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Control of Two - stage Grid - connected PV Inverter

Author: Source: Datetime: 2016-10-05 01:27:38
Commonly used two-stage grid-connected photovoltaic inverter mainly consists of a pre-stage converter and a post-stage grid-side inverter. Under normal circumstances, the output voltage of photovoltaic cells is usually lower than the peak voltage of the grid, so to achieve solar power generator, solar power batteries should be the first direct current output through the front-end converter step-up after the output to the network side Inverter, through the control of the network side of the inverter output AC power into the power grid, in which the DC bus part of the role is to connect the converter and the network side of the inverter, and to achieve the role of power transmission. As the two-stage grid-connected photovoltaic inverter there are two power conversion unit, so the maximum power point tracking control of photovoltaic cells can either be done by the converter of the previous stage, or by the network-side inverter , Respectively, respectively.

Based on the latter side of the network side of the inverter to achieve ^ control system. Among them, the converter of the former stage controls the voltage of the intermediate DC bus through the control of its switch duty ratio so as to balance the energy output of the front and the rear stage, and the latter network side inverter will finish the control and the grid inverter control Unit power factor sine wave current control). In the process of network control based on the later-stage grid-side inverter, firstly, according to the algorithm,solar power generator the variation of the commanded current amplitude of the grid-side inverter is obtained, and then the adjustment amount of the commanded current amplitude of the network side inverter is obtained , The grid voltage synchronization unit sinusoidal signal multiplied by the network side of the inverter output current value of the instantaneous value, with the network side detection current instantaneous value. And then the modulated signal is synthesized with the voltage feedforward signal of the grid. Finally, the double-simplified control signal is realized after comparing with the triangular wave, so as to realize the control and the unit power factor sine wave current control.

In the control of the whole system, the control response speed of the front and the back stage should be coordinated to ensure the dynamic balance of the energy transmission so as to stabilize the bus voltage. In the control system design, the response of the front stage converter The speed should be faster than the level of the network side of the inverter's response speed.
A Two - Stage Grid - Connected Photovoltaic Inverter Control System Based on Pre - Stage Converter. Among them, after the level of the network side of the inverter to achieve DC bus voltage control, and the former level of the converter is to achieve control. Since the output voltage of the converter is controlled by the grid side inverter, the input current of the converter can be adjusted by adjusting the switching duty ratio of the converter, and the output voltage of the photovoltaic cell is adjusted. According to the detection of the output voltage and current of PV cells, the converter can obtain the voltage command to adjust the operating point of the PV cell by control algorithm and then subtract the sample value of the output voltage of the PV cell and go through the regulator for the output of the converter solar power generator. Voltage closed-loop control, in order to achieve the control of solar power batteries; and after the level of the network side of the inverter voltage loop, the current inner loop of the double-loop control strategy, which is based on the principle of power balance to achieve night flow bus stability Voltage control, while the current inner loop is mainly to achieve network side current tracking control, in order to achieve grid-connected inverter unit power factor sine wave current control.

In this control strategy, the output power of the converter is constantly changing due to the change of the environment. In order to ensure that the power output of the converter is transmitted to the grid in time without generating energy accumulation and deficit on the DC bus, it is required that the control system In the design, the control response of DC voltage outer loop of the inverter should be faster than the control response of the front stage converter. In fact, increasing the capacity of the DC bus or using the cut-off negative feedback control of DC bus upper and lower voltage Can prevent the DC bus over-voltage.

In addition, in order to ensure a fast enough control response to the converter, and to make the grid-side inverter control the DC bus voltage well, a control strategy based on the front-stage converter of the PV voltage feed-forward is added. Due to the feedforward control of the output voltage of solar power batteries, the grid-side inverter along the stage can accelerate the synchronous adjustment of the output of the solar power batteries when the environment changes rapidly, thus effectively restraining the fluctuation of the DC bus voltage. TAG: Deployment Fixed SMA Tesvolt Unlimited Volt Army Sonnen Multi-Storage Reliability Shell Manganese 200MW Ørsted Micro