This paper describes the design procedure and performance of an LCL grid filter for a medium-voltage neutral-point clamped converter to be adopted for a multimegawatt (multi-MW) wind turbine. The unique filter design challenges in this application are driven by a combination of the medium-voltage converter, a limited allowable switching frequency, component physical size and weight concerns, and the stringent limits for allowable injected current harmonics. Traditional design procedures of grid filters for lower power and higher switching frequency converters are not valid for a multi-MW filter connecting a medium-voltage converter switching at low frequency to the electric grid. This paper demonstrates a frequency-domain-model-based approach to determine the optimum filter parameters that provide the necessary performance under all operating conditions given the necessary design constraints. To achieve this goal, new concepts, such as virtual-harmonic content and virtual filter losses are introduced. Moreover, a new passive-damping technique that provides the necessary damping with low losses and very little degradation of the high-frequency attenuation is proposed.

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Grid-Filter Design for a Multimegawatt Medium-Voltage Voltage-Source Inverter

This paper compares the expense of power semiconductors and passive components of a (2.3 kV, 2.4 MVA) two-level, three-level neutral-point-clamped, three-level flying-capacitor, four-level flying-capacitor, and five-level series-connected H-bridge voltage source converter on the basis of the state-of-the-art 6.5-, 3.3-, 2.5-, and 1.7-kV insulated gate bipolar transistors for industrial medium-voltage drives. The power semiconductor losses, the loss distribution, the installed switch power, the design of flying capacitors, and the components of an sine filter for retrofit applications are considered.

Comparison of 2.3-kV Medium-Voltage Multilevel Converters for Industrial Medium-Voltage Drives

With the growing use of inverters in distributed generation, the problem of injected harmonics becomes critical. These harmonics require the connection of low pass filters between the inverter and the network. This paper presents a design method for the output LC filter in grid coupled applications in distributed generation systems. The design is according to the harmonics standards that determine the level of current harmonics injected into the grid network. Analytical expressions for the maximum inductor ripple current are derived. The filter capacitor design depends on the allowable level of switching components injected into the grid. Different passive filter damping techniques to suppress resonance affects are investigated and evaluated. Simulated results are included to verify the derived expressions.

/pdf/passive-filter-design-for-three-phase-inverter-interfacing-4r49rhp3co.pdf

Passive Filter Design for Three-Phase Inverter Interfacing in Distributed Generation

A novel inverter-output filter, which cannot only filter the differential-mode voltage dv/dt but also suppress the common-mode voltage dv/dt and their rms values, is proposed in this paper. The filter is in combination with a conventional RLC filter and a common-mode transformer. The main advantage is that the functions of filtering a differential-mode voltage and suppressing a common-mode voltage can be integrated into a single system. Furthermore, the structure and design of the proposed filter are rather simple because only passive components are used. Simulations and experiments are conducted to validate the performance of the proposed filter. Both of their results indicate that about 80% of the rms value of the common-mode voltage are suppressed, while the demand of differential-mode voltage filtering is still met

A Novel Inverter-Output Passive Filter for Reducing Both Differential- and Common-Mode $dv/dt$ at the Motor Terminals in PWM Drive Systems

This paper presents an original design option dedicated to output-filtered pulsewidth modulation inverters used in uninterruptible power systems, embedded networks, or motor drives operating on long cables. It is based on the coupling of interleaved inverter cells by means of intercell transformers (ICTs) and is characterized by very good dynamic behavior on load transients, which is an important issue in such applications. ICT solutions are compared with the classical interleaved solutions using separate inductors. A specific design method is developed to achieve this comparison based on toroidal core shapes. The results obtained with a 600 V, 7.5 kW inverter show the usefulness of ICT-based designs, especially when nanocrystalline magnetic material is used; high specific power and very good dynamic performances are obtained.

Design and Comparison of Inductors and Intercell Transformers for Filtering of PWM Inverter Output

This paper presents a new inverter output filter topology for pulse width modulation (PWM) motor drives. It is shown that the proposed filter effectively reduces high frequency harmonics which can cause serious damage to the motor bearings and insulation. The proposed filter is comprised of a conventional resistance, inductance, capacitance (RLC) network cascaded with an LC trap filter. The LC trap, tuned to the inverter switching frequency, is very effective in reducing the switching harmonics. By using this new topology the need for high damping resistance and low RLC cut-off frequency is eliminated. This reduces the phase shift in the current regulation loop and increases the filter efficiency. Experimental verification of the filter topology is provided with a 180 V inverter and a 25 hp permanent magnet synchronous motor. Space-vector predictive current regulation is implemented as an inner-loop current regulator for the outer-loop speed control using a digital signal processor. The effectiveness of the filter at different motor speeds is presented.

New inverter output filter topology for PWM motor drives

This paper presents a new inverter output filter topology for PWM motor drives. It is shown that the proposed filter effectively reduces high frequency harmonics which cause serious damage to the motor bearings and insulation. The proposed filter is comprised of a conventional RLC network cascaded with an LC trap filter. The LC trap, tuned to the inverter switching frequency is very effective in reducing the switching harmonics. By using this new topology the need for high damping resistance and low RLC cut-off frequency is eliminated. This reduces the phase shift in the current regulation loop and increases the filter efficiency. Experimental verification of the filter topology is provided with a 480 V inverter and a 25 HP permanent magnet synchronous motor. Space-vector predictive current regulation is implemented as an inner-loop current regulator for the outer-loop speed control using a digital signal processor. The effectiveness of the filter at different motor speeds is presented.

S. Reva

Papers

New inverter output filter topology for PWM motor drives

New inverter output filter topology for PWM motor drives