This article presents a predictive torque control (PTC) algorithm for a five-phase (distributed winding) induction motor fed by a three-level neutral-point-clamped inverter to remove the common-mode ...voltage (CMV). In this approach, a finite range of 31 voltage vectors (VVs) is chosen from the total available 243 VVs for the removal of the CMV. The <inline-formula><tex-math notation="LaTeX">xy</tex-math></inline-formula>-subspace current harmonic reduction is achieved with grouped VVs. The developed PTC algorithm has two successive cost functions: <inline-formula><tex-math notation="LaTeX">g_{1h}</tex-math></inline-formula> for stator flux and electromagnetic torque regulation and <inline-formula><tex-math notation="LaTeX">g_{2h}</tex-math></inline-formula> for <inline-formula><tex-math notation="LaTeX">xy</tex-math></inline-formula>-subspace current harmonic reduction. The purpose of these two successive cost functions is to reduce the complexity in determining the independent weighting factors. This algorithm retains the torque and flux responses similar to that of conventional PTC. The minimization in switching frequency is obtained in the presented PTC algorithm with the selected set of VVs. For evaluating and ascertaining the capabilities for CMV elimination and <inline-formula><tex-math notation="LaTeX">xy</tex-math></inline-formula>-subspace harmonic current reduction, the proposed algorithm is compared with the conventional PTC algorithm having a different set of VVs. Experimental outcomes show the significance of the discussed algorithm in the steady state and retain the transient operating conditions.
In order to meet the high performance and efficiency requirements, a new space vector-based discontinuous modulation strategy for neutral-point clamped three-level inverter is presented in this ...paper. Different from the conventional discontinuous PWM (DPWM) strategies, a new clamping state is applied to synthesize the reference voltage under the condition of low modulation index. The rms value of output current ripple for different clamping states are calculated, and then the distribution of the new clamping state and the other two clamping states adopted in conventional DPWMs is optimized based on the calculation results. The switching sequences are redesigned according to the new distribution of the three clamping states. The output voltage and current, switching loss, neutral-point voltage ripple and the common mode voltage of the proposed DPWM strategy and DPWM0-DPWM3 are compared by simulation and experimental results. The results show that by the use of the proposed strategy, the values of total demand distortion of output current (I TDD ) and weighted total harmonic distortion of output voltage (V WTHD ) are the lowest. Furthermore, the product of switching loss and I TDD of the proposed strategy maintains the lowest within a large range of modulation index-load angle plane. It can be concluded that the utilization of the new clamping state and optimal distribution of different clamping states could enhance the output performance of the inverter. Moreover, the high-efficiency requirement can also be realized at the same time.
Parameter mismatches in conventional model predictive current control (MPCC) would worsen torque and THD performance. To eliminate the parameter dependence of MPCC, this letter proposes a model-free ...predictive current control (MFPCC) for a three-level inverter-fed interior permanent magnet synchronous motor (IPMSM). Firstly, to increase the current difference updating frequency in the diode neutral-point-clamped (NPC) three-level inverter, a synchronous updating method is proposed in a manner where the number of updated current differences during one sampling period is increased up to 6. Secondly, for the sake of computational burden alleviation, a candidate vector selection algorithm is introduced in such a way that the number of candidate vectors is reduced to only 7-9. Then, the problem of neutral-point voltage fluctuation which is inherent to the three-level NPC inverter is investigated, and a reasonable replacement method incorporating the redundancy characteristic of small vectors is developed. Finally, experimental results verify that the system robustness against mismatched parameters can be greatly enhanced by use of the proposed control scheme; meanwhile, steady-state performance and dynamic-state response of the system can be improved to some extent as well.
This article presents an improved virtual space vector modulation scheme for the reduced switch count three-level inverter with balanced and unbalanced neutral-point voltage (NPV) conditions. By ...analyzing the effects of unbalanced NPV conditions on basic voltage vectors, the new virtual vectors are constructed by considering the dc unbalancing coefficient and distribution factor for small vectors simultaneously. To facilitate the calculation of duty cycles, the nonorthogonal coordinate system is employed. In addition, an optimized control scheme is developed to obtain the optimized distribution factor, and the relative durations of P-type and N-type small vectors are adjusted to control the voltages across two dc-link capacitors separately. The satisfactory quality of output currents is maintained with both balanced and unbalanced NPV conditions. The feasibility of the proposed scheme is verified by simulated and experimental results.
A novel topology of a three-phase dual-output neutral-point-clamped three-level inverter (DO-NPC-TLI) is proposed. DO-NPC-TLI can achieve two groups of ac voltage outputs with adjustable frequency ...and amplitude. We describe the topology in detail. The proposed topology is based on a neutral-point-clamped three-level inverter (NPC-TLI). A total of eight switches and six clamping diodes are added to the NPC-TLI to form the new topology, and then analyze the working principle of the circuit. With the consideration of neutral point voltage balance, a modulation strategy combining the time-sharing modulation idea and virtual space vector pulsewidth modulation (VSVPWM) is proposed. In order to simplify the complicated calculation process of VSVPWM, a carrier-based PWM based on VSVPWM is proposed. All of the duty ratios are used to calculate the modulation waves of DO-NPC-TLI. The driving signals of switches are generated by comparing the modulation waves with a carrier. The modulation strategy mentioned above is verified by the experiment. The correctness of the experimental results illustrates the effectiveness of the modulation strategy and the feasibility of the proposed topology.
Electric Vehicle is the future of sustainable road transport. One of the important issues with electric vehicles is their inverter failure. This paper presents a fault-tolerant technique with phase ...fault detection and fault removal for a three-phase cascaded H-bridge three-level inverter. The phase fault-detection and fault-removal techniques are based on the switch voltage, switch current and switching signal detection. The cascaded H-bridge three-level inverter is made fault-tolerant by using an additional H-bridge and three bidirectional IGBT switches. The logic of phase fault detection and fault removal is investigated in the MATLAB-Simulink environment and validated in OPAL RT-LAB.
In a three-phase three-level grid-connected inverter, the ac output current ripple actually fluctuates four times per switching period with each fluctuation generating some core loss. However, only ...the two larger fluctuations are considered in most loss estimation methods, resulting in a smaller core loss evaluation. In this letter, an alternative method has, hence, been proposed, beginning with the deduction of fundamental and ripple equivalent circuits from the inverter. These circuits permit current ripple to be calculated, from which its four fluctuations are all considered for forming the dual current-ripple envelopes (DCREs). These DCREs, together with the fundamental current and a selected core loss model, can then be solved to give the estimated fundamental and ripple core loss values. The nonlinear characteristic of the filter inductor has also been considered in the calculation of the DCREs and the core loss. The estimated values have eventually been verified through testing with a 10-kW three-phase T-type three-level grid-connected inverter.
Three-phase multilevel (ML) inverters are used in many medium- and high-power applications such as motor drives and grid-connected systems. Despite the fact that numerous pulsewidth modulation (PWM) ...techniques for ML inverters have been developed, the impact of these modulation schemes on the peak-to-peak output current ripple amplitude has not been addressed yet. In this paper, analysis and comparison of current ripple for two-level (2L) and three-level (3L) voltage source inverters are given. Reference is made to optimal and popular modulation, so-called centered PWM, easily obtained by both carrier-based modulation (phase disposition, with proper common-mode voltage injection) and space vector modulation (nearest three vectors). It is shown that the peak-to-peak current ripple amplitude in 3L inverters can be determined on the basis of the ripple in 2L inverters, obtaining the same results as by directly analyzing the output voltage waveforms of the 3L inverters. This procedure can be readily extended to higher level numbers. The proposed analytical developments are verified by both numerical simulations and experimental tests.
Low-voltage ride-through (LVRT) requirements demand wind-power plants to remain connected to the network in presence of grid-voltage dips. Most dips present positive-, negative-, and zero-sequence ...components. Hence, regulators based on symmetrical components are well suited to control grid-connected converters. A neutral-point-clamped topology has been considered as an active front end of a distributed power-generation system, following the trend of increasing power and voltage levels in wind-power systems. Three different current controllers based on symmetrical components and linear quadratic regulator have been considered. The performance of each controller is evaluated on LVRT requirement fulfillment, grid-current balancing, maximum grid-current value control, and oscillating power flow. Simulation and experimental results show that all three controllers meet LVRT requirements, although different system performance is found for each control approach. Therefore, controller selection depends on the system constraints and the type of preferred performance features.
Virtual space vector pulsewidth modulation (VSVPWM) for the neutral-point (NP)-clamped three-level inverter is briefly reviewed in this paper, as well as its carrier-based realization. The ...carrier-based VSVPWM (CB_VSVPWM) is featured with dual modulation waves and a single carrier. Although CB_VSVPWM can make NP voltage unfluctuating in theory, it does not have the NP voltage recovery ability. In practice, due to the effect of nonidea factor effects, NP voltage may shift. Thus, active NP voltage control (ANPVC) is necessary. To achieve that, three ANPVC approaches are proposed based on CB_VSVPWM in this paper. The NP voltage control ability of CB_VSVPWM with ANPVC is analyzed. Finally, comprehensive experiments are carried out to verify the feasibility of the proposed method.
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