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An Optimized H5 Hysteresis Current Control with Clamped Diodes in Transformer-less Grid-PV Inverter

Sushil Phuyal, Shashwot Shrestha, Swodesh Sharma, Rachana Subedi, Anil Kumar Panjiyar, Mukesh Gautam

TL;DR

The paper tackles leakage currents in transformer-less grid-PV inverters caused by non-constant common-mode voltage (CMV). It introduces the HCH5-D2 topology, adding a PV-side switch and two clamping diodes to DC-decouple the DC and AC paths, stabilizing CMV at $V_{DC}/2$ and damping CMV spikes. A dual-loop control structure combines outer DC-link voltage control with Perturb and Observe MPPT and inner hysteresis current control via Inverse Park transformation, achieving a constant DC-link ($V_{DC}=400$ V) and in-phase grid injection with a unipolar differential-mode voltage. Simulation results in MATLAB/Simulink show dramatically reduced leakage current (from ~285 mA RMS in H4 to ~1.35 mA RMS in HCH5-D2) and compliance with relevant standards, indicating practical advantages for transformer-less PV inverters.

Abstract

With the rise of renewable energy penetration in the grid, photovoltaic (PV) panels are connected to the grid via inverters to supply solar energy. Transformer-less grid-tied PV inverters are gaining popularity because of their improved efficiency, reduced size, and lower costs. However, they can induce a path for leakage currents between the PV and the grid part due to the absence of galvanic isolation between them. This leads to serious electromagnetic interference, loss in efficiency and safety concerns. The leakage current is primarily influenced by the nature of the common mode voltage (CMV), which is determined by the switching techniques of the inverter. In this paper, a novel inverter topology of Hysteresis Controlled H5 with Two Clamping Diodes (HCH5-D2) has been derived. The HCH5-D2 topology helps to decouple the AC part (Grid) and DC part (PV) during the freewheeling to make the CMV constant and in turn, reduces the leakage current. Also, the additional diodes help to reduce the voltage spikes generated during the freewheeling period and maintain the CMV at a constant value. Finally, a 2.2kW grid-connected single-phase HCH5-D2 PV inverter system's MATLAB simulation has been presented with better results when compared with a traditional H4 inverter.

An Optimized H5 Hysteresis Current Control with Clamped Diodes in Transformer-less Grid-PV Inverter

TL;DR

The paper tackles leakage currents in transformer-less grid-PV inverters caused by non-constant common-mode voltage (CMV). It introduces the HCH5-D2 topology, adding a PV-side switch and two clamping diodes to DC-decouple the DC and AC paths, stabilizing CMV at and damping CMV spikes. A dual-loop control structure combines outer DC-link voltage control with Perturb and Observe MPPT and inner hysteresis current control via Inverse Park transformation, achieving a constant DC-link ( V) and in-phase grid injection with a unipolar differential-mode voltage. Simulation results in MATLAB/Simulink show dramatically reduced leakage current (from ~285 mA RMS in H4 to ~1.35 mA RMS in HCH5-D2) and compliance with relevant standards, indicating practical advantages for transformer-less PV inverters.

Abstract

With the rise of renewable energy penetration in the grid, photovoltaic (PV) panels are connected to the grid via inverters to supply solar energy. Transformer-less grid-tied PV inverters are gaining popularity because of their improved efficiency, reduced size, and lower costs. However, they can induce a path for leakage currents between the PV and the grid part due to the absence of galvanic isolation between them. This leads to serious electromagnetic interference, loss in efficiency and safety concerns. The leakage current is primarily influenced by the nature of the common mode voltage (CMV), which is determined by the switching techniques of the inverter. In this paper, a novel inverter topology of Hysteresis Controlled H5 with Two Clamping Diodes (HCH5-D2) has been derived. The HCH5-D2 topology helps to decouple the AC part (Grid) and DC part (PV) during the freewheeling to make the CMV constant and in turn, reduces the leakage current. Also, the additional diodes help to reduce the voltage spikes generated during the freewheeling period and maintain the CMV at a constant value. Finally, a 2.2kW grid-connected single-phase HCH5-D2 PV inverter system's MATLAB simulation has been presented with better results when compared with a traditional H4 inverter.
Paper Structure (15 sections, 6 equations, 13 figures, 3 tables)

This paper contains 15 sections, 6 equations, 13 figures, 3 tables.

Table of Contents

  1. Introduction
  2. Proposed HCH5-D2 Inverter Topology
  3. Conversion of Voltage Sources into Current Sources
  4. Conversion of Current Source into Voltage Source
  5. Leakage Current and Resonant Frequency
  6. Modes of Operation in Proposed HCH5-D2 Inverter
  7. Dual Loop Control Strategy for the proposed HCH5-D2 Inveter
  8. Outer DC Link Voltage Control Loop
  9. Hysteresis Current Control (Inner Grid)
  10. Results
  11. DC-Link Analysis
  12. CMV and DMV Analysis
  13. Leakage Current Comparison
  14. Grid Voltage and Current
  15. Conclusion

Figures (13)

  • Figure 1: Main Circuit of HCH5-D2 Inverter Topology
  • Figure 2: Resonant circuits of H5 inverter
  • Figure 3: Resonant circuit of H5 inverter with current sources
  • Figure 4: Resonant circuits of H5 inverter in various voltage and current source configurations
  • Figure 5: Simplified resonant circuit of H5 inverter in the form of single common-mode voltage source
  • ...and 8 more figures