Lateral Current Reduction by Voltage Drop Compensator for Multiple Autonomously Controlled UPS Connected in Parallel

Sato, Eduardo Kazuhide; Kawamura, Atsuo

doi:10.1541/ieejias.125.934

Cited by 1 publication

(3 citation statements)

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“…We call the term k cÎq as the voltage drop compensator, because it counterbalances the voltage drop caused by k qÎq (12) (13) .…”

Section: Control Of Output Voltage Amplitudementioning

confidence: 99%

“…Some oscillation is observed during transients, so that a lowpass filter, (13) and (14), with a cut-off frequency a is employed after (11) and (12).…”

Section: Control Schemementioning

confidence: 99%

“…Remembering that lowpass filters are used in the computation of the active and reactive currents, we include (13) and (14) in (15) and (16). Thus, it yields, in the time domain,…”

Section: Control Equationsmentioning

confidence: 99%

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Design of an Autonomous Control for Parallel-Connected Uninterruptible Power Supplies

Sato

Kawamura

2006

IEEJ Trans. IA

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Some inherent characteristics of an electrical power system can be conveyed to control multiple uninterruptible power supplies (UPS) connected in parallel in an autonomous manner, i.e. without communication signal exchange. It results in an independent control with two control equations, where the controllable variables are the phase angle and the magnitude of the output voltage.The dynamic equation of a synchronous machine relates frequency of operation and active output power, so that it evolves to the control equation of output voltage phase angle hs:Note that, to deliver the value of the phase angle hs, Eq. 1 only requires information about the active currentÎ p .With respect to another control equation, from the existing relation between voltage magnitude and flow of reactive power, computer simulations using an elementary circuit for two voltage sources connected in parallel show a relation between lateral current (or circulating current) and voltage difference. With employment of (1), circulating current becomes only reactive. It suggests a control equation for output voltage amplitude dv by using the calculation of reactive currentÎ q as follows:where the term k cÎp constitutes the voltage drop compensator to reduce the effect of gain k q .(1) and (2) provide suitable values of phase angle and magnitude, respectively, of the output voltage v, which isIt means that, with only the measurement of the output current, control scheme calculates and filters (with a lowpass filter) the active and reactive components of the measured current; computes the phase angle hs and amplitude dv by using (1) and (2); and delivers a output voltage reference signal in order to achieve stability and load sharing.A small-signal model, which combines control and circuit equations, constitutes the theoretical proof for stability. It consists in a matrix state equation, where the locus of the eigenvalues give information about the stability of a parallel-connected UPS system and aid the selection of the control gains in a stable point. This equation also includes modeling for the voltage limiters and the voltage drop compensator.Gains of the control equations are also adjusted according to the output power rating, i.e.Doing that, it enables the employment of this control even for multiple UPSs with different ratings.Experimental results, using three UPSs connected in parallel with different output power ratings (the ratio is 6 : 3 : 2) and voltage limiters (±1%), confirm stable operation and good load sharing. The proposed independent control was implemented in a digital signal processor (DSP). Atsuo Kawamura * Member This paper proposes an autonomous control for parallel-connected uninterruptible power supply (UPS) systems based on electrical power system interrelations. The controllable variables are the output voltage phase angle and magnitude. Relation between active current and output voltage phase angle is derived from a synchronous machine model. Electrical power systems suggest that voltage regulation and reactive curren...

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“…We call the term k cÎq as the voltage drop compensator, because it counterbalances the voltage drop caused by k qÎq (12) (13) .…”

Section: Control Of Output Voltage Amplitudementioning

confidence: 99%

“…Some oscillation is observed during transients, so that a lowpass filter, (13) and (14), with a cut-off frequency a is employed after (11) and (12).…”

Section: Control Schemementioning

confidence: 99%