The realization and simulation model of phase-locked loop based on SOGI second-order integrator principle is visible: "A dual SOGI phase-locked loop for three-phase grids is implemented and simulated." However, the SOGI-based feature can also realize the lockback ring, which can automatically adapt to the grid frequency change, which greatly enhances the performance of the SOGI principle-locked loop.
SOGI is only 0dB gain only in the resonant frequency center, which means that when the grid frequency changes, the resonant center frequency of the SOGI filter does not change, it will cause the orthogonal waveform of the SOGI output to distort the input waveform, resulting in locking precise. Therefore, in order to solve this problem, you need to get the frequency change information of the grid, and then synchronize the resonance center frequency of the SOGI filter to achieve the best phase-locked performance.
(SOGI frequency response)
Observing the second-order SOGI orthogonal signal generator, to automatically adjust the frequency Wn, first analyze the error signal E, and study how to adjust the resonant center frequency of SOGI using this error signal.
(SOGI)
The transfer function from the input signal V to the error signal E is:
(Error signal transfer function)
The transfer function of this error is actually a second-order parking filter, and the gain of its resonant center frequency is zero. Moreover, the transfer function has an interesting feature. When the frequency W of the input signal is lowered from the SOGI resonant center frequency Wn, the phase angle of the output signal will occur 180 ° hop, and the following will use this characteristic to compare two The value of a frequency.
In order to study the relationship between E (S) and QU (S), the picture below is placed together. It can be seen that when the input frequency is lower than the resonant center frequency Wn of the SOGI, the signals E and QU are in phase, in turn, when the input frequency is higher than the resonant center frequency Wn of the SOGI, the signals E and QUs are inverted.
(Frequency response of error signal transfer function)
Therefore, the frequency error variable EF can be defined as the product of QU and E, as information as seen above. When the input frequency is lower than the Wn, the average value of EF is greater than zero, and the two is equal to zero, and when the input frequency is higher than the Wn, the error is less than zero. So using this feature can design a very simple lock frequency ring, see the figure below:
(SOGI FLL structure)
In this loop, the pixel of the negative gain R is added to the grid frequency, the SOGI is consistent with the input frequency, and the DC component of the EF is controlled to zero, and the lock is realized. Therefore, the SOGI PLL and FL will be combined to realize automatic compensation and tracking of grid frequency disturbance, synchronously adjusting the resonant center frequency of SOGI, lifting the reliability of the lock, and visible simulation model:
(SOGI FLL simulation model)
Run the test, will change the power network frequency and the amplitude, and the phase locked loop can quickly lock:
(SOGI FLL in the case of ideal AC input)
(SOGI FLL in the case of ideal AC input)
In order to test the performance of the SOGI lock rings in the grid's high-end harmonic injection, I specifically built a model of harmonic injection, visible, 1 to 10 free changes:
(Harmonic generation method)
Run test: Even if the Harmonic Injection, the SOGI lock frequency is still very stable and stable, and the performance is really good:
(SOGI FLL simulates in the case of non-ideal AC input)
(SOGI FLL simulates in the case of non-ideal AC input)
Summary: References in the SOGI lock frequency ring, built a single-phase SOGI FLL model, and analog the locking rings in high-hard harmonic interference, all have achieved satisfactory results.
Reference documentation:
1, photovoltaic and wind power generation system grid inverter
2, Software Phase Locked Loop Design USING C2000TM
MicroControllers for Single Phase Grid Connected Inverter --SPRABT3A-JULY 2013-Revised July 2017
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