Title of Invention

A DEVICE FOR OVERSPEED CONTROL OF PERMANENT MAGNET WIND ELECTRIC GENERATOR

Abstract

This invention relates to an overspeed control of a stand alone type permanent magnet wind electric generator. Presently a mechanical overspeed control in the form of a tail fin and yaw fan are normally provided. Under high wind conditions the rotor blades are made parallel to the wind direction and the machine is protected.This change of direction is slow and in cyclonic condition there is chances of damages There is an AC dump load and also a manual brake operating on the principle of electrodynamic braking for PM generator. These are situated in the control room and connected by power cable. In case of damage or theft of power cable this system of speed control becomes ineffective. The present"- invention overcomes these disadvantages as it is mounted near the generator and connected directly with it. Hence it works instantaneously and impervious to damages. The present invention provides a self operated system of speed control wherein the permanent magnet generator is provided with a preset limit and whenever this limit is exceeded it increases the output voltage beyond the present level and activates the device of overspeed control system to operate the electro dynamic brake system.

Full Text

The invention relates to a device for overspeed control of permanent magnet wind electric generator. There are two types of conversion system of wind electric generator namely 1) grid connected type 2) stand alone type. The present invention particularly relates to a control unit for the overspeed control of stand alone type wind electric generators, Stand alone type of wind electric generators are used to provide power in remote areas. They are normally in the range of 1 kW to 4 kW and used to charge storage batteries. There are disadvantages associated with the safety of the stand alone type of wind electric generators. One of the main disadvantages is that the mechanical overspeed control in the form of a tail fin and yaw fan under high wind conditions makes the plane of rotor-blades almost parallel to the wind directions and reducing the speed drastically and thus protects the machine. However, there is a time lag with the process of rotor blades turning about 90° and in such a short time overspeed may occur and the machine may get damaged. Another disadvantage of the present system is that cyclonic weather condition may cause damage to the yawing mechanism thus exposing the machine to overspeeding. Yet another disadvantage of the present system is that when the battery is fully charged and also when wind velocity increases more than normal.,, the machine tends to overspeed. This overspeeding may cause damage to rotor, generator, tower and the entire system. To control such overspeeding an A.C. dump load and a manual brake operating in the principle of electrodynamic braking system acting on the generators is provided. Both these controls are located at the ground and in the control room connected by power cables. There is always a possibility of damage to the cable due to acts of nature , vandalism ,theft, rodents etc. Therefore under such conditions of damage to the output power cable, the electroynamic brake system actueited in the control room becomes ineffective and may cause damage to the machine. Therefore the main object of the present invention is to provide a simple and effective overspeed control device for wind generators which is mounted at the top of the tower and near the generator itself. Another object of the invention is to propose an overspeed control device for wind generators and which is electrically connected to the generator even when the output power cable is damaged. . Yet another object of the this invention is to propose an overspeed control device for wind generators which remains operative even when the mechanical yawing mechanism and or the control circuit in the control room is damaged or malfunctioning. A further object of this invention is to propose an overspeed Control device for wind generators which does not require any external source of power or storage battery. A still further object of this invention is to propose an overspeed control device for wind generators which uses the power generated by the permanent magnet generator for operation of the control circuit as well as for an electrodynamic brake unit. Still another object of this invention is to propose an overspeed control device for wind generators wherein the generator is provided with a preset limit and when this limit is exceeded it increases the output voltage beyond the preset level and activates the device of overspeed control system. Yet another object of the present invention is to provide an overspeed control system wherein the device performs several functions namely 1) power conditioning 2) generator speed sensing 3) overspeed command sending 4) adjust time duration of braking and 5) electrodynamic braking. Further objects of the present invention is to provide an overspeed control system which is simple and reliable using indegenously available components and does not cost much. According to this invention, there is provided a device for overspeed control of permanent magnet wind electric generator comprising a rotor blade (1), yaw fan (3) with tail fin (4) and nacelle (2) of the permanent magnet wind generator (10) mounted on a tower (5) and connected to the control room (9) on the ground with the output cable (8), characterized in that: the said device for overspeed control (7) is mounted on the tower (5) near to the nacelle (2) and is connected to permanent magnet generator (10), the said device (7) such as herein described comprising power conditioner unit (11) generator speed ssensing unit (12), overspeed command sending relay (13), time delay unit (14), electrodynamic brake unit (15), providing automatic and fast overspeed control. The nature of the invention, its objective and further advantage residing in the same will be apparent from the following description made with reference to non limiting exemplary embodiments of the invention represented in the accompanying drawings for a 4 kW permanent magnet wind electric generator. Fig. 1 represents a schematic of 4 kW wind electric generator Fig, 2 represents a schematic of control unit for overspeed control of the rotor of the permanent magnet wind electric generator. Fig. 3 represents a schematic of the circuit for execution of overspeed control device. At present there are two main type of wind energy conversion systems namely, 1) grid connected type 2) stand alone type. The present invention relates to only stand alone type and Fig 1 represents a 4 kW stand alone type wind electric generator. The rotor blade (1) mounted on the P.M generator which is mounted inside the nacelle (2). Mounted on the nacelle (2) is yaw fan (3) and tail fin (4) forming part of the mechanical overspeed control. The nacelle (2) is mounted rotatably on a tower (5) held firmly by guy wires (6) and connected by output cable (8) to the control room (9). Also shown in the figures is the overspeed controller (7) which is part of the present invention and is an electrical overspeed control system which can act faster than mechanical system and is desirable as additional protection. In the present embodiment of a A kW generator, the rotor blade (1) is of aerofoil type and is made of carbon fibre for high strengths and light weight. The nacelle (2) houses the permanent magnet generator of 105V rms, 3 phase, 4 kW, 300 rpm rating with rotating magnets, centrally located fixed stator and gear box. The yaw fan 3 and the tail fin(4),part of the existing mechanical-speed control system is made of aluminum sheet and MS shaft rotates the nacelle (2) to bring the rotor (1 ) into wind direction upto design wind speed .Under high wind conditions the plane of rotor blades is made almost parallel to the wind direction and the machine is protected fromthe destructive forces of wind. The permanent magnet generator (11) is mounted inside the nacelle (2) through suitable shaft and flange. With the blades rotating with wind the permanent magnet generator generates electricity which is brought to the control room (9) through the power calbe (8) . In the present embodiment the cable is of 3 core multistand insulated sheathed copper flexible cable with each core of 10 sq mm cross section. The power generated is used to charge the storage batteries kept inside the control room (9). A battery charge controller is provided in the control room. Normally the control room is located away at some distance.. Whenever the battery is fully charged and also when high velocity winds start blowing the generator has a tendency to overspeed and may cause damage to the rotor blades,generator and the tower. To avoid such over speeding ,an A.C. dump load and a manual brake operating on the principle of electrodynamic braking for for permanent magnet generator is- provided. Both the above controls are located at the ground level in the control room and connected through the output power cables. There is possibility of damage to the output power cable due to acts of nature, vandalism, theft, rodents etc and therefore the electrodynamic brake system becomes ineffective. In the event of further damage to the yawing mechanism (3,4) with the high wind velocity the rotor can pverspeed and damage the system. The present invention overcomes the above drawback with the specially designed and developed electrical overspeed controller (7) which is mounted at the top of the tower(5)very near to the nacelle (2) just below the top mounting plate and below the generator (11) which is mounted inside the nacelle frame (2). Since the overspeed controller is directly connected to the generator it can perform satisfactorily even if the power cable (8) is damaged and any condition of malfunctioning of the control circuit in the control room or malfunctioning of the,yawing mechanism (3,4). The control unit developed for electrical overspeed control of the rotor of the PM generator (10) is shown in Fig. 2 and the circuit for execution of control scheme is shown in Fig.3. The control scheme covers six functional blocks as shown.. Sl.No.10) Permanent Magnet Generator whose speed is to be controlled at high wind/no load conditions. Sl.No.11) Power conditioning unit which receives the power generated by P.M. Generator and conditions it. to suit the requirement of the control circuit. Sl.No.12) Generator speed sensing unit which senses the actual speed of the P.M.Generator. Sl.No.13) Overspeed command sending relay which sends braking command if overspeed is sensed at Sl.No. 12. Sl.No.14) Time Delay Unit to adjust the time of braking to suit the site requirement. Sl.No.15) Electro-Dynamic Brake Unit which helps in braking P. M,. Generator. The circuit for the overspeed control system as shown in Fig. 3 functions as below: The 3-phase A.C. outputof the P.M. Generator is converted to D.C.output by a 3-phase rectifier comprising of the diodes Dl, D2, D3, d4, D5 & D6 . This D.C, Output charges the capacitor bank consisting of capacitors C1 , C2,..Cn connected in parallel through a current limiting resistor R1 . The capacitor bank in turn supplies voltage to the D.C. relay through setting resistor R2. As soon as voltage across the capacitor bank exceeds a preset level the D.C.Relay operates. This happens when P.M.generator exceeds a predetermined speed (3SO r.p.m.) .After operation ofthe D.C.relay the contactor coil is energised through No.,N.C. contacts and R3-C resistor-capacitor combination. Diode D7 ensures that the contactor coil keeps on getting current as long as the capacitor bank remains charged. This in turn ensures that the elecrodynamic brake is applied for sufficient time and also the brake is released when wind velocity becomes sufficiently low. The contactor coil in turn makes 'ON' the three 'NO' contacts.' Due to this the dump load resistors connected in 'delta' R4, R5 abd R6 get the A.C. output from the P.M. wind generator. The ohmic value of these resistors R4, R5 and R6 is adjusted in such a way that sufficiently high current flow through the P.M.Generator windings and this results in electrodynamic braking of the P.M. Generator . The novelty and ingenuity of the circuit lies in the following facts. 1) It is a low cost, simple cirucit which can be assembled using indegenously available components. 2) The circuit performs all the functions as illustrated in Fig 2 (Sl.No.11,12,13,14,15) namely, a) Power conditioning b) Generator speed sending c) Overspeed command sending d) Adjusting time duration of braking and e) Electrodynamic braking. The invention described hereinabove is in relation to a non-limiting embodiment and as defined by the accompanying claims. WE CLAIM 1. A device for overspeed control of permanent magnet wind electric generator comprising a rotor blade (1), yaw fan (3) with tail fin (4) and nacelle (2) of the permanent magnet wind generator (10) mounted on a tower (5) and connected to the control room (9) on the ground with the output cable (8), characterized in that: the said device for overspeed control (7) is mounted on the tower (5) near to the nacelle (2) and is connected to permanent magnet generator (10), the said device (7) such as herein described comprising power conditioner unit (11) generator speed sensing unit (12), overspeed command sending relay (13), time delay unit (14), electrodynamic brake unit (IS), providing automatic and fast overspeed control. 2. A device for overspeed control of permanent magnet wind electric generator as claimed in claim 1, wherein the said power conditioner unit (11) comprises a 3- phase rectifier comprising diodes D1 to D6 provided for conversion of 3-phase AC output of the generator to DC output. 3. A device for overspeed control of permanent wind electric generator as claimed in claim 1 or 2 wherein the said generator speed sensing unit (12) comprises a capacitors bank (C1 to Cn) connected in parallel with the said diodes. 4. A device for overspeed control of permanent wind electric generator as claimed in claim 1 or 3, wherein the said overspeed command sending relay (13) comprises a DC relay which operates through a setting resistor R2 as soon as voltage across capacitor bank exceeds a preset level. 5. A device for overspeed control of permanent wind electric generator as claimed in claim 1 to 4, wherein the said time delay unit comprises a contactor coil energized through NO-NC contacts and a resistor (R3) capacitor (C) combination; a diode (D7) being provided to ensure that contactor coil keeps getting current as long as the said capacitor bank (C1 to Cn) remains charged. 6. A device for overspeed control of permanent wind electric generator as claimed in claim 1 to 5, wherein the said electrodynamic brake unit (15) comprises dump load resistors (R4, R5, R6) connected in delta to the generator output, the values of said resistors (R4, R5, R6) being adjusted such that a high current flows through generator windings which causes electrodynamic braking of the said generator. 7. A device for overspeed control of permanent magnet wind electric generator substantially as hereinabove described and illustrated in the figures 1 to 3 of the accompanying drawings.

Documents:

1998-del-1996-abstract.pdf

1998-del-1996-claims.pdf

1998-del-1996-complete specification (granted).pdf

1998-del-1996-correspondence-others.pdf

1998-del-1996-correspondence-po.pdf

1998-del-1996-description (complete).pdf

1998-del-1996-drawings.pdf

1998-del-1996-form-1.pdf

1998-del-1996-form-2.pdf

1998-del-1996-form-3.pdf

1998-del-1996-gpa.pdf