Nilesh Modi

Frequency response and its enhancement using synchronous condensers in presence of high wind penetration

In recent years wind power integration has substantially increased in southern states of Australia. At present South Australia has the highest wind generation capacity of any region across the country. This large capacity penetration would likely displace existing synchronous generation fleet. These wind generators have neither enough inertia response nor governor support to control major frequency excursion. Under high wind power availability and cheaper import from neighboring region, South Australian grid could depend on few synchronous machines for frequency regulation. Under such a scenario, a big contingency may produce a severe frequency excursion in the network. Consequently, system may face a considerable amount of load shedding, which may degrade the standard of network service quality. To understand these issues, this paper investigates frequency response of a power system in presence of high wind penetration. The network under consideration loosely represents South Australian power system. Additional frequency control strategy, such as deployment of synchronous condensers to enhance network frequency response is also studied.

Revisiting damping performance of the queensland network under wind power penetration

To meet Australian renewable energy target of generating 20% of renewable energy by 2020, large scale wind farms are being planned to be connected to the Queensland network. Considering this large scale wind power integration, it is of prime importance to investigate its influence on power system stability. In this paper, small-signal stability of the Queensland network has been re-visited considering near future wind power penetration. The expected wind power is integrated to the nearest available high voltage bus of the grid via step up transformer and transmission line with appropriate capacity. Aggregated doubly fed induction generator model is used to simulate wind farms. This paper investigates the impact of wind power integration on the damping of electromechanical modes of the Queensland grid. Wind power is accommodated by considering load growth and generator displacement individually for getting useful insight into its impact on damping of the grid. The sensitivity of the system damping performance under large scale wind power integration is assessed and presented through eigenvalue analysis. PSS/E and Mudpack software is used to carry out simulations.

Performance of power oscillation damping controllers with different static load characteristics

Low-frequency inter-area oscillations are threat to secure operation of power systems. Power system stabilizer and Power oscillation damping controllers are used to provide damping to oscillatory modes. Such oscillatory modes, inter-area modes in particular, are significantly affected by change in operating conditions and load characteristics. In this paper, influence of load characteristics on performance of two distinct power oscillation damping controllers is being examined. The interaction between load characteristic and performance of power oscillation damping controller is explored in terms of damping contribution by individual controller on inter-area mode. Eigenvalue analysis approach is used to evaluate the performance of power oscillation controllers, which are designed based on residue compensation technique and H∞ loop-shaping technique respectively. This paper also addresses the dynamic behaviour of the two controllers under different operating conditions and load characteristics.

Impact of load frequency dependence on frequency response of a power system with high non-synchronous penetration

Due to significant development of renewable energy sources, such as wind and photovoltaic (PV), conventional synchronous generators are being economically replaced from the traditional generation mix. Modern wind turbine and PV generators are non-synchronous machines, which usually do not provide inherent inertia and governor control to arrest frequency excursion after a major disturbance. Thus, presence of such high non-synchronous generation may introduce a challenge to maintain system frequency within the satisfied limits following a large generator or an interconnection trip. In addition to non- synchronous penetration level, frequency response of a power system may have significant reliance on frequency dependent loads. These loads, for example induction motors consume less power when there is a fall in system frequency. It facilitates faster arrest of frequency decline after a contingency. As a result, frequency response of a power system may enhance. This paper investigates the effects of load frequency dependence on frequency response of a power system in presence of high non- synchronous generation. It also quantifies the amount of load relief and under frequency load shedding, which a system may encounter after a severe disturbance. In this context, a low inertia power system that loosely resembles the South Australian network is investigated and reported.

Decentralized power system damping controller design using H ∞ loop-shaping technique

Power system low frequency oscillations influence dynamic behaviour of a complex power system and threaten its security. The dynamic performance of power system can be improved by damping low frequency oscillation with the help of supplementary controllers. This paper presents the design of supplementary controller for Static Var Compensator (SVC) to damp low frequency, in particular inter-area oscillations. The controller is designed based on H∞ loop-shaping technique in which the robust stabilization of the normalised coprime factor plant is formulated into a generalized H∞ problem. Moreover, the selection of proper feedback signal from the available measurements of the system plays vital role in designing the controller. The residue analysis is used to select the suitable locally available signal as an input signal to the proposed controller. Two power systems with varying sizes and complexities are used to test with the design of the proposed controller. The power systems include the benchmark, two-area system for low frequency oscillation studies and a modified version of a practical system. Both eigenvalue analysis and time domain simulations are used to study the performance of the proposed H∞ controller.