Phase Shifted Carrier PWM Research Articles

Dual-Phase-Shifted Pulsewidth Modulation of Three-Phase Modular Multilevel Converters

The modular multilevel converter (MMC) has been a crucial component for medium/high-power energy conversion systems due to its modular structure. In the literature, the harmonic analysis of MMC with different modulation methods, including the conventional carrier phase-shifted pulse width modulation (CPS-PWM) method, have been extensively investigated. However, the influence of the carrier displacement angles between three-phase legs on the output performance of an MMC is normally ignored. This paper proposes a dual-phase-shifted PWM (DPS-PWM) for a three-phase MMC which further enhances the performance of the conventional CPS-PWM scheme through proper selection of carrier displacement angles between three phases. First, the operation principle and implementation of the proposed DPS-PWM method is described. Then a two-dimensional (2D) Fourier model is derived to analyze how the carrier displacement angles between stacks and legs affect the harmonics of output voltage and circulating current. It is found that DPS-PWM can suppress specific harmonics in the line-to-line voltage by coordinating the carriers' phase shifting between the three-phase legs without affecting phase voltage and circulating current. Finally, the effectiveness of the DPS-PWM method is verified by simulation and experimental results.

High-Frequency Current Harmonic Analysis and Suppression in Dual Three-Phase PMSMs With Advanced Carrier Phase-Shift PWM

High-Frequency Current Harmonic Analysis and Suppression in Dual Three-Phase PMSMs With Advanced Carrier Phase-Shift PWM

VSG Control for Cascaded Three-Phase Bridge Based Battery Inverter

With the increasing number of new energy sources connected to the grid, the unbalanced output of three-phase grid-connected inverters and the lack of no inertia and damping characteristics in the traditional microgrid control system will seriously affect the stability of voltage, frequency, and power angle for microgrids. This paper proposes a novel cascaded three-phase bridge inverter topology for the battery system used for the electric vehicle. Compared with traditional cascaded H-bridge inverters, the proposed multilevel inverter can achieve self-adaptive balance for three phases. The mathematical model of a cascaded three-phase bridge inverter is established in this paper. Based on the voltage and current equations of a multilevel inverter, a new modulation strategy named carrier phase-shifted-distributed pulse width modulation (CPSD-PWM) was developed, which is more suitable for cascaded three-phase bridge inverters. The harmonic analytic equations of carrier phase-shifted pulse width modulation (CPS-PWM) and CPSD-PWM are constructed by the double Fourier analysis method. Compared with the traditional PWM modulation strategy, the CPSD-PWM can reduce the output harmonics and improve the balance of the three-phase output, which can realize the three-phase adaptive balance in the cascaded three-phase bridge inverter. This paper develops a cascaded three-phase bridge multilevel power converter system based on the virtual synchronous generator (VSG) control strategy. The voltage and frequency of inverter output can be accurately controlled in both island mode and grid-connected mode through active power-frequency regulation and reactive power–voltage regulation, and the stability of primary frequency regulation for the multilevel microgrid inverter can be improved by collaborative optimization of virtual inertia and virtual damping. The CPSD-PWM modulation strategy and VSG control strategy are verified by the simulation results and experimental data for the cascaded three-phase bridge inverter.

Multicell nonisolated resonant modular multilevel dc‐dc converter with self‐voltage balancing and step‐up conversion

SummaryWith the rapid development of renewable energy power generation technologies in high‐voltage direct‐current (HVDC) system, the high step‐up ratio dc‐dc conversion plays an important role to connect dc grids with different voltage levels. This paper presents a multicell nonisolated resonant modular multilevel dc–dc converter (MMDC) for medium‐ and high‐voltage applications. The converter exhibits expandability without using transformer. Moreover, by adding additional switched‐inductor (SL) cells, switched‐capacitor (SC) cells, and the upper arm submodules (SMs), the proposed converter can obtain high gain with low voltage stresses on switches and diodes. The operating states of SMs is regulated by the carrier phase‐shifted pulse width modulation (CPS‐PWM) to guarantee the number of inserted SMs is constant to support the high‐side load at any moment. The converter is operated in resonant mode with resonance between SM capacitors and arm inductor. The step‐up ratio could be regulated by adjusting the number of SL cells, SC cells, and upper arm SMs; thus, more flexible voltage regulation can be realized. In addition, the proposed converter has the voltage self‐balancing capability of capacitors in SMs and SC‐cells without additional balancing control strategy. The topology configuration, parameter design guideline, operating principle, and comparison with other MMDCs are presented. Finally, the theoretical analysis is verified by the simulation and bench‐scaled experimental prototype results.

Topology and Modulation of Fractional-Level MMC for DC Distribution Grids

For the modular multilevel converter (MMC) with a small quantity of submodules, neither nearest level modulation (NLM) nor carrier phase-shifted pulse width modulation (CPS-PWM) can achieve high voltage quality and low operation loss simultaneously. In this paper, a novel fractional-level MMC (FLMMC) topology is proposed, in which fractional-level submodules are introduced to multiply the output levels. To balance the capacitor voltages between conventional submodules and fractional-level submodules, this paper develops a fractional-level modulation (FLM) method suitable for FLMMC. Considering control complexity and device quantity, the FLMMC with two half-level or one-third-level submodules in each arm is investigated in this paper. Simulation and experiment tests are carried out to validate the effectiveness and superiority of FLMMC under FLM. FLMMC can improve the voltage quality without increasing control complexity, circulating current and switching loss, so as to comprehensively adapt to the power quality requirements of dc distribution grids.

A Robust Capacitor Voltage Balancing Method for CPS-PWM-Based Modular Multilevel Converters Accommodating Wide Power Range

Capacitor voltage balancing is one of the most important issues for the safe, reliable, and economical operation of the modular multilevel converter (MMC). This article proposes a modified individual capacitor voltage balancing method for MMCs with phase-shifted carrier pulsewidth modulation (PWM) (CPS-PWM) to solve the problem of the poor dynamic performance that the conventional individual voltage balancing methods suffer at low output power. In the proposed method, the information of arm current is incorporated into the balancing algorithm to cancel out the coupling effect of the output power on balancing control. Compared with conventional balancing methods, the proposed method shows better robustness against varying output power and maintains a good dynamic performance in a wider power range. The complete modeling process and parameter design are presented and considered for system stability. The effectiveness of the proposed method is verified with both MATLAB/Simulink simulation and experimental results.

Research on High Frequency Vibration Reduction Using Carrier Phase Shifted PWM for 4-Module 3-Phase Permanent Magnet Synchronous Motor

This article investigates the effect of the carrier phase shifted pulsewidth modulation on the vibration reduction of inverter-fed multiphase permanent magnet synchronous motors. This approach reduces vibration by changing the order of the carrier harmonic-induced electromagnetic force on the stator. Experiments verify that this method can effectively suppress vibration at a specific carrier frequency, but the vibration reduction effect depends on the carrier frequency, the modal frequency of the motor and the phase-shifted angles.

Improved CPS-PWM Approach for Over-Modulation Operations of Hybrid Modular Multilevel Converter

The over-modulation capability of the hybrid modular multilevel converter (MMC), mixed by half-bridge and full-bridge submodules (SMs), has acquired widespread attention recently, which can significantly increase the design freedom of the hybrid MMC. When the hybrid MMC is applied in the medium-voltage occasions, an improved carrier phase shift pulsewidth modulation (CPS-PWM) approach is put forward in this article for its over-modulation operation under the nominal and variable dc conditions. It is featured with high flexibility, adjustability, and simple implementation. A new standard voltage is introduced to normalize the modulation wave, by which there is always a sufficient margin between the peaks of the normalized modulation wave and carrier waves under any modulation indexes. Also, it can perform well when the nominal dc voltage of the hybrid MMC is not the integer multiple of SM voltage. Moreover, the carrier wave arrangements are decoupled with the number of SMs, dc voltage, and ac voltage, so the variable dc operation of the hybrid MMC can be achieved without rearranging the carrier waves. Finally, the simulations and experiments are carried out to confirm the effectiveness of the proposed CPS-PWM approach for over-modulation operations under the steady-state and variable dc conditions.

A modified CPS-PWM for capacitor voltage reduction of MMC based variable speed drive

<span>In recent years, modular multilevel converters (MMC) have become one of the most popular multilevel converter topologies. Despite its growing popularity, MMC is still less widespread in variable speed drives (VSDs) applications. The reason for this is that the voltage ripple of the MMC submodules (SM) increases during the low-speed constant torque operation. In this paper, carrier phase shift-pulse width modulation (CPS-PWM) is modified to reduce the average voltage of SM and thus accommodate more ripples without exceeding the maximum SM voltage. The proposed method does not involve the injection of circulating current components, thereby resulting in less power loss. In addition to that, the necessity for increasing the SM capacitor rating during low-speed operation is not required. Extensive simulation has been conducted under various speed commands to validate the effectiveness of this method.</span>

High‐frequency harmonic suppression method for interleaved traction converters based on synchronous sampling

High-frequency resonance in traction power supply systems (TPSSs) is of great concern because of its potential to cause great damage to the safety and stable operation of railroad systems; it has been demonstrated that when a locomotive generates a harmonic current with the resonant frequency of the series impedance on the traction network, a large amount of high-frequency harmonic voltage is generated. This paper proposes a high-frequency harmonic suppression method based on synchronous sampled carrier phase-shift PWM modulation strategy (SSCPS-PWM), which has the advantage of not only considering the consistency of sampling the analogue signal by multiple controllers, but also further optimising the precise synchronization between multiple converter pulses. This method generates lower high-frequency harmonic content and is particularly suitable for the field of high-power, low switching frequency, multi-controller locomotive traction converters. The proposed method was simulated and compared with the traditional method for the harmonics injected by the locomotive, and a real railway line with a harsh power supply condition was selected and field tests were conducted in four sections by a 7200kW 6-axle electric locomotive. The test results showed that the proposed method effectively reduced the high-frequency harmonic current of the locomotive and reduced the high-frequency resonant overvoltage in the TPSS.

An isolated modular multi‐level AC/AC converter with high‐frequency link and pulse flip circuit for fractional frequency transmission system application

Based on the modular topology and the traditional voltage-sourced converter (VSC) model, this paper presents an isolated modular multi-level AC/AC converter with high-frequency (HF) link and pulse flip circuit for fractional frequency transmission system (FFTS) application. The proposed converter uses the HF transformer to realize electrical isolation, omitting the industrial frequency (IF) transformer with large volume and heavy weight. In the primary side of the HF transformer, the power transmission is realized by the rectifier and the inverter. In the secondary side of the HF transformer, the double H-bridges are used to realize the natural freewheeling of the leakage current, which solves the problem of voltage overshoot. On the basis of carrier phase-shifted pulse width modulation (CPS-PWM), an improved modulation strategy is proposed to realize the HF output voltage of the inverter. It has the advantages of easy expansion, no circulation current, good output voltage quality, low cost and no need of offshore converter station, so it has great potential in the field of offshore wind power grid connection. The working principle, natural freewheeling modes, modulation method and overall system control scheme of the proposed topology are introduced in detail, and the feasibility of the proposed topology is verified by simulation in MATLAB/Simulink environment and test through APPSIM platform.

Monopolar Symmetrical DC–DC Converter for All DC Offshore Wind Farms

All dc offshore wind farms are gaining popularity for long-distance and high-power offshore wind energy conversion. It calls for high-power dc–dc converter with high step-up ratio for interconnecting the medium-voltage dc collection and the high-voltage dc transmission systems. This article proposes a monopolar symmetrical dc–dc converter, which is featured with partial-power processing and presents less installed capacity of components, low cost, low power loss, lightweight, and small footprint. Moreover, a modified phase-shifted carrier pulsewidth modulation with variable carrier frequency is developed to further reduce the switching loss and keep the dynamic current tracking performance. The effectiveness of the proposed converter has been verified by a simulation study of a 400 MW, ±25 kV/±250 kV model and experimental results of a 5.4 kW, ±60 V/±320 V scaled-down prototype.

Variable Voltage Variable Frequency Modular Multilevel AC/AC Converter With High-Frequency Harmonics Filtering Capability

This article proposes a variable voltage variable frequency modular multilevel ac/ac converter (VVVF-MMC) with a high-frequency isolation link, which can realize voltage and frequency conversion simultaneously with insulated-gate bipolar transistors (IGBTs) of the same rated voltage and current level. The parallel connection of multiple modules is realized by coupling reactors, which can realize large-scale voltage and current transformation and save volume. It combines parallel multiplexing and serial multiplexing technology of submodules (SMs) to increase the equivalent switching frequency, thereby canceling nonzero sequence high-frequency voltage and current harmonics, so it has good power quality in the steady-state. Under the improved carrier phase-shifted pulsewidth modulation (CPS-PWM) strategy, the pulse flip circuit can realize soft switching operation, thereby improving energy conversion efficiency. Furthermore, dc capacitor voltage balancing and parallel SM current balancing control strategies are designed. With the strong filtering ability, the proposed ac/ac converter can be used as the onshore converter station of fractional frequency offshore wind power system. Due to the advantages of small size and high efficiency, it also has broad application prospects in distribution networks and electric drive. Simulation and experimental results validate the effectiveness of the proposed converter topology.

Novel Level-Shifted PWM Technique for Cascaded Multilevel Quasi-Impedance Source Inverter

In a multilevel quasi-impedance source inverter (qZSI), phase-shifted carrier pulsewidth modulation (PS-PWM) is the most popular modulation method as it offers advantages such as simple implementation and evenly powered distribution among all qZSI modules with optimum total harmonic distortion (THD). However, it results in higher switching losses. An approach to solving this problem would be development and implementation of a PWM method which results in lower switching losses. With this aim, a novel hybrid phase-opposition disposed, phase-shifted (PWM) (PODPS-PWM) technique is proposed in this article. With the proposed PWM method, reduced switching losses are achieved. Active state losses are reduced to 6% and switching losses are reduced to at least >39% in qZSI modules. A mathematical relationship between the PS-PWM and the proposed PODPS-PWM has been deduced. For experimental validation, a 1.5-kW seven-level qZSI setup is developed. Different performance aspects are presented, discussed, and analyzed, which help in validating the superior performance of the proposed solution. Moreover, an application for the solar photovoltaic (PV) multilevel inverter system has been discussed, for the partial shading condition. During this condition, the PS-PWM forces the extraction of lower power from the remaining healthy modules. This is due to the evenly powered distribution nature of the PS-PWM. Comparatively, the proposed PWM yields higher power. To validate higher power extraction, simulation results are presented and compared for both modulations under healthy and different partially shaded conditions. Under extreme partial shading conditions, the increase in power extraction is up to 29%.

PCCPS-PWM based vehicle-network high frequency resonance suppression method

In recent years, the safe and stable operation of electrified railways has attracted more and more attention. In particular, the stability of vehicle-grid coupling, which focuses on the phenomenon of vehicle-grid high frequency resonance (HFR), has become a hot research topic. Based on the instability mechanism of vehicle-grid coupling, and from the perspective of grid-side converter modulation strategy, measures to suppress HFR are further proposed. Based on the improvement of commonly used modulation strategies, Periodic Control Carrier Phase-Shift Pulse Width Modulation (PCCPS-PWM) is proposed, this solves the HFR problem caused by the switching characteristic frequency harmonics caused by the inaccurate phase shift angle between the grid-side converters. And it is verified by Matlab simulation and hybrid electric train sets.

Model Predictive Arm Current Control for Modular Multilevel Converter

Arm current control is a promising candidate for modular multilevel converter (MMC) due to it can effectively regulate ac-side current and control the ac component of circulating currents simultaneously. The conventional arm current controller designed in frequency domain based on classical control theory have to design the separate controller for each frequency reference signal. As a result, the controller structure is complicated. And limited by the bandwidth of the arm current compound controller, the control performance will be affected by the grid-side voltage harmonics. Model predictive control (MPC) is an optimal control method in time domain. It not only has fast dynamic response, but also can track multi-band composite signals with high accuracy. To address the above issues of traditional arm current control, this paper proposes a model predictive arm current control strategy. Combined with phase-shifted carrier pulse width modulation (PSC-PWM), the computation burden of the presented method can be independent of the number of cascaded sub-modules (SMs). Simulation and experimental results reveal the proposed MMC integrated control strategy has fast dynamic response with small tracking errors even under non-ideal grid conditions.

High Quality NLM Method for Medium Voltage Hybrid Bridge MMC

Medium voltage hybrid bridge multilevel converter (MMC) usually has a lower number of links. Therefore, the traditional Nearest Level Modulation (NLM) method has the problems of low equivalent switching frequency and poor output quality. And the traditional Carrier Phase-shifted Pulse Width Modulation (CPS-PWM) modulation has problems such as difficulty in hybrid bridge control, difficulty in redundant configuration, and large amount of calculation. In response to the above problems, this paper proposes a new high-quality NLM method. Based on the traditional NLM modulation method, PWM modulation output and module voltage equalization are realized through the time difference between one module input and one module exit in each control cycle. It achieves the purpose of improving the equivalent switching frequency and output power quality, and at the same time has the advantages of the traditional NLM modulation method with small calculation amount, redundant configuration and hybrid bridge modulation. This article describes the three modulation methods and compares their effects. Finally, the theoretical analysis is verified by PSCAD simulation.

Circulating Current Suppression Strategy of Modular Multilevel Converter Based on Model Predictive Control

Modular Multilevel Converter (MMC) has the characteristics of high voltage level and low switching frequency. The traditional modular multilevel converter circulating current control strategy mostly adopts the PI control principle, and the parameter setting is complicated and the accuracy is not high, and the control process is more difficult. Model predictive control strategy is the optimal control method based on the model in the existing time domain. This paper proposes a Model Predictive Control (MPC) method based on carrier phase-shifted pulse width modulation (PSC-PWM) to suppress the circulating current, and output the optimal modulation wave through model prediction. Compared with the traditional control strategy, this strategy is simple to implement, does not require complex tuning calculations, and combines with the traditional capacitor voltage equalization strategy to obtain the output modulation wave. A 7-level MMC simulation control system is built in MATLAB / SIMLINK to verify the theory, comparing with existing control methods, it can be concluded that the proposed method has high calculation efficiency, good control accuracy and strong robustness.

Study of start-up decoupling controller for modular multilevel converter

Modular multilevel converters are widely used in power systems because of their significant advantages. In this paper, a dynamic mathematical model is established by analyzing the topology, operating principle and switching function of the modular multilevel converter, so as to construct an inner and outer loop decoupling controller in dq coordinates. The carrier phase-shift pulse-width modulation is selected to control the sub-module operation, and the uncontrolled pre-charging method is adopted to charge the sub-module. Finally, simulation experiments are carried out in MATLAB/Simulink, and the results show that the control method achieves smooth start-up of the modular multilevel converter.

Research on Multi-Port DC-DC Converter Based on Modular Multilevel Converter and Cascaded H Bridges for MVDC Applications

Aiming at the low-voltage DC distribution network system and combining the characteristics of F2F structure and ISOP-DAB structure DC transformer, this paper proposes a DC transformer structure based on modular multilevel converter (MMC) and cascaded H-bridge. First of all, this paper analyzes several different cases. Case 1 proposes a type of equal carrier-phase-shift pulse-width modulation (CPS-PWM) of MMC, which can produce an equal five-level voltage waveform. In the meanwhile, another unequal CPS-PWM control is proposed to produce an unequal five-level voltage waveform. According to the descriptions of case 2 , the quasi-square-wave-modulation method with a wide gain range can greatly reduce the insulation design difficulty of the intermediate AC side high-frequency transformer and the voltage stress on the AC side. Case 3 demonstrates the extended-phase-shift (EPS) control of three-port DC-DC converter. Combining the voltage sorting algorithm of voltage sequencing and cyclic switching, a strategy of voltage equalization for grouped capacitors is proposed. Considering the various application scenarios of actual working conditions, the soft switching characteristics and multi-port power characteristics of the DC transformer are analyzed. In order to verify the feasibility of the DC transformer structure and its control strategy, a simulation model was built in Matlab/Simulink and the results were verified. The results are in accordance with the theoretical analysis.