Monopole-type photovoltaic off-network inverter and control method thereof

Abstract

The invention belongs to the technical field of electricity, and relates to a monopole-type photovoltaic off-network inverter and a control method thereof. The original side of an isolation transformer achieves bidirectional transformer excitation through a switching tube, the switching tube can achieve no-voltage switching-on and no-voltage switching-off, and meanwhile, during switching-on and switching-off periods, power can be supplied to the secondary side of the transformer; the secondary side of the transformer adopts two high-frequency full-wave rectification circuits, and by controlling the two circuits to output according to a power frequency and then switch to an inverse-parallel connection mode, the modulation of the high-frequency switching tube of the original side of the transformer is combined to form an impulse sequence capable of changing according to a sinusoidal modulation rule, wherein the impulse sequence is changed to 220V alternate current with a power frequency after smoothing. The circuit structure of the monopole-type photovoltaic off-network inverter is simple, small in size, low in cost, easy to control and high in reliability, and can not only be specially used in small photovoltaic off-network inverters, but popularized and applied to other small off-network inverters, vehicle-mounted inverters, UPS power sources, transducers and DC-AC convertors for insolation and pressure boosting.

Description

Technical field: [0001] The invention belongs to the technical field of electricity, and relates to an off-grid inverter and a control method thereof, in particular to a novel high-efficiency single-stage photovoltaic off-grid inverter and a control method thereof for battery panel components. Background technique: [0002] Traditional photovoltaic off-grid micro-inverters generally have the following three structural forms: the first is a non-isolated two-stage structure, that is, the front stage uses a non-isolated Boost circuit to boost the voltage, and the latter stage uses an H-bridge inverter. Its advantages The circuit is relatively simple, but the disadvantage is that the output of the micro-inverter is not isolated from the battery board, which will bring safety hazards, and its efficiency is low. The second is an isolated two-stage structure, that is, the front stage uses an isolated voltage or current-type half-bridge LLC circuit to boost the voltage, and the latt...

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Problems solved by technology

[0002] Traditional photovoltaic off-grid micro-inverters generally have the following three structural forms: the first is a non-isolated two-stage structure, that is, the front stage uses a non-isolated Boost circuit to boost the voltage, and the latter stage uses an H-bridge inverter. Its advantages The circuit is relatively simple, but the disadvantage is that the output of the micro-inverter is not isolated from the battery board, which will bring safety hazards and its efficiency is low

The second is an isolated two-stage structure, that is, the front stage uses an isolated voltage or current-type half-bridge LLC circuit to boost the voltage, and the latter stage uses an H-bridge inverter. The advantage is that the output of the micro-inverter and the battery board realize electrical Isolation eliminates potential safety hazards, and its pre-stage circuit can realize soft switching through resonance. The efficiency of the pre-stage circuit is relatively high. The disadvantage is that the inverter is relatively large in size and high in cost. The pre-stage is a current-type half-bridge LLC. The circuit control is relatively complicated, and two inductors are required, which increases the size of the inverter; the front stage is a voltage-type half-bridge LLC circuit control is relatively complicated, and the upper and lower switch tubes of the bridge arm are easy to pass through and burn the circuit; the third is isolation Type single-stage structure, currently the primary side of the transformer generally adopts flyback type, interleaved flyback type or interleaved flyback active clamping circuit, and the secondary side of the transformer adopts power frequency inverter, that is, the electrical isolation can be realized by using the primary circuit It is also reversible, eliminating the post-stage H-bridge inverter circuit. For flyback or interleaved flyback circuits, the advantage is that the circuit structure is simple and easy to control. The disadvantage is that the transformer is unidirectionally excited, the magnetic core is easily saturated, and the power It is difficult to make it bigger, the switching tube cannot realize soft switching, and the efficiency is relatively low; for the interleaved flyback active clamp circuit, the switching tube in the active clamping branch and the main switching tube are complementary conduction, and the two The switching tubes have realized zero-voltage soft switching, and the withstand voltage of the switching tubes has been reduced, and the efficiency has been relatively improved. However, the existing transformer is unidirectionally excited, the magnetic core is easily saturated, and the power is difficult to increase, which increases the complexity of control.

[0003] Combining the three structural forms of traditional off-grid small photovoltaic inverters, for isolated or non-isolated two-stage small inverters, the latter stage generally uses H-bridge inverters. The shortcomings of burning out the circuit, high difficulty in control, low reliability, and low efficiency, coupled with the cascading of the front and rear stages, the volume of the inverter increases, the reliability decreases, and the efficiency is further reduced. At present, it is gradually being isolated. type structure, but the isolated single-stage structure also has the problem of one-way excitation of the transformer

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