Three-phase Neutral-point Clamped Rectifier Research Articles

Neural network-based three-phase NPC rectifier for DC bus capacitor voltage balancing under perturbed mains supply conditions

This paper presents an artificial neural network-based modified space vector pulse width modulation control approach for better performance of three-phase neutral-point clamped rectifier using optimised switching sequences. Use of optimised switching sequences even under ideal supply conditions, it is depicted that source side and load side parameters deviate from acceptable limits and a DC-bus capacitor voltage unbalance occurs. Under the influence of disturbed supply, source side and load side parameters deviate more beyond acceptable limits which causes a very large unbalance in DC bus capacitor voltages. This non-ideal performance of the converter is responsible for the deterioration of quality of source currents and a large stress on power semiconductor devices. The proposed control scheme employs a three-layer feed-forward neural network at different stages for capacitor voltage balancing of a three-phase three-level neutral-point clamped converter with improved power quality. According to the supply conditions, the neural network varies the speed of the reference vector and forms a required trajectory while passing through the most effective regions of SVPWM hexagon. The proposed controller scheme is modelled in MATLAB/Simulink software. Simulation results show that the proposed implementation of neural-networks controller in three-phase NPC converter displays better performance under ideal and disturbed mains conditions.

Optimising the performance of three-phase neutral-point clamped rectifier under disturbed AC mains

In this paper, a novel simplified control technique is proposed to control three-phase neutral-point clamped bidirectional rectifier using optimised switching sequences for disturbed AC mains. In space-vector modulation (SVM) technique using optimised switching sequences, duty ratio and sampling periods in each region are very important. In other words, reference vector trajectory shape and the time spent by the reference vector in each region are very important to obtain exact switching under any supply conditions. With the use of optimised switching sequences, even under ideal supply conditions, it is depicted that source-side and load-side parameters deviate from acceptable limits, and a DC-bus capacitor voltage unbalance occurs. Under the influence of disturbed AC supply, source-side and load-side parameters deviate more beyond acceptable limits which cause a very large unbalance in DC bus capacitor voltages. This non-ideal performance of the converter is responsible for the deterioration of quality of source currents and a large stress on power semiconductor devices. A new algorithm is proposed in this paper to make the converter performance ideal even under ideal and non-ideal supply conditions. According to supply conditions, the proposed technique varies the speed of the reference vector and, also at the same time, forms a required trajectory while passing through the most effective regions of SVM hexagon. The proposed technique maintains parameters within acceptable limits for source side and load side in terms of unity power factor, low input current total harmonic distortion (THD), minimum switching losses and reduced-rippled, well-regulated DC-bus voltage and also at the same time DC-bus capacitor voltage balance. The simulation results are presented to demonstrate the effectiveness of the proposed control technique.

Experimental verification of a three-phase multilevel rectifier with reduced number of power switches

A three-phase multilevel rectifier with reduced number of power switches to achieve high-power factor, low harmonics and high-voltage capability is presented. In the conventional three-phase neutral point clamped rectifier, 12 power switches are used to draw the sinusoidal line currents with unity power factor. The main drawback of these systems is the large number of power switches used in the circuits. Only six power switches with voltage rating of half DC-link are adopted in the proposed multilevel rectifier. Based on the proposed control strategy, the input power factor is close to unity and line currents are controlled to be balanced and sinusoidal. Simulation and experimental results are provided to verify the effectiveness of the proposed control strategy based on a laboratory prototype.