FIELD OF INVENTION
The present invention relates to a sine wave line interactive uninterruptible power supply (UPS) with bidirectional converter and built-in mobile charger and more particularly to a line interactive UPS that employs a bi-directional power converter (DC to AC and AC to DC) in association with the automatic voltage regulator (AVR) to perform the voltage boost/buck/bypass operation in mains mode.
PIOR ART
The early uninterruptible power supply (UPS) devices mainly include two types namely, the online type UPS and the off-line type UPS. In recent years, a new kind of UPS, the line interactive type has been developed that possesses both the features of the on-line and off-line types. The three kinds of UPS devices are briefly discussed hereinafter.
1. On-line UPS: When the line voltage (local grid voltage) is normal, the line voltage input to the UPS through a filtering circuit and a noise absorbing circuit charges a battery set through a charging circuit and input into an inverter through a rectifying circuit simultaneously. After the line voltage is rectified and converted by the inverter, the stable power with superior quality is further provided to electrical instruments, such as a computer or its any peripheral products. Otherwise, when the line voltage is abnormal, the power for those electrical instruments is provided by the charged battery set.
2. Off-line UPS: The line voltage is directly provided to a load without needing to be processed by
the UPS when the line voltage is normal. Meanwhile, the line voltage is input through a charging
circuit to charge a battery set. When the line voltage is unstable or interrupted, a switch provided
inside the UPS switches the power supply path from line voltage to the battery set, whereby the
load still can obtain power through the charged battery.
3. Line interactive UPS: Basically, a line interactive UPS is similar to the off-line UPS. The
difference however is that the line interactive UPS converts the line voltage under a boost (step-up)
mode or a buck (step-down) mode, when the line voltage is higher or lower than normal and still in
a predetermined tolerable range. Therefore, the converted voltage is provided to the load, and the
UPS system does not need to operate in a battery power supply mode.
Usually, in prior art, the line interactive ups is equipped with transformer having multiple windings like for one winding with different tapings for boost/buck/bypass AVR operation in mains mode, second for charging of the connected battery for backup, third winding for inverter operation for converting battery power into AC power and another auxiliary windings for o/p sensing or auxiliary supplies. Second winding for charging will result in the increase in the size and cost of the transformer significantly if connected battery capacity is high like in case of external battery ups where the battery may vary from a few AH to some hundred AH capacity as per the
requirement of the backup time. In such charging concept, the additional charging control and switching devices are required which make the system again costly.
U.S. Pat. No. 5315533 A is directed to backup uninterruptible power system. The main transformer and the H-bridge type inverter are utilized to provide charging of the battery during normal supply of AC power from the mains. Under normal conditions, the secondary of the main transformer functions as a primary to provide an output voltage on the transformer winding which is connected to the inverter. The intrinsic diodes of the switching devices in the lower arms of the H-bridge are used as rectifier, forming two arms of a full-bridge rectifier which is connected to one side winding of the transformer winding, and with rectifying devices connected to the other side of the transformer winding through a main charging device to the battery. The main charger includes a boost controller which serves to boost the output voltage from the rectifying devices to desired voltage level required to charge the battery.
US Pat no 7,141,892 relates to Power supply method of line interacting UPS. This system becomes complicated and costly for moderate and high power application like 1 KVA, 1.5KA and 2KVA. This system is not suitable for external battery (I/O) because there is no galvanic isolation of battery from input and output AC power.
U.S. Pat. No 20040036361 discloses Power supply method of a line interactive UPS and the line interactive UPS. Voltage and phase compensation is required in AC/AC conversion for boost/buck operation. Design and control become complicated under varying conditions of voltage and frequency of grid supply or alternatively source like AC power generator. Although AYR is eliminated still there are four switching configurations like AC/AC, DC/DC and DC/AC converters and bulky filter components (inductors and high capacitors) which make the system complex and costly for moderate and high power. This system is suitable only for light load like 250VA & 350VA or single PC.
U.S. Pat. No. 4,634,888 describes a UPS in which a pair of high frequency transformer is used. One transformer, together with its power converter, is used to charge the battery during stand-by operation. The second transformer, together with its power converter, is used to discharge the same battery for operating a load during back-up operation. The need for two power transformers and two corresponding power converters make the UPS expensive and overly complex to manufacture in comparison with the UPS of the present invention.
U.S. Pat. No. 4,277,692 describes a UPS which uses a bi-directional power converter operating along with a low frequency push-pull transformer and common mode choke. While such a power supply is lower in cost than the previous UPS, but the use of a choke and low frequency transformer still adds to the cost and weight of the UPS.
U.S. Pat. No 5,440,179 describes UPS with bi-directional power flow outputting square/ quasi sine wave. Square/quasi sine wave has very high harmonic distortion. There is only bypass operations. No boost/ buck AVR operation is available, therefore input window is very limited. There is no galvanic isolation in between battery terminals, DC link and AC input/output. So, this system is not suitable for external batteries and longer backup requirement.
U.S. Pat. No 20030105982, Uninterruptible power supply unit is for suspended mode whereas present invention is for retrieving parameter and their setting through a user friendly graphical user interface.
U.S. Pat. No 6094363 describes an Uninterruptible power supply with AC sine wave output and energy recycle function and CA2114507 is Bimodal fast transfer off-line uninterruptible power supply. There is no boost/ buck operation to regulate the voltage in mains mode. It simply bypasses the grid power to load.
U.S. Pat. No 20060103242 is about Uninterruptible power supply facility. In this invention, external charging operation is provided through external battery with a suitable socket. Separate transformer winding and bridge rectifier is being used in this invention to change external and internal battery.
AU3436884 describes Uninterruptible power supply and line conditioner. The utility power lines are effectively connected to the load by way of a series inductance, and the phase angle between the inverter output voltage and the effective input voltage to the inductance from the power lines controls the proportioning of current to the load and to the battery from the power lines, and from the inverter to the load.
US Pat. No 6608404 discloses a Step wave power converter. This is a single- or multi-phase step wave power converter which includes multiple transformers configured to receive DC voltage from one or more power sources. Each of the transformers includes a primary winding and a secondary winding. The transformers are each configured to supply a step for a step wave AC output.
U.S. Pat. No 6218744 describes a line-interactive single conversion uninterruptible power supply (UPS) utilizing a multiple tapped ferroresonant transformer and a square wave PWM inverter. During normal utility line operation, the line voltage is not modified in any way, except for ferroresonant filtering and regulation. Tap control circuitry insures proper tap selection based on the utility input voltage. During tap transitions in utility out of specification operation, a second power source, such as an inverter with battery, is operated to provide output power to the connected loads. The controller provides inverter control commands to operate the inverter in
accordance with a monitored voltage of the battery. The controller may calculate the inverter control values itself, preferably the controller contains a look-up table of inverter control values associated with the monitored voltage of the battery. Control based on monitored battery voltage will be easier in case of resistive load but it becomes complicated in case of other types of load nature (inductive, nonlinear or mixed load) due to increase in waveform distortion.
US Pat. No 5896282 describes an uninterruptible power supply (UPS) system comprising of an inverter for converting a DC voltage into an AC voltage comprising a full-bridge circuit having four silicon controlled rectifier (SCR) switches, two pulse control circuits for generating control voltage signals to turn on alternate pairs of said switches, a time sequencing circuit, and a power switch circuit.
US Pat. No. 4916329 is directed to uninterruptible power supply device that uses a transformer with a first primary winding and secondary winding tightly coupled to one another to transmit AC input electrical power to a voltage sensitive load. A series regulator switches taps in the first primary to keep the load output voltage within certain limits during minor variations in the AC input voltage. A standby inverter supplies standby power to the load after a loss or large variation in the AC input voltage by driving PWM pulses into a secondary primary winding of the transformer. The battery charger in the normal mode, supplies desired DC electrical power to charge the battery from an additional charger winding provided with the same transformer.
OBJECTS OF THE INVENTION
The objective of this invention is to provide an uninterruptible power supply to the connected load through external batteries of selective capacities.
Another objective of the present invention is to stabilize the output voltage in mains mode operation through boost/buck/bypass operation of an automatic voltage regulator (AVR).
Another objective of the present invention is to achieve very high efficiency in bypass mode of an automatic voltage regulator (AVR).
Another objective of the present invention is to convert the stored DC powers of batteries to sine modulated AC power by using H-bridge DC-AC converter and switch to output load in case of failure / bad quality of input grid power.
Another objective of the present invention is to charge the external batteries of different capacities in mains mode by using same H-bridge converter being used for DC-AC conversion during backup mode.
Another objective of the present invention is to eliminate the extra transformer winding required to charge the batteries.
Another objective of the present invention is to improve the input power factor during battery charging by operating H-bridge in fly-back boost converter mode. This results in significant reduction in the input power requirements and electricity bills.
Another objective of the present invention is to efficiently utilize the features of low cost microcontroller for producing PWMs to generate the sine wave output and to control the charger in various charging mode, doing complex operations and complete control and monitoring of the overall UPS functionalities.
Another objective of the present invention is to have complete isolation of external batteries and input/output AC lines by using isolated input and output line sensing feedback and control circuitry. The battery terminals are completely isolated from the input and output AC power and hence it is completely safe.
Another object of the present invention is to provide a synchronized change over with transfer time suitable for all kinds of IT equipments from mains mode to backup (inverter) mode and vice-versa. Also further object of this invention is to manage the operating and release time of the relays of AVR by special relay driver circuitry for fast correction of AVR in mains mode and fast changeover.
Another objective of the present invention is to provide automatic startup of the UPS in mains mode to charge the batteries when output is disabled and line input supply resumed or made available.
Another objective of the present invention is to provide a UPS system which is simple in construction from production and service point of view and cost effective.
Another objective of the present invention is to provide communication with the PC for monitoring, setting and data logging of various system parameters for required operation and analysis of system performance and power quality etc. Further objective of the present invention is to provide a user interface through GUI software for configuring the system as per requirement like setting of battery low cut, boost and float voltage, charging current setting, input mains voltage and frequency window for AVR and charger operation, output voltage setting and events
logging like number of events of mains failures, mains low/high, frequency limits outage, overload, short circuit, battery low etc.
It is, therefore, the overall object of the present invention to provide an uninterruptible power supply which overcomes the drawbacks and disadvantages of uninterruptible power supplies known in prior art.
The primary objective of the present invention is to provide a line interactive UPS system with bidirectional converter and a built-in mobile charger.
SUMMARY OF THE INVENTION
In the present invention the above said charging winding, additional charging control and switching devices have been eliminated completely by utilizing the H-bridge in bidirectional converter mode. H-bridge works as DC to AC converter to transform the battery power into AC sine wave power when grid power fails or becomes out of specified range. When grid power is available in healthy conditions same H-bridge works in fly-back boost mode for AC to DC conversion to charge the external or internal UPS batteries in mains mode. The intrinsic diodes of H-bridge convert the AC in to DC which is boosted by the PWM switching of the lower devices of the same H-bridge converter. The charging current and charging boost/absorption/float voltages are controlled by the PWM switching under the command of micro-controller. Hence, the cost and size of the proposed system is reduced significantly.
In the present invention, the third auxiliary winding is used to sense the output voltage in both mains AYR and backup mode and to build an auxiliary supply to run the UPS even in absence or discharged battery condition. This auxiliary winding is also used to make isolated power supply by a DC-DC converter, required for a built-in mobile charger provided with UPS. The proposed UPS can be switched on in the absence of the battery to take the regulated supply through AVR or to resume the charging in case grid power resumes in healthy condition.
In the present invention the tapings of AVR transformer are selected in such a way that during AVR mode, UPS will bypass healthy grid power (say 220V±10%, 50Hz/60Hz, or 230V±10%, 50Hz/60Hz or 110V±10%, 60Hz or 120V±10%, 60Hz) directly to the load without any boost/buck operation of the mains supply. In such a case, the efficiency of AVR transformer is very high. UPS will boost the grid power if it is low in amplitude and buck the same if it is high in amplitude.
In the present invention logical circuitry, analog circuitry which is required for sensing of various parameters and generation of sine wave output is eliminated by low cost microcontroller with inbuilt A/D converter to reduce the cost and complexity of the system.
The present system with bidirectional converter used as a DC-AC converter to run the load in backup mode and as an AC-DC converter to charge the external or internal battery bank during mains mode.
To achieve the objective of the present invention, a line interactive UPS first determines an operating mode from a by-pass mode, a line voltage conversion (boost/buck) mode and back up mode, based on the stability of a line voltage and frequency. In by-pass / boost / buck mode of the line voltage, the voltage level of the line voltage is further compared with a predetermined value. If line voltage is within the specified range of bypass mode (say 220V±10%, 50Hz/60Hz, or 230V±10%, 50Hz/60Hz or 110V±10%, 60Hz or 120V±10%, 60Hz) then AYR will bypass the line directly to the load without any boost/buck operation of the voltage. In such a case, AYR will operate in highly efficient mode. If the line voltage is higher than the predetermined value, then AYR will reduce the line voltage by buck operation. Otherwise if the line voltage is lower than the predetermined value, then AYR will increase the line voltage by boost operation.
The invention provides an uninterruptible power supply in which AC line power is used to charge the battery and to operate a load during the mains AYR mode of the UPS. In the back-up mode of operation when AC line power is not available, the battery is used to supply power to the load. The UPS utilizes the only one common transformer winding for inverter and charger function by making use of a single bi-directional power converter. Thus, the UPS of the present invention is lower in cost and complexity than such UPSs known in the prior art.
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.
Principal claim indicates inventive features and subsequent claims reflect advantageous features of the present invention.
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 a block diagram of a first embodiment of a line interactive UPS in accordance with the present invention;
Fig. 2 shows a circuit diagram of Input and output voltage sense, input zero-cross sense and supply circuits;
Fig. 3 shows a circuit diagram of relays configuration for boost/buck/bypass operation;
Fig. 4 shows a circuit diagram of AVR relays driver circuits;
Fig. 5 shows a circuit diagram of Two half bridge driver circuits;
Fig. 6 shows a circuit diagram of H-Bridge bidirectional converter circuit;
Fig. 7 shows a circuit diagram of Charge current sense circuit;
Fig. 8 shows a circuit diagram of Load current sense and short circuit detection and load'. display circuits;
Fig. 9 shows a circuit diagram of Battery level and load level display circuit; Fig. 10 shows circuit diagram of RS232 communication circuit;
WITH REFERENCE TO THE
DETAILED DESCRIPTION OF THE INVENTION WITH ACCOMPANYING DRAWING:-

Reference may be made to fig. 1 indicating the overall view of the functionality of the system i.e. Sine Wave Line Interactive UPS. Micro-controller, bi-directional H- bridge converter and relay drivers operating with a power supply which is made by a combination of power from battery, auxiliary supply winding (W3) of the main transformer and line sensing circuitry. Line sensing circuitry will provide power only during the startup of the UPS in mains mode. The microcontroller monitors and controls the operation of the inverter, AYR (mains boost/buck/bypass operation), and charger though circuits like input voltage sensing, output voltage sensing, battery voltage sensing, zero-cross sensing, current sensing, temperature sensing etc. Micro-controller monitors and controls the operation of inverter and charger through bidirectional H-bridge converter. The H-bridge converter converts the battery DC power into sine wave AC power through sine modulated PWM generated by micro-controller. The amplified output of the H-bridge converter through transformer after filtering can be transferred to load by appropriate combination of the relay switches in case of the failure or bad quality of grid power. Same bi-directional H-bridge is used to charge the battery when grid power is available within the specified range. Micro-controller generates the PWMs to control the charging of the connected batteries in various charging mode. Mobile charger section takes power from auxiliary supply winding (W3) of the main transformer. In this section DC -DC converter with fixed DC voltage and current limited output supplies the power to output socket to charge the battery of mobile charger.
Fig. 2 is a circuit diagram of Input and output voltage sense, input zero-cross sense and supply circuits. In figure 2, the input and output sensing circuit converts the AC voltage levels to corresponding analog signals. The resistor network prior to the CPU ensures that the signal falls between the
operating ranges of the CPU. This analog signal is then fed to the in-built Analog to Digital converter of the CPU which samples these analog signals at a fast sampling rate to obtain the equivalent digital signal. Zero cross detector generates the zero cross signal corresponding to input grid supply. Microcontroller senses this zero cross signal to detect phase and frequency of the input grid supply. Micro-controller, bi-directional H- bridge converter and relay drivers operate with a power supply which is made by a combination of power from battery, auxiliary supply winding (W3) of the main transformer and line sensing circuitry. Line sensing circuitry provides power only during the startup of the UPS in mains mode.
Fig. 3 is a circuit diagram of relays configuration for boost/buck/bypass operation. During the presence of grid supply, micro-controller enables the AYR operation by selecting correct tapings of winding (Wl) by using relay switches or static switches. Micro-controller also enables the charger by PWM switching of H-bridge across winding (W2). Micro-controller operates AYR relay at zero voltage to enhance the life of the relay. Charger works in H-bridge boost converter mode and charges the battery in constant current and constant voltage mode. Micro-controller monitors the battery voltage periodically. As the battery reaches in charged condition, microcontroller switches the charger from boost cum absorption state to float state by changing the internal reference corresponding to float level. Charger has built-in over current and under/over input AC voltage protection. Micro-controller also switches off the charger and AVR function by disconnecting the grid supply through relay switch and activating the DC/AC converter (inverter function) if grid supply fails or is out of specified range.
Fig. 4 is a circuit diagram of AVR relays driver circuit. The micro-controller operates the relays in various combinations through relay driver depending on the mains grid supply and operating mode of the UPS system. Relay driver circuit controls the operation time and release time of the relays.
Fig. 5 is a circuit diagram of two half bridge driver circuits. Two half bridge drivers are used in H-bridge configuration. Micro-controller generates a sine modulated PWMs by using a bipolar pulse width modulation technique in H-bridge configuration.
Fig. 6 is a circuit diagram of the H-Bridge bidirectional converter which converts this DC bus (battery) voltage into AC power. Micro-controller controls the regulated 230VAC sine wave output of the H-bridge converter by sensing and comparing closed feedback signal corresponding to output voltage from AC sensing circuit with internal reference signal.
The output of the H-bridge converter, after filtering, can be transferred to the load by using transfer relay switch whenever there is no grid power available or grid power is out of tolerance limit of this proposed system. Same bi-directional H-bridge is used to charge the battery when grid power is available within the specified range. Micro-controller generates the PWMs to control the charging of the connected batteries in various charging mode.
Fig. 7 is a circuit diagram of Charge current sense circuit of the system which senses the charging current levels. The RC network before the CPU provides a second order filter. This analog signal is then fed to the in-built Analog to Digital converter of the CPU which samples this analog signal at a fast sampling rate to obtain the equivalent digital signal. The CPU then controls the charger operation in boost, absorption & float mode.
Fig. 8 is a circuit diagram of Load current sense and short circuit detection and load level for display circuit depicts the load current sense section of the system. It senses the load current levels of the single phase UPS in the inverter mode. The amplified and filtered analog signal through op-amp and filters is then fed to the in-built Analog to Digital converter of the CPU which samples this analog signal at a fast sampling rate to obtain the equivalent digital signal. The CPU then records these levels to ensure that this parameter of the single phase UPS is within permissible limits. If the received values exceed the full load limits, then CPU generates warning of overload to reduce the load though display and specific buzzer beep. The CPU checks this parameter for '% of load ', 'No load' and 'Overload' conditions. A pulse by pulse current limiting circuit is used to limit the inrush current through MOSFET devices of H-bridge converter in case there is an increase in the output current over specified limits due to either short-circuit at the output of system or load characteristics or transient load. In this condition, CPU interrupts when load current exceeds specified limits. The CPU limits the current pulse within few microseconds by disabling the PWMs. CPU counts these events. If these reach a reference number, then the CPU shuts down the system. System can restart by resetting the system manually through the user interface panel of the system.
Fig. 9 is circuit diagram of Battery level and load level display circuit which indicates the battery level, load level and other condition of UPS systems like mains AVR mode, backup mode, mains on/o.k, output on and output off etc.
Fig. 10 is a circuit diagram of RS232 Communication circuit which shows the interface of the system with the PC. The PC receives/transmits the data from/to the system through RS 232.
It is to be noted that the present invention is susceptible to modifications, adaptations and changes by those skilled in the art. Such variant embodiments employing the concepts and features of mis invention are intended to be within the scope of the present invention, which is further set forth under the following claims:-

WE CLAIM
1. A sine wave line interacting UPS with bi-directional converter comprising of a micro
controller, bi-directional H-bridge converter and relay drivers operating with a power
supply from battery, auxiliary supply winding (Ws) of the main transformer and line
sensing circuitry.
2. A sine wave line interacting UPS as claimed in claim 1 wherein the microcontroller
monitors and controls the operation of the inverter, AYR and mobile charger through
circuits in which the micro-controller monitors and controls the operation of inverter
and charger through bi-directional H-bridge converter.
3. A sine wave line interacting UPS as claimed in claim 2 wherein the circuits are such as
input voltage sensing, output voltage sensing, battery voltage sensing, zero-cross
sensing, current sensing, temperature sensing etc.
4. A sine wave line interacting UPS as claimed in any of the preceding claims comprising
of a filter for filtering the amplified output of the H-bridge converter through
transformer, which can be transferred to load by appropriate combination of relay
switches incase of the failure or bad quality of grid power in which the H-bridge
configuration comprising of two half bridge drivers.
5. A sine wave line interacting UPS as claimed in any of the preceding claims wherein the
micro controller is connected to a user interface panel and display like LED/LCD.
6. A sine wave line interacting UPS as claimed in any of the preceding claims having very
high efficiency in bypass mode of an automatic voltage regulator (AYR).
7. A sine wave line interacting UPS as claimed in any of the preceding claims which
charges the external batteries of different capacities in mains mode by using same H-
bridge converter being used for DC-AC conversion during back-up mode.
8. A sine wave line interacting UPS as claimed in any of the preceding claims which
eliminates the extra transformer winding required to charge the batteries.
9. A sine wave line interacting UPS as claimed in any of the preceding claims which
improves the input power factor during charging of battery by operating H-bridge in
fly-back boost converter mode which results in significant reduction in the input power
requirements and electricity bills.
10. A sine wave line interacting UPS with bi-directional converter substantially as herein described with reference to the accompanying drawing.