Bernhard Piepenbreier

Sensorless Control of PMSM for the Whole Speed Range Using Two-Degree-of-Freedom Current Control and HF Test Current Injection for Low-Speed Range

In this paper, an innovative sensorless two-degree-of-freedom current control scheme for the whole speed range is proposed. It consists of a model-based dynamic feedforward control to set the reference response and model reference tracking controllers providing disturbance rejection and the position error signals needed for sensorless control. For low- and zero-speed operation, alternating test current injection is used to gain a position error signal. A flatness-based test signal precontrol provides compensation for secondary saliencies like cross-saturation and higher harmonics. For mid- and high-speed operation, it is shown how the model-based dynamic feedforward control can be modified to obtain a high-quality position error signal from the tracking controller. No additional model-based estimator evaluating back-EMF information is needed. The effectiveness of the proposed method is proven by experimental results.

Radial Forces in External Rotor Permanent Magnet Synchronous Motors With Non-Overlapping Windings

In external rotor permanent magnet synchronous motors with non-overlapping windings, the higher frequency harmonics of the radial forces generate considerable resonant vibrations and acoustic noise. Therefore, diversity of spatial and specifically frequency harmonic ordinal numbers of representative slot and pole number combinations are derived analytically with open circuit and under load. Amplitudes of radial force waves are calculated by means of the finite element method and 2-D Fourier analysis. The obtained results confirm the analytical investigation. Determining factors on amplitudes are studied on machines having different slot and pole numbers and double-layer windings. Higher frequency harmonics significantly depend on the pole and tooth shape as well as the current profile. With open circuit, the calculations are validated by experiments. The findings are applied to reduce the noise of a centrifugal fan.

High voltage IGBTs and medium frequency transformer in DC-DC converters for railway applications

A converter system made of series-connected converter submodules based on medium frequency (MF)-dc/dc converters can replace the conventional traction transformer that works at frequencies of 16.7 Hz or 50 Hz saving both mass and energy. Engaging multilevel topology permits the connection to the HV catenary with a line choke. MF switching performance of typical and dedicated 6.5 kV IGBTs was characterized and is given herein. The impact of chosen switching frequency and resonance frequency on transformer mass and transformer efficiency was analyzed with a coupled electromagnetic, thermal and hydraulic transformer calculation.

Fast gate drive for SiC-JFET using a conventional driver for MOSFETs and additional protections

A new gate drive for SiC-JFET (silicon carbide junction field effect transistor) is developed and tested on a half-bridge. For the realization of a fast gate drive, which offers full protection for the SiC-JFET, a gate drive concept is firstly chosen. The gate drive unit has an output stage made for MOSFETs, a new kind of fast signal isolator, short circuit protection and overvoltage protection.

A survey on modeling, control, and dc-fault protection of modular multilevel converters for HVDC systems

The modular multilevel converter (MMC) is becoming one of the most promising topology in multilevel converter series especially for high-voltage and high-power applications. This valuable features, nominates MMCs to interface high-voltage and high-power renewable energy resources into modern HVDC electric grids for more penetration of renewable energy. This paper investigates recent modelling, control, and dc-fault protection techniques that have been applied to MMCs.

Identification of differential inductances of permanent magnet synchronous machines using test current signal injection

In this paper a new kind of identification method for differential self and mutual inductances of permanent magnet synchronous machines (PMSMs) is proposed. The precise knowledge of the parameters of PMSMs has become an important issue for many applications in electrical drive engineering. Thereby not only the differential self but also the differential mutual inductances are of interest. To identify these parameters the well-known methods that use high frequency (hf) test voltage injection provide unsatisfying results. The method proposed in this paper uses, in contrast, hf test current injection to identify the differential inductances. A machine model that includes cross saturation is the basis for the identification method. Considering the standstill of the machine, the voltage equations can be simplified. For differential inductance identification the hf test current signal is injected either in the dor q-axis of the rotor-oriented (dq) reference frame. Therefore a proportional-resonant (PR) current controller which is in parallel to the fundamental current controller is utilized. Using the output of the Goertzel algorithm, both the differential self and mutual inductances can be determined. Finally, test bench measurement results of a permanent magnet synchronous linear machine prove the proposed method.

Flatness based sensorless control of PMSM using test current signal injection and compensation for differential cross-coupling inductances at standstill and low speed range

This paper presents a novel flatness based two-degree-of-freedom (2DoF) sensorless control scheme for PMSM at standstill and for low speed range using test current signal injection in the estimated d-axis of the field oriented dq-coordinate system. Asymmetrical winding and saturation might cause the occurrence of differential cross-coupling inductances and as a result the estimated rotor position deviates from the real value. The differential cross-coupling inductances have to be compensated for to overcome this problem. For that a flatness based dynamic feed-forward control is proposed. The control error due to model uncertainties is minimized using a controller that fulfills the internal model principle. The control signal of the high frequency controller in the q-axis is demodulated and afterwards used as the input signal of a tracking-observer to estimate the rotor position.

Identification of high frequency resistances and inductances for sensorless control of PMSM

Recently published papers show that also a saliency in the high frequency (HF) resistances can be used for sensorless control. Those papers assume a diagonal HF resistance matrix. The aim of this paper is to show, based on experimental results, that a phenomenon like cross-saturation for the inductances is also existent for the HF resistances. The voltage drops caused by the HF resistances are typically very small and thus their identification is challenging. Therefore a high precision 3-phase current measurement is used and the dead-time and voltage drop errors caused by the inverter are compensated for. A high frequency test current control allowing zero steady-state control error is needed to overcome the limitations of voltage injection based methods.

Modelling and model based compensation of non-ideal characteristics of two-level voltage source inverters for drive control application

In order to be able to optimize the performance of sophisticated model based AC machine control, precise models of the overall drive system are needed. This way compensation schemes for non-ideal characteristics can be derived based on the model inversion technique. Power electronic converters show the following non-ideal effects which have to be considered: turn-on delay time of the gate drive to prevent dc-link short-circuiting, non-ideal switching characteristics and forward voltages of the power electronic devices. In this paper models for these disturbances are derived and the respective compensation schemes are deduced. In constrast to conventional approaches for converter linearization, an analytic compensation law which allows considering different forward voltage-current characteristics of the diode and transistor is proposed. The effectiveness of this method is proven by means of experimental results.

PMSM model for sensorless control considering saturation induced secondary saliencies

Saliencies in electric machines are caused by the machine geometry and saturation. PMSM typically do not just show a single sinusoidal saliency, which is the main saliency utilized for position tracking. Secondary saliencies are a major source of deterioration for sensorless control, whereby saturation is reported to be the main problem. Cross-saturation, caused by a movement of the main flux away from the d-axis, results in steady-state position estimation errors. Moreover saturation can result in 6n-harmonic components in the inductances in field oriented coordinates. This effect causes position dependent estimation errors. Both effects need to be compensated for, if significant. For model based compensation a machine model with time-variant parameters is needed to cope with nonlinear material characteristics. A general machine model in field oriented coordinates considering multiple saliencies is derived and a method for systematic determination of the position dependent inductances is proposed. The machine model is verified by test bench measurement results.