Two-level Pulse Width Modulation Research Articles

A Common-Mode Voltage Elimination Scheme by Reference Voltage Decomposition for Back-to-Back Two-Level Converters

Common-mode voltage (CMV) can greatly reduce the reliability and performance of back-to-back two-level converter-fed motor drive systems. To address this issue, a novel CMV elimination scheme based on reference voltage decomposition is proposed in this article. Firstly, the reference voltage of each phase is decomposed into two virtual reference voltages, resulting in six virtual reference voltages that are inter-related for back-to-back two-level converters. Then, by comparing each virtual reference voltage with a triangle carrier based on the two-level pulse width modulation (PWM), the final PWM voltage of each phase can be obtained from the differences of the corresponding two virtual PWM outputs. With the proposed method, both the amplitude and RMS value of CMV can be eliminated theoretically with satisfactory output waveform qualities. Simulations and experimental results are presented to verify the proposed method.

Fractional-order neural control of a DFIG supplied by a two-level PWM inverter for dual-rotor wind turbine system

Energy ripples are among the common problems in renewable energies as a result of using less efficient strategies. In this work, a new technique is suggested to control a doubly-fed induction generator (DFIG) using the pulse width modulation (PWM). The new technique is based on the combination of neural networks and fractional-order control to minimize the reactive and active power ripples of the DFIG-based variable speed dual-rotor wind turbine system. The suggested fractional-order neural control (FONC) with the PWM is a simple, robust and a high-performance strategy. Simulation is performed using Matlab software to validate the effectiveness of the designed control of 1.5 MW DFIG and the obtained results are compared with the traditional direct power control (DPC) in different working conditions. In addition, the comparison between the suggested control and the DPC is performed in the cases of changing or not changing the device parameters in terms of ripple ratio, dynamic response, steady-state error, current quality, and overshoot of active and reactive power of the DFIG. As compared to the DPC, the proposed FONC technique improves the active and reactive power ripples by 65.71% and 84.74%, respectively. Also, improves the overshoot of the active and reactive power by 71.33% and 91.72%, respectively. The simulation results demonstrate the high performance and robustness of the FONC technique for the parametric variations of the DFIG-based variable speed dual-rotor wind turbine system compared to the DPC control.

Hybrid Switching Control-Based DC to AC Inverter for Microgrid Using Renewable Energy Sources

Hybrid switching control-based direct current (DC) to alternating current (AC) inverter is a method of controlling the flow of power from DC sources such as solar panels or wind turbines to AC loads in a microgrid. In a microgrid, renewable energy sources are often used to supplement traditional sources of energy and improve overall energy efficiency. To simulate micro-grid systems, an effective three-legged IGBT inverter has been developed using Matlab R2016a/Simulink. The inverter switches are controlled by a pulse controller, which creates the switching gate pulses. This work models the output voltage and current waveforms of the three-phase 180° voltage source inverter that supplies nonlinear loads. To lower the total harmonic distortion (THD) of the current and voltage outputs of the three-phase voltage source converter (VSC), a filter circuit and a two-level pulse width modulation (PWM) generator have been presented. This pulse-width modulation generator compares the modulating signal and a high-frequency triangular carrier wave. Sinusoidal pulse width modulation (SPWM) is used for PWM control. Moreover, the hybrid switching control-based DC-to-AC inverter utilizes a combination of pulse width modulation (PWM) and hysteresis current control techniques to maintain a constant AC output voltage and frequency. PWM control is used to regulate the voltage, while hysteresis current control is used to regulate the current. Additionally, an inductor-capacitor-inductor (LCL) filter is used to improve the stability of the power converter by providing a damping effect on the system. Overall, the LCL filter is a versatile and effective tool for improving the performance of power inverters, especially in applications where high efficiency and low harmonic distortion are important. IUBAT Review—A Multidisciplinary Academic Journal, 6 (1): 25-46

Field-oriented control based on parallel proportional–integral controllers of induction motor drive

This study is a comparative study between a proportional–integral (PI) regulator and a parallel proportional–integral (PPI) regulator for the Induction Motor (IM) drive supplied with a two-level pulse width modulation (PWM) inverter. This motor is controlled by field-oriented control (FOC). However, the proposed FOC strategy is a modification of the classical technique, where the PPI controller was used for this purpose to improve the performance of the IM drive. The designed FOC strategy based on PPI controllers is a robust control strategy and a high performance. The numerical results of the FOC-PPI strategy are compared with the results of the traditional FOC strategy of IM drive at different operating conditions using the Matlab/Simulink environment. Furthermore, the comparison is made in terms of dynamic response, ripple ratio, current quality, and overshoot, and this is in the case of changing or not changing the parameters of the machine. The simulation results illustrate the robustness and efficiency of the suggested FOC-PPI strategy to the parametric variations of the IM drive.

Pulse-width Modulation Techniques in Two-level Voltage Source Inverters – State of the Art and Future Perspectives

Abstract The core of most power electronic systems involving DC/AC conversion is a voltage source inverter (VSI) that runs on some pulsewidth modulation (PWM) strategy. Numerous PWM techniques have been reported in the literature over the past few decades, each having its own merits and limitations. This paper reviews some selected areas of two-level PWM VSI, namely proper utilisation of the DC bus without deteriorating the quality of the output waveform, switching-loss reduction in the linear and over-modulation zones, common-mode voltage and PWM strategies for its reduction or elimination, distortion of the output voltage owing to dead time, and its compensation. These phenomena are explained in brief, followed by discussions on different research works relevant to these areas, and their advantages and disadvantages. Finally, the paper shows prospective directions in which research may continue in these areas in future.

Open-Switch Fault Diagnosis of Three-Phase PWM Converter Systems for Magnet Power Supply on EAST

The three-phase two-level pulsewidth modulation (PWM) converter operates in rectification state or active inverter state according to the corresponding experimental requirements of Experimental Advanced Superconducting Tokamak. However, the current fault diagnosis methods proposed for PWM converters usually deal with only the rectification state or inverter state. To solve this problem, this article proposes a diagnosis method to detect single and double open-circuit faults under both the rectification state and active inverter state. First, an inception-based neural network diagnosis model is proposed, in which 1 × 1, 3 × 3, 5 × 5, and 7 × 7 convolution and 3 × 3 max-pooling processes are conducted in parallel at the input and the output and stacked together to generate the final output. Second, the model is trained using three-phase alternating current current signals to determine the location of open-switch faults with a large number of simulation data samples and fewer experimental data samples. Finally, the experimental result shows that the proposed model can accurately detect approximately 99.14% of the open-switch faults within 12.83 ms (<3/4 cycle) without an additional sensor. Furthermore, the result shows that the proposed model is robust to load voltage transient conditions and nonunity power factor conditions.

Inverter Two-Level PWM Harmonic Enhancement Based on Phase Shift Tuning Technique

Frequency harmonic reduction and elimination is a vital field of research due to its importance in minimizing the percentage of total harmonic distortion in power systems. The two-level Pulse Width Modulation (PWM) method of AC generation is with less sophisticated control circuitry requirement compared to higher level PWM techniques. This paper is proposing a new control methodology with a reduced harmonic spectrum. The new trend here is to manipulate the PWM two-level reference waveform by duplicating the generation process with a tuned phase shifting added to the reference waveform. The new technique results in a harmonic reduction of the unfiltered output with about 50% compared to that of the conventional Bipolar SPWM.

A Review on Direct Power Control of Pulsewidth Modulation Converters

Starting from the principle of instantaneous power theory, this article explores various direct power control (DPC) strategies for three-phase two-level pulsewidth modulation (PWM) converters. After summarizing the fundamental power formula of PWM rectifiers, this article studies the operating principle of the conventional table-based approach and its related improvements. It further looks into the advanced counterparts employing space vector modulation and different nonlinear control strategies. The emphasis is put on the prevailing predictive DPC. Besides, the voltage-sensorless and robust DPC methods based on the virtual flux concept and the state observer or estimator are investigated. Critical issues, including the sample delay, constant switching frequency, duty cycle optimization, objective function, and unbalanced operation are examined.

Multi-Level Multi-Input Converter for Hybrid Renewable Energy Generators

A three-phase multi-level multi-input power converter topology is presented for grid-connected applications. It encompasses a three-phase transformer that is operated on the primary side in an open-end winding configuration. Thus, the primary winding is supplied on one side by a three-phase N-level neutral point clamped inverter and, on the other side, by an auxiliary two-level inverter. A key feature of the proposed approach is that the N-level inverter is able to perform independent management of N − 1 input power sources, thus avoiding the need for additional dc/dc power converters in hybrid multi-source systems. Moreover, it can manage an energy storage system connected to the dc-bus of the two-level inverter. The N-level inverter operates at a low switching frequency and can be equipped with very low on-state voltage drop Insulated-Gate Bipolar Transistor (IGBT) devices, while the auxiliary inverter is instead operated at low voltage according to a conventional high-frequency two-level Pulse Width Modulation (PWM) technique and can be equipped with very low on-state resistance Metal-Oxide-Semiconductor Field-Effect Transistor (MOSFET) devices. Simulations and experimental results confirm the effectiveness of the proposed approach and its good performance in terms of grid current harmonic content and overall efficiency.

The Study on Suppression Common-mode Voltage Strategy Based on Predictive Control

The traditional two-level pulse width modulation strategy will generate a higher common-mode voltage and cause common-mode interference to the inverter load-side equipment. This paper uses predictive control to implement current tracking control. The algorithm is simple to implement and can be adjusted by adjusting the value factor to suppress the common-mode voltage output of the inverter, and the simulation verifies the correctness of the algorithm, which has certain reference value for further research on the suppression of the common-mode voltage on the load side of the inverter.

New Three-Phase Current Reconstruction for PMSM Drive With Hybrid Space Vector Pulsewidth Modulation Technique

Current sensing techniques with reduced number of sensors attract a high interest from industry, for the possibility of cost reduction and sampling mismatch reduction. This article puts forward a new single current sensor (SCS) method for a permanent magnet synchronous motor three-phase current reconstruction, with a novel hybrid pulsewidth modulation (PWM) technique introduced. This method is implemented by changing the position of SCS from dc bus to a current branch, and a modified space vector PWM technique is employed to realize the phase current reconstruction. Compared with traditional SCS control methods, the proposed method can relieve the measurement dead-zones at sector boundary region without introducing extra compensation algorithms. Besides, this method can be realized not only with a single hall-effect current sensor but also a single shunt resistor, which further expands the applications and increases the system reliability as well. This method is also available in other motor control with a two-level three-phase PWM voltage source inverter topology. The accuracy and feasibility of the proposed method is validated by the simulation and experimental results.

Fault-tolerant control strategy for open-circuit fault of two-parallel-connected three-phase AC–DC two-level PWM converter

This paper proposes a fault-tolerant control (FTC) strategy for an open-circuit fault (OCF) of a single IGBT in a two-parallel-connected three-phase AC–DC pulse-width-modulation (PWM) converter system. In the case of the parallel-connected PWM converter system, the OCF of the IGBT causes not only DC-link voltage fluctuation and grid current distortion, but also a zero-sequence circulating current (ZSCC). Although the effect of these problems can be reduced by existing FTC methods which is used in the single PWM converter, it is difficult to totally mitigate the problems due to the ZSCC. Therefore, this paper proposes a new FTC strategy to suppress the ZSCC using the healthy converter in the parallel-connected converter. First, it is analyzed how the difference in common-mode (CM) voltage between the two converters causes ZSCC flowing inside the parallel-connected converter under the fault condition. And then, the limitation of the existing control method for ZSCC is explained. To suppress the ZSCC using the healthy converter, the proposed control method uses a d-axis voltage injection of the healthy converter which does not affect an active power control. The effectiveness of the proposed FTC strategy is verified through experimental results.

Sensor-Fault-Estimation-Based Tolerant Control for Single-Phase Two-Level PWM Rectifier in Electric Traction System

This article presents a fault-estimation-based tolerant control strategy for single-phase two-level pulsewidth modulation rectifier subjected to catenary current sensor fault and dc-link voltage sensor fault. First, an augmented descriptor system is developed for the rectifier, whose augmented state vector consists of the state vector of original system as well as the sensor fault together with the measurement disturbance. Then, a linear reduced-order observer is designed for the descriptor plant. Accurate asymptotic estimation of the original state vector and the disturbed sensor fault are thus achieved simultaneously. Finally, the fault tolerant design method is addressed through sensor fault compensation, which allows the pre-design controller to continue to function normally even when both catenary current sensor and dc-link voltage sensor are faulty. Simulation and hardware-in-the-loop test results confirm the effectiveness of the proposed method.

Frequency-Adaptive Virtual Flux Estimator-Based Predictive Power Control With Suppression of Dc Voltage Ripples Under Unbalanced Network

This article presents a closed-loop virtual-flux (VF) estimator for grid voltage sensorless control of pulsewidth modulation (PWM) rectifier under unbalanced network. Compared with the prior open-loop VF estimator, the proposed method shows better filtering capability and improved robustness against load variation. Considering the grid frequency may deviate from the nominal value in practical application, an adaptive method is further developed for online frequency estimation. Additionally, the finite control set-model predictive power control with power compensation is implemented based on the proposed VF estimator to attenuate dc voltage ripples under unbalanced network. Theoretical analysis show that the twice-grid-frequency ripple component in the dc voltage can be effectively suppressed even with inductance mismatches. Experimental tests on a two-level PWM rectifier confirm the effectiveness of the proposed method.

A Highly Linear OTA-Less 1-1 MASH VCO-Based $\Delta\Sigma$ ADC With an Efficient Phase Quantization Noise Extraction Technique

In this article, an efficient technique is introduced to extract the quantization noise of a multi-phase voltage-controlled oscillator (VCO)-based quantizer (VCOQ) in the time domain as a pulsewidth modulated (PWM) signal. Using this technique, a new highly linear VCO-based 1-1 multi-stage noise shaping (MASH) delta–sigma analog-to-digital converter (ADC) structure is presented. This architecture does not require any operational transconductance amplifier (OTA)-based analog integrators or power-hungry linearization methods. The first stage is a closed-loop multi-phase VCO-based voltage-to-phase (V-to-P) converter, and the second stage is an open-loop multi-phase VCO-based voltage-to-frequency (V-to-F) converter. Using the proposed technique, the phase quantization error of the first stage is extracted as a pulse signal and then fed to the second stage. The input of the first VCO is a very small amplitude signal, and the input of the second VCO is a two-level PWM signal. Therefore, the VCO non-linearity does not limit the overall ADC performance, mitigating the need for power-hungry linearization methods. The prototype achieves second-order noise shaping with a DR/SFDR/SNR/SNDR of 82.7/88.7/80.3/79.7 dB for an input signal BW of 2 MHz. The fabricated design consumes 1.248 mW from a 0.9-V supply.

Full-Scale Physical Simulator of All SiC Traction Motor Drive With Onboard Supercapacitor ESS for Light-Rail Public Transportation

This article deals with the design and laboratory implementation of a full-scale physical simulator of an all-silicon carbide (SiC) traction motor drive for light-rail transit systems (LRTS) with onboard supercapacitor energy storage system (ESS). It consists of a pulsewidth modulation (PWM) rectifier representing the 750 V dc catenary line, a three-phase two-level PWM traction inverter to drive a three-phase squirrel-cage traction motor, a flywheel coupled to the motor shaft to represent the dynamic behavior of the transportation vehicle, a loading generator connected to the grid via a dc-link converter with active front-end, and a supercapacitor ESS containing a bidirectional dc–dc converter supplied from the common dc link. The PWM rectifier, a traction inverter, and a bidirectional dc–dc converter are all SiC power MOSFET-based converters for high efficiency and high power density. A physical simulator is a valuable tool in the design and testing of all SiC converters. It is equipped with software programs for a catenary model, rail track model, and vehicle model, and permits the performance verification of various control, modulation, and energy-saving strategies. The physical simulator system developed in this article also allows the performance verification of a vehicle formation on a prespecified real track and evaluation of benefits of the onboard supercapacitor ESS in real time.

Duty Ratio Stability and Average Steady-State Error of Two-Level Current-Mode Wide-Bandwidth Switching Power Amplifiers

Nowadays, high-frequency switching power amplifiers (SPA) have been studied widely; bulk of the researches were focused on audio power amplifiers. In active magnetic bearing (AMB) systems, high-frequency electromagnetic excitation caused by rotor imbalance can affect the performance of the SPA, so the traditional SPA cannot meet the requirements of the AMB systems. Therefore, on the premise of ensuring larger power, the frequency of the SPA should be improved to ensure the normal operation of the AMB system. Two-level pulsewidth modulation (PWM) current-mode SPAs are widely used in AMB systems. In order to broaden the bandwidth and to reduce the average steady-state error current, SiC power devices based SPA with a high bus voltage and a high switching frequency was designed. The basic principle and the linearized control model of SPAs are introduced. Then, the duty ratio stability and average steady-state error current of the SPAs are analyzed based on the output ripple current. When the PWM modulator is designed by either the discrete devices or the integrated chips, the critical gains to ensure the duty ratio stability are, respectively, analyzed based on the slope matching and the nonideal characteristic of operational amplifiers. Hence, two methods to reduce the average steady-state error current are proposed, respectively. One is to adjust the offset voltage of triangular carrier for the P controller, the other is to use a proportional integral (PI) controller. The offset adjusting method allows the SPA to achieve better dynamic performance and wider bandwidth. The proportional integral (PI) controller can reduce the average steady-state error current but narrows the bandwidth. Finally, the experiment results are in good agreement with the theoretical analyses.

Asymmetrical Cascaded Three-Phase AC–DC Converters With Injection Transformers

In this paper, three generalized configurations of three-phase pulsewidth modulated (PWM) rectifiers are presented. They are composed of cascaded cells, each formed by a three-phase bridge of switching devices and a three-phase transformer to cascade the cells and isolate the load from the power source. One configuration is bidirectional, whereas the other two are unidirectional alternatives that replace power switches for diodes in some legs. The turns ratios of transformers from each cell are designed in order to provide the required gain and number of levels in the inverted multilevel voltage, enhancing power quality while attending requirements for proper operation in each case. Configurations with two and three cells are compared by means of simulations between themselves and with three conventional three-phase PWM rectifiers: the two-level insulated gate bipolar transistor bridge and the multilevel neutral point clamped (NPC) bridge and NPC H-bridge. Many degrees of asymmetry between the transformers in each cell, determined by the turns ratios, are considered to evaluate their impact on the topologies with relation to performance and cost. It is shown that proposed multilevel rectifiers present lower harmonic distortion, semiconductor losses, and switching stress, and some options with intermediate asymmetry are considered as good alternatives to the most asymmetrical cases. Experimental results are also provided for configurations with two cells, to demonstrate their lower harmonic distortion and power losses compared to the conventional isolated two-level PWM rectifier.

Robust Deadbeat Predictive Power Control With a Discrete-Time Disturbance Observer for PWM Rectifiers Under Unbalanced Grid Conditions

This paper presents a robust deadbeat predictive power control (DPPC) for pulsewidth modulation (PWM) rectifiers with the consideration of parameter mismatches under unbalanced grid conditions. First, conventional DPPC is modified to extend its application to both ideal and unbalanced grid conditions. Second, a tracking error of the modified DPPC with inaccurate grid-side impedance is analyzed. Third, a discrete-time power disturbance observer (DPDO) is designed to achieve accurate power control with mismatched parameters. The designed DPDO can predict complex power at the next sampling instant and estimate system disturbance simultaneously. Therefore, the DPDO can contribute to eliminate the steady-state tracking error resulting from disturbances caused by inaccurate parameters and compensate one-step delay in digital implementation. Although satisfactory steady-state performance can be obtained with modified DPPC and DPDO, transient performance still deteriorates significantly with an inaccurate value of the grid-side inductance. Thus, an online adaptive method to estimate mismatched inductance is finally developed based on the proposed DPDO. Both DPPC and DPDO are implemented in the stationary reference frame without coordinate transformation. Theoretical analysis confirms that the proposed DPDO can track disturbance without phase lag or magnitude error. Experimental tests and comparative studies with a prior DPPC on a two-level PWM rectifier validate the effectiveness of the proposed scheme.

Direct Power Control of Pulsewidth Modulated Rectifiers Without DC Voltage Oscillations Under Unbalanced Grid Conditions

Direct power control with space vector modulation (DPC-SVM) features simple structure, fast dynamic performance, and little tuning work. However, the conventional DPC-SVM cannot achieve accurate power control under unbalanced grid conditions. A modified DPC-SVM is thus proposed for accurate power control under both ideal and unbalanced grid conditions. Though the power control accuracy is improved when compared with the conventional DPC-SVM, it still suffers highly distorted grid current and dc voltage oscillations with an unbalanced network. Therefore, a power compensation method is subsequently derived aiming at the following targets: eliminating dc voltage oscillations, achieving sinusoidal grid current, and obtaining unity power factor. To that end, average grid-side reactive power and oscillations in converter-side active power are controlled as zero by simply adding a compensation to original power reference. Additionally, the proposed method does not require extraction of a positive sequence or negative sequence component of grid voltage. Compared with the conventional DPC-SVM in an ideal grid, only additional compensation of power reference is required. As a result, control performance can be significantly improved without substantial increase in complexity. The superiority of the proposed method over the prior DPC-SVM is validated by both simulation and experimental results obtained on a two-level pulsewidth modulation voltage source rectifier.