Method for dc islanding detection based on positive feedback of bus voltage at specific frequency

Patent metadata

Field	Value
Publication number	US-2022011358-A1
Application number	US-202017429006-A
Country	US
Kind code	A1
Filing date	Jun 1, 2020
Priority date	Jul 1, 2019
Publication date	Jan 13, 2022
Grant date	—

Abstract

A method for a direct current (DC) islanding detection based on positive feedback of a bus voltage at a specific frequency, essentially including three steps: extraction of a specific frequency component of the bus voltage, injection of a disturbance component of the specific frequency, and determination of DC islanding. The extraction of the specific frequency component of the bus voltage and the injection of the disturbance component of the specific frequency constitute a positive feedback mechanism in a power management unit control loop. In a grid-connected mode of a DC grid, the positive feedback mechanism fails due to a control action of a voltage management unit on a bus, and the bus voltage remains stable. In an islanding mode of the DC grid, under an action of the positive feedback mechanism, the power management unit allows the bus voltage to generate a self-excited oscillation at the specific frequency.

First claim

What is claimed is:

1 . A method fora direct current (DC) islanding detection based on a positive feedback of a bus voltage at a specific frequency, comprising the following steps:
extraction of a specific frequency component of the bus voltage: collecting information of the bus voltage in real time and sending the information of the bus voltage to a bandpass filter by a power management unit in a DC system to obtain the specific frequency component of the bus voltage, wherein the bandpass filter is a unity gain resonance amplifier, and the specific frequency component is a resonance frequency of the unity gain resonance amplifier; injection of a disturbance component of the specific frequency: sending the specific frequency component of the bus voltage to a proportional amplifier to obtain the disturbance component, and superimposing the disturbance component on a converter control inner loop instruction value or superimposing the disturbance component on a converter control outer loop instruction value, and then forming the positive feedback of the specific frequency component of the bus voltage on a control loop of a converter, wherein a method for selecting the resonance frequency of the unity gain resonance amplifier comprises: a magnitude gain of a transfer function from the disturbance component to the bus voltage is represented by k 2 (f) in an islanding mode, the magnitude gain of the transfer function from the disturbance component to the bus voltage is represented by k 1 (f) in a grid-connected mode, a difference between the transfer function in the islanding mode and the transfer function in the grid-connected mode is defined as G=k 2 (f)−k 1 (f), and a frequency f 0 corresponding to a maximum value of G is selected as the resonance frequency of the unity gain resonance amplifier; and determination of DC islanding: determining whether the DC islanding occurs according to a variation trend of the specific frequency component of the bus voltage, determining that the DC system is operating in the islanding mode when the specific frequency component of the bus voltage continuous to increase and a number of sustained oscillation cycles exceeds a detection set value, or determining that the DC system is operating in the grid-connected mode when there is no specific frequency component in the bus voltage or the specific frequency component continuous to decrease, wherein the detection set value of the number of the sustained oscillation cycles in the determination of the DC islanding is three.

2 . The method according to claim 1 , wherein the step of superimposing the disturbance component on the converter control inner loop instruction value specifically comprises: superimposing the disturbance component on a current instruction value of a converter control inner loop to generate a new control instruction, and sending the new control instruction to a current control inner loop.

3 . The method according to claim 1 , wherein the step of superimposing the disturbance component on the converter control outer loop instruction value specifically comprises: superimposing the disturbance component on a power instruction value of a converter control outer loop to generate a new control instruction, and sending the new control instruction to a power control outer loop.

4 . The method according to claim 1 , wherein the step of superimposing the disturbance component on the converter control outer loop instruction value specifically comprises: superimposing the disturbance component on a photovoltaic port voltage instruction value of a photovoltaic converter control outer loop to generate a new control instruction, and sending the new control instruction to a photovoltaic port voltage control outer loop.

5 . The method according to claim 1 , wherein the step of superimposing the disturbance component on the converter control outer loop instruction value specifically comprises: superimposing the disturbance component on a torque instruction value of a fan converter control outer loop to generate a new control instruction, and sending the new control instruction to a torque control outer loop.

Assignees

• Univ Zhejiang

Inventors

• Li Wuhua
• Huang Qinghui
• Li Chushan
• Yang Heya
• Gu Xiaowei
• Chen Min
• Yang Huan
• He Xiangning

Classifications

• G01R31/00 Primary

  Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere ({measuring superconductive properties G01R33/1238;} testing line transmission systems H04B3/46; testing or measuring semiconductors or solid state devices during manufacture {H10P74/00}) · CPC title

• H02J1/12

  Parallel operation of DC sources having power converters with further DC sources without power converters · CPC title

• H02J1/106

  for load balancing, symmetrisation, or sharing · CPC title

• H02J1/102

  being switching converters (H02J1/108, H02J1/12 take precedence) · CPC title

• G01R19/2513 Primary

  Arrangements for monitoring electric power systems, e.g. power lines or loads; Logging · CPC title