Three-level Active NPC Research Articles

Design and Modeling of Low-Inductive Busbars for a Three-Level ANPC Inverter

Laminated busbars are extensively used to connect components in hard-switched power inverters due to their low stray inductance. The objective of this paper is to demonstrate the design procedure and modeling of laminated busbars of a three-level three-phase Active Neutral Point Clamped (ANPC) inverter, with special emphasis placed on ensuring low stray inductance at an early design stage. In the paper, the partial inductances of the busbars are estimated using an ANSYS Q3D software tool. The stray inductance of the commutation loops is determined analytically and by cosimulation with ANSYS Simplorer and Q3D. Cosimulation allows analysis of the influence of the stray inductance on the performance of the inverter. The modeling results show that the laminated busbars proposed in this paper have low stray inductance. The stray inductances of the commutation loops were measured before the inverter is assembled to verify the modeling results. The approach used reduces the need for late-stage modifications based on prototype testing

Hybrid Seven-Level Cascaded Active Neutral-Point-Clamped-Based Multilevel Converter Under SHE-PWM

This paper presents the hybrid seven-level cascaded active neutral-point-clamped (ANPC)-based multilevel converter. The converter topology is the cascaded connection of a three-level ANPC converter and an H-bridge per phase. The voltage of the H-bridge is actively maintained to the required level through selection of the switching states of the converter. The topology is operated under selective harmonic elimination pulsewidth modulation (SHE-PWM), maintaining the switching frequency of the converter to a minimum. The operating principles, voltage balancing methods, and limitations of the converter are analyzed together with extensive simulation results of the topology. Experimental results from a low-power laboratory prototype are presented that verify the operation of the hybrid converter under SHE-PWM.

Loss Analysis of Three-Level Active Neutral Point Clamped Converter under Fault Tolerance Operation

Compared with traditional three-level neutral-point-clamped (NPC) converter, the recently proposed three-level active NPC (ANPC) converter has the ability to overcome the unbalanced loss distribution, and therefore result in increased output power or switching frequency. In industrial applications, fault tolerance ability of power converters is very important considering system availability, safety and reliability. This paper introduced the control schemes to get stable and continuous output under single device fault for both open-circuit and short-circuit fault cases. By analyzing the phase relationship of reference voltage and load current, the loss calculation method under fault tolerant operation was proposed. Calculation results show that the devices junction temperatures under fault tolerant operation are within the safe operation area (SOA) even they are a little bit higher compared to normal operation, which also confirm the effectiveness of the fault tolerant control schemes.

New Junction Temperature Balancing Method for a Three Level Active NPC Converter

SummaryThe three-level Neutral Point Clamped Voltage Source Converter (3L-NPC VSC, 3L-ANPC VSC) has many attractive features like its high reliability and availability. Nowadays, this technology is mature and can be found in several industrial applications [1], [2]. Some common applications are pumps, fans, compressors, mixers, extruders, crushers, rolling mills, mine hoist drives and excavators.The three-level Active NPC VSC (3L-ANPC VSC) was introduced in 2001 to overcome the drawbacks of the conventional 3L-NPC VSC [3]. The 3L-ANPC VSC includes additionally active switches parallel to the NPC diodes for clamping the neutral tap of the converter. It features 3 extra switch states in contrast to the conventional 3L-NPC VSC, which enable the possibility to reduce the temperature imbalance and/or to increase the output frequency or the converter power. In order to use the potential of the 3L-ANPC VSC and to balance the losses among the semiconductors, the implementation of a temperature balancing strategy is necessary [4] and [5].The medium voltage 3L-ANPC VSC is especially advantageous in the following applications:– High power applications, where the required output power cannot be archived without a serial/parallel connection of devices.– Medium voltage converters, where the switching frequency should be increased without decreasing the converter power (e.g. applications which require a sine filter or high speed applications).– Applications where the nominal converter current is required at low modulation index and low fundamental frequencies (e.g. zero speed operating points, hot and cold rolling mill applications, converters for doubly fed induction generators, etc.).The starting point for the derivation of the new balancing algorithm was the Active Loss Balancing (ALB) system, which is reported in [4] and [5]. The new temperature balancing scheme profits from the features of Predictive Control [6] in order to precalculate the conduction and the switching losses and finally the temperature of each semiconductor up to the future commutation to the zero state, i.e. over the next period of the switching frequency. The precalculated maximal junction temperature will be used for the control strategy in order to determine the optimal switch state to be applied.Some additional features of the new balancing algorithm with respect to the ALB algorithm are: consideration of the conduction losses fed into the balancing algorithm, regard of the temperature ripple between two consecutive commutations and the use of a control criteria (cost function) in the selection of the zero state [6]. The algorithm is implemented in Matlab and compared with the 3L-NPC VSC using experimental data of a 4.5 kV Press-pack IGBT and Diode for the calculation of the losses. The comparison shows a potential to increase the output power of the 3L-ANPC VSC.

Analysis and Design of Active NPC (ANPC) Inverters for Fault-Tolerant Operation of High-Power Electrical Drives

Compared with neutral-point-clamped (NPC) inverters, active NPC (ANPC) inverters enable a substantially increased output power and an improved performance at zero speed for high-power electrical drives. This paper analyzes the operation of three-level (3L) ANPC inverters under device failure conditions, and proposes the fault-tolerant strategies to enable continuous operating of the inverters and drive systems under single and multiple device open- and short-failure conditions. Therefore, the reliability and robustness of the electrical drives are greatly improved. Moreover, the proposed solution adds no additional components to standard 3L-ANPC inverters; thus, the cost for robust operation of drives is lower. Simulation and experiment results are provided for verification. Furthermore, a comprehensive comparison for the reliability function of 3L-ANPC and 3L-NPC inverters is presented. The results show that 3L-ANPC inverters have higher reliability than 3L-NPC inverters when a derating is allowed for the drive system under fault-tolerant operation. If a derated operation is not allowed, the two inverters have similar reliability for device open failure, while 3L-NPC inverters have higher reliability than 3L-ANPC inverters for device short failure.

Generalisation of flying capacitor-based active-neutral-point-clamped multilevel converter using voltage-level modulation

A generalised n-level flying capacitor (FC)-based active-neutral-point-clamped (ANPC) voltage source converter is discussed in this study. The converter is based on the arrangement of a three-level ANPC cell and a number of two-level cells creating an n-level line-to-neutral voltage waveform. The converter is operated under a phase-shifted carrier (PSC) pulse-width modulation (PWM) technique. The mathematical model for the DC-link capacitors' voltage behaviour of the three-phase converter is also presented. It is shown through simulations that the voltage of the FCs can naturally balance to the required level to generate the required waveforms. Selected results are included in the study to support the analysis. Moreover, experimental results taken from a single-phase seven-level FC-based ANPC converter prototype are also presented to verify the theoretical considerations.

Hybrid Flying-Capacitor-Based Active-Neutral-Point-Clamped Five-Level Converter Operated With SHE-PWM

A five-level flying-capacitor (FC)-based active-neutral-point-clamped (ANPC) converter is an arrangement of a three-level ANPC converter and a two-level cell. In this paper, a control strategy is proposed to regulate the voltage across the FCs at their respective reference voltage levels by swapping the switching patterns of the switches based on the polarity of the output current, the polarity of the FC voltage, and the polarity of the fundamental line-to-neutral voltage under selective harmonic elimination pulsewidth modulation. The voltage across the FCs and the dc-link capacitors are simultaneously controlled at their reference voltage levels. The proposed control strategy is applied using power system computer aided design/electromagnetic transients including dc on a static synchronous compensator operating under a power-factor-correction mode to verify its performance. Experimental results are also presented for low and high number of angles per quarter period using a low-power laboratory prototype.

Feedforward Loss Control of Three-Level Active NPC Converters

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> The three-level neutral-point-clamped voltage-source converter (NPC VSC) is widely used in high-power medium-voltage (MV) applications. To overcome its major drawback—the unequal loss distribution among the semiconductors—the use of active NPC (ANPC) switches was previously proposed. In this paper, a simple feedforward loss-control scheme for the ANPC converter is presented. The principle of operation of the ANPC VSC is experimentally verified for the first time. Electrical measurements on a low-voltage test bench prove the proper function of the ANPC converter. Infrared junction temperature measurements confirm the improved loss distribution using the new loss-control scheme. Finally, the authors demonstrate the superior performance of the loss-controlled ANPC converter in various MV applications. </para>