Phase Shifted Carrier PWM Research Articles

CRC and NHPWM method for test bench based on cascaded converter

This study describes a megawatt test bench based on the cascaded converter for the stability test of renewable energy generation system under different grid disturbances. The test bench is composed of two cascaded converters, which are used to control the output of fundamental voltage and harmonic voltage. Aiming at the defects of the traditional repetitive controller (RC) and hybrid pulse-width modulation (HPWM) method, configurable RC (CRC) and novel HPWM (NHPWM) method are presented. By flexibly configuring the zeros and poles of CRC, the harmonic order that can be tracked accurately and the time delay of CRC can be easily changed. Besides, with NHPWM, the number of modules modulated by carrier phase-shifted PWM can be arbitrarily configured according to the output voltage quality and switching loss. Therefore, the flexible CRC and NHPWM are beneficial to achieve high control accuracy of fundamental and harmonic voltage and fast dynamic response while considering the switching loss, which is verified by simulation. The detailed harmonic analysis and calculation method of NHPWM are given, which are also proved correct by comparison of theoretical calculation and simulation results.

Interpreting the Individual Capacitor Voltage Regulation Control of PSC-PWM MMC via Consensus Theory

In computer science, consensus theory has been studied for decades. “Consensus” in a multi-agent system means reaching an agreement regarding a certain quantity of interest. The modular multilevel converter (MMC) is a promising topology for medium- and high-power applications owing to its salient features. In MMC operation, one key point is to regulate the capacitor voltage of each submodule (SM). The SMs in MMCs are interconnected both physically and via a control system, and these SMs can be regarded as a multi-agent system, with the control objective of regulating their capacitor voltages, which could formulate a consensus problem. In this paper, through mathematical derivation, it is found that individual capacitor voltage regulation control of phase-shifted-carrier pulse-width modulation (PSC-PWM) MMC is one special case of consensus theory. Furthermore, based on the consensus theory, the influence of different communication structures on the MMC voltage regulation performance is discussed. The analysis proves that the existing one has the highest rate of convergence. The impact of current-tracking dynamics on consensus-based interpretation is also analyzed. In addition, the proportional relationship between the rate of convergence and the P controller parameter is also justified. The experiments on a seven-level down-scaled prototype are conducted to confirm the analysis.

Ripple Analysis and Capacitor Voltage Balancing of Five-Level Hybrid Clamped Inverter (5L-HC) for Medium-Voltage Applications

The five-level hybrid clamped inverter (5L-HC) is a promising new topology for medium-voltage applications. However, to minimize the capacitors and ensure good performance of the converter, capacitor voltage ripples, as well as voltage balancing control, need further study. Based on carrier-phase-shift PWM (CPS-PWM), this paper gives a rigorous analysis of the ripple characteristics of all the capacitors (which consist of three groups: the flying capacitors, the central dc capacitor, and the upper and lower dc capacitors) under both normal and unbalanced operating conditions. The results can serve as a guide for the optimal design of the capacitors. First, as for the balancing issue, a self-balancing mechanism of the central dc capacitor, which is similar to the better-known self-balancing feature of the flying capacitors, is revealed. Then, a new voltage balancing strategy is proposed for these two groups of capacitors to cope with disturbances arising from various nonideal factors. For the upper and lower dc capacitors, which suffer from intrinsic imbalance, this paper proposes a better method to calculate the optimal zero-sequence voltage (ZSV), which is to be injected to achieve the balancing objective. In this paper, the ripple analysis and balancing strategy proposed are verified with simulations and experiments.

Phase-Shifted Carrier Pulse-Width Modulation Algorithm With Improved Dynamic Performance for Modular Multilevel Converters

High modularity, easy scalability, and superior harmonic performance, comprising the topology with the most potential for medium- to high-voltage high-power applications, are representative features of a modular multilevel converter (MMC). Each application of a MMC requires a proper scheme such that it conforms to control objectives such as correct submodule capacitor voltage balancing control and the suppression of circulating current. Over the past few years, various studies have been presented that meet the MMC requirements through both classical control-based pulse-width modulation and model predictive control, although some drawbacks exist for both control concepts. The dynamic performance of the classical control methods with proportional-integral or proportional-resonant controllers is unsatisfactory, and the requirement of proportional-integral parameters tuning procedure makes converter operation performance depends on proportional-integral parameters adjustment. Meanwhile, model predictive control performance depends significantly on the mathematical model of a system, and weighting factor selection is tedious. In this paper, we propose an improved phase-shifted carrier pulse-width modulation method and capacitor voltage balancing control that inherits the merits from both classical control and model predictive control. Meanwhile, the proposed control method eliminates the requirement of the tedious proportional-integral parameters tuning procedure and improves the dynamic performance compared with the conventional phase-shifted carrier pulse-width modulation-based proportional-integral controller method. Simulations and experiments were conducted to demonstrate the proposed method's properness.

Performance Comparison of Modulation and Sorting Methods for Modular Multilevel Converter

The modulation strategy of modular multilevel converter (MMC) needs to be combined with the sub-module (SM) redistribution strategy to maintain the stability of the SM capacitor voltage while working properly. The submodule (SM) switching frequency and the voltage balancing performance have been compared between two pulse width modulation (PWM) methods, i.e. carrier phase shift PWM (CPS-PWM) and submodule unified PWM (SUPWM), combined with two kinds of sorting methods, i.e. modulation wave compensation method and improved module selection method. The theoretical and simulation results show that when the number of sub-modules and the carrier frequency meet the requirements of ship propulsion, it is difficult for modulation wave compensation method to maintain good performance in different output frequency conditions. Using improved module selection method will increase the switching frequency of the device, but it has a higher performance in voltage balancing. Introduction

An Innovative Rotor Position Detection at Stand-Still and Low Speed with Carrier Phase-Shifted PWM Method

An innovative permanent magnet synchronous motor rotor position detection method using d-q reference-frames derived from PWM inverter switching is presented based on carrier phase-shift PWM method. It also gives the development the polarity identification at standstill for permanent magnet synchronies motor in the rotary frame with position detected of the neutral voltage. The new technique detects the motor position from simple measurements of the neutral point voltage of the motor influenced by the variation of inductances with respect to rotor position. The transfer is derived with constant element and 2nd harmonic element of selfinductance and mutual-inductance between three phase inductances and the inductance of d-axis and q-axis. Theoretical studies are carried out and verified using experiment results with variation rotor position over one electrical cycle at standstill. Rotor position estimation from stator inductance variation with rotor position is effective in zero speed and low speed.

An improved submodule unified pulse modulation scheme for a hybrid modular multilevel converter

This paper presents an improved submodule unified pulse width modulation (SUPWM) scheme for a hybrid modular multilevel converter (MMC) composed of half-bridge submodules (HBSMs) and full-bridge submodules (FBSMs). The proposed SUPWM scheme can achieve an output voltage of (2N+1) (where N is the number of submodules in each arm) levels, which is the same as that of the carrier-phase-shifted PWM (CPSPWM) scheme. Meanwhile, the proposed SUPWM scheme can alleviate the uneven loss distributions between the left leg and right leg in FBSMs of the hybrid MMC. Moreover, the capacitor voltages of the sub-modules can be well balanced without complicated closed-loop voltage balancing controllers. The validity of the proposed SUPWM scheme is verified by both the simulated and experimental results.

Optimized Phase Disposition (PD) Modulation of a Modular Multilevel Converter

This paper presents a theoretical harmonic analysis of phase disposition (PD) and phase-shifted carrier pulse-width modulation strategies for modular multilevel converters (MMCs). It is shown that when these strategies are implemented on a per MMC arm basis, their spectral performances converge because of cancellation of odd carrier sideband groups between each phase leg's arms. An improved PD modulation strategy is then presented that uses a single PD modulator for the entire phase leg, followed by a state machine decoder that evenly distributes switching pulses to all submodules across the phase leg upper and lower arms to balance the distribution of submodule commutation events. The resulting strategy achieves optimum phase leg PD spectral performance and also achieves natural voltage balancing of the MMC submodules. All theoretical findings are supported by simulation and experimental results obtained using a five-level MMC prototype.

PSPWM based Five-Level Shunt Active Filter for Power Quality Improvement in Power System Network

Power quality is a very important phenomenon in modern days and good power quality indicates efficient performance of a power system network. Presence of non-linear loads in power system network degrades the quality of power being delivered to other sensitive loads connected to the same network. Harmonics is one of the key parameters that power engineers are concerned about and good power quality insists for compensation of harmonics in power system. Active power filters prove to be feasible, valuable and successful custom power devices for harmonic compensation. The operation of a Five-Level Cascaded Inverter driven Shunt Active Power Filter for harmonic elimination and to improve power factor is discussed in this paper. Phase-Shifted carrier PWM technique is implemented for generating the gate drive signals of the inverter. The proposed Active Power Filter model was simulated on MATLAB/ SIMULINK platform and results were presented for a system with balanced linear and balanced non-linear load conditions.

Flux-Balancing Scheme for PD-Modulated Parallel-Interleaved Inverters

A simple scheme to realize phase-disposition carrier pulse width modulation (PD PWM) for parallel two-level voltage-source converters (2L-VSCs) is presented in this paper. The proposed implementation only uses a single carrier signal and can easily be implemented using a digital signal processor. The operation of the parallel VSCs with the coupled inductor (CI) under the PD PWM is briefly discussed, and the associated dc flux injection problem is investigated. A CI saturation issue during the band transition under the PD PWM scheme is also explored, and the strategy to avoid this problem is presented. In addition, the proposed strategy also maintains a volt-second balance to synthesize desired reference space voltage vector during the band transition. As a result, a smooth transition from one modulation band to the other is ensured without causing disturbances in the line-to-line voltage. The switching losses and the harmonic performance of the proposed implementation are also compared with the commonly used phase-shifted carrier pulse width modulation. The implementation issues are discussed and the experimental results are also presented.

Logic-Form-Equation-Based Active Capacitor Voltage Balancing Control Technique for Stacked Multicell Converters

This paper proposes a novel active capacitor voltage balancing technique for stacked multicell (SM) converters. The proposed active capacitor voltage balancing control method detects the direction of the load current and measures the voltage of flying capacitors (FCs) to generate a proper switching state in order to form the required output voltage level and regulate the FC voltages at their desired reference levels. The proposed active capacitor voltage balancing control technique can modulate the output voltage through any of the pulse-width-modulation (PWM) techniques such as the phase-shifted carrier PWM or the level-shifted-carrier PWM. The foremost advantage of the proposed active control technique is that it does not demand any complex computations because it is not based on the optimization of the FC voltage-deviation cost functions. A thorough set of simulation results and experimental measurements for the five-level and seven-level SM converters are provided to validate the proposed active capacitor voltage balancing control method.

Control of Active Power Exchange With Auxiliary Power Loop in a Single-Phase Cascaded Multilevel Converter-Based Energy Storage System

Cascaded multilevel converter (CMC)-based energy storage system, which consists of cascaded H-bridge converters and energy storage components, is a promising option to compensate fluctuating electric power of renewable energy. This paper proposes a novel single-phase CMC-based battery storage system, which includes an LC branch. The cascaded converter cells and the LC branch form an auxiliary power loop, which could realize active power exchange between different cells with the proposed dual-frequency phase-shifted carrier pulse width modulation (DF-PSC PWM). The principle and effectiveness of DF-PSC PWM and the power transfer mechanism are analyzed. Meanwhile, the design of the tuned filter, output filter, and the state of charge balancing control system is introduced. The operation principle of the power exchange in the proposed energy storage system has been successfully verified by simulation and experimental results.

A New Reduced-Component Hybrid Flying Capacitor Multicell Converter

This paper presents a new multicell topology based on flying capacitor (FC) structure suitable for multilevel converters. The proposed topology employs the concept of phase-shifted carrier pulse width modulation (PWM) with modified modulating signals to generate appropriate PWM signals. The modulation strategy along with all possible switching states are explained. The implementation of the proposed PWM technique is shown by the help of illustrating waveforms. To show the advantages of the proposed structure, different performance criteria are compared with other FC multicell (FCM) structures. Simulation results are used to further evaluate the potential merits of the proposed topology. It is shown that the proposed structure is superior to other FCM-based structures from different standpoints. Specifically, it reduces the number of high-frequency switches, the number of FCs, and at the same time improves the quality of output voltage. A laboratory-type experimental setup is used to validate the modulation strategy and other theoretical findings.

Asymmetrical carrier phase‐shifted pulse‐width modulation for partly regenerative converter

A cascaded H-bridge-based partly regenerative converter is a low-cost scheme to enable a medium-voltage motor drive to feed back the braking energy to the grid. However, its asymmetrical topology induces serious switching harmonic distortion on the motor side when conventional symmetrical carrier phase-shift pulse-width modulation (SCPS-PWM) is used. This study analyses switching harmonic characteristics in detail and proposes an asymmetrical carrier phase-shift pulse-width modulation (ACPS-PWM) method to improve the switching harmonic performance of the partly regenerative converter by eliminating low-frequency switching harmonics. The proposed method transcends the limitation of SCPS-PWM on carrier phase-shift angles, increasing the controllable degrees of freedom that can be used to multiply the apparent switching frequency without extra hardware or software investment. ACPS-PWM is compared with other modulation methods, and the possibilities for other applications are discussed. Experimental results verify the effectiveness of the proposed method.

An Improved Phase-Shifted Carrier Modulation Scheme for a Hybrid Modular Multilevel Converter

This paper presents an improved phase-shifted carrier pulse width modulation (PSC-PWM) scheme for the hybrid modular multilevel converter (MMC) consisting of half-bridge submodules (HBSMs) and full-bridge submodules (FBSMs). When the traditional PSC-PWM schemes for the HBSMs-based MMC and the FBSMs-based MMC are directly applied to the hybrid MMC, some mismatch pulses will occur on the arm voltages because the HBSMs and the FBSMs have different characteristics. These mismatch pulses not only generate undesirable harmonics on the output voltages, but also induce the significantly uneven loss distributions between the HBSMs and the FBSMs. Therefore, an improved PSC-PWM scheme for the hybrid MMC is proposed in this paper to deal with these issues. The improved PSC-PWM scheme can eliminate the mismatch pluses in the output voltages, alleviate the uneven loss distributions between the HBSMs and the FBSMs, and reduce the total switching loss of the converter. The mathematical analysis of the improved PSC-PWM scheme for the hybrid MMC is conducted and its harmonic characters are investigated. The analysis results are verified and compared with the traditional PSC-PWM scheme by the simulated and experimental results.

Common-Mode Reduction for ANPC With Enhanced Harmonic Profile Using Interleaved Sawtooth Carrier Phase-Disposition PWM

Multilevel active neutral-point-clamped (ANPC) converter is popularly known for its higher medium voltage drives up to 6.9 kV. However, common-mode voltages (CMV) are generated when using the well-established carrier-based pulse width modulation (PWM) modulation technique. As a result, CMV will become the major cause of the premature bearing failures and the conducted electromagnetic interferences. In this paper, a reduced CMV strategy is proposed for the ANPC which employs an alternatively new hybrid carrier-based modulation named as interleaved sawtooth carrier phase-disposition PWM (ISC-PD-PWM). By doing so, enhanced harmonic profile is achieved as compared to the typically used classical phase-shifted carrier PWM (PSC-PWM). Therefore, a comparative evaluation of the seven-level (7L) ANPC performance using the proposed reduced CMV approach is made between the novel hybrid ISC-PD-PWM and the conventional PSC-PWM in terms of harmonic analysis. The experimental results have proven the feasibility of the proposed concepts with the CMV effectively reduced. Such perceived merits make ANPC be more attractive for its motor drives.

A Novel Modulation Scheme and a DC-Link Voltage Balancing Control Strategy for T-Type H-Bridge Cascaded Multilevel Converters

The cascaded multilevel converter is widely adopted to medium/high voltage and high power electronic applications due to the small harmonic components of the output voltage and the facilitation of modularity. In this paper, the operation principle of a T-type H-bridge topology is investigated in detail, and a carrier phase shifted pulse width modulation (CPS-PWM) based control method is proposed for this topology. Taking a virtual five-level waveform achieved by a unipolar double frequency CPS-PWM as the output object, PWM signals of the T-type H-bridge can be obtained by reverse derivation according to its switching modes. In addition, a control method for the T-type H-bridge based cascaded multilevel converter is introduced. Then a single-phase T-type H-bridge cascaded multilevel static var generator (SVG) prototype is built, and a repetitive controller based compound current control strategy is designed with the DC-link voltage balancing control scheme analyzed. Finally, simulation and experimental results validate the correctness and feasibility of the proposed modulation method and control strategy for T-type H-bridge based cascaded multilevel converters.

Review on pulse‐width modulation strategies for common‐mode voltage reduction in three‐phase voltage‐source inverters

With wide application of inverters in modern industry, common-mode voltage (CMV) problems invoked severe negative effects. Hardware and software solutions have been proposed to reduce the CMV. Compared with hardware CMV mitigation solutions, software strategies based on pulse-width modulation (PWM) modifications have aroused widespread attention for their cost-effective and control flexible advantages. Up to date, various reduced CMV PWM (RCMV-PWM) strategies have been reported, such as active zero state PWM, remote state PWM, near state PWM, phase-shifted carrier PWM, carrier peak position modulation and so on. For convenience of understanding and utilising the existed RCMV-PWM strategies, this study conducts a review on this topic. According to the principle of CMV reduction algorithms, the study divides the reported RCMV-PWM strategies into three different categories. It also presents comparisons of CMV reduction techniques and output performances (like CMV value, output ripple and linearity range) between different strategies. Meanwhile, CMV suppression principles, problems in implementation and improvements of each technique are described in detail. Moreover, the inherent characteristics and development tendencies of the RCMV-PWM techniques are discussed so as to offer reference for further research.

A Modified Static Ground Power Unit Based on Novel Modular Active Neutral Point Clamped Converter

Two new configurations of static ground power unit based on 5L active neutral point clamped (ANPC) and novel modular 9L-ANPC converter are proposed. First, a new level shifted phase-shifted carrier pulse-width modulation (LS-PSC-PWM) switching method for the 5L-ANPC converter is defined. By utilizing the proposed method, total harmonic distortion of output voltage is reduced in comparison with traditional PSC-PWM switching method. Then, a novel modular 9L-ANPC multilevel converter and its suggested modulation method is proposed in this paper. In comparison with traditional 9L-ANPC converter, the main advantages of proposed modular 9L-ANPC converter are halving the applied voltages on flying capacitors (FC), reduced number of FCs, and self-balancing of FCs, which is provided by suggested switching method. This results in reduction of the size and cost of converter, and makes it more feasible and reliable. Furthermore, inductance reduction of output LC filter enhances static ground power unit dynamic performances. The simulation and experimental results verified the feasibility and performance of proposed converters.

Generalized Theory of Phase-Shifted Carrier PWM for Cascaded H-Bridge Converters and Modular Multilevel Converters

This paper discusses the generalized theory of phase-shifted carrier pulsewidth modulation (PSC-PWM) for cascaded H-bridge (CHB) converters and modular multilevel converters (MMCs), provides a reasonable classification of the PSC-PWM, and extends the possible phase-shift angles to full range. First, the PSC-PWM for CHB converter is classified into two categories by phase-shift pattern. In addition, by rigorous mathematical derivation, the impact law of the full-range phase-shift angles on harmonic minimization is obtained. And then, it is proved that the generalized theory is equally applicable to MMC, which also merges the former proposed PSC-PWM for MMCs into itself. Moreover, the harmonic analysis of the dead-time error voltage is discussed, which is found to have the same harmonic distribution as the ideal voltage, except for the emerging of odd-order harmonics. In summary, this generalized theory offers a general perspective of the PSC-PWM for CHB converter and MMC, and builds up a scientific and comprehensive understanding for researchers from both academia and industry. Finally, the analytical findings are sufficiently validated by simulation and experimental results.