| The multi-level inverters have been widely used in motor drive applications such aspumps, blowers, compressors and conveyors. As an answer to the increasing demandfor motor drives which have advantages of high-power capacity, low total harmonicdistortion (THD), and low switching frequency, various topologies of multi-levelinverters have come into being. Among which, the five-level active neutral pointclamped (ANPC) inverter is attracting more and more attention in the academia andindustry. That is because the five-level ANPC inverter has many adventages, such asthe DC-link has only one neutral point (NP), each phase has only one floatingcapacitor (FC), and what’s more, it can work well without phase-shifting transformersor clamping diodes.Based on the analysis of the five-level ANPC inverter’s operating principle, theselective harmonic elimination pulse width modulation (SHEPWM) technique isstudied firstly, and the innovative global best particle swarm optimization (gbest PSO)is used to solve the nonlinear transcendental equations of switching angles. Bychoosing appropriate parameters such as the population size, the inertial coefficientand the cognitive and social coefficients, the solutions of switching angles aresearched out efficiently. And different waveforms of the five-level line-to-neutralvoltage are designed for different modulation index ranges. Then, the hysteresiscontrol strategy of the FC voltage is used to stabilizing the voltage across the FC, andthe NP voltage is regulated at its reference level with its self-balancing capability byadjusting the hysteresis band of the FC voltage. The simulation results show that thehysteresis band should be chosen respectively for different modulation indices, andthe principle of adjusting the hysteresis band is to reduce the switching frequency withthe proviso that the NP voltage is balanced well, which is not practical for the result ofincreasing the workload of debugging.Therefore, the space vector pulse width modulation (SVPWM) technique of thefive-level ANPC inverter is further studied. Firstly, the ja-jb-jc virtual coordinate isintroduced to control the zero and nonzero-sequence voltage components respectively,and the complexity of choosing the seven-segment vector sequences and computingthe vectors’ durations can also be avoided in this coordinate. Secondly, all10connecting states between the load and the two DC-link capacitors are studied byanalyzing the5123-phase switching states of five-level ANPC inverters, and a table is built for each connecting state to display all the space vectors which may form thisconnecting state. In this way, all space vectors that may form a certain connectingstate are shown in a certain table, and all space vectors’ characteristics of balancingthe NP voltage are obtained by looking up these tables. Finally, this thesis proposes abalancing strategy of the NP voltage based on the SVPWM technique, and the goodperformance of the strategy is proved by simulation results with different modulationindices.The vector control strategies of the permanent magnet synchronous motor(PMSM) are studied, and a simulation model based on the control strategy ofis d=0is built to prove the five-level ANPC inverter’s characteristics of driving motors. Thesimulation results show that the PMSM has good performance with small torqueripples and fast dynamic responses under the SVPWM technique, and the NP voltageof the ANPC inverter can be balanced well under dynamic conditions with thebalancing strategy proposed in this thesis.Finally, the experimental prototype and software design are introduced. Ascheme for the digital control system based on DSP and dual FPGA is presented indetail, and the modulation strategies studied in this thesis are validatedexperimentally. |
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