MPUs & MCUs
Integrated reference design presents a blueprint for effi cient and cost-effective heat pumps
By Radoslav Valchev, Toshiba Electronics Europe GmbH T
he high coeffi cient of performance (COP) and lower carbon emissions produced by heat pumps make them preferable to more conventional heating and conditioning systems based on gas or oil boilers. However, to encourage wider adoption of this technology, heat pump manufacturers need to optimise the bill of materials used in their construction to ensure they are cost-competitive. In this regard, reference designs produced by component suppliers can be a valuable resource for improving performance, accelerating development times and lowering costs. Heat pumps operate on a straightforward principle: they exchange heat with the environment by alternately compressing and expanding a refrigerant gas. This process makes optimal use of energy—theoretically producing more than 7kW of heat from just 1kW of electrical power. While this COP ratio (7:1) is diffi cult to achieve in practice, systems achieving ratios from 2.5 to 5 are common, but these fi gures are still vastly superior to conventional water boilers whose COP is typically less than 1.
Motor controllers, critical components in heat pumps, are found within both the indoor and outdoor units of the system. The outdoor unit contains a tank of refrigerant as well as a compressor, fan, and an evaporator/condenser unit. A smaller indoor unit includes motors (for driving fl uid fl ows through the system), a second evaporator/condenser and a user interface panel.
The two units use a refrigeration-type process to exchange heat between the indoor and outdoor environments, depending on whether the indoor environment needs to be heated or cooled.
To assist manufacturers in developing
effi cient heat-pump systems and optimising the bill of materials, Toshiba has developed the RD219 reference design based on a single microcontroller unit (MCU) and low-loss power components.
Power conversion is a key focus of this design because heat pumps consume large
40 April 2025 Figure 1 – Vector control and acceleration support in the Advanced Vector Engine Components in Electronics
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amounts of energy. Effi cient rectifi cation of the AC mains supply is essential for a heat pump’s electrical supply, meaning power factor correction (PFC) is an important requirement because it prevents high levels of reactive power from contaminating the mains voltage. PFC can be implemented in several ways, but continuous-conduction mode (CCM) yields the least current ripple. However, a potential consequence of this approach is a generation of a reverse-recovery current superimposed on the current fl owing through the inductor when each power transistor is switched off.
Including a SiC based Schottky diode like Toshiba’s TRS24N65FB helps to reduce losses by lowering the amount of stored charge. Effi ciency can be further improved by using a fast-switching insulated-gate bipolar transistor (IGBT) like the GT30J65MRB.
The compressor motor is the most critical for optimising power conversion effi ciency in a heat pump. This is because it experiences the biggest changes in operating conditions due to varying gas pressures that affect its torque requirements. Therefore, advanced fi eld- oriented control (FOC) is preferred to simpler
control methods (like volts-per-hertz) for improving effi ciency. FOC works by accurately modelling the magnetic fi eld inside the motor to predict the motor’s state (including the rotor position) at any point in time. As load and speed conditions change, the current and voltage supply to each phase are adjusted to ensure that the motor always operates at optimal effi ciency levels. Another benefi t of FOC is that it helps to reduce harmonic distortion in the electrical system, causing the motor to produce less heat and increasing overall system effi ciency. The FOC algorithm
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