Plexim Rt box tsp 2.0.5 User manual

www.plexim.com

Request a PLECS and PLECS Coder trial license

Get the latest RT Box Target Support Package

Check the PLECS and RT Box documentation

RT Box

DEMO MODEL

Modular Multilevel Converter

Multi-tasking simulation of a grid-connected modular multilevel con-

verter on the RT Box 2/3

Last updated in RT Box TSP 2.0.5

Modular Multilevel Converter

1 Overview

This RT Box demo model features a grid-connected modular multilevel converter (MMC) with open-

loop controls. The demo model can be simulated either in single-tasking or multi-tasking mode. To al-

low multi-tasking mode, the physical model has to be split into different parts. This can be done with

the Task Frame component from the PLECS library. This block associates the enclosed components

with a speciﬁed task in a multi-tasking environment. For real-time simulation on the RT Box 2 or RT

Box 3 each speciﬁed task is then executed on a different CPU core to reduce the overall discretization

step size. For the PLECS RT Box 1 only single-tasking mode is available. The chosen discretization

step size and average execution times for the two different tasking modes are shown in Tab. 1.

Table 1: Discretization step size and average execution time of real-time models with both tasking

modes for 5 submodules per arm on RT Box 2

Discretization Step Size Average Execution Time Single-Tasking Average Execution Time Multi-Tasking

6µs3.7 µs2.0 µs

1.1 Requirements

To run this demo model, the following items are needed (available at www.plexim.com):

• One PLECS RT Box 1, 2 or 3 and one PLECS Coder license

• One 37 pin Sub-D cable to connect the digital I/Os of the box front-to-front

• The RT Box Target Support Library

• Follow the step-by-step instructions on conﬁguring PLECS and the RT Box in the Quick Start guide

of the RT Box User Manual.

Note This model contains model initialization commands that are accessible from:

PLECS Standalone: The menu Simulation + Simulation Parameters... + Initializations

PLECS Blockset: Right click in the Simulink model window + Model Properties + Callbacks +

InitFcn*

2 Model

The top level schematic of the demo model is depicted in Fig. 1. Since the demo model runs in open-

loop, the PWM generation and the power circuit run on the same RT Box. To run the subsystem on

an RT Box, the subsystem has to be conﬁgured as atomic and enabled for code generation by right-

clicking on the subsystem and choosing Subsystem +Execution settings....

Plant+OpenloopControls

Swa

PWMa

Swb

PWMb

Swc

PWMc

PWMa1

Swa1

PWMb1

Swb1

PWMb2

Swc1

Figure 1: Top level schematic of MMC demo model

www.plexim.com 1

Modular Multilevel Converter

2.1 Power Circuit

Fig. 2 shows the circuit model of the “Plant”, which comprises an MMC connecting the AC system and

the DC system. The MMC has a conﬁgurable number of submodules per arm with a default value of

5. Every submodule is composed of one full-bridge and a DC-link capacitor and each single-phase pair

of converter arms, together with their arm inductors, is then connected to the AC grid. The converter

arms are implemented with the Full Bridges (Series Connected) power module library component.

This component has two conﬁgurations: a Switched implementation where ideal switches represent

the semiconductors, and an sub-cycle averaged conﬁguration that uses controlled voltage and current

sources. This model is conﬁgured to use the Sub-cycle averaged implementation of the power module

components which is suitable for ofﬂine and real-time simulation.

The implementation of both the power module and the PWM generation is such that the number of

cells can be conﬁgured with a variable num_sm in the Model initialization commands without having to

extend the model with additional wiring or components. This concept is called implicit vectorization of

the model structure and is further explained in the tutorial “Implicit Model Vectorization” available in

the tutorials section of the Plexim website.

Swa

PWM

Capture

PWMa

PWM

Out

Qa+1

Qa+4

Qa+2

Qa+3

U(I)

Qa-2

Qa-3

Qa-1

Qa-4

Swb

PWM

Capture

PWMb

PWM

Out

Qb+1

Qb+4

Qb+2

Qb+3

Qb-2

Qb-3

Qb-1

Qb-4

Swc

PWM

Capture

PWMc

PWM

Out

Qc+1

Qc+4

Qc+2

Qc+3

Qc-2

Qc-3

Qc-1

Qc-4

U(I)

PWMa1

PWM

Out

Swa1

PWM

Capture

PWMb1

PWM

Out

Swb1

PWM

Capture

PWMb2

PWM

Out

Swc1

PWM

Capture

Qa+3

Qa+4

Qa+1

Qa+2

Qa-3

Qa-4

Qa-1

Qa-2

V_3ph

Qb+3

Qb+4

Qb+1

Qb+2

Qb-3

Qb-4

Qb-1

Qb-2

Qc+3

Qc+4

Qc+1

Qc+2

Qc-3

Qc-4

Qc-1

Qc-2

V_dc

Model

Settings

Model

Settings

Model

Settings

Model

Settings

Model

Settings

Model

Settings

Model

Settings

UpperSide

LowerSide

Measurements

Figure 2: Schematic of the grid-connected MMC inverter

Tasking modes

In order to distribute the physical model on different CPU cores of the RT Box 2/3, the model has to be

split with the Task frame component from the PLECS library. The tasking mode can be conﬁgured in

the Coder Options in the Scheduling tab of the Coder Options window, as shown in Fig. 3.

Single-tasking If the Tasking mode is conﬁgured as single-tasking, all task frame components

are ignored and the physical system is executed in a single base task. This conﬁguration is needed for

real-time simulation of the demo model on the RT Box 1.

www.plexim.com 2

Modular Multilevel Converter

Figure 3: Scheduling task in the Coder Options

Multi-tasking If the Tasking mode is conﬁgured as Multi-tasking the physical model is split into

three different tasks and those tasks are associated with the three available CPU cores of the RT Box

2/3, as shown in Fig. 3.

The physical model is split as follows:

• Core 0: AC Grid and phase inductance/resistance and DC bus

• Core 1: All high-side sub-cells and DC-link capacitors

• Core 2: All low-side sub-cells and DC-link capacitors

To allow this system splitting, the physical model has to be split at strategic locations by using a

coupling circuit. To do so, a controlled current source is placed in one part of the model and a con-

trolled voltage source in the other part. Both sources are controlled by the respectively measured volt-

age/current state variables from the other part of the model. To avoid state/source dependence, one

measured signal has to be delayed by one discretization step. This approach is shown in Fig. 4.

z-1

Figure 4: Circuit to allow physical system splitting

The individual CPU load for each core becomes smaller and due to this, the average execution time

can be reduced considerably. A reduced discretization step size leads to a better frequency resolution,

www.plexim.com 3

Modular Multilevel Converter

and therefore ﬁdelity of the real-time simulation is improved.

2.2 Controls

The demo model is operated in open-loop. The PWM generation is executed in the same box and

routed to the digital output be means of the PWM Out block. Those PWM signals are then feed back

to the digital inputs by using a physical loop-back cable. The PWM signals are then brought into the

real-time simulation with the PWM Capture block.

3 Simulation

This model can run both in ofﬂine mode on a computer or in real-time mode on the PLECS RT Box.

Please follow the instructions below to run in real-time mode on an RT Box:

• Connect the Digital In interface to the Digital Out interface of the RT Box, i.e. by using a 37 pin

Sub-D cable.

• From the System tab of the Coder options... window, select the “Plant” and go to the Scheduling

tab. Chose either single-tasking or multi-tasking as the tasking mode and accept your choice.

Please note that multi-tasking mode is only available for RT Box 2 and RT Box 3.

• Return to the System tab, select the “Plant” and Build it onto the RT Box.

• Once the model is uploaded, from the External Mode tab, Connect to the RT Box and Activate

autotriggering.

During the real-time operation under External Mode the measurements can be observed using the

PLECS Scope “Measurements”. The arm voltage and AC grid currents are shown in Fig. 5.

Arm Voltage

Grid current

voltage (V)

-400

-200

200

400

× 1e-20.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5

current (A)

-1000

1000

Figure 5: Real-time measurements obtained on the RT Box in multi-tasking mode

4 Conclusion

This RT Box demo model demonstrates a grid-connected MMC inverter under open-loop control. The

demo model can run both in single-tasking mode on one CPU core of the RT Box 1, 2 or 3, or in multi-

tasking mode on three CPU cores of the RT Box 2 or 3. Multi-tasking has the beneﬁt that the average

execution time can be reduced considerably.

www.plexim.com 4

Revision History:

RT Box TSP 2.0.5 First release

How to Contact Plexim:

+41 44 533 51 00 Phone%

+41 44 533 51 01 Fax

Plexim GmbH Mail)

Technoparkstrasse 1

8005 Zurich

Switzerland

[email protected] Email@

http://www.plexim.com Web

RT Box Demo Model

The software PLECS described in this document is furnished under a license agreement. The software

may be used or copied only under the terms of the license agreement. No part of this manual may be

photocopied or reproduced in any form without prior written consent from Plexim GmbH.

PLECS is a registered trademark of Plexim GmbH. MATLAB, Simulink and Simulink Coder are regis-

tered trademarks of The MathWorks, Inc. Other product or brand names are trademarks or registered

trademarks of their respective holders.

Table of contents

Other Plexim Media Converter manuals