Related notes and applications

A multi-converters system for a micro-grid is presented in AN008: Multi-converters system.

Types of multi-converters control implementation

Different approaches are possible for implementing multi-converter systems on B-Box RCP / B-Board PRO. They are summarized below.

Multi-controller mode (independent)

This is the conventional approach, in which each converter operates independently. They may nevertheless exchange data (such as setpoints, measurements or status information) at a relatively low rate. The typical application is a back-to-back conversion system, which uses one controller for each converter.

Obviously, in multi-controller mode, each controller must execute its own control algorithms. This implies that one control software (C/C++ project, Simulink or PLECS file) must be flashed onto each controller. That said, each controller may be constituted by several - stacked - units, operating in I/O extension mode (master-slave).

Overall, the multi-controller mode takes place between independent controllers, or between independent sets of controllers.

I/O extension mode (aka master-slave mode)

This mode intervenes by default when several B-Boxes or B-Board are connected together using SFP (optical fibers). It offers configuration-free operation for stacked units, with native synchronization and communication. All I/Os and peripherals that belong to slave units can be easily addressed from the master CPU using a device ID only. The master-slave(s) communication latency is optimized to be extremely low.

As such, in I/O extension mode, only one CPU is operating (inside the master). Therefore, only one control software (C/C++ project, Simulink or PLECS file) must - and can - be used.

Networked control mode - synchronization only

This mode supports all the features mentioned in the independent controllers mode, with the addition of the PWM synchronization across the converters.

This configuration offers the best of the two configurations described above, namely:

• Distributing the control algorithm on multiple CPU for better computing power

• Synchronizing PWM across all units

SFP links are used to connect all the units in a single network to benefit from the native imperix RealSync synchronization. However, there is no data exchange between the CPUs once the system is started. The SFP links are only used to synchronize the time-base of the PWMS (CLOCK resources).

In this mode, the user must perform an additional configuration to select which master sends a synchronization signal to which CLK (from C++ or ACG model).

Networked control mode - fully-distributed control

In the fully-distributed control mode, inter-units communication occurs through the SFP links which bring the following advantages over the traditional CAN or Ethernet communication:

• determinist sub-μs transfer delays for up to a few units

• up to hundreds of kHz exchange rate

• data transfers synchronized with the interrupts