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A novel carrier-based discontinuous pulsewidth modulation (CB_DPWM) strategy for T-type three-level converter is proposed in this article. Because one significant advantage of the proposed CB_DPWM is the reduction of common mode voltage (CMV), it is named as RCMV_CB_DPWM hereafter. It also can reduce switching loss and remove dc offset from the neutral point voltage (NPV) simultaneously. RCMV_CB_DPWM has two design freedoms, one is modulation wave and the other is carrier wave. By injecting zero sequence voltage properly, the corresponding clamping mode can be acquired. Moreover, reduced CMV can be achieved by arranging carrier wave flexibly. The integrity of RCMV_CB_DPWM is analyzed as well as its NPV self-equilibrium ability, and an active NPV control method is then introduced. Moreover, its realization is discussed briefly. Finally, the experiments are carried out to verify the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

According to different clamping methods, nine modes (C_MODE1-9) of the traditional discontinuous pulsewidth modulation (DPWM) for neutral-point-clamped three-level converter have been revealed. Since traditional DPWM cannot balance neutral point (NP) voltage under the full range of modulation index (MI) and power factor (PF), two extended modes (E _MODEs) are proposed in this paper, which can balance NP voltage. The proposed extended discontinuous pulsewidth modulation (EDPWM) is characterized by using C_MODEs and E_MODEs alternately.Therefore, EDPWM can balance NP voltage under the full range of MI and PF. Since the switching numbers under C_MODE and E_MODE in one switching cycle are two and three, respectively, the switching loss under EDPWM is lower than that under other pulsewidth modulation (PWM) strategies. The performance of EDPWM is analyzed and compared with traditional DPWM, space vector PWM (SVPWM) and virtual SVPWM (VSVPWM) in terms of switching loss, waveform quality, and the ability of NP voltage control. Finally, the feasibility and superiority of the proposed method are verified by experiments. [ABSTRACT FROM AUTHOR]

In order to reduce switching loss of neutral point clamped three-level inverter (NPC TLI), generally discontinuous pulsewidth modulation (DPWM) is used. But it can result in dc offset and ac ripple on neutral point (NP) voltage. So a novel pulse sequence DPWM (NPSDPWM) is proposed to reduce switching loss and control NP voltage simultaneously in this paper. NP voltage is controlled by choosing proper clamping modes. To avoid unexpected switching action during changing clamping mode, an improved pulse sequence is also presented. The switching loss and NP voltage ripple of NPSDPWM, traditional and proposed DPWM in previous literature are compared, respectively. The experimental results show that NPSDPWM has well NP voltage control ability and the switching losses are reduced effectively. [ABSTRACT FROM AUTHOR]

The three phases of brushless dc motor (BLDCM) are involved in energy conversion during the commutation interval. A novel commutation analysis method of the BLDCM based on coordinate transformation theory is proposed in this paper, though this coordinate transformation theory is popular in the control of three-phase sinusoidal motors, such as induction motors and permanent magnet synchronous motors. The method is intuitive and easy to understand compared with the method based on circuit solving. Combined with the voltage vector diagram of the inverter, commutation control to reduce commutation torque ripple under low speed (LS_RCTR) and high speed (HS_RCTR) is deduced. However, under a heavy load and high-speed condition, long commutation time may result in commutation failure if these commutation controls to RCTR is adopted. To avoid that, commutation time must be controlled. Then, commutation control to reduce commutation time under low-speed (LS_RCT) and high-speed (two cases, named HS_RCT1 and HS_RCT2) are proposed. The improved control of BLDCM presented in this paper can coordinate commutation torque ripple and commutation time in full speed range. Finally, the feasibility and effectiveness of these methods are verified by experiment. [ABSTRACT FROM PUBLISHER]

The parallel three-phase grid-connected converters sharing dc and ac bus can increase the system power level effectively. However, the zero sequence circulating current (ZSCC) will occur inevitably under space vector pulse width modulation or discontinuous pulse width modulation (DPWM). In this paper, the mechanism and the mathematical model of ZSCC are studied. Then, a hybrid PWM (HPWM) strategy is proposed to suppress the ZSCC based on the same zero sequence voltage injected, which is dependent on the common grid information. The dc voltage utilization of HPWM can be extended compared with sinusoidal PWM (SPWM). The number of parallel modules can be infinity theoretically by using HPWM. It is noted that there is no internal commutation among modules (expect the dq current reference). Finally, the feasibility and the effectiveness of the proposed method are verified by experiments. [ABSTRACT FROM AUTHOR]

The parallel three-phase grid-connected converters sharing dc and ac bus can increase the system power level effectively. However, the circulating current will occur inevitably. The existing studies primarily focus on dc, fundamental, and low-frequency circulating current. The high-frequency circulating current (HFCC) caused by asynchronous carriers is studied emphatically in this paper, which is based on the analysis of the change of circulating current in one control cycle. A novel method to suppress HFCC caused by asynchronous carriers of modules is proposed. In this method, the carrier period of slave module is adjustable and the carrier period of the master module is constant. When a large phase shift between modules occurs, an adjusting cycle is inserted to carrier of slave module to realize resynchronizing with master module. It is noted that there is no other commutation between the two modules (expect the dq current reference), such as the carrier information. Finally, the feasibility and effectiveness of the proposed method are verified by experiments. [ABSTRACT FROM PUBLISHER]

The control of brushless dc motors (BLDCMs) is similar to dc motors during the noncommutation interval. However, three phases are involved in electromechanical energy conversion during the commutation interval, making the control of the BLDCM similar to a three-phase ac motor during the commutation interval. A novel commutation analysis method for BLDCMs is proposed based on the coordinate transformation theory, which is used in control of a three-phase ac motor usually. The model of the BLDCM during the commutation interval is acquired in the two-phase stationary frame by using the Clark transformation. The commutation control method for suppressing commutation torque ripple and shortening the commutation time are obtained. Finally, the feasibility and effectiveness of the method is verified by experimental results. [ABSTRACT FROM AUTHOR]

In this paper, a novel discontinuous pulsewidth modulation (DPWM) modulation strategy for a neutral-point-clamped (NPC) three-level converter (TLC) is proposed to reduce the switching loss, reduce common-mode voltage (CMV), and remove dc offset from the neutral-point (NP) voltage simultaneously, which is named as RCMV_DPWM. Based on the space vector diagram with reduced CMV, all clamping modes under RCMV_DPWM are revealed. Then, the NP voltage is controlled by selecting proper clamping mode. The realization of RCMV_DPWM is also discussed. Moreover, the performances of RCMV_DPWM are analyzed and compared with other PWM strategies in term of the NP voltage ripple, switching loss, and waveform quality. Finally, the feasibility and superiority of RCMV_DPWM are verified by experiments. [ABSTRACT FROM AUTHOR]