Tweet

Posted on 01 November 2019

Get your motor running…

Free Bodo's Power Magazines!

 

 

 

Modern appliances depend increasingly on motion control

Semiconductor integration and advances support power-efficient BLDC motor designs. Greater integration and advances in semiconductor technology are enabling more costand power-efficient solutions for brushless DC motor drive circuits.

By Frank Thimm, Georges Tchouangue and Matthias Diephaus, Toshiba

 

To some observers it may appear that the objective of creating ever smaller, faster and more power efficient integrated devices is designed purely to enable the latest generations of portable appliances. While this perception isn’t entirely misleading, pressures on size, speed and efficiency go significantly beyond products such as mobile phones and portable media players. In fact, some of the major target applications for more sophisticated and more integrated devices are often anything but portable.

Modern appliances around the home and in an industrial environment depend increasingly on motion control and in particular, thanks to their preferable mode of operation, variable speed brushless DC motors (BLDC). As a result, the demand for more efficient solutions to drive BLDCs is growing rapidly and it’s coming from an ever more demanding customer base. Like their counterparts in the portable arena, designers of many industrial and home appliance motion control applications are demanding smaller, cheaper, faster and more power efficient solutions. This, in turn, is driving a new phase in motor control technology.

Power delivery

The demand for more sophisticated motor control solutions has created a whole new market for programmable devices such as digital signal processors (DSPs) and microcontrollers (MCUs). However unlike the traditional applications that these devices were developed to address, motor control is inherently a high voltage environment, which has implications on the level of integration that can be achieved. This inevitably means that, where other applications already enjoy a significant amount of single-chip solutions, motor control applications typically require multiple integrated devices - often the level of integration is dictated by the physical capability of the semiconductor substrate to operate under high voltage and current conditions.

But because of the obvious and immediate benefits of greater integration in power electronics, this represents one of the most significant areas of development over recent years. The continued displacement of MOSFETs in favour of discrete IGBTs and vice versa for instance, shows that the technology is making significant advancements.

In addition, it wasn’t too long ago that IGBT modules still provided greater benefits over discrete devices in very high power applications. However, developments such as Toshiba’s high power IGBT technology, now in its fifth generation, are changing that.

Integrating Toshiba’s trench process with low injection ‘enhancement’ mode N channel technology, Toshiba IGBTs combine fast switching characteristics with low saturation voltage and low conduction loss (Figure 1). These discrete IGBTs are now applicable for a host of hard and soft-switching applications, as well as strobe flashes and plasma displays.

IGBTs combine fast switching characteristics with low saturation voltage and low conduction loss

Integrated drive

The popularity of BLDCs is growing in part because of their inherent longevity and accuracy, but also because, when coupled to an inverter, the resulting configuration offers further advantages in efficiency. For this reason, the use of inverters alongside BLDCs in white goods is also on the increase.

Here there is also demand for higher levels of integration and, once again, Toshiba has delivered, with the introduction of a highly integrated single-chip inverter, available in a DIP26 package. Single-chip inverters have become a vital component in tackling the complexity, cost and development effort required for BLDC motor based designs.

The extensive experience gained in developing discrete IGBTs, as well as modules, has enabled Toshiba to include fully integrated IGBTs in the TPD412x family of single-chip inverters. A block diagram of one such inverter is shown in Figure 2.

A block diagram of the fully integrated IGBTs in the TPD412x family of single-chip inverters

Using the latest Silicon on Insulator (SoI) technology, Toshiba has developed a trench isolation structure, allowing both low and high voltage circuits to be integrated in reliable, monolithic devices. As a result, the latest devices provide full three-phase inverter bridge operation and incorporate high- and low-side drivers with six IGBTs, to supply current to the motor stator coils. The product portfolio now includes devices that can provide 250V and 500V maximum supply voltages; the 250V inverters offer a 1A output while the 500V devices provide 1, 2 or 3A, and retain mechanical compatibility.

Available in both PWM and non PWM formats, all members of the family can interface easily to a host microprocessor.

On-chip state machine

Despite the challenges faced in achieving greater integration for high power applications, demand still grows and for good reason; efficiency has become a key differentiator in motion control.

The example given earlier, of DSPs and MCUs being used in this application area, typically comes from the need to implement relatively complex algorithms that transform simple Pulse Width Modulation (PWM) signals into smoother sinusoidal waveforms. These are used to drive each phase of a BLDC motor, as sinusoidal waveforms help minimise electrical and acoustic noise when switching between positive and negative polarities in the driver circuit. This not only promotes more efficient operation, but also helps to reduce vibrations and, so, enhance reliability. However, implementing sinusoidal control also represents an additional and often costly component, as well as significant design effort in terms of both hardware and software development.

For this reason, Toshiba has developed a range of Application Specific Standard Parts (ASSPs) which provide a hardware-based solution, removing the need for an additional MCU by using an integrated State Machine. As semiconductor technology develops, so too do the ASSPs targeting motion control. The TB6582FG, for example, which is the latest offering from Toshiba represents the industry’s first single- chip sensorless motor controller to offer full-wave sine wave PWM motor drive output. Because of its high level of integration (see Figure 3), the TB6582FG can significantly reduce the complexity and component count of applications employing a BLDC motor in the consumer, industrial and automotive sectors.

Single-chip sensorless motor controller to offer full-wave sine wave PWM motor drive output

Sensorless motor drive circuits use the back-EMF produced in the coils of a brushless motor to calculate the rotational speed and direction, removing the need for separate (typically Hall Effect) sensors and associated interface circuitry. Hence it is a popular solution in cost sensitive applications, or those where space is at a premium. The TB6582FG integrates all the circuitry needed to accurately calculate the rotor speed and position using the phase current.

Using a built-in State Machine in place of an MCU to calculate the sine wave output allows for closer integration between the analogue speed inputs – provided by a host processor – and the triangular wave generator producing the output. An integrated ‘dead time’ function in also included, promoting safer operation. The dead time is the point at which polarity change occurs during the motor’s rotation, meaning drive current must be removed via the external power transistors to avoid catastrophic failure. Through its integration, a standard ‘push-pull’ configuration can be achieved, allowing both forward and reverse rotation directions with speed controlled through the duty cycle of the PWM signal, provided by the host processor.

Close coupled outputs

Another important aspect of motor control circuits, and power control in general, is the isolation of high and low voltage circuitry, particularly where international safety standards must be adhered to.

The use of optocouplers has long offered a solution to this problem and because they are fabricated using the same semiconductor technology used elsewhere in the industry, it is possible to follow the same integration path. Toshiba recognises the need to provide the same cost and space saving benefits here as it provides in other aspects of motor control, so has continued to invest in the development of a range of optocouplers aimed at this application area.

The latest addition to this range is the TLP700; a miniature photocoupler that delivers the same isolation and current outputs as previous DIP packaged devices, in a form factor that is 50% smaller (Figure 4).

Miniature photocoupler that delivers the same isolation and current outputs as previous DIP packaged devices

With an isolation voltage of 5000Vrms and a common mode transient immunity rating of +/-10kV/µs, it meets all relevant international safety approvals and is suitable for use in IGBT and power MOSFET gate drive circuits. The device is capable of delivering a peak output current of 2A, allowing it to directly switch around 50A through low power IGBTs.

Like existing members of the family, it comprises a GaAlAs infrared LED and a photodetector IC in a single package, albeit a much smaller package; the SDIP outline measures just 6.8mm x 4.58mm x 3.65mm. Operating from a supply voltage of between 15 and 30V, maximum supply current is just 2mA, yet the device retains a switching time of 500nS.

Summary

The number of innovative solutions available to engineers developing a motor or motion control application continues to grow, as does the demand for even more innovation from semiconductor suppliers. In addition to the parts themselves, for instance, companies such as Toshiba are also developing dedicated reference platforms that bring together the technologies highlighted above to significantly speed the development of motion control applications.

 

 

VN:F [1.9.17_1161]
Rating: 0.0/6 (0 votes cast)

This post was written by:

- who has written 791 posts on PowerGuru - Power Electronics Information Portal.


Contact the author

Leave a Response

You must be logged in to post a comment.