Richard A. Lukaszewski

Universal Induction Motor Model with Low-to-High Frequency Response Characteristics

A three-phase induction motor model that depicts the motor behavior over a wide range of frequencies from 10 Hz to 10 MHz is presented in this paper. The model is universal in the sense that common-mode, differential-mode, and bearing circuit models are combined into one three-phase equivalent circuit model. The proposed model is basically an extension of the low-frequency IEEE Standard 112 circuit model. The proposed model was experimentally simulated and verified with results presented.

Analysis of PWM Frequency Control to Improve the Lifetime of PWM Inverter

Studies show that the power cycling mean time to failure (MTTF) of the insulated-gate bipolar transistor (IGBT) bond wire in an adjustable speed drive may be very short under some very common conditions. This paper proposes a switching frequency reduction method based on the junction temperature variation (ΔTj) of an inverter IGBT. It has the following advantages. First, it reduces the pulsewidth-modulation frequency under low-speed higher torque condition. Second, the inverter is started more smoothly and safely under higher command switching frequency and high-torque condition. Third, the overall MTTF of the inverter IGBT can be improved. The theory analysis, simulation, and experimental result are provided to show these advantages.

Common Mode and Differential Mode Analysis of Three Phase Cables for PWM AC Drives

This paper proposes a new 3-phase transmission line model with the first successful use of 2D finite element analysis (FEA) to extract and predict cable R-L-C parameters over a wide range of frequencies. The significance is that the FEA methodology to extract high frequency parameters were shown to be accurate and eliminates costly cable testing. The 3-phase FEA parameters can also be transformed for use with historical single-line transmission line models. The FEA approach allows unsymmetrical cables to be studied in a 3-phase cable-drive and motor simulation setting. FEA predicted vs. measured R-L-C parameters as function of frequency was within 5-10%. A 3-phase drive-cable-motor power electronic simulator program using predicted FEA parameters to predict CM current and DM motor overshoot (ringing) voltage was found to be within 7-15% of measured waveforms from 10 ft to 1000 ft cable length variation for two different cable type configurations. Analysis provided is also applicable to power system transient studies on AC line connected equipment

Common-Mode Voltage Reduction PWM Algorithm for AC Drives

The impact of common-mode voltage (CMV) generated by pulsewidth modulation (PWM) ac drives on motor bearings is well known. Several algorithms for CMV reduction have been proposed in the literature. While a few algorithms assume ideal switching and fall apart when nonidealities like inverter dead time are considered, some others are effective only in a limited operating range of the drive. In this paper, a previously proposed algorithm is modified for practical implementation to include compensation for dead-time and reflected-wave motor overvoltage stress while still producing output voltage waveforms with reduced common-mode content. Experimental results are provided to show the reduction in CMV over the entire operating range, with other performance attributes such as reflected-wave motor overvoltage that are identical to conventional space-vector PWM. The advantages of applying the algorithm to a fully regenerative ac drive are also demonstrated.

Analysis of IGBT Power Cycling Capabilities Used in Doubly Fed Induction Generator Wind Power System

The doubly fed induction generator (DFIG) is one of the most popular topologies applied in wind power systems. Its main advantage is to adjust the speed of a large system with much lower power converters. This is because its rotor-side converter (RSC) operates under slip frequency and it needs only to support slip power to the overall system. However, this slip frequency is much lower than the grid frequency, and insulated-gate bipolar transistors (IGBTs) in the RSC are susceptible to power cycling failures. This paper provides a method to analyze the power cycle capability of a DFIG power converter under wind power applications. Different current control methods, including minimal stator losses, minimal rotor losses, and minimal overall losses, are analyzed and compared. It is verified that the sizes of the IGBT must be selected appropriately to avoid earlier power cycling failures. Designing a wind power converter into the targeted system is critical for cost reduction without sacrificing the reliability of the whole system.

Evaluation of Power Semiconductors Power Cycling Capabilities for Adjustable Speed Drive

This paper analyzes the power cycling capability of semiconductor under various conditions for adjustable speed drive (ASD). An analysis is made that calculates the mean time to failure (MTTF) of the semiconductor under various conditions, including low speed operation capability, high speed thermal capability and overload capability. After that, the MTTF estimations of the IGBT under different heatsink design and different drive ratings are studied. This paper will show that the MTTF of the inverter may be very short under some very common operating conditions. Thus, it is prudent to size the drive properly in order to avoid earlier failure.

Integrated Differential-Mode and Common-Mode Filter to Mitigate the Effects of Long Motor Leads on AC Drives

PWM AC drives generate high differential mode motor voltages due to the reflected wave phenomenon. The common-mode voltage produced by a PWM inverter also has fast transitions that result in high peak currents to ground. For low power AC drives this can present several issues, such as pump-up of the DC bus and failure of the power module due to high instantaneous currents that are often undetected because of the typical sampling algorithm used. In this paper, existing drive output filter solutions are reviewed and a new filter design is presented, which has integrated differential-mode and common-mode impedance with damping matched to typical cable surge impedance. This eliminates reflections of both differential-mode and common-mode traveling waves, and also reduces peak cable charging currents. Experimental results are provided to demonstrate that the new filter has improved performance to reduce motor differential-mode and common-mode voltage, and drive output common-mode current, thus mitigating the issues specifically seen with low power AC drives. Complete design details for the filter and a particular implementation of the integrated differential-mode and common-mode reactor are also presented.

Analysis of Power Cycling Capability of IGBT Modules in a Conventional Matrix Converter

This paper analyzes the power cycling capability of IGBT modules in a conventional matrix converter used as a motor drive. The analysis is made under various condition for this topology, including low speed operation capability, high speed thermal and power cycle capability and etc. It was found that the power cycling mean time to failure (MTTF) of IGBT in a matrix converter is low when the input and output frequency is close to each other or when the output frequency of the converter is low. As a result, the chip size of the conventional matrix converter may be larger than the other candidates. In the end of the paper, some guidance of designing a matrix converter for long term reliabilities is also discussed.

Analysis of PWM frequency control to improve the lifetime of PWM inverter

Studies have shown that the power cycling Mean Time to Failure (MTTF) of the IGBT bond wire in an adjustable speed drive (ASD) may be very short under some very common conditions. This paper proposes a switching frequency reduction method based on junction temperature variation (ΔTj) of the inverter IGBT. It has the following advantages. Firstly, it only reduces the PWM frequency under low speed higher torque condition; secondly, the inverter can be started more smoothly and safely under higher command switching frequency and high torque condition. Thirdly, the overall MTTF of the inverter IGBT can be improved dramatically. Theory analysis, simulation and experimental result will be provided to show these advantages.

Junction Temperature Prediction of a Multiple-chip IGBT Module under DC Condition

This paper develops a thermal model for a six-pack insulated gate bipolar transistor (IGBT) power module operating as a three phase voltage source inverter. With this model, the temperature of each chip can be derived directly from the losses of the silicon chips and a thermal impedance matrix. The losses of each chip can be calculated through the voltage and current information of the power module. The impedance model can be easily transferred into a micro-processor to predict the online chip temperatures. It largely increases the temperature accuracy when the inverter operates at zero or low output frequency. Theory analysis, simulation and experimental results are provided to verify the effectiveness of this model