DC-bus controller for grid-connected DC/AC converters
Systems, methods, and devices for controlling a DC-bus voltage for a power conditioning system. A control system regulates the DC value of the DC-bus voltage. The control system uses an adaptive DC-value estimator/observer to estimate this DC-value. Instead of having to determine the DC-value of a signal with a low frequency ripple without compromising the signal's dynamic response, a suitably precise estimate for that DC-value is used.
1. A control system for use in controlling a converter, the control system comprising:
a voltage controller for controlling a voltage of said converter;
a current controller for controlling a current of said converter;
an observer/estimator for estimating a DC-bus voltage of said converter; wherein
an estimate of said DC-bus voltage is subtracted from a measured DC-bus voltage of said converter;
said current controller produces a value used to control a timing of opening and closing of switches in said converter; and
said observer/estimator is represented by:
Σ
^
v
BUS
:
{
η
^
.
1
=
2
ω
(
η
^
2
+
η
1
+
V
^
DC
)
+
ξ
1
η
~
1
η
^
.
2
=
-
4
ω
η
1
-
2
ω
η
^
2
+
ξ
2
η
~
1
V
^
.
DC
=
2
μ
ω
η
~
1
where,
ξ 1 ε + , + being a positive constant number,
ξ 2 =2ω, ω being a line frequency,
η 1 =v bus , v bus being the DC-bus voltage,
η
2
=
1
2
ω
v
.
bus
-
v
bus
-
V
D
C
{tilde over (η)} 1 =η 1 −{circumflex over (η)} 1 , {tilde over (η)} 1 being an estimation error of the DC-bus voltage,
{tilde over (η)} 2 =η 2 −{circumflex over (η)} 2 , {tilde over (η)} 2 being an estimation error of η 2 ,
{circumflex over (V)} DC is an estimated value of V DC , V DC being a DC component of the DC bus voltage,
{circumflex over (η)} 2 is an estimated value of η 2 ,
{circumflex over (η)} 1 is an estimated value of η 1 , and
με + , + being a positive constant number.
2. A control system according to claim 1 , wherein said DC-bus voltage has a low frequency ripple.
3. A control system according to claim 1 , wherein said converter is a single-phase DC/AC converter.
4. A control system according to claim 1 , wherein said estimator/observer has error dynamics represented as:
Σ
~
v
BUS
:
{
η
~
.
1
=
2
ω
(
η
~
2
+
V
~
DC
)
-
ξ
1
η
~
1
η
~
.
2
=
-
2
ω
η
~
2
-
ξ
2
η
~
1
V
~
.
DC
=
-
2
μ
ω
η
~
1
where {tilde over (V)} DC =V DC −{circumflex over (V)} DC ,{tilde over (V)} DC being an error of an estimation for V DC .
5. A control system according to claim 4 , wherein error signals for said estimator/observer converge to zero.
6. A component for estimating an output voltage of a converter, the component being represented by:
Σ
^
v
BUS
:
{
η
^
.
1
=
2
ω
(
η
^
2
+
η
1
+
V
^
DC
)
+
ξ
1
η
~
1
η
^
.
2
=
-
4
ω
η
1
-
2
ω
η
^
2
+
ξ
2
η
~
1
V
^
.
DC
=
2
μ
ω
η
~
1
where,
ξ 1 ε + , + being a positive constant number,
ξ 2 =2ω, ω being a line frequency,
{tilde over (η)} 1 =η 1 −{circumflex over (η)} 1 , {tilde over (η)} 1 being an estimation error of a DC-bus voltage,
{tilde over (η)} 2 =η 2 −{circumflex over (η)} 2 , {tilde over (η)} 2 being an estimation error of η 2 ,
η 1 =v bus , v bus being the DC-bus voltage,
η
2
=
1
2
ω
v
.
bus
-
v
bus
-
V
D
C
,
{circumflex over (V)} DC is an estimated value of V DC , V DC being a DC component of the DC-bus voltage,
{circumflex over (η)} 2 is an estimated value of η 2 ,
{circumflex over (η)} 1 is an estimated value of η 1 , and
με + , + being a positive constant number.
7. A component according to claim 6 , wherein said converter is a single-phase DC/AC converter.
8. A component according to claim 6 , wherein said component is part of a control system for controlling said converter.