H. Grotstollen

Optimal PWM based on real-time solution of harmonic elimination equations

Pulse-width modulation of DC/AC power converters (PWM) based on the elimination of low-order harmonics necessitates solving systems of nonlinear equations. Conventional implementations of this technique based on storing off-line calculated solutions have the common problem that the system flexibility is very limited, especially for applications that require both amplitude and frequency control. A new implementation scheme based on real-time solution of nonlinear harmonic elimination equations using a digital signal processor DSP56001 is reported in this paper. With this digital signal processor (DSP), optimal pulse patterns having 15 switching angles in each quarter fundamental period can be determined within 2.15 ms. Details of the system hardware and software are described. New theoretical results concerning the solvability of harmonic elimination equations are also presented.

Symbolic analysis methods for averaged modeling of switching power converters

Symbolic analysis methods for the averaged modeling of switching power converters are presented in this paper. A general averaging method suitable for computer-aided modeling is discussed first. Then, a symbolic analysis package that uses this averaging method to automatically generate an analytical averaged model for a switching power converter is described. The package is implemented using the computer algebra system Mathematica and can be used for modeling DC/DC power converters employing different switching techniques, including hard-switching pulse-width modulation (PWM), quasi-resonant soft switching, and soft transition. Several examples are provided to demonstrate the applications of the package. Further applications of symbolic analysis methods in power electronics are also discussed.

Averaged modelling of switching power converters: reformulation and theoretical basis

Uniform averaged modeling methods for switching power converters (SPCs) are established. Averaging methods for differential equation systems with continuous right-hand sides are discussed and then generalized to discontinuous ones. It is shown that these methods are applicable to most known types of SPC, including PWM, resonant, and quasi-resonant converters. PWM converters under discontinuous conducting mode are taken as examples to further demonstrate the applicability of these methods. It is shown that the currently used state space averaging and its several extensions can be derived from these methods.<<ETX>>

Torque capability and control of a saturated induction motor over a wide range of flux weakening

The first part of this paper covers an investigation of the maximum torque which an induction motor with saturated air gap inductance can generate over its permitted speed range, when voltage as well as current are limited. From the investigation, three regions of operating speed are identified, based on limiting quantities which determine the maximum obtainable torque. In each of these regions a different control strategy must be applied. When maximum torque is not required, efficiency can be optimized but this strategy should not be applied at low torque levels when good dynamic performance is required. The second part illustrates how a modified rotor flux oriented control strategy is applied to achieve full utilization of the torque capability over the whole speed range. Several measures for improving dynamic and transient behavior of the drive in the flux weakening region are suggested. Performance of the new control strategy is verified by experiments. >

Simulation model for ultrasonic motors powered by resonant converters

A rotary traveling wave type ultrasonic motor powered by a resonant converter is modeled to optimize the overall drive performance by simulation and to develop suitable control strategies for the drive. Based on mechanical approaches in modeling the stator under consideration of unsymmetries and reflecting the nonlinear stator/rotor-contact by an elastic contact model, an extended contact model of the stator/rotor interaction with closed form solutions for nonideal traveling waves is derived referring to a two-mode approximation of the stator and piezoceramic. By incorporation of a converter model into the mechanical subsystem, a proper simulation model for ultrasonic drives is presented, whereby some interesting phenomena are verified by simulations and explained by strong graphical means.

Harmonic reduction techniques for single-switch three-phase boost rectifiers

Techniques for reducing harmonic distortion in single-switch three-phase boost rectifiers are presented. Optimal pulse-width modulation methods for the main switch to minimize input harmonic current distortion or to maximize the converter power range are described first. Effects of the voltage control loop on the input current waveform are then investigated by using the harmonic balance method. It is found that through proper design of the voltage controller, the input current harmonics in the closed-loop controlled system can be reduced to almost the same level as when the optimized PWM is applied. Simulation and experimental results are included to validate the analysis.

Enhanced control scheme for three-phase three-level rectifiers at partial load

A prominent boost-type three-level topology (VIENNA Rectifier I), which proved to represent a cost-effective and highly efficient solution for switched-mode rectifiers is inspected toward its operation at discontinuous conduction mode (DCM). This mode of operation occurs not only at high input voltage in conjunction with low load currents but even at medium loading in the vicinity of mains voltage zero crossings. When this circuit is operated in DCM, additional measures are required for improved behavior to avoid conflicts with requirements on total harmonic distortion and regulations as well as safe operation in terms of voltage balancing and overvoltage protection. A detailed analysis of DCM and associated states is performed enabling determination and location of error voltages. Basic rules for the location of error voltages can be found. This leads to a novel optimized modulation and control scheme, facilitating designs without additional inductance. Selected simulation and measurement results prove the enhanced modulation scheme.

Off-line identification of the electrical parameters of an industrial servo drive system

This paper presents a step-by-step method for identifying the electrical parameters of an industrial servomotor drive system at standstill. The servomotor drive system consists of a voltage source inverter and an induction motor. The inverter nonlinearity caused by the turn-on/off time dependency of the current level in the switching transistors is described. The fact that no phase voltage detection for the identification scheme is available leads to a nonlinear mathematical model of the induction servomotor drive system at standstill. This model also includes the saturation effect. With this process model, a three step method is deduced to obtain the stator and rotor resistance, the leakage inductance and the mutual inductance as a function of the magnetizing current. Practical results which are obtained with an industrial induction servomotor drive system are also presented.

Comparison of parameter identification schemes for self-commissioning drive control of nonlinear two-mass systems

A self-commissioning system for the high performance speed and position control of electrical drives requires the structure and parameter identification of nonlinear mechanics. This substantial task within the self-commissioning scheme is carried out by a step by step procedure which includes a new identification method based on the extraction of characteristic features of the system response. Furthermore, optimized least mean squares and instrumental variables approaches are outlined and compared to approaches using self-organizing maps and classical frequency domain analysis. The common applicability of all methods is checked, investigating machine mechanics with 1200 different parameter combinations.

Investigation of low cost control schemes for a selected 3-level switched mode rectifier

Two low-cost modulation schemes are presented for the control of a 3-level switched mode rectifier. One is based on a hysteresis controller and the other on a double ramp comparison. The latter control concept implemented by common PWM ICs yields preferable characteristics for the power interface to telecommunication equipment such as high power density, due to reduced volume for electromagnetic compatibility (EMC) and input current filtering, high control dynamics, low harmonic distortion (THD) and switching losses, which are comparable to those achieved by space vector control, but with less costs and complexity.