Background Art Conventional AC-to-DC power converters are known in which the output of an alternator is input to a step- down transformer, and then is rectified to supply DC operating power for low voltage DC loads. In one arrangement, the output voltage of a conventional automotive alternator is boosted and then reduced through a step-down transformer and rectifier to supply relatively low DC output voltage at a high current level.

In general, low voltage, high current alternators are located on the propulsion engine of a vehicle (automobile, truck, boat, emergency vehicle, aircraft). In many cases, the battery, or batteries, are located in close proximity to the alternator, and leads connecting the

alternator to the battery are short. When it becomes necessary to locate the batteries or high-current loads some distance from the alternator, the problem becomes rather formidable because of the size of the wiring conductors required to avoid excessive voltage drop and power loss.

Disclosure of the Invention A high voltage three-phase alternator is combined with a three-phase step-down transformer, a full wave bridge rectifier and a field regulator circuit to regulate the output of the rectifier by varying the field current in the alternator to provide the desired output from the alternator. The high voltage alternator is driven from the torque output shaft of an internal combustion engine or from some other power take-off of an internal combustion engine or other rotating prime mover. The prime mover can be operated at a fixed or variable speed over a typical range of between 400 and 6000 revolutions per minute (RPM).

The useful output voltage of the alternator is developed by a three-phase wye or delta connected secondary winding to produce useful line to line voltages of 50 to 500 Volts AC. The frequency of the three-phase voltage is determined by the number of poles in the alternator and the rotational speed of the alternator shaft. The RPM of the alternator shaft is determined by the prime mover RPM and

the coupling ratio between the prime mover and the alternator shaft.

The alternator output voltage is coupled into three-phase transformer windings specifically designed to transform the high voltage from the alternator into a high current secondary winding. The output of this secondary winding is rectified and regulated to provide a DC voltage for charging batteries, running power inverters, or supplying precision DC voltage to other loads. The transformer secondary winding is wound to provide a number of different low charging voltages, for example 6 volt, 12 volt, 24 volt, 36 volt, 48 volt or any other configured battery or DC loads.

The primary-to-secondary ratio of the transformer is adjustable to provide different power outputs at various shaft RPM. For example, adding turns to the primary allows the alternator to regulate at higher voltages providing a higher output power at a given RPM. However, this change will decrease the maximum power output at a lower RPM.

Precision regulation of the rectified DC voltage is accomplished by adjusting the current in the field regulator to control the output voltage of the alternator and consequently the primary voltage of the step-down transformer. Because of the high output voltage of the alternator, a relatively large amount of power can be transferred to the primary of the transformer with relatively small diameter conductors. When this high

voltage is transformed to the low voltage secondary and rectified, the result is an unusually efficient transfer of power to produce a low voltage, high current output from small alternator driven by a variable or fixed speed prime mover.

In an alternative embodiment of the invention, the primary winding of the transformer is wound with taps brought out at various points on each of the three primary winding to take further advantage of the high voltage efficiency of the alternator-transformer combination described above. In this embodiment the taps on the transformer are used to effectively change the power vs.

RPM performance without physically changing the transformer for different load requirements. The winding taps are changed manually with a power tap switch, or electro- mechanically with relays, or electronically with power semiconductor switches. When the relays or semiconductor switches are utilized, the tap switching is performed dynamically by sensing the alternator RPM and switching the taps to change the transformer ratio to provide the maximum power from the system at different RPM values. Another advantage of dynamically changing the turns ratio is to allow full utilization of the maximum available horsepower from a given prime mover-to-alternator coupling.

Brief Description of the Drawing Other objects, features, advantages, and details

of the alternator system of this invention appear in the following detailed description of the preferred embodiments of the invention, the detailed description referring to the drawing in which: FIGURE 1 is a schematic diagram showing an alternator system utilizing a tapped primary transformer and three phase switch as used with normal vehicle loads and with additional high current loads; FIGURE 2 is a schematic diagram showing an alternator system as used with normal vehicle loads and with additional high current loads; FIGURE 3 is a speed vs. power curve showing the performance of an alternator with three different stator turns per slot of stator windings; FIGURE 4 is a speed vs. power curve showing the performance of an alternator with three different primary turns on a transformer; and, FIGURE 5 is a no-load voltage vs. speed curve for an alternator with various values of field current.

Best Mode for Carrying Out the Invention Referring to the drawing FIGURE 1, M1 is a prime mover that, when energized, rotates an exciter field winding 16 of an alternator A1 to produce a voltage in stator windings 13,14, and 15, which are connected in a three-phase wye configuration. The voltage generated in

these stator winding produces three-phase current in lines 16,17, and 18 when connected directly to T1, Phase A, Phase B, and Phase C as shown in FIGURE 2, or through tap switches S1, S2, and S3 respectively as shown in FIGURE 1.

Transformer T1 is a three-phase, step-down transformer with a high voltage, low current wye or delta connected primary and a low voltage, high current delta or wye connected secondary. The three output phases are connected to a three-phase full wave rectifier D2.

The resulting DC voltage is connected to both a high current load 70 and a DC storage battery B1. Rectifier D1 is also connected to lines 16,17, and 18 of the alternator A1. Rectifier D1 has a DC voltage output for the purpose of providing high power supply voltage to the electronic logic circuits of voltage regulator 72 when used with a high voltage field winding. Voltage regulator 72 senses the battery voltage and varies the output of the voltage regulator at lines 78 and 79 to adjust the field current of A1, thereby regulating the voltage of the rectifier 68 at lines 75 and 76.

The control circuit 90 senses multiple inputs from temperature sensing devices, output current, battery current, etc. to cause the volt regulator 72 to adjust the

field current flowing in line 78 and 79. Additionally, the control circuit 90 senses alternator RPM to determine the proper time to cause the switch drivers 73 to change the taps on the transformer T1. FIGURE 2 is another embodiment of FIGURE 1 except input switches S1, S2, S3 and the taps from the transformer T1 have been removed to show the simplification of the first embodiment. All other components of FIGURE 2 operate identically to those described in FIGURE 1 above.

Again referring to FIGURE 1, the prime mover M1 may be any machine capable of transferring rotational energy to a rotor that contains a field coil 16 of the alternator Al. The most common machine envisioned is an internal combustion engine that drives a shaft from which power can be coupled to the rotor shaft of the alternator Al. In the preferred embodiment the prime mover M1 can be a diesel, gasoline, or natural gas internal combustion engine primarily used for propelling sailboats, powerboats, trucks, cars and the like. These engines typically deliver brake horsepower to an output shaft of from about ten horsepower to several hundred horsepower.

Alternatively, the prime mover could be dedicated primarily to drive the shaft of the alternator A1, and if so, only the horsepower needed to drive the alternator A1

would be needed. In that case the horsepower requirement would roughly approximate to one horsepower for every 350 watts needed at the output of the rectifier D2. The coupling method from the prime mover MI can be direct from shaft-to-shaft, through a set of pulleys and belts, through a power takeoff by the use of a gearbox, or through some hydraulic power coupling method. The rotational speed of the shaft of the prime mover M1 and the ratio of the coupling method to the shaft of the alternator A1 will determine desired construction of the alternator A1.

In the preferred embodiment, the alternator Al is constructed from parts or modified parts of a conventional low field voltage (14-volt) automotive alternator. In the various embodiments of this invention, a conventional alternator is disassembled, the 12 volt stator winding removed and replaced with high voltage stator windings, the rectifiers removed, and the alternator is reassembled with provisions made to accommodate the higher output voltage.

In the preferred and tested embodiment of the alternator A1 the stator laminations are constructed from a combination of Tempel Steel part 3372 2266 and 3373 1866 and the pole pieces for the rotor are constructed with Peer International part 1B3305. The laminations are assembled and wound with 20 turns per slot of 14.5 AWG magnet wire and the pole pieces are properly assembled on a shaft with

a rotor coil that is wound with multiple turns of 26 AWG magnet wire to act as the field coil. In this configuration the alternator has six poles and therefore the frequency of the AC waveform generated as the pole pieces are rotated inside the stator winding is one-tenth of the shaft RPM.

The 20-turn stator is terminated in a three phase wye configuration and when the pole pieces are rotated inside the stator, a small field current at a high voltage can be used to control the output voltage of the three-phase stator. At a given field current the output voltage of the stator will be directly proportional to the rational speed of the pole pieces of the rotor. Additionally, at a given speed, without saturation, the output stator voltage increases substantially linearly with an increase in field current.

Referring again to FIGURE 1, the transformer T1 is a three-phase transformer that has a wye-connected high voltage primary and a delta-connected low voltage high current secondary. The design and construction of the transformer Tl is matched with the alternator windings, taking into account the relationship of frequency and voltage generated by the alternator. For example, the voltage generated by the alternator A1 is proportional to the frequency. Therefore, the design of the transformer should accommodate the lowest voltage at the lowest frequency and the highest voltage at the highest frequency,

so that the transformer size and weight can be minimized.

As can be seen in the waveforms shown in FIGURE 3, by changing the turns of the stator of A1 without changing the other factors of the alternator, different performance in output power at different RPM of the rotor shaft can be realized. What is not obvious is that substantially the same results can be achieved with the use of a transformer connected between the alternator output and the load with different turns ratios, without changing the stator windings. While the waveforms of FIGURE 3 are generated by using three differently wound stators, the waveform of FIGURE 4 is produced by using one stator and adjusting the primary turns on the transformer T1. The major factor that causes the waveforms of FIGURE 3 and FIGURE 4 to flatten out and to provide diminishing returns of power for a given increase in RPM is the feature of regulating and limiting the output voltage. If the output voltage is allowed to continue to increase, greater efficiency of delivering output power is achieved.

Additionally, this feature is also apparent when transmitting AC power to loads remotely located from the prime mover.

In the several embodiments of the invention the primary turns of the transformer are adjusted with a given number of stator turns to follow different waveforms of output current and rotational speed similar to those in

FIGURE 3. This feature of adjusting either the stator turns or the primary turns on a transformer to achieve different power performance curves extends the adaptability of an engine driven alternator. Therefore, if provisions are made to"jump"from one tap to another on the primary of the transformer as rotational speed increases or decreases, the performance of the entire system is adapted dynamically based on speed and loads.

Referring again to FIGURE 1, the three-phase input switches S1, S2 and S3 are ganged power tap switches, or sets of three-phase relays, or electronic switches connecting the output lines 16,17, and 18 of the alternator A1 alternately to different taps on the primary winding of T1 at lines 44,48, and 52 respectively or alternatively to T1 lines 45,49, and 53 respectively or alternatively to lines 46,50, and 54 respectively. The ganged power tap switch may be used to manually change the performance curve. The relays and electronic switches, along with control circuitry 90 and switch drivers 73, may be used to change the taps dynamically based on speed and load.

Referring again to FIGURE 1, the low voltage, high current secondary winding of the transformer T1 are shown as three separate phase winding. Phase A output is from lines 59 and 60, Phase B output is from lines 61 and

62, and Phase C output is from lines 63 and 64. Lines 59 and 64 are connected to a rectifier 68 at line 66, line 60 and 61 are connected to a rectifier 68 at line 65, and 62 and 63 are connected to a rectifier 68 at line 67 to form a three-phase delta configuration. The rectifier D2 is a three-phase full wave bridge with diodes capable of conducting the desired current. The output of the rectifier D2 on conductor lines 75 and 91 is a DC voltage with a ripple that is six times the output frequency of the alternator A1. This ripple can be smoothed further with capacitors, not shown, or used as is for charging batteries or supplying other DC loads.

The battery 69 can be a Starting, Lighting, or Ignition (SLI) or a house storage battery used to run inverters. If the battery 69 is rated for SLI service then the high current load 70 could be complemented by a large bank of house batteries or other high current DC load.

Lines 76 and 77 are sensed at the battery or at the high current load to provide voltage regulation at the sense point. The sensed DC voltage of line 76 and 77 is compared to the desired voltage provided by a control circuit 90.

Through this comparison an error signal adjusts the voltage and consequently the current through conductor lines 78 and 79 that feed the field coil 16 of alternator A1 thereby

achieving regulation of the voltage from rectifier D1 (component 85).

Rectifier D2 (component 85) is a three-phase rectifier for providing high voltage on lines 86 and 87 for the field regulator circuits in voltage regulator 72.

Industrial Applicability Applications involving mobile equipment sometime require AC-to-DC power service for low voltage DC loads.

Typical mobile applications include recreational vehicles, emergency vehicles such as rescue trucks, ambulances and fire trucks, service repair trucks and small marine vessels such as power boats and sailing boats.

In a certain class of small marine vessels, for example, a prime mover (for example a diesel engine) drives a DC generator for supplying DC electrical service to low voltage loads such as communications equipment and running lights. The prime mover also drives a variable mechanical load, with the principal mechanical load being the propeller, and including auxiliary mechanical loads such as pumps and the like. An example of a small marine vessel of the foregoing type is an intermediate class sailboat or power boat which is equipped with a small diesel engine, a DC generator and a DC storage battery.