Three-phase Pulse Width Modulation Inverter Research Articles

A Cascaded Half-Bridge Three-Level Inverter With an Inductive DC-Link for Flexible Voltage Boosting

Voltage boosting three-level inverters may present a monotonically increasing or decreasing voltage gain when enlarging the pulsewidth modulation (PWM) ratio. To produce a flexible voltage gain, this article proposes a novel three-phase three-level PWM inverter by cascading a traditional two-level three-leg (B6) inverter with half-bridges. The proposed inverter is supplied by an inductive dc-link consisting of a dc source in series with an inductor that is charged by shooting through the half-bridges in the B6 structure. The voltages across the cascaded half-bridges are subsequently boosted, and the output voltage is stepped up due to the cascaded connection. A moderate voltage gain is achieved with proper selections of two modulation variables while maximizing the PWM ratio. In particular, when the two modulation variables are equal, a constant voltage boosting gain of two is maintained irrespective of the PWM ratio. Additionally, low voltages are induced on the components, which facilitates the use of low-voltage devices. The operating principle of the proposed inverter with a modified third-harmonic-injection PWM scheme is presented, followed with theoretical analysis, comparison, and design considerations. Experimental tests on a 1.5-kVA inverter prototype verify its feasibility.

General High-Order Selective Harmonic Repetitive Control for PWM Converters

In this article, a general high-order selective harmonic repetitive control (HO-SHRC) scheme is proposed, which is composed of a standard high-order repetitive controller structure and a new order-expandable SHRC. Different from conventional SHRC, the proposed new SHRC is capable of being applied into the standard high-order repetitive control (HORC) structure for generating any high-order SHRC. The proposed HO-SHRC can be used to improve the steady-state tracking accuracy of the pulsewidth modulation (PWM) converter systems and is robust to system frequency variations without changing the controller parameters online. The order expansion of the controller will lead to the increase of the implementation complexity, but it will bring the overall improvement of the controller performance, such as the improvement of frequency adaptability, steady-state tracking accuracy, and dynamic performance. Therefore, HO-SHRC can achieve a good compromise between the controller performance and the implementation complexity. Moreover, the proposed HO-SHRC provides a general structure for various repetitive controls (RCs), such as conventional RC (CRC), odd-harmonic RC (OHRC), high-order CRC (HO-CRC), and HO-odd-harmonic RC (HO-OHRC). Application examples of second-order (SO)- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$6k~\pm $ </tex-math></inline-formula> 1 RC-controlled three-phase PWM inverter show the effectiveness and advantages of the proposed control scheme.

Power conversion efficiency prioritized AC filter inductor design for three-phase PWM inverter

This study was conducted to develop a design method of power density and efficiency maximization for three-phase pulse-width modulated (PWM) inverters that include AC filter. A tradeoff relationship exists between power density and efficiency. In general, increasing the switching frequency is known to increase the switching device loss and decrease the volume of the passive components. A three-phase PWM inverters design should consider the balance between conversion efficiency and inverter volume. However, best of our knowledge, no practical study has focused on the optimal design of a three-phase PWM inverter that includes an AC filter. This is because the iron loss of the AC filter inductor changes in complicated ways depending on the DC-bias excitation, amplitude of switching ripple current, etc. Therefore, the present authors clarified this iron loss mechanism and realized a highly accurate iron loss calculation method in previous studies. In this paper, the relationship between efficiency and volume for the switching frequency was analyzed when the AC filter inductor was designed for minimal loss by adjusting the core diameter, height, and number of winding turns. The efficiency and volume optimization achieved by designing a proper inductor was verified via comparison with a base design.

An Online Data-Driven Method for Simultaneous Diagnosis of IGBT and Current Sensor Fault of Three-Phase PWM Inverter in Induction Motor Drives

This article presents an online data-driven diagnosis method for multiple insulated gate bipolar transistors (IGBTs) open-circuit faults and current sensor faults in the three-phase pulsewidth modulation inverter. The fast Fourier transform (FFT) algorithm is used to extract the fault frequency spectrum features of the three-phase currents. Then, a feature selection method named ReliefF is introduced to select the most critical features by removing redundant and irrelevant features. In addition, as novel fast learning technology, a random vector functional link network is applied to learn the faulty knowledge from the historical dataset. Based on the well-learned model, the fault type and location of the converter can be accurately identified as long as the three-phase current signals are measured. Offline test results verify that the proposed method can identify the IGBT and sensor faults with an accuracy of 98.83% and outperforms the state-of-the-art learning algorithms. Moreover, the real-time hardware-in-the-loop test results show that the proposed method can successfully identify the IGBT faults and current sensor faults within 22 ms. It is robust to the dc-link voltage fluctuations, model parameters, and speed or load variations. The extensibility of the proposed method is also validated based on the test results in terms of other fault modes and drive systems.

High‐performance speed estimation of induction machines based on adaptive filtering

This paper presents a novel algorithm for sensorless detection of the rotor speed applied to induction machines, which relies on rotor slot harmonics (RSHs). The estimator structure is proposed, for extracting and tracking the RSH found in the stator line current, which offers improved results compared with previously published methods. The proposed method reduces delays, output jitter, and steady-state error. A stability analysis is provided and used in the design procedure to ensure system reliability. The capability of using the estimated signal as speed feedback in a sensorless drive is tested and confirmed. The system employs a bandpass filter with a centre frequency that is adapted according to the estimated speed, a high bandwidth phase-locked loop, and an observer. Tracking limits and parameter design are explained analytically; the method is verified in simulations and confirmed experimentally. Experimental verification is performed on a standard three-phase induction motor, using a three-phase pulse-width modulation inverter.

Optimal time-domain pulse width modulation for three-phase inverters

An optimal time-domain technique for pulse-width modulation (PWM) in three-phase inverters is presented. This technique is based on the time-domain per phase analysis of three-phase inverters for linear, balanced output load circuits. Exact analytical solutions for the output phase currents are presented for first, second, and third order circuits for any sequence of rectangular pulses. Next, the role of symmetries in the structure of three-phase PWM inverter voltages is discussed. Finally, using the exact analytical solutions for phase-currents as well as symmetry considerations, minimization of output current harmonics is set up as an optimization problem. Sample numerical results are presented that highlight improvements in the performance of three-phase inverters.

Ground Leakage Current Caused by Common-Mode Voltage of PWM inverter

In railway tractive vehicles, three-phase PWM (Pulse Width Modulation) inverters generate parasitic Differential-Mode Voltages (DMV) and Common-Mode Voltages (CMV). Parasitic voltages are a side effect of using the width modulation to shape the phase-to-phase inverter’s voltage. In this article, the authors present a mathematical description of the DM and CM voltages and carry out their spectral analysis. Based on the spectral harmonics analysis, the authors present a method for filtration of harmonics of DM and CM voltages aimed at limiting the capacitance parasitic currents: due to DM voltage – phase-to-phase parasitic current and CM voltage – ground parasitic currents. As the final result of the tests, almost complete elimination of leakage parasitic current form PE shock protection system was achieved.

An Intelligent Time-Adaptive Data-Driven Method for Sensor Fault Diagnosis in Induction Motor Drive System

Three-phase pulsewidth modulation inverter fed induction motor drive system is widely applied in high power drive applications. Sensor faults are very common in the drive system, which, once occur, might result in degraded system performance or even system shutdown. In order to rapidly and accurately diagnose the sensor faults, this paper proposes an intelligent time-adaptive data-driven method to identify the fault location and fault type of sensors in the drive system. An emerging machine learning technology named extreme learning machine (ELM) is applied to learn the sensor fault dataset; an ensemble ELM classifier is then designed to improve diagnostic accuracy, based on which a time-adaptive fault diagnosis process is proposed to achieve a high and balanced diagnostic accuracy and speed. As a data-driven method, the proposed method only employs the phase current, dc-link voltage, and speed signals as the inputs to the ensemble ELM classifiers and requires no additional sensors and other hardware. Simulated and experimental tests show that the proposed method can rapidly and accurately detect the fault sensor location and identify offset fault, stuck fault, and noise faults with an average diagnostic accuracy of 98% and the average decision time of 10 ms after the fault occurs. Moreover, such diagnosis method is robust to the fluctuation of catenary voltage and dc-link voltage, fault severity, and variation of model parameters, speed, and load.

Common-Mode Voltage Attenuation of an Active Common-Mode Filter in a Motor Drive System Fed by a PWM Inverter

The switching speeds of next-generation power semiconductor devices, such as those made of silicon carbide and gallium nitride are roughly ten times those of conventional devices (e.g., silicon insulated-gate bipolar transistors). This increases the frequency range of the electromagnetic noise accompanying the switching operations of pulsewidth modulated (PWM) converters and worsens the influence of radiated noise. The authors have previously proposed an active common-mode filter (ACF) that reduces the radiated noise from the power cables connected to a PWM converter and evaluated its effect in reducing radiated noise by using a function generator as a common-mode (CM) noise source. In this paper, the ACF is applied to a motor drive system fed by a three-phase PWM inverter, and the attenuation characteristics of the CM voltage are evaluated. To avoid saturating the ACF, the combination of an active common-noise canceller and the ACF is discussed. The experimental results show that the system constructed in this paper can suppress the CM voltage produced by the PWM inverter over a wide frequency range from 100 to 100 MHz.

Generalized Average Method for Time-Invariant Modeling of Inverters

Models of inverters and other converters based on averaging have been widely used in numerous simulation applications. Generalized averaging can be applied to model both average and switching behavior of converters while retaining the faster run times associated with average-value models. Herein, generalized average models for single- and three-phase pulse width modulation inverters are proposed. These models are based on a quasi-Fourier series representation of the switching functions that includes fundamental and switching frequency components as well as sideband components of the switching frequency. The proposed models are demonstrated both in simulation and experimentally and are found to accurately portray both the fundamental and the switching behavior of the inverter. In particular, the use of sideband components allows accurate representation of the variation in switching ripple magnitude that occurs in the steady state. The generalized average models are found to have simulation run times that are significantly faster than those associated with detailed models. Therefore, the proposed generalized average models are suitable for simulation applications in which both accuracy (including the switching behavior) and fast run times are required (e.g., long simulation times, systems with multiple converters, and repeated simulations).

三相PWMインバータにおける低負荷運転時の効率改善を目的とした三相ACフィルタインダクタの提案

The inductor losses in a three-phase AC filter inductor used in a three-phase pulse-width modulation (PWM) inverter are evaluated. First a three-phase inductor is designed to obtain the same value of inductance for each phase. Then, based on the design, a three-phase inductor that uses two magnetic materials is proposed. The conversion efficiency of a 1kVA three-phase PWM inverter that uses the conventional and proposed AC filter inductors is simulated. Simulation results show that conversion efficiency improves. Finally, the conversion efficiency of an actual three-phase 1kVA PWM inverter that uses the conventional and proposed AC filter inductors is measured. In the experiment, the conversion efficiency obtained for the case of the proposed inductor improves by approximately 1% at low power load as compared to the conventional inductor. Furthermore, the calculated inductor loss es are in good agreement with measured losses. Improvement in efficiency is verified trough simulations and experiments.

Analysis and Minimization of Output Current Ripple for Discontinuous Pulse-Width Modulation Techniques in Three-Phase Inverters

This paper gives the complete analysis of the output current ripple in three-phase voltage source inverters considering the different discontinuous pulse-width modulation (DPWM) strategies. In particular, peak-to-peak current ripple amplitude is analytically evaluated over the fundamental period and compared among the most used DPWMs, including positive and negative clamped (DPWM+ and DPWM−), and the four possible combinations between them, usually named as DPWM0, DPWM1, DPWM2, and DPWM3. The maximum and the average values of peak-to-peak current ripple are estimated, and a simple method to correlate the ripple envelope with the ripple rms is proposed and verified. Furthermore, all the results obtained by DPWMs are compared to the centered pulse-width modulation (CPWM, equivalent to the space vector modulation) to identify the optimal pulse-width modulation (PWM) strategy as a function of the modulation index, taking into account the different average switching frequency. In this way, the PWM technique providing for the minimum output current ripple is identified over the whole modulation range. The analytical developments and the main results are experimentally verified by current ripple measurements with a three-phase PWM inverter prototype supplying an induction motor load.

Design and Analysis of Robust Active Damping for LCL Filters Using Digital Notch Filters

Resonant poles of LCL filters may challenge the entire system stability especially in digital-controlled pulse width modulation (PWM) inverters. In order to tackle the resonance issues, many active damping solutions have been reported. For instance, a notch filter can be employed to damp the resonance, where the notch frequency should be aligned exactly to the resonant frequency of the LCL filter. However, parameter variations of the LCL filter as well as the time delay appearing in digital control systems will induce resonance drifting, and thus break this alignment, possibly deteriorating the original damping. In this paper, the effectiveness of the notch filter-based active damping is first explored, considering the drifts of the resonant frequency. It is revealed that when the resonant frequency drifts away from its nominal value, the phase lead or lag introduced by the notch filter may make itself fail to damp the resonance. Specifically, the phase lag can make the current control stable despite of the resonant frequency drifting, when the grid current is fed back. In contrast, in the case of an inverter current feedback control, the influence of the phase lead or lag on the active damping is dependent on the actual resonant frequency. Accordingly, in this paper, the notch frequency is designed away from the nominal resonant frequency to tolerate the resonance drifting, being the proposed robust active damping. Simulations and experiments performed on a 2.2-kW three-phase grid-connected PWM inverter verify the effectiveness of the proposed design for robust active damping using digital notch filters.

Evaluation of Iron Loss of AC Filter Inductor Used in Three-Phase PWM Inverters Based on an Iron Loss Analyzer

The authors have proposed two methods for iron loss evaluation of the ac filter inductor used in a pulsewidth modulation (PWM) inverter. The first method is a loss map method, which can be used for the iron loss calculation of the ac filter inductor without using a real PWM inverter, and the second method is an iron loss analyzer (ILA), which can measure the iron loss of the ac filter inductor during every switching period on a real PWM inverter. In this paper, the measurement results obtained using the ILA and the results calculated using the loss map method on both the single-phase and three-phase inverters are compared. The calculated iron loss of the ac filter inductor on the three-phase PWM inverter is found to have a relatively large error for certain PWM pulse conditions. In order to reduce the calculation error, the authors propose a modified loss calculation method and demonstrate that the calculation error is reduced to less than 2%.

Wind Turbine Generator–Battery Energy Storage Utility Interface Converter Topology With Medium-Frequency Transformer Link

A medium-voltage (MV) wind turbine generator (WTG)-battery energy storage (BESS) grid interface converter topology with medium-frequency (MF) transformer isolation is introduced in this paper. The system forms a three-port network in which several series stacked ac-ac converters transform the low-frequency (50/60 Hz) utility MV into MF (0.4 to 2 kHz) ac voltage by modulating it with MF square wave. This voltage is then fed to the MF transformer primary windings. The secondary and tertiary windings interface with the WTG side and the BESS side, respectively, after power conversion. The power generated by WTG is transferred to the MF transformer secondary windings through a three-phase pulse width modulation (PWM) rectifier and a three-phase PWM inverter, whereas the power transfer between the BESS and the tertiary winding occurs through a three-phase PWM inverter. It is shown that the utility grid sinusoidal currents, the battery current, and the WTG output currents can be controlled to be of good quality using PI and DQ control strategies. Thus, the proposed MF transformer-based three-port topology results in smaller converter weight/volume. Moreover, the control can handle voltage sags/swells and provide low voltage ride-through capability. Simulation waveforms along with experimental results are shown as proof of concept.

A Generic Digital $nk \pm m$-Order Harmonic Repetitive Control Scheme for PWM Converters

In this paper, a generic digital nk ± m-order harmonic repetitive control ( nk ± m RC) scheme is presented for constant-voltage constant-frequency pulsewidth-modulation (PWM) converters to track/remove any nk ± m-order harmonic frequencies efficiently, e.g., 4k ± 1-order harmonics for single-phase converters or 6k ± 1-order harmonics for three-phase converters. Compared with conventional RC, the proposed nk ± m RC occupies less data memory and can achieve zero-error tracking or perfect disturbance rejection of nk ± m-order harmonics at much faster error convergence rate. What is more, the proposed RC provides a unified formula for various RC schemes. Application examples of 6k ± 1-RC-controlled three-phase PWM inverter and 4k ± 1-RC-controlled single-phase PWM inverter demonstrate the effectiveness and advantages of the proposed RC scheme.

High-Power-Factor Single-Phase Diode Rectifier Driven by Repetitively Controlled IPM Motor

This paper proposes a new power factor correction method using an inverter-driven interior permanent magnet (IPM) motor. The proposed system realizes the high power factor of a single-phase diode rectifier by using a three-phase pulsewidth modulation inverter and an IPM motor. The proposed converter consists of a single-phase diode rectifier, a small film capacitor at the dc link (14 μF and 0.33 J/kVA), a three-phase voltage-source inverter, and an IPM motor. In the proposed system, the inverter has the following two functions: 1) It regulates the velocity of the IPM motor, and 2) it controls the source-side-current waveform. In order to obtain a unity-power-factor operation at the source side, we propose and implement a new control method that regulates the inverter output power. The proposed control method is that the inverter regulates <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">d</i> - <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">q</i> -axis current synchronous with input voltage. An inverter-output-power controller is positioned between a speed controller and a <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">q</i> -axis current controller. The inverter output power is regulated by a proportional-integral and repetitive controller. The maximum power factor obtained by the proposed method is 98.7% at the rated-load conditions. The superior performance of the proposed system is demonstrated by experimental results.

General parallel structure digital repetitive control

This article presents a parallel structure digital repetitive control (PSDRC) scheme, where the internal models of all harmonics are decomposed into multiple parallel connected groups. Compared with conventional repetitive controller, the proposed parallel structure enables repetitive controller to regulate the error convergence rate at each group of harmonic frequencies independently and offers faster total error convergence rate. Moreover, PSDRC can achieve zero-error tracking or perfect disturbance rejection for all harmonics without occupying more data memory. A stability criterion with rigorous proof for PSDRC system is addressed, which is compatible with those existing stability criteria for existing RC schemes. An application example of three-phase pulse-width modulation inverter is provided to demonstrate the effectiveness of the proposed PSDRC scheme.

A High-Performance PWM Algorithm for Common-Mode Voltage Reduction in Three-Phase Voltage Source Inverters

A high-performance pulsewidth modulation (PWM) algorithm with reduced common-mode voltage (CMV) and satisfactory overall performance is proposed for three-phase PWM inverter drives. The algorithm combines the near-state PWM (NSPWM) method that has superior overall performance characteristics at high modulation index, and MAZSPWM, a modified form of the active zero-state PWM method (AZSPWM1), which is suitable for low modulation index range of operation. Since AZSPWM1 has line-to-line voltage pulse reversals with small zero-voltage time intervals, in its naive form, it causes overvoltages, in particular in long-cable motor drive applications. Obtained by reorganizing the duty cycles of the utilized voltage vectors of AZSPWM1, MAZSPWM has sufficiently long zero-voltage time intervals between pulse reversals such that during pulse reversals, overvoltages are avoided. The combined algorithm performs satisfactorily throughout the inverter operating range and the transition from NSPWM to MAZSPWM and vice versa is seamless. The performance of the proposed algorithm is proven by theory, computer simulations, and detailed laboratory experiments. The paper also shows that the proposed reduced CMV PWM algorithm is effective in reducing the motor leakage current, and it is most beneficial when a small common-mode inductor is included in the drive.

Grid-tied Power Conditioning System for Fuel Cell Composed of Three-phase Current-fed DC-DC Converter and PWM Inverter

This paper proposes a grid-tied power conditioning system for fuel cell, which consists of three-phase current-fed DC-DC converter and three-phase PWM inverter. The three-phase current-fed DC-DC converter boosts fuel cell voltage of 26-48 V up to 400 V with zero-voltage switching (ZVS) scheme, while the three-phase PWM(Pulse Width Modulation) inverter controls the active and reactive power supplied to the grid. The operation of the proposed power conditioning system with fuel cell model is verified through simulations with PSCAD/EMTDC software. The feasibility of hardware implementation is verified through experimental works with a laboratory prototype with 1.2 kW proton exchange membrane (PEM) fuel cell stack. The proposed power conditioning system can be commercialized to interconnect the fuel cell with the power grid.