Platform-based variable speed motor solution development

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Platform-based variable speed motor solution development [Copy link]

From refrigerators, washing machines, and dishwashers commonly used in homes to pumps and fans in factories and processing plants, and air conditioning systems in offices, small and medium-sized motors need to be effectively controlled. In commercial, industrial, and domestic environments, we rely on electric motors everywhere, and it is estimated that electric motors consume more than 50% of the world's electricity consumption.

The problem, however, is that most electric motors are not very efficient, with induction motors, AC/DC motors and uneconomical electromechanical drives all being inefficient. Environmental, legislative and commercial considerations, combined with the fact that electric motor-based devices consume large amounts of energy, have made it imperative for engineers to find ways to improve motor efficiency.

Figure 1: IRS2136D series product functional block diagram.

Take a refrigerator, for example, which accounts for about 15% of household electricity, much of which is wasted pumping heat out of the fridge. The single-phase induction motor in a conventional fridge only works at full speed, and the compression motor starts when the internal temperature rises to the desired temperature; when the desired temperature is reached, the motor stops. Or take a washing machine, where most of the electricity is used to heat large amounts of water, so a further improvement in efficiency might be to reduce the amount of water needed during washing.

Take air conditioners, for example, which are typically the largest consumer of electricity in homes and offices and may have multiple motors (for fans and compressors), increasing the opportunity to waste energy. With recent legislation specifically targeting higher SEERs, air conditioner usage in countries like China has increased by about 400% in just five years.

Variable speed motor control

What these applications have in common is that by replacing traditional induction motors (AM1) with inverter-based, variable speed, permanent magnet synchronous motor (PMSM) motion control, engineers can design extremely efficient motors. Improved efficiency reduces operating costs and meets environmental and legislative requirements to reduce electricity consumption. Other benefits are: variable speed solutions produce less acoustic and electrical noise; lower vibrations during operation; higher product reliability and more precise control of the motor. Engineers can therefore design more functionality into the target application.

Until now, the challenge in implementing variable speed motors has been to apply motor control technology without increasing system cost. This is a significant challenge because variable speed solutions require more complex and sophisticated drive and control circuits. Such complexity typically prevents many domestic OEMs from developing in-house. However, time-to-market and cost constraints also mean that buying the latest, pre-packaged motor drive and using a system integrator is generally not an option for independent development. Therefore, new approaches are needed to reduce cost, time and risk in the design and implementation of variable speed motors. To meet this need, integrated, platform-based motor control technology is needed to enable "building blocks" to be combined into the functions required to implement variable speed motor drives while providing application-specific configuration flexibility.

IR's platform for variable speed motor control - called iMOTION - provides design engineers with a comprehensive system-level approach to energy-saving, variable speed sinusoidal current control without position sensors. The platform provides design engineers with everything they need to deploy the benefits of variable speed motor control. iMOTION platform solutions for air conditioners are available now (from IR) and are paired with solutions for home appliances.

Building blocks of simulation

The iMOTION platform building blocks consist of digital controller ICs, analog gate drivers, protection ICs, and power platforms, and are supported by a variety of easy-to-use development and support tools, including reference designs, GUI-based programming tools, and documentation. Here, we will take a closer look at the analog units of the platform, starting with the recently released IRS2136D family.

Figure 2: The IRS2136D is installed in a motor drive circuit together with the iMOTION platform.

The IRS2136D family is a series of high-speed, high-voltage integrated devices that combine three-phase power MOSFET and IGBT driver functions, and integrate comprehensive protection capabilities into a single compact device. Package options include 28-pin SOIC or PDIP package sleeves (doormats) or 44-pin PLCC. Figure 1 shows the functional block diagram provided by these ICs.

IR has utilized its proprietary High Voltage IC (HVIC) technology to design the new devices. This technology is ideal for designing products to drive MOSFETs and IGBTs. The gate drive outputs are designed using latch-up CMOS circuitry, which allows the integration of low voltage drivers with high voltage stage switches to implement high and low side gate drivers in a monolithic IC. In the case of the IRS2136D family, as shown in Figure 1, each device integrates three independent high and low side reference output channels to provide a comprehensive solution for three-phase applications. The high side 600V half-bridge inverter gate driver provides a floating channel that is designed to operate in a boot configuration to be used to drive N-channel power MOSFETs or IGBTs.

The built-in boot diode of each high-side channel plays an important role in further reducing the number of components and circuit complexity. This boot scheme is suitable for most PWM configurations and can be used in parallel with or to replace the external boot network. This flexibility makes the IRS2136D product suitable for a variety of motor control applications, including air conditioners, washing machines, general inverters and micro/small inverter drives.

In addition to their drive capabilities, the new ICs also offer important levels of built-in protection features that previously required external circuitry to implement. Such features include undervoltage lockout for all channels and an overcurrent trip that automatically shuts down the six drivers. The undervoltage lockout feature includes an automatic fault clearing function, while the overcurrent fault condition is automatically cleared after a delay programmed by an external RC network. Also important to the output driver is a high pulse current buffer stage designed to provide cross-conduction protection, which prevents accidental short circuits and increases the reliability of the inverter.

The new IRS2136D operates with a gate driver supply range of 10V to 20V, and its logic inputs are compatible with CMOS or LSTTL outputs down to 3.3V. The analog gate drivers exhibit parametric stability over the product lifecycle, while matching parameters for high-side and low-side channels - such as propagation delays - supports accurate dead-time insertion. Separate power and signal ground connections make it possible to design a single DC line configuration for current sensing on the low-side IGBT.

Complete the design

Taking the air conditioning design as an example, the IRS2136D in Figure 2 is installed in the motor drive circuit together with IR's iMOTION platform. In this case, there are two driver ICs, one for the fan and the other for the compressor, and the power stage consists of IC's high-efficiency loss-blocking channel IGBTs. At the heart of the system is the IRMCF312 digital controller, which combines IR's patented motion control engine (MCE), an analog signal engine (ASE), and an application layer processor. In addition to controlling the PFC circuit, the MCE executes complex sensorless PMSM algorithms for the two motors, while the ASE provides all signal conditioning and conversion circuits for a single shunt sensorless control. The application layer processor defines the operation of the air conditioning system independently from the MCE.