Control of Parallel Three-Phase PWM Converters Under Generalized Unbalanced Operating Conditions

Abstract

This paper proposes a new control scheme for parallel three phase pulse width modulation (PWM) converters under generalized unbalanced operating conditions. An average model of the parallel system in positive-sequence synchronous reference frame (PSRF) is derived to analyze the influence of generalized unbalanced operating conditions in AC side. It is seen that the unbalance factors in filter inductance will not only give rise to negative-sequence circulating current, but also contribute to generating zero-sequence circulating current(ZSCC). The negative-sequence circulating current can be inhibited by suppressing the negative-sequence components in AC output currents of parallel modules with a proportional integral resonant (PIR) controller. An improved feed-forward strategy and a PIR controller for ZSCC control are proposed for unbalanced operating conditions. The disturbances in ZSCC caused by unbalance factors in filter inductance can be rejected with feed-forward strategy. Because the disturbance in ZSCC is the fluctuation in grid frequency which can be suppressed by resonance controller, so a PIR controller is adopted in ZSCC controller. The proposed scheme can effectively suppress the circulating currents between the parallel modules and as a result, the distortions in output currents can be greatly reduced. Experimental results confirm the performance and effectiveness of the proposed method.

Circulation suppression of synchronous/interleaving paralleled 400 Hz three‐phase four‐leg inverter based on third harmonics injection

“…Circulating current can be decoupled into positive, negative, and zero-sequence components as discussed in [24], according to above conclusion, (20) can be derived, and circulating current between two paralleled neutral legs can be derived as (21)…”

Finite-Time Disturbance-Observer-Based Integral Terminal Sliding Mode Controller for Three-Phase Synchronous Rectifier

“…Assuming a balanced three-phase source as reference leads to having only the direct axis component of Ed while the other component is zero (Eq = 0). After substituting (9) in (8), the non-linear state-space equation (10), which describes the dynamic behaviour of SR, can be derived from (7)(8)(9).…”

“…The third model for SR introduced in the synchronous rotational reference frame (dq), to avoid using PR controller. Because of working with DC values, this is a popular controller for SR [7][8][9][10][11][12][13][14][15][16][17], modeling and control of power converters in microgrids have been investigated in [7], and a droop control technique is proposed for active power flow control of converters based on multiple PI controller loops in dq frame. A combination of fuzzy-model-based control and adaptive sliding mode technique has been proposed for the uncertain estimation of a three-phase AC/DC converter in [8].…”

“…Also, this method does not possess disturbances observer and may not show appropriate performance in uncertain conditions. Controller of parallel three-phase PWM converters under generalized unbalanced operating conditions is developed in dq frame in [9]. The authors found a solution for reducing the amount of zero and negative sequence currents due to the unbalance voltage source.…”

Enhanced Circular Chain Control for Parallel Operation of Inverters in UPS Systems

“…To avoid circulating current, the output voltages of the parallel inverters should be synchronized in terms of amplitude and phase, and obviously, the frequency of the output voltages should be the same [4]. In addition, voltage limits of the dc-link capacitors have to be considered in case input rectifiers are unidirectional, which may face excessive voltages due to active power absorption by some inverters because of circulating currents [3,5].…”