain needs to ti determined so that the feedback signal covers voltage range of the A/D converter sufficiently. The usage of Q13 format for fractional point representation and enabling the overflow mode bit for saturation, a calcinated result can never be bigger than the most positive number or smaller than the most negative number. The control scheme is based on power system theory. Consider an example of paralleling of two AC voltage sources as shown in fig. 9A. The active power (P) and reactive power (Q) flow between two voltage sources is dependent on its own voltage rotation and magnitude. From the equations (1) and (2). (Equation Removed) it is clearly understood that the P predominanily dependent on the angle (δP=δM±δS) between two sources voltage and the Q dependent on the difference in their voltage magnitudes (VP=1E1-1V1). Where X 3-phase quantities corresponding to R, Y and B VGX Phase voltage of Grid IGX Phase current of Grid VLX Phase voltage of Load ILX phase current of load IMX Phase current of main inverter VDC Battery voltage/DC bus voltage IBAT Discharging/Charging current of the Battery The estimation of various parameters required for implementation of control strategy is shown in fig. 9B. The Poten ial Transformers (PTs) are used to measure the 3-phase voltages of grid, load and DC bus voltage and Current Transformers (CTs) for the measurement of 3-phase currents in grid, load, Main inverter and DC current of the battery. Structure of Control Hardware The controller card includes one TMS 320F240 DSP for DVR control and the Main inverter control and a 80188 Microcontroller for Annunciation and RS485/ RS 232C PC interface. This card generates the gate pulses for the DVR Inverter and the main inverter. It accepts 12 analog inputs required for control through three 12-bit ADCs 9AD 7864). It also generates the logic signals for Pre-charge relay, main contactor, DVR switches and the Static switch modue. The DSP controller communicates with the 80188 Microcontroller through a Dual Port RAM (DPRAM). Structure of Control Algorithm The flow chart of overall system control algorithm is shown in fig. 11. Initially the power supply is energized from the battery to activate the controller. The DC bus link is slowly charged through a Pre-charging relay. The battery is connected to the DC bus by closing the main contactor when the DC bus has reached the desired voltage level. When the UPS system is switched it on, if the grid s within the specification limit, it tracks the input grid voltage and start it's operation in the normal operation mode only. If the grid is not within the specified limit it cannot be switched on and it will wait for the input grid voltage. Once the UPS system is switched it on in the normal operation mode then it automatically operates either in the normal operation or in the stand-Alone operation depending upon the grid specification limit. When the system is ON, the DVR static switch is always opened and it is closed when the system is OFF. The estimation of various parameters required for implementation of control strategy is shown in fig. 10. The Potential Transformers (PTs) are used to measure the 3-phase voltages of grid, load and DC bus voltage and Current Transformers (CTs) for the measurement of 3-phase currents of the grid, and Main inverter. Where, X 3-phase quantities corresponding to R, Y and B VGX Phase Voltage of Grid IGX Phase current of Grid VLX Phase voltage of Load IMX Phase current of main inverter VDC Battery voltage /Dc Bus voltage STAND-ALONE OPERATION Reference is made to fig. 12 which indicates stand Alone operation. In this operation, the Main Inverter runs at its full modulation index and the DVR Inverter acts as a load voltage regulator so that the load voltage is always within a tolerance limit. The controller block diagram is shown in fig. 4. The magnitude of the output load voltage corresponds to the 3-phase nominal voltage (VIRef) is set as reft rence input for the load voltage regulator control. The actual load voltage magnitude is calculated using equations (1), (2) and (3) from 3-phase transformation of estimated actual 3-phase load voltages (Vlx). This is compared with the reference input and the resultant error is processed in a standard PI controller designed in the continuous z-domain. The switching pattern for the DVR inverter is generated based on this P controller output. The rotating angle ol the M ain inverter and the DVR inverter is controlled by an internal fixed 50Hz reference. Normal Operation Reference is made to fig. 13 which indicates norma! operation. In this operation, the DVR inverter acts as a load voltage regulator and the Main inverter functions both as a STATCOM to correct the power factor of the grid to unity and/or battery charger to charge the battery. When the grid voltage (IVGL) is written the specified limit of ±30%,both the inverters track the incoming grid supply frequency and phase lock to it. After that the static switch is closed and the Main inverter supplies the reactive power, which is required for the load (i.e. acting as STATCOM) and also it charges the battery. Fig. 13 shows the DVR inverter control block diagram. The output load voltage magnitude (VI) is calculated using equations (1), (2) and (3) an the input grid voltage (Vg) is calculated using the same equations replacing load voltages with estimated 3-phase grid voltages (VGX). For effective control of output load voltage, two controllers are implemented in DVR inverter to control the output load voltage. The PI controller implemented in the load voltage side is to correct even a small offset error in the output load voltage. The proport onal control in the input grid voltage side is implemented to correct sudden voltage variations in the grid voltage. The addition of these two controllers c utput is modified into corresponding modulation index for DVR inverter. The rotating angle of DVR inverter is same as the input grid voltage angle. The switching pattern for DVR inverter control is generated according to these calculated valves of modulation index and rotating angle. The control block diagram is Main inverter is shown in fig. 13. The charging of the battery is controlled by controlling the main inverter d-axis current, which is calculated using equation (4). The reactive current drawn from grid is compensated by controlling the actual main inverter q-axis current that is calculated using equal on (5). The respective PI controlled output of d-axis and q-axis control is converted into equivalent d-axis and q-axis voltage references by taking into account of its decoupling effects as shown in fig. 3 is used to generate the switching pattern for main inverter. (Equation Removed) If more that one UPS systems are to be connected together, its load bus is connected common to all UPS systems. A scheme of Master/Salve method of load sharing for redundancy is implemented. In this method, the UPS system that is switched on first acts as a Master and the later on as a slave. The UP system operates either is Stand-alone operation mode or in Normal operation mode depending upon the grid specification limit. If the UPS system is switched ON as a Master, the Main inverter started with soft-start facility and keeps the load always in regulation. After it reaches regulation, the Main inverter tries to check the grid voltage for Normal operation. The system goes to immediate active and reactive power correction it is switched ON as a slave. Reference is made to fig. 14 which indicates s and Alone operation. This case is like a paralleling of all the Main inverters of UPS systems are connected together. Here the Main inverter of Master system acts as a load voltage regulator and keeps the load always in regulation as explained in section 4, 4, 1.1. The main inverters of Slaves are tracking the output load voltage angle and locked to it. After that is controls the I/n, (wherein 'n' is the number of UPS systems) of the load power requirement. The slave control scheme is shown in fig. 13. The 2-phase quantities of load voltage and load current are calculated based on equations (3) and (4) from estimated 3-phase load voltage (V1x) and load currents (ILX). From this values, using equations (7) and (8) the total load active power (PL) and reactive power (Ql) is calculated and I/n th of load power (PL) an (QL) are set as the reference inputs for slave active and reactive power controllers respectively. The 2-phase quantity of Slaves Main inverter voltage is calculated using equations (9) and (10) based on its switching level (S1, S2 and S3) and (Equation Removed) DC bus voltage. The 2-phase quantity of its current is calculated based on equations (3) and (4) from the estimated 3-phase Main inverter currents (Imx). The actual sharing power of Slave Main inverter PSTAT and QSTAT is calculated using equations (7) and (8) by substituting the 2-phase calculated values of VSTAT and IM. It. is used as the feedback inputs for the active and reactive power controllers and the resultant errors are processed in respective standard PI controllers. The output of active power PI controller is used to control the rotating angle of the Slave Main inverter and the reactive powe r controller to vary the modulation index of it in such a way that the load active and reactive power is to be shared equally. Because of the fast and accurate nature of load voltage controller and power controller, both good voltage regulation and good load sharing is achieved with no circulating current between systems. Reference is made to fig. 15 which indicates normal operation. In this case, the Master system operates similar to the independent system as explained earlier. In the Salve system, the DVR inverter control is same as explained earlier and the Main inverter control is modified as shown in fig. 15. In active power controller, the DC bus voltage is maintained to the reference voltage level to top only the extra active power flow from the grid and there is no other active power flow into Main inverter. Since charging power is not shared and only the Master system does it. Also, the Main inverter is sharing only I/n th of load reactive power, which is same as explained earlier for reactive power :ontroller. Because of the high controllability of power controllers, good load sharing is achieved with no circulating current between system. The controller time constants are adjusted in such a way that the active power controller acts faster than the reactive power controller. ADVANTAGE OF PPM UPS SYTSTEM 1. High efficiency of more than 90%. 2. Nearly equal percentage efficiency at all loads. 3. Power factor of the input grid is maintained to unity always and it is independent of grid voltage variations and types of load. 4. Minimum grid current distortion. A compact embedded controller with real time control algorithm for dynamic power manager UPS system with all the following features: 1. Grid power factor is maintained unity, rrespective of the type of load. 2. The system efficiency under normal operation is high, due to low conversion loss. 3. Nearly equal percentage efficiency at all loads. 4. Built in battery charging without any additional hardware. 5. Excellent control of active and reactive power. Hence, capability of paralleling similar systems for redundancy/ load sharing. 6. Synchronization with the grid without the help of external PLL. 7. Capability to track a wide variation in frequency. 8. No grid distortion due to the UPS connection. 9. Sub cycle correction feature leading to high dynamic response. 10. The main inverter can be configured as a static VAR compensator by eliminating elements like DVR inverter and battery. 11. The DVR inverter in Stand-Alone mode can be used as a static voltage regulator by eliminating main inverter. A compact embedded hardware with digital signal processor for dynamic power manager UPS system with all the following features 1. Programmable shoot-through delay for IGBT control signal. 2. Assured inactive control signal under power ON, processor RESET and open circuit conditions . 3. Hardware protection for abnormal conditions. 4. High speed A/D and D/A circuits compatible with DSP performance for better dynamic response 5. On board programmable flash memory. 6. Watchdog timer to take care software runaway. 7. Multi-drop networking facility. It is to be noted that the present invention is susceptible modifications, adaptations and changes by those skilled in the art. Such variant embodiments employing the concepts and fearures of this invention are intended to be within the scope of the present invention, which is further set forth under the following claims:- WE CLAIM: 1. An improved uninterruptible power supply (UPS) system characterized in that at least two inverters, one of which is connected to mains and the other- is connected to load wherein one inverter is main inverter (2) and the other is dynamic voltage restorer (DVR) inverter (1) and the main inverter is connected to the mains through a static switch (5) and the DVR inverter is connected with the supplying the load via a transformer (4) in series, wherein the dynamic voltage restorer inverter and the main inverter are connected to a common battery/DC bus, which enables high reduction in energy waste, reduces harmonic currents thereby minimizing the heating of cables, maintains grid power factor as unity irrespective of the type of load and has low conversion loss with high efficiency. 2. An improved uninterruptible power supply (UPS) system as claimed in claim 1 wherein DVR inverter is rated at 30% of the rated output of the UPS and the main inverter is rated for full capacity. 3. An improved uninterruptible power supply (UPS) system substantially as herein described and illustrated with drawings.

Documents:

1410-DEL-2003-Abstract-07-04-2008.pdf

1410-del-2003-abstract.pdf

1410-DEL-2003-Claims-(03-03-2009).pdf

1410-DEL-2003-Claims-07-04-2008.pdf

1410-del-2003-claims.pdf

1410-del-2003-complete specification (granted).pdf

1410-DEL-2003-Correspondence-Others-(13-01-2009).pdf

1410-DEL-2003-Correspondence-Others-07-04-2008.pdf

1410-del-2003-correspondence-others.pdf

1410-del-2003-correspondence-po.pdf

1410-DEL-2003-Description (Complete)-03-03-2009.pdf

1410-DEL-2003-Description (Complete)-07-04-2008.pdf

1410-del-2003-description (complete).pdf

1410-del-2003-drawings.pdf

1410-DEL-2003-Form-1-(13-01-2009).pdf

1410-del-2003-form-1.pdf

1410-del-2003-form-18.pdf

1410-DEL-2003-Form-2-07-04-2008.pdf

1410-del-2003-form-2.pdf

1410-DEL-2003-Form-3-07-04-2008.pdf

1410-del-2003-form-4.pdf

1410-del-2003-form-5.pdf

1410-DEL-2003-GPA-(03-03-2009).pdf

1410-DEL-2003-GPA-(13-01-2009).pdf

1410-DEL-2003-Petition-137-(13-01-2009).pdf