25-05-2012, 12:45 PM
EFFECTS OF DSTATCOM DEVICES ON THE DYNAMIC PERFORMANCE OF DISTRIBUTION SYSTEMS
[attachment=22984]
INTRODUCTION
This project presents a dynamic study about the influences of ac generators (induction and synchronous machines) and distribution static synchronous compensator
The most common type of distributed generation employs ac rotating machines.
The performance of a DSTATCOM as a voltage controller or a power factor controller is analyzed.
DSTATCOM (Distribution Static Var Compensator) consists of Voltage Source Converter.
A representative example of such devices is the distribution static synchronous compensator (DSTATCOM).
It is primarily used to Control reactive power and Voltage regulation.
It can eliminate Current Harmonics, correction of power factor
DSTATCOM
A DSTATCOM is a controlled reactive source
It includes a voltage source converter and a DC link capacitor connected in shunt.
It is capable of generating and /or absorbing reactive power.
The distribution STATCOM is similar to transmission STATCOM in that it uses a VSC of the required rating.
A voltage source converter is a power electronic device, which can generate a sinusoidal voltage with any required magnitude, frequency and phase angle.
DSTATCOM in Power Distribution Systems
A DSTATCOM is capable of compensating either bus voltage or line current.
If it operates in a voltage control mode, it can make the voltage of the bus a balanced sinusoid irrespective of the unbalance and distortion in the voltage of the supply side or line current.
Similarly when operated in current control mode it can force the source side current to become balanced sinusoids.
Simplified Model
In the simplified model, the converter, the PWM signal generator, and the filter are replaced by a set of three controllable ac voltage sources.
Such sources are controlled by the signal obtained from the controller, which may be either a voltage controller or a power factor controller.
However, the three-phase voltages at the converter output, in volts, are dependent on the dc link voltage [8](ie:
Induction Generator: (Three-phase-to-ground short circuit)
A three-phase-to-ground short circuit was applied at bus 4 at t=0.5s and eliminated after nine cycles (150 ms) by tripping branch 2–4.
In this case, the induction generator was injecting 25 MW into the network at the fault instant.
The generator terminal voltage responses for this contingency are shown in Fig below. It can be verified that the three situations (i.e., without DSTATCOM, with DSTATCOM voltage controller, and with DSTATCOM power factor controller are stable).
However, only with the DSTATCOM, the terminal voltage is rapidly recovered to approximately 1p.u. after fault elimination, whereas without the DSTATCOM, the post fault terminal voltage is equal to0.942 p.u.
In addition, when the DSTATCOM is controlled by the power factor, the prefault terminal voltage is larger than 1p.u. because the controller goal is to keep the unitary power factor.
The rotor speed responses are exhibited in Fig. It can be seen that all cases present a good damping, confirming the fact that the transients of induction generators are very fast.
Note that the pre and post fault rotor speeds are different from each other due to the distinct values of the terminal voltage.
CONCLUSION
The main conclusions obtained from this work are the following.
The DSTATCOM voltage controller has significantly improved the voltage stability performance of induction generators without increasing the short-circuit currents provided by them.
On the other hand, a DSTATCOM power factor controller does not provide any dynamic performance gain.
In a distribution system suffering from short-circuits level and stability constraints, the installation of an induction generator combined with a DSTATCOM voltage controller is a proved to be a good choice for distributed generation expansion.
[attachment=22984]
INTRODUCTION
This project presents a dynamic study about the influences of ac generators (induction and synchronous machines) and distribution static synchronous compensator
The most common type of distributed generation employs ac rotating machines.
The performance of a DSTATCOM as a voltage controller or a power factor controller is analyzed.
DSTATCOM (Distribution Static Var Compensator) consists of Voltage Source Converter.
A representative example of such devices is the distribution static synchronous compensator (DSTATCOM).
It is primarily used to Control reactive power and Voltage regulation.
It can eliminate Current Harmonics, correction of power factor
DSTATCOM
A DSTATCOM is a controlled reactive source
It includes a voltage source converter and a DC link capacitor connected in shunt.
It is capable of generating and /or absorbing reactive power.
The distribution STATCOM is similar to transmission STATCOM in that it uses a VSC of the required rating.
A voltage source converter is a power electronic device, which can generate a sinusoidal voltage with any required magnitude, frequency and phase angle.
DSTATCOM in Power Distribution Systems
A DSTATCOM is capable of compensating either bus voltage or line current.
If it operates in a voltage control mode, it can make the voltage of the bus a balanced sinusoid irrespective of the unbalance and distortion in the voltage of the supply side or line current.
Similarly when operated in current control mode it can force the source side current to become balanced sinusoids.
Simplified Model
In the simplified model, the converter, the PWM signal generator, and the filter are replaced by a set of three controllable ac voltage sources.
Such sources are controlled by the signal obtained from the controller, which may be either a voltage controller or a power factor controller.
However, the three-phase voltages at the converter output, in volts, are dependent on the dc link voltage [8](ie:
Induction Generator: (Three-phase-to-ground short circuit)
A three-phase-to-ground short circuit was applied at bus 4 at t=0.5s and eliminated after nine cycles (150 ms) by tripping branch 2–4.
In this case, the induction generator was injecting 25 MW into the network at the fault instant.
The generator terminal voltage responses for this contingency are shown in Fig below. It can be verified that the three situations (i.e., without DSTATCOM, with DSTATCOM voltage controller, and with DSTATCOM power factor controller are stable).
However, only with the DSTATCOM, the terminal voltage is rapidly recovered to approximately 1p.u. after fault elimination, whereas without the DSTATCOM, the post fault terminal voltage is equal to0.942 p.u.
In addition, when the DSTATCOM is controlled by the power factor, the prefault terminal voltage is larger than 1p.u. because the controller goal is to keep the unitary power factor.
The rotor speed responses are exhibited in Fig. It can be seen that all cases present a good damping, confirming the fact that the transients of induction generators are very fast.
Note that the pre and post fault rotor speeds are different from each other due to the distinct values of the terminal voltage.
CONCLUSION
The main conclusions obtained from this work are the following.
The DSTATCOM voltage controller has significantly improved the voltage stability performance of induction generators without increasing the short-circuit currents provided by them.
On the other hand, a DSTATCOM power factor controller does not provide any dynamic performance gain.
In a distribution system suffering from short-circuits level and stability constraints, the installation of an induction generator combined with a DSTATCOM voltage controller is a proved to be a good choice for distributed generation expansion.