Michael Bragard

The Balance of Renewable Sources and User Demands in Grids: Power Electronics for Modular Battery Energy Storage Systems

The continuously growing amount of renewable sources starts compromising the stability of electrical grids. Contradictory to fossil fuel power plants, energy production of wind and photovoltaic (PV) energy is fluctuating. Although predictions have significantly improved, an outage of multi-MW offshore wind farms poses a challenging problem. One solution could be the integration of storage systems in the grid. After a short overview, this paper focuses on two exemplary battery storage systems, including the required power electronics. The grid integration, as well as the optimal usage of volatile energy reserves, is presented for a 5- kW PV system for home application, as well as for a 100- MW medium-voltage system, intended for wind farm usage. The efficiency and cost of topologies are investigated as a key parameter for large-scale integration of renewable power at medium- and low-voltage.

Design and implementation of a 5 kW photovoltaic system with li-ion battery and additional DC-DC converter

The integration of photovoltaic (PV) generators in the gird is still an ongoing topic. The peak efficiency of todays power electronics is already above 98 %, therefore innovative aspects can grow from new ways of grid integration. This paper focuses on the combination of a 5 kW PV-generator with a li-ion battery. The temporal decoupling of the generation and injection of energy into the European low voltage grid is presented. Compared to a classic PV system, an additional bidirectional DC/DC-converter is required to ensure the charge and discharge of the battery. The power management of the system can be controlled by the grid operator or according to the best profit defined in a feed-in tariff law for renewable energy. Special attention has to be paid to the efficiency of this DC/DC-converter, due to the bidirectional energy passing before a grid injection is possible in case of energy buffering. After a brief introduction and system overview, this paper focuses on the DC/DC-Converter.

The Dual GCT - A New High-Power Device Using Optimized GCT Technology

The performance of high-power inverters is determined strongly by the characteristics of the semiconductor devices. The design of suitable devices is always a compromise between on-state losses and switching losses. In this paper, a new device-the Dual Gate Commutated Thyristor (GCT)-is proposed that combines the advantages of differently optimized GCTs and realizes low conduction and low switching losses in a single semiconductor device. The concept is introduced first, before the analytical design is presented. Next, finite-element-method simulations are employed to extend the investigation to devices that are not yet available. Measurements of a hybrid Dual GCT are added to verify the advantages of the concept. Finally, the results are discussed.

The integrated Emitter Turn-off Thyristor (IETO) - an innovative thyristor based high power semiconductor device using MOS assisted turn-off

This paper focuses on a new realization method of an Emitter Turn-off Thyristor (ETO). The unity gain turn-off capability of the Gate Commutated Thyristor (GCT) requires extremely low parasitic components within the gate path. The concept of the ETO postulates a MOSFET in the cathode current path of the thyristor, which causes several problems. A new approach leading to a significant smaller and less complex driver design is presented. The drawbacks of the known Emitter Turn-Off Thyristor (ETO) are eliminated by the integration of the MOSFETs into the press pack.

A Major Design Step in IETO Concept Realization That Allows Overcurrent Protection and Pushes Limits of Switching Performance

This paper presents the latest prototype of the integrated emitter turn-off thyristor concept, which potentially ranks among thyristor high-power devices like the gate turn-off thyristor and the integrated gate-commutated thyristor (IGCT). Due to modifications of the external driver stage and mechanical press-pack design optimization, this prototype allows for full device characterization. The turn-off capability was increased to 1600 A with an active silicon area of 823 mm2. This leads to a transient peak power of 672.1 kW/cm2. Within this paper, measurements and concept assessment are presented and a comparison to state-of-the-art IGCT devices is provided.

Inverter based test setup for LVRT verification of a full-scale 2 MW wind power converter

With increased wind power penetration, grid codes of system operators require low voltage ride through (LVRT) capability for wind turbines (WT). This paper describes a full power test bench, designed to evaluate the functionality of grid connected converter in nominal operating mode and in case of LVRT. To verify the LVRT capability an inverter based voltage sag generator (VSG) is developed which emulates grid failures.

Design and realization of a credit card size driver stage for high power thyristor based devices with integrated MOS structure

The Emitter Turn-off Thyristor (ETO) is an advantageous concept in sense of a MOS gated thyristor device. The innovative integration of the MOSFETs inside the press-pack housing allows a cable connection between the high power device and the external gate driver. After a short introduction, this paper focuses on the design and the realization of the external driver stage. Besides a mechanical and thermal decoupling of the driver from the high voltage device, the advantages are an extremely compact design in credit card dimensions. Todays IGCT solutions require typically A4 format (210 mm × 297 mm). Measurements of the prototype prove a significant lower power consumption, which stays far below 5 W at all operating conditions. Additional functionality is demonstrated by short circuit detection and handling.

Recording of efficiency-maps of low-power electric drive systems using a flexible Matlab-based test bench

This paper introduces a hardware setup to measure efficiency maps of low-power electric motors and their associated inverters. Here, the power of the device under test (DUT) ranges from some Watts to a few hundred Watts. The torque and speed of the DUT are measured independent of voltage and current in multiple load points. A Matlab-based software approach in combination with an open Texas-Instruments (TI) hardware setup ensures flexibility. Exemplarily, the efficiency field of a Permanent Magnet Synchronous Machine (PMSM) is measured to proof the concept. Brushless-DC (BLDC) motors can be tested as well. The nomenclature in this paper is based on the new European standard DIN EN 50598. Special attention is paid to the calculation of the measurement error.