Variable-Speed Drive Controller (°CCD)

Compressors are a vital element in cooling appliances, ensuring that the entire system runs smoothly and efficiently. Looking into the core of any machine, the effectiveness of a compressor is the optimisation of all components, including motor type, pump type and inverter type.

Secop’s Cool Capacity Drive inverter compressors (°CCD®) are using variable-speed drive technology and have a number of advantages over fixed speed alternatives, mainly because they can be adjusted to cover a broad range of refrigeration demands.

Summary of topics:

Variable-Speed Drive Compressor and Adaptable Capacity Inverter
Why Choose Adaptable Capacity Compressors from Secop
Compressor Efficiency – System Efficiency
Appliance Design
Design Concept
Determining the Correct Speed
Different Levels of Functionality
Secop Whitepaper – Advantages of Adaptable Capacity

Variable-Speed Drive Compressor and Adaptable Capacity Inverter

When it comes down to compressors, a variable speed drive (VSD) control is almost exactly the same as a variable frequency drive (VFD) in the way it controls an DC motor. However, compressors utilise a brush-less permanent magnet motor for improved efficiency and longevity.

The inverter (variable frequency drive) in these compressors generates three phases, with the frequency for each phase being fully adjustable below or above the average of 50/60 Hz normally used in the power grid. When the frequency is changed, the speed and, therefore, the rotations per minute, are also altered. For example, the electronic controller selects a speed between 1000 rpm and 4000 rpm but this will be different in every electro mechanical system. In addition, the speed that a compressor sets can also alter its cooling capacity.

As a general rule, compressor capacity will normally be in linear ratio to the speed. This means: when a 1:4 speed range has been set, the cooling capacity of the unit is likely to fall at around 1:3.7. Specific capacities are challenging to calculate, because each unit can differ depending on the parameters that have been set. With data sheets available to indicate the performance of variable speed drive compressors at different speeds, engineers can find the perfect speed and related capacity for their application requirements.

Aside from a compressor’s speed and capacity settings, it is also important to know about the relevant variable frequency drive (inverter) components. In the case of a variable speed compressor, the inverter is a small electronic unit with an input of 115/230 Vac (Voltage AC). The input is converted into three phases with efficiency levels being measured as high as 98 percent.

With components having such a high efficiency, it means that refrigerators developed using the variable speed compressors can benefit from reduced energy consumption.

When using a variable speed compressor with an inverter (variable frequency drive) in a refrigerator, it is possible to lower the condensing temperature. In addition, a high evaporator temperature at low load rate can be applied. Meaning that when a refrigerator isn’t fully loaded, machines don’t have to work as hard to keep items cool. This can result in energy consumption savings of between 20 and 40 percent when compared against refrigerators that utilise a fixed speed compressor.

The most important advantage of variable frequency technology is adaptable capacity which leads to high efficiency.

Overall, a variable speed drive compressor offers engineers far more options when it comes to building electronic systems and products. By altering the settings for each individual device built, efficiency gains can be made that both benefit a business and the customer, i.e. the initial investment might be slightly higher applying a compressor with inverter but the operating costs and therefore the total cost of ownership will be significantly lower. Especially in high priced energy markets the payback time is extremely short.

BD Nano DC variable-speed compressor
DLV AC variable-speed compressor
NLV AC variable-speed compressor
SLVE AC variable-speed compressor

Why Choose Adaptable Capacity Compressors from Secop

Advantages of adaptable capacity

Improved system efficiency due to higher t0 and lower tc / Up to 40% energy savings
Dynamic speed range from 1:4
Adjustable cooling capacity for actual system demand
Smaller compressor in terms of displacement and size
Lower noise emission due to low speed - up to 5 dB(A)
Released for rough applications, unstable power supply and tropical regions
Bi-frequency at 220-240 V 50-60 Hz and 115 V 60 Hz
12 to 24 V and 48 V DC for mobile cooling
R290 / R600a / R134a / R404A models available household, commercial applications and mobile cooling (LBP/MBP)
HST features; no pressure equalization needed to start up the compressor
Same compressor type for different markets!

The most important advantage of adaptable capacity is reduced energy consumption, which is possible in different ways. The easiest, most efficient and cheapest way to reach this target is to use adaptable capacity compressors

Targets

The aim of all refrigeration appliance design is to define and optimize the essential functions such as: minimal cost, high performance, and high efficiency, minimized compressor size to enable larger internal cabinet volume, low noise levels and stabilized cabinet temperature at different operation loads.

General

Secop adaptable capacity compressors offer the possibility to adjust the refrigeration capacity according to the desired need by controlling the motor speed of the compressor and therefore the cycle times of the piston.The compressors are highly optimized with very high motor and mechanical efficiency. Tests have shown improvements in energy consumption of up to 40 %, depending on the system design. The average noise level can be reduced by up to 5 dB(A). The compressors are small in volume which allows space for a bigger net volume for usage.

Alternatives for energy savings

The most important advantage of adaptable capacity is reduced energy consumption, which is possible in different ways. The easiest, most efficient, and most economical way to reach this target is to use adaptable capacity compressors.

Compressor Efficiency – System Efficiency

Secop adaptable capacity compressors are very efficient. By varying the speed, they also improve system efficiency. Secop adaptable capacity compressors are able to run so that condensing and evaporator temperatures are optimized.

Application

The compressors are designed for nominal voltage 220-240 V and 115 V at frequency 50/60 Hz; also 12-24 V and 48 V DC and refrigerants R290 / R600a / R134a / R404A at medium to low evaporating temperatures (MPB/LBP) for light commercial and residential appliances. The start performances of Secop adaptable capacity compressors are very high. The actual voltage ranges at start can be higher than with fixed-speed compressors.

The Secop variable-speed drive compressor range

Appliance Design

The advantage in energy savings can be influenced by the appliance design; in particular auxiliary consumers greatly influence energy savings.

System efficiency can also be increased thanks to the appliance’s smart design throughout, e.g. fan units run on full speed in fixed speed systems, adaptable capacity compressor systems, can expect lower heat dissipation. Therefore lower fan speeds are used to transfer the heat load.

With some appliance types, the design must be modified slightly. For example, using a similar capillary, or possibly a smaller size as it is used for the fixed speed compressors in the same cabinet.

Cabinets with two different temperature compartments, designed with one evaporator system, should be modified so that the different evaporator sizes can be adapted for longer running times. The ratio of the evaporator sizes in the cooling and the freezing compartments must be newly adjusted due to the longer running times on average.

If the heat load varies the adaptable capacity compressor can be controlled in a way that the compartment temperatures will become more stable.

Influence to ambience

The use of electronically controlled compressors generally has a very positive affect on the environment. Due to the highly efficient motor design, the heat dissipation to the ambience is reduced, which in many areas will reduce the expenses for additional air conditioning of the rooms.

In addition, the lower compressor speed results in lower sound pressure to surroundings, which for residential and commercial compressors is of high importance.

How to select the right compressor

Controlling the compressor speed means that the compressor selection is different to standard compressors.The model is chosen according to the capacity at max. speed. This capacity will cover the load at max. ambient temperature or at pull down, etc. This max. capacity is chosen similar to the rated capacity of a standard fixed speed compressor for the same appliance.

During normal cycling operation, the compressor typically runs at minimum speed, offering the best efficiency, and during peak load operation maximum capacity.
The advantages of this are:

A smaller compressor, in terms of displacement is needed
Longer running periods at normal load conditions with higher evaporation temperature and lower condensing temperature, offering higher compressor efficiency.
Overall system efficiency increases.
Lower rpm means lower noise level
More stabilized cabinet temperatures at some applications

Solar cooling with BD variable-speed compressor
Van box with BD variable-speed compressor
Display freezer with SLV variable-speed compressor

Design Concept

Electrical

The compressors are equipped with permanent magnet rotors (PM motor) and 3 identical stator windings. The electronic unit can be mounted directly on the compressor as well as externally and control the PM motor.

Mechanical

All other components are based either on our conventional compressor types or new developments.

Design limits

In order to secure the lifetime of the compressors, the appliances must meet certain design criteria. The compressor must start and work properly during pressure peaks obtained in the highest ambient temperature and lowest obliging voltage. At this peak load, the condensing temperature must not exceed 70 (R404A = 60) °C. At stable operating conditions the condensing temperature must not exceed 60 (R404A = 55) °C. These limits are the same for our fixed speed compressor ranges and ensure protection of valves, gaskets, oil, and motor insulation.

Electronic unit

The adaptable capacity compressor motors are electronically controlled. No attempt must be made to start the compressor without a complete electronic unit, as specified in the data sheet for the compressor types in question. The electronic unit has a built-in overload protection as well as thermal protection. When this protection is activated, the electronic unit will protect the compressor motor as well as itself. In addition, the electronic unit will automatically restart the compressor after a certain time. Depending on the different compressor designs, the electronic unit provides the compressor with different starting torques, LST, or HST application.

Power supply connections

Mains power is connected to the controller and transformed into a variable DC voltage, which is supplied to the adaptable capacity compressors. In the event of unstable voltage supply, the electronic switch “Power Supply” mode will adapt the need to the compressor. This ensures that start problems due to under voltages are avoided. For the same reason it is not necessary to invest in an additional external voltage stabilizer. Moreover, the electronics include an under voltage protection, which cuts off the mains in situations in which the supply voltages are out of the pre-defined working limits.

Programming software Tool4Cool®

Tool4Cool® is a unique PC software tool that enables you to precisely configure your Secop compressors to your cooling systems. Via microprocessor-based controllers, Tool4Cool® gives you easy access to all parameters. These can be changed, monitored, downloaded, or uploaded to get the optimum performance out of your cooling system.

BD Nano Series Controllers
BD Micro Series Controllers
BD P-Housing Controllers
BD P-/T-Housing 101N07xx-Series Controllers
BD T-Housing 101N08xx-Series Controllers
Secop Gateways

Determining the Correct Speed

The capacity controlled compressors from Secop have different capacity controls, depending on the chosen model.

External reference signal

If customers want to control the compressor capacity using their own controllers, it is possible to connect a reference signal to the compressor controller.

0-5 volt signal

A DC signal (0-5 Volt) can be connected to the compressor controller, from 0% to 100% requested compressor capacity. To secure an appropriate lubrication of the compressor, the motor speed is limited downwards. If the requested compressor capacity is less than the minimum speed, the compressor will be PWM (pulse width modulation) controlled at minimum speed, within a pre-defined period of time.

Frequency signal

A variable, square shaped frequency signal can be connected to the controller, representing the band from minimum to maximum speed. Secop offers different compressor controller types, so please contact Secop for design details concerning the frequency control.

Standard mechanical thermostat control or low voltage on/off signal (AEO)

The compressor is controlled in an “Adaptive Control” mode, where the controller in the electronic unit takes over the RPM management by using the built-in AEO (Adaptive Energy Optimizer) algorithm. This strategy aims for the lowest possible speed at which the refrigerating system will work properly since the COP is highest at low capacity.

The initial start speed of the compressor after the power supply is connected will be at a higher rpm when the thermostat is cut in.
In the succeeding cycles the compressor will start with a speed slightly below the previous cycle, as long as the thermostat cut out has been reached within the defined run time.
If cut out cannot be reached within the defined run time, the compressor speed will be increased slowly, against max speed, until cut out is achieved.
The next cut in will be slightly below last cut out.

PI control

The determination of the actual requested compressor capacity is based on an integrated PI controller, which compares the actual cabinet temperature with a reference temperature. The bigger the deviation between the set point and the actual cabinet temperature, the faster the controller adapts to the compressor capacity. If the requested compressor capacity is lower than the minimum speed, the compressor will be PWM (pulse width modulation) controlled at minimum speed, within a pre-defined period of time. Depending on the requested temperature stability, the period time can be modified. The shorter the period time, the more stable the temperature control. However there are more start and stops and in worst-case scenarios, reduced life time and less energy savings. Due to different load profiles, the settings for the PI controller can be adapted to offer a more stable temperature control.