Abstract
The modular multilevel matrix converter (M <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> C) is an ac-to-ac converter topology suitable for the control of high-power variable-speed drives. The control of this converter is complex, particularly when the two ac system frequencies are similar or identical because large voltage oscillations can be produced in the floating capacitors within the M <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> C. This paper proposes a new vector control system based on nested controllers to regulate the M <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> C over the full range of frequencies. The proposed control scheme is especially useful to mitigate or eliminate the oscillations that arise when the frequencies are similar. An extensive discussion of the model and control of the M <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> C is presented in this work. The effectiveness of the proposed vector control system is demonstrated through simulation studies and experimental validation tests conducted with a 27-cell-5kW M <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> C prototype.
Highlights
M ODULAR Multilevel Cascade Converters (MMCC) are a family of power converters proposed initially for High Voltage DC transmission [1]
A new vector control system based on the representation of the M 3C converter in Σ∆ double-αβ0 coordinates has been proposed to enable the operation of the converter over a wide operating range, including equal input/output port frequencies
The vector control system is orientated using synchronous axis systems rotating at fm±fg
Summary
M ODULAR Multilevel Cascade Converters (MMCC) are a family of power converters proposed initially for High Voltage DC transmission [1]. When the input-port frequency is different to the output-port frequency (i.e. lower or higher by a given threshold), the system is considered to operate in DFM In this zone, the capacitor voltage mean values are controlled using either circulating currents or by injecting a common-mode voltage. On the other hand, when the absolute value of the input-port frequency is very close or equal to the output-port frequency, the system is considered to operate in EFM, where mitigation signals or operation point restrictions are utilised in the control systems to eliminate the oscillations in the floating capacitor voltages [14]–[18]. Different to the control systems previously published for M 3C applications (see [15], [17], [18]) where Proportional and PI controllers implemented in the stationary αβ frame are utilised, which cannot regulate sinusoidal signals with zero steady-state error. The effectiveness of the proposed control system is validated through simulations and experiments conducted with a 27-cell-5kVA prototype
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