Current Balancing Algorithm for Three-Phase Multilevel Current Source Inverters

Abstract

In high power, medium voltage applications, Current Source Inverters CSIs are connected in parallel to accommodate high DC currents. Using a proper multilevel modulation technique, parallel-connected CSIs can operate as a Multilevel CSI (MCSI). The most common modulation technique for MCSIs is the Phase-Shifted Carrier SPWM (PSC-SPWM). The proper operation of the MCSI requires each CSI modules to have the same average current flowing through its sharing inductors. In practice, the average currents of the CSI modules deviate from their nominal values. Therefore, current balancing mechanisms must be implemented. In the literature, several solutions have been proposed to tackle the current imbalance problem. Most of these solutions are based on altering the phase-shift or magnitude of the carrier waveforms of the PSC-SPWM. They require dedicated PI controllers and they are applicable to MCSIs with specific numbers of levels. This paper proposes a Current Balancing Algorithm (CBA) that can be implemented in any MCSI with any number of levels. The proposed CBA does not require any PI controllers, nor does it require any alteration to the PWM carrier waveforms. The CBA is implemented using a modified Level-Shifted SPWM (LS-PWM). The modified LS-SPWM is shown to produce lower THD and lower di/dt when compared to the PSC-SPWM. The CBA and modified LS-SPWM where implemented in a proof-of-concept lab prototype. The experimental results are presented for the five-level and seven-level cases.

Future Renewable Energy Communities Based Flexible Power Systems

“…An MCSC STATCOM that has M CSCs can produce a waveform that has a 2M + 1 levels. The PWM technique used in the individual CSC modules is the same as the so-called "tri-logic" PWM proposed in [50]. To synthesize multilevel waveforms, the Phase-Shifted Carrier PWM (PSC-PWM) is used [51], where the phase-shift between any two adjacent carrier waveforms is set to 2π/M.…”

“…To synthesize multilevel waveforms, the Phase-Shifted Carrier PWM (PSC-PWM) is used [51], where the phase-shift between any two adjacent carrier waveforms is set to 2π/M. In [50], the Current-Source Modular Multilevel Converter (CSMMC) is introduced as the current-source dual of the voltage-source Modular Multilevel Converter (MMC). A CSMMC-based STATCOM is studied in detail in [50].…”

“…In [50], the Current-Source Modular Multilevel Converter (CSMMC) is introduced as the current-source dual of the voltage-source Modular Multilevel Converter (MMC). A CSMMC-based STATCOM is studied in detail in [50]. Each phase leg of the CSMMC is split into an upper arm and a lower arm.…”

“…The submodule inductors are sized to accommodate energy variations at the fundamental and double frequencies. Compared to the MCSC STATCOM, the CSMMC STATCOM requires sized inductors and a few more components [50]. Multilevel current source-based converters have many advantages for grid-connected converters at higher voltage sub-transmission levels, and further advances initially made by the authors [50] will be reported in near future.…”

Yenilenebilir Enerji Kaynaklarına Dayalı Bir Sistemde Güç Kalitesi Analizi, Kontrolü ve İzlemesi

“…Reaktif güç dengeleyici ise, gerilim dalgalanması ve titremeyi baskılayabilir. Dağıtım şebekesinde kullanıma hazır değişken dengeleyicileri arasında sabit kapasitör (SK) [30,31], statik değişken dengeleyiciler (SDD) [32,33] ve statik senkron dengeleyiciler (STATCOM) [34,35] bulunur. Bu cihazlar arasında STATCOM, şebeke gerilimi dalgalanması bastırma ve dengesiz yük dengeleme gibi çoklu fonksiyonlara sahip olduğu için yaygın olarak kullanılmaktadır.…”