#### 期刊菜单

Research on Control Strategy of a Grid-Connected Micro-Inverter
DOI: 10.12677/SG.2019.93014, PDF, HTML, XML, 下载: 961  浏览: 2,170  国家自然科学基金支持

Abstract: In order to improve the performance-cost ratio of photovoltaic grid-connected micro-inverters, a current sampling circuit using blocking diode and bias diode is adopted, and the peak current sampling without additional current sensor is realized. Based on this, the maximum power point tracking (MPPT) method without voltage and current sensor is studied, and an MPPT disturbance algorithm based on the sum of peak current sampling values in half cycle of power grid is proposed to generate the given value of grid-connected current. Based on the given value of grid-connected current, a duty cycle observer is designed to realize the open-loop control of grid-connected micro-inverters. The control method studied in this paper can be implemented in a low cost control chip. The program algorithm is simple and the hardware cost is low. Experiments verify the feasibility of the research method in this paper, thus achieving high reliability and cost performance.

1. 引言

2. 峰值电流的采样电路

Figure 1. Principle diagram of peak current sampling circuit based on shutdown voltage drop

3. 基于峰值电流之和的MPPT扰动观察法

Figure 2. Peak current diagram for two half cycles

${P}_{pv}={U}_{i}\cdot {I}_{i}=\frac{2}{\text{π}}\cdot {U}_{i}\cdot {I}_{p\text{_}i}\left(k\right)$ (1)

${I}_{p\text{_}i}\left(k\right)=\frac{1}{2}\cdot \frac{{t}_{on}\cdot {I}_{pk\text{_}i}\left(k\right)}{{T}_{s}}$ (2)

${t}_{on}={L}_{p}\frac{{I}_{pk\text{_}i}\left(k\right)}{{U}_{i}}$ (3)

${P}_{i}={I}_{i}\cdot {U}_{i}=\frac{{L}_{m}\cdot {I}_{pk_i}^{2}\left(k\right)}{\text{π}\cdot {T}_{s}}$ (4)

${I}_{total}={\sum }_{i=1}^{N}{I}_{pk\text{_}i}\left(k\right)={k}_{coff}\cdot {I}_{pk\text{_}\mathrm{max}}\left(k\right)$ (5)

4. 基于占空比观测器的控制方法

4.1. 反激变换器开关管占空比观测器设计原理

${i}_{s\text{_}peak}=N\cdot {i}_{p\text{_}peak}$ (6)

Figure 3. Program flow chart of MPPT perturbation observation method for summation of peak currents

(a)(b)

Figure 4. (a) Switch closure of flyback converter; (b) Flyback converter switch off

${i}_{p\text{_}peak}=\frac{{V}_{in}}{{L}_{p}}\cdot {t}_{on}$ (7)

${i}_{s\text{_}peak}=\frac{{V}_{out}}{{\left(1/N\right)}^{2}{L}_{p}}\cdot {t}_{off}$ (8)

N为变压器原边与副边匝数比。实际图3中的负载为倒相逆变器，其两端电压为Vout，输出电流即为并网电流的绝对值，设电网电压 ${v}_{grid}={V}_{gm}\cdot \mathrm{sin}\left(\omega t\right)$ ，电网电流 ${i}_{g}={I}_{gm}\cdot \mathrm{sin}\left(\omega t\right)$

1) 临界连续模式

${t}_{on\text{_}BCM}=\frac{{L}_{p}\cdot {i}_{pk\text{_}i}\left(k\right)}{{V}_{pv}}$ (9)

${t}_{off\text{_}BCM}=\frac{{L}_{p}\cdot {i}_{pk\text{_}i}\left(k\right)}{{V}_{out}\cdot {N}^{2}}$ (10)

${i}_{s\text{_}avg\text{_}BCM}\left(\omega t\right)=\frac{N\cdot {i}_{_ref\text{_}BCM}\left(\omega t\right)\cdot {t}_{off\text{_}BCM}\left(\omega t\right)}{2\cdot \left[{t}_{on\text{_}BCM}\left(\omega t\right)+{t}_{off\text{_}BCM}\left(\omega t\right)\right]}$ (11)

${i}_{s\text{_}avg\text{_}BCM}\left(\omega t\right)={I}_{gm\text{_}ref}\mathrm{sin}\left(\omega t\right)$ (12)

${i}_{pk\text{_}i}\left(k\right)=2\cdot {I}_{gm\text{_}ref}\cdot \left[\frac{{V}_{out}\cdot |\mathrm{sin}\left(\omega t\right)|}{{V}_{pv}}+\frac{|\mathrm{sin}\left(\omega t\right)|}{N}\right]$ (13)

2) 断续导通模式

${t}_{off\text{_}DCM}=\frac{{L}_{p}\cdot {i}_{pk\text{_}i}\left(k\right)}{{V}_{out}\cdot {N}^{2}}$ (14)

${i}_{s\text{_}avg\text{_}DCM}\left(\omega t\right)=\frac{0.5\cdot N\cdot {i}_{ref\text{_}DCM}\left(\omega t\right)\cdot {t}_{off\text{_}DCM}\left(\omega t\right)}{{T}_{DCM}}$ (15)

${i}_{s\text{_}avg\text{_}DCM}\left(\omega t\right)={I}_{gm_ref}\cdot \mathrm{sin}\left(\omega t\right)$ (16)

${i}_{pk\text{_}i}\left(k\right)=\sqrt{\frac{2\cdot {I}_{gm\text{_}ref}\cdot {T}_{DCM}\cdot {V}_{out}\cdot N}{{L}_{p}}}\cdot |\mathrm{sin}\left(\omega t\right)|$ (18)

4.2. 并网微逆变器的开环控制策略

Figure 5. Open-loop control diagram

Figure 6. Critical continuous mode and discontinuous mode switching flow chart

5. 实验分析

Table 1. Main performance indicators of dual-channel interleaved flyback photovoltaic grid-connected micro-inverters

Figure 7. Maximum power tracking waveform of micro inverter generation

Figure 8. Driving waveform of four-way MOS transistor in the first stage

Figure 9. Leakage stage voltage test waveform of MOS transistor

Figure 10. Steady-state waveforms of grid-connected current and grid voltage

Figure 11. Efficiency curve

Figure 12. Power factor curve and current total harmonic distortion curve

6. 结论

 [1] 吴达成, 刘馨. 我国光伏产业发展现状及分析[J]. 新材料产业, 2011(3): 2-10. [2] Chen, Y. (2014) A Resonant MOSFET Gate Driver with Efficient Energy Recovery. IEEE Transactions on Power Electronics, 19, 470-477. [3] 董蓓蓓, 熊飞, 李骞, 苟秦晋, 李博江, 贺紫倩. 分布式光伏发电消纳方式的选择策略研究[J]. 供用电, 2017, 34(8): 79-83. [4] Lee, J.-H., Lee, J.-S. and Lee, K.-B. (2015) Current Sensorless MPPT Control Method for Dual-Mode PV Module-Type Interleaved Flyback Inverters. IEEE Transactions on Power Electronics, 15, 54-64. [5] Zhang, Z., Chen, M. and Chen, W. (2014) Analysis and Implementation of Phase Synchronization Control Strategies for BCM Interleaved Flyback Micro-Inverters. IEEE Transactions on power Electronics, 19, 5921-5932. [6] Zhang, J., Huang, X., Wu, X. and Qian, Z. (2010) A High Efficiency Flyback Converter with New Active Clamp Technique. IEEE Transactions on Power Electronics, 25, 1775-1785. [7] 王星星, 嵇保健, 洪峰, 叶尊敬. 一种改进的正反激并网微型逆变器[J]. 电工技术学报, 2017, 32(18): 202-210. [8] 汲德明, 任一峰, 李昕. 单相光伏并网微型逆变器设计[J]. 建筑电气, 2018, 37(10): 45-49. [9] 李崇基. 光伏并网逆变器的仿真及控制策略分析[J]. 科技资讯, 2017, 15(30): 45-46. [10] Kim, Y.C., Lim, Y., Jin, L., et al. (2009) Direct Digital Control of PWM Converter Using Closed-Loop Identification. IEEE International Symposium on Industrial Electronics, Seoul, 5-8 July 2009, 266-271. [11] Qu, L. and Zhang, B. (2008) Research of PWM Converter Control Method in Electric Vehicle. IEEE Vehicle Power and Propulsion Conference, Harbin, 3-5 September 2008, 1-5. [12] El Iysaouy, L., et al. (2018) Impact of Flyback Transformer and Switch Parameters on Efficiency of Single Stage Photovoltaic Mi-croinverter. Open Conference of Electrical, Electronic and Information Sciences, Vilnius, 26 April 2018, 1-4. [13] 郑明才, 赵小超, 胡恩博, 郑金兵. Boost结构太阳能收集电路的MPPT控制方法研究[J]. 电源学报, 2017, 15(6): 36-42. [14] 杨波勇, 王军, 阎铁生, 孙章. 基于DSP的微逆变器双频率控制方法及实现[J]. 电源学报, 2017, 15(6): 68-74. [15] 张雅静, 王秀腾, 陈骞, 范新桥, 梁美. 单级反激微型逆变器控制策略[J]. 北京信息科技大学学报(自然科学版), 2018, 33(5): 11-15.