IEEE Electrification - June 2021 - 38

In the modern home, it is optimal to have a multiconverter
unit connected to the grid and linked to the cloud.
The converter unit should be capable of managing energy
reliably and efficiently, adapting to specific weather conditions
and the electric tariff situation. For the smart converter
to accomplish these complex functions, it needs to
have load-shedding capabilities to react in accordance
with energy limitations in home energy production or,
more broadly, in the city or region. Figure 5 shows modern
appliances classified as a function of the type of residential
load for the power system. The classification for the
three groups is based on the main way in which the energy
is consumed by the appliances.
Description of the House Appliances
The house appliances are categorized into three main
types (see Figure 5).
x Electronic-based appliances: These appliances are of relatively
low power, except for the microwave. Electronic
appliances work at low voltages, and they are
typically fed by an ac/dc power switching supply.
x Resistive-based appliances: Electric water heaters are
resistive systems, and as such, they could be a residential
system stabilizer. Of note, water heaters could
change in the future and use heat-pump-based systems.
The electric clothes dryer is a mixed load, using a
resistor for heating and a motor for driving the drum.
x Motor-drive-based appliances: Traditionally, large
power motor-drive appliances are powered by a single-phase
induction motor with a capacitor connected
to the auxiliary winding during startup. Increasing
demand for efficient appliances causes a migration to
inverter control motors, which shift from single-phase
induction to three-phase dc brushless or reluctance
motors, for the same efficiency argument explained
earlier. Examples include the A/C unit, heat pump,
fans, washer, dishwasher, and garage doors.
According to the Maxwell-Faraday laws, conversion of electromagnetic
energy is only possible with ac. Power systems
have been standardized to operate at 50 or 60 Hz.
However, the constant-frequency ac power systems
needed for standardization are only suitable for a few
electrical apparatuses, such as resistive devices, transformers,
and the great Tesla induction motor. Most complex
electrical equipment operates with an internal
frequency of other than 50 or 60 Hz or may even require
a variable-frequency control. For multiple complex electrical
devices, a controllable variable frequency is needed
to achieve higher efficiency or better performance. This is
especially true for induction motors, which, when fed by
a variable frequency, produce a constant current during
their start and provide better variable speed performance.
Therefore, it is a common practice to rectify the
ac to stable dc bias or rail voltage, which is denoted as a
dc link in power electronics, and then to make the multiple
conversions needed for each specific home appliance.
The process of producing dc from ac is common to a
large variety of home appliances and apparatuses, such
as phones, microwaves, computers, motor driver controllers,
lighting, and LED TV displays, among others. Consequently,
the ac power grid for most modern apparatuses
needs to be converted to dc to enable their operation.
Manufacturers of refrigeration or heating systems, such
as heat pumps, have continuously been under pressure to
deliver a better seasonal energy efficiency ratio (SEER). For
2023, the minimum acceptable SEER for new installations
will increase from the present values of 14 to 15 and from
13 to 14 for the southern and northern U.S. states, respectively.
Figure 6 shows the schematic of a modern motor
driver used in refrigeration, heat pumps, and A/C units,
which is also similar to that used for washers and dryers. It
consists of power source conditioning comprising the rectification
unit and the power factor correction (PFC), highlighted
in blue. The PFC is only necessary for obtaining
certification of the appliances to meet the power quality
specification on the ac side. The rectification step is needed
to produce dc power in the bus link where the inverter is
connected. The inverter produces a variable frequency to
feed the motor and run it at variable speeds. It is a clear
that, in a dc system, the rectification stage and PFC are not
Master
Controller
Inverter
dc Charger
Energy Storage
TV Microwave
Lighting Computer
Electronics
Water
Heater
Range Dryer Washer Dish
Washer Fridge
Resistive
Figure 5. A classification of residential appliances based on load type.
38
IEEE Electrification Magazine / JUNE 2021
Motor
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IEEE Electrification - June 2021

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