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Posted on 21 January 2019

1200V Generation 8 IGBTs

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Specifically Designed For Industrial Motor Drive Applications

For industrial motor drive applications at power levels which do not require IGBT modules, there is a limited amount of optimized IGBT discretes available. IR’s Generation 8 1200V IGBT Co-packs TO247 family of products opens up the door for designers to select the strongest, highest performance, and most rugged IGBT technology in discrete packaging.

By Llewellyn Vaughan-Edmunds, Andrea Gorgerino, Yannick Maurice, International Rectifier Corporation

Governments around the world have been introducing regulations that require an increase of efficiency in applications such as industrial pumps, fans and various motor drives.

For systems typically rated below 15 kW, the designer has an option to use either discrete packages or modules. Typically a discrete solution will be cheaper than the module solution; therefore the designer can determine which method is preferred. Current offerings of 1200V IGBT discretes are generally focused towards higher switching frequencies such as UPS and Solar. IR’s Generation 7 is optimized for these higher speed applications.

As industrial motor drives convert to variable speed, the demand for 1200V IGBTs optimized for switching frequencies in the 10 kHz range increases. However there is a lack of selection for IGBTs optimized for lower switching frequencies in discrete packages. Generation 8 IGBT has been specifically tailored for heavy industrial applications, where ruggedness and reliability are a key requirement. As a best-in-class technology, the Generation 8 has already won several prestigious awards for highest performance and best product solution.

At lower switching frequencies conduction losses in the IGBT dominate the total power losses, as the switching losses are proportional to the switching frequency. With very low VCE(ON) Generation 8 IGBT offers high performances in motor drive application with reduced overall losses.

Applications for Gen 8 IGBT

The three phase inverter topology is the most widely used in industrial motor drives.

3 phase inverter configuration

The Generation 8 IGBT can offer up to 60A (@100C) in a TO-247, and up to 85A in a Super TO-247. This achievement is due to Generation 8 IGBT offering a higher current density than previous generations. In motor control applications switching frequencies are typically in the range from 2 kHz to 20 kHz. Higher frequencies help reduce current ripple and audible noise, however the penalty is higher losses which means higher initial cost because of the need of larger devices and larger cooling, as well as higher running energy costs. In industrial applications these trade-offs usually push applications towards the lower end of this range, reducing losses and costs. Gen 8 IGBT is particularly well suited in these conditions thanks to the very low VCE(ON) that this technology can achieve.

Another important requirement in industrial motor drive applications is the ability for the device to withstand a short circuit condition for enough time to allow the protection circuit to react and turn off the system. Because of the wide range of operating conditions, designers typically need to use large blanking windows in the short circuit protection circuit and this increases the requirements on the IGBT devices.

Therefore the novel Generation 8 has also been designed to be highly robust with 10μs short circuit rating and square reverse bias safe operating capability demanded by industrial motor drive applications.

Forward Voltage Drop

One of the requirements for industrial motor drive applications is lowest voltage drop across the IGBTs when they are conducting. Conduction losses are the most dominant loss for motor drive applications operating below 10 kHz.

Table 1 shows VCE(ON) comparisons of 1200V, 40A IGBT in TO-247 packages (TO-264 for Competitor B), using IR Generation 8 IGBT and three of the main IGBT competitors in the market. It can be seen that IR Generation 8 IGBT has lowest voltage drop.

Switching loss comparison

An important consideration is when the system is running at light load, where the IGBT is running well below its rated current. In this situation, Generation 8 IGBT has consistently lower VCE(ON) compared to the competition as can be seen in Figure 2.

Gen 8 IGBT voltage

Switching Characteristics

To compare the switching characteristics of different devices, it is important to do so in similar conditions. In particular changing the gate drive resistance based on the device characteristics. In this analysis the resistor values were chosen to reach a speed of 5kV/μS, as required by most of today’s industry. Therefore switching characteristics were measured with bus voltage, VDC = 600 V, at TJ = 150 ºC with external Rg = 10Ω for Generation 8 IGBT, Rg = 40Ω for Competitor A Rg = 40Ω for Competitor B, and Rg =50Ω for Competitor C.

At turn OFF it is very important for the IGBTs to have a low voltage overshoot to prevent IGBT over-voltage failure. In these motor drive systems designers need to assemble large capacitors, bus bars, power stage and sensing elements, which results in some level of parasitic inductance which will generate unwanted over voltages.

In order to minimize these voltage overshoots due to system’s parasitic inductance, the IGBTs must have low di/dt and a soft turn-off event.

Figure 3 shows the turn off characteristics at IC = 40A.

IGBT turn off characteristics

From these waveforms, it can be seen that Generation 8 IGBT has lower overvoltage than competitor A. Looking instead at the turn ON transition, Gen 8 IGBT is able to deliver higher di/dt than competitor IGBTs and allows much quicker recovery of its anti-parallel diode, resulting in lower turn on losses. However this higher di/dt does come with higher peak reverse recovery current and this needs to be managed during the drive design.

Figure 4 shows switching losses comparison for an optimized motor drive speed (5kV/us).

Switching losses comparison for an optimized motor drive speed

Thanks to a very fast Turn ON, Gen 8 shows the lowest EON compared to its main competitors. This characteristic allows Gen 8 IGBT to be used in wide frequency range for motor drive application.

Table 1 shows the comparison of switching losses between Gen 8 and its main competitors. It also shows improved switching characteristics with very soft turn OFF to reduce peak voltage and fast Turn ON to reduce switching losses.

Short Circuit Characteristics

Another important requirement for IGBTs used in industrial motor drive applications is the short circuit withstanding capability. IR Gen 8 IGBT is designed to have a minimum of 10 μsec short circuit withstand time at VCE = 600V with a starting TJ = 150 ºC. This is achieved by limiting the saturation current during a short circuit event.

Short circuit waveform

Paralleling of devices

Paralleling of IGBTs can be used effectively to increase the power of motors drives. Gen 8 was particularly optimized to operate in such conditions. It has a positive VCE(ON) temperature coefficient which is inherently stable in temperature. Moreover particular attention was given to the VCE(th) window which is a narrow 1.5V (5.0V to 6.5V): this is very important to balance the current during switching transients without needing to slow the devices too much.

Three Phase Motor Drive

Design using 1200V/40A in TO-247 packages A three phase motor drive design consisting of six 1200V/40A IGBTs is simulated based on the previous measurements to study the power loss of the system at switching frequency of 6 kHz. The simulation is based on the previous measurements taken on actual devices.

Thanks to very low VCE(ON) and low turn ON losses, Gen 8 shows the lowest overall power dissipation in motor drive application, as well as the lower operating junction temperature.

Summary

The design example in this article using 1200V/40A IGBTs in TO-247 package, shows that IR’s latest Gen 8 IGBT silicon technology offers low and very competitive overall losses for motor drive applications operated from 6 kHz to 16kHz. It also highlights that the low voltage drop; soft switching characteristics and rugged short circuit capability are excellent in industrial applications.

IGBT motor drive applications

International Rectifier’s best-in-class Gen 8 IGBTs have been created to target the industrial motor drive market, where there is a significant drive to reduce power consumption globally. As demand for electricity rises, we must ensure power is utilized efficiently. We must keep our focus on reducing our carbon footprint, whilst improving system efficiencies of next generation motor drive designs.

 

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