The modular multilevel converter (MMC) has several submodules in cascade. To control the submodule capacitors voltage, a new generalized dynamic voltage balancing algorithm along with a simple pulse ...width modulator structure is proposed in this paper. With proposed pulse width modulator structure, the dynamic voltage balancing algorithm can be easily implemented with any type of carrier based pulse width modulation (including level-shifted and phase-shifted pulse width modulation) scheme without any modifications. This method does not require the sorting technique for selection of submodule capacitors voltage. The performance of the proposed voltage balancing algorithm is presented for MMC with three-level flying capacitor submodules (MMC-3L-FC). The proposed method is also applicable to the conventional two-level half bridge submodules as well. The effectiveness of the proposed voltage balancing algorithm is verified with the phase-shifted carrier-based pulse with modulation scheme. The results obtained from the MATLAB/SIMULINK simulations on 6-kV/ 2.5-MW system and the dSPACE DS1103-based laboratory prototype of 208-V/3-kVA MMC-3L-FC system are in close relationship, and thus, the proposed methodology is validated.
A Survey on Neutral-Point-Clamped Inverters Rodriguez, Jose; Bernet, Steffen; Steimer, Peter K ...
IEEE transactions on industrial electronics (1982),
2010-July, 2010-07-00, 20100701, Letnik:
57, Številka:
7
Journal Article
Recenzirano
Neutral-point-clamped (NPC) inverters are the most widely used topology of multilevel inverters in high-power applications (several megawatts). This paper presents in a very simple way the basic ...operation and the most used modulation and control techniques developed to date. Special attention is paid to the loss distribution in semiconductors, and an active NPC inverter is presented to overcome this problem. This paper discusses the main fields of application and presents some technological problems such as capacitor balance and losses.
This paper describes the operation of modular multilevel converter, an emerging and highly attractive topology for medium- and high-voltage applications. A new pulsewidth-modulation (PWM) scheme for ...an arbitrary number of voltage levels is introduced and evaluated. On the basis of this PWM scheme, the semiconductor losses are calculated, and the loss distribution is illustrated.
In order to prevent the power switching devices (e.g., an insulated-gate bipolar transistor, IGBT) from shoot-through in voltage-source converters during a switching period, the dead time is added ...either in the hardware driver circuits of the IGBTs or implemented in software in pulse width modulation (PWM) schemes. Both solutions will contribute to a degradation of the injected current quality. As a consequence, the harmonics induced by the dead time (referred to as "dead-time harmonics" hereafter) have to be compensated in order to achieve a satisfactory current quality, as required by standards. In this paper, the emission mechanism of dead-time harmonics in single-phase PWM inverters is, thus, presented considering the modulation schemes in detail. More importantly, a repetitive controller has been adopted to eliminate the dead-time effect in single-phase grid-connected PWM converters. The repetitive controller has been plugged into a proportional-resonant-based fundamental-frequency current controller so as to mitigate the dead-time harmonics and also to maintain the control of the fundamental-frequency grid current in terms of dynamics. Simulations and experiments are provided, which confirm that the repetitive controller can effectively compensate the dead-time harmonics and other low-order distortions, and also, it is a simple method without hardware modifications.
Half-cycle symmetry selective-harmonic-elimination pulsewidth-modulation (SHE-PWM) problems may have a large number of valid solutions, which are beneficial to the optimization design. This paper ...proposes a novel generalized formulation of half-cycle symmetry SHE-PWM problems for multilevel inverters. The advantages of the proposed formulation include simplicity in format, flexibility in PWM waveforms, and a broad solution space. A method to obtain initial values for the SHE-PWM equations according to the reference modulation index M and the initial phase angle of output fundamental voltage is proposed and investigated thoroughly. Take a five-level inverter with M = 0.75 as an example; six sets of solutions for two typical initial phase angles of 0° and 90° are presented. Simulations and experiments are carried out. It is demonstrated that the experimental results agree well with simulated ones, which proves the validity and practicability of the new method proposed.
Module parallel connection for three-phase VSC can increase the system level effectively. However, the circulating currents problem will occur. The circulating currents will distort the three-phase ...currents, increase the power loss and decrease the system efficiency. A novel deadbeat circuiting currents control method is proposed in this paper. Based on the analysis of the average model of parallel system, a circuiting currents deadbeat controller is designed while presenting the design method. The control strategy is realized by adjusting the voltage zero vector of space-vector pulse-width modulation in each paralleled module. No additional hardware is needed through the method. Fast dynamic response can be achieved and the performance of circulating currents is better compared with conventional PI controller. This method can be applied to common dc-link double parallel three-phase voltage converters with communication line. The validity of proposed theory was verified by simulation and experimental results. It is shown that the parallel converters can operate with different line inductor or different line currents by using this novel control strategy.
This article presents a pulsewidth modulation (PWM) controlled series resonant converter (SRC) for a universal EV charger. This article focuses on the boost mode of a SRC. By adapting two PWM boost ...switches with a full bridge rectifier, it is possible for a SRC to cover a very wide range of gain with a high and flat efficiency curve. As the output voltage increases, the secondary side rectifier of the proposed converter gradually converts from a full bridge rectifier to a voltage doubler rectifier. Since the switching frequency is fixed to the resonant frequency in boost mode, the proposed converter naturally achieves "two peak efficiency points" with full bridge and voltage doubler rectifiers. Two peak efficiency points limit the efficiency drop over a wide range of gain, and that is the reason the proposed converter achieves a high and flat efficiency curve. The effectiveness of the proposed converter and control has been verified on an 800 V input and 200-950 V/3.3 kW output prototype.
Performance of a carrier-based pulsewidth modulation (CB-PWM) strategy can be improved by the inclusion of a zero-sequence voltage in the modulation-reference signal. This paper proposes a new CB-PWM ...strategy for a three-level neutral-point-clamped (NPC) converter, which is based on a zero-sequence voltage injection. By inclusion of the zero-sequence voltage, the sinusoidal-modulation reference is modified to 1) carry out the voltage-balancing task of the dc-link capacitors, with no additional control effort, 2) reduce the switching losses, and 3) reduce the low-frequency voltage oscillations of the neutral point. The proposed strategy is an alternative approach to the nearest three-vector (NTV) space-vector modulation (SVM) strategy and is obtained by the analysis of the NTV-SVM strategy and establishing a correlation between the NTV-SVM and the CB-PWM strategies. The salient features of the proposed scheme, as compared with the NTV-SVM strategy, are: 1) its reduced computational processing time which is attractive for digital implementation and 2) its reduced switching losses. Compared with the existing CB-PWM strategies, the proposed strategy offers 1) capability to balance the capacitor voltages and reduce the NP voltage oscillations and 2) reduced switching losses. Performance of the proposed CB-PWM strategy for a three-level NPC converter based on time-domain simulation studies in the MATLAB/SIMULINK environment is evaluated and also experimentally verified.
This paper presents a predictive current control method and its application to a voltage source inverter. The method uses a discrete-time model of the system to predict the future value of the load ...current for all possible voltage vectors generated by the inverter. The voltage vector which minimizes a quality function is selected. The quality function used in this work evaluates the current error at the next sampling time. The performance of the proposed predictive control method is compared with hysteresis and pulsewidth modulation control. The results show that the predictive method controls very effectively the load current and performs very well compared with the classical solutions
This paper studies the relations of space-vector modulation (SVM) and carrier-based pulse-width modulation (PWM) for multilevel inverter. The PWMs' generation of SVM can be achieved by carrier-based ...PWM scheme, but the modulated wave of SVM is acquired by vectors' calculations and switching-states' selection. Based on different selection of redundant switching-states, there are many types of SVM modulated waves, some of which can function equivalently through proper selection of common-mode injections in the case of carrier-based PWM, the others have more freedoms in switching-states' selection than carrier-based PWM. Selection of more switching-states in SVM is propitious to optimize the output voltage, balance the dc power and so on. Then an improved PWM scheme is proposed based on the modulation waves of three-level SVM, which reserves the main advantages of SVM, and can be achieved easily. Finally, a five-level test circuit is built to verify this PWM scheme.
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