Output AC voltage compensation and neutral point voltage feedback control under neutral point voltage unbalanced conditions are discussed. A neutral point voltage feedback control strategy based on zero sequence injection is proposed. Using this strategy, not only output voltage can be guaranteed no distortion but also neutral point voltage can be adjusted at will. The modulation strategy is based on SPWM principal, so it’s very simple to realize, and suitable for enhancing traditional neutral point balance control or applications where need to control up and down DC link voltage separately. The neutral point current control ability of the strategy is given, and the neutral point voltage low frequency fluctuation problem is also analyzed. Simulation and experimental results verify the correctness of this theory.

Output AC voltage compensation and neutral point voltage feedback control under neutral point voltage unbalanced conditions are discussed. A neutral point voltage feedback control strategy based on zero sequence injection is proposed. Using this strategy, not only output voltage can be guaranteed no distortion but also neutral point voltage can be adjusted at will. The modulation strategy is based on SPWM principal, so it’s very simple to realize, and suitable for enhancing traditional neutral point balance control or applications where need to control up and down DC link voltage separately. The neutral point current control ability of the strategy is given, and the neutral point voltage low frequency fluctuation problem is also analyzed. Simulation and experimental results verify the correctness of this theory.

中点箝位型(neutral point clamped,NPC)三电平逆变器已被广泛应用,中点电位的平衡是其关键技术之一。首先建立基于零序电压注入的中点电位的数学模型,然后根据模型分析采用三种不同零序电压注入的计算方法。在实验室搭建三电平并网逆变器实验样机，比较在不同功率因数下，3种不同零序电压注入方法的中点电位动稳态平衡能力。结果表明，3种方法均能很好地平衡中点电位。此外，在实际条件下，上下电容值常会不相等，因此有必要补充在上下电容值误差为12%条件下的实验。实验验证了3种不同零序电压注入方法在上下电容值误差较大时仍能很好地控制中点电位的平衡。

中点箝位型(neutral point clamped,NPC)三电平逆变器已被广泛应用,中点电位的平衡是其关键技术之一。首先建立基于零序电压注入的中点电位的数学模型,然后根据模型分析采用三种不同零序电压注入的计算方法。在实验室搭建三电平并网逆变器实验样机，比较在不同功率因数下，3种不同零序电压注入方法的中点电位动稳态平衡能力。结果表明，3种方法均能很好地平衡中点电位。此外，在实际条件下，上下电容值常会不相等，因此有必要补充在上下电容值误差为12%条件下的实验。实验验证了3种不同零序电压注入方法在上下电容值误差较大时仍能很好地控制中点电位的平衡。

Due to its fault tolerance, a multiphase brushless direct current (BLDC) motor can meet high reliability demand for application in electric vehicles. The voltage-source inverter (VSI) supplying the motor is subjected to open circuit faults. Therefore, it is necessary to design a fault-tolerant (FT) control algorithm with an embedded fault diagnosis (FD) block. In this paper, finite control set-model predictive control (FCS-MPC) is developed to implement the fault-tolerant control algorithm of a five-phase BLDC motor. The developed control method is fast, simple, and flexible. A FD method based on available information from the control block is proposed; this method is simple, robust to common transients in motor and able to localize multiple open circuit faults. The proposed FD and FT control algorithm are embedded in a five-phase BLDC motor drive. In order to validate the theory presented, simulation and experimental results are conducted on a five-phase two-level VSI supplying a five-phase BLDC motor.

The final aim of the control system of grid-connected inverter is to track the reference current. So it is needed to predict the reference current according to the previous two or three switching periods. Due to the mismatch of the model inductance and actual inductance, the impact had on the stability of system for different control algorithms will be different, namely on the premise that the system be stable, different algorithm differs in the tolerance of inductance mismatch. On the basis of analyzing stability of single phase grid-connected inverter control system, advantages and disadvantages of each kind of predictive current control algorithms were compared. The fundamental reason why the control effects differed from each other was indicated. And an improved predictive current control algorithm was proposed that changes the aim of current error from the current difference of previous two periods to a specified one. The proximate calculation of intermediate variable is decreased and the stability of algorithm is improved. The tolerance of inductance dismatch is largely raised. Better stability margin is achieved relative to conventional methods. In the end the superiority is testified through simulation model and experimental platform.

The final aim of the control system of grid-connected inverter is to track the reference current. So it is needed to predict the reference current according to the previous two or three switching periods. Due to the mismatch of the model inductance and actual inductance, the impact had on the stability of system for different control algorithms will be different, namely on the premise that the system be stable, different algorithm differs in the tolerance of inductance mismatch. On the basis of analyzing stability of single phase grid-connected inverter control system, advantages and disadvantages of each kind of predictive current control algorithms were compared. The fundamental reason why the control effects differed from each other was indicated. And an improved predictive current control algorithm was proposed that changes the aim of current error from the current difference of previous two periods to a specified one. The proximate calculation of intermediate variable is decreased and the stability of algorithm is improved. The tolerance of inductance dismatch is largely raised. Better stability margin is achieved relative to conventional methods. In the end the superiority is testified through simulation model and experimental platform.

A state space model for the neutral point clamped three-level grid-connected inverter is derived in detail，based on which a finite set optimal predictive（FSOP）control method is proposed.The proposed FSOP method is used to select the optimal switching vector from a finite set according to a cost function.The finite set is composed of27switching vectors，and the cost function is composed of the error of output current，the neutral point unbalanced voltage and the switching time of devices.The flow chart of FSOP control is given and the control performance is assessed by simulation and experiment.Experimental results show that the proposed FSOP method has a flexible control purpose，and the synthetic performance of the inverter can be optimized just by adjusting the weighting coefficients of factors in the cost function.FSOP control has bypassed the structure of controller plus modulator in the traditional control method and has a quick response in tracking the output current reference signals and balancing the neutral point voltage.

A state space model for the neutral point clamped three-level grid-connected inverter is derived in detail，based on which a finite set optimal predictive（FSOP）control method is proposed.The proposed FSOP method is used to select the optimal switching vector from a finite set according to a cost function.The finite set is composed of27switching vectors，and the cost function is composed of the error of output current，the neutral point unbalanced voltage and the switching time of devices.The flow chart of FSOP control is given and the control performance is assessed by simulation and experiment.Experimental results show that the proposed FSOP method has a flexible control purpose，and the synthetic performance of the inverter can be optimized just by adjusting the weighting coefficients of factors in the cost function.FSOP control has bypassed the structure of controller plus modulator in the traditional control method and has a quick response in tracking the output current reference signals and balancing the neutral point voltage.

The demand for lightweight converters with high control performance and low acoustic noise led to an increase in switching frequencies of hard switched two-level low-voltage 3-phase converters over the last years. For high switching frequencies, converter efficiency suffers and can be kept high only by employing cost intensive switch technology such as SiC diodes or CoolMOS switches; therefore, conventional IGBT technology still prevails. In this paper, the alternative of using three-level converters for low-voltage applications is addressed. The performance and the competitiveness of the three-level T-type converter (3LT(2)C) is analyzed in detail and underlined with a hardware prototype. The 3LT(2)C basically combines the positive aspects of the two-level converter such as low conduction losses, small part count and a simple operation principle with the advantages of the three-level converter such as low switching losses and superior output voltage quality. It is, therefore, considered to be a real alternative to two-level converters for certain low-voltage applications.