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The virtual impedance can suppress the low-frequency oscillation effectively caused by the power coupling effect for the grid-forming direct-drive permanent magnet synchronous generator (D-PMSG). However, there are few studies on the influence of virtual impedance on the subsynchronous oscillation caused by the interaction between the grid-forming D-PMSG and the weak grid. In this paper, the mechanism of virtual impedance improving the stability of virtual synchronous generator (VSG) control for the converter is revealed from the perspective of power coupling, and the influence of virtual impedance on the system stability in subsynchronous frequency range was analysed based on the sequence impedance model. The analysis results show that the virtual inductance cannot effectively improve the oscillation suppression effect, but the virtual resistance can greatly improve the damping characteristics of the system which has a good oscillation suppression effect. However, excessive increase in virtual resistance will cause power coupling oscillation, even subsynchronous oscillation, which shows limitations in subsynchronous oscillation suppression. To solve the problem, a dynamic voltage compensation control method based on active disturbance rejection control (ADRC) was proposed, and the parameters are designed by bandwidth method. The method can suppress the subsynchronous oscillation effectively in a certain frequency range under different grid strength and disturbance conditions. And it shows strong adaptability and good system robustness in weak grid. Finally, the effectiveness of the proposed oscillation suppression strategy was verified by time domain simulation. [ABSTRACT FROM AUTHOR]

To improve the voltage and frequency stability and suppress the voltage harmonics of a microgrid, a virtual synchronous generator (VSG) control strategy based on the harmonic current bypass control is proposed in this paper. First, a robust voltage control link is added to the virtual excitation component of the traditional VSG control strategy to reduce the amplitude error of the inverter's driving voltage caused by the reactive power-voltage droop coefficient. A harmonic current bypass control link is then used to adjust the inverter's voltage signal to reduce the total harmonic distortion of the microgrid. Finally, a simulation model of the microgrid is established using the MATLAB/Simulink software, and its stability is analyzed. In addition, the proposed control strategy is also compared with the traditional droop control and traditional VSG control strategies, focusing on the frequency instability and harmonic suppression performance of the microgrid. The numerical simulation results verified the effectiveness and superiority of the improved VSG control strategy proposed in this paper. [ABSTRACT FROM AUTHOR]

This paper shows a new manner to exploit the STM32F407 board in order to perform the processor in the loop (PIL) testing by reducing significantly the co‐simulation time. This method requires an FT232RL USB‐UART converter board as an external serial communication interface. The main advantage of this external device lies in the setting of its baud‐rate using the aliasing technique. This technique provides an efficient solution to transfer data between embedded board and computer at high baud‐rate. It allows speeding up the PIL testing and, therefore, makes it more flexible. The studied grid connected wind‐turbine system is based on permanent magnetic synchronous generator (PMSG) followed by back‐to‐back bidirectional converters. The grid side converter (GSC) ensures the DC bus voltage control as well as the unity power factor, while the machine side converter (MSC) ensures the PMSG speed control. The method of the decoupled current control is presented for the GSC. The optimum tip speed ratio (OTSR) algorithm–based maximum power point tracking (MPPT) technique is developed for MSC. Both power and control parts are initially designed and simulated in the same MATLAB/Simulink environment. Once the Simulink model behaves properly and meets the desired requirements, the proposed PIL test is then carried out. The C code is automatically generated from controllers and implemented on the STM32F407 board that acts as an external controller, meanwhile power part still works on the host computer. The PIL test results show the efficiency of the chosen control algorithms and dynamic behavior of the full wind‐turbine system. They also show that the controllers simulated under MATLAB/Simulink behave in the same way once executed on the embedded board. [ABSTRACT FROM AUTHOR]

With the increasing penetration rate of distributed renewable energy in power systems, the control strategy of virtual synchronous generator (VSG) is widely used for several years. Some existing VSG control strategies have been able to solve the stability problems caused by the abnormal grid voltage, but the effects of the inertia coefficient and the droop coefficient on the voltage stability are not taken into account. In order to further improve the voltage stability of the microgrid system, a voltage control strategy of VSG based on self-adaptive inertia coefficient and droop coefficient is proposed in this paper. When the voltage is far from the steady state, the increase of the inertia coefficient can decrease the voltage deviation. On the contrary, when it is close to the steady state, the decrease of the inertia coefficient can make the system response speed accelerate. According to the real-time voltage deviation, the droop coefficient can change adaptively to decrease the adjusting time and the voltage deviation during the disturbance. Finally, the simulation model of VSG is built by MATLAB/Simulink for conducting simulation experiments. Compared with other strategies, the correctness and effectiveness of the proposed control strategy are validated. [ABSTRACT FROM AUTHOR]

This paper presents a microgrid composed of photovoltaic (PV) array‐battery energy storage (BES) and a diesel generator (DG) set. A bidirectional DC–DC converter (BDDC) is used to integrate the BES to the DC link of the voltage source converter. The BDDC controls the voltage at the DC link to the output voltage of the maximum power point tracking (MPPT) controller, thereby PV array always operates at its maximum power point (MPP). Another function of the BDDC is to block the second‐order harmonic from the BES, when the microgrid is feeding with unequal loads in the three phases. The magnitude of DG set terminal voltages is regulated by an electronic automatic voltage regulator (AVR) that controls the excitation to the synchronous generator. A fast, accurate and oscillations‐less modified variable step size least mean square based adaptive control is used here for improving the power quality. The main features of this microgrid topology are the operation of the PV array at its MPP in all operating scenarios, regulation of DG set voltages, harmonics elimination, balancing of DG set currents and reactive power compensation for the unity power factor operation. [ABSTRACT FROM AUTHOR]

A new method for synchronous generator static excitation control is proposed in this paper, based on the PI controller and stabilizing feedback action. Compared with the existing solutions, this paper introduces improvements in the system's dynamic performance, robustness, and sensitivity in relation to noise, based on simplified control system structure modification. By introducing the stator voltage stabilizing feedback action, an improved level of dynamic performance is achieved, which also introduces an increased level of robustness. Furthermore, compared with sequential PID and lead-lag compensator based controllers proposed in related standards and technical papers, the system sensitivity in relation to the measurement noise is not compromised, since the differential control action is not included in the proposed controlling structure. The controller design procedure is performed by means of a frequency domain based technique, while its performance is verified by means of simulation and experimental test runs. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

In this paper, a synchronous generator excitation controller based on a novel feedforward control action is proposed. The main purpose of the new feedforward action is to enable a more robust excitation of the synchronous generator operating in varying operating conditions when connected to a power grid, for any superimposed stator voltage controller. Namely, the dynamic performance of the proposed controller is compared with a conventional proportional-integral (PI) controller, and with the PI controller combined with a feedforward action based on the direct component of the stator current. It is analytically shown that the novel controller improves the robustness when compared to 2 aforementioned solutions. Also, by simulation and experimental tests, it is shown that for the loaded synchronous generator, the novel controller, which is designed to have a similar response speed in open circuit as conventional controllers, exhibits up to 2 times faster dynamic performance. [ABSTRACT FROM AUTHOR]

The most common protection scheme for synchronous generators against stator windings fault is the differential protection scheme. In this paper, a new voltage-controlled overcurrent protection scheme is proposed as a backup protection method for the differential protection method. This scheme is designed to operate in conditions in which differential protection fails to do so and is implemented by fuzzy controllers. The fuzzy controllers set the plug setting of the overcurrent relay. In the proposed method, the fault conditions can be determined regardless of variations of voltage and the current of terminal in different operating states of the synchronous generator. This is realized by measuring not only the terminal voltages and currents of the generator, which are usually used in conventional voltage-controlled overcurrent protection schemes but also other variables that promote the accuracy of the proposed scheme. For presenting this protection method, a synchronous generator with internal fault model is used. The fault model is based on the direct-phase representation that uses the conventional and readily available machine data. Simulations for various types of stator faults of synchronous generator validate the proposed method. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]