Analytical evaluation of output current ripple amplitude in three-phase three-level inverters

Nowadays, three-phase multilevel inverters are widely employed in medium and high-power applications, increasing the power ratings, improving the output voltage quality and reducing the conducted electromagnetic interferences. Despite of numerous pulse-width modulation (PWM) techniques have been developed for multilevel inverters, a detailed analysis of the output current ripple amplitude has not been reported yet. In this study, the peak-to-peak current ripple distribution over a fundamental period is analysed in details specifically for three-level three-phase voltage source inverters for both motor-load and grid-connected applications. In particular, the peak-to-peak amplitude of the current ripple is determined analytically as a function of the modulation index. The centred PWM strategy is considered in all the developments, implemented either by carrier-based or space vector (SV) PWM methods. With this modulation, the dc bus utilisation is maximised in a simple and effective way, and a nearly-optimal behaviour is obtained to minimise the current ripple rms. The results obtained in different cases and sub-cases identified in the proposed analytical approach are verified by experimental tests with reference to three-phase three-level neutral-point clamped configuration

A space vector PWM algorithm for a three-level asymmetrical six-phase motor drive

A space vector pulse-width modulation (SVPWM) algorithm for a three-level asymmetrical six-phase drive based on vector space decomposition (VSD) approach is presented in this paper. A modification in zero plane of the transformation matrix is proposed in order to meet the requirement that the realisation of sinusoidal output phase voltages can be obtained through the chosen output leg voltage space vectors. Furthermore, a method of choosing the switching sequences based on all possible one-level transitions of the leg voltages, i.e. a permutation method, is introduced. The algorithm is then validated experimentally and obtained results show that the developed method successfully achieves the desired fundamental phase voltage, although low order harmonics are present due to uncompensated inverter dead time. Last but not least, the performance of the proposed SVPWM algorithm is compared to several carrier-based PWM algorithms including in-phase disposition with ‘double min-max injection’ (PD-DI). This is a little known type of injection, which is verified to obtain identical performance as the presented multilevel algorithm

Experimental Verification of Current Ripple Amplitude in Five-Phase PWM VSIs

Multiphase systems are nowadays considered a viable solution for various industrial applications. Numerous PWM schemes for multiphase voltage source inverters with sinusoidal outputs have been developed, but no detailed analysis of the impact of these modulation schemes on the output peak-to-peak current ripple amplitude has been reported. Determination of the current ripple in multiphase PWM voltage source inverters is interesting from the theoretical point of view and, in some cases, is useful for both design and control purposes. This paper gives the complete analysis of the peak-to-peak current ripple distribution over a fundamental period with experimental verification in the case of five-phase voltage source inverters. In particular, peak-to-peak current ripple amplitude is analytically determined as a function of the modulation index with a symmetrical centered PWM, being the most simple and effective solution to maximize the dc bus utilization, leading to a nearly-optimal modulation to minimize the rms of the current ripple. However, the analysis could be easily extended to either discontinuous or asymmetrical modulation, both carrier-based and space vector PWM

Modular Vector Control of Multi-Three-Phase Permanent Magnet Synchronous Motors

Recent developments in power electronics are making the multiphase machines a competitive alternative to conventional three-phase counterparts. Due to their fault-tolerant features, multiphase drives represent a robust technology in high power/high current, safety-critical applications. Besides, their introduction into transportation electrification is gaining on importance. Among the multiphase solutions, the multi-three-phase machines are receiving a lot of the attention by the industry since they use the well-consolidated three-phase technology, thus reducing the design time and also the cost. Therefore, this paper proposes a modular vector control scheme for multithree-phase permanent magnet synchronous motors. The proposed solution uses a modular modeling approach for the independent and decoupled torque control of each three-phase unit, allowing the implementation of torque sharing strategies among the three-phase sets of the machine. The developed modular control has been validated on a nine-phase permanent magnet machine

LiBAT: A High-Performance AC Battery System for Transport Applications

The paper proposes a novel battery design for high-performance transport applications that is immersion-cooled and switched by a multi-level inverter. Advantages of the proposed AC battery design in terms of weight, modularity, scalability, performance, reliability and safety are presented. To demonstrate the applicability of the design, an electrically powered glider use case is addressed. The derived battery system is evaluated by means of theoretical analysis, simulation and prototyping. Simulations showed that the used multi-level inverter (MLI) power electronics modules could successfully run the motor without additional power electronics and charge batteries from a 110 V AC source. The prototype implementation with a motor-driven propeller demonstrated power levels of up to 3.3 kW, with a behavior in accordance with simulations. Guidelines to further advance the technology readiness level including control strategies and hardware design were derived to overcome limitations in the prototype realization that could not be addressed within the project budget. Finally, research topics to evaluate additional performance metrics such as efficiency and aging behavior are suggested