Grid Imposed Frequency VSC System

8/12/2019 Grid Imposed Frequency VSC System

http://slidepdf.com/reader/full/grid-imposed-frequency-vsc-system 1/27

1

DEMO TITLES

Grid-Imposed Frequency VSC SystemCase I: Voltage-Mode Control

Case II: Current-Mode Control

Case III: AFE Feeds a Grid-Imposed Frequency VSC System

Author: Tshibain TshibunguSimsmart Technologies Inc.

Brossard, Quebec

Canada

A-PDF Merger DEMO : Purchase from www.A-PDF.com to remove the watermark

http://www.a-pdf.com/

http://www.a-pdf.com/



2

1. OBJECTIVE AND DESCRIPTION

The following document will help the user in designing step by step controllers of a Grid-

Imposed Frequency VSC System using voltage or current mode control. A complete model of

AFE feeds a Grid-Imposed Frequency VSC System using current control mode will be simulated.

Three test cases are done in order to test and validate theories using the power electronics

components from the Engineering suite V6 Electrical library.

1.1. Grid –Imposed Frequency VSC System: Control in dq-frame

Two main methods exist for controlling the active power and reactive power in the VSC

system. The first mode is known as voltage-mode control and the second is known as current-

mode control. The following diagram shows the structure of a Grid-Imposed Frequency VSC

System.

The abc reference frame equations are given as follows:

(1)

(2)



3

The following Park transformation will be used to convert abc to dq synchronous reference

frame:

( ⁄ ⁄ ⁄ ⁄ ⁄ ⁄ ⁄ )

(4)

Transforming the following equations into dq synchronous reference frame, we have:

(5)

(6)

The active and reactive powers are given as follows:

[ ] (7)

[ ] (8)

Using a PLL (Phase Locked Loop) where in steady state

(9)

(10)

Voltage-Mode Control

Substituting from (9) and (10) into (5) and (6), we have:

(11)



4

(15)

Where

Thus, the PI controllers that control both powers are calculated using the IMC (Internal Model

Control) and are given as follows:

(16)

Where

Power response time constant

Switching frequency

A feed forward compensation is done in order to calculate and

Current-Mode Control

Using (5) and (6), we have:

Since , the above equations can be written as follows:



5

Thus, the PI controllers that control both currents are calculated using the IMC (Internal Model

Control) and are given as follows:

Where

Current time constant

Switching frequency

A feed forward compensation is done in order to calculate and

1.2. Diagram blocks

The diagram block of Voltage-Mode Control



6

The diagram block control of Current-Mode Control

2. PROCESSES DATA

Example I

Grid Voltage (cosine wave)

Inverter: IGBT with snubber



7

At t = 0.15 s the active power jumps to 1080 kW and t = 0.30 s the reactive power jumps to 520

kVAr.

Example II

Grid Voltage (cosine wave)

Inverter: IGBT with snubber

RL impedance

Initially the active and reactive powers are set to zero. At t = 0.002 s the active power is set to

2500 kW and 1000 kVAr at t = 0.06 s. At t = 0.1 s the active power jumps to -2500 kW.

Example III

A three phase voltage source supplies an AFE threephase rectifier that feeds the inverter of example II. Initially the inverter active and reactive

powers are set to zero. At t = 0.02 s the active power is set to 2500 kW and 500 kVAr at t = 0.1

s. At t = 0.18 s the active power jumps to -2500 kW.

The DC voltage is set to 1250 Volts. The IGBTs are modeled by ideal switches in parallel with

diodes. The capacitor . The AFE is designed in abc reference frame. The IGBTs

are triggered by a hysteresis control which is set to

.

The following parameters are used for the controllers:



8

3. CONTROLLERS DESIGN

Example I

Voltage-Mode Control Design

First of all, we have to calculate the impedance of the transformer seen from the primary side.

From the transformer parameters, we have:

Hence, the impedance of the transformer seen from the primary side is calculated as follows:

Second of all, we have to calculate the grid voltage seen from the primary side of the

transformer. Using a PLL (Phase Locked Loop) where in steady state , we have:

√ √

Where

Turn ratio of the transformer

F ti t t PI t ll th t t l b th l l t d i th



9

Current-Mode Control Design

Using the parameters calculated for Voltage-Mode Control, we have:

For a time constant , PI controllers that control both currents are:

The cross coupling terms for feedforward compensation are:

Example II

Voltage-Mode Control Design

Using a PLL (Phase Locked Loop) where in steady state , we have:

√ √

Where

Turn ratio of the transformer



10

Current-Mode Control Design

Using the parameters calculated for Voltage-Mode Control, we have:

For a time constant , PI controllers that control both currents are:

The cross coupling terms for feedforward compensation are:

Example III

Use controllers of current-mode

4. SIMULATION PARAMETERS

The simulation was run in time domain with sample time of



11

6. ENGINEERING SUITE V6 RESULTS

Example I: Voltage-Mode Control



12



13



14

Example I: Current-Mode Control



15



16



17

Example II: Case of Current-Mode Control



18



19



20

Example III: AFE feeds VSC System in Current-Mode Control



21



22



23



24

Conclusion

This document shows how to design controllers for grid-imposed frequency VSC system in

voltage-mode control and current-mode control.

7. REFERENCE BOOK

1. Voltage-Sourced Converters in Power Systems. Modeling,Control, and Applications.

A. Yazdani / R. Iravani.

GRID-IMPOSED FREQUENCY VOLTAGE SOURCED CONVERTER (VSC) SYSTEM:

CONTROL IN dq FRAME



3

3

A

I a

ΦI a

I b

ΦI b I

c

ΦI c

3

V

V a

Φ V a

C

T

V b

Φ V b

V c

Φ V c

3

Vdc / 2

CONTROL IN dq FRAME

Qref

K

K

Vid

Viq

∑

3

Yn Yn

33

K

Δ

Δ

ITL

ITL

∑ K

d

0

a

Φ

b

cq

∫sbb

saasG

10

10

)( ∑

C

Phase Locked Loop

To dq/abc transform

a

b

c

d

Φ

q

0

C

P

3

Pref

sb b

sa a s G

1 0

1 0

) (

sb b

sa a s G

1 0

1 0

) (

31

ab

c

3

A

I a

Φ I a I b

Φ I b I

c

Φ I

c

≥

≥

≥

ma

mb

mc

C

÷

÷

÷

Voltage-Mode Control

∑

∑





Documents

Grid Imposed Frequency VSC System