BDD: InverterSubsystem | Webel IT Australia

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TRAIL: SysML: Simple model of an air conditioner with a refrigerant cycle and StateMachine driven by Activities in MagicDraw/Cameo

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parts compartment

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SysML Block Definition Diagram (BDD)

This shows a more detailed "focus" Block Definition Diagram (BDD) for the block InverterSubsystem:

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This InverterSubsystem will enable us to demonstrate a simple control loop. The Activities Set aim temperature and Read got temperature represent setting the 'aim' temperature one wishes to achieve in an air-conditioned room/space, and the temperature one 'got' as read using a temperature sensor.

In German control engineering there are nice terms 'Sollwert' and 'Istwert' for the 'aim' and 'got' values.

In a control loop, the 'got' (sensed) value is not in necessarily exactly the same as the actual, physical value being controlled! Typically it will be limited to a certain performance accuracy (and an intrinsic accuracy limit due to the number of bits).

The room temperature will be controlled via the variable frequency of the power driving a Compressor, as we'll see later in an Internal Block Diagram (IBD) overview.

BTW: In some online descriptions of air-conditioners with inverters you'll often find the entire inverter subsystem described as the "inverter", but the actual inverter is actually just one component of a chain with a larger inverter subsystem.

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Overview of ValueTypes and Units

Notes

[MODELLING, STYLE, TIP]{RECOMMENDED} SysMLv1: Associative BDDs are best used as staging diagrams for you the modeller (and SysML-fluent readers). IBDs usually make better presentations diagrams for a wider audience of general engineers and other stakeholders.

[CONVENTION, DISPLAY, MODELLING, STYLE, TIP]{STRONG} Webel: SysMLv1: Highly recommend creating a "focus" Block Definition Diagram (BDD) for each main Block with expanded feature details and relationships to at least nearest neighbours

[DISPLAY, STYLE, TIP, TOOL]{SUGGESTED} Style: use line width 2 or 3 on the border of the "focus" element in "focus" diagrams (such as the main Block or Class of a dedicated Block Definition Diagram or Class Diagram)

[NAMING, TIP]{OPTION} Optionally suffix the "focus" BDD for a Block with '.bdd' so that it won't clash with a corresponding IBD on diagram export. This is not a SysMLv1 concern, it is purely a workflow concern. It has the slight disadvantage that BDD may "indicated" twice.

[MODELLING, NAVIGATION, PATTERN, TIP, TOOL]{STRONG} Webel: UML/SysML: Navigation: ALWAYS offer a way out of a diagram (usually up a hierarchy, but possibly across) using a navigable symbol (linked to a diagram) and/or a diagram symbol. Avoid "cul-de-sacs"! [But beware of shared package cross-dependencies]

[NAMING, PATTERN, TIP]{RECOMMENDED} In the Webel terminology for a basic control loop there is an 'aim' value (controlled via an actuator) and a 'got' value (a value read from a sensor). The 'got' value is NOT necessarily exactly the same as the actual physical value.

[ASSERTION]{STRONG} In a control loop, the 'got' (sensed) value is not in necessarily exactly the same as the actual, physical value being controlled! Typically it will be limited to a certain performance accuracy (and an intrinsic accuracy limit due to the number of bits).

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