GREEN PULSED POWER
ACHIEVED BY EFFICIENT SOLID STATE PULSED POWERTECHNOLOGYB)

A)

A)

Walter Crewson , Mikael Lindholm , Klas ElmquistA)

B)

ScandiNova Systems AB, Uppsala, 75651, SWEDEN
Crewson Electronics INC, Munsonville, NH 03457, USA

Abstract
A unique solid-state pulsed power modulator
technology has been developed, manufactured
and refined by ScandiNova Systems during thepast decade. There are now many systems
installed world-wide for use in Medical,
Industrial-, Defense- and Research-applications.
All these applications have in common the needfor improved power efficiency - defined as
output pulsed power divided by input wall-plug
AC-power. The power efficiency of thetraditional old Thyratron switched PFN1technology is in the range of 40-60%. The newSolid State pulsed power technology provided by
ScandiNova has recorded efficiency in the range
75%-85%. The improved efficiency does not
only mean a reduced operational cost because ofsaving in power consumption, it also meanssavings in the need for external cooling andsaving in space for installation because thesystem can be made more compact. This means asmaller investment because of reduced coolingsystem and reduced size of premises.

modulator are located inside a commonenclosure. The pulse transformer and the load
HV-interface are the only parts surrounded bytransformer oil. The DCPS, Switching Modules
and Control interface are all in air for easy accessand serviceability.

Fig. 1: The principle of the ScandiNova Solid
State System

1 GENERAL FUNCTIONDESCRIPTION

2 ANALYSIS OF POWER
EFFICIENCY

The basic architecture of the ScandiNova
Solid State Modulator is described below andillustrated in Fig. 1. Three-phase line voltage isfed to a DC Power Supply. It charges up all theSwitching Module units to a primary voltage
around 1000V. An external trigger pulse entersthe modulator, gating all the Switches anddischarging some of the stored energy. A pulse
transformer steps up the voltage to the levelneeded for the load in use. All parts of theThe main reason for the higher efficiency of theScandiNova Solid State pulsed power
technology is because that energy conversion
from AC mains power to output pulsed power ismanaged in a more efficient way with small andlimited losses in each one of the conversion steps
than in the older traditional line-type Modulator.

1The first step is the conversion from AC mains
power to DC power. This step has an efficiencyof 90-95% and is handled by the DC Power
Supply internal unit.

PFN is an abbreviation of Pulse Forming Network

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This efficiency results from the combination of a
six-pulse rectifier (efficiency typically 95%) anda series-resonant inverter, operated in the ZCS(zero-current switching) mode, which is also
typically 95% efficient.
The second step is handled by the Switch subunit. In this step the efficiency is in the range of97-98%.
This efficiency results from the fast switching
speed of modern high-current IGBTs, typicallyless than 0.5 uS on/off time. The turn-on is atzero current, so the only dissipative step is at
turn-off, further improving efficiency. Turn-off
commutation and transformer primary reset areboth assisted by high-speed diodes, which draw
turn-off current away from the IGBT switches.

This section describes how the power efficiency
was verified on a High Power Solid StateModulator.
There are two Solid State Klystron Modulatorsof type K2 to be analyzed in this section. Thesethat are used for industrial E-beam sterilizationof medical disposal products (see Fig 2). EachModulator is pulsing a L-band Klystron of type
TH2022B from Thales. Power efficiency andreliability are of high importance in such anapplication. These two systems were installed inDecember 2008 and July 2009 respectively in
San Diego, CA, USA, and had within a year
accumulated 8500 hours of operation forgenerating E-beam.
The performance of the K2-modulator systems isshow in Table 1 below.

The third and final step is handled by the Pulse
Transformer unit. The pulse transformer has atypical efficiency of 98-99%. In this sub-unit thepulse-tuning circuit is also included. The
efficiency of the pulse tuning circuit is verymuch dependent of the need of flatness of the
final pulse but is typically in the range of 95%99%.
This high efficiency results from the fact that ournew drive circuit makes full use of traditional
pulse transformer designs, which have steadily
evolved since the 1940-ies to the 98-99%
efficiency level by adjustments in winding
geometry and improvements in magnetic corematerials. Our circuit allows one to use an
existing pulse transformer unit and simply
replace the core with two or more cores, eachhaving a fraction of the original core crosssection area. Each sub-core is driven by a singleturn primary and a set of pulse modules, giving
the effect of a fractional-turn primary. This gives
a high turns ratio without changing the pulse risetime. The pulse-flattening circuit “throws away”
a part of the pulse voltage early in the pulse, andgradually restores this voltage later in the pulse,compensating for the “droop” in module
capacitor voltage. Typical power losses in thiscircuit are 4 to 7 percent, depending on pulsewidth. The net effect of the pulse transformer
and pulse flattening elements is a power transfer
efficiency > 93%.

2 POWER EFFICIENCYMEASUREMENTS ON A HIGH
POWER MODULATOR SYSTEM

Fig. 2: High Power Klystron Modulator type K2.

Parameter
RF frequency
RF peak power
RF average power
Modulator peak power
Modulator average power
Klystron Pulse Voltage
Klystron Pulse Current
Pulse width (FWHM)
Pulse Repetition Frequency

Unit Value
MHz 1300
MW 20kW36MW 47
kW100kV220
A215
us12Hz180
Input average AC mains power
kW125
Power efficiency%80Table. 1: Perfomance of the High Power
Klystron Modulator type K2.
The input power measurement was done byusing a true rms current clamp sensor type APPA

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30R. The current recorded per phase, the total
inpot power in kVA and kW are shown in thetable below:
Parameter
Unit Value
Voltage phase 1-2
VAC 479
Voltage Phase 2-3
VAC 479
Voltage Phase 1-3
VAC 479
Current phase 1A165Current Phase 2A172
Current Phase 3A173
Apparent powerkVA 141
Power factor%0,87
Input powerkW122
Table. 2: Input power measurement on system no2.
The output power is measured on a resistive
dummy load using a calorimetric method. Bymeasuring the difference in temperature on
cooling water in/out on the dummy load and theflow the power can be calculated by the formula:
P = Q ∆T cH2O
P is the Power into the Load (kW)Q is the flow of the cooling water through theheat exchanger in the Load (liters/sec)∆T is the temperature difference (°C)
cH2O is the heat capacitivity for water (kJ / (kg K)
The results from the calorimetric measurement isshown in Table 3 below.
Parameter
Unit Value
Flow of cooling waterl/min 162
Input temperature°C
20
Output temperature°C
28,9Temp difference°C
8,5
Output power into loadkW
98,2
Table. 3: Calorimetric measurement on theDummy Load.

Parameter
Unit Value
Flow of cooling waterl/min 78
Input temperature°C20
Output temperature°C
25,2
Temp difference°C
5,2Power loss in Modulator
kW
25,2
Table. 4: Calorimetric measurement on theModulator system.
By using the above recorded values the total
power efficiency of the K2-Modulator system
can be established (see Table 4 below).
Parameter
Unit Value
Input power
kW123
Output power
kW
98,2Power efficiency%
80
Table. 4: Calorimetric measurement on theDummy Load.
Finally, the power loss into the air has to beconsidered. The main power loss inside themodulator transferred to the air is from snubber
circuits in each DCPS. At this operational power
level we estimate that each power supply
generates about 90W of heat loss. There are 6
DCPS units in the system, so the total power loss
becomes 540W.
Another power loss (gain) is generated from theDummy Load that, even though it has been
insulated on most of the surface, generates someheat loss to the air. The surfaces have been
covered about 80% but the remaining surface cangenerate about 850W to the air.
The net result is 540W - 850W = -310W, which
will improve the overall result somewhat.

2 CONCLUSIONSIn order to verify the internal power loss of theModulator the calorimetric measurement is alsodone on the cooling of the Modulator systemitself. By measuring the flow and thetemperature difference between inlet and outlet
water the total power loss can be verified. Theresults are shown in Table 4 below:

This new and unique Solid State Pulse PowerTechnology demonstrates a significantly higher
wall-plug to output load efficiency than older
traditional technology. In a general perspective
this “Green Power” can offer a moreenvironmental friendly and long-term costeffective solution for many applications inPulsed Power.

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