North China Electric Power University

Tianshu Bi

Hao Liu

Ke Jia

Cheng Fang Wang

Guoyi Xu

Jiahao Liu

Sudi Xu

Qian Jack Liu

Zhiwei Yang

Bin Yang

Rui Zhang

Jie Lin

Zhe Yang

Cheng Wang

Rui Zhu

Congbo Wang

Yongzhao Lao

Muqing Yang

Zikang Li

Chenyu Ge

Liming Zheng

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

In this disclosure, the energy management problem of the D-LEGS with FFR is analyzed, so as to enhance the frequency stability of the main grid. The post-disturbance frequency response behaviors of both the main grid and the D-IEGS are precisely depicted, where the dead zones, limiting ranges and time constant of the governors are considered. The frequency regulation units of the D-IEGS include GTs and P2G units, whose impacts of providing frequency regulation service on the gas networks are quantified. Considering the time-scale similarity of the frequency dynamics and the dynamics of the GDN, the gas flow dynamics model is adopted. The frequency response dynamics of the GTs and P2G units, and the gas flow dynamics of the GDN, a variable-step difference scheme and a binary variable reduction method are devised.

Frequency regulation method using fast frequency reserve

A method implemented in a power grid including a DFIG wind turbine is provided. The method includes: assuming the DFIG wind turbine to be operated in a MPPT mode; generating a simplified transient model of the DFIG wind turbine, the simplified transient model including an equivalent circuit model, and an equivalent rotor motion model in a nonlinear form; linearizing the equivalent rotor motion model in the nonlinear form to be an equivalent rotor motion model in a linear form with respect to a steady-state operating point of the DFIG wind turbine; and determining a first contribution and a second contribution of the DFIG wind turbines to a post-disturbance frequency of the power grid, in a center of inertia (COI) frequency frame and in a frequency spatial variation frame, respectively, by incorporating the simplified transient model of the DFIG wind turbine into a frequency dynamics analysis.

System and method for stabilizing frequency of the power grid

Online estimation of area-level inertia can be used for frequency stability control in low-inertia power systems. This disclosure provides an area-level inertia online estimation method considering inter-area equivalent frequency dynamics. The disclosed method only needs one phasor measurement unit placed at any bus within each area. The inter-area equivalent frequency dynamics model for the multi-area power system is developed, which is employed to estimate area-level inertia under the small disturbance situation. Then, the area-level inertia estimation model boils down to a nonlinear parameter identification problem. The other boundary conditions of the disclosed method are derived by parameter identifiability.

Method and system for allocating optimal inertia in a power system

A method for primary frequency regulation (PFR)reserve procurement of a renewable energy power system is provided. The renewable energy power system includes synchronous power sources and renewable energy sources, and the renewable energy sources participate in frequency regulation using virtual synchronous machine (VSM) control. The method includes: aggregating generators in the synchronous power sources and renewable energy sources into an equivalent unit having an equivalent governor; based on the equivalent unit, determining system frequency dynamics of the renewable energy power system in a s-domain; transforming the s-domain to a time-domain equation for the system frequency dynamics in both over-damped and under-damped states; according to a first-order optimality condition of the time-domain equation, determining a time domain expression of frequency extremum; stabilizing system frequency of the renewable energy power system by adding a hyperplane based frequency stability constraint; and determining the PFR reserve procurement of the renewable energy power system.

System and method for controlling generators based on the procured capacities in response to power disturbance

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

An exemplary two-step method for power system inertia online estimation is described. The first step is to accurately estimate the POI-level aggregated inertia. The second step is to calculate the system-level inertia constant by weighting all the POI-level aggregated inertia and to monitor the inertia spatial distribution. In one example embodiment, the PMU is installed at POI, the frequency spatial difference is considered, and the mechanical power is carefully treated.

Estimation system for aggregated inertia in a power system

In this disclosure, the energy management problem of the D-IEGS with FFR is analyzed, so as to enhance the frequency stability of the main grid. The post-disturbance frequency response behaviors of both the main grid and the D-IEGS are precisely depicted, where the dead zones, limiting ranges and time constant of the governors are considered. The frequency regulation units of the D-IEGS include GTs and P2G units, whose impacts of providing frequency regulation service on the gas networks are quantified. Considering the time-scale similarity of the frequency dynamics and the dynamics of the GDN, the gas flow dynamics model is adopted. The frequency response dynamics of the GTs and P2G units, and the gas flow dynamics of the GDN, a variable-step difference scheme and a binary variable reduction method are devised.

Energy management of distribution-level integrated electric-gas systems with fast frequency reserve

Online estimation of area-level inertia considering inter-area equivalent frequency dynamics

Simplified transient model of DFIG wind turbine for power system frequency dynamics analysis

System and method of primary frequency reserve procurement of power systems considering multiple damping states and governor limiters

This disclosure provides a method to limit the post-disturbance node maximum RoCoF by optimizing UC decisions. The node initial RoCoF expressions under common disturbance types, including the load, the line switching, and the generator turbine disturbances, are derived. Then, the piecewise linear relationship between the node initial RoCoF and UC decision variables are obtained. To avoid numerical simulation of the node maximum RoCoF, two analytical constraints, i.e., the node initial RoCoF constraint and the COI maximum RoCoF constraint, are formulated in the UC model.

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Beijing, China

Tianshu Bi