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MNPC or NPC – best topology for a multi-level inverter?

Mixed-voltage Neutral Point Clamped (MNPC) and Neutral Point Clamped (NPC) represent two different types of power module topology used in high power applications such as three-phase solar/photovoltaic (PV) inverters and uninterruptible power supplies (UPS), Choosing between the two topologies is mainly a question of switching frequency. NPC delivers at higher switching frequencies and MNPC lower switching frequencies, however the threshold frequency between the two gets ever lower and there are other factors to consider…

MNPC and NPC type semiconductor modules deliver significant advantages when used as as multilevel inverters

  • Low EMI caused by dv/dt issues.
  • High efficiency
  • Reduced stress caused by multiple voltage levels on the DC bus.
  • Can draw low disturbance input current
  • Lower common state voltage (so what?)

How MNPC and NPC modules work

When MNPC and NPC modules are used as an inverter, the DC voltage can be converted into a variable alternating voltage and variable frequency. Unlike a half-bridge or sixpack topology, these topologies offer an additional voltage level at the output. The potential can also have a status of 0 as well as DC+ and DC-.
At real or active power these are switched at just 50Hz and therefore correspond to the positive or negative sinusoidal half-wave. Usually operated at 8kHz for MNPC and 16kHZ for NPC, the outer switches generate the sine wave and therefore requires only half the blocking voltage capability required for conventional topologies. This is significant because semiconductors with a high blocking voltage capability are slower at switching. MNPC and NPC modules with 600 or 650V components can be operated at higher switching frequencies than, for example, 1200V half-bridges.

MNPC Topology

The classic MNPC stage comprises of four IGBTs and four diodes. The topology is also known as T-type of NPC2. The blocking voltage is 600V or 650V for the horizontal (neutral point) switches and 1200V for the outer switches. Some modules come with 1200V and 1700V components. Modules are typically equipped with an NTC of PTC alongside the semiconductors.

NPC Topology

Historically called a three-level module (though, confusingly, the MNPC topology also has three levels), the classic NPC stage uses four IGBTs and six diodes. The blocking voltage is 600, 650 or 1200V.

 

classic MNPC topology (left) and classic NPC topology (right)

So, which is better – MNPC or NPC?

Choosing between the two types is largely based on the switching frequency of the application, though there are other factors. (see below list). Each topology provides better loss characteristics at different frequencies.

NPC allows higher switching frequencies – NPC enables faster switching than MNPC. Above a certain frequency it makes sense to choose NPC rather than MNPC. This does depend on the IGBTs used but as a rule of thumb this was traditionally 16kHz. However, it gets ever lower and now it is more like 10kHz. Manufacturers have considered discontinuing MNPC but some designers prefer to stick with MNPC type because of their familiarity with the topology.

NPC allows a little bit more power. A higher current range due to smaller switches means an NPC can have a higher nominal current rating inside the module. Consequently, NPC allows a little bit more power.

MNPC is easier for emergency switch off – Emergency switch off is easier with MNPC because the switching order is not important. In the case of NPC the IGBTs must be switched in a particular order, typically the outer IGBTS followed by the inner ones to avoid an excessive voltage across one of the 600/650V rated IGBTs.

It depends (indirectly) on the application power rating – Manufacturers typically offer both types for each power rating. However, higher power applications tend to operate at lower switching frequencies and vice-versa. Therefore, whilst  there is a power rating correlation this is more directly related to switching frequency. For high power ratings such as 500kW or above, e.g. solar inverters, MNPC tends to be the better choice because the switching frequencies are usually quite low e.g. 4kHz or 8kHz. For lower power applications, NPC makes more sense because the switching frequency is likely to be higher. Higher switching frequencies mean smaller passive components saving cost, weight and size.

It depends on input voltage – Even at high power ratings it still depends on input voltage. A solar inverter might typically have an input of 1000V and MNPC comes in to play again. But many customers these days want up to 1500V and then you have to use 1700V rated chips and the performance of these 1700V MNPC chips is not so goof do it makes sense to switch to an NPC topology.

Summary of advantages – MNPC v NPC

MNPC

  • Easier emergency switch off
  • Familiarity (more traditional topology)
  • Best for switching >10kHz

NPC

  • Allows a little more power (higher current range)
  • Best for switching >10kHz

 

 

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PPM Power in Electronics Weekly: The pros and cons of Silicon Carbide

Last month Electronics Weekly published an article written by PPM Power colleagues Paul Salter and Joe Petrie on the advantages and disadvantages of silicon carbide (SiC) modules.

Specifically, the article points out:

  • SiC devices offer dramatic improvements over silicon IGBTs in power conversion applications above 600V.
  • SiC-specific packaging is required to facilitate operation at higher frequencies in order to minimise loop inductance and poor performance due to wave propagation effects.
  • SiC-specific gate drivers are needed because silicon IGBTs will not support the switching speed of an SiC device nor the rapid fault response time needed to protect an SiC device in the event of a short circuit. Specifically, soft or augmented turn-off is required to reduce spiking and ringing problems.
  • Because of these consideration, SiC a good choice for new system designs – as opposed to upgrades to existing design, where the advantages of the technology are less realisable.

You can read the full article on Electronics Weekly’s website here.

Paul Salter – Business Development Manager

Joe Petrie – Marketing Manager

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10kV power resistors delivering 5ppm over temperature


Austrian manufacturer of power resistors, EBG have developed new material combinations and processing methods to achieve a thermal coefficient of resistance (TCR) of +/- 5 ppm while maintaining the minimal voltage coefficient of resistance (VCR).

Leading-edge capability with resistive inks and sintering

The SHP series is a new generation of high-precision and high-stability resistors have already been implemented in applications such as in medical power supply units. “To produce such ultra-high precision HV resistors requires leading-edge capability in the use of resistive inks in combination with the sintering process.” Says Louis Klein of EBG.

From 100 MΩ to 250 MΩ

The Non-Inductive SHP series of power resistors currently includes SHP39, SHP52 and SHP78. The series offers a 10 kV operating voltage with a tolerance range ± 1 % to ± 0.1 %. The ohmic range is from 100 MΩ to 250 MΩ though other ranges are possible on request. The overall stability is ± 5ppm/°C from +25 to 65°C (including TCR and VCR)

“Achieving a stability of 5ppm over temperature including the TCR and VCR is a big deal at 10kV”, says Phil Surman – sales director at PPM Power. “and every resistor comes with stability data collected in 10degree steps.”

Typical applications

Typical applications for the SHP series include medical power supplies, motor drives and controls, X-ray, converters and energy regeneration.

Next generation

The next generation currently in development promises broader thermal application areas and even higher thermal stability are currently in development.

About EBG

EBG are based in Kirchbach-Zerlach

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Resistor modules: save space, increase reliability and reduce cost

ULX800

Integrating power semiconductors components is standard industry practice to reduce size, reduce cost and improve reliability. A similar approach is now possible with power resistors, courtesy of Austrian resistor manufacturer EBG.

Multiple resistors of similar or differing values

Thick-film power resistor modules from EBG allow multiple power resistors, of similar or differing ohmic values, to be integrated into a single package, reducing size, increasing reliability and reducing cost. Increasing the level of package integration reduces the overall solution size. Reducing the number of solder joints and thermal interfaces increases reliability.

Fewer interfaces means reduced operational costs

Fewer interfaces, screwed or soldered, means less chance of reliability or manufacturing problems. Any thermal interface (i.e. a connection between the bottom of the resistor and the heat plate) requires thermal paste, which adds time, cost and complexity to manufacturing operations. Reducing the number of components by using integrated resistor modules means fewer components, reduced operational cost and time, and less manufacturing variability of the final product.

How it works

  1. EBG screen-prints resistive elements onto a substrate of aluminium oxide or, for high-performance applications, aluminium nitride.
  2. The resistive ink is baked to cure it.
  3. An additional dielectric layer is printed to cover the conductive ink.
  4. Connecting wires are soldered into place.
  5. The assembly is housed.

High power resistor modules from EBG

EBG offers baseplate-cooled packages, from 50W to 2000W, designed to house multiple resistive elements. The 50W rated AXP-50 series allows four connections, which equate to six different configurations of up to three resistors. In a similar fashion, the ULX-800 uses a slightly larger footprint to deliver a maximum rating of 800W.

AXP50

HXP600

Maximum rating – single vs multiple

When just one ohmic value is required, all the available surface area is used to fabricate the single resistor, which maximises the power rating all the active area is used. When multiple resistors are required, these are printed two or three separate areas on the substrate. The unused space between the layers, necessary to maintain isolation, reduces the maximum possible rating of the part. Therefore, multiple resistors have a lower maximum rating than a single one in the same package.

Simple and complex configurations

The simplest, single element, rated for the full power of the package, with just two terminals. If the application needs two resistors, with reduced power per element, the same package can be configured with two 20W elements. In larger packages like the ULX series, this can be two 300W elements or three 150W elements. The most complex configuration is three elements, which are either independent or form a div.

AXP-50 resistor configurations

ULX800 resistor configurations

Useful links

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New 600W aluminium nitride resistor from EBG

EBG has released a 600W version of the HXP thick film power resistor series. The HXP600 is capable of delivering 100% of its rated power at a bottom case temperature of 85°C. The non-inductive design makes the HXP series particularly well suited for high frequency and pulsed loading applications. Direct mounting on a heat sink means significant cost savings.

  • 1 x 600W, 2 x 240W or 3 x 135W operating power
  • Non-inductive design
  • Materials compliant with UL94 V-0

Specification

  • Resistance tolerance: +/- 5% to +/-10%
  • Temperature coefficient: +/-250ppm/°C (other on request)
  • Maximum working voltage: 500V DC (higher voltage on request)
  • Power rating: 600W at 85°C bottom case temperature
  • Electric strength voltage: Dielectric strength up to 4000V DC against ground
  • Isolation voltage between R1 and R2: 500V (1000V on special request)
  • Partial discharge: 2kVrms

Rated power (%) vs bottom case temperature (°C)

Applications

The main applications are speed drives, power supplies, control devices, telecoms, robotics, motor controls and other switching devices.

Multiple resistor configurations

A standard offering can include up to three resistors in the same package. Configurations of 4, 5 and 6 resistors are also available on special request. The maximum working voltage is 500V. The ohm values available are 0.15kΩ to 5kΩ with tolerances of +/- 10% to +/-5%.

About EBG

EBG is a leading international electronic components manufacturer supplying highly specialised resistive components. The company has a corporate HQ in Austria and operational facilities throughout Europe, the USA and East Asia. More than 85% of EBG production is exported to customers all over the world.

EBG delivers leading-edge resistive technology, including:

  • Very low/controlled temperature and voltage coefficients
  • High stability
  • High-temperature operations
  • Very tight tolerances.

All products meet applicable environmental requirements according to European and US military specifications. The different style options include:

  • Flats
  • Cylindricals
  • Dividers
  • Networks.

EBG’s research and evaluation capabilities include sophisticated X-ray facilities and thermal imaging.

Useful links

 

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Vincotech extend IGBT M7 range of 1200V power modules

Vincotech have extended the range of 1200V power modules for motion control applications featuring IGBT M7 chips. The new modules are available in sixpack and PIM topologies with current ratings from 5A to 200A. They are housed in industry-standard flow and MiniSKiiP® packages.

The Vincotech IGBT M7 range already covers current ratings up to 1800A.

PIM topology

sixpack topology

Lower overall system costs

Ultra-thin wafer processing technology and optimised cell design enables an exceptionally low VCEsat and static losses are reduced by 20%. RFC (Relaxed Field of Cathode) diodes and suppress snap-off recovery allow easier optimisation of EMC behaviour. Consequently, overall system costs are lower.

Multiple sourcing ensures supply-chain safety

20% lower VCEsat

current range vs package vs chip technology

 

Useful links

Integrated Power Modules

MiniSKiiP Integrated Power Modules (IPMs)

Power semiconductors

 

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New 100kV portable HV probe from North Star

 

North Star have added a 100kV model to their PVM series of high voltage probes. The new model offers 0.1% DC accuracy at 100kV, a fast rise time and bandwidth of up to 80MHz.

PVM100 specification

Max DC / Pulsed (kV) Max Freq (MHz) Cable Imp. (Ω) DC – 2Hz 2 Hz – 200 Hz 200 Hz – 5 MHz > 5 MHz Input R/C (MΩ/pf) Divider Ratio Length (inches/cm)
100/150 80 50 <0.15%  <1.5%  <2%  <6% 600/15 2000:1 23/57

Portable HV probe

In contrast to the physically more stable VD series, the PVM series are portable probes, designed for general use where portability and ease of use are essential. They deliver an exceptionally high frequency response in applications such as:

  • Automotive ignition
  • Excimer laser system measurement
  • EMI measurement.

Factory calibrated

PVM probes are intended for use with 1MΩ oscilloscopes, but they are also available with an optional switch that can compensate for various measurement instruments, such as 10MΩ meters. The units are factory-calibrated and do not require adjustment.

Useful links

PVM Series of HV probes

High voltage probes and meters

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PPM Power now supplying Vincotech power modules

PPM Power is now supplying Vincotech power semiconductor modules in the UK. Formerly part of Tyco Electronics and now an affiliated company within Mitsubishi Electric Corporation, Vincotech is a market leader in power modules for motor drives, solar inverters, welding equipment and power supplies.

Highest integration available

“Vincotech modules offer the highest level of integration available in the market, housing dies fabricated using different semiconductor technology,” said Phil Surman, Sales Director at PPM Power. “This provides the best combination of cost and performance. We are very excited about supplying these products to our UK customers.”

Wide portfolio of power modules

Vincotech currently manufactures nineteen different types of power module, including half-bridge, sixpack, booster and power factor correction (PFC) modules. Rectifier modules with integrated brake resistors are also available, as are sixpack modules with integrated rectifiers. Vincotech uses multiple package families, including flow, MiniSKiiP and VINco. Substrate materials include aluminium nitride (AlN) and silicon nitride (Si3N4), which deliver high thermal conductivity.

Vincotech innovation

Innovations from Vincotech include:

  • Sintered die attach replaces all soldered points with sintered connections and allows multiple components to be sintered together.
  • Pre-applied phase-change material supports high thermal conductivity between a power module and heatsink but is solid at room temperature, making it smear-resistant during transportation and assembly.
  • Press-fit pins create a gas-tight, cold-welded connection, which reduces assembly time by eliminating the need for soldering. Solder pins are also available.

Simulation environment

Vincotech also supplies a simulation environment, which allows the user to develop an insight into how parameter adjustments affect losses, temperatures and efficiency.

Useful links

Integrated Power Modules

MiniSKiiP Integrated Power Modules (IPMs)

E3 (Econodual) Integrated Power Modules (IPMs)

Power semiconductors

 

 

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New Genesys+ programmable DC – better performance and functionality

TDK-Lambda has launched the Genesys+™ series of programmable DC power supplies, which uses digital signal processing (DSP) technology to deliver efficiencies of up to 93%, as well as better performance and functionality than the existing Genesys range.

Improvements

  • Programmable control pins
  • Waveform profiles
  • Faster programming response times
  • More advanced master/slave operation.

Same communication protocols

The new series is compatible with Genesys™ and Z+ models, using the same communication protocols and signals. All functions can be programmed from the front panel or remotely. An isolated analogue control and monitoring interface is also provided.

Features

  • Constant current, constant voltage or constant power modes
  • Internal resistance simulation
  • Accepts three-phase 170-265Vac, 342-460Vac or wide range 342-528Vac inputs
  • 1U high, 19″ (483mm) wide rack
  • Five models: 0-10V/500A to 0-600V/8.5A.

Genesys+ 1U Series

Model Output Voltage VDC Output Current (A) Output Power (W) RMS Voltage Ripple RMS Current Ripple Ripple+Noise (p-p) (mV)
G10-500 0 – 10 0 – 500 5000 8 700 75
G20-250 0 – 20 0 – 250 5000 10 300 75
G30-170 0 – 30 0 – 170 5100 12 150 75
G300-17 0 – 300 0 – 17 5100 60 7.5 200
G600-8.5 0 – 600 0 – 8.5 5100 100 4 480

Useful links

Useful documents

pdf-icon

Genesys+ 1U Datasheet

pdf-icon

Genesys+ 1U Brochure

 

 

 

 

 

 

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New parametric search for rectifiers

Dean Technology has launched a parametric search tool for rectifiers. Checkboxes allow a user to include or exclude components from the search results based on rectification-type and package-type.  Sliders can then be used to limit the range of results based on:

  • Repetitive peak reverse voltage
  • Average forward current
  • Maximum forward surge current
  • Maximum forward voltage drop
  • Maximum reverse recovery time

The advanced search can be accessed here:

Parametric searches for suppression products and capacitors will be available soon. PPM will also be launching a parametric search for semiconductor products.

Useful links

Power semiconductors

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More Information?

Telephone +44 (0)1793 784389 or email: sales@ppm.co.uk