North China Electric Power University

Ke Jia

Tianshu Bi

Hao Liu

Qian Jack Liu

Bin Yang

Cheng Fang Wang

Zhe Yang

Cheng Wang

Liming Zheng

Rui Zhu

Zhiwei Yang

Congbo Wang

Zikang Li

Tianshu Bl

Yanbin Li

Qixun Yang

A method for analytically studying fault responses of an inverter-interfaced renewable energy source (IIRES). The IIRES includes a decoupled sequence control (DSC) system, and the DSC system includes a converter, a current controller, a low-voltage ride-through (LVRT) control unit, and positive and negative sequence components calculation (PNSCC) structures. The method includes: determining a detailed fault model of the IIRES; determining a unified model of the PNSCC structures; determining a simplified fault model of the IIRES in a fault detection phase; determining a simplified fault model of the IIRES in a control transient response (CTR) phase; detecting a short-circuit fault; cutting off an outer loop of the DSC system; switching the DSC system to a current control mode through the LVRT unit by the current controller; analyzing the short-circuit fault; and designing an enhanced fault-ride-through control of the IIRESs to suppress an inrush current to protect the IIRES.

Short-circuit fault detection method for a power grid

A method for protecting a power system having inverter-interfaced renewable energy sources is provided. The power system includes an inverter and a control system. The control system includes a current controller including a saturation limiter and a proportional and integral (PI) controller, a phase-locked system, and a low-voltage ride-through (LVRT) control unit. The method includes: by using a Park transformation matrix, determining an output voltage of the inverter; determining a modulated voltage of the output voltage; upon detecting a grid fault, obtaining current references by the LVRT control unit; determining a fault current in a first stage of a transient phase of the grid fault; determining a fault current in a second stage of the transient phase; determining a fault current in a third stage of the transient phase; and switching the control system to a fault control mode by tracking the fault currents in the first, second and third stages, to the current references.

Power frequency line protection procedure

System and method of fault analysis of inverter-interfaced renewable energy source considering decoupled sequence control

A method for protecting a power system having inverter-interfaced renewable energy sources is provided. The power system includes an inverter and a control system. The control system includes a current controller including a saturation limiter and a proportional and integral (PI) controller, a phase-locked system, and a low-voltage ride-through (LVRT)control unit. The method includes: by using a Park transformation matrix, determining an output voltage of the inverter; determining a modulated voltage of the output voltage; upon detecting a grid fault, obtaining current references by the LVRT control unit; determining a fault current in a first stage of a transient phase of the grid fault; determining a fault current in a second stage of the transient phase; determining a fault current in a third stage of the transient phase; and switching the control system to a fault control mode by tracking the fault currents in the first, second and third stages, to the current references.

System and method of protecting power system having inverter-interfaced renewable energy sources

A synchrophasor measurement-based disturbance identification method is described considering different penetration levels of renewable energy. A differential Teager-Kaiser energy operator (dTKEO)-based algorithm is first utilized to improve multiple-disturbances detection accuracy. Then, feature extractions via the integrated additive angular margin (AAM) loss and the long short-term memory (LSTM) network is described. This enables one to deal with intra-class similarity and inter-class variance of disturbances when high penetration renewable energy occurs. With the extracted features, a multi-stage weighted summing (MSWS) loss-based criterion is described for adaptive data window determination and fast disturbance pre-classification. Finally, the re-identification model based on feature similarity is established to identify unknown disturbances, a challenge for existing machine learning algorithms.

Synchrophasor measurement-based disturbance identification method

A data-driven PMU bad data detection algorithm based on spectral clustering using single PMU data is described. The described algorithm does not require the system topology and parameters. First, a data identification method based on a decision tree is described to distinguish event data and bad data by using the slope feature of each set of data. Then, a bad data detection method based on spectral clustering is described. By analyzing the weighted relationships among all the data, this method can detect the bad data that has a small deviation.

PMU date correction using a recovery method

Fast power system disturbance identification using enhanced LSTM network with renewable energy integration

Bad data detection algorithm for PMU based on spectral clustering

The wide application of power electronic components in power systems with renewable energy sources has changed the fault characteristics of conventional power systems, resulting in the performance degradation of conventional protections. To solve these problems, a novel principle of pilot protection based on structural similarity and square error criteria is provided. The structural similarity criterion utilizes the difference of fault characteristics between renewable sources and synchronous generators to identify internal faults, and the square error criterion is used to solve abnormal calculation of the conventional similarity based protection. Compared with conventional differential protections, the disclosed protection shows excellent performance in speed and reliability during various faults.

Renewable power transmission line using the square error method

A sparse voltage measurement-based fault location determination system and method for an alternating current (AC) distribution network is described. This method can use sparse voltage measurements and Bayesian compressive sensing (BCS) algorithm to reconstruct a sparse current vector. A fault location is then determined based on the reconstructed sparse current vector. The disclosed method provides robust fault location results under a variety of asymmetrical fault scenarios. Fewer intelligent electronic devices (IEDs) allocated in the terminal buses are needed for determining the fault location; therefore, this implementation is relatively cost effective.

Alternating current distribution network with a sparse voltage measurement-based fault location determination system

A DC collection system for a PV power plant contains a large number of feeders. When a fault occurs, the fault current rapidly increases, causing electronic devices to block to protect themselves. This blockage presents a challenge to the protection of the DC collection system because of extremely short data windows. To address this challenge, a protection method based on active control of DC/DC converters is disclosed. The fault current control principle is analyzed and derived so that DC/DC converters can provide an injected low-amplitude and controllable post-fault stable current signal. The disclosed protection method is designed based on identifying the direction of the injected signal. Simulation results indicate that the fault section can be accurately identified and that the disclosed protection method performs efficiently against transition resistance and noise.

Flexible direct current system of photovoltaic plant having active control-based protection system

A distance protection system and method based on a high-frequency fault component is provided for a renewal energy source (RES) system. The voltage drop caused by a fault has a full frequency of components and this can be extracted by a wavelet transform. A frequency selection principle that renders high-frequency impedance models a stable impedance phase angle is determined. On this basis, internal and external faults with respect to a transmission line are determined by comparing the magnitude of a high-frequency operating voltage with the magnitude of a high-frequency voltage at the fault point. This disclosed protection system and method can eliminate the influence of frequency offset and weak feed of the RES system by using high-frequency signals generated by voltage drops at the fault point, and can also tolerate signal noises and fault resistance.

Renewable energy source system having a high-frequency fault component based distance protection system

System and method of sparse voltage measurement-based fault location determination using intelligent electronic devices

Structural similarity based pilot protection method and system for renewable power transmission line

A detection and location-based active protection method for flexible DC distribution systems with multi-terminal distributed photovoltaic sources is disclosed. The disclosed protection method actively utilizes the coordinated control between local protection and the converters in the DC distribution system. The converter can then be modified to become an injection source with characteristic signal, providing a known fault signal to build a clear protection boundary. The disclosed protection method can distinguish the correct faulted area by calculating the harmonic impedance of the characteristic signals. Compared with existing DC protection techniques, this disclosed method does not require additional injection equipment and modification of the DC distribution system configuration, nor does it need high data sampling frequency. The disclosed technique is also unaffected by measuring noise and cable-distributed capacitance. The disclosed protection method is therefore feasible for industry application in a large and complex DC network.

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Beijing, China

Ke Jia