Abstract
With the increasing power level of wind power generation system, the traditional topology of power converters can no longer meets the demand of high-power wind power generation systems due to the limitation of device performance. The line voltage cascade type multiple PWM converter (LVC-VSC) is a kind of converter that uses the traditional two-level and six-switch voltage source converter as the basic component unit, and each unit is combined with the line voltage cascade method. This type of converter is suitable for medium-voltage and high-power applications such as wind power generation and metallurgical drives because of its easy modularization, strong scalability and low number of isolated power supplies required. However, for medium-voltage and high-power applications, the switching frequency of power devices in the converter is low, usually limited to a few hundred hertz. The traditional modulation method of line voltage cascade converter has a large number of redundant states, and simply reducing the carrier ratio will cause serious degradation of control performance and system instability. To address this problem, this paper proposes a modulation strategy and a corresponding control method for low switching frequency. The modulation strategy is based on the vector relationship of finite switching states, and the optimal switching sequence is selected according to the modulation system by removing redundant states, thus ensuring the application of different modulation sequences under different modulation depths and ensuring the current quality on the basis of the minimum switching frequency, which effectively solves the control problems at low switching frequency. The experimental results show the correctness and effectiveness of the proposed modulation strategy and control method.
Highlights
With the increasing power level of wind power generation systems, a series of multiple, multilevel converter topologies have been proposed by scholars to meet the application requirements of medium-voltage and high-power applications
For the modulation strategy described in this paper, in order to take full advantage of the minimum number of switching times when adjacent vectors are switched, the threevector sequential waveform is used instead of the traditional five- stage and seven-stage waveform, the latter reduces the current fluctuation to a certain extent, but will greatly increase the switching frequency, which is contrary to the requirement of low switching frequency in medium and high power applications
The experimental algorithm is completed based on dual controller chips, the dsp28335 chip and Altera’s FPGA chip (EP1C6Q240C8), the control algorithm and a small amount of modulation algorithm is completed through the DSP, most of the modulation algorithm is completed through the FPGA, the specific details are shown in the Figure 19
Summary
With the increasing power level of wind power generation systems, a series of multiple, multilevel converter topologies have been proposed by scholars to meet the application requirements of medium-voltage and high-power applications. DC-power inverters such as cascaded H-bridge type and cascaded three-phase bridge type [1,2,3,4,5,6,7]. We take wind power generation as the application background and triple LVC-VSC as the net-side converter to carry out the research work.
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