Modern energy storage inverters play a pivotal role in balancing power fluctuations within renewable energy systems. This paper proposes an enhanced two-stage Dual-Buck energy storage inverter topology, addressing critical challenges in efficiency improvement, leakage current suppression, and seamless grid interaction. The system combines a front-end DC/DC converter with a rear three-phase Dual-Buck inverter, demonstrating superior performance in bidirectional power conversion.
1. Topological Innovation and Operating Modes
The proposed energy storage inverter employs a dual-mode DC/DC conversion stage and a three-phase Dual-Buck full-bridge configuration. The switching loss comparison between full-bridge and half-cycle modes reveals significant advantages:
$$P_{loss}^{full} = \frac{3}{4}U_{dc}I_mf_s(t_r + t_f) + \frac{1}{8}U_{CEO}I_m + \frac{1}{12}mk_1I_m^2$$
$$P_{loss}^{half} = \frac{1}{4\pi}U_{dc}I_mf_s(t_r + t_f) + \frac{1}{8}U_{CEO}I_m + \frac{1}{12\pi}mk_1I_m^2$$
The half-cycle mode reduces switching losses by 68.3% compared to conventional full-bridge operation. Key parameters for the energy storage inverter are summarized below:
| Parameter | Value |
|---|---|
| DC Input Voltage | 100-750V |
| Switching Frequency | 10kHz |
| Filter Inductance | 1.5mH/phase |
| Output Capacitance | 20μF/phase |
2. Leakage Current Mitigation Techniques
For non-isolated energy storage inverters, three modulation strategies are analyzed for common-mode voltage (CMV) suppression:
| Modulation | CMV Swing | Leakage Current | DC Utilization |
|---|---|---|---|
| SVPWM | 0-Udc | 7A peak | 100% |
| AZSPWM2 | Udc/3-2Udc/3 | 2.3A peak | 100% |
| RSPWM | Fixed Udc/3 | 0.5A peak | 66.7% |
The leakage current calculation considers parasitic capacitance Cpv:
$$i_{leak} = C_{pv}\frac{d}{dt}(V_{CM})$$
3. Tri-Loop Control Architecture
The energy storage inverter employs voltage-current-power triple-loop control with the following transfer functions:
Current loop compensation:
$$G_i(s) = \frac{k_{ip}s + k_{ii}}{s(1.5T_ss + 1)}$$
Voltage loop compensation:
$$G_v(s) = \frac{k_{vp}s + k_{vi}}{s(1.5T_ss + 1)(L_fs + R_f)}$$
Power droop characteristics:
$$\Delta f = -m(P – P_0)$$
$$\Delta V = -n(Q – Q_0)$$
4. Seamless Mode Transition
The energy storage inverter achieves smooth grid connection through phase synchronization:
$$\theta_{\text{sync}} = \int \left( \omega_{\text{grid}} + k_p \Delta\theta + k_i \int \Delta\theta \, dt \right) dt$$
Experimental validation shows transient performance during 10kW load switching:
| Parameter | Pre-Sync | Post-Sync |
|---|---|---|
| Voltage THD | 2.8% | 1.2% |
| Frequency Error | 0.5Hz | 0.02Hz |
| Phase Difference | 15° | 0.8° |
This improved Dual-Buck energy storage inverter topology demonstrates 96.2% peak efficiency and <30mA residual current, meeting international safety standards for renewable energy systems. The hybrid modulation strategy combining AZSPWM2 for grid-tied operation and RSPWM for islanding mode provides optimal balance between efficiency and leakage suppression.