Synchronous Pulsewidth Modulation Research Articles

Optimized Design for AC Filter and Switching Frequency of Parallel-Connected Inverters With Global Synchronous Pulsewidth Modulation

This article proposes a new optimized design method for AC filter and switching frequency of parallel-connected inverters with global synchronous pulse width modulation (GSPWM) to improve the efficiency or reduce the cost. Being different from the traditional design methods that only focus on the individual inverter itself, the quantity of parallel-connected inverters and the operational principles of GSPWM are involved as the key considerations for designing the proper ac filter values and switching frequencies. In specific, the general principles and the realization details are comprehensively elaborated. Experimental results are presented to verify the proposed theoretical findings.

Dynamic current control using synchronous pulse-width modulation for permanent magnet machines

It is difficult to use the conventional fixed sampling pulse-width modulation (PWM) method in a motor drive system due to the harmonics and beat phenomenon when the number of switchings is low. Synchronous PWM is a solution to overcome these problems. However, it is difficult to implement a closed-loop current controller, since synchronous PWM only has merits when the switching frequency is synchronized with the operation speed. This paper proposes a closed-loop current controller for synchronous permanent magnet machines which are driven by synchronous PWM. The proposed controller uses the concept of variable time step control. The control variables are the sampling time interval and the output voltage magnitude. The proposed controller dynamically controls the dq-currents, while the steady-state merits of the synchronous PWM are maintained. This paper presents the design procedures and a dynamic analysis of the proposed current controller. The effectiveness of the proposed method is verified by experimental results.

Smooth Transition of Multimode Synchronous Modulation for IPMSM Sensorless Drives in Rail-Transit Applications

In rail-transit application, the multimode synchronous pulsewidth modulation (PWM) strategy is widely used to achieve better control performance in middleor high-speed region, which brings challenges to sensorless control that can enhance the system robustness. Within the synchronous modulation, a regular 21-pulse space vector PWM and a selective harmonic elimination PWM are selected to analysis the influence of PWM modes transition on an interior permanent magnet synchronous machine (IPMSM) sensorless drives. When the carrier ratio is less than 10, as the transition occurs between different PWM modes, the amplitude and phase of low-order harmonics change obviously and affects the position estimation accuracy severely. Here, a fast central 60° transition method for three-phase pulses is designed, then the smooth transition can be achieved in half fundamental period and the estimated position fluctuation is eliminated. In addition, small changes in the fundamental-frequency results in frequent transition between different PWM modes, which deteriorates the sensorless control performance. A frequency hysteresis zone is set and the effect of load-disturbance is also considered. Finally, the feasibility of the proposed sensorless method is verified on a 3.7-kW IPMSM drive platform.

Decomposed Current Controller for a Paralleled Inverter With a Small Interfaced Inductor

In this paper, a current controller for a parallel operation of inverters is described. When inverters operate in parallel, it is a well-known fact that the inverter current is composed of the average current (AVC) and the zero-sequence circulating current (henceforth ZSCC), which inevitably flows between inverters under the parallel operation. Considering this, previous studies concentrated on reducing ZSCC. However, in this paper, it is found that the inverter current has another component, a differential current, in addition to the two components of AVC and ZSCC. Based on these three decomposed current components, three equivalent circuits are derived from n -paralleled inverters. To minimize the differential current and improve the regulation performance of the total output phase current, a decomposed current control scheme is proposed from equivalent circuit models. The proposed algorithm is applied to a system consisting of three paralleled two-level inverters with small shared inductance whose dc links are connected in common. Additionally, synchronous pulsewidth modulation is employed as the PWM method for each inverter. The proposed current controller is compared with two conventional current controllers, one where each inverter controls its own currents and the other where only AVC is controlled. Through experiments, it is shown that these conventional controllers have limitations and the proposed current controller overcomes these limitations. The effectiveness and feasibility of the proposed control scheme are verified through experimental results. Especially, both theoretical analysis and experiment results verify that the proposed method is robust with regard to parameter errors.

A Carrier Synchronization Method for Global Synchronous Pulsewidth Modulation Application Using Phase-Locked Loop

When many distributed parallel inverters are integrated into grid without switching sequence coordinated control capability, the high-frequency harmonics will accumulate randomly at the point of common coupling. Global synchronous pulsewidth modulation (GSPWM) method can significantly attenuate the accumulated switching ripples by intentionally assuming an intelligent optimization algorithm and a communication system. To avoid the dependence on low-latency communication system, this paper proposes a novel phase-locked loop based PWM carrier synchronization (PLL-CS) method for GSPWM system, where the switching sequences can be effectively synchronized as expected without using low-latency synchronization signals. By doing so, the operational reliability of the whole GSPWM system can be significantly improved, while the additional hardware cost of GSPWM can be dramatically reduced, which can enhance the implementation adaptability of GSPWM method. Experimental results have verified the performance of the proposed PLL-CS GSPWM method.

A novel hybrid Phase Shifted-Modified Synchronous Optimal Pulse Width Modulation based 27-level inverter for grid-connected PV system

In grid connected Photovoltaic (PV) systems, Multilevel Inverters (MLI) are commonly employed for providing better reliability and getting minimal harmonics. Most of the MLIs function with Phase-Shifted Pulse Width Modulation (PSPWM) techniques for achieving high level performance. However, in the in existing PSPWM techniques, the harmonic voltage profiles are not efficient. This paper aims to improve the harmonic voltage profile of the 4 KW grid-connected PV system using a novel hybrid PSPWM-Modified Synchronous Optimal PWM (PS-MSOPWM) technique for a 27-level inverter. With the combination of these hybrid PSPWM-Modified SOPWM techniques, optimum switching angles are computed to match the switching frequency with the fundamental frequency. From the results, it is identified that the proposed hybrid modulation method effectively reduces the Total Harmonic Distortion (THD) and exhibits improved reliability of the grid-connected solar system.

Two-Layer Global Synchronous Pulse Width Modulation Method for Attenuating Circulating Leakage Current in PV Station

This paper proposes a two-layer global synchronous pulsewidth modulation (GSPWM) method for attenuating the circulating leakage current of a photovoltaic (PV) station with many inverters connected in parallel, and meanwhile allowing the simple two-level string inverters instead of the commonly used three-level string inverters to directly connect in parallel without the transformer isolation in order to save cost and increase efficiency. The first-layer GSPWM could calculate the optimal phase-shift angles of triangular carriers among the parallel-connected two-level inverters to effectively attenuate their circulating leakage current. The second-layer GSPWM collects the equivalent variable per group provided by the first-layer GSPWM and can still significantly attenuate the total current harmonics at the point of common coupling. Experimental results of a small-scale prototype are presented to verify the performance of the proposed two-layer GSPWM.

Performance and Implementation of Modular Converter Based on Advanced Control Topology

In high power industrial drive use the multi modular converter for high voltage dc transmission system. The reduction of switching frequency, reduce thermal stress and harmonic distortion in the output of the converter by using the modular converter. Synchronous optimal pulse width modulation (SOP) is a developing low gadget exchanging recurrence regulation system for high power converters, which keeps up the nature of converter output current. SOP system has been effectively exhibited for established multilevel topologies and it has been demonstrated that greatest gadget exchanging recurrence can be restricted to evaluated principal recurrence for seven or larger amount inverters without trading off on the nature of yield streams. Be that as it may, execution of SOP procedure for MMC topology is as yet pending. One of the primary difficulties for control of MMC is to keep up drifting capacitor voltages around their ostensible esteem. The objective of our investigation is to propose, break down and actualize improved SOP strategy for MMCs to accomplish low device exchanging recurrence operation, better quality of converter output current and keep up capacitor voltages around their perceived value.

A PWM for Minimum Current Harmonic Distortion in Metro Traction PMSM With Saliency Ratio and Load Angle Constrains

Permanent magnet synchronous motor (PMSM) has the advantages of flexible structure, high power density, and low noise. It is promising to be developed into railway traction system. This application of the PMSM is limited by the low switching frequency of the high power traction inverter. Therefore, it is necessary to restrain the output current harmonics by using the optimized synchronous pulse width modulation (PWM) method. In this paper, the relationship between the load current of PMSM and the output voltage of the inverter using synchronous PWM is analyzed, and the expression of the current harmonics is deduced. Then, a new current harmonic evaluation index considering the saliency ratio and load angle constraints is proposed. Based on this, a novel current harmonic distortion minimization PWM (CHMPWM) algorithm for the PMSM is constructed. Compared with the two existing CHMPWM algorithms, the proposed optimized PWM has better harmonic performance at any modulation index and load angle. Furthermore, according to the results of the proposed CHMPWM, the influence of the load angle variation on optimal switching angle distribution is analyzed when pulse ratio is less than or equal to 11. Experimental results verify the feasibility and effectiveness of the proposed algorithm.

Integrated Half-Bridge CLLC Bidirectional Converter for Energy Storage Systems

This paper proposes an integrated half-bridge CLLC (IHBCLLC) resonant bidirectional dc–dc converter suitable as an interface between two dc voltage buses in various applications including energy storage systems. This converter is an integration of a half-bridge CLLC resonant circuit and a buck/boost circuit. Compared with the traditional pulse frequency modulation and phase-shift controlled CLLC resonant converter, for the proposed convertor, the high voltage gain can be obtained from pulse width modulation. Synchronous pulse width modulation is adopted for the converter, and the switching frequency is equal to the resonant frequency. The CLLC resonant circuit can help MOSFETs to achieve soft switching and high voltage gain. The simulation analysis of the modulation schedule and operating principle of the proposed converter prove that the converter is able to achieve zero-voltage switching or zero-current switching. Experimental results obtained from a 1-kW converter prototype confirm the theoretical analysis and the simulation results.

Research on a new type of electromagnetic transmitter based on PWM technology

An electromagnetic transmitter transmits electromagnetic waves with variable frequencies to the ground to obtain underground structure information and the distribution of mineral resources. In order to improve the power factor and reduce the volume and weight of the transmitter, a novel transmitter topology with pulse width modulation (PWM) rectifier is designed. Similar with the flux-oriented control in the motor speed regulation system, this paper provides flux-oriented control for a permanent magnet synchronous generator PWM rectifier. The mathematical model of the generator rectifier is established under the rotating coordinate system. Then, a novel decoupling control strategy without the exact value of the generator stator inductance is proposed to regulate the active current and the reactive current, and an outer voltage linear control strategy with the control amount of the square of the voltage is proposed to regulate the output voltage. Simulation and experimental results demonstrate the effectiveness of the system.

Generalized Synchronous Optimal Pulse Width Modulation for Multilevel Inverters

With the growing interest of the industry in high-power medium-voltage multilevel inverters and the technological limitation in high voltage power semiconductors switches, synchronous optimal pulse width modulation techniques, originally developed for two-/three-level inverters, became again a topic of interest, now to optimize multilevel waveforms. This work proposes a novel formulation for the problem of optimizing the modulation pattern of multilevel converters, including in a single optimization problem the decision of the directions for each step transition in addition to the switching angles and, thus, completely defining the optimized multilevel waveform at a given modulation index. In addition, experimental results are presented in order to demonstrate the effectiveness of this optimized modulation technique exemplar applied to a five-level NPC H–bridge feeding a permanent magnet synchronous motor.

Global Synchronous Pulse Width Modulation of Distributed Inverters

Traditionally, the parallel-connected multileg inverter could assume the interleaved pulse width modulation (PWM) to attenuate the high-frequency harmonics by using a single controller to generate the corresponding interleaved switching sequences. However, the interleaved PWM cannot be employed in multiple distributed independent inverters installed at different locations with their own controllers because the multiple independent controllers cannot work synchronously and the operational conditions are different among the distributed inverters. The summed current harmonics of multiple distributed inverters could vary at the point of common coupling (PCC) and worsen the power quality of consumers. This paper, therefore, proposes a global synchronous PWM method for the distributed inverters to attenuate the high-frequency current harmonics at PCC. The optimal interleaved switching angles among the distributed inverters are calculated by fully considering line impedances, modulation indexes, switching frequencies, the number of distributed inverters, etc. Particle swarm optimization method is assumed to find the optimal solution. Then, the low-frequency synchronization operation will synchronize the multiple PWM switching sequences in the wanted variation range. Experimental results are presented to prove the validity of this method.

Global synchronous discontinuous pulse width modulation method with fast calculation capability for distributed three-phase inverters

When multiple distributed converters are integrated, the high frequency harmonics will randomly accumulate at the point of common coupling (PCC). This paper proposes a new fast global synchronous discontinuous pulse width modulation (GSDPWM) method of three-phase inverters to effectively attenuate the high frequency current harmonics at PCC. Firstly, the basic principle and the realization method of GSDPWM for three-phase inverters are explained, which can be employed for different modulation types. Then a fast calculation method, which can equally derive the minimized total harmonic distortion (THD) of total current, is proposed to release the calculation burden. Finally, MATLAB simulations and experimental results are presented to verify the performance of GSDPWM.

A Simplified Synchronous Pulse-Width Modulation Method for Three-level Inverter of High-speed Train

A Simplified Synchronous Pulse-Width Modulation Method for Three-level Inverter of High-speed Train

Modeling and control strategy of three phase neutral point clamped multilevel PV inverter connected to the grid

This paper focuses on control design of three phase neutral point clamped multilevel inverters (NPC-MLI) interconnected with PV array to the existing grid together equipped with boost converter. To achieve synchronized pulse width modulation and nominal harmonic performance space vector modulation (SVM) is adopted. The controller method of feed forward as well as integrator anti-windup is adopted for the proportional integral (PI) controllers to minimize the degradation problem. The synchronization and stability of the tracking performance of the controllers are verified by the bode diagram. In the proposed method harmonic current from filter capacitance is tracked and transformed to dq controller to reduce the total harmonic distortion (THD). Different three phase transformer-less inverter topologies with the proposed controller are compared with the traditional method. The reliability of the converters is determined by the thermal behavior of the semiconductor devices which equally affects the robustness and cost of the converters. Therefore a simulation platform is developed in a Matlab/Simulink and PLECS simulation environment to analyze the dynamics of the system. The controllers examine feasible option for three phase grid connected PV inverters.

Suppression of Common-Mode Voltage Using a Multicentral Photovoltaic Inverter Topology With Synchronized PWM

This paper describes an optimal configuration for multicentral inverters in a medium-voltage (MV) grid, which is suitable for large-scale photovoltaic (PV) power plants. We theoretically analyze a proposed common-mode equivalent model for problems associated with multicentral transformerless-type three-phase full bridge (3FB) PV inverters employing two-winding MV transformers. We propose a synchronized pulse width modulation (PWM) control strategy to effectively reduce the common-mode voltages that may simultaneously occur. In addition, we propose that the existing 3FB topology may also have the configuration of a multicentral inverter with a two-winding MV transformer by making a simple circuit modification. Simulation and experimental results of three 350 kW PV inverters in a multicentral configuration verify the effectiveness of the proposed synchronization control strategy. The modified transformerless-type 3FB topology for a multicentral PV inverter configuration is verified using an experimental prototype of a 100 kW PV inverter.

Neutral-Point Potential Balancing Using Synchronous Optimal Pulsewidth Modulation of Multilevel Inverters in Medium-Voltage High-Power AC Drives

This paper presents neutral-point potential (NPP) balancing while maintaining low harmonic distortion using optimal pulsewidth modulation (PWM) of a multilevel inverter for medium-voltage high-power industrial ac drives. This method is applicable for five-level inverters or higher. A high performance of the machine is observed experimentally at low-switching-frequency operation employing the proposed technique. In the past, low distortion and optimal common-mode voltage at low-switching-frequency control have been reported using proposed synchronous optimal PWM.

Generalized Optimal Pulsewidth Modulation of Multilevel Inverters for Low-Switching-Frequency Control of Medium-Voltage High-Power Industrial AC Drives

A generalized optimal pulsewidth modulation (PWM) technique applicable to multilevel inverters for low-switching-frequency control of medium-voltage high-power industrial ac drives is presented. Proposed synchronous optimal PWM method allows setting the maximum switching frequency to a low value without compromising the harmonic distortion of machine currents. Low switching frequency reduces the switching losses of the power semiconductor devices, resulting in higher inverter power output and efficiency. The proposed optimization results in low harmonic distortion at low switching frequency. Experimental results of a five-level inverter drive using optimal PWM are presented.

A Hybrid Multilevel Inverter System Based on Dodecagonal Space Vectors for Medium Voltage IM Drives

Dodecagonal (12-sided) space vector pulsewidth modulation (PWM) schemes are characterized by the complete absence of (6n ± 1)th-order harmonics (for odd n) in the phase voltages, within the linear modulation range and beyond, including overmodulation. This paper presents a new topology suitable for the realization of such multilevel inverter schemes for induction motor (IM) drives, by cascading two-level inverters with flying-capacitor-inverter fed floating H-bridge cells. Now, any standard IM may be used to get the dodecagonal operation which hitherto was possible only with open-end winding IM. To minimize the current total harmonic distortion (THD), a strategy for synchronous PWM is also proposed. It is shown that the proposed method is capable of obtaining better THD figures, compared to conventional dodecagonal schemes. The topology and the PWM strategy are validated through analysis and subsequently verified experimentally.