Faults in electrical networks are among the key factors and sources of network disturbances. Control and automation strategies are among the key fault clearing techniques responsible for the safe operation of the system. Several researchers have revealed various constraints of control and automation strategies such as a slow dynamic response, the inability to switch the network on and off remotely, a high fault clearing time and loss minimization. For a system with wind energy technologies, if the power flow of a wind turbine is perturbed by a fault, the intermediate circuit voltage between the machine side converter and line side converter will rise to unacceptably high values due to the accumulation of energy in the DC link capacitor. To overcome the aforementioned issues, this paper used MATLAB simulations and experiments to analyze and validate the results. The results revealed that fault ride through capability with Supervisory Control and Data Acquisition (SCADA) viewer software, Active Servo software and wind sim packages are more adaptable to the variations of voltage sag, voltage swell and wind speed and avoid loss of synchronism and improve power quality. Furthermore, for protection purposes, a DC chopper and a crowbar should be incorporated into the management of excess energy during faults and a ferrite device included for the reduction of the electromagnetic field.

https://www.mdpi.com/1996-1073/13/16/4260/pdf

Fault Ride through Capability Analysis (FRT) in Wind Power Plants with Doubly Fed Induction Generators for Smart Grid Technologies

The present invention discloses an intelligent control method that a wind power plant participates in the primary frequency modulation and a control system thereof. The intelligent control method comprises the following steps of real-timely acquiring the power grid frequency of the high-voltage end of a wind power plant main transformer, determining whether the power grid frequency exceeds a set frequency dead zone, if the power grid frequency exceeds the set frequency dead zone, representing that the wind power plant needs to participate in the primary frequency modulation; calculating an active power superpose amount delta P needing to be adjusted; before the primary frequency modulation, calculating a draught fan target value Ptotal, and classifying the lists of the draught fans capableof participating in the modulation; according to the superpose amount delta P, making an adjusting cycle number needed by a frequency modulation task, then issuing the instructions of a first adjusting cycle to the wind turbine generator sets; monitoring the execution situations of the wind turbine generator sets, feeding back to an energy management platform, arranging a wind turbine generator optimal execution list to issue the instructions of a second adjusting cycle, and so on, finishing a primary frequency modulation task. According to the present invention, the instructions are issued in twice, the instructions at the first time are the tentative instructions, and by synthesizing the feedback information, the second time instructions are issued, so that the adjustment precision is higher.

Intelligent control method that wind power plant participates in primary frequency modulation and control system thereof

The invention discloses a power generator improvement frequency response characteristic-based robust zone wind power dispatching method. The method comprises the following steps of building an expression of a primary frequency response model having proportion and differential controller feedback; simplifying the expression according to Routh stability criterion; expanding the simplified expressionto a multi-power generator system, and obtaining a standard form of the primary frequency response characteristic of the power system; converting the standard form to time domain, deriving differencebetween a rotor rotational speed of the power generator and a synchronous rotational speed, and acquiring maximum frequency deviation of the multi-power generator system under the condition of disturbance; determining an optimization target and a constraint condition of a robust zone wind power dispatching model according to the improved frequency response characteristic of the power generator; and performing robust zone wind power dispatching on the power system according to the optimization target and the constraint condition. When wind power output abruptly fluctuates, the system frequencyfluctuation range can be enabled to be within a system safety limit all the way, and more wind power can be absorbed.

Power generator improvement frequency response characteristic-based robust zone wind power dispatching method

Effect of changes in wind turbine inertia on the stability of wind power plant under dynamic load conditions

The invention discloses an optimal control method and system for a voltage-source-type wind generation set. The constraint of the load and revolving speed are considered. The system comprises a voltage-source-type current transformer, an axis load optimal control ring, a revolving speed optimal control ring and a variable-speed variable-pitch control ring. The voltage-source-type current transformer outputs f to the axis load optimal control ring and outputs deltaTf, Pg and omegag to the revolving speed optimal control ring, the variable-speed variable-pitch control ring outputs Tgmd to the revolving speed optimal control ring, the revolving speed optimal control ring outputs Tgrd to an adding device and simultaneously outputs omegag to the axis load optimal control ring and the variable-speed variable-pitch control ring, the axis load optimal control ring outputs TBd to the adding device, and the adding device outputs Tgd to the voltage-source-type current transformer. According to the optimal control method and system, cooperation of the active power of a main control system and the current transformer of the voltage-source-type wind generation set is achieved, and the fault of the excessively high or low revolving speed is avoided. The load impact of a transmission chain shaft system of the voltage-source-type wind generation set under the disturbance work condition of the grid frequency is reduced.

Optimal control method and system for voltage-source-type wind generation set

The short-term frequency support will be provided through inertia control of doubly-fed induction generator (DFIG) wind turbines when grid frequency changes, so as to meet the grid frequency deviation requirements. In this paper, a novel inertia control strategy of DFIG wind turbines, which is based on slip feedback controller with incomplete differential PD algorithm, is proposed. Compared with the existing supplementary frequency differentiation inertia control and supplementary frequency proportion differentiation inertia control, the proposed control strategy can achieve better inertial response performance. A simulation model is built on to demonstrate the advantages of the proposed method, simulation result shows that the slip feedback inertia control strategy can more effectively restrain the grid frequency fluctuations with a smoother and shorter recovery process.

A Novel Inertia Control Strategy for DFIG Wind Turbines Based on Slip Feedback

The invention discloses an inertia control method for a double-fed wind turbine generator capable of improving the frequency inertia characteristic of a wind power grid-connected system based on virtual rotational inertia of a double-fed wind generator rotor, and belongs to the control technical field of new energy power generation. The inertia control method comprises the steps of enabling a frequency measured value to pass through a high-pass filter, then defining a transient state changing process of a slip ratio through proportion and differential links to be used as a reference value of a slip ratio feedback link; enabling a slip ratio feedback value to be compared with the slip ratio reference value to obtain a slip ratio deviation signal, and obtaining a rotor current q-axis component fine tuning value through an incomplete differential PD controller; and enabling the obtained fine tuning value to be overlaid to a rotor current instruction of an active power control ring, and performing adjustment on the active output of the wind turbine generator so as to realize inertia control. By adoption of the method, secondary fall off of power grid frequency can be avoided while the rotary speed recovery speed is high; and in addition, the frequency deviation amplitude and the changing speed after frequency disturbance can be effectively lowered, and the frequency stability of an electric power system can be improved.

Bofeng Xu

Papers

A Novel Inertia Control Strategy for DFIG Wind Turbines Based on Slip Feedback

Slip ratio feedback-based inertia control method for double-fed wind turbine generator