The basic purpose of this paper is to provide some information regarding bidirectional four quadrant resonant power conversion and describe possible applications to aircraft electrical systems. As this technology has been developed sufficiently to demonstrate its feasibility, this is an appropriate time to evaluate the benefits of its application to aircraft electrical systems

Hansen, I. G.

English

NASA Technical Reports Server

1V84 1007C
ALL-PURPOSE BIDIRECTIONAL FOUR-QUADRANT CONTROLLFR
..
Irving G. Hansen
National Ae-onautics and Space Administration
Lewis Research Center
C _.veland,Ohio 44135
The basic conventions for defining power f_ow are illustratedin fig-
ure 1. The circuit in the upper left of figure 1 defines a positive voltage
source and positive current flow. When the current and voltage are plotted as
on the upper rlght, they define positive power flow to the load and fall in
the first Quadrant. With a negative voltage source and a negative current
flow, as shown in the lower left of figure 1, the power flow Lo the load is
still positive, but it falls in the third Quadrant as shown in the lower
right. Thus positive power, or power flowing to the load, falls in either the
first or third Quadrant. The other two Quadrants are obviously negative power
(+I x -E or -I x +E) and represent power flowing from the load. In the second
indfourth Quadrants the load is acting as a power source.
Figure 2 shows an example of a bidirectional load. With the switch in
the position shown, the battery is powering the motor, which in turn is
driving a flywheel. When the switch connects the motor to the resistor, the
only source of energy in the circuit is the rotating motor and flywheel.
Assuming an ideal motor with no inductance and proper excitation, the motor
would act as a capacitor. The voltage would remain constant, but the current
would reverse and flow from the motor, now in a generating mode, to the re-
_ sistor. This is illustratedon the plot in the lower'half of figure 2 by the f_
arrows pointing downward from the point in the first Quadrant to the point in
the fourth quadrant. Since with actual motors inductancewould be present,
_ the trajectory would be more like the other path of arrows with the current
i remaining constant and the voltage decreasing and even going negative before
; reaching the point in the fourth Quadrant. In this example the energy flow is
bidirectional and several Quadrants are involved in the transition of energy
from one point to the other. The purpose of the bidirectionalfour-quadrant
controller is to control the flow of energy between the various quadrants.
Figure 3 is a Lissajous pattern showing the locus of operating points for
a load. With a sinusoida] voltage and current, and with some phase angle be-
c tween them, the locus of operating points forms an ellipse as plotted in the
figure. If the load were purely resistive, the ellipse would collapse into a
line lying in the first and third quadrants only. That is because a pure re-
sistance operates only as a load and not as a source. However, with a load
.. containing both resistance and reactance, energy is stored and released as
_ well as dissipated and the locus extends into all four quadrants. Again, re-
viewing the basic definition, the load is dissipative in the first and third
quadrants and is a source in the second and fourth quadrants.
_. A resonant circuit, since it ha_ both resistance and reactance,operates
CT in all four quadrants. This means that it can either deliver or accept power; ,
_!) hence it is bidirectional. There will be limits on the voltage and current as
shown in figure 4. The circuit will not support a voltage above the line
_] labeled voltage limit nor accept a current above the line labeled currentlimit. If the resonant circuit is connected to a source each time the locus
occupies the first quadrant (or the third quadrant with inversion),the load
__ presented to the source will be a steady dc load. The load voltage and cur-
rent will always be the same value each time the switch is closed. This
;89
1984001988-183
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illustrateshow a resonant circuit can accept dc power. If a point on the
locus were chosen in the second or fourth quadrant, the resonant circuit would
act as adc source instead of a load. Alternating-currentoperation is a bit
more complicated since the switch must be closed and inverted at different
times rath6r than for one fixed quadrant. However, if the switch closure is
controlled, frecuencies lower than the resonant frequency can be synthesized
either for loads or sources. Therefore, through the proper use of resonant
circuits and connecting switches, bidirectionalfour-Quadrantac and/or dc
power controllerscan be implemented.
Figure 5 shows a bidirectionalcontroller with associatedplots for both
terminal sets. The plot shown for terminal set 1 indicates that it is accept-
ing power, in this case a dc input. This is the same as the example discussed
previously,where the controller is acting as a dc load. The dashed lines on
the terminal 2 plot indicate the constant power limit at the output. Because
' of the law of conservationof energy the output power cannot be greater than
the input. However, the output can operate in either the _econd or fourth
quadrants and can provide either dc or ac. The controller can also be oper-
ated in an ac-to-ac mode. In that case the controller can be used to provide
power factor correction. However, the amount of correction possible is
limited by the available reactive power.
The upper half of figure 6 shows a half-bridge transistorizedseries-
resonant dc-to-ac converter. When one transistor is switched on, the current
from the dc source flows through the indLctor,the transformer,and one capaci-
tor. The current is initially limited by the inductance,gradually increases,
and then starts to be limited by the capacitor charging. The result is a t
quasi sine wave. The transistor is opened when the current goes through zero, f(_
and somecurrent flows in the opposite direction through the bypass diode
(causing the small bump in the waveform). The second transistor is then
turned on, and the current flows in a direction opposite to that of the first
transistor (causing an ac output). One very important point is that the tran-
sistors are switched off when the current passes through zero. This elimi-
: nates second breakdown,which is one of the major causes of transistor failure
in converter and invertercircuits. As a result, the series-resonantcon-
verter is considerablymore reliable than conventional converters, and the
transistorscan be operated at both high power levels and higher frequencies.
The output of this converter is a high-frequencysinusoid that has lower bar-
' monlcs and slower rlsetlmes than conventional square-waveconverters. As a
: result, the electromagneticinterference (EMIl is much less for this design.
The particular circuit configuration shown in figure 6 acts as a current
source at the output. This can be very desirable for operat,ng loads such as
_ motors, particularlyduring startup. When a current-limltedsource is used,
only the frequency needs to be controlled instead of having to maintain a
constant voltage-to-frequencyV/F ratio as is done with voltage sources.
This circultcan also be reconfigured to act as a voltage source by taking
:_ the output from the capacitors. Both types of configurationshave been
demonstrated.
_ To provide the final controlled output, the hlgh-frequencysinusoidal
_ power of the resonant converter is fed into the circuit shown on the bottom of :
:3_: figure 6. The switches are closed in pairs (synchronousrectification)to
_, connect the transformerto the output momentarily. The synthesizedwaveform
_ i1_ustratedis a sinusoidal ac of much lower frequency than the carrier.
_-_:_ Direct current of either polarity can be synthesized by closing the switches
to maintain one output terminal at the same polarity.
l
190
1984001988-184
Figure 7 shows a fully bidirectional resonant controller with resonant
bridges on both ends. This arrangement allows either port to be used as the
input accepting either ac or dc power. With this circuit arrangement one full
wave bridge is at the source c,_d, the other is at the load end, and the trans-
mission line between operates at the carrier frequency. The capacitance of
the line is made a part of the resonant circuit. This reduces the parts count
and makes use of the line capacitance that would be present in any case.
Systems of this configuration have been tested at 20 kHz with line lengths of
59 m, which is typical of the line length in a large transport aircraft. The
line loss was quite small.
Figure 8 illustrates an a_ distribution system configured for bidirec-
tional resonant power conversion. The distribution bus at the top of the
figure is the high-frequency transmission line as shown on the previous
figure. However, instead of just having an input/output circuit at either end
of the line, several loads or sources are paralleled on the line. The first
bidirectional converter on the left provides dc power to a storage device such
as a battery. If the power f_iled on the main ac bus, the storage device
would feed power back to the bus. The second converter is shown as an inter-
face for ground power. Any appropriBte type of power (dc, 60 Hz, or 400 Hz)
could be used to power other equipment connected to the main bus or even to
start the engines. Power could also be fed from the airplane to perform such
tasks as starting the engines of another aircraft. The next power converter
shown is provided to power various loads on the aircraft. An aircraft system
would have a number of these dedicated converters.
The basic purpose of this paper is to provide some information regarding
bidirectional four-quadrant resonant power conversion and describe possible
applicationsto aircraft electrical systems. As this technology has been .G
developed sufficientlyto demonstrate its feasibility,this is an appropriate
time to evaluate the benefits of its application to aircraft electrical
systems.
REFERENCES
I. Mapham, N.: An SCR Inverter with Good Regulation and Sine Wave Output,
IEEE Trans. Ind. Gen. Appl., vol IGA-3, no. 2, Mar.IApr 1967, pp.
176-187.
2. Schwarz, F. C.: An Improved Method of Resonant Current Pulse Modulation
for Power Converters. IEEE Trans. Ind. Electron. Control Instrum., vol.
IECI-23,no. 2, May 1976, pp. 133-141.
3. Myers, R.; and Peck, R. D.: 200 kHz Power FET Technology in New Modular
Power Supplies. Hewlett-PackardJournal, vol. 32, no. 8, Aug. 1981,
pp. 3-11.
4. Babu, S. R.: A Practic_l Resonant Converter Using High Speed Power
Darlington Transistors. PCI '82, Intertec Communications,Inc., 1982,
pp. 122-141. i
5. Bless, J. J.; Inouye,L.Y.;and Shank, J. H.: High Voltage Series
Resonant Inverter Ion Engine Screen Supply. Power Electronics
Specialists Conference, IEEE, 1974, pp. 97-105. i
6. Bless, J. J.; and Frye, R. J.: Electrical Prototype Power Processer for ! _ :_
30-cm Mercury Electric Propulsion Engine. AIAA Paper 78-684, Apr. 1978.
7. Robson, R.; and Hancock, D.: A lO-kW Series Resonant Converter Design,
Transistor Characterization,and Base-Drive Optimation. NASA CR-165546,
1981.
191
i98400i988-i85
ORIGINAL PAC;_:i_
_i_ OF POOR QUALITY
8. Schwarz, F.C.: Bi-DirectionalFour Quadrant (BDQ4) Power Converter
Dcvelopment. NASA CR-159660, 1979.
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All-purpose bidirectional four-quadrant controller

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