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Design and Implementation of a Software Phase-Locked Loop for Single-Phase PV Grid-Connected Inverter
DOI: 10.12677/OJCS.2019.82002, PDF , HTML, XML, 下载: 1,109  浏览: 4,348  国家自然科学基金支持

Abstract: Based on the closed-loop structure of traditional three-phase Phase-Locked loop, a software phase-locked loop (PLL) is proposed for single-phase PV grid-connected inverter in this paper. The operation principle of the presented phase-locked loop is analyzed and its mathematical model is deduced. Also, the software implementation method of the phase-locked loop is presented. Then, the influence resulted from the change of amplitude, frequency and phase on the grid voltage is simulated by PSIM software. The results show that the proposed software phase-locked loop can effectively and quickly realize the phase tracking at any time in the cycle, without waiting for the zero-crossing signal of the grid. The software phase-locked loop proposed in this paper is respectively applied to DSP TMS320F28035 and TMS320F2808 which belong to 500 W dual-channel single-phase PV grid-connected micro-inverter and 5 kW single-phase PV grid-connected inverter respectively. The results show that the proposed software phase-locked loop can achieve the voltage phase tracking and frequency locking well, thus verifying the proposed control method for single phase-locked loop.

1. 引言

2. 软件PLL原理

2.1. PLL原理

$\left\{\begin{array}{l}{v}_{d}={v}_{\alpha }\cdot \mathrm{cos}\theta +{v}_{\beta }\cdot \mathrm{sin}\theta \\ {v}_{q}={v}_{\beta }\cdot \mathrm{cos}\theta -{v}_{\alpha }\cdot \mathrm{sin}\theta \end{array}$ (1)

θ表示锁相环得到的相位角，vgrid表示电网电压。

$\left\{\begin{array}{l}{v}_{d}={v}_{\text{grid}}\cdot \mathrm{cos}\theta \\ {v}_{q}=-{v}_{\text{grid}}\cdot \mathrm{sin}\theta \end{array}$ (2)

$\left\{\begin{array}{l}{v}_{d}={V}_{\text{grid}}\cdot \mathrm{sin}\phi \cdot \mathrm{cos}\theta \\ {v}_{q}=-{V}_{\text{grid}}\cdot \mathrm{sin}\phi \cdot \mathrm{sin}\theta \end{array}$ (3)

$\left\{\begin{array}{l}{v}_{d}=\frac{{V}_{\text{grid}}}{2}\cdot \left[\mathrm{sin}\left(\phi -\theta \right)+\mathrm{sin}\left(\phi +\theta \right)\right]\\ {v}_{q}=\frac{{V}_{\text{grid}}}{2}\cdot \left[\mathrm{cos}\left(\phi +\theta \right)-\mathrm{cos}\left(\phi -\theta \right)\right]\end{array}$ (4)

 (5)

(6)

$\frac{\text{d}{v}_{q}}{\text{d}t}=\frac{\text{d}{v}_{q}}{\text{d}\phi }\cdot \frac{\text{d}\phi }{\text{d}t}+\frac{\text{d}{v}_{q}}{\text{d}\theta }\cdot \frac{\text{d}\theta }{\text{d}t}$ (7)

$\frac{\text{d}{v}_{q}}{\text{d}t}=\frac{{V}_{\text{grid}}}{2}\cdot \left[-\mathrm{sin}\left(\phi +\theta \right)\right]\cdot \left(2\cdot {\omega }_{ff}\right)$ (8)

${\omega }_{err}=\frac{\text{d}{v}_{q}}{\text{d}t}\cdot \frac{1}{2{\omega }_{ff}}+{v}_{d}=\frac{{V}_{\text{grid}}}{2}\cdot \mathrm{sin}\left(\phi -\theta \right)$ (9)

2.2. 软件PLL的实现方法

Figure 1. Control block diagram of phase-locked loop

Figure 2. Schematic diagram of phase superposition

Figure 3. Program flow diagram of PLL

vq对时间的微分在程序中是这样实现的：在s域，vq对时间的微分可以用 $s\cdot {v}_{q}$ 表示，对于 $s\cdot {v}_{q}$ 进行离散化可以得到如下式子：

 (10)

$\frac{1}{2{\omega }_{ff}}G\left(z\right)=\frac{{f}_{s}}{2{\omega }_{ff}}\cdot \left({v}_{q}-{v}_{q}\cdot {z}^{-1}\right)$ (11)

$\frac{{f}_{s}}{2{\omega }_{ff}}\left({v}_{q}\left(k\right)-{v}_{q}\left(k-1\right)\right)$ (12)

(13)

3. PLL仿真

3.1. 软件PLL仿真

Figure 4. Simulation circuit diagram of the phase-locked loop

Figure 5. Simulation diagram of voltage mutation

Figure 6. Simulation diagram of frequency mutation

Figure 7. Simulation diagram of phase mutation

Figure 8. Simulation diagram of phase locking with high order harmonics

3.2. 双通道微逆变器的仿真实现软件PLL算法

3.3. H6桥逆变器中的软件PLL算法

Figure 9. Micro-inverter system simulation model

Figure 10. Simulation waveform

Figure 11. Single-phase grid-connected inverter system simulation model

Figure 12. Simulation waveform

4. 实验结果与分析

Figure 13. Simulation diagram of phase mutation

Figure 14. Experimental prototype of the dual-channel micro-inverter

Figure 15. Grid-connected experimental waveforms

Figure 16. Experimental prototype of the single-phase grid-connected inverter

Figure 17. Grid-connected experimental waveforms

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