Nisai H. Fuengwarodsakul

High-dynamic four-quadrant switched reluctance drive based on DITC

This paper presents the development of a four-quadrant switched reluctance machine (SRM) drive for high dynamic applications. Comprehensive fundamentals and analysis for operating switched reluctance machines in four quadrants are presented. The drive is designed based on a high dynamic control strategy called Direct Instantaneous Torque Control (DITC). The functionality of DITC is discussed in detail for both motoring and generating operation. A methodology to generate switching functions directly by the hysteresis torque controllers for SRMs is proposed. The proposed controller was prototyped and tested on a digital signal processor/field-programmable gate array development platform. High dynamic operation in both motoring and generating mode and the transition between these modes are validated by experimental results presented at the end of this paper.

Flux Linkage Determination for Correct Modeling of Switched Reluctance Machines - Dynamic Measurement versus Static Computation

This paper presents a study on the determination of flux-linkage characteristics of switched reluctance machines. These characteristics are used to describe the behavior of individual machines for modeling as well as control purposes. Typically, the flux-linkage characteristics are either obtained by static FEM-calculations or by measurements. With the example of a 55 kW switched reluctance machine (SRM) it is shown that these two characterization methods do not inherently yield the same results but that they can differ more than 10%. FEM simulations are performed to analyze the dynamic processes occurring during flux-linkage measurements. It was found that current displacements due to winding eddy currents are responsible for a transient reduction of phase inductance and flux-linkage. Finally, it is investigated whether the results of static or dynamic flux- linkage determination are more accurate for look-up table based torque control.

Predictive PWM-based Direct Instantaneous Torque Control of Switched Reluctance Drives

A method of direct instantaneous torque control for switched reluctance motor drives using pulse width modulation based on flux linkage prediction is presented in this paper. The torque characteristic of the machine allows a prediction of reference flux linkage for the next sampling time-step. By estimating this flux linkage, the necessary average phase voltage for the next PWM-period can be calculated to control a constant instantaneous torque output. Moreover, the sampling time of the control can be extended, which allows implementation on low cost microcontrollers. Furthermore, a novel strategy of torque prediction is proposed, which allows complete elimination of inherent torque ripple during phase commutation, without using offline-calculated current or flux profiles. The functionality of this strategy is verified by computer simulation and experiments.

Control Scheme for Switched Reluctance Drives with Minimized DC-Link Capacitance

This paper presents a control scheme which allows minimization of dc-link capacitance in switched reluctance drives. In SRMs the demagnetization energy of the outgoing phase causes a voltage increase in the dc-link. Therefore, large dc-link capacitors are required in conventional drives to absorb this energy to avoid overvoltages. The proposed control scheme balances the power flow between phases in such a way that the demagnetization energy of the outgoing phase does not flow back into the dc-link but directly into the incoming phase. Using this scheme, electrolytic capacitors can be replaced by film or ceramic capacitors leading to longer life-time and higher reliability.

Sensorless direct instantaneous torque control for switched reluctance machines

This paper presents a position-sensorless torque controller for switched reluctance machines (SRMs) based on direct instantaneous torque control (DITC). An indirect position estimation to eliminate the need of the position encoder is developed based on current-flux-linkage method. The current-flux-linkage method has advantages of simplicity and requires less computation time. Therefore, the controller can be implemented with a high control bandwidth. The accuracy of position estimation and effects of estimation errors are studied. The functionality of the developed controller and its performance are investigated and verified by experiments over a wide operating range

Characteristic measurement system for automotive class switched reluctance machines

Flux-linkage characteristics and torque characteristics, which are regarded as fingerprints of switched reluctance machines (SRM), are indispensable fundamental data required in modeling the machine behavior for both simulation and control purposes. In contrast to other types of electrical machines, e.g. induction machines and synchronous machines, SRMs are basically characterized by a strongly nonlinear behavior due to typical operation in the magnetic saturation region. Hence, no analytical function can be applied to describe characteristics of SRMs precisely. An accurate SRM model inevitably needs the complete machine characteristics in form of data-intensive look-up tables to represent the machine behavior. Generally, the SRM characteristics can be calculated by finite element (FE) simulation. However, real SRMs can be different from the simulation model due to end-winding effects, which are normally not considered in the FE-simulation model. Hence, the experimental measurement is preferred. Measuring and preparing the SRM characteristics is a complicated and time-consuming task, if done manually. The time-expense as well as possible human errors in determining the SRM characteristics can be minimized, if the measurement procedures are automated. This paper presents an automated characteristic measurement system for SRM. The measurement system was designed for automotive class SRMs, e.g. starter-generator, hybrid or main propulsion motor. The applied measurement methods, the system design and construction are described in the paper. Furthermore, constraints and discussions concerning the measurement accuracy are presented

Single-Phase Switched Reluctance Drive With Saturation-Based Starting Method

This paper presents the design and an encoder-based starting strategy for a low-cost single-phase switched reluctance machine (SRM). The single-phase SRM cannot produce a continuous torque over one revolution. Therefore, applications that do not require a continuous torque, e.g., pumps and fans, are especially suitable. Another issue of single-phase machines is start up. The starting direction is affected by the initial rotor position. Due to the functional concept of SRM the machine produces no torque at aligned and unaligned position of the rotor and consequently, cannot be started from these positions. To start up from every rotor position a saturation-based starting method is used. The design of the rotor with the saturable area is shown and the principles of an encoder-based starting strategy for a fast start-up under 0.5 s are introduced. Finally, the build prototype and experimental results of the starting strategy are shown.

Simulation model of a switched reluctance drive in 42 V application

In modeling switched reluctance drives for low-voltage applications, an accurate converter model is mandatory. The voltage drop across the semiconductor devices is significant in comparison to the available dc-bus voltage and must be taken into account. Furthermore, in 42 V applications, in which batteries are utilized as the energy source, the dc-bus voltage extremely fluctuates due to the load-dependent behavior of batteries. Therefore, the battery behavior should be also regarded in the drive system model. This paper presents the modeling of a switched reluctance drive for 42 V application regarding behavior of the converter as well as the energy source. The entire switched reluctance drive system is modeled in a single simulation platform MATLAB/Simulink. The model accuracy is verified by the experimental results presented at the end of the paper.

Control strategy of solar/wind energy power plant with supercapacitor energy storage for smart DC microgrid

This paper presents an original control algorithm for a hybrid energy system with a renewable energy source: a photovoltaic (PV) array and a wind turbine (WD). A single storage device, a supercapacitor (SC) module, is in the proposed structure. The very fast power response and high specific power of a SC complements the insufficient power output of the main sources to produce the compatibility and performance characteristics needed in a load. To verify the proposed principle, a hardware system is realized with analog circuits and with numerical calculation (dSPACE) for the energy control loops. Experimental results with small-scale devices, namely, a wind turbine generator (500 W), a photovoltaic array (800 W, 31 A) manufactured by the Ekarat Solar Company and a SC module (100 F, 32 V), illustrate the excellent energy-management scheme during load cycles.

Rapid prototyping tool for switched reluctance drive controls in traction applications

This paper presents the design concepts and applications of a rapid prototyping platform for development and test of switched reluctance drive controls. For traction applications, a powerful and flexible hardware is required for the development of sophisticated switched reluctance drive controls capable of high dynamic performance. This platform is constructed based on a versatile DSP/FPGA digital processing unit. External control functions and interfaces are additionally integrated to fulfill the requirements of traction drives. The feasibility of the platform is demonstrated by two examples presented in this paper.