This paper proposes a direct power control (DPC) strategy employed for the neutral-point-clamped (NPC) three-level PWM rectifier. Mathematic model of NPC three-level rectifier is conducted firstly as a theoretical base. This topology generates a higher number of output voltage levels, increasing the flexibility for selecting an appropriate voltage vector. The direct instantaneous power control technique for the converter, which has been developed to control the instantaneous active and reactive power directly by selecting the optimum switching state of the converter, is discussed in detail in the paper. The neutral-point potential is controlled according to the direction of the mid-point current and a study of each switching vectorpsilas influence to active and reactive power. Theoretical analysis is presented and the performance of the proposed method is verified by simulation and experiment.
[Show abstract][Hide abstract] ABSTRACT: This paper presents a novel Direct Power Control strategy for a three-phase grid connected multilevel inverter. The proposed DPC strategy combines discrete-time sliding mode control and predictive control. The active and reactive power are directly controlled by inverter switching states, represented by a switching vector, using the value of the power error computed from samples of phase voltages and currents. An appropriate switching vector is selected for each sampling period to minimize average value of the switching functions on the time interval on three sampling periods. The prediction of phase voltages and currents is necessary for algorithm implementation. The switching frequency is constant, and the digital control implementation is simple. The designed control system is tested using a simulation model of a three-level neutral-point clamped multilevel inverter. Simulation results confirm the design aims.
Power Engineering, Energy and Electrical Drives (POWERENG), 2013 Fourth International Conference on; 01/2013
[Show abstract][Hide abstract] ABSTRACT: In this paper, a new switching table for direct power control (DPC) strategy is proposed for three-level NPC rectifier. The strategy is developed by analyzing active and reactive power and introducing convenient controllers to optimize the voltage selection which is the fundamental task in that control method. The dc-link voltages are maintained at the required level using hysteresis controller for the NP current exploiting the redundancy states of the rectifier. With a simple switching table, the excellent dynamic and transient performances are achieved under unity power factor operation. Simulation results verify the validity and feasibility of the proposed strategies.
[Show abstract][Hide abstract] ABSTRACT: This paper presents a mathematical model of three-level voltage PWM rectifier, and derives a power control model from the theory of instantaneous power. In the vector-space, the influences on instantaneous power exercised by all the switching vectors are studied and illustrated separately, then a direct power control (DPC) scheme for three-level PWM rectifier which uses multistage band hysteresis comparator is proposed, and a novel switching table is designed. Meanwhile, the neutral-point voltage unbalance is inhibited by selecting the redundancy switching states of small voltage vectors. Simulation and experimental results show that the proposed strategy can not only stabilize the DC bus voltage but also realize the unity power factor operation and the balance of neutral-point voltage. Moreover, the proposed method can improve the performance of the three-level rectifier.
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