Search

• The limitation of the recent control methods (FCIN and FCOUT) are analyzed by analytical expressions. • The proposed method greatly improves the system stability, since it overcomes the limitation that the recent control methods do not consider the duty cycle perturbations. • The proposed method is simple and readily realized in the traditional control structure because it constructs an integrator and a high pass filter path outside the PLL. The interaction between the inverter and the grid in weak grids may produce resonances that lead to reduced power quality and instability concern. The recently proposed control methods based on eliminating disturbances in the control loop avoid the challenging control parameter design faced by the existing stability-enhancing control methods. They are effective to overcome the instability concern, but may not be able to maintain stable operation of the system in certain situations. Moreover, they affect the steady-state output current of the system under the fluctuation of the grid. This paper proposes a phase feed-forward method in the dq-frame to overcome the problems encountered by these control methods, such as duty cycle perturbation and grid phase jump. The proposed method constructs an integrator and a high pass filter path outside the PLL. It is simple and readily realized in the traditional control structure. Simulation and experimental results are presented to demonstrate the effectiveness of the proposed control method. [ABSTRACT FROM AUTHOR]

Synchronization with the grid voltage is critical in the control of grid-connected power converters. Under unbalanced grid condition, the conventional synchronous reference frame phase-locked loop (SRF-PLL) does not work well due to the effect of the fundamental negative sequence component. This paper proposes a new synchronization method, the sinusoidal amplitude integrator based phase locked loop (SAI-based PLL), to efficiently eradicate the effect of the fundamental negative sequence component. As a result, it can accurately and quickly estimate the amplitude and phase angle of the fundamental components of grid voltages in unbalanced grid conditions. In addition, when dc offset and harmonics are contained in the grid voltage, a multi-SAI-based PLL method is developed to extract the synchronization signal. The proposed SAI-based PLL incorporates the sinusoidal amplitude integrator into the conventional SRF-PLL. Its operation is analyzed using the complex-vector notation. Simulation and experimental results on the performance of the proposed SAI-based PLL and comparison with other synchronization methods are presented. [ABSTRACT FROM AUTHOR]

• A quasi-online condition monitoring technique for wind power converter is proposed. • This method enables concurrent health monitoring of power module and cooling system. • This approach does not need to measure the power loss and junction temperature. The power converter plays an important role in the energy conversion and management of wind turbine system. It is one of the core components in the system, but also one of the most prone to fail components according to industry-wide survey. Condition monitoring of power converter can improve the reliable operation of wind turbine system and reduce its unscheduled downtime. In this paper, a novel quasi-online monitoring technique based on the time-constants of heat sink temperature is proposed to check the health status of wind power converter. Advantages of the proposed technique include: (1) This approach enables the monitoring of power module degradation and cooling system deterioration in the converter simultaneously. (2) This method does not need to measure the junction temperature and power loss which reduces the cost and complexity of operation. Experimental tests were conducted to verify the effectiveness of this technique. Results also indicate that the maximum coefficient of variation of time-constants is below 1.7% under different converter operating conditions and ambient temperatures. In addition, the maximum error of time-constants in the application of condition monitoring is less than 3.1%. [ABSTRACT FROM AUTHOR]

• The relationship between the operating points, solar irradiance and cell temperature is analyzed. • A multivariable small signal admittance model considering the solar irradiance and cell temperature is built. • In order to analyze the PV system stability with the model, a novel stability analysis method is proposed. The method can obtain the system stability under all operating points at a time, whereas current analysis methods do not. • More accurate stability results are obtained due to consideration of PV cell temperature. In recent years, solar photovoltaic (PV) power technology has been applied widely. The interaction between the PV generator and the grid, however, may cause the stability issue and oscillation in practical applications. Hence it is very important to analyze the stability of grid-connected PV system. Due to the fluctuation of solar irradiance, the operating characteristics of the grid-connected system alter, and the grid-connected system shows different stability at the altered operating points. Therefore, it is vital to analyze the grid-connected PV system stability at all operating points in the entire operation range. The impedance-based analysis method is a useful tool for stability analysis of the system. However, since the operating point of the system often alters continuously, it is difficult to use conventional impedance/admittance model to characterize the system performance. To overcome this drawback, this paper attempts to incorporate the solar irradiance into the conventional PV generator admittance model and develops a multivariable small signal admittance model for PV generator. Moreover, the PV cell temperature influence is also considered in the model. Further, a new analysis method is proposed to enable the stability analysis. Simulation and experiment were conducted to demonstrate the effectiveness of the model and the stability analysis method. [ABSTRACT FROM AUTHOR]