In this paper, the properties and operation of the virtual-space-vector pulse-width modulation (PWM) for a three-level neutral-point-clamped inverter with unbalanced dc-links are studied. By quantitatively analyzing the characteristics of the revised space-vector diagram (SVD) with unbalanced dc-links, the defined virtual SVD (VSVD) for the unbalanced case is theoretically proven identical to the VSVD of the conventional virtual-space-vector PWM (VSVPWM) strategy with balanced dc-links. The well-developed and fast-processing methods to calculate the durations of the nearest three virtual vectors for the conventional VSVPWM can be directly utilized. In addition, a control strategy to realize the asymmetric control of the dc-link voltages with VSVPWM is also studied, and this method can adjust the unbalancing degree with a high accuracy for any modulation indexes and load power factors. Simulated and experimental results are given to validate the effectiveness.

A simplified pulse width modulation (PWM) strategy for a neutral-point-clamped three-level converter with unbalanced dc links is proposed in this paper to achieve high-quality line-to-line output voltages and to maximize the linear modulation range. The simplified strategy takes the direct output voltage modulation by calculating the special solutions of the voltage-second balance equations without detecting the position of the reference vector in the asymmetrical and complicated space voltage vector diagrams to reduce the calculation time. A novel solution based on the state transition is proposed to extend the maximum linear modulation index to 1.15. Furthermore, the asymmetric control of the split dc link by the proposed PWM is implemented by adjusting the special solutions. The difference between the conventional space vector PWM and the proposed strategy is conducted to illustrate the advantages of the simplified strategy. The effectiveness of the proposed modulation strategy is verified by simulation and experiment results.

Crosstalk phenomena taking place between synapses can influence signal transmission and, in some cases, brain functions. It is thus important to discover the dynamic behaviors of the neural network infected by synaptic crosstalk. To achieve this, in this paper, a new circuit is structured to emulate the Coupled Hyperbolic Memristors, which is then utilized to simulate the synaptic crosstalk of a Hopfield Neural Network (HNN). Thereafter, the HNN’s multi-stability, asymmetry attractors, and anti-monotonicity are observed with various crosstalk strengths. The dynamic behaviors of the HNN are presented using bifurcation diagrams, dynamic maps, and Lyapunov exponent spectrums, considering different levels of crosstalk strengths. Simulation results also reveal that different crosstalk strengths can lead to wide-ranging nonlinear behaviors in the HNN systems.

Presently, the neutral-point potential offset is an inherent problem for three-level converters on three-phase four-wire active power filters. The conventional three-dimensional space vector pulse width modulation (3-D-SVPWM) strategy is adopted as a normal solution to the problem, but the selection of space vector sectors for four-wire converter is both abstract and complicated in practice. This paper proposes a new PWM strategy accordingly to simplify the selection process and the calculation of duration. Compared to the conventional 3D-SVPWM, the proposed method locates the sector of optimal vector directly with the polarity of three-phase reference voltage. Then, by applying voltage-second balance rule, it can perform a fast calculation of the duration and generate PWM signals to control the switching devices' on/off. As an approach to correct the imbalance dc-link capacitor voltage, this strategy reconstructs the switching sequence. A portion of state O duration is disassembled into states P and N to suppress the neutral-point potential offset. The proposed strategy is validated with a range of experiments. The results indicate that this simplified PWM strategy can effectively reduce the computational burden, and also the dc-link capacitor voltage is well controlled.