Title of Invention	CONTROL SYSTEM FOR A SUBMERSIBLE PUMP
Abstract	The present invention provides a variable frequency controller for a submersible pump. The submersible motor & pump system works under input voltage fluctuations and variable water table levels with improved efficiency. An enclosure system is provided for the variable frequency controller which is suitable for outdoor mounting.

Full Text

Field of Invention [001] The present invention relates to submersible pumping systems. More particularly, the present invention relates to a method and system of controlling the motor, to ensure improved performance of the pump under varying conditions. Background and Prior art [002] Submersible pumps are pumps with motor and pump assembly being submerged in the fluid to be pumped. Submersible pumps are used in many applications. The present invention relates to variable speed submersible pumps used for water abstraction or in water wells. [003] Figure 1 shows a block diagram of a fixed speed submersible pump (100) using a fixed speed motor. The system consists of a fixed frequency input AC supply (101), a fixed speed controller (102). The fixed speed controller (101) controls the motor (103), which is connected to the fixed speed pump (104). [004] As the pump works at a fixed frequency, the electrical and mechanical. characteristics are fixed and do not vary for the given pump. The pump has non-linear characteristics. There is low discharge at high heads. But as the discharge increases beyond a certain level, the head of the pump falls off exponentially. This puts limits on the usability of the pump at high discharge conditions. So a pump can either be a high discharge pump or a high head pump. This causes problems in areas where there is large variation in water table level. When the water table is deep, one needs high head. Figure 10 shows a graph of head versus discharge. The curve 1001 shows the response of a submersible pump that's electrical and mechanical characteristics do not vary. It is clear that as the discharge increases beyond a point the head falls exponentially. [005] Head 1, 2 and 3 are the different heads correspond to the water levels Level 1, 2 and 3 respectively. As can be seen from figure 2, at the lowest level of water (level 1), the head is the highest (head 1) and so on. [006] If a user chooses a high head pump, the user can pump water from deep wells. But when the water table rises, the pump cannot give the needed high discharge and operates very in-efficiently. [007] If a user chooses a high discharge pump, the user can get a high discharge efficiently when the water table rises. However when the water table goes deep the chosen pump cannot deliver any water. [008] The fixed speed motor pump characteristics are such that the power increases as the discharge level increases. Hence, higher the discharge, higher is the power level. [009] In fixed speed motor based pumps, during high voltage condition, the motor draws more power; the output of the pump increases, the motor delivers higher power and it can get overloaded and burnt. During low voltage condition, a motor draws lesser power and the output of the pump drops. As a result of being a fixed frequency system, the entire characteristics are tuned to operate optimally at a single point, i.e. the nominal frequency and nominal voltage. [010] Earlier systems with a variable frequency drive tried to correct the output on basis of the input voltage alone, resulting in a solution for the over voltage part. Also the variable frequency controller triggers the control only after the voltage change crossed a threshold value. No correction was applied until the voltage change crossed the threshold. [011] The Patent US 5883489 titled "High speed deep well pump for residential use" reveals a method of controlling the motor by varying the input supply frequency to the motor based on the current measured. When current is measured to vary frequency, the concept works well if the input voltage range does not change too much. Such systems will normally function satisfactorily within a voltage variation range of 5-10 %. However when the voltage variation is beyond this, then the current will vary significantly for the same power. Hence the current based frequency variation becomes unsuitable. [012] The patent US7117120 titled "control systems for centrifugal pumps" reveals a method of variable frequency control by measuring the instantaneous values of current and voltage drawn by the motor to calculate torque and speed. A system like this requires a very expensive electronics system [013] Generally, variable frequency controllers have an inductor on the input side to limit the current. The inductor has impedance, and as current passes through it, both core and copper losses occurs. This loss translates itself into heat and this heat needs to be dissipated. The drive also has a heat sink on which the switching electronic components (Insulated Gate Bipolar Transistors - IGBT) and the input rectifier are mounted. This heat sink also needs to be force air cooled. [014] One can use either a natural air cooled inductor or a force air cooled inductor. The natural air cooled inductor needs to be very big as it needs to have a much larger surface area of exposure to the ambient air and higher cost as the material used for the inductor is much more. A force air cooled inductor is needed in order to optimize on size of the inductor and thereby the overall cost of the system. One could have two separate fans; one for the inductor and the other for the heat sink. But this would increase the cost as well as decrease the system reliability (due to increase in the number of components). [015] Hence to cool both inductor and heat sink one can use a common fan which functions in a serial manner. Here the air first flows over the inductor and then over the heat sink or vice-versa. In such a case the enclosure becomes very tall. Further the variable frequency controllers also provide for air entry and exit openings on the bottom and top by using meshes / slots. The provision of air entry and exit via bottom and top makes these enclosures unsuitable for outdoor mounting, necessitating the mounting within a top enclosed space. This puts severe restrictions on the use of such systems in a submersible pump installation as such pumps and their control panels are possibly needed to be housed in open air environments. Objects of the invention [016] A primary object of the invention is to increase the usable range of the pump and to ensure better water supply despite water table variations and also to ensure that the motor power is held constant thereby improving throughput under varying water table levels and preventing the motor from getting overloaded. [017] Another object of the invention is to improve performance in bad power conditions, namely low voltage and high voltage conditions. [018] Yet another objective is to provide a new method of enclosing the variable frequency controller, and at the same time making the enclosure suitable for outside mounting. Summary of invention: [019] In one aspect, the present invention provides a method of controlling the operation of a submersible pump wherein the pump is driven by a variable speed motor which is provided with variable frequency to the motor based on the input voltage variations and discharge conditions; said method comprising of (a) measuring the DC current and DC voltage and hence measuring the DC power; (b) using the DC power to determine head/discharge levels and DC voltage to determine input voltage conditions in the DSP; and (c) varying the motor speed by giving variable frequency and voltage while maintaining constant power based on PWM signals. [020] In another aspect, the present invention provides a control system controlling the operation of a submersible pump wherein the pump is driven by a variable speed motor which in turn is controlled by a variable frequency controller for providing variable frequency and voltage to the motor based on the input voltage variations and discharge conditions; said system comprising: (a) a rectifier for converting the mains AC supply to DC supply; (b) a voltage and current sensor for measuring the DC values of voltage and current; (c) an inductor at the DC side to improve the power factor by limiting the current; and (d) a DSP controller to compute the DC power and the overall operation of the system. [021] In another aspect, the present invention provides an enclosure system comprising of a common forced air cooling for the variable frequency controller, the fan positioned over the bottom mesh such that the air is pulled in from the bottom mesh and gets out through the top mesh which is protected by a canopy which is open at the sides for letting out the hot air. The canopy protects the variable frequency controller by preventing any liquid or solid particles entering the enclosure from the top side. Brief description of figures [022] The above aspects of the invention are described in detail with reference to the attached drawings, where; Figure 1 shows the block diagram of a submersible pump, controlled by a fixed speed motor. Figure 2 is a diagrammatic representation of the pumping system, excluding the variable frequency drive controller, in accordance with various embodiments of the present invention. Figure 3 shows the block diagram of a submersible pump, controlled by a variable speed motor. Figure 4 is a system diagram illustrating the various units of the variable frequency drive controller, in accordance with various embodiments of the present invention. Figure 5 is the circuit diagram of the DC voltage sensor, in accordance with various embodiments of the present invention. Figure 6 is the circuit diagram of the DC current sensor, in accordance with various embodiments of the present invention. Figure 7 is the graphical representation of the enclosure system, in accordance with various embodiments of the present invention. Figure 8 shows the enclosure, its components and the placement of the components with respect to each other Figure 9 is a flow chart depicting the system flow of the variable frequency drive controller, in accordance with various embodiments of the present invention Figure 10 is a graph showing head v/s discharge characteristics, in accordance with variable embodiments of the present invention. Table 1 shows the efficiency percentage of the new pump using the variable frequency controller in comparison with three other pumps at working voltage of 210 volts Figure 11 shows the efficiency profile comparison graph of the new pump using variable frequency controller in comparison with three other pumps. Detailed description [023] Referring to figure 2, the figure shows the basic pumping system (200) over which control is needed. The parts of the system are a bore well (201) where the water to be pumped out is present, a multi-stage pump (203) which performs the pumping action along with a motor (202). The water pumped out by the pump is carried along the pipe (204) to the overhead tank (205) which is located on top of the building (206). Total dynamic head commonly known as head of the pump refers to the height in meters till the surface of the water. The pump discharge is the amount of water that can be pumped out in liters per minute. Head 1, 2 and 3 are the different heads correspond to the water levels Level 1, 2 and 3 respectively. As can be seen from figure 2, at the lowest level of water (level 1), the head is the highest (head 1) and so on. [024] Figure 3 shows a block diagram of a variable speed submersible pump (300) using a variable speed motor. The system consists of a variable frequency input AC supply (301), a variable speed controller (302). The variable speed controller (301) controls the motor (303), which is connected to the variable speed pump (304). [025] Figure 4 explains the building blocks of the variable frequency controller system (400) for the pump is shown. The input supply AC main (401) supplies the specified voltage to the variable frequency controller (402). The AC mains voltage gets converted to an uncontrolled DC bus voltage by using a full bridge diode rectifier (403).The inductor (404) and the capacitors (405, 410) form a capacitive filter, which reduces the DC ripple voltage. The inductive filter (404) limits the rise and fall of the mains current, hence improving the input power factor by 12-15 %. This results in an input current reduction by 12-15%. This improved power factor reduces the mains RMS current demanded by the drive. A DC current sensing block (411) is placed in the negative current path (VDC -ve). The DC current sensing block (411) senses the DC current drawn by the drive. The resistors (406, 407 and 408) form the voltage divider network and are connected across VDC +ve and VDC -ve. The voltage across resistor (408) is a representation of the DC bus voltage by constant multiplication factor and is measured by the VDC sensing block (409). [026] The switched mode power supply block - SMPS (412) uses the DC rectifier power. The SMPS (412) supplies power to the digital signal processor - DSP (413), the DC current sensing block (210), the VDC voltage sensing block (208) and the IGBT drive module (414). The values of current and voltage sensed by the DC current sensing block (411) and the V DC sensing block (409) are sent to the DSP (413). The DSP (413) houses the entire control and protection algorithms. The DSP (413) gets the DC bus voltage and DC current, and processes this signal to generate PWM signals to control the IGBT switching module (415). The PWM signals are sent to the IGBT switching module (415) through the IGBT gate drive module (414). The IGBT gate drive module (414) amplifies the signal and drives the IGBT switching module (415) to generate the required three phase AC voltage to drive the three phase induction motor (202). This motor (202) is attached to the pump (203). [027] Referring to figure 5, the DC voltage sensor (500) circuit is shown. The operational amplifier (501) forms a buffer and the DC voltage is fed to the buffer (501) through a resistor (502). The output of the buffer (501) is fed to the ADC (analog to digital converter) pin of the DSP through a current limiting resistor (505). [028] Referring to figure 6, the DC current sensor (600) is shown. The current sensor converts the low voltage DC equivalent of the DC current signal into a sufficient DC voltage by a constant multiplication factor i.e. it amplifies the signal to a level which is good enough for the DSP to process and supplies it to the DSP. The equivalent DC voltage is fed through resistors (601, 602). The op-amp (604) followed by the low pass filter formed by resistor (606) and capacitor (607) filters the high frequency band. This is followed by a buffer (609), the output of which is fed to a double stage RC filter, formed by resistors (611,613) and capacitors (612, 614). This is followed by another buffer (616), which is fed to another ADC channel of the DSP through a current limiting resistor (620). [029] The DC power, calculated by the DSP is a reflection of the power required by the motor. DC power = DC voltage x DC current [030] In submersible pumps the relationship between power, head, discharge v/s motor rpm (frequency) is as follows - Discharge a Motor rpm Head a Motor rpm2 Power a Motor rpm3 [031] In case the DC power is of a lower value, the variable frequency controller increases the frequency supplied to the motor. This causes the power taken by the motor to increase and it also increases the head and the discharge of the pump. [032] If the DC power is of a higher value, the variable frequency controller reduces the frequency supplied to the motor. This causes the power taken by the motor to decrease and it also decreases the discharge and the head of the pump. [033] Hence by changing the frequency supplied to the motor, the DC power is brought always to the desired value. [034] Further to this the DC voltage is measured continuously and this is taken as a representation of the input voltage. On basis of the measured DC voltage, the variable frequency controller automatically corrects the output to ensure that the voltage given to the motor is the best possible at all times. This correction is done continuously and very rapidly, many times within a single supply voltage cycle. [035] In case of high input voltage conditions, the variable frequency controller adjusts the output in a manner to ensure that the voltage given to the motor is maintained consistent. If the input voltage goes above a second predetermined threshold level the variable frequency controller switches off the motor running the pump. Hence the motor cannot get subjected to an over-voltage condition. In a fixed frequency system which does not have this correction, the motor gets overloaded in over-voltage condition. This is avoided by the variable frequency controller by ensuring consistent supply, and thereby ensuring that the motor does not get overloaded. [036] In case of low input voltage conditions, the power consumed by a fixed speed motor drops, and hence the output of the pump also drops. This reduces both the throughput of the pump as well as the efficiency of the pump in low input voltage conditions. [037] In case of a similar low input voltage condition, the variable frequency controller continuously adjusts the voltage given to the motor in very small time intervals. This allows for the motor to have higher voltage available to it than would be available from other similar controller devices. A higher than otherwise possible voltage to the motor ensures that the power level of the motor is higher by a similar factor and hence the output is also higher. This ensures that the output and the efficiency of the pump does not drop off, as much as would have happened if the motor was run with a normal variable frequency controller. If the input voltage goes below a first predetermined threshold level the variable frequency controller switches off the motor running the pump. [038] Further to this, in the low input voltage conditions, the motor power is lower, leading to a lower level of DC power. As the DC power is lower, the variable frequency controller increases the output frequency to the motor. This increase in frequency increases the power taken by the motor and also increases the output (head and discharge) of the pump. [039] With both these factors, a) very rapid correction of output voltage based on measurement of DC voltage, and b) increase of frequency to ensure consistent DC power, the variable frequency controller is able to ensure a much higher throughput and hence a much higher efficiency than a conventional pump in low input voltage conditions. [040] The conventional pump works at a fixed frequency. As it works at a fixed input supply frequency, the electrical and mechanical characteristics are fixed and do not vary for a given pump. The pump has non-linear characteristics. There is low discharge at high heads. But as the discharge increases beyond a certain level, the head of the pump falls off exponentially (figure 10 - 1001). This puts limits on the usability of the pump in varying conditions. One can have either a high discharge pump or a high head pump. [041] With the variable frequency controller, the frequency to the motor is varied. This ensures that as the discharge increases, the frequency reduces and though this causes the head of the pump to decrease, it enables the pump characteristics to be almost linear. In this case the new pump combination has linear characteristics even in the high discharge area. Hence the head of the pump reduces proportionately with increase in discharge and does not fall away exponentially (figure 10 - 1002). Hence this pump system can be used more effectively in high discharge cases, thereby increasing the usable range of the pump. It thus also becomes very helpful in places where the water table variation is high. [042] Referring to figure 7, it shows an enclosure system, suitable for outdoor mounting for the variable frequency drive control system. The figure shows the variable frequency controller (703) placed in the enclosure system. A common forced air cooling i.e. a fan (702) cools the variable frequency controller (703). The fan pulls the air through the bottom mesh (701). This air passes over the variable frequency controller (703) and exits the enclosure through a top mesh (704), which is protected by a canopy (705), with open sides, as shown in figure 7. The problem of outdoor mounting is also solved by providing a mesh at the bottom (701) (rain water cannot enter from the bottom), while the top is covered with a canopy (705) with an overhang (706), which allows air to exit via the sides without making an opening on the top side. This ensures that the enclosure becomes rain proof, while allowing the entry and exit for air. As the top is covered, the enclosure becomes suitable for outdoor mounting - and hence removes the restrictions placed by the other variable frequency drives. The canopy protects the variable frequency controller by preventing any external elements from entering the enclosure from the top. These external elements include solid and liquid particles like water, dust, sand, leaves. [043] Referring to Figure 8 it shows the enclosure, its components and the placement of the components with respect to each other (800). The bottom mesh (701) is attached to the bottom cover (802) as shown in the figure. Using a terminal plate (803) these two are connected to the cooling fan (702). The cooling fan (702) sucks in air from the bottom mesh (801) and this passes through the internal cavity of the enclosure which contains the variable frequency controller (703). The air absorbs the heat generated by the IGBT switches, capacitors, rectifier and the inductor. The hot air exits through the top mesh (704) which in turn has a canopy (705) covering it such that it allows the hot air to hit the canopy (706) and exit from sides of the overhang (706). [044] Referring to figure 9, it shows a flow chart showing the entire system flow for the variable frequency controller system. The DC line voltage and DC line current are measured by the respective sensing blocks (902). Then, these analog values of the current and voltage are passed onto the DSP, which are then converted into digital values by the analog to digital converter, present in the DSP (903). The DC power needed by the motor to drive the pump at improved efficiency is calculated by a simple multiplication and constant output power is maintained (904). Output voltage and frequency to the motor are varied based on the DC power within a band (905). The frequency and voltage are varied till the pump starts to operate at desired output power (constant power) (906). The pulse width modulator block, present in the DSP produces pulses, which control the IGBT switching module through the IGBT gate drive module (907). [045] Referring to table 1, it shows the efficiency (in percentage) of the new pump using the variable frequency controller in comparison to three other pumps. The pumps: 4W10H1.0, 4W8B1.0 and 4W14G1.0 are standard 50 Hz pumps with 10 stages, 8 stages and 14 stages respectively. The efficiency of the three pumps and the new pump for different values of heads is shown in the table. The new pump shows a better band of efficiency at all the different heads. At a head of 11.5 meters the new pump variable frequency controller gives an efficiency of 13.35% which is higher in comparison to 10% of the other three pumps. At a head of 76 meters the new pump using the variable frequency controller gives an efficiency of 17.99% in comparison to 10.17% of 4W14GL0 while 4W10H1.0 and 4W8B1.0 do not give any discharge at 76 meters. Therefore, the new pump can work at both high heads and low heads. [046] Referring to Figure 11, it shows the efficiency profile comparison graph of the new pump using the variable frequency controller in comparison to the three pumps: 4W10H1.0, 4W8B1.0 and 4W14G1.0. The graph is plotted based on the values shown in Table 1. From the graph it is clear that the new pump shows a better band of efficiency for different heads in comparison to the three pumps. What is claimed is: 1. A method of controlling the operation of a submersible pump wherein the pump is driven by a variable speed motor for providing variable frequency to motor of the submersible pump based on the input voltage variations and discharge conditions, said method comprising of: a. measuring DC current and DC voltage and hence measuring the DC power; b. using the DC power to determine head/discharge levels in the DSP; c. using the DC voltage to determine the input voltage conditions in the DSP; and d. varying the motor operating conditions to give improved efficiency by varying the frequency and voltage to the motor controlling the pump while maintaining constant power based on PWM signals. 2. The method according to claim 1, wherein the measurement of DC current is done by a DC current sensor and the measurement of DC voltage is done by a DC voltage sensor. 3. The method according to claim 1, wherein the method further comprises the steps of: 1. the DSP converting the analog values of the DC current and the DC voltage to digital values and computes the DC power; 2. the DSP using the computed DC power for determination of head/discharge levels; 3. the DSP using the DC voltage to determine the input voltage conditions. 4. The method according to claim 1, wherein the DC power is brought to a desired value by varying the frequency supplied to the motor. 5. The method according to claim 4, wherein the step of varying the frequency further comprises of increasing the frequency supplied to the motor when input DC power is lower than the average voltage levels, whereby the head and the discharge of the pump are increased. 6. The method according to claim 4, wherein the step of varying the frequency further comprises of decreasing the frequency supplied to the motor when input DC power is higher than the average voltage levels, whereby the head and the discharge of the pump are decreased. 7. The method according to claim 1, wherein the DC voltage is measured continuously to obtain an accurate representation of the input voltage. 8. The method according to claim 1, wherein said variable frequency controller continuously corrects the output to ensure supply of optimum voltage to the motor for the operation of the submersible pump. 9. The method according to claim 1, wherein the step of varying the voltage based on input supply further comprises of said variable frequency controller supplying the motor with a constant voltage such that constant power is taken by the motor to avoid motor overload during high input voltage conditions. 10. The method according to claim 1, wherein the step of varying the voltage based on input voltage supply further comprises of said variable frequency controller supplying a higher than average voltage to the motor to ensure operation at improved discharge efficiency under low voltage conditions. 11. The method according to claim 12, wherein said variable frequency controller continuously adjusts the voltage given to the motor in pre-determined time intervals. 12. The method according to claim 1, wherein the frequency and voltage given to the motor are varied for improving the efficiency while maintaining constant power, whereby higher discharge for a wide range of heads is ensured. 13. The method according to claim 1, the method further comprising the step of switching off the motor when the input voltage goes below a first pre-determined threshold level. 14. The method according to claim 1, the method further comprising the step of switching off the motor when the input voltage goes above a second pre-determined threshold level. 15. A variable speed controller controlling the operation of a submersible pump wherein the submersible pump is driven by a variable speed motor, said variable speed controller providing variable frequency to the variable speed motor based on the input voltage variations and discharge conditions, said variable speed controller comprising: a. a rectifier for converting mains AC supply to DC supply; b. an inductor at the DC side to improve the power factor by limiting rectified current; c. a voltage and a current sensor for measuring DC values of voltage and current respectively drawn by said variable speed controller; d. a digital signal processor (DSP) for generating pulse width modulation (PWM) pulses by computing the DC power from the measured DC current and DC voltage values; and e. an insulated gate bipolar transistor that uses the PWM pulses generated by said DSP to generate variable frequency and voltage to control the variable speed motor. 16. A compact enclosure for the variable frequency controller system comprising of a. a bottom mesh for allowing entry of air; b. a top mesh for allowing exit of air; c. a top canopy with open sides located above said top mesh, where said top canopy blocks the entry of any external elements, at the same time allowing the exit of air, hereby rendering the enclosure suitable for outdoor mounting; d. a fan for air forced cooling located above the bottom mesh; and e. cavity for placing the variable frequency controller system, enclosed by front, side and rear walls of said enclosure. 17. The enclosure as claimed in claim, wherein said canopy is open at the sides with said open sides being protected by an overhang. Dated this 11th day of June 2007 ATTORNEY FOR APPLICANT

Documents:

1250-CHE-2007 AMENDED CLAIMS 16-05-2012.pdf

1250-CHE-2007 AMENDED PAGES OF SPECIFICATION 16-05-2012.pdf

1250-CHE-2007 CORRESPONDENCE OTHERS 06-10-2010.pdf

1250-CHE-2007 CORRESPONDENCE OTHERS 16-05-2012.pdf

1250-CHE-2007 AMENDED CLAIMS 04-04-2012.pdf

1250-CHE-2007 AMENDED CLAIMS 06-10-2010.pdf

1250-CHE-2007 AMENDED PAGES OF SPECIFICATION 06-10-2010.pdf

1250-CHE-2007 AMENDED PAGES OF SPECIFICATION 04-04-2012.pdf

1250-CHE-2007 CORRESPONDENCE OTHERS 12-03-2012.pdf

1250-CHE-2007 CORRESPONDENCE OTHERS 04-04-2012.pdf

1250-CHE-2007 CORRESPONDENCE OTHERS 21-03-2012.pdf

1250-CHE-2007 FORM-13 04-04-2012.pdf

1250-CHE-2007 FORM-13 06-10-2010.pdf

1250-CHE-2007 FORM-13 21-03-2012.pdf

1250-che-2007 form-3 06-10-2010.pdf

1250-CHE-2007 POWER OF ATTORNEY 21-03-2012.pdf

1250-che-2007-abstract.pdf

1250-che-2007-claims.pdf

1250-che-2007-correspondnece-others.pdf

1250-che-2007-description(complete).pdf

1250-che-2007-drawings.pdf

1250-che-2007-form 1.pdf

1250-che-2007-form 26.pdf

1250-che-2007-form 3.pdf

1250-che-2007-form 5.pdf

1250-che-2007-from9.pdf