210MAE Instrumentation and Control
Assignment Brief
Module Title:
Instrumentation and Control
Coursework type:
Descriptive, analytical Modelling and Simulation
Percentage of Module Mark:
25%
Submission arrangement online via CUMoodle: Yes
File types and method of recording: Microsoft Word
Mark and Feedback date: (15/04/2020)
Mark and Feedback method: written via Gradebook
Module Learning Outcomes Assessed: 1. Develop and apply knowledge and understanding of scientific principles and methodology necessary to underpin their education in mechanical and related engineering disciplines, to enable appreciation of its scientific and engineering context and to support their understanding of future developments and technologies [IMechE_US1]. 2. Demonstrate an understanding of and ability to apply a systems approach to engineering problems [IMechE_E4]. 3. Apply knowledge of characteristics of particular equipment and processes [IMechE_P1]. 4. Appraise technical literature and other information sources [IMechE_P4]. 5. Demonstrate engineering workshop and laboratory skills [IMechE_P2].
Institution of Mechanical Engineers [IMechE]
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1.0 INTRODUCTION – COURSEWORK MOTIVATION
The current state of the British railway infrastructure is such that it is not capable of supporting the increasing demand presented [1]. To address operational demand on the railway in the UK, in 2012, the Rail Technical Strategy (RTS) was produced [2]. RTS 2012 considers the potential future challenges of the railway over a 30 year period and presents long term strategies for the railway industry and government. The RTS 2012 is based on the following 4Cs as a guiding principles, these are defined as:
i. Increased capacity
ii. Improved customer experience
iii. Reduced carbon
iv. Reduced capital and operational cost
To further address the RTS, in 2017 a capability delivery plan (CDP) was developed [3]. In the CDP, 12 ‘key capabilities’ are identified in which the railway industry view as development areas in order to meet the industry objectives of increasing capacity and improving customer services in a sustained and affordable manner. With the primary aim to increase capacity on the railway, one of the ‘key capabilities’ involves the use of moving block technology to run autonomous trains (ATs) closer together.
Currently the railway uses fixed block signalling, see Figure 1-1. This involves the railway network being effectively divided into blocks, with movement of trains into these blocks controlled by signals. The details of the blocks (i.e. length) are determined based on a number of factors, e.g. braking distance of trains and the last known location of the train ahead. A given train cannot occupy a block that is already occupied (red lights will be shown), see Figure 1-1. Whilst such a system maintains safety levels, fixed block signalling can cause large delays in operation for a given railway network. Consequently, journey times are increased and this reduces the overall capacity of the network. In summary, fixed block signalling is a mode whereby all trains within a given network are stationary unless otherwise authorised to move. Moving block technology involves the scrapping of the fixed block signalling. Instead, the operation of trains require accurate train positioning, fast reliable fail-safe switches, predictive braking and vehicle-to-vehicle (V2V) communication. The integration of such technology effectively means ATs will be in operation, where the trains maintain a constant separation distance, which is moving. In contrast to fixed block technology, in moving block technology the trains are moving unless otherwise instructed to stop. The technology needed for ATs has been demonstrated effectively in the automotive sector through the development of autonomous vehicles (AVs), with trials successfully taking place in Coventry and Worldwide [4] and [5]. In recent months, Russian ATs have been in operation [6].
The task presented to you in this coursework assignment is to investigate the following:
Question 1: the current timetabled operation of trains using fixed block
Question 2: the operation of closer running of ATs using moving block
Figure 1-1: Fixed Block Signalling (Left) and Moving Block Technology (Right)
Train 1
Train 1
Train 2
Train 2
Moving block Moving block Moving blockMoving block
D
Direction of Travelirection of Travel
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2.0 MODELLING AND ANALYSIS OF THE CURRENT RAILWAY NETWORK (50 MARKS)
Question 1 – Modelling of One Train (Open-Loop System)
As introduced in the previous Section, the current railway network uses fixed block signalling. Question 1 of the coursework involves the open-loop modelling and analysis of trains on the railway network, see Figure 2-1. The actuator is effectively the power unit of the train (this could be electric or diesel/electric), the open-loop controller effectively modulates the actuator from either fully on to fully off (or 100% to 0% in engineering units) and the process is the motion of the train. When fully on, the system effectively applies a tractive force to ‘move’ the train forward, hence the output is longitudinal displacement. The question involves the use of hand calculations and the software package MATLAB & Simulink.
Figure 2-1: General Form of an Open-Loop Control System
Undertake the following tasks:
i. Produce a list of assumptions required for the modelling of one train, e.g. assume an ideal actuator. (4 marks)
ii. The train dynamic motion model (i.e. process) comprises of a second order differential equation (ODE). This is given by:
𝑚𝑡𝑟𝑑2𝑥𝑑𝑡2=𝐹𝑡𝑟−𝑅𝑑𝑥𝑑𝑡
where 𝑚𝑡𝑟 denotes the effective mass of the train (base train mass + passengers), 𝑑2𝑥𝑑𝑡2 denotes the acceleration of the train (+ve for accelerating and –ve for decelerating or braking), 𝐹𝑡𝑟 denotes the traction force (+ve for accelerating and –ve for decelerating or braking) and 𝑅 denotes the train resistance (considering aerodynamic drag, length of train and the mechanical resistance between the train and the tracks).
Convert the above ODE into transfer function form. (4 marks)
𝑮𝒑
(Process)
(Process)
𝑪
(Controller)
(Controller)
𝑼
(
(InputInput))
𝒀 (Output)(Output)
±
𝑼∗ (Control (Control input)input)
𝑮𝒂 (Actuator)(Actuator)
𝑮 (System)(System)
𝑫 (Disturbance)(Disturbance)
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iii. Determine the phase variable canonical form of the train process. (4 marks)
iv. Your task is to set-up the input to the process using MATLAB & Simulink. The input to the process is to modelled using a series of step inputs, applied for varying periods of time. The input should be set-up such that a value of 8 implies maximum acceleration of the train and a value of 0 implies deceleration. The timetable of the train is given in Table 2-1, where the middle column gives journey time details, e.g. time to travel from station a to b is 7 minutes. The third column details the train dwell time (time a train stands at a platform for the passengers to board or alight), e.g. 2 minutes at all stations. Hint: the signal builder should be used for this question.
Table 2-1: Train Timetable of One Train Station Journey time [minutes] Train dwell time [minutes]
a
—
2
b
7
2
c
7
2
(8 marks)
v. Using MATLAB & Simulink, your task is to initially simulate the motion of one train using the properties given in Table 2-2. The following graphical outputs should be produced:
▪ Time versus displacement, known as a train graph
▪ Time versus velocity
▪ Time versus acceleration
The model developed in this Section is known as your ‘baseline model’, hence it represents a simplified representation of the present day operation.
Table 2-2: Train Properties Variable Value
Acceleration [𝑚/𝑠2]
0.37
Deceleration – Regular [𝑚/𝑠2]
0.88
Deceleration – Emergency [𝑚/𝑠2]
1.18
Mass of Train [𝑘𝑔]
466000
Applied force [𝑁]
172420
Resistance [Ns/m]
23000
Max Velocity [𝑚𝑝ℎ]
111.85
Max Velocity [𝑚/𝑠]
50.00
(10 marks)
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vi. Using MATLAB & Simulink, investigate the following disturbances acting on the baseline model developed in part v.) ▪ Changes in the train performance, e.g. due to mechanical resistance between the train and the tracks due to the time of year, i.e. winter versus summer
▪ A gradient change For both of these disturbances, investigate a maximum of four variations away from the baseline train model (hence, in total the baseline and four results should be recorded). You should comment on how the above factors affect the open-loop system performance of the train on the railway network.
(10 marks)
vii. Two trains are now to be modelled on the railway network. Using MATLAB & Simulink you are now asked to investigate the following: ▪ Based on the train timetable in Table 2-1, simulate Train 2 leaving the station 3 minutes after Train 1 and following the same route ▪ Apply one of the disturbances from part vi.) to the two train simulation ▪ Create a new timetable that compensates for the effects of the disturbance Provide evidence to demonstrate that your new timetable works effectively.
(10 marks)
Page 6 of 10
3.0 CLOSER RUNNING OF AUTONOMOUS TRAINS (50 MARKS)
Question 2 – Determining the Benefits of Closer Running (Feedback Control System)
As introduced in Section 1.0, future railway operation is likely to use moving block technology. Moving block technology will involve a train maintaining a set separation distance to a train ahead, see Figure 3-1. In this Question, Train 1 will operate using a feedback control system to maintain a desired velocity (based on train line speeds). A feedback control system will be developed for Train 2, where the separation distance (or headway) denoted 𝑑, between the two trains is to be investigated, i.e. to determine what separation distance is ‘safe’. You should assume that a sensor used in the feedback control system allows Train 2 to perfectly determine the headway to Train 1, hence to accurately determine the measured distance between the two trains. Use the timetable from Question 1 for Train 1 and the results from this study should then be interpreted to determine the benefits of closer running, i.e. quantify the dis-benefits of the current railway operation compared to that potentially offered by closer running of autonomous trains (ATs). This question will involve the use of hand calculations and the software package MATLAB & Simulink.
Figure 3-1: Moving Block Technology with focus on the Separation Distance
Undertake the following tasks:
i. Using MATLAB & Simulink, develop a feedback control system for Train 1 to follow a desired speed profile, given in Table 3-1. For this Question, the controller should consist of some form of PID configuration. In addition, implement disturbances into your model which may arise in practice, e.g. train resistance and gradient. You are expected to explain your approach to configuring and tuning the controller (simply presenting graphical outputs with no explanation will result in minimum marks).
Note that for the whole of this Question: the applied force is automatically derived from the controller output (i.e. there is no need to include the normalised force gain block as in the open-loop case). Table 3-1: Speed Limit Profile for Train 1
Velocity [m/s] Start time [s] End time [s]
40
0
250
35
250
420
(15 marks)
Train 1
Train 1
Train 2
Train 2
Moving block
Moving block Moving blockMoving block
Direction of Travel
Direction of Travel
Separation distance
Separation distance 𝑑
Page 7 of 10
ii. Using MATLAB & Simulink, develop a feedback control system for Train 2 to follow a desired separation distance to Train 1, where the speed profile of Train 1 is given in Table 3-2. Use your controller from Part i. to control the velocity of Train 1. Configure the controller for Train 2 to achieve a ‘safe’ separation distance. As in Part i., implement disturbances which may arise in practice. In addition, explore the effect of an emergency braking scenario of Train 1. Provide graphical outputs from your experimental simulations to suggest what you consider to be a sensible separation distance between Train 1 and Train 2. You are expected to explain your approach to configuring and tuning the controller (simply presenting graphical outputs with no explanation will result in minimum marks).
Hint: use the configuration given in Figure 3-2 to form the error signal. In your report, you should explain the logic behind this configuration.
Figure 3-2: Forming the Error Signal Based on Train 1 and Train 2 Displacement and Desired Separation Distance
Table 3-2: Speed Limit Profile for Train 1
Velocity [m/s] Start time [s] End time [s]
40
0
1200
(20 marks)
iii. Based on your findings in the coursework, quantity the benefits of implementing closer running of ATs compared to today’s railway system operation. You may wish to refer to the 4Cs of capacity introduced in Section 1.0, hence attempt to ascertain the benefits in terms of capacity closer running of ATs provides. For this part of the Question, you may use the timetable from Question 1.
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