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Modular multilevel converter (MMC) is one of the recent developed converter for high power applications. However, the major drawback of this converter in variable speed drives is that the capacitor ripple voltage increases at lower speed, when the load torque remains constant. This ripple voltage can be reduced by reducing the dc-bus voltage at lower speeds, while the capacitor voltages are maintained...
For high PV penetration, grid ancillary services such as dynamic voltage support and low-voltage ride-through (LVRT) operation are recommended by network operators. This paper proposes an integrated controller for LVRT capability of a three-phase grid-tied PV system connected to a LV grid. Generally X/R ratio is low for LV grids, therefore the active power injection is given higher priority than the...
Cascaded multicell converter is proved to be an effective solution for medium voltage high power drives. Three-phase diode bridge rectifiers with complex transformer configuration are normally used in this converter, which do not have regenerative capability. Three-phase or single-phase pulsewidth-modulated (PWM) rectifiers are used at the front end to achieve regenerative capability and input power...
In this paper, two control strategies based on space vector modulation (SVM) technique are developed for a five-level current source converter (CSC) based STATCOM. In case of control strategy-1, DC-link currents are kept constant, and the reactive power is varied by changing the modulation index. On the other hand, in case of control strategy-2, DC-link currents are varied in accordance with reactive...
Cascaded H-bridge (CHB) converter is one of the popular solution for medium voltage transformerless static synchronous compensator (STATCOM) applications. The semiconductor devices of this converter are switched at low frequency. Therefore, conduction losses contribute to major part of the losses in this converter. To reduce the conduction losses, a cascaded U-cell (CUC) multilevel converter is derived...
Islanding detection is mandatory for grid connected inverter-based distributed generation systems. At present, there are passive, active, hybrid and communication based islanding detection techniques. The effectiveness of these methods depends on the Non-Detection Zone (NDZ), cost, complexity and degradation in inverter output power quality. This paper analyses various possibilities of active/reactive...
In this paper, a simple static var compensating scheme using a cascaded two-level inverter-based multilevel inverter is proposed. The topology consists of two standard two-level inverters connected in cascade through open-end windings of a three-phase transformer. The dc-link voltages of the inverters are regulated at different levels to obtain four-level operation. The simulation study is carried...
Most of the loads found in various commercial installations require front end ac-dc conversion. Various storage systems and renewable sources interact with these loads and the ac grid through dc-ac converters. These multistage conversions reduce system efficiency. To avoid this, an ac distribution system can be replaced by a dc distribution system within a commercial facility. It results in improved...
In this paper a new direct torque control method for doubly-fed induction generator (DFIG) based wind power generation system is presented. The angle and magnitude of rotor voltage are controlled to achieve independent control of electromagnetic torque and reactive power respectively. Space vector modulation is used to address the limitations, like variable switching frequency and torque ripple, of...
This paper presents a new direct torque control (DTC) method for doubly-fed induction generator (DFIG) based wind power generation system. The angle and magnitude of rotor voltage are controlled to achieve independent control of electromagnetic torque and reactive power respectively. Space vector modulation (SVM) is used to address the limitations, of variable switching frequency and torque ripple,...
A new scheme for a 4-level Static Compensator (STATCOM) integrating two 2-Level converters, supplying / absorbing reactive power to / from the grid is proposed in this paper. Reduced component count and simpler layout of switches are the attractive features of the proposed topology over the existing diode clamped multilevel converter. Furthermore, less number of dc links and smaller dc link capacitor...
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