What are the advantages and disadvantages of using power system stabilizers (PSS) to damp out oscillations?

1 How PSS work

PSS work by sensing the speed or power variations of the generator and sending a feedback signal to the excitation system. The feedback signal modifies the voltage reference of the exciter, which in turn affects the terminal voltage and the reactive power output of the generator. The feedback signal is tuned to have a phase lead or lag depending on the direction and frequency of the oscillation, so that it can counteract the effect of the disturbance and restore the equilibrium of the power system.

2 Advantages of PSS

One of the main advantages of PSS is that they can enhance the damping of the power system without affecting the steady-state operation. PSS can also increase the power transfer capability and the stability margin of the system by preventing or reducing the risk of losing synchronism among the generators. PSS can also improve the voltage regulation and the transient response of the system by compensating for the lagging effect of the exciter. Moreover, PSS are relatively easy to install and maintain, as they do not require major modifications to the existing equipment or network.

3 Disadvantages of PSS

However, PSS also have some drawbacks that need to be considered. One of them is that PSS can introduce undesirable interactions or resonances with other control devices or system components, such as governors, transformers, or transmission lines. These interactions can reduce the effectiveness or even destabilize the system if not properly accounted for. Another drawback is that PSS can be sensitive to parameter variations or uncertainties, such as changes in load, generation, or network configuration. These variations can affect the performance or tuning of the PSS and require periodic adjustments or re-designs. A third drawback is that PSS can be vulnerable to faults or failures, such as loss of sensor signals, communication errors, or hardware malfunctions. These faults or failures can cause the PSS to malfunction or lose its functionality, which can compromise the stability or security of the system.

4 Alternatives to PSS

To improve the damping of power system oscillations, some alternatives or complementary methods have been proposed or implemented. These include Flexible AC transmission systems (FACTS) devices, such as static VAR compensators (SVC), static synchronous compensators (STATCOM), or unified power flow controllers (UPFC). Additionally, Power system damping controllers (PSDC) and Wide-area measurement systems (WAMS), such as phasor measurement units (PMU) or synchrophasors, can provide real-time and synchronized data of system states. Lastly, Wide-area control systems (WACS), such as phasor-based controllers (PBC) or coordinated voltage control (CVC), can design and implement optimal or adaptive control strategies for damping oscillations or enhancing stability.

5 How to choose PSS

When deciding between PSS or any alternative method, several factors must be taken into account, such as the characteristics and objectives of the power system, the availability and cost of resources and technologies, and the trade-offs and constraints involved. To evaluate and compare different options, criteria such as effectiveness, robustness, compatibility, flexibility, reliability, efficiency, and affordability should be considered. Effectiveness determines how well the method can damp out oscillations and improve stability. Robustness evaluates how resilient the method is to parameter variations or disturbances. Compatibility assesses how compatible the method is with other control devices or system components. Flexibility examines how adaptable the method is to changes in load or network configuration. Reliability looks at fault tolerance, redundancy, or protection. Efficiency evaluates power consumption, losses, or emissions. Finally, affordability measures capital, operation, or maintenance costs.

6 Here’s what else to consider

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