Seppo E. Saarakkala

Speed Control of Electrical Drives Using Classical Control Methods

A classical-control approach to the design and analysis of proportional-integral (PI) speed controllers for electrical drives is presented. After vindicating the fact that traditional one-degree-of-freedom PI control generally gives unsatisfactory performance, a well-performing two-degrees-of-freedom PI controller is designed, with analytic parameter selection. The robustness of the obtained closed-loop system is analyzed, and is found to be satisfactory.

Discrete-Time Observer Design for Sensorless Synchronous Motor Drives

This paper deals with the speed and position estimation of interior permanent-magnet synchronous motor (IPMSM) and synchronous reluctance motor (SyRM) drives. A speed-adaptive full-order observer is designed and analyzed in the discrete-time domain. The observer design is based on the exact discrete-time motor model, which inherently takes the delays in the control system into account. The proposed observer is experimentally evaluated using a 6.7-kW SyRM drive. The analysis and experimental results indicate that drastic performance improvements can be obtained with the direct discrete-time design, especially if the sampling frequency is relatively low compared to the fundamental frequency.

Parameter estimation of two-mass mechanical loads in electric drives

This paper presents a method for parameter estimation of two-mass mechanical loads. A discrete-time polynomial model with an output error (OE) structure is used in parameter estimation. Four different identification setups are obtained when open-loop estimation and various possibilities of choosing the input and output signals in closed-loop estimation are considered. All four setups are analyzed, and the identifiabilities are compared. It is discovered that all four identification setups can be used to obtain reasonable parameter estimates.

Sensorless Self-Commissioning of Synchronous Reluctance Motors at Standstill Without Rotor Locking

This paper proposes a standstill method for identification of the magnetic model of synchronous reluctance motors (SyRMs). The saturation and cross-saturation effects are properly taken into account. The motor is fed by an inverter with a short sequence of bipolar voltage pulses that are first applied on the rotor d- and q-axes separately and then simultaneously on both the axes. The stator flux linkages are computed by integrating the induced voltages. Using the current and flux samples, the parameters of an algebraic magnetic model are estimated by means of linear least squares. The proposed method is robust against the stator resistance variations and inverter nonlinearities due to the high test voltages (of the order of the rated voltage). The fitted model matches very well with the reference saturation characteristics, measured using a constant-speed method, and enables extrapolation outside the sample range. The method was tested with a 2.2-kW SyRM, whose shaft was uncoupled from any mechanical load, which is the most demanding condition for this method. The proposed method can be used for automatic self-commissioning of sensorless SyRM drives at standstill.

Identification of Two-Mass Mechanical Systems Using Torque Excitation: Design and Experimental Evaluation

This paper deals with methods for parameter estimation of two-mass mechanical systems in electric drives. Estimates of mechanical parameters are needed in the start-up of a drive for automatic tuning of model-based speed and position controllers. A discrete-time output error (OE) model is applied to parameter estimation. The resulting pulse-transfer function is transformed into a continuous-time transfer function, and parameters of the two-mass system model are analytically solved from the coefficients of this transfer function. An open-loop identification setup and two closed-speed-loop identification setups (direct and indirect) are designed and experimentally compared. The experiments are carried out at nonzero speed to reduce the effect of nonlinear friction phenomena on the parameter estimates. According to results, all three identification setups are applicable for the parameter estimation of two-mass mechanical systems.

Speed control of two-mass mechanical loads in electric drives

This paper deals with model-based two-degrees-of-freedom (2DOF) speed control of two-mass systems. An analytic gain selection of a proportional integral (PI) type feedback controller is proposed. The gains are given as functions of system parameters and desired dominant closed-loop poles. An analytic design of a prefilter is given to complete the 2DOF structure, using the pole-zero distribution of the feedback loop. The prefilter design covers step, ramp, and parabolic reference tracking. The proposed 2DOF controller is evaluated by means of simulations and experiments. The experimental setup consists of two 4-kW servo motors coupled together with a toothed belt. It was found that the proposed controller gives good reference tracking for step and dynamic commands as well as robust and fast load-torque rejection.

Identification of two-mass mechanical systems in closed-loop speed control

This paper presents a method to identify the parameters of a two-mass mechanical system, when the system is operating in closed-loop speed control. When the speed and the torque controllers are known, the proposed method can be applied for the parameter estimation of a system, which has a higher mechanical resonance frequency than the torque-control loop bandwidth. Moreover, if the loading torque is known a priori, the method may be used for systems that are loaded during the identification.

Physical drawbacks of linear high-speed tooth belt drives

Production rate plays an important role in industrial applications, which means higher demands for accelerations and speeds of the systems. The requirements for accuracy and repeatability are also increasing. A solution for these demands is a high-speed tooth belt linear drive; however, the drawbacks of system of this kind are non-linear friction and flexibility of the belt, which make the precision control of the system difficult. In this paper, the frictions and flexibility of the high-speed tooth belt linear drive are analyzed.

Finite element analysis for bearingless operation of a multi flux barrier synchronous reluctance motor

Self levitation principle for electrical machines has been a promising research area in the last two decades. Bearingless operation of a motor with two different windings (torque and levitation force windings) requires certain design parameters such as winding space and conductors per slot to be chosen correctly. This paper discusses the design aspects of a bearingless synchronous reluctance motor (SynRM) with multiple flux barriers. This type of machine can be very effective in the smooth torque and levitation force production. A finite element analysis is presented to identify the feasibility and practical challenges for the bearingless operation of a SynRM.

Speed control of electrical drives using classical control methods

A classical-control approach to the design and analysis of proportional-integral (PI) speed controllers for electrical drives is presented. After vindicating the fact that traditional one-degree-of-freedom PI control generally gives unsatisfactory performance, a well-performing two-degrees-of-freedom PI controller is designed, with analytic parameter selection. The robustness of the obtained closed-loop system is analyzed, and is found to be satisfactory.