Sharif Digital Repository

This paper proposes a control strategy for the autonomous (islanded) operation of a four-wire, electronically-coupled distributed generation (DG) unit which can feed a highly unbalanced load, e.g., due to the presence of single-phase loads. In the grid-connected mode, the power-electronic interface of the DG unit enables the exchange of real and reactive power with the distribution network, based on the conventional dq-frame current control strategy. The current control scheme is disabled subsequent to the detection of an islanding event, and the proposed controller is activated. The proposed control strategy utilizes: i) an internal oscillator to maintain the island frequency and ii) a... 

A methodology for controlling three phase PFC Sepic converter is presented, and behavior of the system is evaluated. The converter is connected in delta at the input and parallel at the output side, and is controlled by variable hysteresis current control method. By this approach, the current drawn by each of the individual converters is controlled to be in phase with its own input voltage. Detailed design criteria for the power and control stages of the single-phase SEPIC converter are presented and effects of this method on THD are verified  

CT saturation is a phenomenon that can cause inaccurate fault current measurement and may result in related protective relay failure to block the high current flow under a fault condition in a power system. Hence, it is required to develop a method to detect occurrence of CT saturation with a good accuracy under presence of noise in a power system. In this paper, a new method having the afore-mentioned characteristics is presented. The main benefit of exploiting the introduced approach here for detecting CT saturation is its high level of reliability as well as its reasonable operational speed in CT saturation detection. In other words, these two properties are implemented to this method.... 

Nowadays, Programmable Electronic AC Load (PEAL) is widely used to test various devices such as solar inverters, UPSs, filters, generators, and generally test all AC power and measuring devices. In this paper, Model Predictive Current Control (MPCC) is used for control of a programmable AC load. In each period, switching state that minimizes the cost function is selected and applied to the converter. Cost function is the square of the current components error. The effect of the horizon of prediction on the quality of the load current is investigated. To decrease the calculations burden, a limited search pool is used. Simulation results confirm that using two steps prediction horizon with... 

This paper investigates several current control methods for load balancing and power factor correction based on distribution Static Compensator (STATCOM). Two different configurations are considered for STATCOM; a three leg inverter, and three single phase inverters. It is assumed that the STATCOM is associated with a load that is remote from the supply. After a brief introduction, control structure based on PWM method and simulation results using PSCAD are presented. Next, the same system is simulated using hystersis control method. Both methods employ the instantaneous symmetrical components theory for load balancing and power factor correction. At the end, a comparison between two methods... 

We present a complete top-down design of a low-power multi-channel clock recovery circuit based on gated current-controlled oscillators. The flow includes several tools and methods used to specify block constraints, to design and verify the topology down to the transistor level, as well as to achieve a power consumption as low as 5mW/Gbit/s. Statistical simulation is used to estimate the achievable bit error rate in presence of phase and frequency errors and to prove the feasibility of the concept. VHDL modeling provides extensive verification of the topology. Thermal noise modeling based on well-known concepts delivers design parameters for the device sizing and biasing. We present two... 

This paper presents an effective current injection method for a single phase grid-connected PV inverter with LCL filter. The main objective of the proposed control strategy is to compensate the resonance effect of the LCL filter. In the proposed control strategy, a resonance compensator is augmented to the conventional proportional resonance (PR) controller to attenuate current oscillations in resonance frequency of LCL filter. The proposed strategy robustly regulates the output current of grid connected inverter in various grid impedances and provides a high quality current injection capability for the PV inverter in harmonic polluted condition of the grid voltage. The performance of the... 

In this paper, the Line-Modulated Fixed Off-Time method is used as the current control strategy for a Power Factor Corrector (PFC) pre-regulator. A zero voltage switching PWM (ZVS-PWM) auxiliary circuit is configured to perform ZVS in the switches. Soft commutation of the main switch is achieved without additional current stress. A significant reduction in the total conduction loss is achieved, since the circulating current for the soft switching flows only through the auxiliary circuit and a minimum number of switching devices are involved in the circulating current path .The proposed rectifier uses a single converter instead of the conventional configuration composed of a four-diode... 

This paper proposes a straightforward control method for voltage control of a three-phase transformer-based inverter in uninterruptible power supplies or distributed generation systems. The approach offers a dual-loop design consisting inner current control loop and outer voltage loop. Sliding mode current controller provides desired bandwidth for voltage controller which consists of a state feedback term for stabilization and resonant term for harmonic damping. The proposed scheme provides fast dynamic response and low total harmonic distortion even for high power inverters with the limitations of switching frequency and LC filter components. Experimental studies for 2KVA linear and... 

This paper presents a decentralized control strategy for the autonomous (islanded) operation of parallel connection of two distributed generation (DG) units. The DG units are electronically interfaced to the host grid at the same point of common coupling (PCC), where the local load is also supplied. In the grid-connected mode, the voltage-sourced converter (VSC) of each DG unit controls the exchange of real and reactive power components with the host grid, based on the conventional dq-current control strategy. In the islanded mode, one of the DG units provides voltage and frequency control for the island, and the other DG unit continues to operate with the pre-islanding dq-current control... 

DC-link voltage and output current control loops are two cascaded loops in the control structure of grid-connected inverters. A high DC-link voltage loop bandwidth (DCL-BW) provides more disturbance rejection capability for the control loop and is preferred from control system perspective. However, for stability issues, this BW is limited and must be sufficiently less than that of the current control loop. Among the different control schemes, instantaneous active reactive control (IARC) method provides the highest possible DCL-BW (i.e., 0.02 × switching frequency). Having this degree of freedom in the controller design, a proper methodology should be defined for selection of DCL-BW. In this...