Increasing penetration of renewable energy sources reveals the concept of dc microgrid which has the advantages of low cost and low losses because of the elimination of the AC/DC conversion processes.The most frequently encountered power quality problem in DC microgrid is voltage fluctuations due to the intermittent nature of renewable energy sources. Direct current (DC) electric spring (DCES), which is an emerging power quality device in DC microgrids, is employed in order to mitigate the effect of the related problem. In this paper, z source converter integrated DCES topology (zDCES) is proposed to provide a wide compensation voltage range with lower duty cycle range and a remarkable decrease in the battery nominal voltage in comparison with conventional systems. The proposed system composed of full-bridge converter, z source converter and battery pack. zDCES provides high voltage gain by using z source converter with passive components without any need for additional switches. The shoot through control, which is used to achieve high gain in z source converter, is implemented using existing full-bridge switches. The performance of the proposed system is compared with the traditional DCES system. The performance of the zDCES is validated with a case study with different voltage fluctuation states.
- DC electric spring
- High gain
- Z source converter
- DC microgrid
- Power quality
Fig. 1. Equivalent circuit of zDCES.
EXPECTED SIMULATION RESULTS:
Fig. 2. Duty cycle variations during source voltage fluctuations.
Fig. 3. PCC voltages during source voltage fluctuations.
Fig. 4. Performance waveforms of the proposed zDCES..
In this paper, a z source converter integrated full-bridge converter based DCES topology and control method have been proposed. The main superior aspects of the proposed Zdces topology are reduced battery voltage and lower duty cycle range as well as providing a wider compensation voltage range. Also, a wide range bipolar voltage at the output ports of the zDCES is achieved by z source converter without additional switches rather than relatively high voltage battery packs or HFT conversion rate methods used in traditional DCES topologies. Thus, a low cost solution has been developed to alleviate the voltage fluctuation problem. In order to verify the effectiveness of the proposed zDCES system, a case study that includes different dynamic operational changes has been conducted. Besides, to show the superiority of the zDCES system is compared with conventional DCES. Performance results show that the proposed system can keep the busbar voltage constant with a lower duty cycle range while the other system requires a higher duty cycle range. Hence, a wide voltage range can be provided in the input port of the fullbridge converter by z source converter in contrast to other systems. Besides, the zDCES can keep the voltage fluctuation in a lower range when compared with conventional DCES. As a result, zDCES shows better and more flexible mitigation performance for all operational conditions.
 Y. Yang, S. Tan, S.Y.R. Hui, Mitigating distribution power loss of DC microgrids with DC electric springs, IEEE Trans. Smart Grid 9 (2018) 5897–5906.
 M. Wang, S. Yan, S. Tan, S.Y. Hui, Hybrid-DC electric springs for DC voltage regulation and harmonic cancellation in DC microgrids, IEEE Trans. Power Electron. 33 (2018) 1167–1177.
 K. Mok, M. Wang, S. Tan, S.Y.R. Hui, DC electric springs—A technology for stabilizing DC power distribution systems, IEEE Trans. Power Electron. 32 (2017) 1088–1105
 H. Zhao, M. Hong, W. Lin, K.A. Loparo, Voltage and frequency regulation of microgrid with battery energy storage systems, IEEE Trans. Smart Grid 10 (1) (2019) 414–424.
 D. Kumar, F. Zare, A. Ghosh, DC microgrid technology: system architectures, AC grid interfaces, grounding schemes, power quality, communication networks, applications, and standardizations aspects, IEEE Access 5 (2017) 12230–12256.