⚡ electrical engineering

An Improved Switched-Inductor-Capacitor Z-Source Inverter with Enhanced Boost Capability and Reduced Voltage Stress

This paper presents an improved switched-inductor-capacitor Z-source inverter (ISLC-ZSI) that achieves enhanced boost capability with reduced voltage stress and continuous input current, validated through theoretical analysis, simulation, and experimental results for low-voltage renewable energy applications.

Original authors: Masoumeh Gholami, Reza Noroozian, Mehran Moslehi Bajestan, Hamed Bizhani

Published 2026-08-31

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CC BY 4.0

Original authors: Masoumeh Gholami, Reza Noroozian, Mehran Moslehi Bajestan, Hamed Bizhani

Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). ✨ This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer

In the world of clean energy, a persistent challenge stands between the humble power of the sun and the robust needs of our homes: the voltage gap. Solar panels and fuel cells generate electricity, but often at a voltage far too low to run standard appliances or feed into the electrical grid. To bridge this gap, engineers traditionally use a two-step process. First, a separate device boosts the low voltage up to a usable level; then, a second device converts that steady direct current into the alternating current that powers our lights and motors. While effective, this two-stage approach is bulky, expensive, and wastes energy in the process of conversion. For decades, researchers have sought a single device that could handle both tasks simultaneously, but early attempts at such "single-stage" converters suffered from their own flaws, including unstable power flow and a tendency to damage their own internal components when pushed to high performance.

A team of engineers from Iran and Poland has now proposed a refined solution to this long-standing puzzle. They have designed a new type of power converter, a device that can take low-voltage electricity from renewable sources and instantly boost it to a high level while converting it to alternating current, all within a single, streamlined unit. Their innovation, detailed in a recent study, focuses on a specific internal structure known as an impedance network. Think of this network as a sophisticated traffic system for electricity, using a mix of coils and storage tanks to manage the flow. The researchers found that by swapping a specific one-way valve in this system with a storage tank, they could create a path that allows the device to achieve much higher voltage boosts without needing to force the system into extreme operating conditions. This modification not only increases the power output but also smooths out the flow of electricity entering the device, a critical feature for delicate renewable sources like solar panels that cannot handle sudden surges or interruptions.

The core of this new design lies in how it handles a momentary internal short circuit, a state the researchers call a "shoot-through" interval. In older designs, achieving a high voltage boost required these short circuits to last a long time, which put immense strain on the electronic switches and capacitors inside, often leading to premature failure. The new configuration, which the team calls an improved switched-inductor-capacitor Z-source inverter, achieves a significantly higher boost factor even when these intervals are very brief. This means the device can operate more efficiently and with less stress on its components. The researchers demonstrated that this setup allows for a continuous, unbroken flow of current from the input source, eliminating the jagged, pulsing flow found in earlier models. This continuity is vital for connecting to sensitive energy sources, ensuring that the power delivered is steady and reliable.

To verify their theory, the team built a physical prototype and ran it through rigorous computer simulations. They set the device to accept an input voltage of 40 volts, a typical level for small-scale renewable systems, and successfully boosted it to approximately 142 volts on the output side. This represents a substantial increase in power capability. During these tests, the device operated with a high degree of stability, maintaining a smooth output waveform with very little distortion. The researchers measured the voltage across the internal components and found that the electrical stress on the capacitors and diodes was lower than in many competing high-performance designs. This reduction in stress suggests that the device could be more durable and require less maintenance over its lifespan. The team also calculated the energy losses within the system, finding that the majority of the power was successfully converted, with only a small fraction lost as heat in the switches, diodes, and other parts.

The study confirms that this new topology offers a compelling balance between performance and complexity. Unlike some previous attempts that achieved high voltage gains by adding a confusing array of extra components, this design uses a similar number of parts to existing models but arranges them in a way that yields superior results. The researchers highlighted that the device maintains a common ground connection between the input and the output, a feature that simplifies installation and improves safety for renewable energy applications. While the work remains in the stage of simulation and laboratory prototyping, the results provide a strong foundation for future development. By solving the issues of voltage stress and input continuity, this improved inverter offers a promising path toward more efficient, compact, and reliable power systems for the next generation of clean energy technologies.

Technical Summary: An Improved Switched-Inductor-Capacitor Z-Source Inverter with Enhanced Boost Capability and Reduced Voltage Stress

Problem Statement
The integration of low-voltage renewable energy sources, such as photovoltaic modules and fuel cells, into AC grids or loads requires efficient DC–AC conversion with significant voltage-boosting capabilities. Conventional voltage-source inverters (VSIs) lack inherent boost functionality, necessitating a two-stage conversion process (DC–DC followed by DC–AC) that increases system cost, volume, and complexity while reducing overall efficiency. Furthermore, VSIs are susceptible to destructive shoot-through faults. While the Z-source inverter (ZSI) introduced by Peng offers a single-stage buck-boost solution by utilizing controlled shoot-through (ST) intervals, the classical ZSI suffers from discontinuous input current, limited voltage gain, and high voltage stress on passive and semiconductor components. Existing high-gain impedance-source topologies often address these issues at the cost of increased component counts, discontinuous input currents, or the loss of a unified ground reference between the input source and the DC-link.

Methodology
This paper proposes an Improved Switched-Inductor-Capacitor Z-Source Inverter (ISLC-ZSI). The topology is derived by modifying the Improved Switched-Inductor Z-source Inverter (SL-IZSI). The core structural innovation involves replacing the central diode within a switched-inductor cell with a capacitor and reconfiguring the impedance network. This modification aims to maintain continuous input current while enhancing the boost factor.

The study employs the following analytical and experimental methods:

Steady-State Analysis: The operating modes are categorized into Shoot-Through (ST) and Non-Shoot-Through (Non-ST) states. Using volt-second balance for inductors and charge-balance for capacitors, the authors derive analytical expressions for the boost factor, voltage gain, and component voltage stresses.
Component Sizing: Design equations are established for inductors and capacitors based on permissible current and voltage ripples, respectively.
Loss Analysis: A comprehensive power loss model is developed, accounting for conduction and switching losses in switches, diode conduction and reverse-recovery losses, and resistive losses in inductors and capacitors (ESR).
Comparative Evaluation: The proposed topology is benchmarked against seven existing impedance-source inverters (including SLZSI, SL-IZSI, EBZSI, and others) regarding component count, boosting performance, voltage gain, input current continuity, and device stress.
Validation: Theoretical findings are validated through MATLAB/Simulink simulations and a laboratory prototype controlled by a TMS320F28377s processor.

Key Contributions
The paper presents the following primary technical contributions:

Enhanced Boosting Capability: The proposed ISLC-ZSI achieves a significantly higher voltage boost factor at a relatively small shoot-through duty ratio ( $D$ ) compared to representative high-gain topologies. This allows for operation over a wider modulation index range.
Continuous Input Current: Unlike the classical ZSI and some high-gain variants, the proposed topology ensures continuous current flow at the input side, making it suitable for sensitive renewable sources like fuel cells and PV modules.
Reduced Electrical Stress: The topology alleviates voltage stress on capacitors, diodes, and active switches compared to several existing high-gain structures, while maintaining a unified ground path between the DC input and the DC-link.
Structural Efficiency: The proposed design achieves these improvements without a significant increase in the total number of passive and active components compared to most existing topologies.

Results

Analytical Performance: The derived boost factor is given by $B = \frac{2(1+D)}{1-4D}$ , and the voltage gain is $G = \frac{M \cdot 2(1+D)}{1-4D}$ , where $M$ is the modulation index. The analysis confirms that a small $D$ yields a high gain.
Simulation and Experimental Validation:
- Conditions: Simulations and experiments were conducted with an input voltage of 40 V, a shoot-through duty ratio ( $D$ ) of 0.1, and a modulation index ( $M$ ) of 0.9.
- Voltage Gain: The system successfully boosted the 40 V input to a DC-link voltage of approximately 142 V (simulation) and 139 V (experimental), resulting in a boost coefficient of roughly 3.72.
- Waveforms: The output AC line-to-line voltage reached approximately 110 V. The Total Harmonic Distortion (THD) of the output voltage was measured at 1.33% in simulation.
- Stress Verification: Measured capacitor voltages ( $V_{C1} \approx 76$ V, $V_{C2} \approx 21$ V, $V_{C} \approx 58$ V) and diode voltages aligned closely with theoretical calculations, with a deviation of approximately 10% attributed to non-ideal component characteristics.
Efficiency: The power loss analysis indicated that diode losses constituted the majority of losses (62.3%), followed by inductor losses (23%). The system demonstrated an efficiency of approximately 94% at an output power of 250 W with a duty ratio of 0.15.

Significance
The paper concludes that the ISLC-ZSI is a viable and effective solution for single-stage DC–AC conversion in low-voltage renewable energy systems. By combining high boosting capability, continuous input current, and reduced component stress within a unified ground-reference framework, the topology addresses critical limitations of both classical VSIs and existing impedance-source inverters. The authors assert that the proposed inverter is particularly well-suited for photovoltaic and fuel-cell applications where high voltage gain, reliability, and efficient integration are paramount. The experimental results confirm the practical feasibility of the theoretical model, validating the topology as a competitive alternative for clean-energy interfaces.

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