# Unit Commitment with Ancillary Services in a Day-Ahead Power Market
## 4 Simulation Results
### Unit Commitment in Summer  
A typical summer day solved by DPSO-SQP is shown in Figure 5. The total demands for the electric energy, AGC, RSR, and SR are 55,3734 MWh, 11,041 MWh, 16,605 MWh, and 27,681 MWh, respectively. The daily cost of the unit commitment on this summer day is MNT 1094.307.  
The electric energy and demands on ancillary services on a typical summer day are shown in Tables 3 and 4. The gas-fired units of TPC and IPP provided 51.48% energy. The gas-fired units also provided most ancillary services: AGC (86.78%), RSR (89.02%), SR 46.28%. The electric energy of an oil-fired unit in the summer day is higher than that in the non-summer season by 8655 MWh (i.e., 2.15%) and the proportions of AGC (13.21%), RSR (10.98%), and SR (53.72%) also greatly increased.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multicolumn{2}{c}{**Type of Unit**} & \multicolumn{1}{c}{**Electric Energy**} & \multicolumn{1}{c}{**AGC Demand**} & \multicolumn{1}{c}{**RSR Demand**} & \multicolumn{1}{c}{**SR Demand**} \\  & & **(MWh)** & **(MWh)** & **(MWh)** & **(MWh)** \\ \hline \multirow{3}{*}{TPC} & Coal-fired unit & 182,400 & 0 & 0 & 0 \\  & Gas-fired unit & 204,157 & 5710 & 4943 & 7803 \\  & Oil-fired unit & 3240 & 140 & 0 & 42 \\ \hline \multirow{3}{*}{IPP} & Coal-fired unit & 74,348 & 0 & 0 & 0 \\  & Gas-fired unit & 29,381 & 3995 & 9847 & 16,818 \\ \hline \multicolumn{2}{c}{Total} & 493,526 & 9845 & 14,790 & 24,663 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Assigned quantities of various units on a typical non-summer day.  
Figure 4: Unit commitment in non-summer.  
This paper uses DPSO-SQP to calculate the minimum cost of electric energy in summer and non-summer, which are MNT 918.020 and MNT 900.081, respectively. According to the case study in this paper, costs in non-summer and summer are higher without ancillary services by MNT 17.939 and MNT 36.857, as shown in Table 5. The cost saving of unit commitment with ancillary services in summer is twice as high as that in non-summer. As power system operations are often accompanied by uncertainties--especially nowadays by the impact of renewable energies, where the generation could have a sudden change due to volatile weather conditions--appropriate ancillary service is important to ensure the safe and stable operation of the system, which must be considered in the power market.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \multicolumn{2}{c}{**Type of Unit**} & **Electric Energy** & **AGC Demand** & **RSR Demand** & **SR Demand** \\ \hline \multirow{3}{*}{TPC} & Coal-fired unit & 32.94\% & 0.00\% & 0.00\% & 0.00\% \\  & Gas-fired unit & 41.83\% & 28.50\% & 25.48\% & 23.77\% \\  & Oil-fired unit & 2.15\% & 13.21\% & 10.98\% & 53.72\% \\ \hline \multirow{3}{*}{IPP} & Coal-fired unit & 13.43\% & 0.00\% & 0.00\% & 0.00\% \\  & Gas-fired unit & 9.65\% & 58.28\% & 63.54\% & 22.51\% \\ \hline \multicolumn{2}{c}{Total} & 100.00\% & 100.00\% & 100.00\% & 100.00\% \\ \hline \end{tabular}
\end{table}
Table 4: Proportions of various units on a typical summer day.  
Figure 5: Unit commitment in summer.  
\begin{table}
\begin{tabular}{c c c} \hline \multicolumn{2}{c}{**Non-Summer**} & **Summer** \\ \hline Unit commitment with ancillary service & MNT 918.020 & MNT 1094.307 \\ Unit commitment without ancillary service & MNT 900.081 & MNT 1057.450 \\ Gap & MNT 17.939 & MNT 36.857 \\ \hline \end{tabular}
\end{table}
Table 5: Electric energy and ancillary service cost comparison.