Balanced boost/buck DC to DC converter

A DC to DC converter includes a first transistor having a first power terminal connected to one side of a DC power supply and a second power terminal connected to one end of an inductor. A second transistor has a first power terminal connected to the other end of the inductor and a second power terminal connected to the other side of the DC power supply. A pair of capacitors is connected in series and defined therebetween a node which is connected to a ground potential. A third transistor has a first power terminal connected to the one end of the inductor and a second power terminal connected to one end of the pair of capacitors. A fourth transistor has a first power terminal connected to the other end of the pair of capacitors and a second power terminal connected to the other end of the inductor. Each transistor includes a diode connected between the first power terminal and the second power terminal thereof. Each diode is oriented to conduct current in a direction opposite its corresponding transistor. A controller is connected to a control terminal of each transistor for controlling the switching thereof. The DC to DC converter can be operated to increase or decrease a DC voltage between the DC power supply and the pair of capacitors connected in series. Connecting the ground potential to the node between the pair of capacitors avoids generating large potential differences between the DC power supply and the pair of capacitors.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to power converters, and more particularly, 
to DC to DC converters. 
2. Background Art 
Turbine generator systems often include a gas powered turbine to provide 
motive force to an alternator which provides single phase or polyphase AC 
power to a load. When starting the turbine from a rest position, the 
alternator can be driven as a motor to provide motive force to the turbine 
until it is running at a self-sustaining, operational speed. When starting 
the turbine utilizing the alternator as a motor, it is often necessary to 
convert DC voltage generated by one or more batteries into an AC voltage 
of sufficient potential for use by the alternator when driven as a motor. 
Typically, a power inverter system electrically connected between the 
batteries and the alternator is utilized to increase the potential of the 
DC voltage and to convert the increased potential DC voltage into an AC 
voltage for use by the alternator. More specifically, the power inverter 
system includes a DC to DC converter to increase the DC voltage of the 
batteries and a DC to AC power inverter to convert the increased DC 
voltage into an AC voltage usable by the alternator. 
A problem with prior art power inverter systems is that the ground 
potential of the batteries can float such that when the turbine generator 
is operating, a large potential difference can exist between the batteries 
and electrical components of the power inverter system. This large 
potential difference requires that instrumentation connected between the 
chassis and the electrical components of the power inverter system be 
isolated from ground potentials that can achieve 1000 volts DC or more. 
It is therefore an object of the present invention to provide a power 
inverter system which avoids large potential differences between the 
chassis of the turbine generator and the electrical component of the power 
inverter system. It is an object of the present invention to provide a 
power inverter system which can charge the batteries after the turbine 
generator is running at operating speed. It is an object of the present 
invention to provide a power inverter system having a DC to DC converter 
which boosts and controls both the positive and negative DC bus voltages 
and which provides a common electrical voltage reference which can be 
adjusted to a potential between, preferably intermediate, the positive and 
negative voltages of the DC bus. It is an object of the present invention 
to provide a power inverter system that can generate a low impedance 
electrical voltage reference (hereinafter "neutral") that can be utilized 
as a current return path for the electrical components of the power 
inverter system. It is an object of the present invention to utilize this 
low impedance electrical neutral as a ground reference for a three-phase 
output voltage generated by the power inverter system. It is an object of 
the present invention to provide this neutral without additional 
electronic components and associated control circuitry. Still other 
objects of the present invention will become apparent to those of ordinary 
skill in the art upon reading and understanding the following detailed 
description. 
SUMMARY OF THE INVENTION 
Accordingly, I have invented a DC to DC converter having an inductor and a 
first transistor having a first power terminal connectable to one side of 
a DC power supply and a second power terminal connected to one end of the 
inductor. A second transistor has a first terminal connected to the other 
end of the inductor and a second power terminal connected to another side 
of the DC power supply. A pair of capacitors is connected in series and 
defines a node therebetween which is connected to a ground potential. A 
third transistor has a first power terminal connected to one end of the 
inductor and a second power terminal connected to one end of the pair of 
capacitors. A fourth transistor has a first power terminal connected to 
the other end of the pair of capacitors and a second power terminal 
connected to the other end of the inductor. A controller is connected to a 
control terminal of each transistor for controlling the switching thereof. 
The ground potential can be connected to the second power terminal of the 
second transistor or to a node between a pair of series connected 
batteries of the DC power supply. The inductor can include a pair of 
inductors connected in series and defining a node therebetween which is 
connected to the ground potential. Each transistor can include a diode 
connected between the first power terminal and the second power terminal 
thereof. Each diode is oriented to conduct current in a direction opposite 
its corresponding transistor. 
I have also invented a DC to DC converter having a first switch and a 
second switch connected in series between a first input/output of the 
converter and a second input/output of the converter. The first switch and 
the second switch define therebetween a first node. A third switch and a 
fourth switch are connected in series between the first input/output of 
the converter and the second input/output of the converter. The third 
switch and the fourth switch define therebetween a second node. An 
inductor is connected between the first node and the second node. A pair 
of capacitors is connected in series across the second input/output of the 
converter. The pair of capacitors defines a third node therebetween which 
is connected to a ground potential. A controller is connected to control 
the switching of at least one of the switches. 
The ground potential can be connected to an end of the series connected 
third and fourth switches at the first input/output of the converter. The 
inductor can include a pair of inductors connected in series and defining 
a node therebetween which is connected to the ground potential. The first 
input/output of the converter can be connected to a DC voltage source and 
the ground reference can be electrically referenced between a positive 
terminal and a negative terminal of the DC voltage source. The DC voltage 
source can include a pair of DC voltage sources connected in series and 
the ground potential can be connected between the pair of DC voltage 
sources. A diode can be connected in parallel with each switch so that 
during operation of the converter each switch conducts current in one 
direction and the diode connected in parallel with each switch conducts 
current in an opposite direction. 
The DC to DC converter can include a DC to DC converter/regulator having an 
input and an output. The input can be connected to the second input/output 
of the converter. The converter/regulator includes a first pair of diodes 
connected in series to conduct current from the output to the input which 
is connected to the end of the series connected third switch and fourth 
switch at the second input/output of the converter. The first pair of 
diodes defines therebetween a fourth node. A second pair of diodes is 
connected in series to conduct current from the input which is connected 
to an end of the series connected first switch and second switch at the 
second input/output of the converter to the output. The second pair of 
diodes defines therebetween a fifth node. A pair of inductors is connected 
in series between the fourth node and the fifth node. The pair of 
inductors defines therebetween a sixth node which is connected to the 
ground potential. A pair of capacitors is connected in series across the 
output. The pair of capacitors defines therebetween a seventh node which 
is connected to the ground potential. A fifth switch is connected in 
parallel with one of the diodes of the first pair of diodes adjacent the 
input and a sixth switch is connected in parallel with one of the diodes 
of the second pair of diodes adjacent the input. During operation of the 
regulator, the fifth switch conducts current in one direction and the 
diode connected in parallel with the fifth switch conducts current in an 
opposite direction and the sixth switch conducts current in one direction 
and the diode in parallel with the sixth switch conducts current in an 
opposite direction. 
Lastly, I have invented a DC to DC converter having a first pair of diodes 
connected in series and defining therebetween a first node. The first pair 
of diodes is connected to conduct current from a first input/output of the 
converter to a second input/output of the converter. A second pair of 
diodes is connected in series and defines therebetween a second node. The 
second pair of diodes is connected to conduct current from the second 
input/output of the converter to the first input/output of the converter. 
A pair of inductors is connected in series between the first node and the 
second node. The pair of inductors defines therebetween a third node which 
is connected to a reference ground. A pair of capacitors is connected in 
series across the second input/output of the converter. The pair of 
capacitors defines therebetween a fourth node which is connected to the 
reference ground. A first switch is connected in parallel with one diode 
of the first pair of diodes adjacent the first input/output of the 
converter. A second switch is connected in parallel with one diode of the 
second pair of diodes adjacent the first input/output of the converter. A 
controller controls the switching of the switches so that during operation 
of the converter, the first and second switches are controlled to conduct 
current between the first input/output of the converter and the pair of 
inductors. 
The first input/output can be connected to a DC voltage source having a 
positive terminal and a negative terminal. The reference ground can be 
electrically referenced between the positive terminal and the negative 
terminal of the DC voltage source. A third switch can be connected in 
parallel with the other diode of the first pair of diodes adjacent the 
second input/output of the converter and a fourth switch can be connected 
in parallel with the other diode of the second pair of diodes adjacent the 
second input/output of the converter. During operation of the converter, 
the third and fourth switches are controlled to conduct between the pair 
of inductors and the second input/output of the converter. Preferably, the 
controller controls the switching of the switches so that the first and 
second switches conduct current simultaneously, the third and fourth 
switches conduct current simultaneously, and the first and second switches 
conduct current when the third and fourth switches block current, and vice 
versa.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
With reference to FIG. 1, a typical turbine/generator system 2 includes a 
turbine 4 which supplies motive force to a three-phase alternator 6 in a 
manner known in the art. In response to motive force being supplied 
thereto from the turbine 4, the three-phase alternator 6 generates 
three-phase electrical power which is supplied to a load 8. 
During start-up of the turbine 4, electrical power can be supplied to the 
three-phase alternator 6 from a DC power supply 10 via an inverter system 
12. The power inverter system 12 includes a DC to DC converter 14, a DC to 
three-phase inverter/rectifier 16 and a control system 18. The DC to DC 
converter 14 includes a first input/output 20 connected to the DC power 
supply 10 and a second input/output 22 connected to a first input/output 
24 of the DC to three-phase inverter/rectifier 16. The DC to three-phase 
inverter/rectifier 16 has a second input/output connected to the 
three-phase alternator 6. 
When the three-phase alternator 6 is utilized as a motor during start-up of 
the turbine 4, the inverter system 12 converts DC voltage received at the 
first input/output 20 of the DC to DC converter 14 into three-phase AC 
voltage at the second input/output 26 of the DC to three-phase 
inverter/rectifier 16. When the turbine is running at a self-sustaining 
speed, the inverter system 12 terminates supplying three-phase power to 
the three-phase alternator 6. At an appropriate time, the inverter system 
12 converts three-phase AC power received from the three-phase alternator 
6 at the second input/output 26 of the DC to three-phase 
inverter/rectifier 16 into DC power at the first input/output 20 of the DC 
to DC converter 14. The DC power generated at the first input/output 20 of 
the DC to DC converter 14 is utilized to charge the DC power supply 10, 
which includes one or more batteries that are utilized to supply power to 
the power inverter system 12 when the three-phase alternator 6 is utilized 
as a motor to provide motive force to the turbine 4 during start-up. 
With reference to FIG. 2, and with ongoing reference to FIG. 1, the DC 
power supply 10 has a positive terminal 28 and a negative terminal 30 
connected to the first input/output 20 of the DC to DC converter 14. The 
DC to DC converter 14 has a first transistor 32 having a collector or 
first power terminal 34 connected to the positive terminal 28 of the DC 
power supply 10 and an emitter or second power terminal 36 connected to 
one side of an inductor 38. A second transistor 40 has a collector or 
first power terminal 42 connected to a side of the inductor 38 opposite 
the emitter terminal 36 of the first transistor 32 and an emitter or 
second power terminal 44 which is connected to the negative terminal 30 of 
the DC power supply 10. Preferably, the negative terminal 30 of the DC 
power supply 10 and the emitter terminal 44 of the second transistor 40 
are connected to a ground potential or reference ground 46. 
A third transistor 48 has a collector or first power terminal 50 and an 
emitter or second power terminal 52. The collector terminal 50 of the 
third transistor 48 is connected to the emitter terminal 36 of the first 
transistor 32. A fourth transistor 54 has a collector or first power 
terminal 56 and an emitter or second power terminal 58. The emitter 
terminal 58 of the fourth transistor 54 is connected to the collector 
terminal 42 of the second transistor 40. A pair of capacitors 60 and 62 is 
connected in series between the emitter terminal 52 of the third 
transistor 48 and the collector terminal 56 of the fourth transistor 54. 
The capacitors 60 and 62 define a node 64 therebetween which is connected 
to the ground potential or reference ground 46. Diodes 66, 68, 70 and 72 
are connected between the emitter terminals and the collector terminals of 
transistors 32, 40, 48 and 54 to conduct current in a direction opposite 
transistors 32, 40, 48 and 54, respectively. The control system 18 is 
connected to the base or control terminal of each transistor 32, 40, 48 
and 54 to control the switching ON and OFF thereof. The control system is 
also connected to the ground potential or reference ground 46. 
In operation, the control system 18 causes the first and second transistors 
32 and 40 to switch ON thereby creating a current path from the DC power 
supply 10 through the inductor 38. When the current through the inductor 
38 increases to a sufficient extent, the control system 18 causes the 
first and second transistors 32 and 40 to switch OFF. The current flowing 
through the inductor 38 when the first and second transistors 32 and 40 
switch OFF flows through diodes 70 and 72 and capacitors 60 and 62 thereby 
charging capacitors 60 and 62. When the current through the inductor 38 
decreases to a sufficient extent, the control system 18 causes the first 
and second transistors 32 and 40 to switch ON thereby creating the current 
path between the DC power supply 10 and the inductor 38. Thereafter, the 
control system 18 repeats switching the first and second transistors 32 
and 40 OFF and ON when the current through the inductor 38 increases and 
decreases to a sufficient extent, respectively, to maintain a charge, and 
hence the voltage, in the capacitors 60 and 62 at a desired level when the 
DC to three-phase inverter/rectifier 16 supplies power to the three-phase 
alternator 6 operating as a motor during start-up of the turbine 4. When 
the DC to DC converter 14 supplies power from the DC power supply 10 to 
the DC to three-phase inverter/rectifier 16, the control system 18 causes 
the third and fourth transistors 48 and 54 to remain switched OFF. 
When the turbine 4 is running at a self-sustaining speed, a rectifier of 
the DC to three-phase inverter/rectifier 16 converts three-phase AC 
voltage received at the second input/output 26 thereof into a rectified DC 
voltage at the first input/output 24 thereof. The control system 18 causes 
the DC to DC converter 14 to convert the rectified DC voltage received at 
the second input/output 22 thereof into a regulated DC voltage at the 
first input/output 20 thereof. The DC voltage generated by the DC to DC 
converter 14 at the first input/output 20 thereof is utilized to charge 
batteries or other storage elements of the DC power supply 10. 
More specifically, when the DC to DC converter 14 is utilized to charge the 
DC power supply 10, the control system 18 causes the third and fourth 
transistors 48 and 54 to switch ON thereby creating a current path between 
the second input/output 22 and the inductor 38. When the current through 
the inductor 38 increases to a sufficient extent, the control system 18 
causes the third and fourth transistors 48 and 54 to switch OFF. The 
current flowing through the inductor 38 when the third and fourth 
transistors 48 and 54 switch OFF flows through diodes 66 and 68 and the DC 
power supply 10 thereby charging the DC power supply 10. 
When the current through the inductor 38 decreases to a sufficient extent, 
the control system 18 causes the third and fourth transistors 48 and 54 to 
switch ON thereby creating the current path between the second 
input/output 22 and the inductor 38. Thereafter, the control system 18 
repeats switching the third and fourth transistors 48 and 54 OFF and ON 
when the current through the inductor 38 increases and decreases to a 
sufficient extent, respectively, to maintain the voltage at the first 
input/output 20 at a desired level for charging the DC power supply 10. 
When the DC to DC converter 14 supplies power from the DC to three-phase 
inverter/rectifier 16 to the DC power supply 10, the control system causes 
the first and second transistors 32 and 40 to remain switched OFF. 
Connecting the negative terminal 30 of the DC power supply 10, the node 64 
and the control system 18 to the ground potential or reference ground 46 
maintains the DC power supply 10, the capacitors 60 and 62 and the control 
system 18 referenced to a known potential thereby avoiding the voltage 
across the capacitors 60 and 62, the voltage at the negative terminal 30 
of the DC power supply 10 and/or the voltage of electrical sub-systems of 
the control system 18 from floating to undesirable and potentially 
dangerous levels. 
Preferably, the DC to DC converter 14 includes a capacitor 74 connected 
between the collector terminal 34 of the first transistor 32 and the 
emitter terminal 44 of the second transistor 40 for filtering AC signals 
coupled between the DC power supply 10 and the first input/output 20 of 
the DC to DC converter 14. Voltage sense leads 76 can be connected between 
the control system 18 and the second input/output 22 of the DC to DC 
converter 14, and voltage sense leads 78 can be connected between the 
control system 18 and the first input/output 20 of the DC to DC converter 
14. The voltage sense leads 76 and 78 enable the control system 18 to 
measure the voltage across the capacitors 60 and 62 and the DC power 
supply 10, respectively. Utilizing the voltages sensed on the voltage 
sense leads 76 and 78, the control system 18 can control the switching of 
the first and second transistors 32 and 40 to generate a desired DC 
voltage at the second input/output 22 of the DC to DC converter 14, and 
can control the switching of the third and fourth transistors 48 and 54 to 
generate a desired DC voltage at the first input/output 20 of the DC to DC 
converter 14. Preferably, the DC power supply 10 includes batteries 80 and 
82 connected in series between the positive terminal 28 and the negative 
terminal 30 thereof. 
A variation of the DC to DC converter 14 of FIG. 2 is shown in FIG. 3, 
where like reference numbers correspond to like elements. In the DC to DC 
converter 14 shown in FIG. 3, the inductor 38 includes a pair of inductors 
84 and 86 connected in series and defining a node 88 therebetween. The 
node 88 is connected to the ground potential or reference ground 46. In 
the embodiment shown in FIG. 3, the ground potential 46 is also connected 
to a node 90 between batteries 80 and 82, not to the negative terminal 30 
of the DC power supply 10 as shown in FIG. 2. An advantage of referencing 
the DC to DC convertor 14 shown in FIGS. 2 and 3 to the ground potential 
or reference ground 46 and referencing the negative terminal 30 or the 
node 90 of the DC power supply 10 to the ground potential or reference 
ground 46 is that the three-phase alternator 6 can utilize a shaft 
position sensor for feedback to the control system 18 for both speed and 
position sensing, thus avoiding the need for separate shaft positioning 
and speed systems with a corresponding reduction in cost and complexity. 
Moreover, since the DC power supply 10 and the second input/output 22 of 
the DC to DC converter 14 are referenced to the same ground potential or 
reference ground 46, large potential differences between the DC power 
supply 10 and the node 64 are avoided. Thus, when electrical sub-systems 
such as the control system 18, ignition exciters, pressure transducers, 
speed pickups, temperature measuring devices, and the like, are connected 
to and derive their operating power and ground potential or reference 
ground 46 from the DC power supply 10, large potential differences are 
avoided between these electrical sub-systems and node 64. 
With reference to FIG. 4, a DC to DC converter/regulator 100 can be 
connected between the second input/output 22 of the DC to DC converter 14 
and the first input/output 24 of the DC to three-phase inverter/rectifier 
16 to regulate the voltage supplied to the first input/output 24 of the DC 
to three-phase inverter/rectifier 16. The DC to DC converter/regulator 100 
has an input 102 connected to the second input/output 22 of the DC to DC 
converter 14 and an output 104 connected to the first input/output 24 of 
the DC to three-phase inverter/rectifier 16. The DC to DC 
converter/regulator 100 regulates DC power received at the input 102 
thereof and provides a regulated voltage at the output 104 thereof. If the 
DC to DC converter/regulator 100 is configured to supply power 
unidirectionally from the DC to DC converter 14 to the DC to three-phase 
inverter/rectifier 16, a switch 106 is connected between the first 
input/output 24 of the DC to three-phase inverter/rectifier 16 and the 
second input/output 22 of the DC to DC converter 14. When the rectifier of 
the DC to three-phase inverter/rectifier 16 supplies power to the DC to DC 
converter 14, the control system 18 causes the switch 106 to activate and 
connect the first input/output 24 of the DC to three-phase 
inverter/rectifier 16 and the second input/output 22 of the DC to DC 
converter 14, thereby bypassing the DC to DC converter/regulator 100. If, 
however, the DC to DC converter/regulator 100 can supply power 
bidirectionally, the switch 106 can be omitted. 
With reference to FIG. 5, and with ongoing reference to FIG. 4, an 
embodiment of the DC to DC converter/regulator 100 which unidirectionally 
supplies power between the DC to DC converter 14 and the DC to three-phase 
inverter 16 is shown. The DC to DC converter/regulator 100 includes a 
first transistor 108 having a collector or first power terminal 110 
connected to a positive terminal of the second input/output 22 of the DC 
to DC converter 14. The first transistor 108 has an emitter or second 
power terminal 112 which is connected to one side of an inductor 114. A 
second transistor 116 has a collector or first power terminal 118 
connected to a side of the inductor 114 opposite the first transistor 108 
and an emitter or second power terminal 120 connected to a negative 
terminal of the second input/output 22 of the DC to DC converter 14. The 
control system 18 is connected to the base or control terminals of the 
first and second transistors 108 and 116 to control the switching ON and 
OFF thereof. Diodes 122 and 124 are connected between the collector 
terminals and the emitter terminals of transistors 108 and 116 to conduct 
current in a direction opposite their corresponding transistors 108 and 
116. 
A diode 126 has a cathode terminal 128 connected to the emitter terminal 
112 of the first transistor 108. A diode 130 has an anode terminal 132 
connected to the collector terminal 118 of the second transistor 116. 
Connected between an anode terminal 134 of the diode 126 and the cathode 
terminal 136 of the diode 130 are a pair of capacitors 138 and 140 
connected in series. The capacitors 138 and 140 define therebetween a node 
142 which is connected to a ground potential or reference ground 146. 
Preferably, the ground potential or reference ground 146 is connected to 
the ground potential or reference ground 46 shown in FIGS. 2 and 3. The 
inductor 114 preferably includes a pair of inductors 148 and 150 connected 
in series and defining therebetween a node 152 which is connected to the 
ground potential or reference ground 146. The inductor 114, however, can 
be a single inductor having a center tap at node 152. 
In operation, the control system 18 causes the first and second transistors 
108 and 116 to switch ON thereby creating a current path between the input 
102 of the DC to DC converter/regulator 100 and the inductor 114. When the 
current in the inductor 114 increases to a sufficient extent, the control 
system 18 causes the first nd second transistors 108 and 116 to switch 
OFF. The current flowing in the inductor 114 when the first and second 
transistors 108 and 116 switch OFF flows through diodes 126 and 130 and 
capacitors 138 and 140 thereby charging capacitors 138 and 140. When the 
current flowing in inductor 114 decreases to a sufficient extent, the 
control system 18 causes the first and second transistors 108 and 116 to 
switch ON thereby creating the current path between the input 102 of the 
DC to DC converter/regulator 100 and the inductor 114. Thereafter, by 
selectively controlling the switching OFF and ON of the first and second 
transistors 108 and 116, the control system 18 can charge the capacitors 
138 and 140 to a desired extent as measured by voltage sense leads 154 
connected between the control system 18 and the output 104 of the DC to DC 
converter/regulator 100. 
Connecting the nodes 142 and 152 to the ground potential or reference 
ground 146 balances the current flowing through the inductor 114, balances 
the charging voltage of capacitors 138 and 140, avoids generating 
undesirable potential differences between the DC power supply 10 and the 
electronic components of the DC to DC converter/regulator 100 and creates 
a low impedance path for a neutral current supplied via the ground 
potential or reference ground 146 connected to load 8, shown in FIG. 4. 
Preferably, the DC to DC converter/regulator 100 includes a capacitor 168 
across the input 102 thereof for filtering high frequency and/or ripple 
components generated at the second input/output 22 of the DC to DC 
converter 14. 
The DC to DC converter/regulator 100 can be configured to bidirectionally 
regulate power between the DC to DC converter 14 and the DC to three-phase 
inverter 16 by including in parallel with diodes 126 and 130, a third 
transistor 156 and a fourth transistor 158, respectively, shown in phantom 
in FIG. 5. The third and fourth transistors 156 and 158 in parallel with 
diodes 126 and 130 transforms the input 102 into a first input/output of 
the DC to DC converter/regulator 100 and transforms the output 104 into a 
second input/output of the DC to DC converter/regulator 100. The third 
transistor 156 has a collector or first power terminal 160 connected to 
the cathode terminal 128 of diode 126 and an emitter or second power 
terminal 162 connected to the anode terminal 134 of the diode 126. The 
fourth transistor 158 has a collector or first power terminal 164 
connected to the cathode terminal 136 of the diode 130 and an emitter or 
second power terminal 166 connected to the anode terminal 132 of the diode 
130. The base or control terminals of the third and fourth transistors 156 
and 158 are connected to the control system 18. It should be noted that 
the DC to DC converter/regulator 100 including the third and fourth 
transistors 156 and 158 has the same electrical circuit topology as the DC 
to DC converter 14 shown in FIG. 3. Hence, the DC to DC 
converter/regulator 100 shown in FIG. 5 can be operated in the same manner 
described above for the DC to DC converter shown in FIGS. 2 and 3. 
The control system 18 controls the operation of the DC to DC converter 14, 
the DC to three-phase inverter/rectifier 16 and, if provided, the DC to DC 
converter/regulator 100 as a function of a position sense signal generated 
by a shaft position sensor (not shown) of the three-phase alternator 6 and 
supplied to the control system 18 via a sense line 170, shown best in 
FIGS. 1 and 4. More specifically, during start-up of the turbine 4 
utilizing the three-phase alternator 6 as a motor, the control system 18 
coordinates the operation of the DC to DC converter 14, the DC to DC 
converter/regulator 100 and the DC to three-phase inverter/rectifier 16 as 
a function of the position sense signal on sense line 170 and the voltages 
sensed by voltage sense leads 76, 78 and 154 to selectively increase the 
frequency and/or voltage of the three-phase power generated by the DC to 
three-phase inverter/rectifier 16 and supplied to the three-phase 
alternator 6. 
When the turbine is running at a self-sustaining speed, the control system 
18 terminates the DC to DC converter 14, the DC to DC converter/regulator 
100 and the DC to three-phase inverter/rectifier 16 supplying power to the 
three-phase alternator 6 and initiates supplying power from the 
three-phase alternator 6 to the DC power supply 10. More specifically, the 
control system 18 utilizes the position sense signal on sense line 170 and 
the voltages sensed by voltage sense leads 76, 78 and 154 to coordinate 
the operation of the DC to DC converter 14 and the DC to DC 
converter/regulator 100 to convert the rectified DC voltage produced at 
the first input/output 24 of the DC to three-phase inverter/rectifier 16 
into a DC voltage at the first input/output 20 of the DC to DC converter 
14 to charge the DC power supply 10 to a desired voltage. Alternatively, 
the control system 18 coordinates the operation of the switch 106 and the 
DC to DC converter 14 to charge the DC power supply 10 to a desired 
voltage. 
The invention has been described with reference to the preferred 
embodiments. Obvious modifications and alterations will occur to others 
upon reading and understanding the preceding detailed description. For 
example, an inverter and an alternator having more or less than three 
phases can be utilized. It is intended that the invention be construed as 
including all such modifications and alterations insofar as they come with 
the scope of the appended claims or the equivalents thereof.