Title of Invention

AN ENERGY CONTROLLER FOR PROVIDING ELECTRIC POWER OF PREDETERMINED VOLTAGE AND FREQUENCY TO LOAD

Abstract

ABSTRACT' l.An energy controller for providing electric power of predetermined voltage and frequency to a load consisting of a front end converter comprising a single phase/three phase isolator, line filter, a single phase /three phase diode rectifier, dc filter, power factor improvement circuit, input cur rent/voltage sensing circuits and under/over voltage protection circuits, said converter rectifying the input ac supply while ensuring that the input sinusoidal current is drawn at unity power factor; a PWM inverter comprising IGBTs and snubber circuits, the input of the inverter receiving the output of the converter; a control circuit including a line voltage monitor for monitoring the input line voltage and setting the operating point of the load, a microprocessor based PWM generator and gate drive circuits, for providing PWM gate pulses for the IGBTs and thus for generating a pulse width modulated wave form of predetermined amplitude and frequency at the inverter output, the said output of the inverter being the input to the said 1 road.

Full Text

This invention relates to an energy controller for providing electric power of predetermined voltage and frequency to a load In countries where the generated electricity is not enough to meet the demand, the distribution voltage level is lower than the rated value. Electrical equipment when operated at lower voltages do not perform well and operate at lower efficiencies resulting in more losses The electricity used for agricultural purpose in a country like India amounts to about 20-25% of the total electricity generated. The agriculture fields and farms are mostly located in remote areas where the electricity supply is not adequate in quantity. The irrigation pumping is done using induction motors. Since most of the rural areas do have only single phase supply, the motors used are single phase type of which the efficiency is still low compared to a three phase motor of the same rating. In places where three phase motors are used, the performance is not good since the supply voltage is usually low. The energy controller proposed herein is targeted for driving pump sets used for irrigation in the agricultural sector. The controller will provide three phase supply of required voltage and frequency to drive the pump motor. It can accept either single phase or three phase input supply as the case may be. The intelligent controller ensures the following functions: -it draws sinusoidal current at unity power factor from the input side -the motor is started with soft-start, limiting the starting current to about 1.5 times of the rated value -at reduced mains voltage conditions (which is normally encountered in rural areas), the current drawn from the mains supply is also reduced. In ordinary cases where the pump motor is connected directly to the commercial supply, as the input voltage drops, the current drawn from the motor increases sharply, resulting in the damage of the motor. Apart from motors of pump sets, the energy controller proposed herein can find wide and varied application in cases where a predetermined voltage and frequency are required at the input of electrical equipment. The energy controller for providing electric power of predetermined voltage and frequency to a load, according to this invention, consists of a front end converter comprising a single phase/three phase isolator, line filter, a single phase/three phase diode rectifier, dc filter, power factor improvement circuit, input current/voltage sensing circuits and under/over voltage protection circuits, said converter rectifying the input ac supply while ensuring that the input sinusoidal current is drawn at unity power factor; a PWM inverter comprising IGBTs and snubber circuits, the input of the inverter receiving the output of the converter; a control circuit including a line voltage monitor for monitoring the input line voltage and setting the operating point of the load, a microprocessor based PWM generator and gate drive circuits, for providing PWM gate pulses for the IGBTs and thus for generating a pulse width modulated wave form of predetermined amplitide and frequency at the inverter output, the said output of the inverter being the input to the said load. This invention will now be described in further detail with reference to the accompanying drawings which illustrate, by way of example, one of the various possible embodiments of the energy controller proposed herein, Fig.l illustrating the circuit layout of the said embodiment Fig,2 illustrating the circuit layout of the front end converter Fig.3 illustrating the circuit layout of the PWM Inverter and Control Circuit Fig.4 illustrating details of the layout illustrated in Fig.2 Fig.5 illustrating details of the layout illustrated in Fig, 3 Fig.6 illustrating a booster chopper pertaining to the front end converter step-up stage and Fig.7 illustrating the system characteristics The layout diagram of the energy controller is shown in Fig. 1. It consists of front end converter, PWM inverter and control circuit. The front-end converter Fig. 2 consists of a single phase/three phase isolator depending on single phase/three supply, a line filter and single phase/three phase diode rectifier, DC filter and power factor improvement circuit. This converter rectifies the input AC supply and ensures that the controller draws input sinusoidal current at unity power factor. Front end converter Fig. 4 i.e. the converter part of the motor drive circuit consists of input contactor Kl, fuses F1-F3, line filters L1-L3. The AC input is rectified using diode rectifier consisting of diodes D1-D7 and filter consisting of capacitors C1-C4. F4-F7 are fuses for the control portion. Tl is the transformer for isolating. CT1-CT3 and A/M selector switch are provided for measuring the input current. V/M selector switch and v/m for measuring the input voltage. Input over voltage/under voltage protection circuits are also included. In cases where single phase input is used, only R and Y inputs are used. The DC voltage is boosted to the required level using a voltage booster stage as shown in Fig. 6. The energy stored in the inductor L while the device Q is ON, is transferred to the capacitor C when the device becomes OFF. The line voltage is monitored in the microprocessor based control circuit, and the output frequency is adjusted accordingly. The PWM inverter and control electronic Fig. 5 consists of DC-DC converter, line voltage monitor, microprocessor based PWM generator gate drive circuits, PWM inverter, ON/OFF switch and indications such as ON, trip etc. Stepping up of the rectified voltage to the required levels is done by DC-DC converter. Control Electronic portions which include line voltage monitor PWM generator signals for the PWM inverter, ON/OFF switch releases or blocks the gate signals. PWM inverter Fig. 3 consists of HI, CI to R6, C6. The inverter stage generates a pulse width modulated output waveform of required amplitude and frequency. PWM gate pulses for the IGBTs are obtained from the control circuits consisting of line voltage monitor, which monitors the input line voltage and sets the operating point of the pump motor for effective energy saving. Output CTS CT1-CT3 and A/M selector switch and ammeter are provided for output current measuring and V/M selector switch and v/m for voltage feedback and providing necessary current protection. The inverter output is fed to the motor. The three phase PWM inverter stage generates a pulse width modulated output waveform of required amplitude and frequency. The inverter switches consist of advanced power devices. Insulated Gate Bipolar Transistor (IGBT). The intelligent controller monitors the input line voltage and sets the operating point of the pump motor for effective energy saving. It is seen from the curves Pig.7 that by adjusting the operating point of the pump, considerable energy saving is there while operating at low supply voltages. About 40% energy saving results when operated at 70% of the supply voltage, What is noteworthy about the proposed enery controller is: a) The controller generates three phase output from the available single phase input,thereby facilitating the use of energy efficient three phase motors, and promotion of energy conservation measures. b) At reduced input voltages also, the motor will be able to pump the water. The controller output will be adjusted to meet the above condition, and also the current drawn from the grid will be kept minimum, to avoid further dip in the supply voltage. In normal cases, as the supply voltage drops, the motors will take more current resulting in further reduction of the supply voltage. Energy saving of about 40% is achieved when operated at reduced voltages i.e. about 70% of the nominal voltage. c) The starting current of the motor will be limited within 1.50 times its rated current. This will be achieved by maintaining the voltage to frequency ratio constant during starting. d) The speed of the motor is adjusted with the drop in supply voltage, so that the required torque is maintained while ensuring the minimum pumping head required. By this technique, energy storage is more while operating at reduced input voltages. We Claim: l.An energy controller for proximal electric power or predetermined voltage and frequency to a load consisting of a front end converter comprising a single phase/three phase isolator, line filter a single phase/three phase diode rectifier, dc filter, power factor improvement circuit, input current/voltage sensing circuits and under/over voltage protection circuits, said converter rectifying the input ac supply while ensuring that the input sinusoidal current is drawn at unity power factor; a PWM inverter comprising IGBTs and snubber circuits, the input of the inverter receiving the output of the converter; a control circuit including a line voltage monitor for monitoring the input line voltage and setting the operating point of the load, a microprocessor based PWM generator and gate drive circuits, for providing PWM gate pulses for the IGBTs and thus for generating a pulse width modulated wave form of predetermined amplitude and frequency at the inverter output, the said output of the inverter being the input to the said 1 oat. 2.An energy controller as claimed in Claim 1 wherein a dc booster is provided for the said converter for stepping up its output dc voltage. 3.An energy controller as claimed in Claim 1 or Claim 2 wherein the inverter circuit includes current transformers, current/voltage sensing circuits. 4.An energy controller for providing electric power of predetermined voltage and frequency to a load, substantial as herein described with reference to, and as illustrated in, the accompanying drawings.

Documents:

724-mas-1996 abstract duplicate.pdf

724-mas-1996 abstract.pdf

724-mas-1996 claims duplicate.pdf

724-mas-1996 claims.pdf

724-mas-1996 correspondence-others.pdf

724-mas-1996 correspondence-po.pdf

724-mas-1996 description (complete) duplicate.pdf

724-mas-1996 description (complete).pdf

724-mas-1996 drawings.pdf

724-mas-1996 form-1.pdf

724-mas-1996 form-26.pdf

724-mas-1996 form-4.pdf