Vol 87, No 4 (2016)

A comparative analysis of the dynamic characteristics of field-oriented induction motor drive control systems relying on the main magnetic flux linkage vector reference, space-vector pulse width modulation (SVPWM) of the voltage inverter output, and direct torque control (DTC) is carried out using the Matlab/Simulink program package, with the parameters of the induction motor model used being the same. A changeover from stepless vector control systems to systems using microprocessors and modern controllable frequency converters operating on the principle of relay control entails possible changes in the properties of the electric drives being controlled. In this connection, there is a need to compare the dynamic performance characteristics of an electric drive with a slave vector control system (with an idealized frequency converter), referred to as electric drive 1 (ED1), an electric drive with a DTC system (ED2), and an electric drive using direct torque control and SVPWM (ED3). Modeling has shown that the response time of the torque control loop in all the control systems considered is the same, the time delay being no more than 0.01 s. On the whole, speed control transients in all of the above systems take their course in one and the same way. The differences in flux linkage control transients between ED2 and ED3, on the one hand, and ED1, on the other hand, are due to the differences between the methods used to form the electromagnetic torque. No provision is made in the above control systems for the stabilization of the magnitude of the flux linkage vector. At low loads, the flux linkage automatically follows the load. In an ED3 with direct torque control, the calculation of the necessary instant magnitudes of the voltage vector projections and the SVPWM based formation of the voltages applied to the motor allows implementation of a fast-response control system with minimal harmonic distortions and torque pulsations. The control system coefficients are calculated beforehand. The speed controller is adjusted to the technical optimum. In the main flux linkage oriented control system, it is also desirable to use an SVPWM-based formation of the motor voltage.

This paper presents the results of a study of magnetic rotor systems of high-speed electromechanical energy converters in the Ansoft Maxwell software package, followed by experimental test. Two magnetic systems were considered: with semicircular and cylindrical permanent magnets. It has been found out that the system with semicircular permanent magnets makes it possible to create an electromechanical energy converter with less dense current in the windings and lower losses at identical weight and dimensions. Moreover, the rotor magnet system with semicircular permanent magnets reduces mechanical stresses in the shrouding rotor shell and, correspondingly, its mechanical expansions during operation. We have considered a case of selecting the number of terminal pairs of high-speed electrical machines with permanent magnets, which required preliminary calculations of losses in the magnetic circuit with aimed parameters for different numbers of terminals.

Brushless permanent magnet machines (BPMMs) have a greater efficiency and smaller overall dimensions than do other types of machines and are widely used in electric drives for various purposes. Two types of BPMMs are used in practice: BPMMs with a classical double-layer-distributed stator winding and BPMMs with a toothed-step stator winding. There exists another type of BPMM with a transverse magnetic flux (transverse flux motors, TFMs) which is being actively studied. In TFM electric motors, the magnetic lines of fluxes of the poles of rotor end perpendicular to the direction of rotor rotation. Stator windings in these machines are fabricated as rings coaxial with rotor, and the magnetic circuit of stator consists of separate fragments. Specialists assert electric TFMs have a higher specific power—the ratio between the output power and the mass of the machine—than the electric motors of other type. They are of interest, first and foremost, for electric drives without reducing gears. In most TFM, only a half of the poles of rotor are magnetically connected with circular phases of stator. In this work, the TFM design with disk rotor is described, in which the magnetic flux of all poles of rotor is coupled to the circular phases of stator. The stator magnetic circuit in this machine consists of P-like elements, and alternation of polarity of these elements is provided due to the change of their position. As a result, the magnetic flux coupled to the circular phase increases doubles, as do the machine torque and power. Some results of modeling of a three-phase electric motor are presented. The results were obtained using the Ansys Maxwell computer code, including a graph of the change of torque on the shaft of a machine under rotation of the rotor under conditions of sinusoidal currents in phases.

Two ways to construct a pulse ac voltage stabilizer (PACVS) are discussed in the present paper. In the first one, the acting, average, and amplitude voltages are controlled. An observation interval equal to or a multiple of half of the period of measured voltage is required for it. In the second variant, the instant values of the ac voltages are controlled, which allows one to correct the voltage from and compensate for the short voltage jumps and drops. It is shown that PACVS construction using a booster circuit decreases the demands made on the voltage of transistors and filter capacitor, in addition to impairing the quality of the stabilization and correction of the voltage form. Since it uses the feedback principle of the output voltage form, it is appropriate to construct the PACVS by means of the control principle over disturbance. This enables one to increase the stabilizer speed, since it responds directly to the source of the change in the output voltage rather than the consequence. It is shown that the smoothing action depends on the capacitor capacity and throttle inductance product, while the output resistance and the filter oscillation decrease with increasing capacity and decreasing inductance. An example of a PACVS controlling the instant values of the output voltage and the results of its investigation in MATLAB and Simulink are given.

A functional diagram of a temperature controller of electric resistance furnaces with temperature difference compensation in thermal zones by means of automatic correction of power arriving to the thermal zone is given. The additional power required for compensation of the temperature difference in thermal zones of the furnace is determined. The power depends on the temperature difference between thermal zones during heating, heating temperature, and given permissible temperature difference between thermal zones. Dependences of the relative additional power upon the temperature difference between thermal zones at heating temperatures in a range of 700–1600°C and permissible temperature differences between thermal zones 5, 15, 30, and 50°C are determined. Recommendations on the control system adjustment are given. The adaptive control system for thermal zones of electric resistance furnaces is developed.

Problems of upgrading high-speed electric drives of a lathe feed for machining such bulk and precise products of engineering industry as internal combustion engine pistons with a complex ovate-barrel-like shape are considered. It is shown that these electric drives must have astaticism with respect to chip loading to decrease shape errors. When machining the piston surface, there are both uninterrupted cutting zones and cutting zones with an interruption on part of the spindle revolution as well (for example, when passing bores by a cutter etc.). It is shown that, at the same time, it is reasonable to have the structure with an integrally proportional controller and in the case of cutting interruption with a proportional controller. A controller is proposed with the structure changed as a function of the cutting feature. Application of the adaptive controller with the variable structure in the control system of lathe feed drives for noncircular turning decreases the shape error caused by uninterrupted cutting by 5–20 times in comparison with the linear integrally proportional controller. The additional effect of the application of the adaptive control is attained due to a significant (by several times) increase in the useful life of an expensive diamond cutting tool. The control of the controller structure is effective both in systems with the software formation of controlling actions and in systems using self-training principles.