A Novel Impedance-Network-Based Electric Spring

Abstract

An electric spring (ES) can well maintain the balance between supply and demand to compensate for the intermittent nature of small-scale renewable energy resources (RES). Despite its popularity, the second generation of ES (ES-2) is deemed to have a few practical problems. The most conspicuous one is the requirement of accurate dead-time control is in the ES circuit to avoid bridge shoot-through problem, which is necessitated by the series-connection of multiple voltage sources and/or converters to realize a wide voltage range. This however could cause output voltage waveform distortions. In this study, inspired by the Z-source network structure, we propose a novel ES topology with a specifically designed impedance network, i.e., an impedance-network-based (i.e., a network of passive devices such as inductors and capacitors) ES (IN-ES), which intrinsically has a wide voltage range and is immune to the bridge shoot-through issue (i.e., switch tubes on the same bridge arm of the inverter are turned ON/OFF at the same time). Detailed theoretical derivation, simulation and experimentation are conducted in this study, which verify the unique advantageous features of the proposed IN-ES, demonstrating a wide voltage operation range, undistorted waveforms and safe operations. INDEX TERMS Impedance-network-based electric spring, novel ES structure, bridge shoot-through, terminal voltage control. NOMENCLATURE V in DC input voltage of ESs L s Inverter filter inductor C s The penalty function V g Voltage of emulated power grid Z line Line impedance of emulated power grid r line Line resistance of emulated power grid x line Inductive reactance of DC emulated power grid V es Compensation voltage of ESs V nc Voltage across non-critical load V R Resistance voltage of non-critical load V L Reactance voltage of non-critical load Z nc Non-critical load Z c Critical load V c Voltage across critical load I Ls Filtered inductor current of inverter I es Current through non-critical load V C1 Voltage across DC side capacitance V p Voltage across the inverter bridge E Cs Capacitor stores energy I i Equivalent current source current

Review of impedance source power converter for electrical applications

“…This section deals with some special type of Z source converters such as trans Z source/ Y source/ Γ-Z-source /T source converters which are used for AC-AC, DC-DC conversions for renewable energy applications. [123]- [135].…”

“…Zhang et al proposed a novel electric spring topology with a specifically designed impedance network, which intrinsically has a wide voltage range and immune to the bridge shoot-through. Detailed theoretical derivation, simulation and experimentation are conducted to verify its advantageous features by demonstrating a wide voltage operation range, undistorted waveforms and safe operations [135].…”