Consider the following open-loop transfer functions, where G(s) = Y(s) / U(s) . Y(s) is the Laplace transform of the output, and U(s) is the Laplace transform of the input control signal: i. \G(s) = \(\frac{(s+3)}{(s+4)^2}\) ii. G(s) = \(\frac{s}{(s+5)(s+7)}\) iii. G(s) = \(\frac{20 s(s+7)}{(s+3)(s+7)(s+9)}\) iv. G(s) = \(\frac{30(s+2)(s+3)}{(s+4)(s+5)(s+6)}\) v. G(s) = \(\frac{s^2+8 s+15}{\left(s^2+4 s+10\right)\left(s^2+3 s+12\right)}\) For each of these transfer functions, do the following: [Section: 12.2] a. Draw the signal-flow graph in phase-variable form. b. Add state-variable feedback to the signal-flow graph. c. For each closed-loop signal-flow graph, write the state equations. d. Write, by inspection, the closed-loop transfer function, T(s), for your closed-loop signal-flow graphs. e. Verify your answers for T(s) by finding the closed loop transfer functions from the state equations and Eq. (3.73).
Read moreTable of Contents
Textbook Solutions for Control Systems Engineering
Question
The use of feedback control to vary the pitch angle in the blades of a variable speed wind turbine allows power generation optimization under variable wind conditions (Liu, 2008). At a specific operating point, it is possible to linearize turbine models. For example, the model of a three-blade turbine with a 15 m radius working in 12 m/s wind-speed and generating 220 V can be expressed as
\(\dot{\mathbf{x}}=\left[\begin{array}{ccccc} -5 & 0 & 0 & 0 & 0 \\ 0 & 0 & 1 & 0 & 0 \\ -10.5229 & -1066.67 & -3.38028 & 23.5107 & 0 \\ 0 & 993.804 & 3.125 & -23.5107 & 0 \\ 0 & 0 & 0 & 10 & -10 \end{array}\right] \mathbf{x}\)
\(+\left[\begin{array}{l} 5 \\ 0 \\ 0 \\ 0 \\ 0 \end{array}\right] u\)
\(y=\left[\begin{array}{lllll} 0 & 0 & 0 & 1.223 x 10^5 & 0 \end{array}\right] x\)
where the state variable vector is given by
\(\mathbf{x}=\left[\begin{array}{lllll} \beta & \xi & \dot{\xi} & \omega_g & \omega_{g m} \end{array}\right]\)
Here, \(\beta\) = pitch angle of the wind turbine blades, \(\xi\) = relative angle of the secondary shaft, \(\omega_g\) = generator speed, and \(\omega_{g m}\) = generator measurement speed. The system input is u, the pitch angle reference, and the output is y, the active power generated.
a. Find a state feedback vector gain such that the system responds with a 10% overshoot and a settling time of 2 seconds for a step input.
b. Use MATLAB to verify the operation of the system under state feedback.
Solution
The first step in solving 12 problem number 40 trying to solve the problem we have to refer to the textbook question: The use of feedback control to vary the pitch angle in the blades of a variable speed wind turbine allows power generation optimization under variable wind conditions (Liu, 2008). At a specific operating point, it is possible to linearize turbine models. For example, the model of a three-blade turbine with a 15 m radius working in 12 m/s wind-speed and generating 220 V can be expressed as\(\dot{\mathbf{x}}=\left[\begin{array}{ccccc} -5 & 0 & 0 & 0 & 0 \\ 0 & 0 & 1 & 0 & 0 \\ -10.5229 & -1066.67 & -3.38028 & 23.5107 & 0 \\ 0 & 993.804 & 3.125 & -23.5107 & 0 \\ 0 & 0 & 0 & 10 & -10 \end{array}\right] \mathbf{x}\)\(+\left[\begin{array}{l} 5 \\ 0 \\ 0 \\ 0 \\ 0 \end{array}\right] u\)\(y=\left[\begin{array}{lllll} 0 & 0 & 0 & 1.223 x 10^5 & 0 \end{array}\right] x\)where the state variable vector is given by\(\mathbf{x}=\left[\begin{array}{lllll} \beta & \xi & \dot{\xi} & \omega_g & \omega_{g m} \end{array}\right]\)Here, \(\beta\) = pitch angle of the wind turbine blades, \(\xi\) = relative angle of the secondary shaft, \(\omega_g\) = generator speed, and \(\omega_{g m}\) = generator measurement speed. The system input is u, the pitch angle reference, and the output is y, the active power generated.a. Find a state feedback vector gain such that the system responds with a 10% overshoot and a settling time of 2 seconds for a step input.b. Use MATLAB to verify the operation of the system under state feedback.
From the textbook chapter DESIGN VIA STATE SPACE you will find a few key concepts needed to solve this.
Visible to paid subscribers only
Step 3 of 7)Visible to paid subscribers only
full solution