grid imposed frequency vsc system
TRANSCRIPT
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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
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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)
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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)
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(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:
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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
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The diagram block control of Current-Mode Control
2. PROCESSES DATA
Example I
Grid Voltage (cosine wave)
Inverter: IGBT with snubber
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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:
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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
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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
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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
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6. ENGINEERING SUITE V6 RESULTS
Example I: Voltage-Mode Control
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Example I: Current-Mode Control
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Example II: Case of Current-Mode Control
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Example III: AFE feeds VSC System in Current-Mode Control
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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
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