Adaptive Zero-Sequence Voltage Injection for Modular Solid-State Transformer to Compensate for Asymmetrical Fault Conditions

Unruh, Roland; Lange, Jarren Hilton; Schafmeister, Frank; Böcker, Joachim

doi:10.23919/epe21ecceeurope50061.2021.9570542

Cited by 5 publications

(6 citation statements)

References 36 publications

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“…Such a modulation strategy is known in literature within the context of non-modular/monolithic three-phase PFC acdc converters [21] (featuring a single dc output voltage) and cascaded modular H-bridge converters [20], and the CM voltage ūCM,opt increases the LF module input power pa in the vicinity of ωt = 30 • and decreases pa around ωt = 90 • compared to pa,0 representing the LF input power for conventional operation as comparison.…”

Section: Optimal CM Voltage Waveform Resultsmentioning

confidence: 99%

“…7. Considered PFC rectifier control structure comprising the saturable CM voltage modulator from [20,25] setting uCM,s such that in each module x the LF switch node voltage ūx N(t) remains below the limit imposed by the dc-link voltage U dc,x (t), i.e., ūx In closing it can be stated that the optimal CM modulation of Sec. II-C enables operation with lower dc-link capacitor values C dc and/or lower average dc-link voltage Ūdc compared to conventional operation and the goal is hence to verify these findings in practice.…”

Section: Minimum Dc-link Voltage / Capacitance Operationmentioning

confidence: 99%

“…INJECTION MODULATION The identified optimum modulation requires a special control structure for the three PFC rectifier front-ends [20]- [23,25] as for a given point in time one out of three phases completely ceases switching and clamps the switch node potential to either the positive or negative dc-link rail and the remaining two phases realize sinusoidal three-phase grid currents i a , i b , i c resulting in a collaborative control where the burden of the grid current control is shared among the PFC rectifier front-ends.…”

Section: Pfc Rectifier Control With Optimal CMmentioning

confidence: 99%

“…Next, the measured grid voltages are added as feedforward terms to the phase current controller outputs. The optimal CM voltage injection is realized by means of the saturable CM voltage modulator from [20] with the main controller voltage waveforms highlighted in Fig. 8: A large open-loop CM voltage reference ū * CM = M 3rd • Ûac sin(3ω ac t) (with e.g., M 3rd = 1.0) is added as a feedforward term to the controller outputs.…”

Section: Pfc Rectifier Control With Optimal CMmentioning

confidence: 99%

“…It was shown in [14,17] that third-harmonic injection modulation, which results in a CM voltage u CM between the grid starpoint N and the module starpoint N in Fig. 1a, allows to redirect the pulsating single-phase input power among the modules, where sinusoidal grid currents i a , i b , i c are maintained due to the open starpoint configuration (a similar concept is also known from cascaded modular H-bridge converters [18]- [20]). Thereby, the dc-link energy buffering requirement can be reduced by up to 30 % compared to conventional modulation (and up to 39 % for phase-shifted third-harmonic voltage injection) [17] and further the minimally required dclink voltage Ūdc and/or dc-link capacitance value C dc can be reduced.…”

Section: Introductionmentioning

confidence: 99%

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Optimal Common-Mode Voltage Injection for Phase-Modular Three-Phase PFC Rectifiers Minimizing Energy Buffering Requirement

Menzi,

Marugg,

Langbauer

et al. 2023

IEEE Open J. Power Electron.

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Realizing an isolated three-phase Power Factor Correction (PFC) ac-dc converter as a phase-modular system, i.e, by star-connecting three single-phase PFC rectifier frontends with individual isolated dc-dc converter stages generating a common dc output voltage advantageously facilitates the use of standard single-phase converter modules. Further the low dc-link voltage level of typically 400 V (for a grid with 230 Vrms line-to-neutral voltage) allows to employ high performance 600 V power semiconductors. The main drawback of this concept, however, is the fact that the time-varying single-phase input power only sums to a constant three-phase output power at the isolated dc output, such that large dc-link capacitor values are required in each module (in the range of several 100 µF for a 6 kW system), thereby limiting the achievable power density. It is known from literature that the dc-link energy buffering requirement ∆E dc can be reduced by means of a third-harmonic common-mode (CM) voltage injection modulation and this paper identifies the optimal CM voltage waveform with respect to minimizing ∆E dc , i.e., reducing ∆E dc to the theoretical minimum by combining a bruteforce evaluation of the time-domain CM voltage waveform with phase-symmetry considerations. Additionally, converter operation with minimum dc-link voltage and/or dc-link capacitor values is analyzed and a saturable grid current controller allowing operation of the PFC rectifier front-ends with the optimal CM voltage waveform is investigated. Experimental results with a 6 kW prototype system yield a reduction in ∆E dc by up to 42 % (compared to conventional sinusoidal modulation), which closely matches the theoretical prediction. Also, PFC rectifier operation with a dc-link voltage level as low as 285 V (i.e., below the 325 Vpk grid line-to-neutral voltage amplitude) and with ultra-low dc-link capacitor values is demonstrated.

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Section: Optimal CM Voltage Waveform Resultsmentioning

confidence: 99%

Section: Minimum Dc-link Voltage / Capacitance Operationmentioning

confidence: 99%