Jörgen Linner

Automated Design of a High-Power High-Frequency LCC Resonant Converter for Electrostatic Precipitators

This work presents an automated design procedure for series parallel resonant converters (LCC) employed in electrostatic precipitator (ESP) power supplies, which reduces the designer effort significantly. The requirements for the power supplies in ESP applications and means to derive an accurate mathematical model of the LCC converter, such as the power loss from commercial insulated-gate bipolar transistors, are described in detail in this paper. The converter parameters, such as resonant tank elements, are selected in order to improve the overall efficiency of the system, when a typical ESP energization operation range is considered. The analysis comprises two different control strategies: the conventional variable frequency control and the dual control. Both control strategies are analyzed by comparing semiconductor losses of five commercial modules. Finally, the circuit operation and design are verified with a 60 kW LCC resonant converter test setup.

An Experimental Evaluation of SiC Switches in Soft-Switching Converters

Soft-switching converters equipped with insulated gate bipolar transistors (IGBTs) in silicon (Si) have to be dimensioned with respect to additional losses due to the dynamic conduction losses originating from the conductivity modulation lag. Replacing the IGBTs with emerging silicon carbide (SiC) transistors could reduce not only the dynamic conduction losses but also other loss components of the IGBTs. In the present paper, therefore, several types of SiC transistors are compared to a state-of-the-art 1200-V Si IGBT. First, the conduction losses with sinusoidal current at a fixed amplitude (150 A) are investigated at different frequencies up to 200 kHz. It was found that the SiC transistors showed no signs of dynamic conduction losses in the studied frequency range. Second, the SiC transistors were compared to the Si IGBT in a realistic soft-switching converter test system. Using a calorimetric approach, it was found that all SiC transistors showed loss reductions of more than 50%. In some cases loss reductions of 65% were achieved even if the chip area of the SiC transistor was only 11% of that of the Si IGBT. It was concluded that by increasing the chip area to a third of the Si IGBT, the SiC vertical trench junction field-effect transistor could yield a loss reduction of approximately 90%. The reverse conduction capability of the channel of unipolar devices is also identified to be an important property for loss reductions. A majority of the new SiC devices are challenging from a gate/base driver point-of-view. This aspect must also be taken into consideration when making new designs of soft-switching converters using new SiC transistors.

Comparison of 2- and 3-level active filters with enhanced bridge-leg loss distribution

In this paper an efficiency comparison between 3-phase shunt active filters derived from the 2-level VSC, the 3-level NPC, Active NPC (A-NPC) and the T-type VSC is presented. In order to address the loss distribution issue of the 3-level topologies, while keeping the efficiency of the system high, a space vector modulation scheme incorporating a special clamping of the phase is proposed. It is shown that 3-level active filters can have their losses well distributed over the chip dies, leading to only a small difference in their operating temperatures. Additionally, a semiconductor area based comparison is used to further evaluate the studied active filter systems. Finally, experimental results obtained with a 12kVAr/48kHz 3-level NPC based shunt active filter employing custom SiC power modules are presented in order to demonstrate the performance and feasibility of this solution.

A novel control strategy applied to the series loaded resonant converter

An novel control strategy of the series loaded resonant converter is presented. The main objective of the control strategy is to minimize the switching losses in the main switching elements (IGBT). The results are experimentally verified on a 60 kW/25 kHz prototype converter. The IGBT losses obtained with the proposed control strategy are compared with those of the commonly used frequency control and phase-shift control strategies. With the proposed control strategy it is found that the losses are reduced in the entire operating range compared to phase-shift control. The same statement is valid also for frequency control, except for the highest output voltage

Optimal design of resonant converter for Electrostatic Precipitators

This work presents a design optimization procedure for Series Parallel Resonant Converters (LCC) employed in Electrostatic Precipitator (ESP) power supplies. The system parameters, such as resonant tank elements, are selected in order to reduce semiconductor losses when a typical ESP energization operation range is considered. Here, the sum of the power losses of the switches are predicted for a set of parameters by mathematical models of the LCC resonant converter, and also by loss characteristics of suitable commercially available IGBTs obtained from experimental analysis and datasheet values. The analysis comprises two different control strategies: the conventional Variable Frequency (VF) control and the Dual Control (DC). Finally, the circuit operation and design are verified with a 60kW charging capability LCC resonant converter test set-up. Both control strategies are analyzed by comparing semiconductors losses for five commercial modules.

Comparison of electrostatic precipitator power supplies with low effects on the mains

In this article, the distortions caused by the power supplies employed in Electrostatic Precipitators (ESP) are investigated, and means for improving the line power quality are proposed. Multi-pulse and PWM rectifier topologies and other concepts including hybrid systems and active filters are evaluated in order to identify suitable systems for ESP applications. A comparison of the studied systems rated to 60 kW and fully designed employing commercial components is shown. The ESP systems efficiency, power density, current harmonic THD, among others features are used for the assessment. The loss calculations are extended to a variable chip area to allow a fair comparison between the studied systems. Finally, the VIENNA 6-switches rectifier and active filter concepts are chosen and experimental analyses are carried out, verifying the performance and feasibility of the proposed systems.

Line power quality improvement for pulsed Electrostatic Precipitator systems

In this article the distortions caused by the pulsed operation of a group of power supplies (PS) feeding an Electrostatic Precipitator (ESP) are investigated, and means for improving the line quality are proposed. In order to reduce the Total Harmonic Distortions (THD) of the line current and also improve the loading balance between the phases, the pulses of the individual power supplies are scheduled and controlled together, so that the power consumption becomes more continuous. The proposed system optimization is experimentally verified with two commercially available ESP supplies, each having power capabilities of 120kW. The study shows the advantages of the pulses scheduling strategy namely reduction of both reactive power consumption and line current peaks; better current THD; better power balance among mains phases; and better utilization of mains components.

On cascading of the series loaded resonant converter

In this paper a novel method for cascading H-bridge and resonant tanks in a SLR, series loaded resonant, converter is presented. The main focus is on load sharing. Different methods are discussed. Their robustness regarding variations in operating frequency, values of the components and parasitic elements are evaluated. The results are validated both by simulations and by experiments. For the experimental part a 120 kW/70 kV system has been designed and tested. The measurements confirm the simulations, where the proposed method shows an equal sharing of the load (current) even when operating the system close to resonance with a +/- 10% worst-case variation of the resonant tank components. The method is derived for two subsystems, but can be generalised to any number of subsystems. Thus, enabling the use of compact, standardised modules connected together forming very powerful systems.

Comparison of concepts for improving the line power quality of Electrostatic Precipitator systems

In this article the distortions caused by the pulsed operation of a group of power supplies (PS) feeding an Electrostatic Precipitator (ESP) are investigated, and means for improving the line power quality are proposed. In order to reduce the Total Harmonic Distortions (THD) of the line current and also to improve the loading balance between the grid phases for pulsed operation, the pulses of the individual power supplies are scheduled and controlled together, so that the power consumption becomes more continuous. As an alternative to the three-phase diode bridge rectifiers, which are used as front-end converters in modern ESP power supplies, multi-pulse and PWM rectifier topologies described in the literature and other concepts including hybrid systems as well as active filters are evaluated in order to identify a suitable topology for ESP applications. A comparison of the proposed ESP systems, considering the implementation complexity, power semiconductor losses, circuit elements stresses, etc. is presented.

Line power quality improvement for ESP systems using multi-pulse and active filter concepts

A simple way to improve the line power quality in Electrostatic Precipitator (ESP) applications by using both the characteristics of its electrical installation and the typical ESP high power supply is presented in this work. A multi-pulse system is built by selecting a combination of suitable MV/LV distribution transformers, preserving the simplicity and reliability of the typical ESP installation. In addition, processing only about 10% of the total system apparent power, shunts Active Filters (AFs) are placed on the low voltage side of the transformer (LV) for high order harmonic-current-mitigation (>7th harmonic). In case of imbalance in the transformer loading, the AFs can also act to adjust the current 5th and 7th harmonics, which are then effectively eliminated by the multipulse system. The theory presented in this work is verified experimentally by a 12 pulse system comprising two passive rectifiers and a designed 12kVAr active filter.