Turbine expansion ratio estimation for model-based boost control
A method for controlling a turbine of an engine system to achieve a desired boost pressure is provided. The method determines a desired exhaust gas pressure based on the desired boost pressure by using a model for a power balance between the turbine and a compressor of the engine system. The method generates a base command for controlling a position of a vane of the turbine based on a ratio of the desired exhaust gas pressure to a measured turbine outlet pressure.
1. A method for controlling a turbine of an engine system to achieve a commanded boost pressure, the method comprising:
determining, in a control module, an exhaust gas pressure based on the commanded boost pressure by using a model for a power balance between the turbine and a compressor of the engine system using an equation
p
ex
,
dsr
=
p
to
f
(
m
.
ex
T
ex
p
to
,
P
c
,
dsr
h
t
)
,
wherein where p ex,dsr is exhaust gas pressure; p to is a measured turbine outlet pressure, {dot over (m)} ex is an estimated exhaust gas flow rate, T ex is an estimated temperature of the exhaust gas, p to is a measured turbine outlet pressure, P c,dsr is a power to be generated by the compressor, and h t is an exhaust gas enthalpy flow;
generating, at the control module, a base command for controlling a position of a vane of the turbine to a threshold ratio of the exhaust gas pressure to a measured turbine outlet pressure;
sending a vane position command from the control module to the turbine of the engine system; and
adjusting the vane position of the turbine.
2. The method of claim 1 , further comprising:
generating a compensation command based on a difference between the commanded boost pressure and a measured boost pressure;
generating a final command based on the base command and the compensation command; and
sending the final command to the turbine to control the turbine.
3. The method of claim 1 , wherein the turbine is a variable geometry turbine (VGT).
4. The method of claim 1 , wherein the generating the base command comprises using a function
f
(
p
ex
p
to
,
m
.
ex
p
ex
RT
ex
·
f
1
(
p
ex
p
to
)
)
,
wherein p ex is an estimated exhaust gas pressure, p to is a measured turbine outlet pressure, p ex /p to is a turbine expansion ratio, {dot over (m)} ex is an exhaust gas flow rate, T ex is an estimated exhaust gas temperature, and R is ideal gas constant.
5. The method of claim 1 , further comprising mapping the ratio of the exhaust gas pressure to the measured turbine outlet pressure to a look up table for estimated turbine expansion ratio values indexed by different velocity values of an engine of the engine system and different desired compressor pressure ratio values.
6. The method of claim 1 , further comprising mapping the ratio of the exhaust gas pressure to the measured turbine outlet pressure to a look up table for estimated turbine expansion ratio values indexed by different velocity values of an engine of the engine system and different fuel consumption rate values of the engine.
7. An engine system comprising:
an engine;
a turbine driven by exhaust gas from the engine;
a compressor driven by the turbine; and
a control module for controlling the turbine to achieve a commanded boost pressure, the control module comprising a processor coupled to a memory, the control module configured to:
determine an exhaust gas pressure based on the commanded boost pressure by using a model for a power balance between the turbine and a compressor of the engine system using an equation
p
ex
,
dsr
=
p
to
f
(
m
.
ex
T
ex
p
to
,
P
c
,
dsr
h
t
)
,
wherein where p ex,dsr is exhaust gas pressure; p to is a measured turbine outlet pressure, {dot over (m)} ex is an estimated exhaust gas flow rate, T ex is an estimated temperature of the exhaust gas, p to is a measured turbine outlet pressure, P c,dsr is a power to be generated by the compressor, and h t is an exhaust gas enthalpy flow;
generate a base command for controlling a position of a vane of the turbine to a threshold ratio of the exhaust gas pressure to a measured turbine outlet pressure.
8. The engine system of claim 7 , wherein the control module is further configured to:
generate a compensation command based on a difference between the commanded boost pressure and a measured boost pressure;
generate a final command based on the base command and the compensation command; and
send the final command to the turbine to control the turbine.
9. The engine system of claim 7 , wherein the turbine is a variable geometry turbine (VGT).
10. The engine system of claim 7 , wherein the control module is configured to generate the base command by using a function
f
(
p
ex
p
to
,
m
.
ex
p
ex
RT
ex
·
f
1
(
p
ex
p
to
)
)
,
wherein p ex is an estimated exhaust gas pressure, p to is a measured turbine outlet pressure, p ex /p to is a turbine expansion ratio, {dot over (m)} ex is an exhaust gas flow rate, T ex is an estimated exhaust gas temperature, and R is ideal gas constant.
11. The engine system of claim 7 , wherein the control module is further configured to map the ratio of the exhaust gas pressure to the measured turbine outlet pressure to a look up table for estimated turbine expansion ratio values indexed by different velocity values of an engine of the engine system and different desired compressor pressure ratio values.
12. The engine system of claim 7 , wherein the control module is further configured to map the ratio of the exhaust gas pressure to the measured turbine outlet pressure to a look up table for estimated turbine expansion ratio values indexed by different velocity values of an engine of the engine system and different fuel consumption rate values of the engine.
13. A control system for controlling a turbine of an engine system to achieve a commanded boost pressure, the control system comprising:
a first module configured to determine a exhaust gas pressure based on the commanded boost pressure by using a model for a power balance between the turbine and a compressor of the engine system using an equation
p
ex
,
dsr
=
p
to
f
(
m
.
ex
T
ex
p
to
,
P
c
,
dsr
h
t
)
,
wherein where p ex,dsr is exhaust gas pressure; p to is a measured turbine outlet pressure, {dot over (m)} ex is an estimated exhaust gas flow rate, T ex is an estimated temperature of the exhaust gas, p to is a measured turbine outlet pressure, P c,dsr is a power to be generated by the compressor, and h t is an exhaust gas enthalpy flow; and
a second module configured to generate a base command for controlling a position of a vane of the turbine to a threshold ratio of the exhaust gas pressure to a measured turbine outlet pressure.
14. The control system of claim 13 , further comprising a third module configured to:
generate a compensation command based on a difference between the commanded boost pressure and a measured boost pressure;
generate a final command based on the base command and the compensation command; and
send the final command to the turbine to control the turbine.
15. The control system of claim 13 , wherein the turbine is a variable geometry turbine (VGT).
16. The control system of claim 13 , wherein the second module is configured to generate the base command by using a function
f
(
p
ex
p
to
,
m
.
ex
p
ex
RT
ex
·
f
1
(
p
ex
p
to
)
)
,
wherein p ex is an estimated exhaust gas pressure, p to is a measured turbine outlet pressure, p ex /p to is a turbine expansion ratio, {dot over (m)} ex is an exhaust gas flow rate, T ex is an estimated exhaust gas temperature, and R is ideal gas constant.
17. The control system of claim 13 , wherein the second module is configured to generate the ratio of the exhaust gas pressure to the measured turbine outlet pressure by using a look up table for estimated turbine expansion ratio values indexed by different velocity values of an engine of the engine system and different desired compressor pressure ratio values.