A New Energy Management Strategy for IPACS of Spacecrafts

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A New Energy Management Strategy for IPACS of
Spacecrafts

• W. ZHANG1
• Beijing Univ. of Aerospace and Astronautics,
  Beijing, P.R.China, 100083
• and
• J.ZHANG2
• Beijing Institute of Technology, Beijing,
  P.R.China, 100081
• 1 Graduate Student, School of Astronautics,
  Beijing Univ. of Aerospace and Astronautics,
  100083.
• 2 Associate Professor, School of Mechatronics
  Engineering, Beijing Institute of Technology,
  100081
• Email zhangjingrui_at_bit.edu.cn

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IPACS Integrated Power and Attitude Control
System
Energy System for Normal Satellites
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Several disadvantage of chemical batteries
? low energy desity,large mass(except Li-ion
battery) ? limited charge-discharge
cycles(Li-ion battery lt10000 times, other
chemical batteries about 25000-30000 times) ?
little depth of discharge, normally 2040
Lead to the
position of IPACS IPACS can accomplish the energy
storage and the attitude control simultaneously
by using Flywheels / Variable speed control
moment gyros IPACS has advantages in energy
storage than chemical batteries
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The work before ---- without the limitation of
power, In fact the power provided by the solar
arrays is limited, the power of flywheels
motor is also limited.
Energy stored the energy consumed, i.e. it
requires to arrive the energy balance.
Ref.8 proposed a simple energy management
strategy. assumed that the power
provided by solar arrays was constant.
With the temperature rising the power (by the
solar arrays) reduced step-by-step and tended to
a constant.
So it is necessary to further discuss the energy
management
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• A spacecraft equipped with 4 flywheels (3
  orthogonal 1 skew)
• A Lyapunov-typed controller of IPACS is
  designed.
• A control law to accomplish simultaneously the
  attitude control / energy storage.
• A new strategy of energy management is proposed
  with considering limitations
• A simulation example illustrates the validity of
  the designed IPACS.

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Dynamics of Spacecraft

,
,
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The kinematics of the spacecraft
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The Controller Design Approach
Theorem If the following control laws are used
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With
the system is Lyapunov stable, where k1 , k2 ,
k3, e are the constant parameters.
,
Proof Omitted
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Control Law of the Flywheels
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(9)
, so
In fact, S1 is the project matrix of
lies in the null space of matrix
, i.e.
does not produce the torque.
To design an IPACS, the flywheels should provide
the control torque and store the energy
simultaneously
(12)
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One can choose the vector q so that the power
equation is satisfied. Substituting Eq.(9) into
Eq.(12) yields
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Energy Management
In the works before it was assumed that the solar
arrays provided a constant power during the
sunlight period
just enters into the sunlight period----the plane
of the array is cold
the efficiency of power conversion is rising
along with the rising of arrays temperature----
the efficiency is decreasing About 6 minutes
after leaving the eclipse area---- drops until
P0. If the power provided by the solar arrays is
assumed as the constant, it may lose the energy
more than 5
Assuming that the power is presented as follows
during the sunlight period
Ps(t) is the power provided to the flywheels by
the solar arrays t is the running time of the
spacecraft on the obit ? and ? are two
constants.
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The stored power should be restrained since the
angular velocity of the flywheels is limited
(e.g. by the intensity of the material) and the
angular acceleration of the flywheels is
restricted by the input power
one can use the energy management strategy as
follows
Here, Pmax is the allowed maximum input power of
the flywheels Pc(t) is practical resumed power
required by attitude control P(t) is the
practical stored power by the flywheels ?r is a
designed rotating speed which should be close to
?max and leave a certain range
for the attitude control
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Simulation Results
Consider the parameters and the initial condition
of the spacecraft as

• ?0 0.0011 rad/s
• 1.1,
• 0.38,
• P01000 W,
• Pmax2500 W

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the flywheels have the configuration of 3
orthogonal 1 skew, with the parameter ?r
45000 rpm , ?max 50000 rpm, and
The environment torque considered as disturb can
be presented
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The simulation results of IPACS for a spacecraft
during four orbital periods are shown in
Fig.1-Fig.6, which is carried out based on
Eqs.(3)(4)(12)(17)
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Conclusion

• A Lyapunov-typed controller has been designed for
  a spacecraft with 4 flywheels (3 orthogonal 1
  skew)
• This controller keeps in strong nonlinear
  property of the system (not to use the assumption
  of small angles)
• Presented a control law of the flywheels to
  accomplish the attitude control and energy
  storage simultaneously
• Aiming at the limitations existed in the power
  conversion characteristic of solar arrays and the
  input power of motor, Proposed a new energy
  management strategy
• Reduce the size and mass of solar arrays
• Economize the cost of spacecraft

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Thanks