Sawtooth Carrier Research Articles

Bidirectional Power Control Strategy for On-Board Charger Based on Single-Stage Three-Phase Converter

To solve the problems of large switching losses and the need for large-capacity electrolytic capacitances in three-phase DC/AC on-board chargers for vehicle-to-grid (V2G) applications, this paper proposes a single-stage bidirectional high-frequency isolated converter that eliminates the need for large-capacity capacitances. Combined with the proposed modulation scheme, it can theoretically reduce the switching loss by about two-thirds with the three-phase converter compared with the conventional modulation scheme, improving the converter’s operating efficiency and power density. Firstly, based on the characteristics of the proposed topology, a hybrid modulation scheme is proposed, which combines a phase-shift modulation scheme based on double modulation waves and a sawtooth carrier with a 1/3 modulation scheme, and the theoretical feasibility of the hybrid modulation scheme is verified using a mathematical modeling equation. Secondly, this paper provides a detailed analysis of the four operating modes of the two full-bridge circuits and the commutation process of the three-phase converter within 1/6 of the fundamental frequency cycle (P1 modulation interval). Then, the control strategy is given for the constant-current and constant-voltage charging and constant-current discharging for electric vehicle batteries. Finally, simulation results verify the correctness of the proposed topology and modulation scheme in vehicle–grid interaction.

Modulation-Based DC-Bias Elimination of DAB Converter Under Second Harmonic

As a basic unit of solid-state transformer (SST), the single-phase system composed of H-bridge and dual-active-bridge (DAB) is becoming an exciting topic for its high-efficiency, flexible power flow. However, the inherent second-harmonic power brings dc-link voltage ripple and phase shift oscillation, especially for the back-to-back systems with bilateral harmonics. In this paper, the behavior of DAB's high-frequency link under second harmonic is modeled and described, revealing the inevitable dc-bias and current-stress increase. A modulation-based dc-bias eliminating strategy is presented, which uses two sawtooth carriers to generate a transitional period without any calculations. To reduce magnetic material's waste, a second-harmonic correction to transformer design is proposed. Moreover, the optimal inductance for single-phase shift (SPS) with minimal current stress and full-range ZVS is obtained. These strategies enhance the ripple immunity of DAB, enabling the reduction of dc-link capacitance. Comprehensive simulations and experiments are performed to validate the accuracy and effectiveness of these optimizations.

Model Predictive Torque Control for a Dual Three-phase PMSM Using Modified Dual Virtual Vector Modulation Method

Single voltage vectors applied in the conventional model predictive torque control (MPTC) for multiphase motors do not only suffer from serious torque and stator flux ripples but also cause the large harmonic current. To address the aforementioned challenges, an MPTC using a modified dual virtual vector modulation method is proposed to improve the operational performance of a dual three-phase permanent magnet synchronous motor. Virtual voltage vectors are synthesized as the candidate control set to restrain the harmonic current. A transformation method is introduced to consider both the stator flux and torque in the duty cycle modulation. The torque and stator flux ripples are simultaneously reduced by addressing the limitations of nonuniform units. Furthermore, the null voltage vector is then inserted to expand the modulation range and improve the steady-state performance. Moreover, the sawtooth carrier is adopted to address the challenge of the asymmetric switch sequence caused by the modified modulation. Finally, the experimental results are presented to verify the effectiveness and superiority of the proposed MPTC method.

Zero-sequence Current Suppressing Strategy for Dual Three-phase Permanent Magnet Synchronous Machines Connected with Single Neutral Point

Dual three-phase permanent-magnet synchronous machines (DTP-PMSM) connected with a single neutral point provide a loop for zero-sequence current (ZSC). This paper proposes a novel space vector pulse width modulation (SVPWM) strategy to suppress the ZSC. Five vectors are selected as basic voltage vectors in one switching period. The fundamental and harmonic planes and the zero-sequence plane are taken into consideration to synthesis the reference voltage vector. To suppress the ZSC, a non-zero zero-sequence voltage (ZSV) is generated to compensate the third harmonic back-EMF. Rather than triangular carrier modulation, the sawtooth carrier modulation strategy is used to generate asymmetric PWM signals. The modulation range is investigated to explore the variation of modulation range caused by considering the zero-sequence plane. With the proposed method, the ZSC can be considerably reduced. The simulated and experimental results are presented to validate the effectiveness of the proposed modulation strategy.

Improved PWM Methods to Reduce the Common Mode Voltage of the Five-Phase Open-Winding Drive Topology

With the phase angle and shape modifications for carriers, two improved carrier-based pulse width modulation (CPWM) methods with common-mode voltage (CMV) suppression effects for the five-phase open-winding drive topologies are introduced. Theoretical analysis reveals that, by employing reversed triangular carriers for two inverters under the carrier-reversed PWM (CRPWM), CMV contributions of two bridge legs belonging to the same phase can be cancelled, realizing the zero CMV effect. By dynamically employing positive and negative sawtooth carriers for all bridge legs under the carrier-switching PWM (CSPWM), the CMV contribution of each inverter can be reduced, decreasing both the amplitude and step frequency of the CMV. Current qualities and dead-time effects on CMV under the above PWM methods are analyzed. Moreover, performances of two PWM methods are verified by experiments implemented on a five-phase open-winding topology with the induction motor load.

Improved Modulation Strategy for Reactive Energy Transmission Loss of Auxiliary Commutated Circuit of Novel Parallel RDCL Inverter

To overcome the challenges of large reactive energy transmission loss and high current stress, which ocurr during the operation of auxiliary commutated circuit (ACC) of novel parallel resonant dc-link inverter (PRDCLI), an improved modulation strategy for reactive energy transmission loss is herein proposed based on the discontinuous pulsewidth modulation (DPWM), which adopts sawtooth carrier wave with alternating positive and negative slopes and shunt dead zone. Compared with the original modulation strategy, based on minimizing the ACC operation frequency, the proposed modulation strategy is able to realize all switches soft-switching, and avoid the superposition of resonant current and load current during the operation of ACC, thus, effectively reducing the reactive energy transmission loss and the current stress of auxiliary switches of the ACC. Under the proposed modulation strategy, the equivalent circuits in different operation modes are divided, and the operation principle, voltage/current stress, loss distribution, and optimal parameter design method of novel PRDCLI are researched. Eventually, the proposed modulation strategy is verified by experiments on a 5-kW/40-kHz prototype made by SiC <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">mosfet</small> .

Simulative Study to Reduce DC-Link Capacitor of Drive Train for Electric Vehicles

E-mobility is an emerging means of transportation, mainly due to the environmental impact of petroleum-based fuel vehicles and oil prices’ peak. However, electric vehicles face several challenges by the nature of technology. Consequently, electric vehicles have a limited travel range and are extremely heavy. In this research, an investigation is carried out on different measures to reduce the DC-link capacitor size in the drive train of an electric vehicle. The investigation is based on software simulations. The DC-link capacitor must be dimensioned with regards to relevant points of operation, which are defined by the rotation speed and torque of the motor as well as the available DC-link voltage. This also includes the field-oriented control (FOC). In order to optimally operate a three-phase inverter in the electric drive train, a suitable type and sizing of the capacitor was studied based on mathematical equations and simulations. Two measures were examined in this study: firstly, an auxiliary passive notch filter introduced in the electric drive train circuit is explored. Based on this measure, an advanced modulation scheme exploiting the control of individual currents within segmented windings of the PMSM is investigated in detail. It was seen that saw-tooth carrier modulation used in the parallel three-phase inverter is found to reduce DC-link capacitor size in the electric drive train circuit by 70%.

Universal Control Scheme to Achieve Seamless Dynamic Transition of Dual-Active-Bridge Converters Using Zero-Current-Prediction

This manuscript proposes a zero-current-prediction (ZCP) based digital control scheme to achieve the seamless dynamic transition of dual-active-bridge (DAB) converters. Compared with existing methods, only an extra variable between the master PWM and the sawtooth carrier is added. This extra variable is only determined by the voltage conversion ratio and the change of the existing phase shifts between master and slave legs. It accurately predicts the zero crossings of the inductor current and tunes it with the end of the carrier period. When the output power varies, the controller updates the digital registers at the beginning of the new carrier period, when the inductor current is zero. Thus, a seamless dynamic transition is achieved with zero dc bias current. This proposed digital control scheme is universally valid for the mainstream modulation methods of DAB converter. Moreover, it is adaptive to any load conditions, regardless of the zero-voltage-switching (ZVS) conditions and power flow directions. A hardware prototype is designed, tested, and compared with the conventional control method. The experimental results well validate the advantages of the proposed concept.

A Novel Switching Sequence for Asymmetrical 15-Level Packed U Cell Inverter Topology with Improved Total Harmonic Distortion

Multilevel inverters (MLIs) have a major drawback of a utilizing more number of power semiconductor components (PSC), switching losses, increasing of voltage stress on the switches while going for higher level generations. In this work, drawbacks of conventional MLI topologies have been overcome through an advanced MLI topology called packed U cell (PUC). PUC-15 level MLI topology is developed by using lesser number of PSC, so that losses and voltage stress on switch is less when compared to conventional topologies. In this article, the novel switching sequence of PUC-15 topology is developed. It controls the switching stress due to its random switching operation. The PUC-15 switching sequence is controlled by using advanced sawtooth carrier- and triangular carrier- based multi-carrier sinusoidal pulse width modulation. The functionality of novel switching sequence and PWM techniques are confirmed via simulations, and results are compared in terms of total harmonic distortion (THD) at disparate modulation indexes. The measured FFT analysis of %THD is lesser than 5% which is under IEEE-519 standard for both voltage and current.

A Compensation Method for the 2nd Harmonic Component in the Input Currents of Three-Phase Current-Fed PFC Rectifier with Sawtooth Carrier PWM Scheme

A Compensation Method for the 2nd Harmonic Component in the Input Currents of Three-Phase Current-Fed PFC Rectifier with Sawtooth Carrier PWM Scheme

Simple discontinuous PWM strategies to reduce the switching losses of an indirect matrix converter

This work proposes the new discontinuous pulse width modulation (DPWM) schemes for an indirect matrix converter (IMC) to reduce the switching losses. The use of discontinuous modulation signals reduces the switching losses of the IMC by reducing the switching counts per cycle of the output converter. The key feature of the proposed schemes is the easy implementation as compared to existing DPWM schemes of the IMC. The major drawback of the existing DPWM schemes is the absence of zero current commutation (ZCC). In the absence of ZCC, the switchings of the input converter are accomplished through four-step commutation which adds the difficulties to the implementation. The proposed scheme overcomes above limitation by using the triangular carrier instead of the sawtooth carrier for the modulation of input converter. Consequently, the ZCC is enabled on the input converter which allows the use of two-step commutation. The two-step commutation simplifies the implementation to a great extent. The presented scheme provides the required input/output performance similar to continuous PWM (CPWM) schemes. The proposed work is verified by the simulation and experimental results. The reduction in the switching losses of the IMC by the new scheme is verified based on the comparison with the CPWM scheme.

Sawtooth Carrier-Based PWM Methods With Common-Mode Voltage Reduction for Symmetrical Multiphase Two-Level Inverters With Odd Phase Number

The increased phase number of multiphase systems enables us to exploit more degrees of freedom, such as the shape of phase carriers in pulsewidth modulation (PWM). The sawtooth carrier-based PWM (SCPWM) techniques are proposed in this article to reduce common-mode voltage (CMV) in both the peak-to-peak amplitude and the changing frequency, and it can be easily extended to symmetrical multiphase two-level inverters with any odd phase number. Theoretical analysis reveals that the switching between mirror-symmetrical carriers within one phase narrows the range of the sum of switching states in all phases, which leads to the reduction of CMV amplitude. Meanwhile, the overlapping of sawtooth carriers' straight edges among different phases slows down the change of the sum of switching states, which results in the decrease of CMV changing frequency. Moreover, the effects of voltage harmonics injection and switches' dead-time settings on the CMV reduction performance under the proposed SCPWM techniques are investigated. Finally, the experiment results in a five-phase induction machine and multiphase RL loads verify the improved CMV performance and the extensibility of the proposed SCPWM methods.

Modified Single-Edge SVPWM Technique to Reduce the Switching Losses and Increase PWM Harmonics Frequency for Three-Phase VSIs

This article proposed a modified single-edge space vector pulsewidth modulation (MS-SVPWM) technique by adjusting the zero vectors of saw-tooth carrier SVPWM technique for three-phase voltage source inverters to reduce the switching losses and increase the PWM noises frequency. Mathematical analysis and implementation of the proposed MS-SVPWM are demonstrated in detail. The differences in PWM noises reduction between MS-SVPWM and modified SVPWM technique are compared by time-varying PWM noises analysis, computer simulation, and experimental results. With the same average switching frequency of conventional SVPWM, MS-SVPWM could increase the PWM harmonics frequency by 50%. Employing the same carrier frequency, MS-SVPWM could reduce average switching frequency by 33% compared with conventional SVPWM technique, and the switching losses could be reduced by more than 25% when the phase angle is less than 60°. Reduction of switching losses could ease the cooling requirements and result in greater compactness of the system, especially vital concern in high-power applications and limited-space environments. The detailed experimental results confirm the effectiveness of the proposed MS-SVPWM at last.

Random Asymmetric Carrier PWM Method for PMSM Vibration Reduction

The underwater noise can be caused by the radial electromagnetic vibration of permanent magnet synchronous motor (PMSM) for electric propulsion. The difficulty in decreasing the underwater noise is not only the high-frequency but also low-frequency vibration reduction. This paper proposes a novel random asymmetric carrier pulse width modulation (RACPWM) method for PMSM vibration reduction in the whole frequency range. Instead of the conventional symmetric triangular carrier PWM, the asymmetric carrier PWM (ACPWM) is used to decrease the low-frequency phase current harmonics and the associated low-frequency vibration. Meanwhile, in order to suppress the high-frequency vibration, the RACPWM control based on the amplitude randomization of the sawtooth carrier is further presented to reduce the high-frequency phase current harmonics. Moreover, the RACPWM is equivalent to the random slope ACPWM in view of the output signals. Furthermore, without the need of any additional circuits in the drive, the presented method is simple to implement by software. Simulation and experimental results show that the proposed RACPWM method can effectively reduce both the low-frequency and the high-frequency vibration.

A Sawtooth Carrier-Based PWM for Asymmetrical Six-Phase Inverters With Improved Common-Mode Voltage Performance

A sawtooth carrier-based sinusoidal pulse width modulation (SC-SPWM) technique for asymmetrical six-phase two-level inverters is proposed in this paper, which could reduce both the peak-to-peak amplitude and the changing frequency of the common-mode voltage (CMV). The intersection-plotting method reveals that the mirror symmetrical sawtooth carriers for two three-phase groups can help optimize the distribution of overlapping areas, which is the CMV reduction mechanism of SC-SPWM. Additionally, the Fourier analysis is employed to quantitatively evaluate the modulation index and harmonic performance of SC-SPWM compared with the conventional SPWM and two phase-shifted SPWM methods. Also, further analysis demonstrates that dead time does not affect the reduction of CMV in a noticeable way. Finally, both simulation and experimental results coincide with the theoretical analysis that the proposed SC-SPWM shows the best performance in reducing the CMV amplitude and changing frequency among these four SPWM methods, though it leads to a higher phase current distortion.

Evaluation of Level-Shifted and Phase-Shifted PWM Schemes for Seven Level Single-Phase Packed U Cell Inverter

An evaluation of level shifted and phase shifted triangular and sawtooth carrier modulation schemes for a seven level packed U cell (PUC) inverter is presented in this paper. The investigated PUC is the recently introduced topology for multilevel inverter having reduced switch count in comparison to the conventional topologies of multilevel inverters. The PUC inverter has six switches for 7 level inverter which is very less in comparison to the conventional topologies. In this paper, the level-shifted pulse width modulation (LS-PWM) and phase-shifted PWM (PS-PWM) for triangular and sawtooth carrier are presented and compared. A comparative harmonic analysis for all the cases is performed and results are presented in the paper. The difference in harmonics of the two modulation methods given by the theoretical approach for both the carrier is validated by the experimental results. DC voltage controller and load current controller of the PUC inverter are also designed and presented. The investigated PUC topology is tested in dynamic and steady state conditions and results obtained are presented. The analysis is done and validated using simulation in MATLAB Simulink environment and experimental approaches using FPGA platform.

An Aperiodic Modulation Method to Mitigate Electromagnetic Interference in Impedance Source DC–DC Converters

Rapid voltage and current transitions in switched-mode power converter circuits generate electromagnetic interference (EMI) which may interfere with other electronic systems. High-speed (e.g., wide bandgap) switching devices can improve circuit efficiency and compactness, but may increase the bandwidth of the interference generated. The peak interference is concentrated at harmonics of the fundamental switching frequency, and so may be reduced by modulating the converter switching frequency. However, converter topologies incorporating more than one switching device may not be suited to modulation of the switching frequency, and coordinated modulation of other pulse parameters is required to suppress interference. A relatively simple implementation of a hybrid pulse modulation technique is presented to suppress EMI in a quasi-Z-source converter comprising an impedance-source network and GaN-based H-bridge switching circuit. The technique uses two anharmonically related periodic signals to generate a modulated sawtooth carrier, which in turn generates coordinated switching pulses aperiodically modulated in position and width within a constant switching period. Experimental results demonstrated 10 dB suppression of the peak interference with negligible impact upon the converter's efficiency or output voltage. The proposed pulse modulation technique and its method of implementation are generic, and are expected to be widely applicable to other switched-mode dc–dc power converters.

Performance Evaluation of the Single-Phase Split-Source Inverter Using an Alternative DC–AC Configuration

This paper investigates and evaluates the performance of a single-phase split-source inverter (SSI), where an alternative unidirectional dc–ac configuration is used. Such configuration is utilized in order to use two common-cathode diodes in a single device instead of using two separate diodes, resulting in minimum parasitic inductance in the commutation paths. In this paper, the analysis and modulation of the single-phase SSI using this alternative configuration is discussed, and the analysis of the low-frequency component in the dc side is introduced. Moreover, the features behind employing the triangular, the trailing-edge sawtooth, and the leading-edge sawtooth carriers with the single-phase SSI are discussed, and the differences among these carriers are highlighted. In order to highlight the performance of the proposed SSI, a comparative study is conducted with the two-stage architecture and the single-phase quasi-Z-source inverter (qZSI). The introduced analysis is enhanced with simulation results using MATLAB/PLECS models, where a 1-kVA single-phase SSI is designed and simulated. Finally, the designed 1-kVA single-phase SSI is implemented experimentally and tested at different operating points, i.e., at different voltage gains, and a maximum efficiency of $95.5\%$ is obtained.

Hybrid inverter concept for extreme bandwidth high‐power AC source

A hybrid inverter concept for switch-mode power amplifiers as used, e.g. in power-hardware-in-the-loop testing is proposed. A main converter operating from the supplying DC voltage generates a multilevel output voltage by means of parallel-interleaved operation of several bridge legs and combination of the bridge leg output voltages with coupled inductors into a multilevel waveform. A second, series-connected inverter features a floating DC bus with only a fraction of the main converter's DC voltage, which enables a significantly higher switching frequency. The series inverter compensates the deviation of the main inverter's multilevel output voltage from the reference voltage, whereby pulse-width modulation with sawtooth carriers is employed, and hence defines the effective switching frequency of the hybrid inverter's overall output voltage. This allows for a higher output filter cutoff frequency and ultimately features a significant increase of the full-range system bandwidth, which improves by more than an order of magnitude for the considered 100 kVA example system compared with a conventional approach. Finally, closed-loop circuit simulations verify the high performance of the proposed system.

Comparison of Starting Current Characteristics for Three-Phase Induction Motor Due to Phase-control Soft Starter and Asynchronous PWM AC Chopper

This paper presents the comparison of starting current characteristics of a three-phase induction motor fed by two types of soft starters. The first soft starter under investigation is a conventional AC voltage controller on the basis of a phase-control technique. The other is the proposed asynchronous PWM AC chopper which is developed from the conventional synchronous PWM AC chopper. In this paper, the proposed asynchronous PWM AC chopper control scheme is developed by generating only two asynchronous PWM signals for a three-phase main power circuit (6 switching devices) from a single voltage control signal which is compared with a single sawtooth carrier signal. By this approach, the PWM signals are independent and easy to implement since the PWM signals do not need to be synchronized with a three-phase voltage source. Details of both soft starters are discussed. The experimental and simulation results of the starting currents are shown. It is found that the asynchronous PWM AC chopper efficiently works as a suitable soft starter for the three-phase induction motor due to that the starting currents are reduced and are sinusoidal with less harmonic contents, when being compared with the starting current waveforms using the conventional phase-control starting technique. Also the proposed soft starter offers low starting electromagnetic torque pulsation.