H. de Paula

Methodology for Cable Modeling and Simulation for High-Frequency Phenomena Studies in PWM Motor Drives

The analysis of the transient overvoltages in a pulsewidth modulation (PWM) motor drive system comprises a wide frequency range, which starts with the low values corresponding to the motor speed, includes the switching harmonics, which can reach up to few hundreds of kHz, and also the cable resonance frequency, which value can be in the MHz range, depending on the cable length. In this context, this work presents a time domain methodology for cable modeling able to represent the cable parameters variation due to skin effect in this broad range of frequencies. The proposed technique reproduces accurately the wave propagation and reflection phenomena, thus showing to be very appropriate to transient overvoltage studies in PWM motor drives. A new alternative to represent the frequency-dependent cable earth-return path is also included, allowing the computation of the zero-sequence currents generated by the common-mode voltage produced by the inverter. Simulations using the proposed methodology are conducted and the obtained results are compared with measurements, showing good agreement.

Avoiding undesirable high-frequency phenomena in long cable drives: Rectifier-to-inverter connection through long DC cable — part I: Evaluation of the losses reduction and copper economy

Problems involving long cable PWM motor drive systems are well documented in the literature. Solutions based on passive filters are conventionally used to suppress the undesired high-frequency phenomena that take place in such systems, but, in turn, bring up new considerations concerning filter size, weight, cost and electrical losses. In this context, an alternative concept of a motor drive system that overcome all these problems is outlined in this paper, where the long cable is used to connect the rectifier to the inverter, thus establishing a DC power transmission link. This paper briefly discusses the benefits and important issues concerning the proposed system and presents a comprehensive analysis regarding one of its advantages, which is the copper (and cost) economy in relation to the traditional systems.

Rectifier-to-Inverter Connection Through Long DC Cable—Part II: The Complete Copper Economy Characterization

High-frequency problems involving long cable PWM motor drive systems are well documented in the literature. Solutions based on passive filters are conventionally used to suppress these undesired phenomena that take place in such systems, but, in turn, bring up new considerations concerning filter size, weight, cost, and electrical losses. In this context, a concept of an alternative motor drive system that overcomes all these problems was outlined by the authors in a previous paper, where the long cable was used to connect the rectifier to the inverter, thus establishing a dc power transmission link. In addition, other important issues concerning the proposed system have also been adressed, along with a comprehensive analysis of the power losses in the (long) dc or ac cable and a preliminary estimation of the copper amount reduction in favor of dc transmission. In the present paper, the results from a more recent and general study for the complete copper economy characterization are presented, demonstrating that the proposed drive system configuration, aside from eliminating the whole high-frequency problem, is always advantageous also from the copper economy point of view.

Effects of magnetic saturation on induction machines driven by static converters

The effects of magnetic saturation on the operation of induction motors driven by static converters are analyzed. A mathematical model based on magnetic harmonic functions is used to account for saturation. Distortions on the air gap flux due to non-linear magnetic characteristics lead to appearance of space harmonics in the resultant flux density distribution. This causes specific distortions in stator and rotor time quantities, which are different from those due to static converter. Operation with six pulse and sinusoidal PWM converters under saturated conditions is considered. Comparisons of experimental and simulated results are presented and found to be in very good agreement.

Rectifier-to-inverter connection through long DC cable - part II: The complete copper economy characterization

High-frequency problems involving long cable PWM motor drive systems are well documented in the literature. Solutions based on passive filters are conventionally used to suppress these undesired phenomena that take place in such systems, but, in turn, bring up new considerations concerning filter size, weight, cost, and electrical losses. In this context, a concept of an alternative motor drive system that overcomes all these problems was outlined by the authors in a previous paper, where the long cable was used to connect the rectifier to the inverter, thus establishing a dc power transmission link. In addition, other important issues concerning the proposed system have also been adressed, along with a comprehensive analysis of the power losses in the (long) dc or ac cable and a preliminary estimation of the copper amount reduction in favor of dc transmission. In the present paper, the results from a more recent and general study for the complete copper economy characterization are presented, demonstrating that the proposed drive system configuration, aside from eliminating the whole high-frequency problem, is always advantageous also from the copper economy point of view.

Desgaste prematuro e falhas recorrentes dos rolamentos de um MIT: Estudo de caso

This paper provides an analysis about early incipient faults in three-phase induction motor bearings when driven by inverters, focusing on a real industrial case. The preliminarily defined potential faults were firstly discussed on a theoretical basis afterwards being experimentally assessed by means of vibration, stator current and common mode current data acquisition and analysis. Following the investigation, it was concluded that the presence of common mode currents at the verified levels can cause damages to motor bearings. This result could be confirmed when the machine stopped working due to another failure of the bearings.

Uma proposta para a modelagem de inversores para o estudo de correntes de modo comum em sistemas de acionamento de motores

As far as PWM inverters are concerned, it is well known that the common-mode voltage generated during its normal operation produces high-frequency earth return currents which cause several problems in industrial electric systems. The computational study of such currents requires the appropriate modeling of the inverter, transformer, motor and cable for high-frequency phenomena studies. Regarding the inverter, it is usually modeled for this purpose by the inclusion of a capacitor to ground in order to represent the potential path of the common-mode currents. Since this representation is way too simple, this work presents a more detailed modeling of the inverter bridge, in which the capacitances of the switches collectors, DC link and clamping diodes (in the case of a three-level unit) are included. Once the representation of the whole bridge is not necessary, the proposed methodology reduces the amount of non-linear devices in the simulation, being thus attractive from the computational effort point of view.

A new configuration for motor drive systems based on long cable connection between rectifier and inverter — Part I: Analysis of the losses reduction and copper economy

Problems involving long cable PWM motor drive systems are well documented in the literature. Solutions based on passive filters are conventionally used to suppress the undesired high-frequency phenomena that take place in such systems, but, in turn, bring up new considerations concerning filter size, weight, cost and electrical losses. In this context, an alternative concept of a motor drive system that overcome all these problems is outlined in this paper, where the long cable is used to connect the rectifier to the inverter, thus establishing a DC power transmission link. This paper briefly discusses the benefits and important issues concerning the proposed system and presents a comprehensive analysis regarding one of its advantages, which is the copper (and cost) economy in relation to the traditional systems.

A new strategy for differential overvoltages and common-mode currents determination in PWM induction motor drives

The analysis of the transient overvoltages in a PWM motor drive system comprises a wide frequency range, which starts with the low values corresponding to the motor speed, includes the switching harmonics, which can reach up to few hundreds of kHz, and also the cable resonant frequency, which value can be in the MHz range, depending on the cable length. In this context, this work presents a time domain methodology for cable modeling able to represent the cable parameters variation due to skin effect in this broad range of frequencies. Three different methods for cable parameter estimation are also studied and compared in order to be used as an effective tool in the analysis, since frequency-dependent parameter cable models typically require cable parameters in different frequencies as input data for their determination. Since measurements are often unavailable, parameter estimation is strongly desirable. The frequency-dependent cable earth-return model is also included, allowing the computation of the zero-sequence currents generated by the common-mode voltage produced by the inverter. Simulations using the proposed methodology are conducted and the obtained results are compared with measurements, showing good agreement

Cabling analysis focusing the high frequency phenomena in inverter-based industrial drives

Several undesired high-frequency phenomena take place in industrial drive systems supplied by PWM frequency converters. Along with the well known transient overvoltages at the motor terminals due to the inverter pulses propagation and reflection, transient currents flow between the phase conductors and from them to the ground, resulting in further problems. In this paper, the influence of the cabling characteristics on the intensity of these phenomena is adressed by means of a theoretical-computational investigation. The obtained results provide useful and practical information concerning industrial cable installation issues.