Research and Design of Single-Phase Energy Storage Inverter
With increasing global energy demands and environmental concerns, energy storage inverters have become critical components in modern power systems. This paper presents a systematic study on a two-stage single-phase energy storage inverter featuring push-pull DC-DC conversion and full-bridge inversion. The design addresses key challenges in efficiency improvement, thermal management, and control strategy optimization.
1. System Architecture and DC-DC Stage Design
The proposed energy storage inverter adopts a cascaded structure comprising a push-pull resonant converter and H-bridge inverter. The DC-DC stage converts 48V battery voltage to 350V DC bus voltage through high-frequency transformation. The voltage conversion ratio is expressed as:
$$M = \frac{V_{dc}}{V_{in}} = \frac{n}{2D(1-D)}$$
where \(n\) represents transformer turns ratio and \(D\) denotes duty cycle. Key parameters of the push-pull converter are optimized through loss analysis:
| Component | Design Specification |
|---|---|
| Transformer Core | EE42 (Ae=1.75cm²) |
| Primary Winding | 6 turns (40×φ0.6mm) |
| Secondary Winding | 9 turns (36×φ0.4mm) |
| Resonant Frequency | 45kHz |
2. Inverter Stage Control Strategy
The full-bridge inverter implements voltage-current dual-loop control with unipolar PWM modulation. The control system dynamics are described by:
$$G_{inv}(s) = \frac{1}{LCs^2 + (R_sC + \frac{L}{R_L})s + 1}$$
The current loop bandwidth is designed as:
$$f_{c\_current} = \frac{1}{10}f_{sw} = 1kHz$$
Key control parameters are optimized through Bode analysis:
| Parameter | Value |
|---|---|
| Filter Inductance | 3.5mH |
| Filter Capacitance | 10μF |
| Voltage Loop Kp | 0.85 |
| Current Loop Ki | 120 |
3. Loss Analysis and Thermal Management
Power device losses are calculated using improved electro-thermal models considering junction temperature effects. For IGBT modules:
$$P_{total} = P_{cond} + P_{sw} = (V_{ce0}I_{avg} + r_{ce}I_{rms}^2) + f_{sw}(E_{on} + E_{off})$$
Thermal impedance network parameters:
$$Z_{th} = \sum_{i=1}^4 R_{thi}(1-e^{-t/\tau_i})$$
Experimental measurements validate the thermal design:
| Component | Tmax(°C) |
|---|---|
| IGBT Module | 57 |
| High-Frequency Transformer | 56 |
| Output Inductor | 103 |
4. Experimental Verification
The energy storage inverter prototype achieves 90% peak efficiency with THD < 3% under full load. Key performance metrics:
$$THD = \sqrt{\sum_{h=2}^{50}\left(\frac{V_h}{V_1}\right)^2} \times 100\% < 3\%$$
Dynamic response test shows voltage recovery within 10ms for 0-100% load step changes, demonstrating the effectiveness of the proposed control strategy in maintaining power quality for energy storage applications.
5. Advanced Modulation Technique
A hybrid modulation strategy combining low-frequency switching and unipolar PWM reduces switching losses by 38% compared to conventional methods. The improved switching sequence follows:
$$S_{mod} = \begin{cases}
\text{P-state} & \text{when } V_{ref} > V_{tri+} \\
\text{O-state} & \text{when } V_{tri-} < V_{ref} < V_{tri+} \\ \text{N-state} & \text{when } V_{ref} < V_{tri-} \end{cases}$$
This energy storage inverter design provides a practical solution for portable power systems, demonstrating excellent performance in efficiency, power density, and operational reliability.