182.

J. Holtz, M. Höltgen and J. O. Krah, "A Space Vector Modulator for the High-Switching Frequency Control of Three-Level SiC Inverters", IEEE Transactions on Power Electronics, vol. 29, no. 5, pp. 2618--2626, 2014.

Abstract:
Operating three-level inverters at very high switching frequency improves the dynamics of servo drives. It reduces the cost and size of harmonic filters that lessen the dv/dt stress of drive motor windings and bearings. Low harmonic current distortion is a further benefit. Other applications are line-side front end converters, uninterruptable power supplies (UPS), and photovoltaic installations. The requirements of very high-switching frequency control are beyond the computing power of modern microcontrollers and digital signal processors. The problem is overcome by a three-level space vector modulation scheme that defines the switching sequence by taking a sequence of logic decisions instead of doing time-consuming arithmetic operations. The control of the inverter neutral point potential is an inherent part of the scheme and does not need additional algorithms. Implementation in an FPGA permits operating at switching frequencies up to 100 kHz. Experimental results are presented.

181.

T. Boller, J. Holtz and A. K. Rathore, "Neutral-Point Potential Balancing Using Synchronous Optimal Pulsewidth Modulation of Multilevel Inverters in Medium-Voltage High-Power AC Drives", IEEE Transactions on Industry Applications, vol. 50, no. 1, pp. 549--557, 2014.

Abstract:
This paper presents neutral-point potential (NPP) balancing while maintaining low harmonic distortion using optimal pulsewidth modulation (PWM) of a multilevel inverter for medium-voltage high-power industrial ac drives. This method is applicable for five-level inverters or higher. A high performance of the machine is observed experimentally at low-switching-frequency operation employing the proposed technique. In the past, low distortion and optimal common-mode voltage at low-switching-frequency control have been reported using proposed synchronous optimal PWM.

180.

A. Uphues, K. Nötzold, R. Wegener and S. Soter, "Frequency adaptive PR-controller for compensation of current harmonics" in IECON 2014 - 40th Annual Conference of the IEEE Industrial Electronics Society, 2014, pp. 2103--2108.

Abstract:
The use of proportional resonant (PR) current controller in grid side wind power converters instead of the traditional proportional integral (PI) controller has gained a large popularity. Particularly its capability for compensating harmonics in the current waveforms is an essential feature. Due to the replacing of the generator side converter by a simple diode rectifier, harmonics with variable frequencies into dependence of the generator frequency appear in the current waveforms. To reach the IEEE standard for the total harmonic distortion (THD) a frequency adaptive PR-controller for compensating these harmonics is required.

179.

F. Senicar, M. Döpker, A. Bartsch, B. Krüger and S. Soter, "Inverter based method for measurement of PMSM machine parameters based on the elimination of power stage characteristics" in IECON 2014 - 40th Annual Conference of the IEEE Industrial Electronics Society, 2014, pp. 702--708.

Abstract:
This paper presents the precise measurement of the stator inductance as well as the stator resistance, using an inverter. Precise measurement results are created, although the actual output voltage of the inverter is not known exactly. This paper analyzes the different effects of an output power stage, and how they degrade the quality of the output voltage. This knowledge is used to cancel out this output voltage error in enabling a precise measurement of the machine parameters. This allows an easy auto commissioning of the current controller and furthermore an auto commissioning of an optimal torque control. The presented methods are verified with extensive measurement results.

178.

T. Boller, J. Holtz and A. K. Rathore, "Neutral point potential balancing using synchronous optimal pulsewidth modulation of multilevel inverters in medium voltage high power AC drives" in 2014 IEEE Energy Conversion Congress and Exposition (ECCE), 2014, pp. 4802--4807.

Abstract:
This paper presents neutral point potential (NPP) balancing while maintaining low harmonic distortion using optimal pulsewidth modulation (PWM) of multilevel inverter for medium voltage high power industrial AC drives. This method is applicable for five-level inverters or higher. High performance of the machine is observed experimentally at low switching frequency operation employing the proposed technique. In the past, low distortion and optimal common mode voltage at low switching frequency control have been reported using proposed synchronous optimal pulse modulation.

177.

A. Edpuganti, A. K. Rathore and J. Holtz, "New optimal pulsewidth modulation for single DC-link dual inverter fed open-end stator winding induction motor drives" in 2014 IEEE Energy Conversion Congress and Exposition (ECCE), 2014, pp. 3865--3871.

Abstract:
The multilevel topologies of dual inverters feeding an open-end stator winding induction motor has been introduced around two decades ago. However, these topologies require common-mode inductor in series with motor windings to suppress zero-sequence or common-mode currents. In medium-voltage high power drives, low device switching frequencies are preferred to improve the overall efficiency of drive system. On the other hand, low device switching frequencies leads to higher total harmonic distortion (THD) of stator currents. Therefore, the objective of our study was to propose a new optimal pulsewidth modulation to eliminate zero-sequence currents and minimize harmonic distortion of stator currents, while operating power semiconductor devices at low device switching frequencies. The main idea is to select switching patterns such that all zero-sequence components are eliminated and then, perform optimization for every steady-state operating point to minimize the THD of stator currents. The proposed modulation has been validated on dual two-level and dual three-level inverters fed 1.5-kW open-end stator winding Induction motor drive.

176.

T. Boller, J. Holtz and A. K. Rathore, "Optimal pulsewidth modulation of a dual three-level inverter system operated from a single dc link" in 2014 IEEE Energy Conversion Congress and Exposition (ECCE), 2014, pp. 3406--3410.

Abstract:
Operating a dual three-level inverter system from a single dc link circuit is an economic solution for generating five-level output voltage waveforms and to double the output power compared to a single three-level inverter. Such inverter system is used for feeding a drive motor with open stator windings. A mechanism is then required to reduce the common mode voltage components of the motor voltages. This paper describes an off-line optimization method that minimizes both the harmonic distortion of the motor currents and the common mode voltage components. The optimization permits reducing the switching frequency to a very low value of 200 Hz without compromising on harmonic distortion. High performance operation of the drive system at low switching frequency is experimentally demonstrated.

175.

A. K. Rathore, J. Holtz and T. Boller, "Optimal pulsewidth modulation of multilevel inverters for low switching frequency control of medium voltage high power industrial AC drives" in 2014 IEEE Energy Conversion Congress and Exposition (ECCE), 2014, pp. 4569--4574.

Abstract:
This paper presents an optimal pulsewidth modulation (PWM) technique for low switching frequency control of multilevel inverters for medium voltage high power industrial AC drives applications. Synchronous optimal PWM permits setting the maximum switching frequency to a low value without compromising in THD. Low switching frequency reduces the switching losses of the power semiconductor devices, resulting in higher inverter power output and efficiency. Experimental results of a five-level inverter drive using optimal PWM are presented. Two types of topologies are discussed: 1) Isolated dc link topology and 2) Common dc link topology with common mode inductor.

174.

A. Bartsch, K. Klitzke, F. Senicar and S. Soter, "Optimized design of a scalable FPGA based inverter by implementing an application-specific instruction-set processor" in IECON 2014 - 40th Annual Conference of the IEEE Industrial Electronics Society, 2014, pp. 1672--1678.

Abstract:
This paper presents an improvement of a field programmable gate array (FPGA) based scalable inverter drive to control electrical machines. In order to enhance the average utilization of the resources (logic cells and dedicated hardware) of the FPGA, an application-specific instruction-set processor (ASIP) is designed and implemented on the FPGA. To promote better organization of the source code, it is possible to write instructions in a MATLAB based syntax, which are translated into the instruction set for the ASIP.

173.

J. Holtz and X. Qi, "Optimal Control of Medium-Voltage Drives---An Overview", IEEE Transactions on Industrial Electronics, vol. 60, no. 12, pp. 5472--5481, 2013.

Abstract:
Carrier modulation is the most common method for inverter control of ac drive systems. Operation at switching frequencies of several kilohertz is customary to restrain the harmonic distortion of the motor currents. Lower switching frequency is preferred for medium-voltage drives, owing to the higher switching losses of the semiconductor devices. This calls for optimizing the performance of the pulsewidth modulator. Improvements are achieved by abolishing carrier modulation with its equidistant time spacing of the voltage pulses. Optimal pulse patterns can be precalculated for every steady-state operating point of the drive. The patterns are stored in a memory of the drive system, from which they are retrieved and used for inverter control. Control at transient operation is achieved by adapting the optimal steady-state pulse patterns to the respective situation. Specific trajectories of the motor current space vector are then created by online optimization. An alternative method of online optimization relies on predicting the space vector trajectories for the next possible inverter switching states. The switching state that leads to minimum switching frequency is then selected. Optimal pulsewidth modulation reduces harmonic distortion. It permits operation at very low switching frequency and reduces the switching losses. This increases the current-carrying capability of the semiconductor devices to the extent that the power rating of an inverter approximately doubles.