DC-Link Neutral Point Control for 3L-NPC Converters Utilizing Selective Harmonic Elimination PWM

Selective harmonic elimination–pulsewidth modulation (SHE–PWM) is a modulation technique widely used to improve the efficiency and harmonic content in medium-voltage high-power converters. Among these converters, the three-level neutral-point-clamped (3L-NPC) converter is one of the most utilized topologies. However, the 3L-NPC converter requires a proper balancing of dc-link capacitor voltages. This article presents a control technique, based on pulse shifting method, to regulate the neutral point voltage when SHE-PWM is utilized. The proposed technique performs well with any power factor and it can also be directly applied to T-type converters and easily extrapolated to other multilevel topologies. The proposed method is experimentally validated in a scaled-down power converter and a full-scale medium-voltage 3L-NPC converter

DC-link Voltage Balancing Strategy based on SVM and Reactive Power Exchange for a 5L-MPC Back-to-Back Converter for Medium Voltage Drives

The reduced capability of multilevel converters with more than one intermediate node to balance the dc-link capacitors voltage, as well as the lack of standard modulation methods to improve their balancing performance, makes these converter topologies unattractive for real power applications. This is especially true when the load demands active power. One of these topologies is the five-level multipoint clamped (5L-MPC) converter. The back-to-back (B2B) configuration of two 5L-MPC converters and the use of a space vector modulation (SVM) that exploits the voltage balancing capability of the redundant switching vectors extend the operation conditions range in which a proper voltage balance can be achieved. However, if practical modulation restrictions are considered (limitation of voltage steps, dead times, switching losses, etc.), the voltage balance cannot be achieved for all operation conditions. In this paper, an SVM which takes into account practical restrictions is proposed. In order to guarantee the voltage balance at any operation condition, the grid-side rectifier exchanges reactive power with the grid-side LCL filter. Thus, the voltage balance of the dc-link is guaranteed while a unity grid-side power factor is achieved. The proposed modulation scheme and the voltage balancing strategy are experimentally validated in a 6.6 kV 1.5 MW 5L-MPC B2B converter

Simple voltage balancing method to protect series-connected devices experimentally verified in a 5L-MPC converter

This paper presents a solution for the voltage balance problem of the series-connected devices that can be applied to multilevel converters in which the series-connected devices need to block twice their switched voltage. The solution is based on two ideas, the control of the switching commands to achieve proper switching losses balance and the use of additional circuitry to achieve proper voltage balance during their blocking state. The proposed strategy is experimentally validated into a 5-level multipoint clamped full-scale converter. However, it can be used in any other converter topology in which the devices need to block twice their switched voltage

Comprehensive analysis of voltage balancing techniques for 5L NPC converters

The reduced capability of the 5L-NPC Inverter to balance the voltages of the four DC-bus capacitors makes this converter unattractive for real power applications. This is especially true if the load demands active power. The Back-to-Back (B2B) configuration of two 5L-NPC converters and the use of a Space Vector Modulation (SVM) that exploits the voltage balancing capabilities of the redundant switching vectors, extend the operating conditions range in which a proper voltage balance can be achieved. However, if practical modulation restrictions are considered (limitation of voltage steps, dead times, switching losses, etc.) the voltage balance cannot be achieved for all operation conditions. This paper introduces the main restrictions that should be considered for the 5L-NPC modulation strategy. The voltage balancing limits of the proposed SVM scheme are shown and additional considerations to improve the voltage balancing capability are proposed and evaluated

Medium voltage-high power converter topologies comparison procedure for a 6.6kV Drive Application using 4.5kV IGBT Modules

This paper presents a general comparison procedure for medium voltage - high power multilevel converter topologies and semiconductors, which is mainly based on analyzing the performance limits of the converters output characteristics such as the output voltage, current, active power, efficiency, etc. Afterwards, the general procedure is applied to compare some of the most relevant converter topologies oriented to a 6.6 kV drive application supplying quadratic torque loads and using 4.5 kV IGBT modules. The paper concludes evaluating the comparison factors of the different converter topologies and selected semiconductors obtained by the proposed procedure. The proposed procedure can potentially be extrapolated to any desired application framework

Impact of silicon carbide devices in 2 MW DFIG based wind energy system

Renewable energies are going through a major increment, mainly wind and photovoltaic energies, being market competitiveness the main driver for their massive penetration. As power converters are used to interface renewable energy systems with the utility grid, their optimization is crucial. For their superior conduction and switching capabilities, silicon carbide (SiC) semiconductors are considered for their use in the optimization of power electronics in doubly fed induction generator (DFIG) based wind energy systems (WES). Potential efficiency gain and volume reduction due to the use of SiC semiconductors are studied by simulation, explaining the models in detail. Commercial products are evaluated to calculate cooling systems (CS) and output filters volumes. The performance and volume of SiC converter is analyzed and compared to its Si counterpart, at different wind speeds and switching frequencies. A design for maximum efficiency and minimum CS volume, and another for minimum output filters volume without efficiency penalty are achieved. A switching frequency optimization is performed to obtain the minimum combined volume between the CS and output filter, still improving the Si converters efficiency at nominal wind speed conditions. The conclusion is that SiC semiconductors can improve the power converters efficiency and overall size in DFIG WES

System Level Optimization of 5 MW Wind Converter using 3L-NPC Topology in Medium Voltage with 1 . 7 kV IGBT

Market competitiveness is the main driver in the massive adoption of wind energy, and the optimization of the power converter is crucial for this purpose. Because it has higher efficiency than the two level Voltage Source Converter (2L-VSC), the three level Neutral Point Clamped (3L-NPC) topology is considered for the converter optimization. Due to reduced voltage stress in 3L-NPC, the system voltage can be increased up to Medium Voltage while keeping the same 1.7 kV semiconductors used for 2L-VSC. Potential extra efficiency due to the increased voltage, cooling system and filter volume reduction are studied by simulation. Commercial cooling systems and capacitors are analyzed to calculate volumes, while analytical expressions are used for the inductors. A system level optimization is proposed achieving filter and combined volume reduction, as well as efficiency increment. The benefits of using three level converters to increase the application voltage, without increasing the semiconductors voltage range are shown at system level

Electric Vehicle Inverter Electro-Thermal Models Oriented to Simulation Speed and Accuracy Multi-Objective Targets

With the increasing demand for electric vehicles, the requirements of the market are changing ever faster. Therefore, there is a need to improve the electric car’s design time, where simulations could be an appropriate tool for this task. In this paper, the modeling and simulation of an inverter for an electric vehicle are presented. Four different modeling approaches are proposed, depending on the required simulation speed and accuracy in each case. In addition, these models can provide up to 150 different electric modeling and three different thermal modeling variants. Therefore, in total, there were 450 different electrical and thermal variants. These variants are easily selectable and usable and offer different options to calculate the electrical parameters of the inverter. Finally, the speed and accuracy of the different models were compared and the obtained results presented

SiC erdieroaleak energia eolikoan LCoEa hobetzeko

This research identifies the wind energy as the main renewable source. In order to improve its LCoE, SiC semiconductors are proposed, together with different voltage levels and topologies. After analyzing various configurations, two that improve current LCoE are found. The first considers current cost of SiC, and uses a two level topology, achieving little improvement. The second considers the expected cost reduction of SiC due to technological maturity, and it is shown that a three level NPC is the best topology, with higher LCoE improvement.Ikerketa honetan energia eolikoa energia berriztagarri nagusi bezala identifikatzen da. Beraren LCoEa (Levelized Cost of Energy ingelesez) hobetzeko, SiC erdieroaleak proposatzen dira, baita tentsio maila eta topologia berriak ere. Konfigurazio ezberdinak aztertzen dira, LCoEa hobetzen duten bi aurkituz. Lehenengoak, gaur egungo SiC-en kostua kontuan izanik bi mailako topologia erabiltzen du, hobekuntza txikia lortuz. Bigarrenean, teknologiaren heldutasunagatik iritsiko den kostu jaitsiera aurre ikusten da, eta hiru mailako NPC (Neutral Point Clamped ingelesez) topologia erabiltzea dela onena ikusten da, LCoE hobekuntza handia lortuz