The aim of the experiment is to study the frequency response of a power system when subject to load power changes. Isolated and interconnected systems will be examined here.
\n\n\nIn any power system, it is important to maintain the system frequency in order to maintain stability. Frequency is affected by changes in power. Small changes in load power demand can have noticeable changes on the system frequency. In this experiment, the effect of load power changes on the frequency of two systems (Areas A and B) will be examined and simple proportional-integral (PI) control will be introduced.
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System stability can be maintained with help of interconnection between systems. This allows drops or surges in demand to be counteracted by the other system. In implementing this type of set-up, the power flow between systems should also be monitored. In this experiment, an interconnected set-up (Areas A and B with an interconnector between them) will be monitored for frequency changes and inter-area power flow. Again, simple PI control will be implemented along with frequency bias settings.
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An example of a Simulink model of a single-area power system is shown in Figure 1. This model will be used and adapted throughout this experiment. The system parameters are given in Table 1. An interconnector will be introduced. The interconnector’s parameters are given in Table 2.
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\n| \n Parameter \n | \n\n Description \n | \n\n Area A \n | \n\n Area B \n | \n\n Units \n | \n
| \n Tp \n | \n\n Power System Time Constant \n | \n\n {TpA} \n | \n\n {TpB} \n | \n\n s \n | \n
| \n Kp \n | \n\n Power System Gain \n | \n\n {KpA} \n | \n\n {KpB} \n | \n\n Hz/puMW \n | \n
| \n TG \n | \n\n Generators Time Constant \n | \n\n {TgA} \n | \n\n {TgB} \n | \n\n s \n | \n
| \n TT \n | \n\n Turbines Time Constant \n | \n\n {TtA} \n | \n\n {TtB} \n | \n\n s \n | \n
| \n R \n | \n\n Droop \n | \n\n {RA} \n | \n\n {RB} \n | \n\n Hz/puMW \n | \n
| \n M \n | \n\n Step Change in Demand \n | \n\n {MA} \n | \n\n {MB} \n | \n\n pu \n | \n
| \n Ki \n | \n\n Initial Controller Gain \n | \n\n {KiA} \n | \n\n {KiB} \n | \n\n\n | \n
| \n Parameter \n | \n\n Description \n | \n\n Value \n | \n\n Units \n | \n
| \n TAB \n | \n\n Capacity \n | \n\n {Tab} \n | \n\n pu \n | \n
| \n $\\delta_A^0 - \\delta_B^0$ \n | \n\n Initial Voltage Angle Difference \n | \n\n {delta} \n | \n\n rad \n | \n
Using the simple model shown (create one for each area), examine the frequency response of each area. Plot this result. Determine the final variation in frequency in each area. Compare this to calculation using the Final Value Theorem.
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Create an appropriate block for use on the frequency output to observe the time error on the scope. Plot this result. Determine the time error (in ms) due to the step change in demand in the system after 30 seconds. Compare this to calculation using the Final Value Theorem.
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Introduce PI control to Areas A and B separately, by adding appropriate control blocks to the model. Repeat sections 1 and 2 above for this new configuration.
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Using the model, examine the response of the system frequency for various values of integral gain. Determine the value of Ki which will cause instability in the system (this is called the critical gain). Explain the significance of this value.
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Remove the integral controllers from both areas (this can be done easily by setting Ki to zero) and adapt the model to introduce the interconnector. Repeat sections 1 and 2 above for this new configuration.
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Add a scope to the system to investigate the power flow and overall energy transfer between the systems. Plot these results. Calculate both using the Final Value Theorem and compare to the results.
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Add ACE control to the system from section 5 to ensure that both the power flow between the areas and the frequency return to their pre-disturbance values. Select appropriate values of Ki (the integral control gain) and B (the frequency bias parameter) to obtain a reasonable response. Examine the power and frequency responses and plot these results.
\n\nIn your report, include your results and models and comment on the frequency behaviour of each configuration. Comment on the effect of the integral gain on the controlled systems. Confirm the calculations of all final values by application of the Final Value Theorem. Discuss your selection of the parameters Ki and B in the analysis of the interconnected system. Why is power frequency control required in a power system?
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