Gerd Griepentrog

Comparison of different control strategies for series-series compensated inductive power transmission systems

For automotive battery charging, the series-series compensated inductive power transmission shows a lot of advantages compared to other compensation techniques. As shown in many recent [1], [2] and older publications, the main advantages are the independency of the secondary current from the load at resonant frequency and the zero phase shift between primary current and voltage. As shown in [3], very high efficiencies from grid to battery of nearly 94-95% can be reached by driving the IPT-system at constant frequency and by adapting the input and the output DC-link voltages. To achieve this control method, extra DC/DC-converters need to be added inside the power transmission path. To avoid the thereby associated higher hardware and also software effort, alternative control strategies needing fewer components are of major interest. In this paper, different control strategies and modulation schemes with and without additional DC/DC-converters are presented, theoretically evaluated with a special emphasis on partial load transmission efficiency and a selection is measured in a real system. The various control strategies were compared on one single coil geometry. The aim is to find a control method which minimizes the total system costs and maximizes the system efficiency at the same time.

Finite element method based electromagnetic modeling of three-phase EMI filters

Finite element method (FEM) based electromagnetic simulation is commonly used for low frequency problems such as motor and transformer design. But it is rarely used for electromagnetic interference (EMI) filters design and analysis. FEM based EMI filters simulation has a number of clear advantages in comparison with conventional approaches. It takes into account mutual couplings and self-parasitics, frequency dependency of permeability can be easy included, values of components can be quickly optimized. In this article a design procedure of a three-phase EMI filter based on FEM simulation supplemented with analytical calculation is proposed. Frequency dependency of permeability, impact of parasitics on insertion losses and mutual coupling between components are taken into account. Differential and common mode insertion losses are represented in accordance with CISPR 17. A complete process of the three-phase EMI filter design and analyses is presented. Use of an optimization tool for further insertion losses improvement is demonstrated.

Suppression of conducted, high frequency signals in aerospace DC/AC converters designed with SiC MOSFETs

This paper presents the impact of voltage fall time of SiC MOSFETs, applied in converters of aerospace DC fed AC drives, on a HF conducted EMI signals. Simple frequency domain behavioral model is proposed for the use. Simulation results and real system measurements are successfully compared. It was shown that appropriate tuning of MOSFET voltage fall time by means of gate driver design allows to selectively suppress common mode noise in the high frequency range. Associated EMI filter design is showing that such suggestion can be used to compensate negative impact of equivalent parallel capacitance of the common mode chokes, leading to simplified filter structure. Resulting impact on the switching energy loss per one commutation cycle is also discussed.

Comparison between grid-feeding and grid-supporting inverters regarding power quality

In this paper a comparison between grid-feeding and grid-supporting inverters is shown based on simulation and measurement of inverter output impedances. The output impedance of a grid-feeding inverter with current control shows capacitive behavior compared to inductive behavior of a grid-supporting inverter with voltage control.

Non-ideal model of the common mode choke for EMI filters

In this article issues related to mathematical modelling of a three-phase common mode choke (CMC) are presented. Influence of the CMC characteristics on the electromagnetic interference (EMI) filter insertion losses is investigated. A novel behavioural model of a three-phase CMC including saturation and non-linear permeability effects in the frequency domain is proposed. Those two phenomena are considered simultaneously in the proposed CMC model. The magnetic hysteresis is based on a mathematical function, describing a dependency between current and inductance and the frequency dependent permeability is realized as a passive electrical network consisting of inductors, capacitors and resistors. The values of the passive components are determined according to permeability characteristics of a particular magnetic material, using the Foster network synthesis algorithm. CMC models based on four different soft-magnetic materials are implemented in LTspice and validated with measurements. A one-stage EMI filter is designed using the behavioural CMC model. Insertion losses of the designed filter with four different CMCs are measured and compared with mathematical models.

Self-sensing method for a switched reluctance motor using delta-sigma modulators and neural networks

A self-sensing method for switched reluctance motors (SRM) for low speed and stand-still is introduced in this paper. The approach utilizes current slopes excited by voltage pulses that are injected into idle phases. To obtain an undisturbed signal for rotor position estimation, a simple integration of the bit-stream output of the delta-sigma modulators in the current measurement path is applied. Thereafter a neural network approximates the actual rotor position from the integrated currents of the idle phases. In comparison with look-up-table based approaches multiple input signals for the approximation are used. The results are evaluated on a test-bench with an 8/6 SRM in open loop operation.

Investigating effects of Delta-Sigma modulation for current measurement on FCS-MPC of IM: Hardware in the loop results

In this paper, the effects of time delays from ΔΣ-ADCs, used for current measurement, on Finite Control Set Model Predictive Control (FCS-MPC) is investigated. For this goal, two FCS-MPC controllers with 50 kHz and 100 kHz sampling rate and one step prediction horizon, were developed and implemented in real time on FPGA in order to control the electrical torque of an Induction Machine (IM). With the help of Hardware In the Loop (HIL) setups, the performance of FCS-MPC with 18 bits and 21 bits ΔΣ-ADC modulation techniques as well as without any ΔΣ-ADC is investigated. Regarding the time delays from ΔΣ-ADCs, the results show higher Total Demand Distortion (TDD) as well as higher RMS of error on electrical torque with increasing time delay i.e. higher output bit-word. On the other hand, the phase currents have less TDD with higher output bit-word.

Prediction of harmonic current frequencies and amplitudes generated in power inductors due to saturation in ferrite and iron powder cores

Reversible and amplitude permeability along with their respective measurement techniques are introduced. They are then used to estimate the current specters resulting from voltage specters applied to cores of power inductors with an AC amplitude high enough to result in saturation. The frequency domain calculation is verified by measurement and it is concluded that when using amplitude permeability the specters can be predicted with satisfying accuracy without time consuming time domain simulation. Reversible permeability is not suitable for modeling inductors under single or multiple AC voltages beyond the nominal current range.

Dynamic programming-based optimal torque control of induction machine

This paper introduces a novel optimal torque control scheme based on dynamic programming for control of inverter fed induction machines. Utilizing dynamic programming method, a cost function is minimized in order to identify optimum sequence of inverter switching operations for the whole prediction horizon at every sampling instant. The proposed optimal control strategy significantly reduces the inverter switching frequency while the stator flux and electromagnetic torque follow their reference values with much less ripple. Simulation is done on accurate model of inverter fed induction machine and the results confirm the superior performance of the introduced optimal control strategy compared to direct torque control and direct self-control strategies. Furthermore, due to short calculation time needed for this method, it is applicable for online control of inverter fed induction machine. The method is a general approach which can be applied on different types of electrical drives and adapted towards different distinct applications.