Veröffentlichungen
- 120.J. Juliet and J. Holtz, "Sensorless acquisition of the rotor position angle for induction motors with arbitrary stator windings" in 2008 IEEE Industry Applications Society Annual Meeting, 2008, pp. 1321-1328 vol.2.
ISBN: 0197-2618
Abstract:
The anisotropy of a cage rotor is utilized to determine the angular position of the rotor in an induction machine. The switching transients generated by a pulsewidth-controlled inverter serve as test signals. The response of the three-inverter terminal currents is exploited to derive a quasi-instantaneous rotor position signal. The position is sensed at the inverter through the 3-phase motor cable by measuring the current derivatives. The method does not require additional wire connections. It is applicable to induction motors having the stator windings connected either in wye or in delta. The results are supported by measurements from an experimental setup. - 119.H. Abu-Rub, H. Schmirgel and J. Holtz, "Sensorless Control of Induction Motors for Maximum Steady-State Torque and Fast Dynamics at Field Weakening" in 2008 IEEE Industry Applications Society Annual Meeting, 2008, pp. 96--103.
ISBN: 0197-2618
Abstract:
A method is described that fully utilizes both the maximum inverter voltage and current for steady-state torque production at field weakening. The control algorithm thus provides the maximum possible torque in the entire field weakening region. Dynamic requirements when operating at maximum voltage are met by creating a temporary voltage margin to enable a fast reaction of the current controller. The control algorithm is insensitive to changes of the machine parameters and to variations of the dc link voltage. The approach is based on a stator flux oriented scheme and permits operation without using a speed sensor - 118.M. Wlas, H. Abu-Rub and J. Holtz, "Speed sensorless nonlinear control of induction motor in the field weakening region" in 2008 13th International Power Electronics and Motion Control Conference, 2008, pp. 1084--1089.
Abstract:
In the paper it is presented speed sensorless nonlinear control system using multiscalar model based MMB operating in the lower field weakening speed region. Nonlinear control methods can improve the performance of induction motor drives in transients. The maximum available output torque, which guarantees satisfactory motor dynamics in field weakening region, is calculated using the steady state dependencies of induction motor model. Full dynamic reaction to commanded changes or to disturbances that occur during operation at the voltage limit is enabled by reducing the excitation level in a fastest possible way. Experimental results are presented to demonstrate reliability of proposed controller. In the experimental implementation a 22 kW induction motor is used. The whole control scheme (including multiscalar control, speed computation and space vector PWM) are implemented on a DSP and FPGA. - 117.N. Oikonomou and J. Holtz, "Stator Flux Trajectory Tracking Control for High-Performance Drives" in 2008 IEEE Industry Applications Society Annual Meeting, 2008, pp. 1268--1275.
ISBN: 0197-2618
Abstract:
Medium voltage ac machines driven by high-power inverters operate at reduced switching frequency in order to restrain the switching losses of the power semiconductor switches. When synchronous optimal pulsewidth modulation is employed, the harmonic distortion of the machine currents is minimized under steady-state conditions. High-performance drives may be subjected to sudden changes of velocity and load. Conventional current-based closed loop control schemes cannot ensure dynamic operation without adversely affecting the preoptimized modulation patterns. To obtain high dynamic control in combination with synchronous optimal pulsewidth modulation, the estimated fundamental component of the stator flux linkage vector is used as a feedback signal. Closed loop control is established by employing a deadbeat algorithm. The harmonic component of the stator flux linkage vector is minimized in real-time, using the optimal stator flux trajectory as a reference. Experimental results obtained from a 30-kW prototype drive operated at only 200 Hz switching frequency demonstrate the effectiveness of the approach - 116.J. Holtz and N. Oikonomou, "Synchronous optimal pulsewidth modulation and stator flux trajectory control for medium voltage drives" in 2008 IEEE Industry Applications Society Annual Meeting, 2008, pp. 1748-1791 Vol. 3.
ISBN: 0197-2618
Abstract:
High-power PWM inverters for medium voltage drives operate at low switching frequency to maintain the switching losses of the power semiconductor devices at an acceptable level. For these applications, synchronous optimal pulsewidth modulation methods permit a good trade-off between switching losses and harmonic distortion of the machine currents. The optimization of the pulse patterns is done off-line on the assumption of steady-state conditions. Dynamic modulation errors, and high overcurrents as a consequence, are encountered when the operating conditions change during operation. To overcome this problem, the stator flux linkage vector, including its harmonics, is subjected to closed loop control. A stator flux trajectory controller is employed for this purpose. Experimental results obtained from an industrial 1-MVA, 4.16 kV three-level inverter ac drive are presented. - 115.G. Schmitt, R. Kennel and J. Holtz, "Voltage gradient limitation of IGBTS by optimised gate-current profiles" in 2008 IEEE Power Electronics Specialists Conference, 2008, pp. 3592--3596.
ISBN: 2377-6617
Abstract:
Using MOS-controlled semiconductors provide the opportunity to directly affect the voltage and currents gradients during the switching transients at the gate. An active gate driver is presented that imposes optimised gate current profiles in order to limit the dv/dt and di/dt. When limiting the dv/dt to 1 kV/mus the switching losses are be reduced by 35{%} in comparison to the common limitation method by gate resistor. The switch-off losses are improved about 10{%} by employing an optimised gate signal. - 114.J. Holtz and N. Oikonomou, "Neutral Point Potential Balancing Algorithm at Low Modulation Index for Three-Level Inverter Medium-Voltage Drives", IEEE Transactions on Industry Applications, vol. 43, no. 3, pp. 761--768, 2007.
Abstract:
Three-level inverters produce low harmonic distortion of the ac currents even when operated at moderate switching frequency. This makes them the preferred candidates for high-power medium-voltage applications. To improve the utilization of the semiconductor devices, synchronous optimal pulsewidth modulation is employed. This permits reducing the switching frequency to very low values. Carrier modulation is maintained in the lower range of the modulation index. Operation at very low switching frequency increases the steady-state ripple of the neutral point potential. An intrinsic natural balancing mechanism of the neutral point clamped inverter topology eliminates long-term neutral point potential offsets. Transient conditions, however, may create successive increments of the offset to high values, which requires fast compensation. The novel method of selecting the appropriate redundant inverter sub-bridge meets this requirement without incurring additional penalties. The effectiveness of the approach is documented by experiments obtained from a medium-voltage motor drive fed by a 1-MVA three-level inverter - 113.J. Holtz and N. Oikonomou, "Synchronous Optimal Pulsewidth Modulation and Stator Flux Trajectory Control for Medium-Voltage Drives", IEEE Transactions on Industry Applications, vol. 43, no. 2, pp. 600--608, 2007.
Abstract:
Employing synchronous optimal pulsewidth modulation (PWM) techniques permits operating the PWM inverter of medium-voltage drives at very low switching frequency. The switching losses of the power semiconductor devices are thus reduced. The benefit is that a given inverter produces higher fundamental power. The optimal pulse patterns are determined by offline calculation, assuming steady-state operation of the drive machine. Dynamic modulation errors and high overcurrents, as a consequence, are therefore encountered when the operating conditions change. To overcome this problem, the harmonic components of the stator flux linkage vector are subjected to closed-loop control. The target trajectory is derived from the respective pulse pattern in use, while the actual stator flux trajectory is estimated. The approach is insensitive to parameter variations. It eliminates excessive transients when the operating conditions change. Experimental results obtained from an industrial 1-MVA 4.16-kV three-level inverter ac drive are presented - 112.S. Soter and R. Wegener, "Development of Induction Machines in Wind Power Technology" in 2007 IEEE International Electric Machines & Drives Conference, 2007, pp. 1490--1495.
Abstract:
This paper gives an overview of the development of the induction machine as a generator for wind turbines from the middle of the 20th century up to now. After a short history chapter the different energy conversion concepts are presented. At first a squirrel cage machine is direct coupled to the grid (Danish concept). To adjust the machine speed the second step is a wound rotor machine with collector rings to change rotor resistance. This concept allows the first adaption of the operating point of the wind turbine and the induction machine. Another concept is to connect the stator of a squirrel cage machine with a full inline voltage source converter to the grid to get the flexibility in rotational speed and to control the reactive power. The doubly fed induction machine is the latest development. This concept uses a bidirectional voltage source converter in the rotor circuit with a rated power of only 30{%} of the rated generator power. Now it is possible to change the rotational speed and the reactive power independently and in a wide range. A generalized control scheme of a modern doubly fed induction machine (DFIG) is shown in the last part to explain the variability and the range of application. Today over 70{%} of the wind turbines are build up with DFIG. - 111.R. Wegener, F. Senicar, C. Junge and S. Soter, "Low Cost Position Sensor for Permanent Magnet Linear Drive" in 2007 IEEE 2nd International Conference on Power Electronics and Drive Systems (PEDS), 2007, pp. 1367--1371.
ISBN: 2164-5264
Abstract:
This paper deals with a custom made low cost sensor for measuring the position of a permanent magnet linear motor. The principle how to measure position and movement direction with two analog hall sensor elements is described. The following simulated and detailed error and failure treatment is very important to know exactly the performance and the possibilities of this low cost sensor element. Afterwards this position sensor is build and some measurements with a linear machine is done. After filtering, the accuracy of the two signals is high enough to be an input of a converter control to determine the correct current which has to be injected. If there is another higher ranking closed-loop control, e.g. pressure, flow or force, in the control system this low cost sensor is sufficient and works very well. It is possible to implement the very small sensor in the housing of the linear drive. This sensor costs less than 15 dollar and can not be compared to a very precise working linear senor for some hundred dollar in order to position the linear drive very exact but the accuracy is high enough to build a lower ranking closed-loop control and to stabilize a complex control system of converter, linear drive and load.
