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Inverter stability analysis method for weak network far-mid end severe voltage drop and inverter stability analysis system for weak network far-mid end severe voltage drop

A technology of voltage sag and analysis method, applied in the direction of AC network voltage adjustment, AC network circuit, electrical components, etc., can solve the problem of less research and other issues

Active Publication Date: 2018-04-06
STATE GRID ZHEJIANG ELECTRIC POWER COMPANY ECONOMIC TECHN INST +2
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Problems solved by technology

[0004] At present, the research on the inverter low voltage ride through process mainly focuses on the small disturbance stability analysis. There have been no reports on the impact of the impact on the power grid; there are relatively few studies on the stability of large disturbances, and these studies have ignored the severe voltage drop at the remote end of the high inductance grid (here, the voltage drops below 0.2pu, which is a severe voltage drop), Typical low-voltage ride-through control strategy may cause large disturbance stability problems in inverters

Method used

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  • Inverter stability analysis method for weak network far-mid end severe voltage drop and inverter stability analysis system for weak network far-mid end severe voltage drop
  • Inverter stability analysis method for weak network far-mid end severe voltage drop and inverter stability analysis system for weak network far-mid end severe voltage drop
  • Inverter stability analysis method for weak network far-mid end severe voltage drop and inverter stability analysis system for weak network far-mid end severe voltage drop

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Embodiment 1

[0046] This embodiment provides a method for analyzing the stability of an inverter when a severe voltage drop occurs at a remote end in a weak network.

[0047] The inverter low voltage ride through control method and its structure are as follows: figure 1 The definitions and physical meanings of some variables are shown in Table 1 below. Among them, the low voltage ride-through (Low Voltage Ride-Through, LVRT) control strategy includes two parts: a current control link and a current dq axis control command.

[0048] Symbol definition and explanation of part system variable in the accompanying drawing of the present invention in table 1

[0049]

[0050] Dynamic mathematical model of current control link:

[0051]

[0052] In the formula: the first item on the right side of the equation is the PI control link of the conventional current inner loop, the second item on the right side of the equation is the current feedforward compensation item, and the third item on the...

specific Embodiment

[0090] In order to verify the validity of the above theoretical analysis, in the MATLAB / Simulink environment for figure 1 The system shown is simulated. The normal control mode of the inverter is "active power / AC voltage" control mode, and the system runs stably at P e = 0.6pu and V t =1pu, t=0.3s when the far-end voltage drop fault occurs. The main parameters are detailed in Table 3.

[0091] Table 3 Simulink simulation parameters

[0092] System rated voltage / V

380

System rated frequency / Hz

50

System rated capacity / kVA

10

Filter inductance L f / pu

0.15

filter capacitor C f / pu

0.05

Damping resistance R d

0.1

Current inner loop parameter k p_acc 、k i_acc

1、15

PLL parameter k p_pll 、k i_pll

80、3500

Feedforward gain factor a f

40

[0093] Figure 4 Given the line impedance X ∑ =0.5pu, the gain coefficient is k=4, and the voltage drop degree is E=0.1pu, the inve...

Embodiment 2

[0097] This embodiment provides an inverter stability analysis system when the middle and remote terminals of a weak network suffer severe voltage drops, including:

[0098] Inverter system quasi-steady-state model establishment module: perform Thevenin equivalent treatment on the AC power grid, and establish a quasi-steady-state model of the inverter system considering typical low-voltage ride-through control strategies during faults;

[0099] Stability criterion establishment module: use the phase plane method to analyze whether there is an equilibrium point in the inverter system, and establish the stability criterion of the inverter system under the quasi-steady state model of the inverter system;

[0100] Small-disturbance stability analysis module: In the case that there is a balance point in the inverter system during a fault, a small-signal model of the system is established to analyze the small-disturbance stability of the inverter system;

[0101] Inverter system sta...

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Abstract

The invention discloses an inverter stability analysis method for weak network far-mid end severe voltage drop and an inverter stability analysis system for weak network far-mid end severe voltage drop. AC power grid is Thevenin equivalent, and an inverter system quasi-steady-state model considering the typical low voltage ride through control strategy in the fault period is established; existenceof the balance point of the system is analyzed by using a phase plane method, and the inverter system stability criterion under the quasi-steady-state model is established; a system small signal model is established to analyze the system small interference stability under the condition that the balance point exists; and finally whether the inverter system is stable in case of far-end severe voltage drop is judged through combination of the stability criterion and small interference stability analysis. According to the method, the instability mechanism of the inverter accessed to the high impedance power grid in case of far-end severe voltage drop is analyzed from the perspective of big interference and small interference so that the theory is clear, and the method can be applied to inverter system stability analysis in case of far-end severe voltage fault of the new energy power station grid-connected system with the inverter acting as the interface.

Description

technical field [0001] The invention relates to an inverter of electric power equipment, in particular to a method and system for analyzing the stability of the inverter when the middle and far end of a weak network suffer severe voltage drop. Background technique [0002] As renewable energy such as photovoltaics and wind energy are connected to the power system in large quantities, it is proposed to have low-voltage ride-through capability for renewable energy generation to be connected to the grid at home and abroad. In addition, during the voltage drop period, the grid-connected guidelines require wind farms and photovoltaic power stations to inject reactive current proportional to the voltage drop to support the grid voltage, and the remaining capacity is issued in the form of active power to prevent large active power shortages in the grid And affect the system frequency stability. [0003] Grid-connected guidelines usually take the AC grid as a strong grid (that is, ...

Claims

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Application Information

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IPC IPC(8): H02J3/00H02J3/16H02J3/38
CPCH02J3/00H02J3/16H02J3/38H02J2203/20Y02E40/30
Inventor 徐谦辛焕海戴攀章枫
Owner STATE GRID ZHEJIANG ELECTRIC POWER COMPANY ECONOMIC TECHN INST