A single-stage photovoltaic off-grid inverter and its control method

Abstract

The invention belongs to the field of electrical technology, and relates to a single-stage photovoltaic off-grid inverter and a control method thereof. A switch tube is used on the primary side of the isolation transformer to realize two-way excitation of the transformer, and the switch tube can realize both zero-voltage turn-on and zero-voltage switching. The voltage is turned off, and energy can be transmitted to the secondary side of the transformer during the turn-on and turn-off periods; the secondary side of the transformer adopts two sets of high-frequency full-wave rectification circuits, which are controlled to output according to the power frequency, and then connected in reverse parallel, combined with the high-frequency switch on the primary side of the transformer The modulation of the tube forms a pulse sequence that changes according to the law of sinusoidal modulation, and becomes a power frequency 220V AC after filtering; its circuit structure is simple, small in size, low in cost, high in efficiency, easy to control, and high in reliability. In addition to small off-grid inverters, it can also be applied to other small off-grid inverters, vehicle-mounted inverters, UPS power supplies, frequency converters, and isolated step-up DC-AC converters.

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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