Title of Invention

''A MICRO-HYDEL POWER GENERATING DEVICE FOR SUPPLYING POWER TO SINGLE PHASE LOAD''

Abstract

The subject invention relates to a microhydel power generating system for supplying power to single phase load comprising a turbine operated by the controlled flow of water enabling the said turbine to produce initial voltage to operate self excited induction motor, a plurality of exciting capacitors are connected to said induction motor to first increase the said initially induced voltage and subsequently settling down the said voltage by means of magnetic saturation of the said motor, a single phase consumer load circuit is provided; an electronic load controller circuit is connected across the terminals of the said generating system in parallel to utilize the left over power consumed by the said single phase consumer load circuit and switched capacitor as VAR compensator are provided to compensate the reactive component of the said consumer load circuit as an optional feature.

Full Text

The Present invention relates to a microhydel power generating device for supply pant to single phase load. Reference is made to co-pending application No. 338/Del/2000. More specifically, the subject invention relates to a micro hydel power generating system based on capacitor self excited hydro turbine driven induction motor for supplying power to a single phase load. The object of the invention is to generate electricity from microhydel potential unit to supply the same to local communities independent of the grid and to maintain the terminal voltage constant to ensure constant output power. Small hydro power located in different hilly and remote regions is identified as a promising source to generate electricity to give energy to local community. In large number of sites the power capacity is low typically in the ranges of 1 to 100kW and it is not economically and technically feasible to feed such low power to the grid. Even the quality of the grid in such isolated locations are often very poor with wide variation of voltage and frequency in addition to unreliable supply due to frequent failures. However, installation of transmission lines to such remote locations itself is not a practical and economical solution. In the conventionally available systems synchronous generators are used which are found to be expensive, complex in constructions and less reliable due to continuous maintenance requirements. Such generators are built in frames which are of Screen Protected Drip Proof (SPDP) type and not totally enclosed and hence vulnerable to environmental hazards. Moreover, these generators require electronic voltage regulators to alter the field current to obtain required terminal voltage, as the input power to a hydro turbine driven generator is nearly constant due to fixed head and discharge, it is necessary to have a control mechanism to maintain the input power constant independent of customer load. To overcome the drawbacks and limitations involved in the available conventional power generation systems , the present invention has been developed. In the subject invention, the synchronous generator has been replaced by Induction Generator, which is simple, cheap, rugged and more reliable. The self excitation capacitors are used to facilitate autonomous operation. An electronic load controller is provided to take the dump load which automatically takes care of constancy of output power at varying customer loads by changing adaptively the power consumed by a parallel connected dummy load. The variation in power factor is controlled by the application of an electronic system. Further, the means are provided to adjust different constant power inputs which may vary seasonally through changes in the hydro potential. The subject invention relates to a power generation unit to feed single phase loads. A combination of capacitors are connected across two of the three phases of the generator separately in such a way that the currents in the three windings are nearly balanced by delivering power to a single phase load connected across two of the three terminals. In an embodiment of the subject invention, a three phase induction motor is used as Self excited induction generator to feed single phase loads. A single phase transformer of turns ratio √3:1 is interphased between the generator terminals and the load. Since the rated voltage of induction machine and single phase loads are different and in the ratio as aforementioned. In an other embodiment of the subject invention , the use of transformer is avoided by designing the self excited induction motor to reduce the turns of the motor by a factor 1/3 as compared to the available conventional motors. However, such specially designed motor can thus be used as a motor to supply to a single phase load. In an other embodiment of the subject invention a specially designed two. winding induction motor is used where, a fixed capacitor is connected across one phase and a single phase load is connected across the second phase. The load controller is employed to provide single phase load to the consumers. Such a unit is preferred at low power ratings say below 10kW. The subject system consists of a self excited induction motor operated as generator by connecting appropriate combination of terminal capacitors. This generator is mechanically coupled to a hydro turbine to feed single phase load. When the motor is rotated by the turbine, a small voltage is induced in the three phase stator windings which would continuously rise due to the capacitors and finally settles down to a steady state voltage limited by a magnetic saturation in the generator. Due to the consistency of input power, the output power is also constant at all customer loads. At the terminals of the generator, two parallel circuits are drawn - one going to the customer loads and another for a dummy load such that the total power of the two circuits shall always remain constant. An electronic load controller is provided which controls the power consumed by the dummy load dependent on the customer load as the customer load may vary from zero to the full rated load equal to the input hydro power minus losses. The electronic load controller consists of an uncontrolled full wave rectifier unit which feeds a fixed resistance dummy load through an electronic switch at the DC side of the rectifier. The electronic switch consists of a power transistor which can be turned ON or OFF by giving proper voltage signal at the gate. By controlling the time of ON or OFF, the average current, voltage and power at the resistor is controlled. Means are provided to control the duty cycle which is defined as the ratio of ON time to the sum of ON time and OFF time. The ON time and OFF time are regularly repeated up to the order of 20,000 times a second by a separate control circuit, the pulse width modulation (PWM) controller circuit. In order to effect the AC generator terminal voltage constant, an analog DC feed back signal is obtained in proportion to the generator terminal voltage through a transformer and rectifier unit. This signal is then compared with another fixed voltage. The difference in these two signals is the error signal, which is then fed to a proportional integral controller (PI) whose output decides the duty cycle of the pulse width modulation signal which will ultimately trigger the transistor after proper amplification and isolation through a gate trigger circuit. When the error signal is zero i.e. when the terminal voltage is at the desired value, there will be no triggering of the transistor and the power consumed by the resistor would be zero due to zero current. As the error signal becomes non zero, the duty cycle gets adjusted to feed necessary power to maintain the voltage. All these adjustments are effectuated by the load controller. A switched capacitor system as an optional feature is connected in parallel across the load, to control the lagging power factor. The switched capacitor used in the subject system consists of binary weighted capacitors i.e. a set of 2 or 3 capacitors with values double the other next one, which are connected in parallel with the fixed capacitor. These capacitors are connected in series with electronic switches and this combination is connected in parallel across the fixed capacitors connected at Self excited induction generator terminals. The capacitors can be switched into or switched out of the circuit by turning ON or turning OFF of the thyristors operating as electronic switches. Binary weighted capacitors are used for switching in order to reduce the number of capacitors used. The values of capacitors are fixed such that the generator is able to deliver the rated output to a unity power factor load when it is running at rated speed. When the reactive power demand by the load on the generator increases additional capacitors are switched in parallel to the fixed capacitors. The value of capacitor to be switched is decided by sensing the lagging current drawn by the load. The value of current sensed at the zero crossing instant of voltage gives the reactive current drawn by the load. This reactive current is given as input to a control logic circuit. In the control logic unit the reactive current value sensed is compared with reference values in comparators. In each comparator if the sensed value exceeds the reference value, a high output signal is generated which in turn is used for gating the corresponding thyristor. The reference value at the comparators are fixed in proportion to the terminal voltage values at different inducive loads. The reactive current is sensed in every cycle and compensation of reactive VAR is provided. Accordingly, the present invention relates to a micro-hydel power generating device for supplying power to single phase load comprising: a turbine operated by the controlled flow of water enabling the said turbine to rotate; a self excited induction motor coupled to the said turbine to produce an initially induced voltage in stator windings of said motor; a plurality of exciting capacitors connected to said self excited induction motor to first increase the said initially induced voltage and subsequently settling down to a steady voltage due to magnetic saturation of the said motor; a single phase load consumer circuit; an electronic load controller circuit connected across the terminals of the said motor in parallel to utilize the left over power consumed by the said single phase load consumer circuit; and optionally a switched capacitor VAR compensator for compensating the reactive component of the said consumer load circuit. The present invention can better be understood with reference to the accompanying drawings , which are for illustrative purposes and should not in any way be construed to restrict the scope of the invention keeping in view that certain modifications and improvements are possible without deviating from the scope of the invention. BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS Figure 1: depicts the schematic of micro hydel system feeding single phase load comprising of microhydel turbine, self excited induction generator, capacitors, electronic load controller and customer load. Figure 2: depicts the schematic of micro hydel system feeding single phase load comprising of microhydel turbine, self excited induction generator, capacitors, electronic load controller, customer load and VAR compensator as an optional feature. Figure 3 depicts the three phase self excited induction generator feeding single phase loads using a standard three phase motor with (3/2): 1 transformer Figure 4 depicts the specially wound three phase motor with reduced turns per phase without transformer. Figure 5 depicts a specially wound two phase Self excited induction generator feeding single phase load. Figure 6 depicts the control circuit of the load controller. Figure 7 depicts the switched capacitor scheme to maintain the output power factor. Figure 8 depicts the switching of thyristors DETAILED DESCRIPTION OF THE INVENTION The micro hydel turbine is started and run to operate at appropriate speed by the self excitation of the capacitors. A voltage is induced in the stator windings of the Self excited induction generator [2] as shown in figure 1. The value of the capacitors [3] are fixed to give the rated terminal voltage V at rated speed and rated output. The rated output constant power P is decided by the input water power. The power consumed by the consumer load varies from zero to P, while the input water power is slightly more than P to account for the losses and is generally held constant in a given season and location. The means are provided to make the output power of the generator [2] constant, independent of the consumer single phase load [4] by suitably apportioning of the surplus power to be transferred to the dump load [ 8] through the load controller [5]. As shown in figure 1, the load controller circuit [5] has a single phase rectifier [6], a chopper switch [ 7] and a resistive dump load [ 8]. The single phase rectifier [6] converts the AC voltage across certain points on the parallel circuits shown as A, B C to a DC voltage across P, Q to nearly fixed value Vdc. The chopper switch [7] is switched ON and OFF at preset intervals on a continuous basis. Let the ON time be ton and the OFF time be toff. The ratio ton/(ton + toff) called the duty cycle D is controlled through an external control circuit. Thus the power through the dump load [8] is effectively varied from zero to P so that the total power absorbed by the single phase consumer load [4] plus dump load [ 8] is nearly a constant. The voltage Vac is maintained constant across the single phase consumer load (4). The property of the Self excited induction generator is such that so long as the output power, capacitance and speed are maintained constant, Vac remains constant. By controlling duty cycle D the constant output power is achieved. The VAR compensator [9] is provided as shown in figure 2 as an optional feature to nullify any reactive component of current through partly inductive loads which results in voltage reduction to make voltage Vac constant as the consumer load [4] may not be purely resistive and may draw certain reactive component of current. In the control circuit of the load controller [5] as shown in figure i, from a low power uncontrolled rectifier unit, V^ which is a DC voltage proportional to the actual ac voltage Vac is obtained. The power uncontrolled rectifier unit consists of a step down transformer and a diode rectifier with a capacitive filter. A DC bus which is powered from the self excited induction generator output [2] as shown in figure 1 is provided to maintain the Vref at fixed voltage. The Vac varies from 0-415V rms and the Vref is maintained at fixed voltage 5V. The difference between Vref and Vfb is fed to a PI (proportional and integral) controller [2] as shown in figure 6, consisting of electronic circuits, which in turn is connected to a Pulse Width Modulated Controller [3]. The load controller [5] is made operational only after the self excited induction generator has built up voltage to its rated value. This is achieved by logically adding in a block [4] the output of the Pulse Width Modulated Controller [3] with a signal which is the output of block [7]. In block [7] a pulse is generated when the'feed back voltage represented by Vft , which is proportional to the rated voltage of the self excited induction generator output voltage, exceeds a fixed reference voltage represented by Vref. Output of block [4] is fed to an opto isolator [5] which isolates the control circuit from power circuit. The gate driver circuit [6] consists of standard electronic circuits gives proper amplification for the signal which drives the electronic switch. Output of gate driver circuit [6] goes to the gate of the power transistor which may be selected from a Insulated Gate Bipolar Transistor (IGBT) or Metal Oxide Semiconductor Field Effect Transistor (MOSFET). The circuit diagram of the switched capacitor based VAR compensator to maintain the output power factor is shown in figure 7, and Figure 8 shows the control circuit. In the Block [1] as shown in figure 7, capacitors C and 2C are designed to compensate the reactive components in steps. Block [2] is having a pair of antiparallel electronic devices called thyristors which are switched by a control circuit. By switching [3] or [4], capacitors C or 2C may be brought into the circuit. As the voltage drops due to reactive component of the load, switch [3] or [4] or both are put to ON state to bring in capacitors C or 2C respectively. The facilitations of the switching of the thyristors is explained in the control circuit as shown in Figure 8. In the said circuit a reactive current sensing circuit [2] is provided for the detection of the value of current at the instant when the voltage is zero and this is the maximum reactive current which has to be reduced to zero by the switching arrangement, which is achieved through electronic circuits. The switching of the capacitors are controlled by control logic unit [3] which decides which of the capacitors is to be switched. This is facilitated by comparing the sensed reactive current with three different references which corresponds to different capacitors respectively. This circuit [3] includes standard electronic circuits mainly with operational amplifier integrated circuits. Output of circuit [3] is fed to the firing circuit [4] which in turn sends the gate triggering pulses to the thyristors. The triggering of thyristors is synchronized with the voltage zero crossing by logically adding the output of control logic unit [3] with the output of zero crossing detector [5]. Another embodiment of the same arrangement in which the generator feeds a single phase load is depicted in figure 3, where the stator winding of the Self excited induction generator is generally delta connected and a standard three phase induction motor is employed. Two capacitors C1 and C2 are provided to give minimum unbalanced currents in the stator windings with balance in the three phase voltages Vab, Vbc and Vca shall be employed. Voltage Vt is the single phase voltage taken from the terminals A,C which is stepped down using a transformer to feed standard load at phase voltage VL. Another embodiment of the subject invention as shown in figure 3 is depicted in Figure 4, where the transformer is eliminated by reducing the number of turns of the winding of segment 18 by a factor of 3. This enables the voltage across AC to be approximately 230V which is the standard voltage required for single phase loads. A specially wound two phase Self excited induction generator feeding single phase load as shown in figure 5, where "A" and "M" represents auxiliary and main winding of the generator in which voltage is caused across "M" through the capacitor which is decided to give rated single phase voltage to a load which is connected across it at rated speed. The present invention is a mere statement of invention, various modifications and improvements which are obvious in nature shall come in the preview of the subject application, hence the same should not be construed to restrict the scope of the invention. WE CLAIM: 1. A micro-hydel power generating device for supplying power to single phase load comprising: a turbine operated by the controlled flow of water enabling the said turbine to rotate; a self excited induction motor coupled to the said turbine to produce an initially induced voltage in stator windings of said motor; a plurality of exciting capacitors connected to said self excited induction motor to first increase the said initially induced voltage and subsequently settling down to a steady voltage due to magnetic saturation of the said motor; a single phase load consumer circuit; an electronic load controller circuit connected across the terminals of the said motor in parallel to utilize the left over power consumed by the said single phase load consumer circuit. 2. A micro-hydel power generating device as claimed in claim 1, wherein said device is provided with a switched capacitor VAR compensator for compensating the reactive component of the said consumer load circuit. 3. A micro-hydel power generating device as claimed in claim 1, wherein the said motor is a three phase self excited induction motor. 4. A micro-hydel power generating device as claimed in claim 1, wherein the said motor is a two winding self excited induction motor. 5. A micro-hydel power generating device as claimed in claim 1, wherein said electronic load controller circuit comprises a single phase rectifier, a chopper switch circuit and a fixed resistance load circuit. 6. A micro-hydel power generating device as claimed in claim 5, wherein said chopper switch circuit is an electronic circuit connected at DC side of the said rectifier comprising a step down transformer, a diode rectifier and a capacitive filter. 7. A micro-hydel power generating device as claimed in claim 6, wherein the said electronic circuit connected to said single phase rectifier supplies the said left over power to the said fixed resistance load circuit. 8. A micro-hydel power generating device as claimed in claim 7, wherein the said electronic circuit comprises a power transistor which is turned ON or OFF after receiving voltage signal at particular time interval, thereby determining the duty cycle. 9. A micro-hydel power generating device as claimed in claim 1, wherein said electronic load controller circuit comprises means to control the said duty cycle, being the ratio of ON time to the sum of ON time and OFF time, said means being pulse width modulation circuit.. 10. A micro-hydel power generating device as claimed in claim 6, wherein said transformer and said rectifier unit provides DC feed back signal in proportion to the terminal voltage to effect the AC generator terminal voltage constant and to detect error signal by comparing the DC feed back signal with fixed voltage. 11. A micro-hydel power generating device as claimed in claim 8, wherein said transistor is triggered after amplification and isolation through a gate circuit to decide the said duty cycle of the said pulse width modulation circuit after feeding the said error signal to a proportional integral controller circuit. 12. A micro-hydel power generating device as claimed in claim 8, wherein said power transistor is selected from a Insulated Gate Bipolar Transistor (IGBT) or Metal Oxide Semiconductor Field Effect Transistor (MOSFET). 13. A micro-hydel power generating device as claimed in claim 1, wherein said switched capacitor VAR compensator comprises a combination of binary weighted capacitors and antiparallel electronic devices operable by a control circuit in obtaining and estimating the reactive current to compensate for the reactive component of the said load current to maintain the generated output voltage constant. 14. A micro-hydel power generating device as claimed in claim 13, wherein said antiparallel electronic devices are thyristors. 15. A micro-hydel power generating device as claimed in claim 13, wherein said control circuit is a amplifier integrated circuit. 16. A micro-hydel power generating device as claimed in claim 1, comprising a transformer connected between the said single phase consumer load circuit and the said self excited induction motor to feed single phase consumer load. 17. A micro-hydel power generating device as claimed in claim 16, wherein the said transformer is a step down transformer. 18. A micro-hydel power generating device as claimed in claim 1, wherein the said self excited induction motor comprises windings having lesser number of turns as compared to conventional motor enabling the supply of standard voltage across the single phase load. 19. A micro-hydel power generating device substantially as herein described with reference to accompanying drawings.

Documents:

354-del-2000-abstract.pdf

354-del-2000-claims.pdf

354-del-2000-correspondence-others.pdf

354-del-2000-correspondence-po.pdf

354-DEL-2000-Description (Complete).pdf

354-del-2000-drawings.pdf

354-del-2000-form-1.pdf

354-del-2000-form-19.pdf

354-del-2000-form-2.pdf

354-del-2000-form-26.pdf

354-del-2000-form-3.pdf

354-del-2000-form-5.pdf

354-del-2000-gpa.pdf

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