Module 1
State Feedback Current Control:
Continuous-Time Design
Marko Hinkkanen
Politecnico di Torino, February 2017
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Introduction
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Model-based controllers are preferred, since they can be automatically tuned
based on the known (identified) model parameters
▶
Various control methods exist: state feedback control is considered here
▶
Control systems are implemented digitally, but they are often designed in the
continuous-time domain
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Simple Example System
▶
Generic LR load with the disturbance voltage is first considered for simplicity
▶
It could represent, for example, one axis of a 3-phase motor in the dq frame
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Simple system is chosen in order to be able to focus on the control challenges
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Later, magnetic saturation of L as well as LCL filters will be considered
▶
Controllers and their tuning principles can be extended to 3-phase AC motor
drives and grid converters in a straightforward manner
▶
Observers can be designed and tuned using the same principles
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Current Control System
Closed-loop current control enables:
1. Current limitation
2. Precise and fast current control
Example system: LR circuit and the
disturbace voltage
u = Ri + L
di
dt
+ e
Current
controller
PWM
u
ref
i
ref
U
dc
q
A
, q
B
L
e
u
R
i
i
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Nonidealities due to Digital Implementation and Actuator
Saturation
u
ref
(k)
i
ref
(k)
i(k)
Current
controller
Plant model seen by the controller
Synchronized Voltage saturation
due to the finite U
dc
computational delay
i(t)
e(t)
1
sL + R
z
−1
u(t)
PWM modeled
as a zero-order hold
ZOH
sampling
Unavoidable
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