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Electrical resonance with the grid is an increasingly common problem for wind turbines and PV inverters, especially those connected to a weak grid. Such resonance problems can usually be solved by modifying turbine or PV inverter control to reshape its output impedance. There are, however, situations where this may not be effective or not feasible at all due to e.g. limitations in turbine design or...
A model predictive control system for delta-connected modular multilevel converter is proposed in this paper. The control system is based on offline computed optimal pulse patterns, which are modified online using model predictive control. Optimized pulse patterns facilitate the shaping of the grid current spectrum at low switching frequencies. Unlike conventional control methods with optimal pulse...
The series HVDC tap based on modular multilevel converter (MMC) has been proposed to provide power supply for rural places. However, most of current capacitor voltage balancing control strategies are not suitable for series MMC tap. In this paper, the principle of power transfer between phases, arms and sub-modules (SMs) in a series MMC are analyzed. A hierarchical capacitor voltage balancing control...
This paper proposes the modeling of single phase symmetric flying capacitor multilevel inverter (SFC-MLI) for Static synchronous compensator (STATCOM) application. The proposed topology is composed of cascade-connected five-level SFC modules. The linear current controller with phase shifted and phase disposition pulse-width modulation (PS-PD-PWM) base switching technique has been implemented. To takes...
In this paper reactive power compensation using an infinite level inverter based STATCOM is proposed. Nowadays, the society is becoming increasingly dependent on the electrical supply. New equipment's are more sensitive to power quality variations. This causes the transmission line to transfer equal or sometimes more than its capacity, which leads to overloading, voltage fluctuations etc. in the system...
In this paper, the effect of capacitor voltage ripple on current quality in a cascaded H-bridge (CHB) low-capacitance static compensator (LC-StatCom) with symmetrical I-V characteristics is investigated. Total harmonic distortion of the synthesized ac voltage of an H-bridge converter operating with different capacitor voltage ripples is evaluated for both inductive and capacitive operating modes....
In order to obtain an effective control range analysis method of different capacitor voltage balancing control strategies, this paper proposes a control range analysis method based on virtual loss difference resistance model. In this paper, the virtual loss difference resistance model is established on the submodules of cascaded converters. The control ranges of several conventional capacitor voltage...
A novel approach for mitigation of power quality issues have been presented in the paper. This paper introduces a Center-Point-Clamped AC-AC Buck-Boost Converter based power quality device for industrial and residential customers at the leaf end of the distribution network. This converter utilizes the principle of center-point-clamping to reduce the voltage stress on the power semiconductor switches...
This paper presents a comparison between two DC-voltage balancing strategies for cascaded star-connected multilevel STATCOM: zero-sequence voltage, and negative-sequence current control. Different levels of unbalance and grid strengths are considered. The impact of the control strategies on the convert ratings in terms of voltage and current requirements are compared and the operating range of the...
In this paper a comparative loss analysis between a cascaded H-bridge (CHB) low-capacitance static compensator (LC-StatCom) with symmetrical I-V characteristics and a conventional CHB StatCom is presented. Effect of the capacitor voltage ripples on switching and conduction losses are determined through theoretical analysis. Simulation-based analyses on a 350-VA three-cell CHB LC-StatCom system are...
This paper presents sequence impedance modeling and analysis of modular multilevel converters (MMC) in a single-star configuration for Static VAR Compensation (STATCOM) application. Prior work on impedance modeling of MMC has focused on the double-star configuration for high-voltage dc (HVDC) transmission applications. In the single-star configuration, each phase uses only a single arm of switching...
The voltage stability security is a very important and relevant issue in the modern power networks. The voltage instability can drive the system to a blackout. One of the methodologies to deal with this problem is analysing the trajectory sensitivity of the system. The STATCOM is an important hardware that is used to improve the voltage stability of an electric power network. The main objective of...
This paper aims to develop a coordinated controller to enhance the low voltage ride through (LVRT) performance of a permanent magnet synchronous generator (PMSG) based variable speed wind energy conversion system (WECS). This coordinated control comprises of a pitch angle control, a flux weakening control and a static synchronous compensator (STATCOM) control. The pitch angle control is adjusted to...
Static Synchronous Compensators (STATCOMs) have been applied for offshore wind power plants to satisfy the grid codes under both normal operation and grid fault conditions. This paper investigates the performances of two types of Modular Multilevel Cascade Converters (MMCC) for STATCOM applications, with the special focus on asymmetrical Low-Voltage-Ride-Through (LVRT) operation under grid faults...
A study assessing a wind farm's reactive power compensation system topology and the impact of priority of utilizing each component part thereof on electrical losses is presented here; the estimated losses were assessed over a period of 25 years at a typical onshore wind farm in the UK. STATCOM based hybrid solutions not only offer benefits of reduced initial CAPEX but they also offer substantial electrical...
This study investigates the cell voltages and arm currents in double-star modular multilevel converters (DSMMCs) based on power balance and current tracking control law. DSMMCs have been widely applied to static synchronous compensators, high-voltage direct-current transmission, back-to-back power transfer systems, wind/solar power generation and battery storage systems. The size of capacitors in...
This paper discusses the control strategy of DC-capacitor voltage in single-phase STATCOM with drastically reduced capacitance. Reduced capacitance results in a high amplitude of the capacitor voltage oscillation; therefore, the peak voltage control is important to keep the dimensional size of the capacitor compact. A good dynamic peak voltage estimation method has been proposed for the control. This...
A comparative analysis of efficiency of the time-delayed feedback for nonlinear dynamics control of composite power converters is carried out. In each case, the method efficiency is estimated both by the area of the desired dynamic mode in the space of two system parameters and by the critical value of the proportional controller gain. Dynamic modes maps are given for each type of a composite converter...
This paper, identifies a problem associated with the grid in order to supply power without any impurity and their solutions, particularly in terms of compensating the reactive power. The deviation in the system is computed and it is compensated using a STATCOM. Here the STATCOM is a five level cascaded H-bridge inverter controlled using level shift PWM technique modelled for three phase system. The...
STATCOM is reactive power compensator based upon a voltage source converter which uses power electronic devices with turn-off capability as switching devices. Its main function is to support bus voltage of which it is connected to the system by providing quick response to supply or absorb reactive power. For damping power oscillations purpose, it is required to employ power oscillation damping (POD)...
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