Multilevel Technology with ALSPA VDM6000

Transcription

1 Multilevel Technology with ALSPA VDM6 A World Leading Converter Topology Multilevel converters have created considerable interest in industrial applications, particulary in drives. Today, several successful installations show there is a promising future for this innovative topology, a topology that did not exist ten years ago. These converters allow an increase in power rating and voltage without sacrificing the purity of the voltage waveform and the consequent motor de-rating. Semiconductors need not be graded and can be put in series without any pre-selection. Finally, energy levels can be minimised under fault conditions. The benefits of this converter no longer have to be proven for highpower variable speed drives. In the years to come, it will inevitably become the topolgy of choice in all sectors of energy conversion. Voltage [ s ] Time [ s ] Time [ s ] Voltage [ s ] Converter output voltage of a 4-level voltagesource DC link converter without a filter red: phase/phase (TDHV < 16 %) green: phase/neutral conductor Motor currents of a 4-level voltage-source DC link converter without a filter (motor-reactance X = 16 %) (total harmonics : < 2 %)

2 The Drive System ALSPA VDM6 - Medium voltage drive 4.6 MVA; 3.3kV 12-pulse converter with precharge Multlevel Inverter DC-circuit Cell-modules Motorfilter GD Transformator Optional output filter Motor V dc Fibre optics Measurement CELL-module Fibre optics MOT Measurement Thyristor command command ALSPA VDM6 - Basic topology of the power circuit

3 The Inverter the heart of the drive The inverter of the ALSPA VDM6 is the heart of the drive. The advanced topology, patented by CNRS (National Center of Scientific Research, in France), and further development by ALSTOM, allows inverter units to be connected in series without needing static or dynamic sharing components across the terminals. The topology is based on the multilevel concept and is formed by series connection of standard two-level groups. All of the, PWM power two-level groups are of the same construction. Depending on the motor voltage there are six, nine or twelve withdrawable switch assemblies which make up a complete bridge within the cubicle. ALSPA VDM6 - Inverter, watercooled version Advantages for the user The new ALSTOM ALSPA VDM6 Medium Voltage Power Drive System is based on patent protected multilevel technology. It maintains a high quality voltage waveform at the motor even at the highest voltages and powers. The benefits for the customers are Full power without derating Very low voltage stress for the motor insulation Lowest pulsating torques on the motor shaft Low leakage currents in the protective conductors No costly output filters required Highest possible dynamic performance for process orientated drives Excellently suited for retrofit to existing fixed speed motor applications Optimal use of standard semicondutor devices (s) No problems with voltage sharing at the semiconductor elements High efficiency due to no need for snubber devices Optimal protection due to limited energy under fault conditions du / dt - Limiter Phase to phase output voltage (without filter) Motor currents Multilevel Type Inverter (ALSPA VDM6) Inverter topology and typical waveform of the inverter output voltage and currents

4 Construction The simplicity of construction brought about by the multilevel structure greatly contributes to equipment reliability due to: Use of high level technology Flying capacitors that allow, for short-circuits at the load, a clamping effect against any potential overvoltage. IND or SYN Moreover, such a topology allows a very simple and compact construction with minimal cable inductance, minimal switching overvoltage and minimal losses The number of connections to a module is minimal: 4-Level Inverter Four Power connections Four optical fibres for gating plus the 24 V supply to the gate drivers. The two water connections use fast disconnect couplings. One inverter phase Many talk about Multilevel-Technology, ALSTOM has it! Physical arrangement of one phase

5 Alternative topologies with ALSPA VDM6 Higher outputs can be implemented by parallel connection of inverters, and also by connecting converters in series by means of a tandem configuration. In the tandem configuration, a motor with open windings can be supplied from both sides with two independent inverters. With two ALSPA VDM6 rated 3.3 kv, 4.6 MVA, then 6.6 kv motors can be supplied up to 9.2 MVA. Basic topology inverter, 4-Level In this case each winding is supplied from two separate DC current busses. The independance of the two busses makes it possible to introduce an overmodulation of 3 rd harmonic, which gives 3.8 kv at the terminals of each winding. This gives an apparent phase to phase voltage at the motor of 6.6 kv Tandem configuration with one DC-link Tandem configuration with two DC-link (P=12) Power supply with three DC-links (P=18)

6 Inverter Output Voltages in Comparison of waveforms 2 Level Classic solution for Low Voltage Drives 3 Level Classic solution for Voltages higher than 1 V 4 Level Multilevel-Technology (protected for ALSTOM by patent) ALSTOM Power Conversion France Tel: +33 () Fax: +33 () Germany Tel: +49 () Fax: +49 () UK Tel: +44 () Fax: +44 () USA Tel: Fax: ALSTOM Publication No. DCG 162 en The logo ALSTOM and their frameworks are trademarks and service trademark applications of ALSTOM NW 3.