Neutral-point Clamped Voltage Source Converter Research Articles

Commutation Behavior Analysis of a Dual 3L-ANPC-VSC Phase-Leg PEBB Using 4.5-kV and 1.5-kA HV-IGBT Modules

Three-level neutral-point clamped voltage source converter (3L-NPC-VSC) is widely used in high-power and medium-voltage (MV) applications and the most used multilevel VSC topology. 3L-Active-NPC-VSC (3L-ANPC-VSC) was introduced to overcome the unequal losses distribution as main structural drawback of the 3L-NPC-VSC. During the switching event of semiconductor devices, the stray inductance takes a special role in the commutation path of the switching current. Mutual coupling inductance between the components participating in the commutation path has to be considered for a theoretical assessment of the total stray inductance of each commutation path. Besides, the measurement of the commutation path stray inductance has to be carried out during the turn- on of the semiconductor device, instead of during the turn- off , to consider the reverse blocking voltage of the opposite switching semiconductor device. This paper shows how a dual 3L-ANPC-VSC phase-leg has been carefully designed and assembled to build a ±10 MVAr five-level VSC for MV-static synchronous compensator applications. The minimization of the stray inductance, the equalization of the total switching power losses for all commutation paths and power density maximization with snubberless operation are within the main technical design requisites. On the basis of the theoretical analysis, the stray inductance of all the commutation paths has been extracted, considering mutual coupling effect, by means of three-dimensional finite-element-analysis simulations. Once the design concept is theoretically validated, the estimated values have been compared with the experimental results obtained from the performance of double-pulse tests for each commutation path. This paper presents, for the first time, all the analysis details of the 3L-ANPC-VSC commutation behavior using 4.5-kV and 1.5-kA trench high-voltage insulated-gate bipolar transistor modules.

해상풍력단지에서의 PMSG 풍력발전기를 활용한 계통연계점 불평형 전원 보상

This paper proposes a control algorithm for permanent magnet synchronous generators with a back-to-back three-level neutral-point clamped voltage source converter in a medium-voltage off-shore wind power system under unbalanced grid conditions. Specifically, the proposed control algorithm compensates for unbalanced grid voltage at the PCC (Point of Common Coupling) in a collector bus of an off-shore wind power system. This control algorithm has been formulated based on symmetrical components in positive and negative synchronous rotating reference frames under generalized unbalanced operating conditions. Instantaneous active and reactive power is described in terms of symmetrical components of measured grid input voltages and currents. Negative sequential component of AC input current is injected into the PCC in the proposed control strategy. The amplitude of negative sequential component is calculated to minimize the negative sequential component of grid voltage under the limitation of current capability in a voltage source converter. The proposed control algorithm enables the provision of balanced voltage at the PCC resulting in the high quality generated power from off-shore wind power systems under unbalanced network conditions.

계통 불평형시 과도 응답 특성이 개선된 고압 이중여자 유도형 풍력발전 시스템의 제어 전략

【This paper investigates control algorithms for a doubly fed induction generator with a back-to-back three-level neutral-point clamped voltage source converter in a medium-voltage wind power system under unbalanced grid conditions. Negative sequence control algorithms to compensate for unbalanced conditions have been investigated with respect to four performance factors: fault ride-through capability, instantaneous active power pulsation, harmonic distortions, and torque pulsation. The control algorithm having zero amplitude of torque ripple indicates the most cost-effective performance in terms of torque pulsation. The least active power pulsation is produced by a control algorithm that nullifies the oscillating component of the instantaneous stator active and reactive power. A combination of these two control algorithms depending on operating requirements and depth of grid unbalance presents the most optimized performance factors under generalized unbalanced operating conditions, leading to a high-performance DFIG wind turbine system with unbalanced grid adaptive features.】

Dynamic Operation and Control Schemes for Static Synchronous Series Compensator

This paper deals with dynamic impedance compensation and control schemes for changes in load as well as change in line reactance in transmission lines. Static Synchronous Series Compensator (SSSC) designed to compensate the reactive power to the transmission line. Here SSSC uses Neutral Point Clamped (NPC) Voltage Source Converter (VSC) to generate three phase voltage waveforms. It can provide dynamic response by quickly changing the equivalent reactance (capacitive) to desired level of compensation. The paper discusses the performance characteristics of SSSC with the Direct and Indirect controllers. Modeling and simulation of the transmission line with NPC VSC based SSSC and its performance is evaluated.

Minimization of Active Power and Torque Ripple for a Doubly Fed Induction Generator in Medium Voltage Wind Power Systems under Unbalanced Grid Conditions

This paper investigates control algorithms for a doubly fed induction generator with a back-to-back three-level neutral-point clamped voltage source converter in medium voltage wind power systems under unbalanced grid conditions. Three different control algorithms to compensate for unbalanced conditions have been investigated with respect to four performance factors; fault ride-through capability, instantaneous active power pulsation, harmonic distortions and torque pulsation. The control algorithm having a zero amplitude of torque ripple shows the most cost-effective performance concerning torque pulsation. The least active power pulsation is produced by the control algorithm that nullifies the oscillating component of the instantaneous stator active and reactive powers. A combination of these two control algorithms depending on the operating requirements and the depth of the grid unbalance presents the most optimized performance factors under generalized unbalanced operating conditions leading to high performance DFIG wind turbine systems.

Wind power and hydrogen generation system with cooperatively controlled three‐level NPC‐VSC based energy capacitor

AbstractOne of the recent challenges for transmission system operators (TSO) or power grid companies is to smoothen the output power fluctuation of wind generator due to the random variation of wind speed. In addition to the output power fluctuation of fixed‐speed wind turbine generator system (WTGS), it suffers greatly from terminal voltage fluctuation. The fixed capacitor bank connected to its terminal cannot maintain constant terminal voltage under randomly varying wind speed. On the other hand, besides the continuous growth of wind power, hydrogen generation system is also becoming very popular nowadays using the electrical energy from wind power plants. This study proposes a three‐level neutral point clamped voltage source converter (NPC‐VSC) based energy capacitor system (ECS), composed of electric double layer capacitor (EDLC) and power electronic converters, to smoothen output power and terminal voltage fluctuations of grid connected fixed speed wind farm. A simple low pass filter (LPF) is adopted in this study to generate the power reference of ECS. Another salient feature of this study is the generation of hydrogen by using wind generator output power. Effective topology of wind power and hydrogen generation system with cooperatively controlled NPC‐VSC based ECS is proposed from the cost and performance points of view. Copyright © 2009 John Wiley & Sons, Ltd.

Control electronic platform based on floating-point DSP and FPGA for a NPC multilevel back-to-back converter

Modern energy concepts as Distributed Power Generation are changing the appearance of electric distribution and transmission and challenging power electronics researchers, which try to develop new solutions of electronic controllers. The aim is to enable the implementation of new and more complex control algorithms to verify the last standards related to the grid energy quality for new power converters, and, also, for equipments which nowadays are operating. This paper presents the design, implementation and test of a novel real-time controller for a Neutral Point Clamped (NPC) (three-level) multilevel converter based on a floating-point Digital Signal Processor (DSP) and on a Field-Programmable Gate Array (FPGA), by operating in a cooperative way. Although the proposed system can be readily applied to any power electronic application, in this work, it is focused on the next system: a 150 kVA back-to-back three-level NPC Voltage Source Converter (VSC) for wind power applications.