# Supercapacitor-Based Energy Storage in Elevators to Improve Energy Efficiency of Buildings
## 5 Simulation Results
### Reference Cycle  
The reference cycle consists of running an empty elevator from the ground floor to the top floor and vice versa. When the mass of the counterweight is equal to the sum of the mass of the car and 50% of the load, the reference cycle represents the elevator travel with the highest possible regenerative energy production (while the elevator travels from the ground floor to the top floor) and the highest possible energy consumption (while the elevator travels from the top floor to the ground floor). Therefore, high energy savings can be achieved during the reference cycle.  
The speed setpoint and load profile during the reference cycle are shown in Figure 10(a). The elevator first operates in regenerative mode and stores the energy in the SC bank, then it operates in motor mode and the energy is used for motor operation. The initial voltage of the supercapacitor bank was assumed to be 200 V. The reference voltage for the DC bus in EESS was set to 600 V. The results are shown in Figures 11 and 12. The energy consumption was compared with that of the elevator system without EESS.  
The input power of the elevator system, with and without EESS, is shown in Figure 10(b). It can be seen that the EESS reduces the peak power of the grid by about 43 %. Also, the total energy consumption of the elevator system with EESS is 103 kJ, while the total energy consumption without EESS is 215 kJ. With the EESS, an energy saving of about 52 % is achieved during the reference cycle.  
The DC bus voltage is shown in Figure 11(a). In regenerative mode, the DC bus voltage is about 650 V. At about 20 s, a regenerative power peak occurs, which shows up as a voltage peak of 720 V on the DC bus. This is due to the regenerative power being slightly higher than the value of the power that can be stored in the SC bank. In motor mode, the bus voltage drops from DC to about 530 V as the line voltage drops and the power consumed by the elevator is higher than the power supplied by the EESS.  
The power of the SC bank and the power dissipation at the braking resistor are shown in Figure 11(b). It can be observed that the power dissipation at the braking resistor occurs at about 20 s during the voltage peak on the DC bus (Figure 11(a)). When the SC bank accumulates energy, the SC bank power is positive. When the SC bank dissipates energy, the power of the SC bank is negative. In regenerative mode, the power of the SC bank is  
Figure 10: Simulation model of the elevator system with EESS.  
constant until the maximum regenerative power is reached. In motor mode, the power of the SC bank decreases over time.  
The current and voltage of the SC bank are shown in Figure 12c; when the SC bank accumulates energy, the current is positive, and when it dissipates energy, it is negative. In a regenerative mode, the SC bank current decreases while the SC bank voltage increases. The result is the constant power of the SC bank. In an elevator motor mode, the current of the SC bank is constant, while the voltage decreases.  
Figure 11: Simulation results for the reference cycle. (**a**) Elevator speed setpoint and mass of the load. (**b**) Input power.