Research on Shaft Subsynchronous Oscillation Characteristics of Parallel Generators and SSDC Application in Mitigating SSO of Multi-Generators

Abstract

Subsynchronous oscillation (SSO) of generators caused by high voltage direct current (HVDC) systems can be solved by applying supplemental subsynchronous damping controller (SSDC). SSDC application in mitigating SSO of single-generator systems has been studied intensively. This paper focuses on SSDC application in mitigating SSO of multi-generator systems. The phase relationship of the speed signals of the generators under their common mechanical natural frequencies is a key consideration in SSDC design. The paper studies in detail the phase relationship of the speed signals of two generators in parallel under their shared mechanical natural frequency, revealing regardless of whether the two generators are identical or not, there always exists a common-mode and an anti-mode under their common natural frequency, and the phase relationship of the speed signals of the generators depends on the extent to which the anti-mode is stimulated. The paper further demonstrates that to guarantee the effectiveness of SSDC, the anti-phase mode component of its input signal should be eliminated. Based on the above analysis, the paper introduces the design process of SSDC for multi-generator systems and verifies its effectiveness through simulation in Power Systems Computer Aided Design/Electromagnetic Transients including Direct Current (PSCAD/EMTDC).

Phase-Controlled Thyristor Sub-Synchronous Damper Converter for a Liquefied Natural Gas Plant

“…The electrical and control system parameters of the proposed SSD are reported in Table 3. Considering the generic TNF, it could be possible to adopt a simpler control strategy as previously proposed in [13,17,21] where: a constant value of ϕ SSD is set to verify the condition in (16); ϕ SG could be exactly determined through the SG electrical parameters; and ϕ PCC could be estimated, for example, through time-domain simulation software [17]. However, the assessment of ϕ PCC depends on the equivalent network impedance.…”

“…The SSD converter insertion reduces the torque oscillation at 5% of the initial value in 5.9 s. In Figure 5, the limit of 5% is marked with a red area. Assuming the same operating conditions, the performance of the proposed control method is compared with the results related to the damping techniques presented in [14,17]. The main difference between the proposed SSD control system (Figure 2) and the methods used [14,17] is the adaptive reference phase control.…”

“…Considering the LNG plant configurations examined in [2], in this paper a subsynchronous damper (SSD) based on a thyristor rectifier is presented to mitigate torsional oscillations. The power converter is controlled to provide an additional torque oscillation at the air-gap of the TG unit, as introduced in [16] and developed in [17]. The additional torque can be expressed as the sum of the synchronous torque and the damped torque, in accordance with the complex torque coefficient method.…”

“…It is common practice [13,17,21] to operate the SSD with a constant phase. Unfortunately, this approach allows for satisfying performance only for a set of the power system possible configurations.…”

Parameter identification of subsynchronous oscillation based on FastICA and MP algorithms

“…When the sending AC system or DC system is disturbed, a kind of energy exchange between the DC control system and the shaft system of rectifier thermal power unit system is possible. If there is a negative feedback in this energy exchange, serious subsynchronous oscillation (SSO) might be experienced by thermal power units [5–7].…”