A Hysteresis Current-Regulated Control for Multi-Level Drives

Most multi-level converters are controlled through the use of voltage-source based control techniques such as space-vector modulation or multi-level sine-triangle modulation. However, in many applications such as field oriented drives, a high bandwidth current-source inverter based control is more desirable. In this paper, the concept of a multi-level hysteresis current-source control is set forth. The new control is experimentally verified using a four-level converter/induction motor drive system and the results are compared to a space vector modulation controller. A dynamic study involving a step change in current command demonstrates the controls high bandwidth

A New Walking Pattern SVM Technique for Five-Phase Motor Drives

As multi-phase motor drives become more popular and practical, new research in this area investigates potential advantages including lower torque ripple and better power density. The added dimensions of a multi-phase machine leads to a completely different operating nature than standard three-phase machines and merits research into new modulation methods. The five-phase and six-phase machines have been traditionally studied in the literature applying voltage-source modulation methods such as sine-triangle modulation and space- vector modulation for current harmonic elimination. Recent research of five-phase induction motor drives addressed nearest three vectors switching; which adds current harmonics but lowers torque ripple and considerably extends the drives voltage range. This paper introduces a new walking pattern SVM method which frees up the vector and sequence selection. The new method is demonstrated using detailed simulation and is shown to further reduce torque ripple

Extended Operation of Flying Capacitor Multilevel Inverters

Recent research in flying capacitor multilevel inverters (FCMIs) has shown that the number of voltage levels can be extended by changing the ratio of the capacitor voltages. For the three-cell FCMI, four levels of operation are expected if the traditional ratio of the capacitor voltages is 1:2:3. However, by altering the ratio, the inverter can operate as a five-, six-, seven-, or eight-level inverter. According to previous research, the eight-level case is referred to as maximally distended (or full binary combination schema) since it utilizes all possible transistor switching states. However, this case does not have enough per-phase redundancy to ensure capacitor voltage balancing under all modes of operation. In this paper, redundancy involving all phases is used along with per-phase redundancy to improve capacitor voltage balancing. It is shown that the four- and five-level cases are suitable for motor drive operation and can maintain capacitor voltage balance under a wide range of power factors and modulation indices. The six-, seven-, and eight-level cases are suitable for reactive power transfer in applications such as static var compensation. Simulation and laboratory measurements verify the proposed joint-phase redundancy control

Advanced Control and Analysis of Cascaded Multilevel Converters Based on P-Q Compensation

This paper introduces new controls for the cascaded multilevel power converter. This converter is also sometimes referred to as a ldquohybrid converterrdquo since it splits high-voltage/low-frequency and low-voltage/pulsewidth-modulation (PWM)-frequency power production between ldquobulkrdquo and ldquoconditioningrdquo converters respectively. Cascaded multilevel converters achieve higher power quality with a given switch count when compared to traditional multilevel converters. This is a particularly favorable option for high power and high performance applications such as naval ship propulsion. This paper first presents a new control method for the topology using three-level bulk and conditioning inverters connected in series through a three-phase load. This control avoids PWM frequency switching in the bulk inverter. The conditioning inverter uses a capacitor source and its control is based on compensating the real and reactive (P-Q) power difference between the bulk inverter and the load. The new control explicitly commands power into the conditioning inverter so that its capacitor voltage remains constant. A unique space vector analysis of hybrid converter modulation is introduced to quantitatively determine operating limitations. The conclusion is then generalized for all types of controls of the hybrid multilevel converters (involving three-level converter cells). The proposed control methods and analytical conclusions are verified by simulation and laboratory measurements

Multilevel Multi-Phase Propulsion Drives

This paper presents a comprehensive analysis of the 5-phase induction motor driven by voltage-source inverter drives and particularly its steady-state performance evaluation. The performance of various modulation methods are analyzed with insightful look into their harmonic content and torque ripple. Three separate methods are proposed to reduce the torque ripple for low, middle and high modulation index regions while eliminating or controlling the non-torque-producing harmonics within the current machine rating. A complete set of simulations are carried out to verify the concepts and proposed methods. The multi-level multiphase topology is introduced and it is compared to the two-level system. The modification of switching sequence for reduction of torque ripple is applied to the three-level 5-phase motor drive. Application of the multilevel multi-phase concept to high power motor drives (as well as motor design and selection) is discussed

Power Engineering Laboratory Facilities at the University of Missouri--Rolla

One of the significant niche areas at UMR is the area of electric power. For this reason UMR has invested in its power program over the years. The extent of this program ranges from power systems, motor drives, high-frequency effects in electric machines, acoustic noise of electric machines, FACTS device for electric utility applications, and naval propulsion power systems. The various laboratory facilities at UMR which supports these activities have been described in detail in this paper

A Four-Level Crossing dc/dc Converter Based Drive System

This paper introduces a novel crossing front-end dc/dc converter for a four-level drive system which provides a voltage boost as well as dc capacitor bank voltage regulation. The primary advantage of the proposed converter is that it simplifies the control of the four-level diode-clamped inverter since capacitor voltage balancing is not required by the inverter control. Furthermore, the inverter modulation index can be varied up to its physical limitation. An average-value model of the converter is derived and used for insight and analysis of the converter operation. Detailed simulations of the four-level drive system demonstrate the effectiveness of the proposed system

Direct Torque Control of Five-Phase Induction Motor Using Space Vector Modulation with Harmonics Elimination and Optimal Switching Sequence

In this paper an effective direct torque control (DTC) for a 5-phase induction motor with sinusoidally distributed windings is developed. First by coordinate transformation, the converter/motor models are represented by two independent equivalent d-q circuit models; and the 5-phase VSI input are decoupled into the torque producing and non-torque producing harmonics sets. Then with the torque production component of the induction motor model, the space vector modulation (SVM) can be applied to the five-phase induction motor DTC control, resulting in considerable torque ripple reduction over the lookup table method. Based on the decoupled system model, the current distortion issue due to lack of back EMF for certain harmonics is analyzed. Two equally effective SVM schemes with the harmonic cancellation effect are introduced to solve this problem. To analyze the DTC control torque ripple, an insightful perspective (also applicable to 3-phase analysis) is introduced to predict the torque ripple pattern evolution with changing motor speed and stator flux angular position. Therefore the switching sequence for lowest torque ripple can be determined and re-arranged online. Finally, with the overall optimal switching scheme adopted, detailed simulations verify the effectiveness of the new control

AC Impedance Measurement by Line-to-Line Injected Current

Naval ship as well as aerospace power systems are incorporating a greater degree of power electronic switching sources and loads. Although these components provide exceptional performance, they are prone to instability due to their high efficiency and constant power characteristics which lead to a negative impedance nature. When designing these systems, system integrators must consider the impedance versus frequency at an interface (which designates source and load). Stability criteria have been developed in terms of source and load impedance for both DC and AC systems and it is often helpful to have techniques for impedance measurement. For DC systems, the measurement techniques have been well established. This paper introduces a new method of impedance measurement for three-phase AC systems. By injecting a line-to-line (unbalanced without zero sequence) current between two lines of the AC system, all impedance information may be determined. Since the current injection is line-to-line, the measurement device may be used for AC or DC interfaces. Simulation and laboratory measurements demonstrate the effectiveness of this new technique