This section only applies to 3-phase DC/AC conversion stages.
3.6. Macrocell connections¶
Contents
The connections subsystem is dedicated to the electrical connections at the input and output of the macrocell. Those connections are illustrated by the figure below, in the case of a 3-phase DC/AC conversion stage.
These impact the overall efficiency of the converter. The following connections types are available for users:
Ideal connections
3.6.1. Ideal connections¶
This is the “by default” configuration for the connections subsystem. These connections are assumed to be ideal; therefore, losses are neglected.
3.6.2. Bus bar¶
The bus bar is a type of electrical connection commonly used in industrial applications. An illustrative example is given below.
The number of bus bars is directly linked to the number of voltage terminals on each side of the macrocell.
On the DC side, the number of bus bars is given by the macrocell topology:
\(n_{DC\;bus\;bar} = 2\) for 2-Level and Flying Capacitors
\(n_{DC\;bus\;bar} = 3\) for NPC, T-Type and SMC
On the AC side, the number of bus bars is given by the converter topology by itself, and by the number of legs in parallel:
\(n_{AC\;bus\;bar} = 3\;\times\) Number of interleaved legs
To illustrate this, an example below with a 2-level macrocell and with 3 legs in parallel per AC phase.
Warning
It is assumed that each bus bar on DC side and AC side, respectively, is identical.
In GT-PowerForge, this subsystem can be represented using the following model:
3.6.2.1. DC R Model¶
The purpose of this model is to estimate the bus bar losses based on DC (0Hz) resistance values imposed by the user. This model also proposes a basic estimation on the mass, volume and cost of the total subsystem.
3.6.2.1.1. Losses estimation¶
A bus bar is modeled by simple DC resistance \(R_{DC\;bus\;bar}\) :
By knowing the value of the current passing through the busbar (DC or RMS, depending on the nature of the current), the associated losses can be determined:
\(P_{loss\;per\;bus\;bar} = R_{DC\;bus\;bar} \times I^{2}\)
The losses can be expressed as follows:
Total bus bar losses on the DC side: \(P_{loss\;DC\;total} = P_{loss\;per\;DC\;bus} \times n_{DC\;bus\;bar}\)
Total bus bar losses on the AC side \(P_{loss\;AC\;total} = P_{loss\;per\;AC\;phase} \times n_{AC\;bus\;bar}\)
Total bus bar \(P_{loss} = P_{loss\;DC\;total} + P_{loss\;AC\;total}\)
3.6.2.1.2. Mass, volume and cost estimations¶
The total mass of the entire subsystem is based on the following formula:
\(Mass = a + b \times (Mass_{macrocell} + Mass_{capacitors} + Mass_{cooling})\)
With:
\(a\) : Constant mass [kg],
\(Mass_{macrocell}\) : Mass of the macrocell, including the flying capacitors [kg],
\(Mass_{capacitors}\) : Mass of the capacitors in the DC filter, including damping capacitors [kg],
\(Mass_{cooling}\) : Mass of the cooling [kg].
The volume and costs are related to the subsystem’s mass as shown in the following formulas:
\(Volume = Mass \times Density\)
With:
\(Density\) : Volumetric mass density (material property) [kg/m³]
And :
\(Cost = Constant \ cost + Cost \ density \times Mass\)
With:
\(Cost \ density\) : Weight cost [Currency/kg]
3.6.3. References¶
- 1
Erroui. “High power conversion chain for hybrid aircraft propulsion”, Electric power. Institut National Polytechnique de Toulouse - INPT, 2019.
- 2
Pettes-Duler. “Conception intégrée optimale du système propulsif d’un avion régional hybride électrique” Institut National Polytechnique de Toulouse - INPT, 2021