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Control method of three-phase photovoltaic grid-connected inverter when grid voltage is unbalanced

A grid voltage and inverter technology, applied in the field of three-phase photovoltaic grid-connected inverter control, can solve the problems of grid-connected converter heating, unclear reference current setting method, power oscillation, etc.

Inactive Publication Date: 2015-12-30
NORTH CHINA ELECTRIC POWER UNIV (BAODING) +1
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Problems solved by technology

[0003] When the power grid is unbalanced and faulty, the grid-connected three-phase current also becomes unbalanced, and the power generation system will generate a large amount of negative sequence current, which will cause the grid-connected converter to generate heat and increase losses, which will lead to poor performance and poor performance of the grid-connected converter. Grid-connected power quality of power generation system drops significantly
In addition, the grid voltage imbalance will also cause the power fed into the grid by the power generation system to oscillate, causing voltage fluctuations on the DC side of the photovoltaic system, seriously affecting the safe and stable operation of the photovoltaic system and the grid
[0004] Under appropriate conditions, make full use of new energy grid-connected control and energy storage technology or static var compensator to compensate the reactive power of the grid to meet the friendly needs of the grid. The size of the reactive power required to support the grid voltage needs to be passed Accurate and reasonable calculation and setting of the grid-connected reference current value is realized. Currently, the reference current setting method is not clear

Method used

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  • Control method of three-phase photovoltaic grid-connected inverter when grid voltage is unbalanced
  • Control method of three-phase photovoltaic grid-connected inverter when grid voltage is unbalanced
  • Control method of three-phase photovoltaic grid-connected inverter when grid voltage is unbalanced

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Experimental program
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Effect test

Embodiment 1

[0062] Depend on Figure 1-6 It can be seen from the described embodiment that this embodiment includes the following steps:

[0063] Step 1 Establish the main circuit and inverter control system of the three-phase photovoltaic grid-connected system, which includes solar photovoltaic cell array PV, boost circuit T, filter capacitor C, grid-connected inverter U3, LCL filter, the first current Transformer TA1, second current transformer TA2, voltage transformer TV, DSP controller U1, drive circuit U2 and analog-to-digital converter ADC; the output terminal of the solar photovoltaic cell array PV passes through the step-up circuit T, The filter capacitor C is connected to the input terminal of the grid-connected inverter U3; the output terminal of the grid-connected inverter U3 is connected to the grid through the LCL filter; the first current transformer TA1 and the voltage transformer TV are respectively Installed on the output line of the grid side end of the LCL filter; the ...

Embodiment 2

[0099] Step 6 in the second embodiment is different from step 6 in the first embodiment, and the others are the same as the first embodiment.

[0100] Step 6 of present embodiment two is as follows:

[0101] Step 6 The steps of reference current calculation;

[0102] When an asymmetrical fault occurs in the power grid, at 0.3s~0.4s (see Figure 5-6 ) still inject active reference current into the power grid, at this time the component of the active reference current in the stationary coordinate system , for:

[0103] ;

[0104] in, P* It is the active power converted by the photovoltaic array, and its value is 10000W.

[0105] Effect description: At this time, the inverter can still work stably, but the grid-side voltage drops and the current increases. Excessive current may cause the grid protection device to operate. And the active power and reactive power start to oscillate.

Embodiment 3

[0107] Step 6 in the third embodiment is different from step 6 in the first embodiment, and the others are the same as the first embodiment.

[0108] Step 6 of present embodiment three is as follows:

[0109] Step 6 The steps of reference current calculation;

[0110] When an asymmetrical fault occurs in the grid, during 0.4s-0.45s (see Figure 5-6 ), using the reactive reference current control method, k 2 =1, the component of the reference current in the stationary coordinate system , for:

[0111] ,

[0112] current limit value I= 30A, k 2 =1, Q* The expression is:

[0113] ,

[0114] Effect description: The voltage of each phase on the grid side has been improved, and the current on the grid side is limited within 30A. Active power oscillation still exists, but it is weaker than before using the strategy.

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Abstract

The invention relates to a method for controlling a three-phase photovoltaic grid-connected inverter when a power grid voltage is unbalanced. The method comprises the steps of establishing a three-phase photovoltaic grid-connected system main circuit and an inverter control system, collecting signals, carrying out clark transform, synchronizing power grids, extracting the phase sequence, calculating a reference current, controlling a current loop, carrying out inverse clark transform, controlling PWM and driving an inverter. The method has the advantages that a photovoltaic power source is efficiently connected to the power grids under the situation that the power grids are normal; the grid-connected current harmonics are effectively eliminated through an LCL filter, and high-power factor grid connection is achieved through a PR current controller; when the power grids break down, the faults can be omitted, and three control targets of voltage supporting, voltage balancing and power vibration eliminating are achieved.

Description

technical field [0001] The invention belongs to the technical field of three-phase photovoltaic grid-connected inverter control, and relates to a control method for a three-phase photovoltaic grid-connected inverter when the grid voltage is unbalanced. Background technique [0002] As a large number of new energy power generation systems are connected to the grid, the output power of the grid-connected power inverter cannot be ignored compared with the rated power of the connection point. At this time, the grid voltage and frequency will be affected by the control performance of the power converter. The grid-connected control function of the power inverter is becoming more and more powerful. It not only needs to be connected to the grid with high power factor to transmit active power when the grid is running normally, but also to pass through the fault and inject reactive power when the grid fails. , adjust the voltage, and actively provide voltage support to the grid. [0...

Claims

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Application Information

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Patent Type & Authority Patents(China)
IPC IPC(8): H02J3/38H02M7/48
CPCY02E10/56
Inventor 李建文李永刚雷亚雄李忠良
Owner NORTH CHINA ELECTRIC POWER UNIV (BAODING)
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