Neutral-point Potential Balancing Research Articles

A Modified SVPWM Strategy for Reducing PWM Voltage Noise and Balancing Neutral Point Potential

PWM (pulse width modulation) is the most widely applied current conversion technology, but the high-frequency harmonics it causes have a significant negative impact on inverter system performance. This paper focuses on the three-phase T-type three-level inverter as the research object and addresses existing PWM voltage noise and midpoint potential imbalance issues by proposing an improved random SVPWM strategy, named Neutral Point Potential Balance Random Space Vector PWM (NPB–RSVPWM). The NPB–RSVPWM strategy includes three main steps: (1) introducing a midpoint potential balancing control loop to adjust the synthesis timing of the effective vectors to generate pulse signals, optimizing midpoint potential balance; (2) employing a randomly varying carrier frequency in place of the carrier used in the SVPWM strategy to generate the driving signals for switching devices; and (3) controlling the inverter through the driving pulse signals. This strategy optimizes the synthesis sequence of traditional SVPWM strategy vectors and incorporates random frequency modulation techniques. The mathematical model analyzes PWM harmonic expressions corresponding to fixed switching frequencies, and a random frequency carrier is chosen to suppress these PWM harmonics. The effective vector’s equivalent circuit is analyzed, proposing a technique for optimized vector synthesis timing. The simulation and experimental results verify that the NPB–RSVPWM technique can disperse PWM harmonic energy, reduce voltage noise, and optimize midpoint potential balance. Under the NPB–RSVPWM strategy, the line voltage spectrum becomes uniform, the maximum harmonic content is greatly reduced, and the fluctuation in the DC side midpoint potential is significantly improved. Compared with the traditional SVPWM strategy and random PWM strategy, the NPB–RSVPWM strategy has a lower voltage noise, smaller total harmonic distortion, and a more stable midpoint potential. The effectiveness and feasibility of the NPB–RSVPWM strategy are verified by simulation and experimental results.

Hybrid varied virtual vector modulation method of parallel three-level inverter considering neutral point potential and phase current balance

Hybrid varied virtual vector modulation method of parallel three-level inverter considering neutral point potential and phase current balance

A Mathematical Structural Modulation Method for Neutral-Point Potential Balancing of Three-Level Neutral-Point-Clamped Converters

To achieve the fast neutral-point potential balance of three-level neutral-point-clamped (3L-NPC) converters, a mathematical structural modulation method is presented in this paper, featuring fast balance capability, low computation, and easy implementation. In this method, the duty cycle is decomposed into the differential-mode component (DMC) and the common-mode component (CMC). The CMC is used to synthesize the AC output voltage while the DMC is adopted to control the neutral-point potential. Based on the fractional-order sliding-mode control theory, the DMC is constructed. As a result, neutral-point potential balancing in a pre-calculated time is achieved. Finally, the effectiveness of the proposed method is verified by experimental results.

A Simplified Space Vector Pulse Width Modulation Strategy for NPC Six-Phase Three-Level Inverter Considering Neutral-Point Potential Balancing

A Simplified Space Vector Pulse Width Modulation Strategy for NPC Six-Phase Three-Level Inverter Considering Neutral-Point Potential Balancing

Gradient-Based Predictive Pulse Pattern Control with Active Neutral Point Potential Balancing for Medium-Voltage Induction Motor Drives

Gradient-Based Predictive Pulse Pattern Control with Active Neutral Point Potential Balancing for Medium-Voltage Induction Motor Drives

A Fault-Tolerant Control Strategy for Three-Level Grid-Connected NPC Inverters after Single-Arm Failure with Optimized SVPWM

Three-level NPC inverters have been widely used in grid-connected systems due to their superior performance compared with two-level inverters, but more switches lead to high fault probability. Meanwhile, the neutral point potential (NPP) fluctuation of the DC link is an inherent problem of three-level NPC inverters. To keep the three-level NPC inverter running stably after single-arm failure, a fault-tolerant control strategy based on an optimised space vector pulse width modulation (SVPWM) is proposed in this paper. Firstly, the common-mode voltage (CMV) of the postfault three-level NPC inverter is analysed and then the preliminary synthesis principles of the reference voltage vector are determined. Then, in order to ensure the NPP balance and the quality of the grid-connected currents, the reference voltage vector synthesis rules are optimised, a low-pass filter (LPF) and a hysteresis comparator are designed, respectively, to ensure the quality of grid-connected currents and effectively decrease the DC link NPP deviation. Finally, the simulation results show that the proposed fault-tolerant control strategy can realize the stable and reliable operation of the grid-connected three-level NPC inverter after single-arm failure, and the CMV can be reduced significantly, the quality of grid-connected currents is also improved. The proposed fault-tolerant strategy also shows good performance when the grid-connected currents change.

An Improved FCS-MPC Based on Novel Sector Optimization and Capacitor Charge Balance Algorithm for T-Type 3P-3L Converters

Conventional FCS-MPC suffers from high computational burden and cumbersome weight factor design, especially for three-phase three-level (3P-3L) converters. In this paper, an improved FCS-MPC is proposed for T-type 3P-3L converters to reduce computational burden, eliminate weight factor and improve system performance. Three improvements are as follows. First, a sector optimization method based on effective vector radiation range is proposed to determine the optimal vector for current tracking without vector enumeration, and combined virtual vector is adopted to supersede basic vector and avoid affecting neutral-point (NP) potential. Second, a capacitor charge balance algorithm is proposed to determine the optimal vector for NP potential balance without weight factor, which minimizes negative effects on current tracking. Third, a hybrid vector output mode is proposed to give full consideration to current tracking and NP potential balance performance. Finally, advantages of proposed MPC are verified in simulation and experiment, where code execution time and current THD are reduced by 16.1 μs and 1.27%, steady-state current error and capacitor voltage deviation are experimentally reduced by 0.8 A and 0.6 V, and transient DC voltage recovery time and capacitor voltage deviation are experimentally reduced by 2 ms and 0.4 V compared with conventional FCS-MPC.

Dead-Time Compensation in Active NPC Three-Level Inverters Considering Current Ripple

Existence of dead time that makes the ultimate terminal voltage being inconsistent with the modulation voltage, is recognized as the main reason for leading output voltage distortion, as well as the corresponding low-frequency current harmonics through the filter inductance in inverters. The distortion becomes particularly severe in high power-density high efficiency applications where the wide bandgap semiconductors are gradually being adopted, providing higher switching frequency with small junction capacitance. In order to explain this phenomenon, the mechanism of three-phase current distortion in the vicinity of phase current zero-crossing point is thoroughly studied by vector analysis in the space-vector (SV) plane. The relevant factors that lead to the degradation of current quality are also summarized. Improved compensation strategy has been proposed to ameliorate the current distortion. Compared with the conventional method, an additional item for current ripple compensation is introduced, the value of which is obtained by the deadbeat predictive method. This simple scheme avoids the compensation error caused by current ripple and significantly reduces the current total harmonic distortion (THD) value under the case of small inductance. Furthermore, neutral-point (NP) potential balance control is also considered in conjunction with the scheme. Simulations and experiments are carried out in an active NP clamped (ANPC) inverter platform, which demonstrates the validity of theoretical analysis and the proposed method.

A simplified space vector pulse width modulation method for a three‐level four‐leg inverter considering the neutral point potential balance

AbstractThis paper presents a simple three‐dimensional space vector modulation method in ghγ coordinates for a three‐level four‐leg neutral‐point‐clamped inverter. The idea uses redundant vectors as centre points to establish two‐level space vector diagrams simplifying the original space, the first sector of which is designated as subspaces, where a modulation process is implemented. The duty cycle and all possible switching sequences in a tetrahedron can be calculated automatically without manual storage and can avoid a full‐scale search process. Additionally, the neutral point potential can be balanced by three types of charge through cancellation. Such features enable the inverter to demonstrate good performance under closed‐loop control. Moreover, the proposed method can be applied to a multilevel inverter. Simulation and experimental results demonstrate the effectiveness of the proposed concept.

Modulation method of parallel interleaved three-level inverter considering neutral point potential and phase current balance

Modulation method of parallel interleaved three-level inverter considering neutral point potential and phase current balance

ANN Optimization of Weighting Factors Using Genetic Algorithm for Model Predictive Control of PMSM Drives

Model predictive control (MPC) has become one of the most attractive control techniques due to its outstanding dynamic performance for permanent magnet synchronous motor (PMSM) drives. However, the tuning of weighting factors for the cost function of MPC is a time-consuming procedure and weighting factors can significantly affect torque ripples of PMSM drives. For the purpose of optimizing the weighting factors in cost functions of MPC, this article proposes an artificial neural network (ANN) based method, which applies genetic algorithm as the back propagation algorithm. Since this method is trained offline, it does not increase any computation complexity of MPC. Consequently, any optimization targets that combine the performance metrics of MPC are defined and the optimal weighting factors for the given targets can be fast and precisely found through the proposed method. Besides, this method is robust to the variations of motor parameters like stator resistance and permanent magnet flux. The superiority of the proposed method over conventional ANN is evaluated by comparative simulations, in terms of current total harmonic distortion, tracking performance, and neutral-point potential balance. Finally, the feasibility and robustness of the proposed method are verified on the platform of PMSM drives fed by three-level T-type inverter.

A novel neutral-point potential balance control method based on voltage feedback for neutral-point clamped three-level inverter

Neutral-point potential imbalance is not only an inherent problem of neutral-point clamped three-level converters, but also the key factor affecting their performance. The traditional capacitor neutral-point potential balance control methods based on space vector modulation, such as VSVPWM, have several shortcomings including the uncompensated region of neutral-point voltage and the slow dynamic response. A novel voltage feedback control method on neutral-point potential balance is proposed in this paper. A coefficient is introduced to define the degree of neutral-point potential imbalance. The composite signal composed of this coefficient and neutral point current is designed. Based on the improved reasonable sectors’ division, the suitable small vectors are selected by this composite signal to obtain the switching sequence of power devices. The voltage feedback control method is employed to realize accurate neutral-point potential balance of NPC three-level inverter. The experimental results show that this method can quickly balance the neutral-point potential fluctuation caused by disturbance. It has the advantages of low switching loss, stable output voltage and current waveform, and good dynamic performance.

Reduced Vector Model Predictive Control of ANPC Inverter for PMSM Drives With Optimized Commutation

In this work, a new reduced vector model predictive control (RV-MPC) method is proposed for full silicon-carbide (SiC)-MOSFET modules-based three-level active neutral-point-clamped (3L-ANPC) inverter fed permanent magnet synchronous motor (PMSM) drives. The main purpose of this approach is to reduce the computational burden of conventional MPC for ANPC inverters while optimizing the current commutation paths. To reduce the computational burden, the proposed algorithm is implemented by two steps. In the first step, the expected <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">dq</i> -axis voltages are predicted, and then, the positive and negative half cycles are determined through a hysteresis sign calculation algorithm. In the second step, only eight switching states need to be enumerated under the defined half period, which is remarkably reduced from 27 to 8. The neutral point potential balance and switching effort penalization are also considered in the proposed method. Moreover, the ANPC inverter can achieve more even loss distribution and better thermal characteristics with the optimized commutation, which is profitable for the high-power drive applications. The effectiveness of the proposed approach is evaluated by simulations and experimentally verified on a platform of 11-kW PMSM drives.

Model-Based Design and Experimental Validation of Control System for a Three-Level Inverter

Considering the disadvantages of the traditional development pattern in an embedded control system for an inverter, that is, the single-process thinking and separation of software and hardware, a novel method, which is a model-based design, for developing a double closed-loop control system for the diode-clamped three-level inverter was proposed. System control models, including the PWM control algorithm model, the voltage control model, the neutral-point potential balancing model, and the frequency control model, were built with the MATLAB platform. The code-generation capacity and the operation effect were verified through a series of tests. The inverter with diode clamp and neutral-point potential control was developed. Codes were generated automatically and downloaded to the eZdsp28335 control chip. Experimental waveforms of the phase voltage, line voltage and current were analyzed under regulating the voltage and frequency. The experimental results demonstrate that the models and the generated codes are correct. Further studies have proven the feasibility of the system development model.

Model Predictive Current Control for the Grid‐Connecting Three‐Level NPC Inverters Based on an Effective Harmonic Extraction Method Under a Low‐Switching Frequency

Current control of the grid‐connecting inverters usually has an important influence on the control performance especially when the inverters operate at a low‐switching frequency for it would result in a severe harmonic distortion in the output current components. To improve the current control performance, a novel model predictive current control (MPCC) strategy based on an effective harmonic extraction method was present for a high‐power three‐level NPC inverter in this paper. First, an effective amplitudes extraction method called generalized sliding discrete Fourier transform (GSDFT) was designed for the fundamental and low‐order harmonic current components, and which would be taken as a part of the cost function for the MPCC besides the consideration of switch losses and neutral point potential balancing issues. Experimental results verify that this kind of novel control strategy not only has a characteristic similar with the selective harmonic elimination, also could realize a nice current control performance even the switching frequency is low than 500 Hz as well as a neutral point potential balancing. © 2022 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC.

A Novel Low-Frequency Virtual Space Vector Modulation With the Improved Continuity of Output Average-Voltage and Bus Voltage Utilization for Single-Phase Neutral Point Clamped Three-Level Inverter

In the high-power superconducting fusion converter, the single-phase neutral point clamped (NPC) three-level converter is applied to replace the traditional thyristor converter using an integrated gate-commutated thyristor (IGCT) as a power device. The operating frequency of IGCT is usually lower, only a few hundred Hz. An optimized hybrid space vector pulsewidth modulation (SVPWM)-8H is proposed to solve the problems of discontinuous output average voltage, low dc bus voltage utilization rate, dead time compensation, and neutral point potential balance. The new sectors are inserted to make the range of output average voltage of adjacent sectors intersect, which improves the continuity of output average voltage. Furthermore, some sectors are composed of four vectors to reduce the minimum working time of redundant small vectors, improving the dc bus voltage utilization ratio and the converter’s performance. Moreover, by analyzing the influence of dead time on redundant small vectors, redundant vectors are rearranged to make redundant small vectors’ working time synchronously in sector and sector switching, which reduces the influence of dead time on neutral point potential balance. Finally, by analyzing the influence of dead time on the output average voltage, dead time compensation is applied, which reduces the difficulty of compensation implementation. Simulations and experiments verify the rationality of the optimized hybrid SVPWM-8H.

A Carrier-Based Common-Mode Voltage Elimination Method for Back-to-Back Three-Level NPC Converters

As the increase of power and voltage level of back-to-back three-level neutral-point clamped (NPC) converters, the high-amplitude and high-frequency common-mode voltage (CMV) has become an urgent problem. To address this, a CMV elimination method based on pulsewidth modulation pulse alignment for back-to-back three-level NPC converter is proposed. On this basis, a neutral-point potential balance method based on zero-sequence voltage (ZSV) is also proposed. In order to decouple the CMV elimination and the neutral-point potential balance, the same optimal ZSV is injected into both the rectifier and inverter sides, and the CMV elimination will not be affected. Simulation and experiments are presented to verify the effectiveness of the proposed method.

Three-Level Indirect Matrix Converter With Neutral-Point Potential Balance Scheme for Adjustable Speed Drives

To improve the performance and explore a new solution of adjustable speed drive systems, a T-type three-level indirect matrix converter (T3LIMC) topology and its modulation scheme are presented in this article. The presented topology is composed of an <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LC</i> input filter, a current-source rectifier, and a T-type three-level inverter, where the split dc source voltage of the inverter is formed by two input line-line voltages and the neutral-point voltage. A multicarrier-based modulation scheme for the inverter and a specific zero-sequence voltage are also developed, and the desired neutral-point current of the inverter is constructed to compensate for the input currents. Consequently, the balanced neutral-point potential and symmetric sinusoidal input currents are achieved without additional control effort. In addition to advantages such as bidirectional power flow, sinusoidal input–output currents, controllable input power factor, no dc-link energy storage elements, and compact structure, the T3LIMC also improves the output waveform quality by generating the three-level output voltages. Meanwhile, the zero current switching (ZCS) operation of the rectifier helps to improve efficiency. Finally, the functionality and effectiveness of the presented topology and modulation scheme are verified by experimental results.

Harmonic Analysis and Neutral-Point Potential Control of Interleaved Parallel Three-Level Inverters for Flywheel Energy Storage System

Flywheel energy storage system is a popular energy storage technology, in which inverters are the center of electrical energy conversion, directly affecting the power capacity. Parallel operation of three-level inverters is an effective approach to achieve larger motor drive power and the interleaved operation can improve the harmonic characteristics. However, harmonic analysis models of the interleaved parallel three-level inverters are rare in the literature and how the neutral-point potential imbalance affects the harmonics characteristics has not been discussed. This article establishes the harmonic calculation for balanced and unbalanced neutral-point potential through the five-level voltage capability of the interleaved parallel three-level inverters. Moreover, a neutral-point potential control method based on zero-sequence voltage injection is proposed. The implement process of the method is proposed, and how the operating frequency affect the ability of the neutral-point potential balance is studied. Finally, the simulation and experiment results verify the feasibility and practicability of the established harmonic analysis models and the neutral-point potential control method.

A Novel Neutral-Point Potential Balance Control Method Based on Voltage Feedback for Neutral-Point Clamped Three-Level Inverter

A Novel Neutral-Point Potential Balance Control Method Based on Voltage Feedback for Neutral-Point Clamped Three-Level Inverter