# Design of a Sustainable and Efficient Transportation Station (SETS) Based on Renewable Sources and Efficient Electric Drives

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## Abstract

**:**

## 1. Introduction

## 2. Previous Work and Contributions

## 3. Integration of Renewable Sources

_{c}), the output of the wind generator is zero. If the wind speed is between the cut-in wind speed (v

_{c}) and the rated wind speed (v

_{r}), v

_{c}< v < v

_{r}, the wind generator is controlled to operate at the maximum power point. This operation is enabled by controlling the machine to track the optimal power line as depicted in Figure 2. The optimal power line of a wind generator depends on the cube of wind speed as seen in [24,25]

_{g}is wind generator output power, η

_{g}is a wind generator power efficiency, η

_{R}is a power conversion efficiency of a rectifier, C

_{p max}is the maximum value of a rotor power coefficient, ρ is the density of air, R is a rotor radius, and v is wind speed. Since the PMSM wind generator requires a rectifier that performs ac–dc power conversion, the power conversion efficiency of the rectifier is also considered in Equation (1). By assuming the blade angle pitch is 0°, the maximum value of the rotor power coefficient, C

_{p max}, can be determined as [25,26]

_{m}is the mechanical rotor speed. For wind speed that is higher than the rated wind speed (v > v

_{r}), the wind generator is controlled so that the output power is limited to the rated power value. Such an operation pattern is used to prevent possible damage in the wind turbine. If a detailed modeling approaches for a wind generator is required, previous studies [25] could be consulted.

_{pv}), which consists of a PV module and a power converter, can be approximated as [28,29,30]

_{m}and I

_{m}are respectively the PV panel output voltage and current at the MPP, T

_{std}and G

_{std}are respectively the PV panel surface temperature and solar irradiance at the standard test condition (i.e., 25 °C and 1000 W/m

^{2}), V

_{std}and I

_{std}are respectively the rated PV panel output voltage and current at the standard test condition which can be found in the manufacturer’s datasheet, K

_{i}and K

_{v}are respectively the PV panel temperature coefficients, and η

_{c}is the conversion efficiency of the power converter. Since a great deal of research has been conducted on detailed modeling of PV modules [31,32], an alternative PV module model could be considered depending on the required fidelity level.

## 4. Design of Efficient Ventilation System

_{d}is the d-axis inductance, L

_{q}is the q-axis inductance, i

_{ds}is the d-axis stator current, and i

_{qs}is the q-axis stator current. From Equation (6), the torque is determined by the difference between the two inductances (L

_{d}− L

_{q}) and the stator current values. While the inductance difference is affected by how the machine is designed, the current values are the variables that should be controlled for the SynRM operation. A typical block diagram for a SynRM controller is shown in Figure 4 [34]. As shown in Figure 4, the speed of the SynRM can be controlled by using a cascaded control configuration.

## 5. Verification Results and Directions of Future Work

_{10}) was measured for both control approaches. The measurement was performed at an actual subway station, Suraksan Station of the Seoul Metropolitan Subway System, from 19:00 to 23:30. The results of Figure 6 show that the particle pollution level is not degraded by adopting the variable speed approach. In fact, the maximum value of the particle pollution decreased by adopting the variable speed approach. While the maximum value of the particle pollution with the constant speed drive approach exceeded 70 ug/m

^{3}, the values of the variable speed approach did not exceed 60 ug/m

^{3}throughout the overall measurement period. The results of both Figure 5 (i.e., power consumption comparison) and Figure 6 (i.e., air quality comparison) show that the variable speed approach can provide satisfactory air quality performance in a more efficient manner.

^{2}). For the wind generator, it was assumed that a 12.8 kW, 12-pole permanent magnet synchronous generator (PMSG) that has a blade radius of 3 m was used. Since the energy storage should be able to discharge and charge power depending on the power balance of the system (i.e., difference between the load power and the source power), the power flow of the battery is expected to be bi-directional as depicted in Figure 7. While it is possible to connect the battery through a power converter, the simulation of this paper was conducted using a configuration without such converter. In this study, it was also assumed that the SETS could receive power from the main grid. This power transfer can ensure that the SETS loads could still be powered if the output of the renewable sources is extremely low.

## 6. Conclusions

## Acknowledgments

## Author Contributions

## Conflicts of Interest

## References

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**Figure 3.**Block diagram of an electric drive system for ventilation systems and their design choices.

**Table 1.**Electric drive configuration candidates [12].

On/Off Control (Fixed Speed) | Variable Speed Control | |
---|---|---|

Induction Machine | Case 1 (IM_Const) | Case 2 (IM_Var) |

Synchronous Reluctance Machine | Case 3 (SynRM_Const) | Case 4 (SynRM_Var) |

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**MDPI and ACS Style**

Kim, M.; Kim, J.; Bae, S.
Design of a Sustainable and Efficient Transportation Station (SETS) Based on Renewable Sources and Efficient Electric Drives. *Symmetry* **2016**, *8*, 146.
https://doi.org/10.3390/sym8120146

**AMA Style**

Kim M, Kim J, Bae S.
Design of a Sustainable and Efficient Transportation Station (SETS) Based on Renewable Sources and Efficient Electric Drives. *Symmetry*. 2016; 8(12):146.
https://doi.org/10.3390/sym8120146

**Chicago/Turabian Style**

Kim, Myungchin, Jeongtae Kim, and Sungwoo Bae.
2016. "Design of a Sustainable and Efficient Transportation Station (SETS) Based on Renewable Sources and Efficient Electric Drives" *Symmetry* 8, no. 12: 146.
https://doi.org/10.3390/sym8120146