Zero current switching between winding sets in a permanent magnet alternator having a split winding stator

An apparatus for selectively rectifying one of a pair of output voltages associated with one of a a pair of output winding sets of a polyphase alternating current generator has a single controlled bridge rectifier selectively coupled to one of the winding sets. The bridge rectifier is selectively coupled in accordance with a predetermined rotational speed of the rotor. Transitions between the two winding sets is caused to occur at zero current conditions of the windings.

BACKGROUND OF THE INVENTION 
This invention relates to voltage regulating apparatus for variable speed 
permanent magnet alternating current generators. 
Voltage regulator systems for permanent magnet alternating current 
generators are known, examples being the systems disclosed in the U.S. 
Pat. Nos: 3,443,197; 3,369,170; 3,427,529. In the systems of these patents 
the output or stator winding of a permanent magnet alternator is connected 
to a bridge rectifier that is comprised of controlled rectifiers and 
diodes. By turning the controlled rectifiers on and off as a function of 
the output voltage of the bridge rectifier, the direct output voltage of 
the bridge rectifier is maintained substantially constant. 
One of the problems associated with the systems of the type disclosed in 
the above referenced patents is that the systems have high copper losses 
in the stator winding and poor power factor at high rotor speeds. 
A voltage regulating circuit for a variable speed permanent magnet 
alternating current generator which reduces the copper loss in the stator 
or output winding of the generator and improves the power factor at high 
rotor speeds has been disclosed in U.S. Pat. No. 5,214,371 assigned to the 
assignee of the present invention. In that circuit, a stator or output 
winding is comprised of two sets of windings. The first winding set has a 
larger number of turns than the second winding set. The first winding set 
is connected to a first bridge rectifier that has a plurality of 
controlled rectifiers, and the second winding set is connected to a second 
bridge rectifier that has a plurality of controlled rectifiers. The system 
is arranged to enable the first bridge rectifier and disable the second 
bridge rectifier when the speed of the rotor of the generator is below a 
predetermined speed. At rotor speeds above the predetermined speed, the 
second bridge rectifier is enabled and the first bridge rectified is 
disabled. Both bridge rectifiers feed a direct voltage load which may be 
the battery or other loads in a motor vehicle electrical system. The 
output voltage of the bridge rectifiers is sensed and the system controls 
the conduction angle of the controlled rectifiers as a function of the 
sensed bridge rectifier output voltage to maintain the output voltage of 
the bridge rectifier that is enabled substantially constant. 
While the advances embodied in the circuit of U.S. Pat. 5,214,371 as 
outlined are significant, some improvements, particularly with respect to 
circuit complexity and component parts proliferation are desirable. 
SUMMARY OF THE INVENTION 
Therefore, in accordance with one aspect of the present invention, a 
voltage regulator system for a permanent magnet alternating current 
generator is provided having a single controlled bridge rectification 
means and steering means for selecting as the input thereto one of the 
first and second winding sets of a split winding stator. 
According to one embodiment of the invention, the controlled bridge 
rectification means comprises a semi-controlled bridge having both 
controlled rectifiers and diodes. 
In accordance with another aspect of the present invention, the steering 
means is characterized by zero current switching of winding sets so as to 
avoid problems associated therewith. 
According to yet another aspect of the present invention, a low cost 
three-pole double-throw relay controlled to switch under zero current 
conditions is utilized as the steering means to provide selection as 
between the two sets of windings. 
According to these and other aspects and objects of the present invention, 
a vehicle electrical system having a permanent magnet multi-phase 
alternating current generator has a first winding set with a larger number 
of turns per phase than a second winding set. Each of the winding sets has 
AC output voltage terminals, only one set of which supplies voltage to a 
single full-wave rectification means at any on time for rectifying the AC 
output voltage thereof into a DC output voltage. 
A steering means is operative in a first mode to couple the bridge to the 
first winding set and decouple the bridge from the second winding set. 
Likewise, it is operative in a second mode to couple the bridge to the 
second winding sets and decouple the bridge from the first winding set. 
Means are provided for selecting the first mode when alternator rotor 
speed is below a predetermined speed and for selecting the second mode 
when the speed is above the predetermined speed. 
In accordance with a preferred embodiment of the invention, the full-wave 
rectifier bridge comprises a plurality of controlled rectifiers whose 
conduction is controlled such that the transition between first and second 
coil sets is caused to occur under conditions of zero winding current.

DETAILED DESCRIPTION OF THE INVENTION 
Referring first to FIG. 1 the reference numeral 10 designates a permanent 
magnet alternating current generator that has a rotor 12 and a three phase 
Y-connected output for stator winding 14. The rotor 12 is driven at a 
variable speed by an engine 13 on a motor vehicle. The rotor 12 has 
permanent magnets (not illustrated) and as it rotates an alternating 
voltage is induced or generated in output winding 14. The frequency of the 
alternating voltage generated in winding 14 is directly proportional to 
the speed of rotation of rotor 12. Further, the magnitude or amplitude of 
this voltage is a function of rotor speed, that is, as rotor speed 
increases the amplitude of the voltage increases and vice-versa. Output 
winding 14 has a neutral 15 and is comprised of phase windings 16, 18 and 
20. Each phase winding has a tap which are designated respectively as 16A, 
18A and 20A. The ends of the phase windings are connected respectively to 
junctions 16B, 18B and 20B. The phase winding taps 16A, 18A and 20A can be 
arranged such that the voltage between the neutral 15 and a given tap is 
about one third of the voltage between the neutral 15 and an end of a 
given phase winding. Thus, by way of example, the voltage between neutral 
15 and tap 16A can be about one third of the voltage between the neutral 
15 and the end 16B of phase winding 16. Thus in terms of the number of 
stator winding turns if the number of turns between neutral 15 and tap 16A 
is N turns, the number of turns between tap 16A and junction 16B would be 
2N turns. This same relationship holds true for the other taps 18A and 
20A. The system of this invention has a three phase full wave bridge 
rectifier or converter 22 comprised of three controlled rectifiers 24, 26 
and 28, and three diodes 30, 32, and 34. The cathodes of controlled 
rectifiers 24, 26 and 28 are connected to a conductor 36 which forms the 
positive direct voltage output terminal or line for bridge rectifier 22. 
The anodes of diodes 30, 32 and 34 are connected to a conductor 38 which 
is grounded. Conductor 38 is the negative direct voltage output terminal 
or line for bridge rectifier 22. 
Bridge rectifier 22 has alternating current input terminals 40, 42 and 44. 
Terminal 40 is selectively connected to one of junctions 16A and 16B by 
conductor 46 and a respective one of conductors 46A and 46B associated 
respectively with junctions 16A and 16B. In a similar fashion, terminal 42 
is connected to one of junctions 18A and 18B by conductor 48 and a 
selected one of conductors 48A and 48B associated with junctions 18A and 
18B, respectively. Likewise, terminal 44 is connected to one of junctions 
20A and 20B by conductor 50 and a selected one of conductors 50A and 50B 
associated with junctions 20A and 20B, respectively. Selection between the 
respective pair of conductor paths available to couple input terminals 40, 
42 and 44 to one of the two available junctions on respective split 
windings 16, 18 and 20 is accomplished by steering means 130 illustrated 
as a three pole double terminal relay in the present embodiment and 
hereinafter referred to as relay 130. For example, conductor 46 serves to 
couple terminal 40 to one of terminals 126 and 128 in accordance with the 
energization state of coil 62. Coil 62 is illustrated with one side 
thereof coupled to voltage source B+, typically vehicle system voltage, 
and the other side thereof coupled to ground through switching transistor 
66. An unenergized coil 62 results in a normally closed relay state 
wherein conductor 46 is coupled to terminal 126 and ultimately via 
conductor 46B to junction 16B. Likewise, conductor 48 serves to couple 
input terminal 42 to one of terminals 131 and 132 in accordance with the 
energization state of relay coil 62. The upper terminal 131 as illustrated 
in FIG. 1 is the terminal selectably engaged when the coil 62 is in a 
deenergized state thereby coupling junction 18B to terminal 42 via 
conductor 48B, terminal 130 and conductor 48. The arrangement of conductor 
50 in coupling input terminal 44 to one of the junctions 20A and 20B 
operates in a like fashion via terminals 134 and 136 and corresponding to 
energization state of coil 62. Therefore, upon deenergization, the 
normally closed position of relay 130 serves to couple junction 20B to 
terminal 44 via conductor 50B, terminal 134 and conductor 50. Energization 
of relay coil 62 causes all conductors 46, 48 and 50 to be coupled to the 
respective lower terminals 128, 132 and 136 of relay 130 thereby coupling 
input terminals 40, 42 and 44 to junctions 16A, 18A and 20A respectively. 
The conductor 36 is connected to a positive power supply conductor 56 on a 
motor vehicle. A storage battery 54 for the motor vehicle electrical 
system has its positive side connected to conductor 56 and its negative 
side connected to ground. The battery 54 may be a 12 volt motor vehicle 
storage battery. Conductor 56 further feeds various other motor vehicle 
electrical loads 58 on the vehicle. A switch 60 is illustrated for 
controlling the energization of vehicle electrical loads 58. 
It can now be appreciated that whenever bridge rectifier 22 is enabled, it 
will rectify the AC voltages generated in phase windings 16, 18 and 20 and 
will develop a direct voltage between conductors 36 and 38. Further, as 
will be explained in more detail hereinafter, the conduction angle of 
controlled rectifiers 24, 26 and 28 is controlled so that the direct 
voltage appearing between conductors 36 and 38 is maintained at a 
substantially constant value of about 14 volts irrespective of rotor 
speed. In this regard, the voltage generated in the phase windings 16, 18 
and 20 varies as a function of engine and rotor speed and it is therefore 
necessary to control the direct voltage output of bridge rectifier 22 to 
provide a substantially constant direct voltage output for battery 54 and 
the other motor vehicle loads. It can be appreciated that while bridge 
rectifier 22 is enabled or in operation, relay 130 determines whether the 
entire phase windings 16, 18 and 20 carry current or only those portions 
of the phase windings between tap points 16A, 18A and 20A and neutral 15 
carry current. The system operates such that only one of the two taps for 
each coil will be coupled to the bridge rectifier 22 at a time. Putting it 
another way, when relay 130 is energized, only a portion of the coils 16, 
18 and 20 are utilized and when relay 130 is deenergized, the entire coils 
16, 18 and 20 are utilized. 
The system of this invention has a controlled rectifier firing angle 
control or control rectifier firing pulse generator 100 which operates to 
control the conduction angle of the controlled rectifiers 24, 26 and 28. 
Since control rectifier firing angle controls are known to those skilled 
in the art, control 100 has not been shown in detail. The firing pulse 
generator 100 receives input voltages via three input lines each 
designated as 102. The conductors or lines 102 are respectively connected 
to three lines or conductors each designed as 103. The lines 103 connect 
the output of a signal conditioner circuit 104 and the input of the 
frequency to voltage converter 105. The output of converter 105 is 
connected to a line or conductor 106. The converter 105 provides a voltage 
on line 106 that is proportional to the frequency of the voltage pulses on 
lines 103. 
The input of signal conditioner 104 is respectively connected to the ends 
16B, 18B and 20B of phase windings 16, 18 and 20 by three conductors or 
lines each designated as 107. The AC voltages generated in the phase 
windings are therefore applied to the input of signal conditioner 104. The 
signal conditioner 104 produces a series of square wave pulses that are 
applied to lines 103. Each square wave pulse is developed during a 
positive half cycle of an input AC phase voltage from the phase windings 
16, 18 and 20. The frequency of the square wave pulses on lines 103 is 
directly proportional to the frequency of the alternating voltage 
generated in phase windings 16, 18 and 20 which, in turn, is directly 
proportional to the speed of rotation of rotor 12. The voltage on line 106 
is applied to one input of the firing pulse generator 100 by conductor 109 
and to one input of a voltage comparator 108. The other input of voltage 
comparator 108 is connected to a source of constant reference direct 
voltage 111. The purpose of the voltage comparator 108 will be described 
hereinafter. The system of this invention has a proportional and integral 
controller 110. One input of controller 110 is connected to a junction 112 
between voltage divider resistors 114 and 116. Resistors 114 and 116 sends 
the direct voltage between conductor 56 and ground and the voltage at 
junction 112 therefore is a function of the voltage between conductor 56 
and ground. The other input to controller 110 is connected to a source of 
constant reference direct voltage 118. The magnitude of the output voltage 
of controller 110 that is applied to line 119 depends on the difference 
between the reference voltage 118 and the voltage at junction 112. The 
line 119 is connected to an input of the pulse generator 100. If it is 
assumed it is desired to maintain a voltage of 14 volts between conductor 
56 and ground, the signal developed by controller 110 on line 119 will, if 
the voltage between conductor 56 and ground is above 14 volts, tend to 
reduce the conduction angle of the controlled rectifiers by means of pulse 
generator 100. If the voltage between conductor 56 and ground 15 is below 
14 volts, the signal on line 119 developed by controller 110 tends to 
increase the conduction angle of the controlled rectifiers of the bridge 
rectifiers by means of pulse generator 100. 
The output of controlled rectifier firing angle control 100 is connected to 
three conductors which are labelled 24a, 26a and 28a. These three 
conductors are connected as inputs to a respective gate of controlled 
rectifiers 24, 26 and 28. The relay 130 is controlled as a function of the 
speed of rotation of rotor 12 and its speed varies with changes in the 
speed of engine 13. To this end, the selection control circuit labelled 70 
is connected to the output of voltage comparator 108. The voltage 
comparator 108 compares the direct voltage on line 106 with the constant 
direct reference voltage provided by source 111. The magnitude of the 
voltage on line 106, as previously described, is proportional to the speed 
of rotation of rotor 12. The output of comparator 108 goes high and low 
depending upon the speed of rotation of rotor 12. When engine speed, and 
accordingly the speed of rotor 12, is below a predetermined speed the 
output of the comparator 108 is low. Accordingly, relay coil 62 is not 
energized and relay contacts 126, 131 and 134 are coupled to the bridge 
22. Therefore, at engine and rotor speeds below a predetermined speed, 
relay 130 couples the full coils 16, 18 and 20 to the bridge rectifier 22. 
Similarly, when engine speed and hence the speed of rotor 12 is higher 
than the predetermined speed, the output of comparator 108 goes high 
thereby energizing relay 130. Contacts 128, 132 and 136 are thereby 
coupled to bridge rectifier 22. Accordingly, only a portion of coils 16, 
18 and 20 are coupled to bridge rectifier 22. 
In further explanation of the operation of this invention, circuit 70 will 
be explained with reference to FIGS. 1 and 2A-2G. The output from 
comparator 108 is buffered via amplifier 71 which serves to drive 
switching transistor 66 into saturation via line 93 and biasing resistor 
68. Diode 64 provides transient voltage protection upon switching of relay 
130 coil 62. A high state at the output of comparator 108 results in a 
high output from buffer amplifier 71 which in turn causes energization of 
relay coil 62. The output of comparator 108 is labeled 91 in FIG. 1 and 
corresponds to FIG. 2A. The output of buffer amplifier 71 labeled 93 
follows the output of comparator 108 and is represented in FIG. 2B. The 
signal on line 93 comprises the relay command and an intermediate bridge 
command. FIG. 2C represents relay 130 steady state as between the 
energized and deenergized positions. A low state in FIG. 2C represents a 
deenergized relay 130 with contacts in the normally closed position 
thereby connecting the full windings 16, 18 and 20 to the bridge rectifier 
22. Likewise, a high state shown in FIG. 2C represents the relay 130 in an 
energized steady state wherein only a portion of coils 16, 18 and 20 are 
connected to the bridge rectifier 22. An amount of delay between the time 
the relay is commanded into an energized state and attainment of the relay 
energized steady state is labeled Tc in reference to FIGS. 2B and 2C. An 
amount of time delay Tc comprises electrical delay due to the reactance of 
the relay coil 62 as well as mechanical delay due to switch bounce. The 
output 91 from comparator 108 is also inverted at 73 and therefrom input 
to and gate 72. The output 93 from buffer amplifier 71 similarly is fed 
into and gate 79 via line 92. It is assumed that lines 78 and 76 are at a 
high state at least during times when respective gates 79 and 72 are 
desirably activated. Lines 78 and and 76 are therfore either tied to a 
high logic level signal or alternatively may be tied to a signal 
indicative of the relay 130 position. For example, when relay 130 is 
deenergized a high signal is desirably applied to line 76 to enable gate 
72 and when relay 130 is energized a high signal is desirably applied to 
line 78 to enable gate 79. Gate 72 output line 97 is represented by FIG. 
2E and is referred to as the low RPM bridge enable signal. Output 99 of 
and gate 79 is illustrated in FIG. 2F and is referred to as the high RPM 
bridge enable signal. When the output of comparator 108 is high, gate 79 
is enabled to pass a high signal therethrough and similarly when the 
output from comparator 108 is low, gate 72 is enabled to pass a high 
signal therethrough. Gates 72 and 79 are alternately enabled in dependence 
upon the state of output 91 of comparator 108. 
If during operation of AC generator 10 relay 130 contacts were allowed to 
switch as between the two available contact positions, electrical arcing 
would be caused to occur due to the current coupled through the stationary 
and movable contacts. This undesirably would cause pitting and very short 
useful life of such a relay. Consequently it is desirable to cause 
switching to occur during periods of operation wherein current is 
substantially zero to avoid this problem. In accordance with this 
objective, firing pulse generator 100 is caused to be disabled when a low 
signal is introduced thereto on line 81. At any point during the operation 
of alternator 10 wherein the state of the output of comparator 108 
changes, thereby indicating a transition from low speed to high speed or 
vice-versa, line 81 is caused to go low for a predetermined period of time 
in order that bridge rectifier 22 is disabled. This disablement of bridge 
rectifier 22 in turn causes current to go to zero and allow a window 
wherein zero current switching of the movable contacts of relay 130 from 
one position to another. The signal on line 81 is referred to as the 
bridge enable command and is illustrated in FIG. 2G. When a state change 
occurs at the output of comparator 108, the one of gates 79 and 72 which 
had been enabled by the previous state of lines 92 and 93, resepectively, 
now becomes disabled and the outputs of both gates 79 and 72 on lines 99 
and 97 go low thereby resulting in a low output on line 81 from gate 74. 
After a period of time Td has expired, it is desirable to enable the one 
of the gates 79 and 72 which, in the previous speed range of operation, 
was disabled. This delay Td is chosen such that it is greater than the 
delay Tc associated with attainment of a steady state in relay 130 after 
the relay command is applied thereto via line 93. Such a time delay is 
introduced in the present embodiment by the RC time constant established 
in circuit 77 disposed between the output of buffer amplifier 71 and the 
inputs to gates 79 and 72. Gate 79 has an input directly thereto whereas 
gate 72 has an inverted input thereto. This signal at point 95 shown in 
FIG. 1 corresponds to FIG. 2D and referred to as the bridge enable delay. 
With reference now specifically to FIGS. 2A-2G, and initially assuming low 
speed operation and steady state alternator operation, at time T0 high 
speed operation is attained and the relay and intermediate bridge command 
attains a high state. This causes the low RPM bridge enable signal to go 
low due to a disabled gate 72 and, consequently, the bridge enable command 
also goes low. At this time, bridge rectifier 22 has been disabled and 
current therethrough goes to zero. After a time Tc, the relay attains a 
steady state as illustrated as a high state in FIG. 2C, the contact 
switching which occurred as a result of the relay enable command therefore 
having occurred during zero current conditions. Low RPM bridge enable 
signal, high RPM bridge enable signal and bridge enable command 
illustrated in FIGS. 2E-2G remain low. After the predetermined time delay 
TD as established by RC network changes state, high RPM bridge enable 
signal as illustrated in FIG. 2F goes high thereby also causing bridge 
enable command as illustrated in FIG. 2G to go high and reestablish 
operation of bridge rectifier 22. Similarly moving on to time T1, high 
speed operation ends and low speed operation begins as illustrated by a 
change of state of RPM signal illustrated in FIG. 2A. The relay and 
intermediate bridge command illustrated in FIG. 2B goes low and thereby 
causes high RPM bridge enable signal illustrated in FIG. 2F likewise to go 
low due to disabling of gate 79. Bridge enable command illustrated in FIG. 
2G follows, thereby disabling bridge rectifier 22 in preparation for the 
change in relay state. Again, after a time Tc associated with the delay in 
relay activation and accounting for switch bounce, the relay achieves 
steady state as illustrated by a low condition in FIG. 2C. The time delay 
Td established by the RC network thereafter causes the bridge enable delay 
signal illustrated in FIG. 2D to change states from high to low which in 
turn allows low RPM bridge enable signal to attain a high state as 
illustrated in FIG. 2E. Low RPM bridge enable signal now being high, also 
establishes the bridge enable command high in FIG. 2G thereby reenabling 
bridge rectifier 22. 
While the invention has been described in terms a preferred embodiment, it 
is anticipated that various modifications and alternative embodiments will 
be apparent to those skilled in the art and thus the scope of the 
invention is intended to encompass such modifications and alternative 
embodiments in accord with the claims as follows.