Level Neutral Point Clamped Converter Research Articles

Direct-Switch Duty-Cycle Control of Grid-Connected n-Level Neutral-Point-Clamped Converter

Capacitor voltage imbalance is a well-recognized issue for neutral-point-clamped (NPC) converters. Hardware solutions increase the system cost and complexity, while existing software solutions generally involve sophisticated algorithms, making it difficult to extend them for more voltage levels and full power factor range. In this paper, a new control method, termed direct-switch duty-cycle control (DSDCC), is proposed and generalized for the grid-connected <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">n</i> -level NPC ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">n</i> L-NPC) converter. This method has the advantages of balancing the capacitor voltages for the full range of power factors on the ac side. The main significance of the DSDCC is that it can achieve near-optimal performance with simple and fast control implementation for two reasons. Firstly, the DSDCC is based on the model directly concerning switches' duty cycles, which can easily generate gating signals for the converter with only one carrier. Secondly, instead of searching for an optimal control solution, near-optimal switch duty-cycles are derived such that the controller design can be greatly simplified. The extremely fast execution time of the proposed control algorithm is only about 3% of that of model predictive control for 5-level NPC converters. Experimental results are included to validate the proposed method with a 5L-NPC converter.

Carrier-based Closed-loop DC-link Voltage Balancing Algorithm for Four Level NPC Converters Based on Redundant Level Modulation

Four-level neutral-point-clamped (NPC) multilevel converter topologies have been proposed and actively studied for low/medium voltage applications. As an inherent issue with these topologies, the voltage balancing of dc-link capacitors is challenging, especially when it operates as a single-end inverter/rectifier with high power factors and high modulation indexes. This article proposes a closed-loop voltage balancing algorithm that is effective and simple to implement with regular level-shifted carriers for a four-level NPC converter, e.g., a π-type converter. This approach is based on the redundant level modulation (RLM), which utilizes one additional voltage level in one switching cycle to gain extra controllability of the capacitor voltages without distorting/undermining the fundamental-frequency output voltage. An algorithm based on analytical expressions and logical operations is developed to achieve a dynamic closed-loop voltage balancing with RLM. The proposed method is effective over the full span of linear modulation indexes (M = 0 ~ 1.15) and power factors. The proposed algorithm is validated and evaluated in both simulations and experiments.

Analysis of grid connected hybrid renewable energy system

This paper proposes a DC-linked hybrid renewable energy system (HRES) connected to the grid through a three level neutral point clamped converter. The proposed structure consists of a wind generator (with Maximum Power Point Tracking (MPPT)), power limitation, and pitch control modes) with a flywheel energy storage system, a photovoltaic generator (MPPT and power limitation modes) with a battery, and a super-capacitor connected to each capacitor of the DC link of the three level converter. With the aim of managing the power flow between the HRES, the grid, and the variable load demand, we designed a power management strategy according to the global state of charge of the storage system, the weather conditions, and the load demand. In order to show the efficiency of the proposed structure and management algorithm, numerical simulation was performed using MATLAB/Simulink.

An effective IGBT driver circuit for three level neutral point clamped converters

This paper presents a low-cost IGBT driver circuit for a three-level neutral point clamped (3L-NPC) converters. The driver circuit is built with IR2110 with an external dead-time circuit based on Schmitt trigger. Originally, the IR2110 is designed to drive two switches of a half-bridge inverter in a complementary manner. Two IR2110 are used to drive one phase of the 3L-NPC converter. Each pulse leading edge is delayed for around ten microseconds to prevent the shoot-through phenomenon. The circuit manipulates the pulses generated from the digital controller is introduced in details. The low and high voltage side of the driver circuit are optically isolated. The proposed circuit design is experimentally tested its applicability for driving 3L-NPC converters is verified.

An effective IGBT driver circuit for three level neutral point clamped converters

An effective IGBT driver circuit for three level neutral point clamped converters

A New Backward Euler Stabilized Optimum Controller for NPC Back-to-Back Five Level Converters

This paper presents a backward Euler stabilized-based control strategy applied to a neutral point clamped (NPC) back-to-back connected five level converters. A generalized method is used to obtain the back-to-back NPC converter system model. The backward Euler stabilized-based control strategy uses one set of calculations to compute the optimum voltage vector needed to reach the references and to balance the voltage of the DC-bus capacitors. The output voltage vector is selected using a modified cost functional that includes variable tracking errors in the functional weights, whereas in classic approaches, the weights are considered constant. The proposed modified cost functional enables AC current tracking and DC-bus voltage balancing in a wide range of operating conditions. The paper main contributions are: (i) a backward Euler stabilized-based control strategy applied to a double, back-to-back connected, five level NPC converter; (ii) the use of cost functional weight varying as a function of the controlled variable tracking errors to enforce the controlled variables and to balance the DC capacitor voltages; and (iii) the demonstration of system feasibility for this type of converter topology and control strategy, ensuring a high enough computational efficiency and extending the modulation index from 0.6 to 0.93. Experimental results are presented using a prototype of a five level NPC back-to-back converter.

Исследование векторной ШИМ с различными таблицами переключения силовых ключей трехуровневого преобразователя

This paper addresses the study of three level neutral point clamped (NPC) converter based on different feasibility of space vector pulse wide modulation (SVPWM). This paper will review of a classical SVPWM technique with various switching sequences of the base space vectors (BSVs) within the range of sampling periods for three level NPC converters. The studies by mathematical modeling of the three level NPC converter and SVPWM technique in the Matlab/Simulink program were carried out. It was established that the increasing of switching sequence of the BSVs within the range of the sampling period can be used for decreasing of total harmonic distortional (THD). The THD diagrams of the various switching sequences of the BSVs within the different range of the sampling periods for the three level NPC converter are presented. The research results can be used to assess the electromagnetic compatibility (EMC) evaluation powerful three level NPC active rectifiers or inverters and select switching sequence of the BSVs within the range of the sampling period to minimize the THD voltage and current.

Multilevel Converters for Industrial Applications [Book News

This book first emphasizes the generalized multilevel converter topology with a common dc bus with its basic cell and then details the genesis of the neutral point clamped (NPC) topology and diode-clamped multilevel converters. It also includes the operation of the flying capacitor multilevel converter, the cascaded cell multilevel converter, and the hybrid asymmetric topologies. The book also covers state-of-the art multilevel modulation methods, including space vector modulation, the derivation of the boundary of voltage balancing in NPC multilevel converters, and the optimization of the dc capacitor voltage balance. Two case studies are included: 1) The application of cascade asymmetric multilevel converters in distribution static compensator (DSTATCOM) and 2) a medium-voltage induction motor (IM) drive using two back-to-back connected, five level NPC converters.

Operational limits of a three level neutral point clamped converter used for controlling a hybrid energy storage system

This work analyses the use of a Three-Level Neutral Point Clamped (3LNPC) converter to control the power flow of a Hybrid Energy Storage System (HESS) and at the same time interconnect it with the common AC bus of a microgrid.Nowadays there is not any storage technology capable of offering a high energy storage capacity, a high power capacity and a fast response at the same time. Therefore, the necessity of hybridising more than one storage technology is a widely accepted idea in order to satisfy the mentioned requirements.This work shows how the operational limits of the 3LNPC converter can be calculated and integrated in a control structure to facilitate an optimal use of the HESS according to the rules fixed by the user.