Hybrid-clamped three-electric-level three-phase four-wired photovoltaic system based on 3D-SPWM (three-dimensional sinusoidal pulse width modulation)

Abstract

The invention relates to a hybrid-clamped three-electric-level three-phase four-wired photovoltaic system based on 3D-SPWM (three-dimensional sinusoidal pulse width modulation). By the use of a 3D-SPWM control method, system leak current is reduced effectively, neutral-point potential balance is guaranteed, balance of outputting three-phase voltage by the photovoltaic system in independent operation is guaranteed, and balance of three-phase grid-connecting current in grid-connecting operation is guaranteed. In addition, neutral current can be lowered effectively by controlling zero-sequence component. The photovoltaic system comprises three-phase bridge arms connected in parallel. Each bridge arm comprise four IGBTs (insulated gate bipolar transistors) connected in series, a neutral point of each phase bridge arm is connected with a corresponding resistor through a filter, and the resistors are grounded. A pair of a capacitor C1 and a capacitor C2 in series connection are connected at an input end of each bridge arm in parallel, the capacitors C1 and the capacitors C2 are connected with an acquisition photovoltaic array. A pair of diodes are connected between the first IGBT and the fourth IGBT of each bridge arm in series,and neutral points of the capacitors C1 and the capacitors C2 are grounded. In addition, clamped capacitors Cxi are connected on each pair of diodes in parallel, wherein i is equal to a, b and c. The IGBTs are controlled by a control circuit in a 3D-SPWM manner to balance potential at the neutral points.

Description

technical field [0001] The invention relates to a hybrid clamping three-level three-phase four-wire photovoltaic system based on 3D-SPWM. Background technique [0002] Three-level inverters have the characteristics of high withstand voltage, small switching stress, and high-quality output waveforms, and are widely used in high-voltage and high-power occasions. With the rapid development of the photovoltaic industry, three-level and even more level inverters are gradually applied to photovoltaic power generation systems. However, for the non-isolated traditional diode-clamped three-level inverter system, it is difficult to solve problems such as the balance of the midpoint potential, the system leakage current, and the anti-three-phase load imbalance. For the cascaded non-isolated three-level photovoltaic inverter system, since it requires multiple independent power sources (usually independent photovoltaic panels), there is a parasitic capacitance between each independent p...

AI Technical Summary

Problems solved by technology

However, for the non-isolated traditional diode-clamped three-level inverter system, it is difficult to solve the problems of the balance of the point potential, the system leakage current and the anti-three-phase load unbalance at the same time.

For the cascaded non-isolated three-level photovoltaic inverter system, since it requires multiple independent power sources (usually independent photovoltaic panels), there is a parasitic capacitance between each independent photovoltaic panel and the ground, so the system leakage Current suppression becomes more complex and difficult

In addition, for the cascaded three-level photovoltaic system, since each battery module has its own MPPT control, it is easy to cause the unbalance of the three-phase grid-connected current, so it is necessary to add an additional control algorithm, which greatly reduces the Reliability and real-time performance of the system

[0003] Three-phase four-wire traditional diode-clamped inverters have been widely used in the fields of active filtering and special power supplies. The three-level inverters with this structure require complex 3D-SVPWM control algorithms. Midpoint potential balance problem, which will increase the complexity of system control and seriously affect system reliability

Furthermore, some literature points out that 3D-SVPWM and 3D-SPWM in the three-phase four-wire system are normalized, that is, there is no difference between the two in terms of control performance indicators

The complexity of 3D-SVPWM control is significantly higher than that of 3D-SPWM, but for the three-phase four-wire diode-clamped inverter, the control of the midpoint potential needs to analyze the influence of each vector on the midpoint potential, while 3D-SPWM Due to the poor flexibility, it is difficult to control the balance of the midpoint potential

In short, the control of the traditional diode-clamped inverter of the three-phase four-wire system is too complicated and difficult to realize

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