SOGI based phase-locked loop free photovoltaic inverter control method in imbalance power grid

Abstract

The invention discloses an SOGI based phase-locked loop free photovoltaic inverter control method in the imbalance power grid. The method comprises the following steps that Clark transformation is carried out on three phases of voltage signals Ea, Eb and Ec obtained by a sampling conditioning circuit to obtain components Ealpha and Ebeta in a rest frame; SOGI is used to carry out orthogonal treatment on the Ealpha and Ebeta to obtain a group of orthogonal signals Valpha1 and Valpha2 and another group of orthogonal signals Vbeta1 and Vbeta2; the orthogonal signals are separated to obtain positive-sequence voltage components Valpha+ and Vbeta+ and negative-sequence voltage components Valpha- and Vbeta-; a cosine signal costheta and a sine signal sintheta needed by rotation transformation areneeded according to relation between the phase angle theta of the positive-sequence fundamental wave voltage and the Valpha+ and Vbeta+; and a photovoltaic inverter is controlled in the synchronous coordinate system by using the sine and cosine signals, Valpha- and Vbeta-. Via the method, the photovoltaic inverter in the imbalance power grid can be controlled without a phase-locked loop, and thesystem structure is simple; and positive and negative voltage feedforward is introduced to inhibit grid-connected negative-sequence current, and the waveform quality of the grid-connected current in the imbalance power grid is ensured.

Description

technical field [0001] The invention relates to the technical field of grid-connected power generation of photovoltaic inverters, in particular to a phase-locked loop-free and stable operation control method for photovoltaic inverters under unbalanced power grids. Background technique [0002] In recent years, with the vigorous development of power electronics technology, the penetration rate of distributed energy sources such as photovoltaics and wind power in power systems is increasing day by day. For photovoltaic grid-connected power generation systems, accurate acquisition of the fundamental voltage amplitude and phase information of the grid is crucial to the power control of the system. Single synchronous frame software phase-locked loop (SRF-SPLL) is widely used in the grid-connected control of photovoltaic inverters because of its simple structure and fast dynamic response. However, in the case of unbalanced power grid, the phase-locked loop of single synchronous c...

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Problems solved by technology

However, in the case of unbalanced power grid, the single synchronous coordinate system phase-locked loop is affected by the negative sequence component of the voltage, which greatly reduces the phase-locking accuracy, resulting in the unstable operation of the entire photovoltaic grid-connected system.

Although some scholars have proposed to improve by installing a low-pass filter before the SRF-SPLL, although the phase-locking accuracy can be improved to a certain extent, the bandwidth of the entire phase-locking link is low, and the dynamic response is slow, which increases the control of the system. Delay, thereby reducing the grid-connected power quality of the photovoltaic inverter

Some researchers have also proposed to use a software phase-locked loop based on dual synchronous coordinate system decoupling. This method has high steady-state accuracy, but its structure contains more phase feedback links. Once the phase jump occurs in the grid voltage, use this method. This method will have problems such as large dynamic overshoot and long transition time, which is not conducive to the stable operation of photovoltaic inverters.

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