FC topologies
FC can be 2-quadrant (2Q) and 4-quadrant (4Q):
- 2Q FC can transfer power only in one direction - from the grid to the electric machine (motor),
- 4Q FC can transfer power not only from the grid to the machine but also from the machine (generator) to the grid.
Usually the operational mode (motoring, generating or both) of the application defines what FC should be chosen, 2Q or 4Q. For example a wind turbine requires 4Q FC with fully-controlled inventor scheme at the grid side. Sometimes operational requirements in applications which typically require 2Q, may require 4Q - for example large fan with high inertia may require considerable braking capability to slow down in reasonably short time.
FC can be low-voltage (LV) and medium-voltage (MV). LV FC usually have only 2-level (2L) topology, MV – several alternative topologies (3L-NPC, SCHB, etc.). Both the LV and MV topologies can be 2Q and 4Q.
The choice of LV or MV is usually defined by the power level, but other features of the application, e.g. long cable can also affect the choice.
Some FC require input transformer, some don't.
As in DriveConstructor we deal with VSC only, all the topologies included in the software and presented below have "VSC" in the designations.
Converters of 2-level topology
2Q-2L-VSC-6p, 2Q-2L-VSC-12p and 4Q-2L-VSC
2Q FC inventor scheme at the grid side can be 6-pusle («6p») and 12-pulse («12p»). Difference between «6p» and «12p» is in size, weight, cost, efficiency and influence on the grid (THD). 4Q FC is larger, heavier, more expensive and has lower efficiency than 2Q FC. 4Q produce lower THD in the grid. 2-level FC are usually LV.
Fig.1a. 2Q-2L-VSC-6p.1
Fig.1b. Icon designation.
Note that on Fig.1a motor side of the FC is the right side, while on Fig.1b - left side.
Fig.2a. 2Q-2L-VSC-12p.1
Fig.2b. Icon designation.
Fig.3a. 4Q-2L-VSC.1
Fig.3b. Icon designation.
Converters with 3- and multi-level topologies
2Q-3L-NPC-VSC and 4Q-3L-NPC-VSC
3-level FC are usually MV. NPC stands for Neutral-Point Clamped.
Fig.4a. 2Q-3L-NPC-VSC.1
Fig.4b. Icon designation.
Fig.5a. 4Q-3L-NPC-VSC.1
Fig.5b. Icon designation.
2Q-ML-SCHB-VSC and 4Q-ML-SCHB-VSC
SCHB stands for Series-Connected H-Bridge.
Fig.6a. 2Q-ML-SCHB-VSC topology.
Fig.6b. 2Q-ML-SCHB-VSC cell.
Fig.6c. Icon designation.
Fig.6d. 4Q-ML-SCHB-VSC cell.
Fig.6e. Icon designation.