1 PWM controller, 3 unique challenges – solved for string inverters, motor drives and e-meters

Other Parts Discussed in Post: UCC28C44

If you’re designing with controllers for industrial equipment, you’ve likely asked yourself such questions as:

  • “What voltage levels do I need?”
  • “Do I care about the current level?”
  • “What frequency does the controller need to run at?"
  • “Will this device need to withstand high temperatures and magnetic immunity?”

Some of these parameters might be more concerning than others, and their importance varies when designing string inverters, motor drives and e-meters.

When designing string inverters, some of the major challenges with pulse-width modulation (PWM) controllers are high startup currents. Low startup currents are important in string inverters because of the high bus voltage. If there is a high startup current, the startup resistors will require more power dissipation. Using fewer resistors can result in a less-reliable power supply because the operating temperature is higher. But if you use more resistors to limit the temperature rise of the system, that of course increases the number of components in the design, and the likelihood of a component failing. String inverters need to operate reliably in severe environments with high ambient temperatures and high altitudes. So having a controller with an extended operating temperature range is important.

Motor drives also utilize an inverter stage, yet have their own unique requirements. Electric motors need to function at a certain torque and speed in order to provide the necessary amount of electricity to whatever it is powering. Most often, a motor will provide an excess of torque and speed. Mechanical controls can adjust these levels, but this can cause inefficiency and wasted energy. A motor’s speed should match the process that it is performing, and an AC drive can maximize a motor’s ability to do this. AC drives can vary the speed and frequency of the motor efficiently. Power from an electrical supply goes into the drive, and the drive regulates what is fed to the motor. The power fed into the drive runs through a rectifier, converting AC power into DC power. The DC power is then fed into capacitors to smooth out the electrical waveform, and finally, into an inverter that changes the DC power into the AC power that goes into the motor. This final step is where the PWM controller comes in. Without a PWM controller, the motor can’t adjust the frequency and speed to the necessary inputs of what it is supplying.

In recent years, e-meters have become more high-tech with power-line communication. This communication carries data on a conductor that is used simultaneously for AC electric power transmission or electric power distribution to consumers. Because of these demands, new e-meters require a higher voltage and need a controller to operate. E-meters also require protection against magnetic interference, and a bias supply with proper undervoltage lockout (UVLO) limits, in order to protect the integrity of the system. A controller with a programmable frequency can have a major impact on a designer’s ability to tune the system.

Despite the unique requirements of string inverters, motor drives and e-meters, it’s possible to mitigate your design challenges with TI’s UCC28C44 family of PWM controllers, which use bipolar complementary metal-oxide semiconductor technology to enable low power consumption. This technology offers improved efficiency, faster current sensing and faster oscillator frequency. The devices have many features and performance advantages, including high (and fixed) frequency operation up to 1 MHz, reduced startup and operating current limits, and overload protection (UVLO). They also have an extended –40°C to 105°C operating temperature. Given these advantages, you can use the UCC28C44 product family for applications including switch-mode power supplies, general-purpose DC/DC or offline isolated power converters, and board-mounted power modules.

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