Phần 19 KHÓA ĐÀO TẠO TÍNH TOÁN ỔN ĐỊNH VÀ ỨNG DỤNG TRÊN PHẦN MỀM PSSE CHO KỸ SƯ HỆ THỐNG ĐIỆN (Mô phỏng đường dây siêu cao áp HDVC trong tính toán ổn định động)

Phần 19 KHÓA ĐÀO TẠO TÍNH TOÁN ỔN ĐỊNH VÀ ỨNG DỤNG TRÊN PHẦN MỀM PSSE CHO KỸ SƯ HỆ THỐNG ĐIỆN (Mô phỏng đường dây siêu cao áp HDVC trong tính toán ổn định động): • General Considerations• HVDC Dynamic Models HVDC Dynamic Models• Complete HVDC Model in Dynamic Studies

A Division of Global Power

POWER SYSTEM STABILITY CALCULATION TRAINING

D 8 HVDC Si l ti P t 2 Day 8 - HVDC Simulation Part 2

November 26, 2013 Prepared by: Mohamed El Chehaly

OUTLINE OUTLINE

• General Considerations

• HVDC Dynamic Models HVDC Dynamic Models

• Complete HVDC Model in Dynamic Studies p y

GENERAL CONSIDERATIONS

Introduction

 DC transmission behavior is dominated by

its controls

 It is not practical to model the detailed

dynamics of the controls because the

bandwidth of these controls is far greater

than that of PSS®E

than that of PSS®E

 Each converter bridge is controlled by a

local feedback loop

 These local loops work independently to

maintain bridge current or voltage at

maintain bridge current or voltage at

desired value

Introduction

 The desired values are provided by an

outer control loop that works in a

outer control loop that works in a

supervisory role and coordinates the

action of the several converter bridges

action of the several converter bridges

and the AC power system

Control Loops

 A rectifier bridge may be regarded as an

adjustable voltage source forcing current

through transmission system resistance

and inductance against the constant

voltage source of the inverter

Control Loops

 A simple current control: open-loop basis

with a gain equal to DC resistance

 A step change in current is applied

Control Loops

 DC rectifier is a feedback loop controller

that adjusts firing delay to control the DC

current to a setpoint

 A step change in current is applied eBook for You

PSS®E Models and Control Loops

 Several PSS®E models (CDC4T CDC6T )

PSS®E Models and Control Loops

 Several PSS®E models (CDC4T, CDC6T…)

treat DC converter pairs as if they move

point when any of their input signals are

changed

 HVDC dynamic models calculate the real

and reactive power loading of the

converters using steady-state converter

PSS®E Models and Control Loops

 Several models are not concerned with the

PSS®E Models and Control Loops

 Several models are not concerned with the

internal dynamic behavior of converters

and DC lines

and DC lines

models are not able to directly represent

the mode of operation where the rectifier

firing angle is not at a limit and the

inverter margin angle is also not at a limit

or controlling voltage (CDC4T, CDC6T…)

PSS®E Models and Control Loops

 HVDC models such as CDCVUP represent

PSS®E Models and Control Loops

p the temporary dynamic condition when

neither converter is at a firing angle or

margin angle limit and both are fighting for

control of current

 PSS®E l i l d d l (CASEA1 d

 PSS®E also include models (CASEA1 and

CDCRL) that represent some

shorter than by other PSS®E models

Actions by the Controls

 Three distinct types of action by the

Actions by the Controls

controls

 Normal regulation of DC converter operation to

maintain specified constant current or constant

power transfer with coordination of rectifier and

inverter current setpoints

 Temporary overriding of DC converter normal

operating setpoints in response to disturbances of

AC system voltages during faults

 Modulation of the DC power setpoint by a

supplementary control device (assist in the

supplementary control device (assist in the

damping of rotor angle swings)

Actions by the Controls

 Normal regulation

Actions by the Controls

g

 With sufficient AC voltage for alpha control

Actions by the Controls

 Normal regulation

Actions by the Controls

g

 With depressed AC voltage

Actions by the Controls

 Response following disturbance

 When AC or DC voltages reach abnormal levels

Actions by the Controls

 When AC or DC voltages reach abnormal levels

that may cause commutation failures, excessive

currents or unacceptable harmonics

 PSS®E DC models execute these overriding

control actions when positive sequence AC

voltages or DC voltages reach specified levels

 The modeling of protective action is not possible

The protection of DC converter is dependent on individual phase-to-ground and phase-to-phase voltage wave forms and these are not available in PSS®E

The protection of each bridge is determined by the internal details of firing controls with a low-frequency band

Protective Actions

 Block

 Protective blocking is used to stop the flow of both

Protective Actions

 Protective blocking is used to stop the flow of both

AC and DC current in order to limit the effect of the

fault

 Rectifier usually blocked when an AC fault is

applied on the AC side of the rectifier

 This is achieved by simply removing the firing

pulses to all the valves in the converter

 Blocking can be simulated by changing the g y g g

appropriate ICON or by raising the blocking

voltage threshold to force a block

Abnormal firing angle or misfire

 Provides a DC short circuit across the converter

 Provides a DC short-circuit across the converter

bridge

 Blocking four valves in the 6-pulse bridge and

firing the remaining two as a bypass pair

 The DC side is shorted and the AC side is open

Protective Actions

 Commutation failure

 May occur following an AC system disturbance

Protective Actions

 May occur following an AC system disturbance

close to the inverter station

 Probability increased when voltage on the AC side y g

of the inverter is decreased by 0.1 p.u

 Repeated commutation failures can lead to

blocking of the valves

 Happen if the commutation of current from one

the commutating voltage reverses across the

ongoing valve

 Extinction angle is too small

Protective Actions

 Commutation failure

 Equivalent circuit for three phase bridge converter

Protective Actions

 Equivalent circuit for three-phase bridge converter

Protective Actions

 Commutation failure

 Due to voltage magnitude reduction

Protective Actions

 Due to voltage magnitude reduction

Protective Actions

 Commutation failure

 Due to increased DC current

Protective Actions

 Due to increased DC current

HVDC DYNAMIC MODELS eBook for You

Model CDC4

Model CDC4

 Ranges of alpha and gamma angles in

power flow and dynamics

Model CDC4

Model CDC4

 Changing VSCHED, SETVAL and MDC can

only be done in power flow

Model CDC4

Model CDC4

 CDC4 i t i th d i d t t

 CDC4 maintains the desired constant

voltage stays above VCMODE

 If the DC voltage falls below VCMODE, the

DC model switches to nominal current

 Can be reset to constant power control if Ca be eset to co sta t po e co t o

DC voltage is above VCMODE and after a

time delay TCMODE

Model CDC4

Model CDC4

 CDC4 d l t ti t k b th DC

 CDC4 models two actions taken by the DC

converters during AC system

disturbances

 The rectifier and inverter are both blocked if the

AC voltage at the rectifier falls below the per unit

value VBLOCK

 The inverter bypass switch is closed if the inverter

end DC voltage falls below the kV value VBYPAS

The rectifier continues to maintain DC current at

scheduled value

Model CDC4

Model CDC4

 Blocking mode

 Low DC voltage does not cause blocking of the

 Low DC voltage does not cause blocking of the

rectifier unless the rectifier AC voltage is low

Model CDC4

Model CDC4

 Blocking mode

 If blocked the rectifier remains blocked for a

 If blocked, the rectifier remains blocked for a

minimum of TBLOCK

Model CDC4

Model CDC4

 Blocking mode

 It may restart if the AC voltage is above VUNBL

Model CDC4

Model CDC4

 Bypassing mode

 If bypassed the inverter remains bypassed for a

 If bypassed, the inverter remains bypassed for a

minimum of TBYPAS

Model CDC4

Model CDC4

 Bypassing mode

 Low AC voltage at the inverter does not cause

 Low AC voltage at the inverter does not cause

bypassing unless the inverter DC voltage is low

Model CDC4

Model CDC4

 Bypassing mode

 It may restart if the AC voltage is above VUNBY

Model CDC4

Model CDC4

 Ramp-up following a block or bypass

 Ramp defined by VRAMP for voltage and CRAMP

 Ramp defined by VRAMP for voltage and CRAMP

for current

 The voltage and current will instantaneously g y

increase to RSVOLT and RSCUR

Model CDC4

Model CDC4

 Ramp-up following a block or bypass

 Slow ramp up can lead to instability at the inverter

 Slow ramp-up can lead to instability at the inverter

due to the lack of enough real power

 Fast ramp-up can lead to multiple commutation p p p

failures

 Includes additional protection from the

proposed modern lines

 More suitable to model commutation failures

 Different power control mode than CDC4 p

 It will use measured voltage rather than measured

current for power control if the power output is

set at the rectifier end

Model CDC6

Model CDC6

 Blocking and unblocking schemes

Auxiliary Signal Models

Auxiliary Signal Models

 Based on bus frequency deviation

Auxiliary Signal Models

Auxiliary Signal Models

 PAUX1T: Frequency sensitive auxiliary

 PAUX1T: Frequency sensitive auxiliary

model

Auxiliary Signal Models

Auxiliary Signal Models

 PAUX2T: Bus voltage angle sensitivity

 PAUX2T: Bus voltage angle sensitivity

auxiliary signal model

Auxiliary Signal Models

Auxiliary Signal Models

 DCVRFT: HVDC AC voltage controller

Auxiliary Signal Models

Auxiliary Signal Models

 HVDCAT: General purpose auxiliary signal

 HVDCAT: General purpose auxiliary signal

model

Model CDC6T Data

Model CDC6T Data

Model CDC6T Data

Model CDC6T Data

Model CDC6T Data

Model CDC6T Data

Model CDC6T Variables for Pole 1

Model CDC6T Variables for Pole 1

Model CDC6T Variables for Pole 2

Model CDC6T Variables for Pole 2

Test Model CDC6T (HVDC test dyr)

Test Model CDC6T (HVDC test.dyr)

 Apply a three-phase fault at the rectifier

QUESTIONS?

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