Improved Space Vector Pulse Width Research Articles

The voltage feedforward based pulse width modulation strategy under the fluctuated dc‐link voltage for a unidirectional five‐level ac motor drive system with open‐end winding connection

SummaryIn a unidirectional five‐level ac motor drive system with open‐end winding connection, because of the variation of operating frequency of ac motor, the instantaneous power fluctuation of rectifier stage and inverter stage will generate larger voltage ripple on each phase dc‐link capacitors, and further lead to a large amount of current harmonics in output currents of inverter. To cope with this problem, an improved space vector pulse width modulation (SVPWM) strategy based on dc‐link voltage feedforward is proposed. In this paper, the effects of zero sequence current harmonics caused by dc‐link voltage ripple on ac motor are firstly analyzed, including the stator winding flux linkage equation, voltage equation, and electromagnetic torque. Then, the generating mechanism of dc‐link voltage ripple and the current harmonics are discussed in detail in terms of instantaneous power fluctuation of each single‐phase converter. Based on this, an improved SVPWM strategy by modifying the modulation signal is proposed to suppress the generation of current harmonics. Finally, a 2.2 kW prototype experimental results are given, which verify the feasibility and advancement of the proposed modulation strategy.

Decoupled and compensated space vector pulse width modulation algorithm for dual‐channel PMSM with unbalanced power supplies

SummaryThis paper investigates an improved space vector pulse width modulation (SVPWM) and channel‐decoupled method for dual‐channel permanent magnet synchronous machine (PMSM) powered by unbalanced battery packs. Recently, individual power supplied voltage source inverter (VSI) is introduced considering insufficient power rating and unsafe driving in electrical vehicles (EVs). However, the issues of strong coupling and unbalanced power supplies exist between channels. Firstly, a modular topology is constructed to improve the reliability and security of the system. Secondly, the channel‐decoupled method is introduced based on multi‐dq rather than the conventional vector space decomposition (VSD) to eliminate coupling among multi‐channel. Thereafter, the variable distribution of voltage vectors (VVs) is corrected by the proposed SVPWM, where the switch can be operated appropriately. Finally, the comparative experiments are carried out focusing on decoupling and unbalanced power supplies, and the results present superior performance in terms of low torque fluctuation and balanced channel currents.

Grid-Tied Neutral Point Clamped based Centralised Photovoltaic Inverter with Improved DC Link Voltage Balancing and Harmonic Minimisation Control

Abstract This paper proposes an improved space vector pulse width modulation (SVPWM) based DC link voltage balancing control of a three-phase three-level neutral point clamped (NPC) centralised inverter supplying the generated power from photo voltaic (PV) array to a three-phase utility grid. Two possible schemes have been developed based on the power conversion stage between PV array and the utility grid namely, two-stage (three-level boost converter three-phase three-level NPC inverter) and single-stage (three-phase three-level NPC inverter alone). The comparison between these two schemes has been thoroughly discussed in terms of the control strategies employed, power loss analysis and efficiency. The performance of the centralised inverter under different modes of operation has been investigated by developing the required control strategies for smooth operation. Using the proposed control strategy, the centralised inverter can be operated as a static synchronous compensator (STATCOM) during night time, if needed. The power loss incurred in the power-electronic converters has been analysed for constant and also for variable ambient temperature. The effectiveness of the centralised inverter as an active filter (AF) has also been verified when a three-phase non-linear load is considered in the system.

Decoupling Control Analysis of a Flux Reversal Linear Rotary Permanent Magnet Actuator

In order to meet the requirement of industrial production, a control system of a novel flux reversal linear rotary permanent magnet actuator (FR-LRPMA) is developed in this paper, and the electromagnetic and motion decoupled process is analyzed in detail. Firstly, the control equation of FR-LRPMA is derived in the nine phase stator coordinate system and dual dq-axis mover coordinate system. Then the control model of FR-LRPMA is built in MATLAB/Simulink using improved space vector pulse width modulation (SVPWM), and the linear, rotary and spiral motions of the proposed actuator are achieved. Finally, the prototype of the actuator is manufactured, and the experiment platform of FR-LRPMA is set up to measure the cogging torque and linear detent force, validating the simulation results. It is concluded that the control system of FR-LRPMA can be converted into two independent single freedom motors by dual dq transformation. The improved SVPWM is effective in the control system, and the method can be used to solve the electromagnetic and motion decoupling problems.

An Improved Space Vector Pulse Width Modulation for Nine-Level Asymmetric Cascaded H-Bridge Three-Phase Inverter

This paper presents an improved space vector pulse width modulation (SVPWM) for nine-level cascaded H-bridge inverter with unequal DC voltage sources. This technique is based on the use of $$60^{\circ }$$ spaced r–s coordinate system to achieve SVPWM of multilevel three-phase inverter. In order to realize nine-level inverter, conventional SVPWM requires 1296 lookup tables, which is difficult to realize in the form of lookup tables, but the proposed technique does not require any lookup tables in the process of SVPWM realization, and it is generalized algorithm for any inverter levels. Hence, the system memory requirement is very less. The proposed modulation technique improves the nature of inverter output voltage and its total harmonic distortion value. Simulation results have been carried out using MATLAB/SIMULINK software tool. A comparative analysis is performed with classical pulse width modulation (PWM) techniques like sinusoidal PWM and third harmonic injection PWM at different modulation indices. To validate the simulation results and to confirm the practicality of the proposed control algorithm, experimental verification has been done.

Fault-Tolerant Direct Thrust Force Control for a Dual Inverter Fed Open-End Winding Linear Vernier Permanent-Magnet Motor Using Improved SVPWM

This paper proposed a new fault-tolerant direct thrust force control (DTFC) for a dual inverter fed open-end winding linear vernier permanent-magnet (LVPM) motor. First, the topology and structural characteristics are briefly presented. Second, the mathematical model of the LVPM motor is derived. Then, a new fault-tolerant DTFC is proposed, in which inverter fed open-end winding technique is adopted. When inverter switch fault occurs in open-end winding driving system, the connection point between the motor port and the fault switch is cut off, and motor port is connected to power source neutral point. An improved space vector pulse width modulation is reconfigured by the rest of switches to implement DTFC. Finally, experimented results are given to verify the proposed fault-tolerant control strategy.

Fault-Tolerant Control Strategy for Neutral-Point-Clamped Three-Level Inverter

A fault-tolerant control technique is discussed for the Neutral-Point-Clamped (NPC) three-level inverter, which ensures that the NPC inverter operates normally even under device failures. A two-level leg is added to the NPC inverter; when the device open circuit fault occurs, the load of this faulty phase is connected to the neutral point of this two-level leg through the bidirectional thyristors. An improved Space Vector Pulse Width Modulation (SVPWM) strategy called “addition and subtraction substitution SVPWM” is proposed to effectively suppress fluctuation in capacitor neutral-point voltages by readjusting the sequence and action time of voltage vectors. The fault-tolerant topology in this paper has the advantages of fewer switching devices and lower circuit costs. Experimental results show that the proposed fault-tolerant system can operate in balance of capacitor neutral-point voltages at full output power and the reliability of the inverter is greatly enhanced.

Design of a reduced component count single‐phase to three‐phase quasi‐Z‐source converter

This study proposes a cost-effective four-switch single-phase to three-phase converter with an improved space vector pulse width modulation method. This structure employs the quasi-Z-source (QZs) topology that can be utilised in induction motor drive applications. Compared with conventional four-switch structures, buck-boost operation is a unique property of this configuration. This four-switch QZs structure decreases the switching losses, load current total harmonic distortion and cost in comparison with traditional six-switch structures. Without using any extra filtering circuits, the applied modulation method can work well to reject the influence of DC-link voltage ripples on the converter voltage, which can be accomplished by either power supply or voltage variations in the four-switch structure. The closed-loop modulation strategy recognises via sensing any unbalanced voltage that occurs across two split capacitors, and by applying the changes in the vector's activation interval time, the three-phase output voltage can be balanced. The simulation and experimental results of the suggested converter with the improved modulation method have demonstrated the converter's performance and the potential of the structure to be further developed.

The elimination of leakage currents in the neutral point clamped photovoltaic grid-connected inverter by the improved space vector pulse width modulation method

In this paper, the reason of high-frequency leakage current in neutral point clamped photovoltaic grid-connected inverters that adopts traditional modulations is analysed. In order to solve the problem, this article puts forward two improved methods based on the three-level space vector pulse width modulation (SVPWM), which can reduce the leakage current by applying three medium vectors or using only two medium vectors and one specific zero vector to compose the reference vector. In addition, the system control method adopts the coordination control of the current inner loop and the DC voltage outer loop, which can reduce voltage fluctuation at the DC side. Thereby, the suppression of leakage current can be realised without requiring any modification on the multilevel inverter. Compared with the traditional three-level sinusoidal pulse width modulation (SPWM) and SVPWM, the two new methods are advantageous in having a stable common-mode voltage, low leakage current, and low harmonic component of grid current. The theoretical analysis and results show the effectiveness of the proposed methods.