Research on Control of Improved Dual-Buck Energy Storage Inverter

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This study focuses on enhancing the efficiency and reliability of energy storage inverter by proposing an improved two-stage Dual-Buck topology. The research addresses critical challenges in non-isolated inverters, including leakage current suppression, DC voltage utilization, and seamless grid-tied/off-grid switching. Key contributions include a detailed analysis of operating modes, modulation strategies, and control system design.

1. Topology Analysis of Improved Dual-Buck Energy Storage Inverter

The proposed two-stage structure combines a DC/DC boost converter with a three-phase Dual-Buck inverter. Key advantages include:

  • Elimination of bridge-arm shoot-through risk
  • 50% reduction in switching losses compared to full-bridge operation
  • Dual-mode DC/DC conversion for extended component lifespan

The switching loss comparison between full-bridge and half-cycle modes is calculated as:

$$P_{loss}^{full} = \frac{1}{4}U_{dc}I_mf_s(t_r + t_f)$$
$$P_{loss}^{half} = \frac{1}{\pi}U_{dc}I_mf_s(t_r + t_f)$$

Operation Mode Switching Loss (W) Conduction Loss (W)
Full-Bridge 139.54 60.71
Half-Cycle 44.40 37.75

2. Leakage Current Suppression Strategies

Three modulation strategies are analyzed for common-mode voltage (CMV) control:

Modulation CMV Fluctuation Leakage Current (A) DC Utilization
SVPWM 0 → Udc 7.0 100%
AZSPWM2 Udc/3 → 2Udc/3 2.3 100%
RSPWM Fixed CMV 0.5 66.7%

The leakage current model is derived as:

$$i_{leak} = C_{pv}\frac{d(u_{CM})}{dt}$$
$$u_{CM} = \frac{u_{AN} + u_{BN} + u_{CN}}{3}$$

3. Control Strategy Design

A three-loop control system is developed for the energy storage inverter:

  1. Power Loop: Droop control for grid synchronization
    $$f = f_0 – m(P – P_0)$$
    $$V = V_0 – n(Q – Q_0)$$
  2. Voltage Loop:
    $$G_v(s) = \frac{k_{vp}s + k_{vi}}{s}\cdot\frac{1}{1.5T_ss + 1}$$
  3. Current Loop:
    $$G_i(s) = \frac{k_{ip}s + k_{ii}}{s}\cdot\frac{1}{Ls + R}$$

4. Experimental Validation

The hardware-in-loop tests using RT-LAB demonstrate:

  • DC bus voltage regulation: 100V → 750V with <2% ripple
  • Grid-connected current THD: <3% at 10kW output
  • Seamless mode transition within 20ms

Key performance metrics:

$$THD = \sqrt{\sum_{h=2}^{50}\left(\frac{I_h}{I_1}\right)^2} \times 100\% < 3\%$$ $$t_{transition} = \frac{1}{3f_{grid}} = 6.67ms$$

5. Conclusion

The improved Dual-Buck energy storage inverter demonstrates superior performance in:

  1. Reducing switching losses by 68.3% through half-cycle operation
  2. Suppressing leakage current to 33% of conventional inverters using AZSPWM2
  3. Achieving 98.2% efficiency in 10kW grid-tied operation

This research provides a comprehensive solution for next-generation energy storage inverter, particularly suitable for distributed renewable energy systems requiring high reliability and bidirectional power flow capability.

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