Pulse Width Modulated Voltage Source Research Articles

Design, Analysis, and Impacts of Sinusoidal LC Filter on Pulsewidth Modulated Inverter Fed-Induction Motor Drive

Squirrel-cage induction motor (SQIM) fed by a pulsewidth modulated voltage source inverter (VSI) is subjected to voltage and current surges. It may cause additional losses in the motor, insulation failure, high bearing current, and electromagnetic interference. To mitigate these problems, sinusoidal LC filter is placed at the ac-side of the VSI. This paper proposes a new methodology to design the filter. In this method, the filter inductance is chosen based on the maximum ripple in the inverter ac-side current and the voltage drop across the filter inductor, and the filter capacitor is chosen based on the steady-state reactive power demand of the SQIM. The effects of the designed filter on the switch current, losses in the drive, temperature of the dc-link capacitor, dv/dt at the motor terminal, stator flux, and air-gap torque of the SQIM are discussed. The performance of the drive with the filters, designed by the proposed method and the standard method, are experimentally tested on a two-level silicon carbide VSI-fed SQIM and comparative analysis is carried out. The impact of the designed filter on the drive is also shown when the neutral point of the filter capacitors is connected with the mid-point of the dc link. The stability of the closed-loop controlled SQIM drive with the proposed filter, and simulation results are presented to verify its performance.

Parameters Uncertainty Immunization of Global Synchronous Pulsewidth Modulated VSIs With Round P&O Algorithm

This letter proposes a closed-loop scheme for global synchronous pulsewidth modulated voltage source inverters with round perturbation and observation (R-P&O) algorithm to immunize the parameters uncertainty, e.g., line impedance and filter impedance variation. In specific, the rms value of measured total current harmonics at point of common coupling will be periodically sent to each inverter as feedback signal using the low-cost narrowband communication system. Then, the inverters will assume the R-P&O scheme to correct the phase shift angles among pulsewidth modulation carriers for intentionally minimizing the total current harmonics. Doing so, the closed-loop scheme can achieve the expected performance even under the severe parameters’ variation. The experimental results verified the performance of the proposed method.

A Control Strategy for Suppressing Zero-Sequence Circulating Current in Paralleled Three-Phase Voltage-Source PWM Converters

In microgrids, paralleled converters can increase the system capacity and conversion efficiency but also generate zero-sequence circulating current, which will distort the AC-side current and increase power losses. Studies have shown that, for two paralleled three-phase voltage-source pulse width modulation (PWM) converters with common DC bus controlled by space vector PWM, the zero-sequence circulating current is mainly related to the difference of the zero-sequence duty ratio between the converters. Therefore, based on the traditional control ideal of zero-vector action time adjustment, this paper proposes a zero-sequence circulating current suppression strategy using proportional–integral quasi-resonant control and feedforward compensation control. Firstly, the dual-loop decoupled control was utilized in a single converter. Then, in order to reduce the amplitude and main harmonic components of the circulating current, a zero-vector duty ratio adjusting factor was initially generated by a proportional–integral quasi-resonant controller. Finally, to eliminate the difference of zero-sequence duty ratio between the converters, the adjusting factor was corrected by a feedforward compensation link. The simulation mode of Matlab/Simulink was constructed for the paralleled converters based on the proposed control strategy. The results verify that this strategy can effectively suppress the zero-sequence circulating current and improve power quality.

Single-Phase Inverter Deadbeat Control with One-Carrier-Period Lag

This paper presents a novel digital control scheme for the regulation of single-phase voltage source pulse width modulation (PWM) inverters used in AC power sources. The proposed scheme adopts two deadbeat controllers to regulate the inner current loop and the outer voltage loop of the PWM inverter. For the overhead of digital processing, the change of duty of PWM lags one carrier period behind the sampling signal, which is modeled as a first-order lag unit in a discrete domain. Based on this precise modeling, the deadbeat controllers make the inverter get a fast dynamic response, so that the inverter’s output voltage is obtained with a very low total harmonic distortion (THD), even when the load is fluctuating. The parameter sensitivity of the deadbeat control was analyzed, which shows that the proposed deadbeat control system can operate stably when the LC filter’s parameters vary within the range allowed. The experimental results of a 2kW inverter prototype show that the THD of the output voltage is less than 3% under resistive and rectifier loads, which verifies the feasibility of the proposed scheme. An additional advantage of the proposed scheme is that the parameter design of the controller can be fully programmed without the experience of a designer.

Linear Active Disturbance Rejection Control for Three-Phase Voltage-Source PWM Rectifier

Three-phase voltage-source pulse width modulation (PWM) rectifier has been widely employed in various industrial applications. For the traditional dual-loop PI control of three-phase voltage-source PWM rectifier, the voltage loop and current loop have poor disturbance rejection performance and long response time. A linear active disturbance rejection control (LADRC) strategy is proposed for three-phase voltage-source PWM rectifier in this paper. The coupling variable and external disturbance in the model of PWM rectifier are observed and compensated by linear extended state observer (LESO) in two-phase synchronous reference frame. The LADRC outer-voltage loop controller and LADRC inner-current loop controller of PWM rectifier are designed. The proposed control strategy is compared and verified with PI control and ADRC by MATLAB/Simulink. Simulation and experimental results confirm the superiority of proposed control strategy in dynamic performance and disturbance rejection.

An Improved Open-Switch Fault Diagnosis Technique of a PWM Voltage Source Rectifier Based on Current Distortion

Numerous studies show that power semiconductors are significant contributors to the overall failure rate of pulsewidth modulation (PWM) voltage source rectifier (VSR) systems. Aimed at this problem, this paper presents an improved diagnosis system for open-circuit faults of a three-phase PWM VSR based on ac current distortion characteristics, which consists of a diagnosis module, a register module, and a decision module. The diagnostic module employs a hysteresis comparator to judge the change trend of the currents, and thereby diagnoses the single open-circuit (OC) faults. The register module is employed to achieve multi-switch OC fault diagnosis, and the decision module is used to output the final result. The proposed method extends the previous work to multi-switch OC fault conditions as well as improves the diagnosis accuracy. The experimental results show that the proposed method can correctly achieve fault diagnosis, including 6 kinds of single-switch faults and 15 kinds of different double-switch faults. Additionally, the proposed method also shows superior anti-interference performance and high robustness under abrupt load transient conditions, different power factor conditions, unbalanced and/or distorted grid voltage conditions, and different ac filter structure conditions. Furthermore, the average diagnostic time of this method is only 3.68 ms.

Developing a grid-connected DFIG strategy for the integration of wind power with harmonic current mitigation

<p>The aim of this paper is to present a study of the efficiency of the electrical part of a wind generation system. Two back-to-back PWM voltage-fed inverters connected between the stator and the rotor are used to allow bidirectional power flow. The second inverter grid side, has a role of a power active filter, to eliminate the harmonic generated by the non linear load, in the same time gives an active and reactive power needed by the rotor of DFIG. The harmonics of switching frequency in the current stator, pose a major problem in the moment where commutations in the diode bridge, to solve this problem, we introduce a small-sized passive LC filter for the purpose of eliminating high-frequency shaft voltage and grid current from a DFIG driven by a voltage-source pulse width-modulation rotor inverter controlled with SVM. The control theory is discussed, and the controller implementation is described. Design criteria are also given. The results of simulation tests show excellent static and dynamic performances.</p>

Fast Calculation of Carrier Harmonic Loss in Permanent Magnet of IPMSM Under PWM VSI Supply Over Entire Working Range

A method for fast calculating the high-frequency harmonic loss (HFHL) in the permanent magnet (PM) of interior PM synchronous machine under the pulsewidth modulated voltage source inverter supply is proposed. The combination of the frozen differential reluctivity tensor method and the linear frequency finite-element analysis (FEA) is proposed to investigate the relationship between the high-frequency harmonic voltages (HFHVs) in the rotor reference frame and the flux density variations in the PM, which is described quantitatively with the proposed analytical model using several dimensionless parameters. Then, the PM HFHLs are calculated analytically with the models using the flux density variations as input. The relative errors between the HFHLs calculated analytically and those obtained from the time-stepping FEA are within 15% at eight arbitrary working conditions. The proposed method can be used to calculate the PM HFHL in both two- and three-dimensional cases, which is testified with the experiment. Quadratic polynomial is used to fit the relationship between the dimensionless parameters and the fundamental currents. With the fitted polynomial and the analytical spectra of the HFHVs obtained from the double Fourier integration method, the PM HFHL map over entire working range can be calculated in one hour.

Evaluation of DC-Link Voltage Switching Ripple in Multiphase PWM Voltage Source Inverters

This article presents a generalized approach toward the dc-link voltage switching ripple analysis in the two-level multiphase pulsewidth modulation (PWM) voltage source inverters with a balanced load. Since the voltage ripple is one of the crucial sizing criteria for a dc-link capacitor, a simple and practical equation for designing the dc-link capacitor, based on the maximum (peak-to-peak) value of the dc-link voltage ripple, has been proposed for the multiphase inverters. The amplitude of the dc-link voltage switching ripple is analytically derived as a function of operating conditions. The effect of the number of phases on the dc-link capacitor size is investigated as well. It is found that considering the same total output current, the dc-link capacitor size is reduced by increasing the number of phases up to seven. However, from the point of view of the dc-link capacitor size, there are no benefits of further increasing the number of phases. Reference is made to two commonly used modulation strategies—sinusoidal PWM and continuous symmetric centered PWM (i.e., space vector). The mathematical models are derived with an aim to provide the precise dc-link capacitor sizing and hence improve the power density of the whole system. The comparison of different phase numbers has been made. Proposed theoretical developments are verified by the simulation and experimental tests.

Active Power Decoupling Design of a Single-Phase AC–DC Converter

The second-order ripple power of single-phase converter causes second-order ripple voltages on the DC bus. For eliminating second-order ripple components, passive power decoupling methods including DC bus electrolytic capacitors have some shortcomings, such as low power density and poor stability of converters. Thus, an active power decoupling method based on a single-phase converter is proposed in this paper. The control method, taking single-phase voltage source pulse width modulation (PWM) rectifier (single-phase VSR) as the basic converter and adopting a buck-boost power decoupling circuit, introduces second-order ripple of DC bus voltage into a power decoupling circuit. The ripple acts as compensation of the phase deviation between the command value and the actual value of the second-order ripple current. Therefore, estimation of the second-order ripple current is more accurate, the power decoupling circuit absorbs the second-order ripple power behind the H-bridge more completely, and the DC bus voltage ripple is effectively suppressed accordingly. Finally, experimental results of the single-phase VSR are given to verify the validity of the proposed method.

A Simple Flexible and Robust Control Strategy for Wind Energy Conversion Systems Connected to a Utility Grid

This paper presents a simple and robust control strategy for a variable speed wind turbine conversion system using a squirrel-cage induction generator and a three-phase voltage source (AC/DC/AC) Pulse Width Modulation (PWM) converter connected to the utility grid through an LCL filter. The control strategy integrates for the generator side an adaptive radial basis function (RBF) neurosliding mode controller associated with the rotor flux oriented vector control which is used to regulate the turbine rotation speed, rotor flux, and the DC bus voltage. For the grid side, the inverter current and voltage regulation as well as the current injected into the grid are regulated by PI controllers for two modes of operation, namely, the stand-alone mode and grid connected mode. The main contribution of this article is the introduction of a new and simple control algorithm allowing automatic mode switching method based on wind speed. The proposed scheme is very efficient and can be easily implemented in practice. Simulation results illustrate the effectiveness and feasibility of the proposed algorithm.

Distributed energy resources integration in single-phase microgrids: An application of IDA-PBC and PI-PBC approaches

This paper presents a unified Hamiltonian formulation for controlling distributed energy resources (DERs) in ac single-phase microgrids (SP-MGs) via proportional-integral passivity-based control (PI-PBC), and interconnection and damping assignment passivity-based control (IDA-PBC). The proposed Hamiltonian formulation allows us to consider both pulse-width modulated voltage source converters (PWM-VSC) and pulse-width modulated current source converters (PWM-CSC) under a unified model. Renewable generation and supercapacitor energy storage systems are integrated via PWM-VSC technologies, while superconducting coils are integrated through PWM-CSC technologies. IDA-PBC and PI-PBC theories enable us to design control strategies begin that consider Lyapunov’s stability theory combined with the well-known advantages of proportional and integral control actions. Our simulation’s results corroborate the applicability of the proposed control approaches under stability paradigm. MATLAB/Simulink is employed for computational implementations via begin the SimPowerSystems toolbox.

Direct Power Control of PWM Rectifier With Feedforward Compensation of DC-Bus Voltage Ripple Under Unbalanced Grid Conditions

Three-phase voltage source pulsewidth modulation (PWM) rectifiers can achieve constant dc voltage and sinusoidal grid currents under ideal grid voltages. However, under unbalanced grid voltage conditions, there are ripples at twice the grid frequency in the dc voltage, and the grid currents become highly distorted. To address the aforementioned problems, control methods developed under ideal grid voltage conditions should be modified. Various techniques have been proposed in the literature to calculate the new current reference or power reference. However, most methods use conventional pq theory and only consider the grid-side power control. Hence, the dc voltage ripples are not completely eliminated. Furthermore, the derived mathematical expressions for reference calculations are usually very complicated. In contrast to current methods, this paper proposes a very simple yet effective direct power control (DPC) method based on extended pq theory. By analyzing the instantaneous extended power of the line inductance, a simple and concise power compensation is analytically derived and added to the original power references. As a result, the dc voltage ripples are significantly reduced, and the grid currents remain sinusoidal even under unbalanced grid voltage conditions. The proposed method is compared to conventional DPC methods, and its effectiveness is confirmed by the presented experimental results.

Design of Backstepping Direct Power Control for Three-Phase PWM Rectifier

This study focuses on the backstepping control (BSC) design for the direct power control of a three-phase voltage-source pulsewidth-modulation rectifier. The power factor of this three-phase rectifier can be adjusted by controlling the instantaneous reactive power and the dc output voltage simultaneously. In the proposed BSC system with the consideration of system uncertainties, it can be divided into two independent backstepping controllers by introducing two decoupling control signals, and the corresponding controller parameters can be adjusted independently. As a result, both the stable dc-bus output voltage and the sinusoidal input current with a lower total-harmonic-distortion value can be obtained. Moreover, instantaneous active and reactive powers also can be indirectly controlled. In addition, the robustness against power grid fluctuation, step load change, and filter inductance variation can be achieved. The effectiveness of the proposed BSC system is verified by numerical simulations as well as realistic experiments, and its merits are indicated in comparisons with traditional proportional-integral control and proportional-resonant control.

Generic pulse width modulation model, based on generalized inverses and applied to voltage source inverters

PurposeThis paper aims to develop a method for a unified model of pulse width modulation (PWM) voltage source inverters (VSI). This generic method, based on a common and easy-to-use carrier-based modulation, allows to generate the exhaustive solution set for a given PWM-VSI.Design/methodology/approachThe use of the generalized inverse theory is developed to express the PWM solution set for the duty cycle. Indeed, the infinite number of PWM solutions is demonstrated. To explore this solution set, the unified model described exhibits degrees of freedom. The admissible margins to set the degree of freedom are highlighted. Some experimental results are presented.FindingsIt is demonstrated how the degree of freedom can be directly connected with efficiency indicators such as common mode voltage, inverter linearity and switching losses. The expression of the PWM solution set boundaries is clearly expressed.Research limitations/implicationsFurther studies should explore how the degree of freedom can be connected with parameters associated with the current (and not the voltage as described in this paper).Practical implicationsThe paper includes implications for the development of a more generic approach for PWM multilevel VSI.Originality/valueThis paper fulfils a mathematical frame to ease the expression of PWM scheme.

A Harmonic Based Pilot Protection Scheme for VSC-MTDC Grids with PWM Converters

This paper presents a selective harmonic-based pilot protection scheme for detecting faults happened in the DC transmission section of VSC-MTDC grids with pulse width modulation (PWM) voltage source converters (VSCs). When a DC fault occurs in VSC-MTDC grids with PWM converters, first carrier frequency harmonic (FCFH) currents will be generated by all VSCs through the grid. FCFH currents have different flowing directions depending on the characteristics and the location of the fault. According to the characteristics of the existing FCFH in the fault currents, a selective pilot protection algorithm is designed for VSC-MTDC grids. Considering the internal and external DC transmission faults for specific zones, and the circulating flow of FCFH current in the DC link capacitors, the relays cannot detect FCFH currents for external faults, while for the internal faults, FCFH currents are clearly detected. To design the selective protection algorithm, Hilbert-Huang transform (HHT) is used to detect the instantaneous frequency and the instantaneous amplitude of the high frequency intrinsic mode function (IMF)s, which are extracted from the fault current waves. Multiple faults with different characteristics are applied to CIGRE DCS-2 VSC-MTDC grid with two-level and three-level VSCs modeled in PSCAD, and the HHT-based selective protection scheme is designed in MATLAB. According to the results, the proposed algorithm can truly discriminate between internal and external faults.

New Insights Into Model Predictive Control for Three-Phase Power Converters

Deadbeat control (DBC) has been investigated for decades because of its simple concept and satisfactory performance. Recently, finite control set-model predictive control (FCS-MPC) attracted wide attention in the control of power converters. Unlike DBC, FCS-MPC does not employ a modulator and directly manipulate switching states by minimizing a cost function. To improve the steady-state performance, some improved FCS-MPCs introducing two or three vectors during one control period were proposed in the existing literature. This paper proposes new insights into multiple-vector FCS-MPC for power converters by investigating its relationship with space vector modulation based DBC (SVM-DBC). Analytical studies show that two kinds of predictive methods can be unified in one framework when the control target is to minimize the tracking error. Different from enumeration-based vector selection in conventional FCS-MPC, the vector sequence and duration of the proposed multiple-vector FCS-MPC are directly reconstructed from SVM-DBC. Theoretical analysis on the state-of-the-art DBC and FCS-MPC, as well as experimental test on a three-phase two-level voltage source pulsewidth modulation rectifier confirms the effectiveness of the proposed method.

Power Loss Analysis Model of a Dc-Dc Buck-Boost Converter with an Interfaced Three Phase Inverter for Medium Voltage Application

This paper presents a comprehensive mathematical modelling of a DC to DC Buck-Boost converter. The different power losses associated with the Buck-Boost circuit are also presented. Analysis of the converter power loss is graphically represented at varied duty cycles and load resistance values. A low frequency pulse width modulated inverter is interfaced with the Buck-Boost converter using MATLAB/SIMULINK. For an efficient performance and attenuation of low order harmonics, the low frequency pulse width modulated inverter is substituted with a high frequency pulse width modulated voltage source inverter. A comparison is therefore drawn to show the significant change in the percentage harmonic reduction of the two different frequency modulations. All simulation results are achieved using MATLAB 7.14 version. The simulation results however show that Mosfet switching loss decreases with an increase in the duty cycle whereas Diode and Inductor conduction losses increase with an increase in the duty cycle values.

Open Switch Fault Diagnosis Method for PWM Voltage Source Rectifier Based on Deep Learning Approach

With the development of machine learning technology, numerous studies have been proposed to diagnose the open circuit (OC) faults in the pulse width modulation (PWM) voltage source rectifier (VSR) systems. However, most methods require system signals of more than one current period, which show poor real-time performance. Aiming at this problem, this paper presents an improved diagnosis system based on deep belief networks (DBN) and least square support vector machine (LSSVM). First, the double chain quantum genetic algorithm (DCQGA) is employed to obtain the proper length of measured signals and DBN structure parameters. Then, the fault features are extracted from the signals through DBN. Finally, these features are used to train the LSSVM fault classifier to construct the diagnosis model. The experimental results show that the proposed method can achieve the fault diagnosis including six kinds of single switch faults and 15 kinds of different double switches faults correctly. Besides, the proposed method also shows the superior anti-interference performance and high robustness on abrupt load transient conditions, unbalanced, and/or distorted grid voltage conditions, as well as, different power factor conditions. Furthermore, the average diagnostic time of this method is only 2.57 ms.

A Theoretical Analysis of Pulsating Torque Components in AC Machines With Variable Frequency Drives and Dynamic Mechanical Loads

This paper analytically investigates expressions of an oscillating motor's air-gap torque resulting simultaneously from dynamic electromagnetic and dynamic mechanical components. The electromagnetic torque is generated in the air gap when the motor is supplied by variable frequency drives (VFDs), such as pulsewidth modulated voltage source inverters or load commutated inverters. Whereas, the mechanical torque components might result from dynamic mechanical processes, such as wind turbine blades, oil and gas fluid fluctuation, and, for emulating dynamic mechanical loads, a load-side VFD. Simple and straightforward analytical relationships between electrical and mechanical harmonics are developed to understand the propagation of mechanical dynamics to the electric side and vice versa. Intensive numerical simulations have been carried out to support the theoretical analysis. Time and frequency domain results confirm the robustness of the proposed relationships. Finally, laboratory experimental test results also confirm the accuracy of the proposed relationships.