Designing for efficient heat pumps

Designing for efficient heat pumps

There is little doubt that heat pumps are going to make a significant contribution in the push for net-zero. As a technology, they are able to deliver more heat energy than the electricity used to power them, up to 5x in some cases.

However, these remain high power devices and minimising electrical losses within them remains a key goal for all designers. All heat pumps contain several power conversion stages including the AC input stage that converts the grid to DC for the control electronics and motor inverters. An active PFC stage is needed here, usually requiring a microcontroller (MCU) to implement.

In particular, the higher powered motors such as the one used in the compressor must be controlled to be efficient. There will also be a number of circulating pumps and fans in a typical heat pump and efficient control of these is also important. Simpler motor control approaches have disadvantages that result in increased energy loss, so designers are turning to field-oriented control (FOC) as a preferred solution.

By accurately modelling the motor's magnetic field and using that mathematical model to predict the motor’s state, FOC minimises losses overall and improves efficiency. FOC enables precise control of motor speed and torque, allowing for rapid adjustments to changing load conditions – particularly important in the compressor motor.

FOC helps to reduce harmonic distortion in the electrical system by controlling the current waveform applied to the motor to a sinusoidal shape. This results in smoother operation and reduced losses associated with harmonic currents, contributing to overall energy savings.

However, complex mathematical modelling requires a processor. Most MCUs lack the necessary instruction sets and DSPs are not ideal for interrupt driven I/O control. So, FOC often entails using multiple processors and, with another processor for the PFC, systems become complex and expensive.

Designed specifically for FOC with the required instructions and interrupt-driven I/O control, Toshiba’s TMPM4KL incorporates their highly optimised Advanced Vector Engine (A-VE) that simplifies design and enhances performance. The highly capable MCU can control multiple motors, the PFC stage and solenoid valves, eliminating several components.

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