Carrier-based PWM Research Articles

Three-Phase Four-Leg Drive for DC-Biased Sinusoidal Current Vernier Reluctance Machine

This paper proposes a three-phase four-leg drive for dc-biased sinusoidal current vernier reluctance machine (DC-VRM). By adding an asymmetrical neutral leg to the conventional three-phase inverter, the dc field excitation current can be generated. Compared to the open-winding inverter (conventional drive topology), the three-phase four-leg inverter greatly reduces the number of power devices, and the asymmetrical neutral leg does not have short-circuit straight-through risk. The topology ensures that the stator current can flow in both directions and maximum torque per copper loss can be obtained in DC-VRM. Equivalent carrier-based pulsewidth modulation (PWM) strategy is proposed to produce the dc-biased sinusoidal current and maximize the dc bus utilization. The proposed carrier-based PWM has several different equivalent methods. Compared to the conventional DC-VRM drive, the power loss of the proposed drive with equivalent space vector PWM (SVPWM) can be reduced significantly and can be further reduced by discontinuous PWM minimum (DPWMMIN) in the rated condition. The proposed drive has the characteristics of low cost, high power density, and high efficiency compared to the conventional DC-VRM drive.

A Constant Switching Frequency Multiple-Vector-Based Model Predictive Current Control of Five-Phase PMSM With Nonsinusoidal Back EMF

Most of the existing finite-control-set model predictive current control (FCS-MPCC) schemes for multi-phase motor suffer from heavy computational burden, inevitable low-order harmonic currents, and variable switching frequencies. Some virtual voltage vector (V3)-based FCS-MPCC schemes can effectively suppress harmonic current by zeroing the harmonic subspace voltage on average during one sampling period. However, they fail when the motor has a nonsinusoidal back electromotive force. In order to solve the aforementioned issues, this paper proposes a constant switching frequency multiple-vector-based FCS-MPCC scheme. Unlike the traditional FCS-MPCC schemes, the proposed scheme selects optimal V3s and their duty ratios in two orthogonal subspaces. Thus, it can simultaneously track the references in both orthogonal subspaces. In this approach, the optimal V3s and their duty ratios are directly obtained from the principle of deadbeat current control without time-consuming enumeration-based state predictions and cost function calculations. In addition, the obtained optimal V3s and their duty ratios are adopted to rearrange the pulse sequence to obtain constant switching frequency and can be simply synthesized by carrier-based pulsewidth modulation. Furthermore, a discrete time disturbance observer is designed to improve the robustness of the proposed FCS-MPCC against parameter mismatch. Finally, comparative experiments with traditional MPCC schemes for five-phase surface-mounted permanent magnet synchronous machine are carried out to verify the effectiveness of the proposed scheme.

Active Harmonic Filtering Using Multilevel H-bridge Inverter Based STATCOM

This paper proposed three-phase multilevel cascaded H-bridge inverter (MCHI) based active harmonic filtering (AHF) compensator, or refer to as static synchronous compensator (STATCOM), to minimize the harmonic components in a transmission network. There are three main elements to form a STATCOM, namely: control scheme, modulation technique and inverter topology. In this work, the synchronous reference frame (SRF) based controller is designed and implemented to produce the desired modulating signals (i.e., one for each phase) for the pulse width modulation (PWM) module. For simplicity, the carrier based pulse width modulation (CBPWM) with in phase disposition (IPD) technique is employed to generate the pulse trains and drive the three-phase five-level CHI. On the other hand, two three-phase non-linear loading conditions, which structured by different transformer winding configurations and power rectifier circuits, are utilized to verify the feasibility of the proposed AHF. The effectiveness and the theoretical prediction of the proposed approach is investigated and validated through simulation studies using MATLAB SIMULINK software package.

A Novel Fault-Tolerant Technique for Active-Neutral-Point-Clamped Inverter Using Carrier-Based PWM

This paper presents a novel fault-tolerant method for active–neutral-point-clamped (ANPC) inverter using a modified carrier-based pulsewidth modulation. At a fault event, the ANPC inverter is divided into subinverters, and the modulating signal is modified to two modulating signals. The modified modulating signals are used to control the subinverters and allow continuous operation of the three-level ANPC inverter during faulty conditions even up to four open-switch faults per phase. This technique provides the fault-tolerant capability of the ANPC inverter without the need to add any additional phase legs or complex control strategies. Furthermore, the proposed technique ensures the voltage balancing of the dc-link capacitors. The performance of the proposed fault-tolerant technique is verified through simulation studies in MATLAB/Simulink under different faulty conditions. The feasibility of the proposed technique is also verified experimentally.

Power‐efficient aliasing‐free PWM transmitter

Linearity and efficiency are important parameters in determining the performance of any wireless transmitter. Pulse-width modulation (PWM) based transmitters offer high efficiency but suffer from low linearity due to image and aliasing distortions. Although the problem of linearity can be addressed by using an aliasing-free PWM (AF-PWM), these transmitters have a lower efficiency as they can only use linear power amplifiers (PAs). Moreover, an all-digital implementation of such transmitters is not possible. The aliasing-compensated PWM transmitter (AC-PWMT) has a higher efficiency due to the use of switch-mode PAs (SMPAs) but uses outphasing to eliminate image and aliasing distortions and requires a larger silicon area. In this study, the authors propose a novel transmitter that eliminates both aliasing and image distortions while using a single SMPA. The transmitter can be implemented using all-digital techniques and achieves a higher efficiency as compared to both AF-PWM and AC-PWM based transmitters. Measurement results show an improvement of 11.3, 7.2, and 4.3 dBc in the ACLR as compared to the carrier-based PWM transmitter (C-PWMT), AF-PWMT, and AC-PWMT, respectively. The efficiency of the proposed transmitter is similar to that of C-PWMT, which is an improvement of 5% over AF-PWMT.

Efficiency‐optimised modulation technique of three‐level NPC inverter

The three-level NPC inverter has many advantages, such as the characteristics of high output power, low device stress, and low harmonic distortion of output waveform. It is widely used in the fields of high-voltage conversion and reactive power compensation. As the most commonly used multi-level inverter, three-level NPC inverter has its own disadvantage which is the NP potential fluctuations. It may lead to poor output performance even damage to the devices. Therefore, the problem of NP potential fluctuation of three-level NPC inverter has been the hotspot of its research. This paper presents an efficiency-optimised dual modulation wave carrier-based PWM (DMWPWM) strategy of three-level NPC inverter. First, the basic principle of traditional DMWPWM is analysed, and the deficiency of traditional DMWPWM modulation technique is described. Then, the efficiency-optimised DMWPWM strategy is deduced. Compared with traditional DMWPWM strategy, the new strategy inherits the advantage of traditional DMWPWM that the NP voltage balance can be maintained in any modulation index and power factor. Moreover, it can reduce the system switching loss which leads to efficiency improvement, and it is simple and easy to implement. Finally, the proposed modulation technique is verified by simulation.

Extension of Virtual-Signal-Injection-Based MTPA Control for Five-Phase IPMSM Into Fault-Tolerant Operation

This paper introduces a novel fault-tolerant control for the maximum torque per ampere (MTPA) operation in five-phase interior permanent magnet synchronous machine (IPMSM), termed MTPA fault-tolerant control. The key of this fault-tolerant control is that the reluctance torque is considered and used by MTPA under open-circuit fault. Based on the decoupled model of five-phase IPMSM on synchronous frame and the computing method of d -axis and q -axis voltages under various open-circuit faults, the virtual signal injection control (VSIC) can be applied to realize the MTPA under the fault-tolerant operation by the postfault field-oriented control (FOC) and carrier-based PWM (CPWM). This method is parameter independent in tracking of the MTPA points under the fault-tolerant operation. Besides, it can effectively reduce the amplitude of the fundamental current and improve efficiency compared with traditional $i_{d} = {\text{0}}$ fault-tolerant control. Moreover, it is robust to current and voltage harmonics and machine torque disturbances under the postfault operation. The proposed method is verified by experiments under various postfault operating conditions on an IPMSM prototype drive system.

Three-Phase Three-Level Flying Capacitor PV Generation System with an Embedded Ripple Correlation Control MPPT Algorithm

This paper presents the implementation of a maximum power point tracking (MPPT) algorithm in a multilevel three-phase photovoltaic (PV) system using the ripple correlation control (RCC) method. Basically, RCC adopts the inherent oscillations of PV current and voltage as perturbation, and it has been predominantly used for single-phase configurations, where the oscillations correspond to the 2nd order harmonics. The implementation of an RCC-MPPT algorithm in a three-phase system has not been presented yet in the literature. In this paper, the considered three-phase three-level converter is a three-level flying capacitor (FC) inverter. The proffered RCC method uses the 3rd harmonic components of PV current and voltage for the estimation of the voltage derivative of the power dPpv/dVpv (or current, dIpv/dVpv), compelling the PV array to operate at or very close to the maximum power point. The analysis and calculation of the low-frequency PV current and voltage ripple harmonic components in the three-phase flying capacitor inverter is presented first, with reference to centered carrier-based three-level PWM. The whole grid-connected PV generation scheme has been implemented by MATLAB/Simulink, and detailed numerical simulations verified the effectiveness of the control method in both steady-state and dynamic conditions, emulating different sun irradiance transients.

A Modified One-Cycle-Control Method for Modular Multilevel Converters

In this paper, a new One-Cycle-Control (OCC) method is designed for a modular multilevel converter (MMC) based on the principle of the equivalent resistance constant. The proposed controller has a simple structure and a small amount of calculation by cancelling the current inner loop proportional integral (PI) controller and the inverse transform in the traditional direct-quadrature (DQ) control. Compared to the traditional OCC controller, the new one separates the control method from the modulation strategy, making it possible to use not only carrier-based pulse-width modulation (PWM), but also nearest level modulation PWM to generate drive signals. Besides, the independent control of the active and the reactive power is implemented by injecting a reference current with the same phase of the supply voltage or a reference current which lags the supply voltage by π/2 into the controller, so the converter can operate in four quadrants and it can work in either a grid-connect or off-grid environment. The feasibility and the performance of the proposed OCC method have been validated by both the simulation under the MATLAB/SIMULINK (R2012a) environment and experimental results.

Influence of Digital Delay on the Zero-Sequence Voltage Injection Neutral-Point Potential Balance Algorithm for Three-Level NPC Inverters and Its Compensation Method

Three-level neutral-point-clamped (NPC) inverters need to ensure the balance of the neutral-point (NP) potential during operation. The zero-sequence voltage injection balance algorithms based on the carrier-based pulse width modulation (CBPWM) have been proposed in many papers and proved to be effective in controlling the NP potential. In industrial applications, the algorithms are mostly implemented by digital controllers, which have inherent computation digital delay. However, there is little attention to how the digital delay influences the balance algorithms. In this paper, the influence of the digital delay on the zero-sequence voltage injection balance algorithm has been studied in detail. It is found that the digital delay causes a fluctuation of the NP potential. The frequency of the fluctuation is 1/6 control frequency, and the amplitude of the fluctuation is related to the control frequency, the modulation index, the output current, and the dc-side capacitance. Furthermore, in order to eliminate the NP potential fluctuation caused by the digital delay, a digital delay compensation method is proposed in this paper. The correctness of the theoretical analysis and the effectiveness of the compensation method have been verified by the simulation and experiment results.

An Overall Minimized Switching Loss Discontinuous PWM Strategy for Neutral Point Clamped Three Level Inverters

Aim at reducing switching loss (SL) of neutral-point clamped three-level inverter (NPC TLI) as much as possible, a novel SL minimized discontinuous pulse width modulation (SLMDPWM) strategy is proposed in this paper. The core of SLMDPWM is that the specific maximum or middle phase current is clamped to positive bus, NP or negative bus according to modulation index and power factor angle. The realization of SLMDPWM based on carrier-based PWM (CBPWM) is revealed to simplify the calculation process. The performance characteristics of SLMDPWM and DPWM I-IV in term of the output voltage, SL and NP voltage ripple are compared by simulation and experimental results, and conclusion can be acquired that the SL of SLMDPWM is reduced significantly.

HIL-RT Implementation of UHVDC Transmission System Based on Series-Connected VSC Modules

This paper presents an ultra-high-voltage direct current (UHVDC) transmission system based on the series-connected voltage source converter (VSC) modules. A detailed DC voltage equalization control strategy is developed for the series-connected VSC modules at both terminals of the UHVDC transmission system. Moreover, the phase-shifted triangle carrier concept is applied for generating the pulse width modulation (PWM) signals to eliminate AC line current harmonics and reduce converter switching losses. Besides, harmonic elimination comparison between applying the conventional sine pulse width modulation (SPWM) and the phase-shifted triangle carrier-based pulse width modulation (PSCPWM) techniques is done. Furthermore, a hardware-in-the-loop (HIL) real-time (RT) UHVDC validation model was set up by connecting a real-time simulator of OPAL-RT which ran the power electronics-power system parts and a dSPACE 1103-based prototype controller which was used to implement the control part. Finally, the real-time dynamic performance of the series-connected VSC models UHVDC system is validated in operation at different transient and steady state modes.

A Carrier-based PWM Control Strategy for Three-level NPC Inverter Based on Bootstrap Gate Drive Circuit

This paper proposes a pulsewidth modulation (PWM) control strategy for the efficient operation of the three-phase three-level neutral-point-clamped (NPC) inverters based on a bootstrap gate drive circuit. The bootstrap circuit used in the three-level NPC inverter has advantages in terms of the cost reduction and the compact circuit design. However, the bootstrap circuit has a drawback due to the low gate-emitter voltage during the low-frequency and variable load condition of the inverter system. This problem leads to lower efficiency and reliability of the inverter. Therefore, this paper analyzes the causes of the voltage decrease in bootstrap capacitors and proposes PWM control strategy to increase the voltage level of bootstrap capacitors for the efficient operation of the inverter. The proposed PWM control strategy provides efficient and stable operation of the inverter system by selecting the unipolar, dipolar, or partial-dipolar modulation methods according to the fundamental output frequency and load current of the inverter system. Furthermore, this paper proposes a design method of the size of bootstrap capacitors for the optimal circuit design. The effectiveness of the proposed PWM control strategy is verified using the experimental results.

Feedforward Proportional Carrier-Based PWM for Cascaded H-Bridge PV Inverter

In this paper, a feedforward proportional carrier-based pulsewidth modulation (PWM) is proposed for the dc link control of the single-phase cascaded H-bridge multilevel photovoltaic inverter. The conventional carrier-based PWM techniques, such as the phase-shifted PWM and the level-shifted PWM, require multiple individual dc voltage controllers for the individual maximum power point tracking (MPPT). Thus, the control structure and the controllers’ designs are quite complex. Several noncarrier-based PWM techniques, such as the feedforward space vector modulation, the sorting-algorithm-based modulation, and the lookup table-based modulation, have the capability of individual dc voltage regulation. Although these noncarrier-based PWM techniques require only one total dc voltage controller in the outer voltage loop, the implementations of them are much more complicated than those of the carrier-based PWM techniques. In this paper, with the proposed feedforward proportional carrier-based PWM, each individual modulation signal is directly generated by multiplying the current loop controller’s output and the modulation signal’s feedforward proportional factor. With the feedforward PWM and the total dc voltage control, the individual dc voltage regulation is achieved. This carrier-based PWM combines the strengths of both the traditional carrier-based PWM and the noncarrier-based PWM. It is not only easy for implementation, but also requires only one total dc voltage controller in the outer voltage loop. The detailed description, derivation, and analysis of this modulation are included in this paper. In addition, the simulations and experiments demonstrate the performance of the dc link control and the individual MPPT using the proposed PWM and the control strategy.

Research of the equivalent relationship between the space vector and the triangular carrier-based PWM modulation strategies in the flying capacitor multilevel inverters

ABSTRACTThe equivalent relationship between the carrier-based modulation (CBPWM) and the space vector modulation (SVPWM) based on the flying capacitor multilevel inverters has not been analysed systematically. Due to the redundancies of the flying capacitor multilevel inverters, this paper firstly focuses on the switching sequence and the working ratio of each switching state and then proposes a novel method of decomposing modulation wave. This method can distribute the ratio of redundancies arbitrarily to satisfy the requirements of the output. Taking three- and five-level inverters as examples, by injecting a zero-sequence voltage into the CBPWM modulation wave and then decomposing the new modulation wave, we can get the same sequence of SVPWM modulation. This method takes the advantages of using simple CBPWM to realise the complex output of SVPWM, such as double- and quadruple-frequency output. At last, we deduce the equivalent relationship between the SVPWM and CBPWM in n-level with an arbitrary number of segments. Experimental results verify the correctness of the equivalent relationship.

A Carrier-Based PWM for Three-Level T-Type Inverter to Tolerate Open-Circuit Fault

This paper investigates the open-circuit faults of switching devices in the three-level T-Type inverter and proposes a new tolerant control method. The three-phase current and variation of the neutral-point voltage are detected to determine the fault switch. A carrier-based pulse width modulation is developed to tolerate switch fault by transiting from three-level to two-level switching. This makes the modulation scheme easier to be implemented compared to space vector modulation. For the neutral-point fault, the fault phase is operated by two-level modulation to produce the same rating voltage. On the other hand, the inverter is able to produce balanced voltage with reduced rating by keeping the phase of half-bridge fault to the neutral-point voltage. The neutral-point voltage is also able to be balanced by using two-level modulation since it does not contribute the neutral-point current. The performance and effectiveness of the proposed tolerant control are verified by a laboratory build.

Model Predictive Control of High Power Converters and Industrial Drives [Book News

Conventionally, power electronic converters and drives have been controlled by linear single-nput, single-output control loops. Particularly for high-power converters with multiple coupled dynamics and tight operating constraints, model predictive control (MPC) is expected to evolve into the control method of choice. MPC allows one to increase lower the current distortions, reduce the converter hardware, achieve very fast transient responses, and ensure the reliable operation within safe operating area constraints. The first six chapters of this book offer a three phase power electronics, electrical machines, carrier-based pulsewidth modulation, optimized pulse patterns, state-of-the-art art converter control methods, and the principle of MPC. Chapters 7-14 include an in-depth treatment of MPC methods that fully exploit the performance potential of high-power converters. These control methods combine the fast control responses of deadbeat control with the optimal steady-state performance of optimized pulse patterns by resolving the antagonism between the two. Each chapter is supplemented with an adequate well-selected list of recent references at the end. This is a well-written and richly illustrated text achieving a balance between mathematical rigor and physical insight.

A New Two-Phase Five-Level Converter for Three-Phase Isolated Grid-Tied Systems With Inherent Capacitor Balancing and Reduced Component Count

This paper presents a single dc source fed five-level converter topology for medium-voltage high-power isolated grid-tied systems with reduced power switch count. The proposed converter generates two-phase systems of voltages that are further converted to three phases by using Scott-T transformer connection. Compared to existing topologies, the proposed converter requires fewer power switches, gate drivers, and power diodes. An added advantage is that only a single dc source is required. An important feature of this topology is that the dc-link capacitor voltages have an inherent ability to self-balance by themselves without the need for extra balance circuitry and special control algorithms. The voltage stress across the power devices of the proposed converter is equal to half of dc-link voltage. A level-shifted carrier-based pulsewidth modulation scheme is used to inject current into the grid at unity power factor. Analysis and simulation and experimental results are presented to validate the performance of the proposed converter under grid-tied operation.

An Improved PWM Scheme for Three-Level Inverter Extending Operation Into Overmodulation Region With Neutral-Point Voltage Balancing for Full Power-Factor Range

This paper presents a carrier-based pulsewidth modulation (PWM) strategy for a three-level neutral-point-clamped (NPC) inverter that exhibits good control over dc-link capacitor voltages and mitigates low-frequency oscillations in the neutral point (NP) for operation extending into overmodulation region. The overmodulation signals are derived in a generalized way by first determining a bias signal from the zero-sequence injected signals, and then adding the bias with the modulating signals. Such an approach enables seamless transition across different modulation modes covering full modulation depth. It is shown that the incorporation of a signal compression factor generates a nonzero duty ratio for NP connectivity in every PWM cycle in overmodulation region, and thereby creates a room for addition of unbalance compensation signal which can be used to generate neutral current to mitigate existing unbalance in capacitor voltages in the overmodulation region. The compensating signals are in phase with the load currents exhibiting linearity in compensation for full power-factor range. A thorough investigation of the PWM algorithm for operation in both undermodulation and overmodulation with NP voltage regulation is carried out. The performances of the proposed scheme are evaluated through extensive simulation and validated by experiments using a three-level NPC inverter prototype with induction motor load.

New Fault-Tolerant Control Strategy of Five-Phase Induction Motor with Four-Phase and Three-Phase Modes of Operation

The developed torque with minimum oscillations is one of the difficulties faced when designing drive systems. High ripple torque contents result in fluctuations and acoustic noise that impact the life of a drive system. A multiphase machine can offer a better alternative to a conventional three-phase machine in faulty situations by reducing the number of interruptions in industrial operation. This paper proposes a unique fault-tolerant control strategy for a five-phase induction motor. The paper considers a variable-voltage, variable-frequency control five-phase induction motor in one- and two-phase open circuit faults. The four-phase and three-phase operation modes for these faults are utilized with a modified voltage reference signal. The suggested remedial strategy is the method for compensating a faulty open phase of the machine through a modified reference signal. A modified voltage reference signal can be efficiently executed by a carrier-based pulse width modulation (PWM) system. A test bench for the execution of the fault-tolerant control strategy of the motor drive system is presented in detail along with the experimental results.