NASA/TM--2002-211812 IECEC-2002-20078

Single Axis Attitude Control and

Regulation With Two Flywheels

Peter E. Kascak and Ralph H. Jansen

University of _Ibledo, _I-bledo, Ohio

Barbara Kem_y

Glerm Research Center, Cleveland, Ohio

Timothy R Dever

QSS Group, Inc., Cleveland, Ohio

DC Bus

August 2002
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NASA/TM--2002-211812 IECEC-2002-20078

Single Axis Attitude Control and

Regulation With Two Flywheels

Peter E. Kascak and Ralph H. Jansen

University of "Ibledo, _I-bledo, Ohio

Barbara Keimy

Glem_ Research Center, Cleveland, Ohio

Timothy R Dever

QSS Group, Inc., Cleveland, Ohio

DC Bus

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August 2002
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Available electronically at http://gltrs.zrc.nasa.gov
Single Axis Attitude Control and DC Bus Regulation With Two Flywheels

Peter E. Kascak and Ralph H. Jansen

University of Toledo

Toledo, Ohio 43606

216-433-8408, peter.e.kascak@grc.nasa.gov

216-433-6038, ralph.h.jansen @grc. nasa.gov

Barbara Kenny

National Aeronautics and Space Administration

Glenn Research Center

Cleveland, Ohio 44135

216-433-6289, barbara.h.kenny @ grc.nasa.gov

Timothy R Dever

QSS Group, Inc.

Cleveland, Ohio 44135

216-433-2384, timothy.p.dever @grc.nasa.gov

ABSTRACT

A computer simulation of a flywheel energy

storage single axis attitude control system is

described. The simulation models hardware which

will be experimentally tested in the future. This

hardware consists of two counter rotating flywheels

mounted to an airtable. The airtable allows one axis

of rotational motion. An inertia DC bus coordinator is

set forth that allows the two control problems, bus

regulation and attitude control, to be separated.

Simulation results are presented with a previously

derived flywheel bus regulator (Kascak, 2001) and a

simple PID attitude controller.

INTRODUCTION

Flywheel system and technology development

work has been an ongoing activity at NASA Glenn

FIGURE 1 - HIGH ENERGY FLYWHEEL

FACILITY

Research Center over the past several years. Most

recently, work has been conducted under the

Aerospace Flywheel Technology Program (AFT) and

the Flywheel Energy Storage System Program

(FESS). This paper discusses simulation results of a

control algorithm for combined power bus regulation

and single degree of freedom torque and momentum

control using a two flywheel system. A discussion of

related programs sponsored by NASA and the US Air

Force has been done. (McLallin, 2001).

The algorithm presented will be experimentally

verified in the Attitude Control and Energy Storage

Experiment Phase 0 (ACESE_0). In this experiment

two technology demonstrator flywheel modules

developed under FESS and a previous flight program

will be integrated at NASA GRC's High Energy

Flywheel Facility (HEFF). Figure 1 shows the facility

which consists of an airtable where the modules are

I

Flywheel 1 L

! 1

k

\

Cables

o

Air Table

FIGURE 2 - HIGH ENERGY FLYWHEEL

FACILITY SCHEMATIC

NASA/T_2002-211812 1
mounted surrounded by a water containment safety

system (Trase 2002). Thermal, vacuum, and

instrumentation support hardware can be seen on the

upper platform. A simple schematic of the setup is

shown in Figure 2. The experiment will be a

hardware demonstration of a flywheel system which

provides both power bus regulation and a single axis

torque and attitude control. The long term objective is

to extend this work to a bus regulation and three

degree of freedom attitude control system

representative of a satellite platform.

NOMENCLATURE

IDc - DC current provided by flywheel system (A)

IDc,m - DC current into flywheel inverter m (A)

Ip/s - DC current out of flae power supply (A)

Jx - moment of inertia about axis x (kg*m 2)

L d - direct axis self inductance (H)

Lq - quadrature axis self inductance (H)

p - derivative operator

P - number of poles

T d - disturbance torque (N'm)

T e - electromagnetic torque (N'm)

Tp - platform torque (N'm)

l/z) c - DC bus Voltage (V)

;Laf - mutual flux linkages by rotor magnets, (V* s)

co r2 - electrical frequency (rad/s)

R_1202 Controller

SYSTEM MODEL

The ACESE 0 simulation is divided into two

parts, the controllers and the plant models (Figure 3).

Each controller regulates progressively higher level

states as we move from the inner to outer control

loop. Plant models are provided for each hardware

subcomponent. The model does not include

switching effects, motor torque ripple, or other higher

order effects that are required to estimate power or

torque quality. The purpose of the model is to

develop a functional controller for the hardware

demonstration.

Plant models were developed for the two flywheel

modules, a single degree of freedom platform

mounted on an airtable, a power supply, an electrical

load, and the DC bus.

The controller has two nested loops and a

coordinator. The innermost loop is a motor current

regulator for each flywheel. The outer loop has a DC

bus regulation algorithm and attitude control algorithm

operating simultaneously. The system level

commands of bus voltage and pointing angle get

issued to the highest level loop. The coordinator

parses the demands from the bus regulator and

attitude controller into current commands for each

flywheel module.

Inputs to the system controllers include: V*Dc,

I*j,o,ge (to DC Bus regulator) and theta* (to attitude

regulator). The parameters that are varied are: V_....

I1i,,m(power supply plant model), load resistance (load

plant model), and disturbance torque (platform plant

model).

DO Bus Regulator

V_m

Mechanical Plant Models

The flywheel modules which will be incorporated

into HEFF are called D1 and HSS. The mechanical

plant models included in the system are the D1

flywheel module, the HSS flywheel module, and the

Hardware

Idc* Iqsr'l

wrl

............ !)='7 I ......... = =[ ........

labe Vb I Vb Wrl [rad/s)

rotor theta (rad} V¢ V¢ rotor thetal (rad)

ilrbtT__ , -*tv0o

II I Current RegU ator 1 I FM Plant Model 1 (D1) I

,' I

EElFM Plant Model 2 (HS$)Iqsr*2 Va I I

IIr;I...... ',

Current Regulator g II

Ill ,,

_ra_

Load Plant Model

Torquel Theta table_-

Torque2

Disturbance torque W table

11DOF Platform Plant Model I --

1:Z v@_

DCbus Voltage

Plant Model

FIGURE 3 - SYSTEM MODEL

NASA/T_2002-211812 2
single degree of freedom plant model.

The D1 Flywheel Module (D1) and the High

Speed Shaft (HSS) flywheel module used in this test

are not identical, however they both have generally

the same topology. They each have magnetically

suspended rotors with permanent magnet

motor/generators, mechanical touchdown bearings,

and an integral housing/vacuum enclosure. Table 1

contains the flywheel module properties.

The mechanical system is modeled as a single

degree of freedom second order system. The airtable

and all the components mounted on it other than the

flywheel rotors will be referred to as the platform. The

platform components are modeled as inertias about

the spin axis of air table. These components are the

base, avionics, and flywheel stator assemblies. The

flywheel rotors are included as torques acting on the

platform. Figure 4 shows a free body diagram of the

system. Axes 0,1, and 2 represent the rotation axes

of the platform, flywheel 1, and flywheel 2

respectively. The equation of motion for the platform

is:

Jgo +Ceo (I)

The work in this paper does not include platform

damping and stiffness effects; these are set to zero in

the model. The terms are included for future

modeling of the cable harness stiffness and bearing

damping in the experimental hardware.

The total inertia about the 0 axis, Jo, is the sum of

the inertia of the base, avionics, flywheel stator

assemblies and flywheel rotors.

Jo =J_ +Jb +

(J_a +rn_aX_)+(J_a +rn_aX_) (2)

(J_2 + rn_2x_) + (J,2 + rn,2x_)

The base and avionics are modeled as circular

cylinders. The flywheel stators are considered

circular cylindrical shells located on a parallel axis.

The flywheel rotors are circular cylinders on parallel

axis. The standard equations are applied (Meriam

and Kraige, 1986).

] 2

Jzz = 7 lttr circular cylinder (3)

FM 1 Properties

mr1 : rotor mass

J1 :rotor intertia

ms1: stator mass

Jsl: stator inertia

Flywheel 1

I 01

4-, Flywheel2

00 _ I 02

FM 2 Properties

mr2 :rotor mass

J2 : rotor intertia

ms2: stator mass

Js2: stator inertia

Base Prope__CSonP '

: rc°$e: s

mb : plate mass

Jb :plate intertia Ja : avionics intertia Air Table

FIGURE 4 - FREE BODY DIAGRAM

J= = mr 2 circular cylindrical shell (4)

2

Jaxis a = Jaxis b +mda to b parallel axis (5)

The torques applied to the platform are equal and

opposite to the torque applied to the rotors of each

flywheel model. Resultant torques from rotor

translation are neglected. The platform inertia reacts

to the sum of the torques.

ZT=Tp=-Te]-Te2 (6)

The flywheel module is modeled as a single

degree of freedom rotor with a torque applied by the

motor/generator. The motor is modeled as a

synchronous permanent magnet machine (Krishnan,

1996).

Electrical Plant Models

The electrical model includes: the DC bus voltage

plant model, the power supply plant model, and the

load plant model.

The DC bus is modeled as a capacitor with

various current sources charging or discharging it

TABLE 1 -SYSTEM PROPERTIES

[ Value [ Property

System

J0

c

k

25.22 kg.m2 platform inertia about axis 0

0 platform damping

0 platform stiffness

D1 Flywheel Module

mr1

Jr1

ms1

Jsl

Xl

Lql

Ldl

Rsl

)_afl

Bt

17.2 kg

0.0664 kg.m2

rotor mass

rotor polar moment of inertia

61.2 kg stator mass

560 kg.m2 stator polar moment of

inertia

0.254 m distance from axis 0 to 1

0.000025 H q axis inductance of motor

0.000019 H d axis inductance of motor

0.0145 _ I-n stator resistance of motor

0.00733 V-s rotor magnet flux linkage

0 viscous drag on rotor

HSS Flywheel Module

mr2

Jr2

ms2

Js2

x2

Lq2

Lq2

Rs2

)_af2

B2

6.53kg rotor mass

0.00377 kg.m2 rotor polar moment of inertia

56.7 kg stator mass

518 kg.m2 stator polar moment of

inertia

0.254 m distance from axis 0 to 1

0.000142 H q axis inductance of motor

0.000101 H d axis inductance of motor

0.035 _ I-n stator resistance of motor

0.014456 V-s rotor magnet flux linkage

0 viscous drag on rotor

40.1 kg base mass

2939 kg.m 2 base polar moment of inertia

Base

mb

Jb

Avionics

ma

Ja

40.1kg

2939 kg.m 2

avionics mass

avionics polar moment of

inertia

C 5860 FF dc bus capacitance

NASA/T_2002-211812 3
(Figure 5). These currents are the inputs to the DC

bus model and consist of: the DC currents provided

by the flywheels (IDol ÷ IDC2), the power supply current

(Ip/s), and the load current (Iiood).

IDCl

Ip/s

Flywheel 2

FIGURE 5- DC BUS MODEL

The power supply is modeled as a voltage

regulating current source. The power supply model

has two inputs, one for a voltage setpoint and one for

a current limit. The power supply will provide

whatever current, Ip/s, is necessary to keep the bus

voltage at the voltage setpoint as long as the current

is less than the current limit. To accomplish this in the

model the error between the voltage setpoint and the

bus voltage is taken. This error is run through a PI

control law to provide a current command. This

current command is compared to the current limit. If

the command is less than the current limit, Ip/s is equal

to the current command. If the current command is

greater than the current limit, Ip/s is equal to the

current limit.

The load is modeled as a resistor. Thus the

current consumed by the load is just the DC bus

voltage divided by the value of the resistor.

Controller Model

The controller model includes: a current regulator

for each flywheel, a DC bus regulator, an attitude

regulator, and an inertia and DC bus coordinator

(Figure3).

The two motors are controlled by field orientation,

with back emf voltage decoupling (Krishnan 1999).

The d-axis rotational reference frame current is

commanded to zero and the q-axis rotational

reference frame current command varies to provide

attitude control and bus regulation. A detailed

description of the innerloop controller, albeit without

voltage decoupling, can be found in Kenny (2001).

There are three modes of DC bus regulation:

charge, charge reduction, and discharge. The charge

mode represents operation in full sun when the

photovoltaics system provides current and voltage

regulation. In the charge mode the DC bus regulator

charges the flywheel system at the charge setpoint

(I*chorge). The charge reduction mode represents

operation in partial sun when the current generated by

the photovoltaics system is not sufficient to meet both

the load demand and the flywheel charge setpoint.

During this mode of operation the flywheel system

regulates the DC bus voltage to V*d_. The discharge

mode represents operation in eclipse when the

photovoltaics system provides less current than

required by the load. In both charge reduction mode

and discharge mode the DC bus regulation algorithm

uses the DC current from each of the two flywheel

inverters to regulate the bus voltage. More detail on

the DC bus regulator and the modes of operation can

be found in Kascak (2001).

The q-axis rotational reference frame current

.*r

commands to the two flywheel motor controllers, _ q,.1

.._ and _ q,.:, provide both attitude control and DC bus

regulation. The first relationship necessary to

determine the appropriate current commands is the

power balance. The AC power in one of the flywheel

motors can be expressed as shown in Novotny et. al

(1996).

Pflywheel = 3 (V_qJ_q_, + V_j_,) (7)

Exploiting the fact that the d-axis current is

regulated to zero and equating the AC and DC power,

the following is obtained where ID<m is the DC current

into one of the flywheel motor inverters.

VDCID<m: (8)

The q-axis voltage equation is (Krishnan, 1999)

r .r .r .r

vq, = lq, R, + Lq, plq, +la,_ _La, +co _X_f (9)

In steady state the derivative term goes to zero. Also

the d-axis current is regulated to zero. Finally the

resistive term is much smaller than the back emf term

especially at high speeds, thus we have (Kascak

2001),

VDCIDc,m _3 (O)r)Vafirqs) (10)

Equation (11) expresses the DC current in terms

of the rotational reference frame q-axis current, Fqs,

with a dependence on a motor constant, Xo_ the rotor

speed, o)_, and the DC bus voltage FDO

IDC m _ --l qs

, 2VDc (11)

The total DC bus current, IDC, is the sum of the

two motor inverter DC currents, IDCZ and IDC:. This

can be expressed as shown in (12) in terms of the

rotational reference frame q-axis current, i%,.,for each

motor.

• r .r

IDC = Ctq_q + diq_, 2 (12)

3CO_lX_fl

C -- --

2VDc (13)

d- 30) r2Xaf2

2VDc (14)

The torque applied to the platform is equal and

opposite to the torque applied to the rotor. The

expression for torque produced by the flywheel PM

motors is given as (Krishnan, 1999) :

-

NASA/T_2002-211812 4
However the rotational reference frame d-axis current

is controlled to be zero. Thus the torque can be

expressed as:

3P

Te .r

2 2 .v.j_q, (16)

The total torque that is applied to the platform is the

negative sum of the two motor torques, Tel and Te:.

This is expressed (from 6) as:

• F .F

Tp = -Tel - Te2 = -alq, l -blq,2 (17)

3P1;_

a=---_-2 .fl (18)

b = 3P2 _ (19)

2 2 d2

By solving equations (12) and (17)

simultaneously, the control variables i_,.1 and i_,.: can

be found which provide the desired DC bus current,

IDc, and the platform torque, Tp. The result is given in

equations (20) and (21).

blDc + dTp • F __

l qsl cb - da (20)

.F

•r Tp +a/qs 1 (21)

lqs2 -- -- b

Thus the required values of irq,_ and irqs2 to provide

the desired amount of DC current and the desired

amount of torque to the platform are found.

RESULTS

System model simulations were run for three

different test cases: DC bus regulation throughout

mode transitions with a constant platform angle,

platform angle and DC bus response to a step change

in commanded angle with a constant electrical load,

and the system response to a step change in

disturbance torque. Commanded variable and

system parameter settings for each of these

simulations are summarized in Table 2.

DC Bus Requlation

This simulation verifies that the controller maintains

DC bus voltage regulation and platform angle

regulation as the system transitions through all three

modes of operation: charge, charge reduction, and

TABLE 2 - SIMULATION PARAMETERS

Test

DC Bus

Regulation

Angle

Regulation

Torque

Disturbance

Rejection

Commanded Values

Bus Attitude

Regulator Regulator

V#c=130 theta*=0

/%_,_e=15.4 Td=O

VDC=130 theta *=

I%_,_=15.4 1.0° step

Td =0

VDc= 130 theta*=0

I%_,_=15.4 Td =0.05

N-m step

Bus Condition

Power Load

Supply

6-0 kW 2 kW

ramp

0 kW 0

kW

0 kW 0

kW

discharge. The mode transitions were achieved by

starting the model in charge mode with the power

supply current limit set to maximum (from t=0 to t=l

sec.), then decreasing the limit linearly to zero (from

t=l to t=3 sec.). This represents the spacecraft

moving out of full sun and into eclipse.

While examining bus performance, it is helpful to

refer to (22), which is derived from Figure 5:

Iio_d = Ip/s IDcl IDc2 (22)

Power modes for this simulation are displayed in

Figure 6. For the first second of the simulation, the

system is in charge mode; the power supply regulates

the bus voltage. The dc bus voltage is held at 135

volts by the power supply. The two flywheel units are

being charged at IDce and I1)c2 respectively where IDce

+ IDC 2 I'charge

At t=l second, the system transitions into charge

reduction mode as the power supply current limit is

reduced. At this point the sum of the load current,

Izooj, and the commanded charge current, I*j,o,ge, is

greater than the amount of current the power supply

can provide and the power supply can no longer

regulate the bus voltage. The flywheel system takes

over bus regulation, as can be seen by the drop in VDc

power supply current

...........................

o I "N. N

bus voltage "%*"_*.

\'\ I_,

"\.

_ [ Iload - _"N i................................... .\

_ I0 i- Idol Idc2 "%*'_*"N...%.

i...................................... _: .............. ":x ........ c

time (see)

FIGURE 6- DC BUS RESPONSE DURING

REGULATION

DO Bus Regulation Simulation Platform Angle Response

001

tim ec)

FIGURE 7- PLATFORM ANGLE DURING DC

BUS REGULATION

NASA/T_2002-211812 5
to the flywheel system voltage regulation set point

value. This setpoint, _Dc, is 130 volts but due to the

large capacitor in the model it takes approximately 0.1

seconds for the system to reach its final value.

The system transitions from charge reduction to

discharge mode when the power supply current can

no longer meet the load current requirements and IDcl

and IDc2 swing negative. At this point, the flywheels

are discharging; current from the flywheels is required

to meet the needs of the load. In this mode, the

flywheel system is still maintaining DC bus regulation.

In this simulation, this transition occurs at about two

seconds. In the modes when the flywheel regulates

the DC bus the voltage is held within 0.1 volts of the

setpoint.

Figure 7 displays the platform angle change

during the mode transitions. There is no change in

the commanded or actual platform angle during the

mode transitions.

An,qle Re,qulation

The angle regulation simulation examines

platform angle and bus voltage regulation as the

system responds to a step change in commanded

platform angle. This represents a commanded

spacecraft direction change. For this simulation, the

i  ̧

'°i i_/ i "

i [ v i

k 1

I ] 1 2 3 4 5 6 7 8 9 10 .1

time (sec)

FIGURE 8- PLATFORM RESPONSE DURING

ANGLE REGULATION

Angle Regulation Simulation DC Bus Response

130 6

130

1298

Bus Voltage

......................................................... i/

1 2 3 4 5 6 7 8 9 10

time (sec)

FIGURE 9- DC BUS DURING ANGLE

REGULATION

system is in discharge mode, with a minimal electrical

load. Simulation parameters are summarized in row 2

of Table 2.

The attitude regulator (see Fig. 3) is a simple

PID, with gains set heuristically to limit the flywheel

motor currents to 30 A. In this simulation, a one

degree step change is made in theta*, which is the

angle commanded into the attitude regulator. The

results are summarized in Figure 8. Note that the

angle settles to the set point and the torque settles

back to zero within a few seconds; this represents

satisfactory response to a step change in commanded

angle.

The bus regulation during this step change in

angle is displayed in Figure 9. Since the system is in

discharge mode, all of the current for the load is

provided by the flywheel system. In deriving equation

(11), it is assumed that the q-axis rotor reference

frame current, irqs, is in steady state; however, with a

step change in angle, the q-axis current jumps

abruptly, causing some error in the DC current. There

is a brief spike in the IDc current, and a resultant dip in

bus voltage. Note that the system responds very

quickly to the error; the bus voltage is regulated to

within 0.5 volt of the commanded value, which is less

than 0.5% of the nominal bus voltage setpoint.

x 104 Angle Regulation Simulation Flywheel Rotor Speeds

4O2

401

4005

E

\

HSS Speed

\

\

\\\

.... \ _ .............. "-_=:27Z? 77-------27 77 7ZZZZZ ........,......m.

1 2 3 4 5 6 7 8 9 10 11

time (sec)

FIGURE 10- FLYWHEEL SPEEDS DURING

ANGLE REGULATION

x !, Angle Regulation Simulation Platform Velocity Torque Response

_i \, i

ii _ platfon r Ang ula r Velocity i

!! \ _ o

i i '\ i :

"'"J'_ platfonr Torque

1 2 3 4 5 6 7 8 9 10

time (sec)

FIGURE 11- PLATFORM SPEED DURING

ANGLE REGULATION

NASA/T_2002-211812 6
A physical understanding of the dynamics of the

platform motion can be achieved by examining the

flywheel speeds and the platform torque and angular

velocity during the step change. A plot of the speeds

of the two flywheels during the step in commanded

angle is shown in Figure 10. In this plot, the HSS

flywheel speed is plotted as the negative of its actual

speed, so the two speeds can be observed on the

same plot. The same torque command results in a

greater speed change in the HSS as compared to D1

due to the differences in the flywheels' inertia. From

about 0.5 to 1.3 seconds, the HSS flywheel

accelerates in the negative speed direction and the

D1 flywheel decelerates, generating a positive

platform torque and a positive angular velocity of the

platform. After 1.3 seconds, the flywheel

accelerations change direction, exerting a net

negative torque on the platform, slowing it down as it

reaches the position setpoint.

Figure 11 shows the corresponding platform

angular velocity and the total torque, Tp.

Torque Disturbance Rejection

The final simulation demonstrates the

disturbance rejection capability of the controller. A

step change in torque is applied to the platform

dynamics (the "Tj' input to the "IDOF Platform Plant

Model" of Fig. 3) and the capability of the controller to

maintain the platform angle at the setpoint is studied.

The system is in discharge mode, with a minimal

electrical load. Simulation parameters are

summarized in row 3 of Table 2. This represents a

physical disturbance to the spacecraft.

The applied torque disturbance is 0.05 N*m

which is about 10% of the maximum torque capability

of either flywheel. Figure 12 shows the application of

the torque disturbance at 0.5 seconds. The sum of

the torque on the platform thus jumps from zero to

0.05 N*m at 0.5 seconds. This causes the platform

to begin to rotate away from its setpoint of 0 degrees.

The resulting position error is acted upon by the PID

in the attitude regulator block (figure 3) and creates

*r *r the appropriate current commands, I qsl and I qs2,to

the flywheels as shown in Fig. 13. This results in a

net torque applied to the platform to counteract the

disturbance torque and reduce the position error as

shown in Fig. 12.

Figure 14 shows the speed of each of the

flywheels as the disturbance torque is rejected and

the platform position is returned to its original position.

CONCLUSIONS

This paper presents the simulation results of a

combined flywheel energy storage system and a

single axis attitude control system. The simulation

demonstrates that it is possible to use two flywheels

to simultaneously provide energy storage for the

electrical system while regulating the spacecraft

platform attitude in a single axis. A new control

algorithm was developed which uses the platform

angle requirement and the electrical system power

requirement to determine the appropriate current

005"

_' \,Table Angle

/J",,

_," "_ Disturbance Torque \

. x

iV \

,............ !i .........................."__:2::::_::: ................................

' \_'_ Sum of the Table Torques

00, J i i i i i i i i 02

10 15 20 25 30 35 40 45

Time (Seconds)

FIGURE 12- PLATFORM DURING TORQUE

DISTURBANCE REJECTION

Bus Reaction to Step in Disturbance Torque ( 05 N'm)

_.__ Q axis rotor reference_ fram_2rf2rt D1 ...............

Vdc (Bus Voltage) _,, i_

ss

:,[ -_ .......... 9--a-sju-2t-2Lr2f-gr-£rs&f-r-a-!r&-c2r-r£r-t--m-_£ ...................... 1,4

It

1 i i i i i i i i

10 15 20 25 30 35 40 45 _

Time (Seconds)

FIGURE 13- DC BUS DURING TORQUE

DISTURBANCE REJECTION

x 104 Torque Disturbance Speed Response

4 0:

3S

3 9(

£

3 9_

3S

............................................... D1 Speed

"x.x.

",..\

\\ \.

\.

\\

\

\

\\ HSS Speed

\

5 10 15 20 25 30 35 40 45

Time (Seconds)

FIGURE 14- FLYWHEEL SPEEDS DURING

TORQUE DISTURBANCE REJECTION

commands to the two flywheel motor controllers. A

complete system model was developed to test the

new controller in simulation. The model includes both

the electrical and mechanical components: the

flywheel motor/generator units and their control, the

DC bus and the electrical load, the platform inertial

model and the new control algorithm. Simulation

results show that the new controller can successfully

maintain commanded platform angle through all mode

NASA/T_2002-211812 7
transitions, and can regulate the DC bus voltage

under charge reduction and discharge conditions

while maintaining the correct platform angle. In

addition, a step change in platform angle can be

achieved with minimal impact (less than 0.5%) on the

DC bus voltage. The system also can reject step

torque disturbances.

Future work includes demonstrating this control

algorithm experimentally using two flywheel units, an

air table and an electrical load. Additionally, more

work will be done to optimize the controller to achieve

the best possible overall system response.

This work is a first step toward an overall

program which will ultimately reduce the cost and

mass of future space vehicles with the combination of

the energy storage and the attitude control systems.

REFERENCES

Kascak, P. E. et al., 2001, "International Space

Station Bus Regulation With NASA Glenn Research

Center Flywheel Energy Storage System

Development Unit," NASA/TM-2001-211138, NASA

Glenn Research Center, Cleveland, OH.

Kenny, B. H. et al., 2001, "Advanced Motor

Control Test Facility for NASA GRC Flywheel Energy

Storage System Technology Development Unit,"

NASA/TM-2001-210986, NASA Glenn Research

Center, Cleveland, OH.

Krishnan, R., Permanent Magnet Synchronous

and Brushless DC Motor Drives: Theory, Operation,

Performance, Modeling, Simulation, Analysis and

Design, Virginia Tech., Blacksburg, Virginia, 1999.

McLallin, K. L. et al., 2001, "Aerospace Flywheel

Technology Development for IPACS Applications,"

NASA/TM-2001-211093, NASA Glenn Research

Center, Cleveland, OH.

Meriam, Kraige, Engineering Mechanics

Dynamics 2nd Edition, University of California Santa

Barbara, California, 1986.

Novotny, D. W. and T. A. Lipo, Vector Control

and Dynamics of AC Drives, Oxford Science

Publications, Oxford, 1996.

Trase, L., "The Evaluation and Implementation of

a Water Containment System to Support Aerospace

Flywheel Testing," to be published at 2002 IECEC,

Washington, DC.

NASA/T_2002-211812 8
Form Approved REPORT DOCUMENTATION PAGE

OMB No. 0704-0188

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1. AGENCY USE ONLY (Leave blank) 2. REPORT DATE 3, REPORT TYPE AND DATES COVERED

August 2002 Technical Memorandum

4. TITLE AND SUBTITLE 5. FUNDING NUMBERS

Single Axis Attitude Control and DC Bus Regulation With Two Flywheels

& AUTHOR(S)

Peter E. Kasc_{, Ralph El. Jansen, Barbara Kenny, and Timothy P. Dover

7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(KS)

National Aeronautics and Space Administration

John It. Glenn Resem'ch Center at Lewis Field

Cleveland, Ohio 44135 - 3191

WU-755-1A-09-00

8. PERFORMING ORGANIZATION

REPORT NUMBER

E---13507

9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(KS) 10. SPONSORING/MONITORING

AGENCY REPORT NUMBER

National Aeronautics and Space Administration

Washington, DC 20546- 0001 NASA TM-------2002- 211812

IECEC---2002---20078

11. SUPPLEMENTARY NOTES

Prepared for the 37th Intersociety Energy Conversion Engineering Conference sponsored by the Institute of Electrical

and Electronics Engineers, Electron Devices Society, Washington, DC, June 28-August 2, 2002. Peter E. Kascak and

Ralph El. Jansem University of Toledo, Toledo, Ohio 43606; Barbara Kenny, NASA Glenn Research Center;

and Timothy R Dover, QSS Group, Inc., Cleveland, Ohio 44135. Responsible person, Peter E. Kascak, organization

code 5450, 216-433-8408.

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Unclassified - Unlimited

Subject Categories: 20, 33, 37, and 44 Distribution: Nonstandard

Available electronically at bttp://glt:.-s._rc.nasa._ov

_l-his pnblication is available from the NASA Center for AeroSpace Im'brmadon, 301-621-0390.

12b. DISTRNBUTION CODE

13. ABSTRACT (Maximum 200 words)

A computer simulation of a flywheel energy storage single axis attitude conlrol system is described. The simulation

models hardware which will be experimentally tested in the future. This hardware consists of lwo counter rotating

flywheels mounted lo an airtable. The airlable allows one axis of rotational modon. An inertia DC bus coordinator is set

R)rth that allows the two control problems, bus regulation and utlimde control, lo be separated. Simulation resulls are

presenmd with a previously derived flywheel bus regulator and a simple PID attitude controller.

14. SUBJECT TERMS

Flywheels; Reaction wheels; Counter-rotating wheels; Electric motors;

Electromechanical devices

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OF REPORT

Unclassified

NSN 7540-01-280-5500

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14

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