Regulated Permanent Magnet D.C. Power Supply

1. Field of the Invention

The present invention relates to permanent magnet generators, and in particular to a multiple winding permanent magnet generator including switching circuitry for selectively coupling the windings of the generator to provide the desired output voltage.

2. Description of the Prior Art

It is well known that the output voltage from a permanent magnet generator is directly proportional to the RPM of the generator drive shaft. Constant output voltages from permanent magnet generators are typically obtained by either closely regulating the RPM of the generator shaft or by providing a specially designed electronic voltage regulator which is capable of operating over wide RPM ranges. This latter type of voltage regulating device is not only expensive but also highly inefficient.

Remotely located diesel driven pumps or electrical generating apparatus are frequently utilized to provide an emergency or stand-by backup feature. These diesel engines are designed to be activated only when needed and rarely have access to a source of electrical power for maintaining a battery in a charged state.

The more modern diesel engines used in these applications incorporate an electronically controlled fuel injection system which must have a voltage source of a predetermined minimum magnitude in order to permit normal operation of the engine. These infrequently operated diesel engines are started by high pressure air starting systems which are capable of rotating the engine at rates of over 100 RPM. It is therefore a requirement that a mechanically rotatable power source be provided for powering at a sufficient level, the diesel engine electronic fuel injection system at an engine RPM of less than the maximum obtainable RPM from the diesel engine pneumatic starting system.

U.S. Pat. No. 3,396,325 (Hopkinson) discloses a permanent magnet generator the output voltage of which is controlled by a special control winding which requires a low power external power supply for proper operation. U.S. Pat. No. 3,401,290 (Potter) discloses a permanent magnet electric generator having an axially movable stator for adjusting the output voltage thereof. U.S. Pat. No. 3,443,135 (Lombard) discloses a permanent magnet variable voltage alternator having a two part, movable permanent magnet rotor. U.S. Pat. No. 3,360,667 (Gordon) discloses a generator having mechanically movable field magnets for changing the output voltage thereof. U.S. Pat. No. 3,713,015 (Frister) discloses an alternating current generator having a two part permanent magnet rotor which is adjustable in response to the output voltage thereof. U.S. Pat. No. 3,214,675 (Foster) discloses a permanent magnet generator having a supplemental rotary flux coil to regulate the output voltage thereof. U.S. Pat. No. 4,015,189 (Gordon) discloses a supplemental field excitation apparatus for the permanent magnet rotor of a pilot exciter to control the load regulation of a generator field winding.

U.S. Pat. No. 2,648,044 (Opel) discloses a voltage regulated generator having a control winding which utilizes the saturation region of operation to effect voltage regulation. U.S. Pat. No. 3,160,772 (Miron) discloses a plural voltage alternator having dual alternating current windings in a single field electromagnet. U.S. Pat. No. 3,551,784 (Shaw) discloses an alternating current generator having plural output windings for generating alternating current outputs which are electrically isolated from one another.

The following U.S. Pat. Nos. are also of interest: 3,237,034 (Krasnow) and 3,242,365 (Kaober).

The present invention contemplates a regulated D.C. power supply comprising a variable RPM drive means and means for generating a magnetic field. First winding means is coupled to said drive means and positioned within the magnetic field for generating a first output voltage proportional to the RPM of said drive means. Second winding means is coupled to said drive means and positioned within the magnetic field for generating a second output voltage proportional to the RPM of said drive means. The first output voltage is greater than and generally directly proportional to the second output voltage. Control means is coupled to said first and second winding means for selectively connecting said first and said second winding means to produce an output voltage as close as possible to a predetermined value as the RPM of said drive means changes. Regulator means may also be provided following said control means to regulate the output voltage from said control means to a level as close as possible to a desired output voltage.

The invention is pointed out with particularity in the appended claims. However, other objects and advantages together with the operation of the invention, may be better understood by reference to the following detailed description taken in connection with the following illustrations wherein:

FIG. 1 is a block diagram of a D.C. power supply of the present invention.

FIG. 2 illustrates the permanent magnet and first and second winding means of the present invention.

FIG. 3 is a graph illustrating the output voltage of the D.C. power supply of the present invention as a function of engine operating RPM.

FIG. 4 is a partial schematic diagram of the control means and regulator means illustrated in FIG. 1.

FIG. 5 is an electrical schematic diagram of the remaining portion of the control means illustrated in FIG. 4.

In order to better illustrate the advantages of the invention and its contributions to the art, a preferred hardware embodiment of the invention will now be described in some detail.

Referring now to FIGS. 1 and 2, the D.C. power supply of the present invention includes first winding means 10, second winding means 12, control means 14 and regulator means 16. Winding means 10 is fabricated with a greater number of turns of wire than is the case with winding means 12. Thus for all RPM conditions the first winding means will generate a higher output voltage than will the second winding means. A permanent magnet 18 creates a magnetic field which penetrates the area in which the first and second winding means rotate.

The output voltage from winding means 10 is coupled to a pair of output conductors 1 and 2 by a pair of carbon brushes 20 and 22 in a conventional manner. In a similar manner the output voltage from second winding means 12 is coupled to output conductors 3 and 4. Low value filter capacitors 24 and 26 are coupled across output conductors 1 and 2 and 3 and 4 to attenuate brush noise.

A single shaft 28 is coupled to the crank shaft or a power takeoff shaft of an internal combustion engine or to some other type of variable RPM drive means. Shaft 28 is coupled to the iron core on which first and second winding means are wound and thus causes both winding means to rotate at the same RPM.

Referring now to FIG. 3, a graph of the output voltages from winding means 10 and 12 with respect to the RPM shaft 28 will now be discussed. The symbol V.sub.12 is used to designate the output voltage across lines 1 and 2 from first winding means 10 and while the symbol V.sub.34 designates the output voltage from second winding means 12. As can be seen from FIG. 3, the line designated by reference number 30 indicates a plot of the output voltage V.sub.12 with respect to RPM. Reference number 32 indicates a plot of voltage V.sub.34 with respect to RPM, while reference number 34 indicates a plot of the sum of V.sub.12 plus V.sub.34 with respect to RPM.

In the preferred embodiment of the present invention it is desired to maintain the peak input voltage to regulator means 16 at a level not to exceed approximately 30 volts. As the drive means which is coupled to shaft 28 begins to rotate from a 0 RPM level, windings 10 and 12 are connected in a series aiding configuration by control means 14 in order to produce the maximum obtainable output voltage equal to the output voltage across conductors 1 and 2 plus the output voltage across conductors 3 and 4. Reference number 34 indicates the slope of this output voltage with respect to RPM. If electronic circuitry such an electronically controlled governor for a diesel engine requires a minimum operating voltage of 12 volts, it can be seen that an RPM of approximately 200 will enable the present invention to produce this required operating voltage. As the RPM increases to approximately 500, the output voltage from control means 14 will approach 30 volts. Since 30 volts is the desired maximum input voltage to regulator means 16, the electrical circuitry within control means 14 will actuate switching means within control means 14 at the voltage indicated by reference number 36 to disconnect second winding means 12 and to couple only output voltage V.sub.12 to the input of regulator means 16.

Once again, as the shaft RPM increases the output voltage V.sub.12 from control means 14 will increase until it reaches the maximum desired output voltage at a point indicated by reference number 38. At this point, control means 14 will once again actuate its switching means to disconnect winding means 10 and connect winding means 12 in order to produce a voltage equal to V.sub.34 at the output of control means 14. As the RPM of shaft 28 continues to increase output voltage V.sub.34 will slowly continue increasing, but at a relatively low rate.

Referring now to FIG. 4, the operation of the switching means within control means 14 will now be discussed. The electronic control for switching means illustrated in FIG. 4 will be discussed below in connection with FIG. 5.

The switching means of the present invention includes a pair of relays K1 and K2. Relay K1 includes a pair of normally open contacts 40 and a pair of normally closed contacts 42. Relay K2 includes a pair of normally closed contacts 44 and a pair of normally open contacts 46.

Referring now to FIGS. 4 and 5, the switching means which controls relay K1 and K2 includes voltage comparator circuits 48 and 50. The input of each voltage comparator circuit may be coupled to the output of either winding means and in the preferred embodiment is coupled to the output of winding means 12. The structure and operation of voltage comparators 48 and 50 is identical and for the purposes of explanation, the operation of only one of these will be discussed.

Resistor R2 is coupled between the input of a voltage comparator integrated circuit IC1, such as the LM399 manufactured by National Semiconductor, and potentiometer R1. The setting of the tap on potentiometer R1 is adjusted so that with IC1 will trigger at the shaft RPM indicated by reference number 36 in FIG. 3. Similarly, the tap on potentiometer R1 in voltage comparator circuit 50 is set so that comparator IC2 will trigger at the shaft RPM indicated by reference number 38 in FIG. 3.

When voltage comparator IC1 triggers and generates an output pulse, transistor Q1 is turned on causing current to flow through the coil of relay K1. Actuation of relay K1 causes the contacts of the relay to reverse positions. A reference voltage for voltage comparators IC1 and IC2 is provided by a voltage divider network consisting of resistors R7 and R8. The following table indicates the values of the resistors used in voltage comparison circuits 48 and 50:

As a result of the operation of voltage comparators 48 and 50 in the switching means, the relay contacts will be in the positions shown in FIG. 4 when the RPM of shaft 28 is at a point to the left of reference number 36 in FIG. 3. For RPM ranges between the point indicated by reference number 36 and reference number 38, relay K1 will close causing relay contacts 40 to close and relay contacts 42 to open. Thus for shaft RPMs greater than those indicated by reference number 36 but less than those indicated by reference number 38, winding means 10 will be coupled directly to the input of regulator means 16.

As the shaft RPM further increases to the point indicated by reference number 38, voltage comparison circuit 50 will be actuated causing relay contacts 44 to open and relay contacts 46 to close. In this configuration, winding means 12 will be directly coupled to the input of regulator means 16.

Resistors R3 and R9 are provided in a feedback path for integrated circuits IC1 and IC2 to incorporate a hysteresis effect to prevent operating instability during switching.

Referring to FIG. 4, regulator 16 includes inexpensive and efficient series regulators 52 and 54. In the preferred embodiment, a 12 volt regulator such as the National Semiconductor LM340-12 and a 5 volt regulator such as the National Semiconductor LM340-5 are utilized. These regulators function very effectively as a result of the comparatively small input voltage swing.

High value electrolytic filter capacitors C1, C2 and C3 are provided to improve the effectiveness and regulation of regulator means 16.

It will be apparent to those skilled in the art that the disclosed D.C. power supply may be modified in numerous ways and may assume many embodiments other than the preferred form specifically set out and described above. For example, a more sophisticated control means could be provided which would enable windings 10 and 12 to be switched into a series opposing relationship to permit operation at even higher Shaft RPMs without exceeding a predetermined maximum output voltage to the regulator means. Furthermore, numerous other winding means could be provided together with more sophisticated control means to effectuate substantially more sophisticated control over the output voltage of the power supply. Accordingly, it is intended by the appended claims to cover all such modifications of the invention which fall within the true spirit and scope of the invention.