PWM Voltage Source Inverter Research Articles

A Novel Harmonic Compensator for Consumer Electronic Equipment Using the Correlation Function

This paper proposes a novel harmonic compensator for consumer electronic equipment that act as harmonic voltage sources in single-phase circuits, using the correlation function. The distribution transformer is equipped with an additional winding on the secondary side, and a single-phase voltage-source PWM inverter is connected to the added winding, acting as a shunt active filter. The leakage inductor on the secondary side winding behaves as though connected in series to the consumer electronic equipment. The shunt active filter can thus be used to compensate harmonic currents on the source side without an inductor series-connected to the harmonic voltage source. The basic principle of the proposed compensation method is discussed in detail. Digital computer simulation is implemented to verify the validity of the proposed compensation method. Experimental results demonstrate the novelty and excellent practicability of the proposed harmonic compensator with the proposed harmonic current detection method using the correlation function.

Implementation of a Hybrid Filter with a Potential Application to Adjustable Speed Compressor Drives for Air Quality Control

This article presents a TMS320C31 DSP-based implementation of a hybrid active filter to compensate the harmonics of an R-C nonlinear load. A diode bridge rectifier with an R-C load is considered to represent variable-speed compressor load. The topology of a hybrid filter combines a shunt passive filter (PF) and a shunt active filter (AF). An inductor, placed in series with the line between the AF andthe PF, not only reduces the load harmonics but also creates a harmonics voltage source at the input of diode bridge rectifier. This harmonics voltage source makes the PF more effective and reduces its susceptibility to possible mistuning in the parameters. The PF is tuned to compensate 5th and 7th harmonics, while the AF compensates the rest of the harmonics of the load current. A PWM voltage source inverter (VSI) with an indirect current-controlled technique is used as an AF. The control algorithm of a shunt AF is based on a dc bus voltage feedback loop and load current feedforward loop. A proportional plus integral control is used on the self-supporting dc bus voltage of the shunt AF. It is demonstrated that an R-C nonlinear load draws current with higher peak value and needs a hybrid solution for the load current harmonics. Experimental verification of simulated results is carried out on a scaled-down prototype module of the hybrid filter.

Mixed p‐z approach for analytical analysis of an induction motor fed from space‐vector PWM voltage source inverter

AbstractThis paper proposes an analytical method for calculating both the steady‐state and transient performance of an induction motor fed from the three‐phase voltage source inverter. As a modulation technique of the inverter we consider space vector modulation. The proposed method makes use of the Laplace and modified Z‐transformation of the space vectors (mixed p‐z approach) to predict current response of induction motor. From the Laplace transform of the stator voltage vector we can also derive Fourier analysis to predict the voltage harmonic spectrum. Experimental tests have been carried out confirming the validity of the analytical results.

A hysteresis current control for single-phase multilevel voltage source inverters: PLD implementation

In most high-performance applications of voltage source pulse-width modulation inverters, current control is an essential part of the overall control system. In this paper, a hysteresis current control technique for a single-phase five-level inverter with flying-capacitor topology is proposed. Logic controls and a programmable logic device are suitable for handling a large number of switches and implementation of state transitions. This method also considers how to improve unbalanced voltages of capacitors using voltage vectors in order to minimize switching losses. The simulation and experimental results describe and verify the current control technique for the inverter.

A three-phase parallel active power filter operating with PCC voltage compensation with consideration for an unbalanced load

The performance and dynamic characteristics of a three-phase parallel active power filter (APF) with point of the common coupling (PCC) voltage compensation with consideration for an unbalanced load is presented and analyzed in this paper. The proposed scheme employs a pulse-width modulation (PWM) voltage-source inverter and has two operation modes. First, it operates as a conventional active filter with reactive power compensation when PCC voltage is within the 15% voltage drop range. Second, it operates as a voltage compensator when PCC voltage is not within the 15% voltage drop range. Both the APF and the voltage compensator compensate asymmetries caused by nonlinear loads. Finally, the validity of this scheme is investigated through the analysis of simulation and experimental results for a prototype APF system rated at 10 kVA.

Analytical closed-form solution of a space-vector modulated VSI feeding an induction motor drive

The paper presents the analysis of the time response of the stator and rotor currents in induction motor fed by space-vector pulse-width modulated voltage source inverter. This mathematical model uses the Laplace and modified Z-transform. The solution is made in two steps: (a) finding the Laplace transform of the stator voltage space vectors; and (b) finding the inverse transform of the load currents (original function) using the modified Z-transform. The solution is not dependent on the number of the pulses of the PWM pattern. All the analytical waveforms were visualized from the derived relations with the program MATHCAD. Experimental results prove the feasibility of the proposed mathematical model.

Analysis of power and power spectral density in PWM inverters with randomized switching frequency

A novel method for accurate calculation of power spectra of the pulsewidth modulation (PWM) voltage-source inverter with randomized switching frequency is presented. The case of a limited pool of switching frequencies, convenient and adequate for technical purposes, is considered, and a mathematical background for this type of random PWM (RPWM) is provided. It is shown that the limited-pool RPWM gives rise to not only a continuous spectrum, but, also, under certain circumstances, pure power spectral components (harmonics), typical for the deterministic PWM. Criteria for the existence of harmonics are given, and formulae for both the power and the power spectral density are derived and verified experimentally.

Analytical Closed-Form Solution of a Space-Vector Modulated VSI Feeding an Induction Motor Drive

This paper presents the analysis of the time response of the stator and rotor currents in an induction motor fed by a space-vector pulse-width modulated voltage source inverter. This mathematical model uses the Laplace and modified Z-transform. The solution is made in two steps: 1) finding the Laplace transform of the stator voltage space vectors and 2) finding the inverse transform of the load currents (original function) using the modified Z-transform. The solution is not dependent on the number of the pulses of the PWM pattern. All the analytical waveforms were visualized from the derived relations with the program MATHCAD. Experimental results prove the feasibility of the proposed mathematical model.

Elimination of low-frequency harmonics caused by PWM in a three-phase soft-switched boost rectifier

This paper presents three major causes of low-frequency harmonics in a high-frequency soft-switched three-phase pulsewidth modulation (PWM) boost rectifier: pulsewidth limits; an improper space-vector modulation scheme; and dead time. Among these, the pulsewidth limits are related to soft-switching techniques. To eliminate undesirable low-frequency harmonics, each cause is illustrated and a solution is provided. Both simulation and experimental results prove the effectiveness of the proposed solutions. Due to the similarities between boost rectifiers and voltage-source inverters, the conclusions of this paper are also applicable to high-frequency PWM voltage-source inverters.

A Three-phase Voltage-Source PWM Inverter System Characterized by Sinusoidal Output Voltage with Neither Common-mode Voltage nor Normal-mode Voltage

This paper deals with an inverter system integrating a small-rated passive EMI filter with a three-phase voltage-source PWM inverter. The purpose of the EMI filter is to eliminate both common-mode and normal-mode voltages from the output voltage of the inverter. The motivation of this research is based on the well-known fact that the higher the carrier or switching frequency, the smaller and the more effective the EMI filter. An experimental system consisting of a 5-kVA inverter, a 3.7-kW induction motor, and a specially-designed passive EMI filter was constructed to verify the viability and effectiveness of the EMI filter. As a result, it is shown experimentally that both three-phase line-to-line and line-to-neutral output voltages look purely sinusoidal as if the inverter system were an ideal variable-voltage, variable-frequency power supply when viewed from the motor terminals. This results in completely solving serious issues related to common-mode and normal-mode voltages produced by the inverter.

Sine-triangle versus space-vector modulation for three-level PWM voltage-source inverters

This paper studies the inherent relations between sine-triangle and space-vector pulsewidth modulation schemes for three-level voltage-source inverters. It is shown that the two schemes can function equivalently through proper selection of common-mode injections in the case of sine-triangle modulation, or dwell times in equivalent redundant switching states in the case of space-vector modulation. Simulation and measurement results illustrate that understanding of these relations can lead to a more efficient and flexible three-level modulator with desired or optimal performance.

Configurations and characteristics of active canceling and compensating circuits for reducing common‐mode voltage generated by voltage‐source PWM inverters

AbstractThis paper deals with active circuits for cancellation and compensation of common‐mode voltage caused by a PWM inverter. A nonnegligible amount of leakage or ground current flows through stray capacitors between stator windings and the motor frame due to a large step change in the common‐mode voltage at every switching operation of the PWM inverter. First, it is shown experimentally that the active common‐noise canceler (ACC), which has been proposed by the authors, is effective in reducing not only conducted EMI but also motor shaft voltage and bearing current. Next, a new ACC characterized by an isolated power supply is developed to enlarge the applicable voltage range in which it is possible to integrate the ACC with a PWM inverter. Furthermore, the authors propose another type of ACC, the purpose of which is not to achieve complete cancellation but to restrain only a slope in a change of the common‐mode voltage applied to the motor. As a result, the core size of the common‐mode transformer used in the active compensating circuit becomes considerably smaller. Some experimental results show good effects of the proposed active circuits on both ground current and conducted EMI. © 2001 Scripta Technica, Electr Eng Jpn, 137(1): 57–65, 2001

Current control of unbalanced electrical systems

The vector modeling approach is employed to describe the behavior of unbalanced three-phase (three-wire), unbalanced two-phase and single-phase systems. In the case of single-phase systems, a fictitious circuit is introduced in order to create the vector model. Continuous-time and discrete-time current controllers based on the vector approach are presented. The current control scheme is based on two controllers, one for the positive sequence and another for the negative sequence. The controllers are implemented in the synchronous reference frame and in the stationary reference frame. In the stationary reference frame, the use of the same integral gains for both controllers simplifies the equations of the control law especially for single-phase systems. Simulation and experimental results obtained with a pulsewidth modulation voltage-source inverter supplying unbalanced systems are presented.

Capacitively coupled discharging currents in bearings of induction motor fed from PWM (pulsewidth modulation) inverters

This paper examines ac motor bearing currents (Electric Discharge Machining – EDM) resulting from a shaft voltage when operated under pulse-width modulation voltage source inverters. The mechanism for electrostatic shaft voltage buildup and bearing current occurrence is briefly explained. The basic cause of bearing currents is an instantaneous electrical asymmetry on the output of the inverter and distributed stray capacitance couplings in the drive system, especially inside of the motor. It is pointed out that bearing current event is an electrostatic discharge phenomenon. Using the experimental data and a simulation model, it is shown that EDM currents do not flow to a grounding arrangement as has been suggested in previous works, but circulate inside of the motor.

Dual AC-drive system with a reduced switch count

A dual current-regulated pulsewidth-modulated voltage-source inverter based on multiple two-phase PWM inverters, also called a B4 topology, requiring a dual AC-drive system with reduced switch count is proposed. The drive utilizes a total of only eight switches to produce two sets of three-phase or two-phase sinusoidal output currents that can be employed to feed three-phase or two-phase induction motors. A suitable control strategy of this new scheme is shown to minimize the single-phase current now through the DC-link capacitors, which is a common problem in reduced-switch-count topologies. In order to verify the performance of the motor drive system, an application on traction of an electric vehicle is carried out. Results show that the AC current through the DC link can be minimized, and when utilizing two-phase motors on the proposed dual drive, the reduced voltage gain problem, also common in B4 topologies feeding three-phase motors, can be solved.

A comprehensive study of neutral-point voltage balancing problem in three-level neutral-point-clamped voltage source PWM inverters

This paper explores the fundamental limitations of the neutral-point voltage balancing problem for different loading conditions of three-level voltage source inverters. A new model in the DQ coordinate frame utilizing current switching functions is developed as a means to investigate theoretical limitations and to offer a more intuitive insight into the problem. The low-frequency ripple of the neutral point caused by certain loading conditions is reported and quantified.

A position-sensorless IPM motor drive system using a position estimation based on magnetic saliency

This paper describes position-sensorless control of an interior permanent magnet synchronous motor (IPM motor), which is characterized by real-time position estimation based on magnetic saliency. The real-time estimation algorithm proposed in this paper determines the inductance matrix including rotor position information from current harmonics produced by switching operations of an inverter driving the IPM motor, and then estimates the rotor position every period of pulse-width modulation (PWM). Position estimation without any special signal injection is achieved with a satisfactory response and accuracy even at a standstill and at low speed. An experimental system consisting of an IPM motor and a voltage-source PWM inverter has been implemented and tested to confirm the effectiveness and versatility of the approach. Some experimental results show that the experimental system has the function of electrically locking the loaded motor, along with a position response of 20 rad/s and a settling time of 300 ms. © 2000 Scripta Technica, Electr Eng Jpn, 131(2): 68–79, 2000

Comparison of thyristor-controlled reactors and voltage-source inverters for compensation of flicker caused by arc furnaces

The objective of this paper is to compare the performance of thyristor-controlled reactors (TCR) and shunt-connected PWM voltage source inverters (PWM-VSI) for compensation of flicker caused by arc furnaces. First of all, arc-furnace principles are presented in order to explain the main characteristics of the problem. Secondly, traditional TCR control are analyzed. An improved measuring procedure is suggested to enhance TCR performance showing that it achieves faster compensation than more traditional methods. Thirdly, PWM-VSI control for flicker compensation is described in detail using Park's transformation. The analysis shows how real and reactive power control can be decoupled. Continuous-time and discrete-time models are considered. Finally, a TCR control and a PWM-VSI control are compared by simulation using data and measurements from a real arc-furnace installation. The analysis considers three different periods of the production cycle: (a) bore-down, (b) fusion, and (c) refining. It is clear from the results obtained that a shunt-connected PWM-VSI is better than a TCR for flicker compensation. This can be easily justified noting that the bandwidth of the PWM-VSI control system is far better than that of the TCR control. However, the control system for a PWM-VSI inverter is more complicated than that of a TCR. Besides, the latter uses a better-established technology than the former.

Configurations and Characteristics of Active Canceling and Compensating Circuits for Reducing Common-Mode Voltage Generated by Voltage-Source PWM Inverters

This paper deals with active circuits for cancellation and compensation of common-mode voltage caused by a PWM inverter. A non-negligible amount of leakage or ground current would flow through stary capacitors between stator windings and a motor frame due to a large step change in the common-mode voltage at every switching operation of the PWM inverter. First, it is shown experimentally that the active common-noise canceler (ACC), which has been proposed by the authors, is effective in reducing not only conducted EMI but also motor shaft voltage and bearing current. Next, a new ACC characterized by an isolated power supply is developed to enlarge an applicable voltage range in which it is possible to integrate the ACC with a PWM inverter. Furthermore, the authors proposes another type of ACC, the purpose of which is, not to achieve complete cancellation, but to restrain only a slope in a change of the common-mode voltage applied to the the motor. As a result, the core size of the common mode transformer used in the active compensating circuit becomes smaller considerably. Some experimental results show good effects of the proposed active circuits on both ground current and conducted EMI.

PWM-VSI inverter-assisted stand-alone dual stator winding induction generator

This paper presents a novel usage of a dual stator winding three-phase induction machine as a stand-alone generator with both controlled output load voltage magnitude and frequency. This generator, with both three-phase power and control windings housed in the stator structure, has the load connected to the power winding and a three-phase pulsewidth modulation (PWM) voltage-source inverter sourcing the control winding. The input to the PWM inverter is either a battery source or a charged DC capacitor. The operational characteristics of these generator schemes with either of the two inverter sources are investigated and shown to have desirable performance. How the load voltage magnitude depends on the various control and design parameters such as rotor speed, compensating capacitance, and load impedance is determined using a detailed mathematical model of the system.