Overview

Innovative

Magna-Power Electronics MT SERIES combines the best of dc power processing with multiprocessor embedded control. A combination of high and medium frequency power processing technologies improves response, shrinks package size, and reduces cost. MT SERIES power supplies are current fed and are more tolerant to abusive loads than conventional switching power supplies.

Scalable Power

MT SERIES power supplies offer both master/slave parallel and series operation. This enables two or more power supplies to be placed in parallel for increased output current or in series for increased output voltage. With master/slave operation, power supplies operate at near equal voltage and current.

Unparalelled Control

MT SERIES power supplies can be configured through the front panel for different applications. The power supply can be programmed to have its control functions accessible from the front panel, rear connector, or through RS232, optional IEEE-488, or optional Ethernet communications. Sensing can be established at the output terminal of the power supply or through a rear terminal block for sensing at the load. An external interlock can be set to enable operation only when an external connection is made. Even calibration has been simplified with front panel access to calibration digital potentiometers.

MT SERIES power supplies incorporate an optically isolated feedback system. The result is that all user interface circuitry is referenced to earth ground -- not the negative terminal of the power supply. This enables users to connect external circuitry without concern of ground loops or voltage breakdown.

Load Dependent Air

MT SERIES power supplies are designed to operate at rated load 24 hours per day. Standard air cooled units are equipped with variable speed, load dependent blowers to maintain comfortable margins for removing heat from sensitive power semiconductors. Variable speed operation maximizes fan life and a minimizes external environmental hazards.

Designed for Safety

MT SERIES power supplies have extensive diagnostic functions -- all of which, when activated, take command to shut down the system. Diagnostic functions include phase loss, excessive thermal conditions, over voltage trip, over current trip, fuse clearing, and program line. Program line monitors externally applied analog set point signals to insure they are within the specified range. Upon a diagnostic fault condition, main power is disconnected and the diagnostic condition is latched into memory. Pressing the clear key clears the memory. All diagnostic functions can be monitored through a rear connector. Furthermore, control functions can also be set through the rear connector to allow simultaneous control of one or more MT SERIES units.

MT SERIES supplies have three levels of over voltage/current protection: shutdown of controlling insulated gate bipolar transistors (IGBT’s), disconnect of main power, and input fuses. After an over voltage/current trip condition, the supply must be reset.

Integrated Harmonic Neutralizer (250 kW Modules Only)

Magna-Power Electronics integrated 250 kW harmonic neutralizers eliminate families of harmonic components by multiplying the number of input phases with specially wound autotransformers. These transformers; in combination with equally loaded, high-power, dc power supplies; offer a cost effective solution to maintaining power quality at acceptable levels.

Why Neutralize Harmonics?

Input current harmonics are a by-product of nearly all power supplies. Power can only be delivered to the load if the frequency and phase of the voltage and current match. For a three phase power supply using a three phase input rectifier, the input current has a theoretical spectrum of 6n±1 where n is an integer incrementing from 1; this is known as a 6-pulse waveform. This means that a power supply with a three phase input rectifier will produce input currents at 1, 5, 7, 11, 13, 17, 19 ... times the fundamental frequency. The theoretical magnitude decays as the reciprocal of the harmonic component. The 5th and 7th harmonic components have magnitudes of 20% and 14% of the fundamental component, respectively.

Harmonics currents in power systems can find unusual paths and can cause problems if the magnitude is significant and there are loads sensitive to harmonic frequencies. For example, lighting ballasts have series connected capacitors and inductors which can be excited by harmonic currents. IEEE has introduced standard, IEEE 519, which defines recommended limits. Implementing this standard requires a knowledge of the power system and other loads producing harmonics. Unfortunately, the standard can allow the same power supply to possibly exceed limits in one application and not in another. In the same respect, a power supply may or may not can cause a harmonic related problem with or without meeting IEEE 519. The best solution to minimize the risk of a harmonic problem is to eliminate the harmonic current at the source.

Figure 1. (a) 6 and (b) 12-pulse waveforms

Magna-Power Electronics’ harmonic neutralizers suppress families of harmonics by increasing the number of power phases. It can be used when multiple power supplies are used in series or parallel and are equally loaded. Harmonic neutralizers can produce 12-pulse waveforms which have harmonic current components on the order of 12n±1. Figure 1 shows the theoretical difference between 6-pulse and 12-pulse waveforms. Figure 2 shows the resulting spectral differences. Harmonic neutralizers are protected with appropriate sized circuit breakers.

Figure 2. Normalized input harmonic current spectrum for (a) 6, (b) 12, and (c) 18-pulse waveforms