31results about How to "Reduce output harmonic content" patented technology

The present invention provides a method and device for predicting and compensating DC bus ripple voltage of an AC motor driver, using the predicted value of DC bus voltage, performing voltage compensation calculation through a ripple voltage compensation algorithm, and obtaining Ualpha* and Ualpha* required by the SVPWM space vector modulation algorithm Ubeta*, then execute the SVPWM space vector modulation algorithm, set the PWM buffer register, update the flag, and the CPU will automatically load the new value and output the PWM waveform in the next reload cycle. The present invention solves the problem of time delay in the implementation of the DC bus voltage sampling and compensation method in the prior art, performs precise compensation control on the DC bus ripple voltage, and avoids the distortion of the pulse width modulation output of the driver as much as possible, and the distortion of the output voltage and current waveform , reduce the output harmonic content and improve the driving performance of the driver.

The invention provides a low-frequency model predictive control method based on a hybrid modular multilevel converter, which realizes a low-frequency model predictive control strategy based on upper, middle and lower layers of control: The current, circulating current and bridge arm capacitor voltage control the required bridge arm output level, and effectively reduce the amount of optimization calculation; the middle layer control uses the H bridge module control algorithm to stabilize the H bridge module capacitor voltage and calculate its equivalent output level. And determine the switching number of the half-bridge sub-module of the bridge arm; the lower layer control determines the switching signal of each sub-module according to the optimal control strategy of the sub-module capacitor voltage, realizes the balanced control of the sub-module capacitor voltage, and reduces the average switching of the sub-module frequency.

The invention discloses a three-phase three-level inverter based on a switched capacitor. The inverter includes a capacitor voltage stabilizing unit and an output unit, wherein the capacitor voltage stabilizing unit generates a capacitor voltage equal to an input voltage, the capacitor voltage and the input voltage are connected in series and superposed to generate a direct current three-level voltage, and the capacitor voltage stabilizing unit may have two different forms; and the output unit performs inversion of the direct current three-level voltage generated by the capacitor voltage stabilizing unit into a required three-phase alternating voltage, and a T type three-phase three-level inverter structure or diode clamping type three-phase three-level converter structure is adopted. Thethree-phase three-level inverter based on a switched capacitor can realize bus capacitor voltage self balancing, reduce resource occupation of a controller, and can reduce output harmonic content, andthe highest amplitude of an output alternating current phase voltage can be two times that of an input direct voltage.

The invention provides a single-input switched capacitor multi-level inverter and its modulation method. The switching device controls the working state of the capacitor to realize the conversion and transmission of electric energy, and has the advantages of small size, high efficiency, and high power density; The inverter is based on the series-parallel conversion of the switched capacitor structure, which can generate more output levels with fewer power devices, simplifies the topology structure, and reduces the output harmonic content. It has the advantages of small number of devices, simple control, single power input, Capacitive self-balancing and independent application to inductive loads and other advantages.

The invention discloses a T-type multi-level inverter circuit, which comprises two T-type three-level circuits, two switch tubes, two pairs of anti-series switch tubes and an LC filter circuit; two T-type three-level circuit input The opposite polarity ends of the power supply are connected through two switch tubes, and two pairs of anti-series switch tubes connect the input power of the T-type three-level circuit to the same polarity end, and the LC filter circuit is connected to the inverter bridge arms of the two T-type three-level circuits On the central node, the ratio of the input power supply voltages of the two T-shaped three-level circuits is 5. The invention uses fewer switching tubes to generate more levels, greatly reduces the number of power switching tubes, further reduces the cost of the multi-level inverter, improves the efficiency of the inverter, and reduces the switching frequency at the same time.

The invention relates to a method for controlling midpoint voltage balance of a three-level ANPC converter, comprising the following steps: (1), adopting a SVPWM pulse sequence to act on the three-level ANPC converter; (2), detecting the DC side capacitance of the converter in real time Voltage, get the midpoint voltage value, and compare it with the midpoint voltage reference value to determine whether the DC side capacitor needs to be charged or discharged; (3), real-time detection of the positive and negative of the three-phase load current of the converter; (4), comprehensive steps ( 2) and the detection value of step (3), dynamically adjust the duty ratio of the zero state of the switching sequence to the three-phase bridge arm in each switching cycle until the midpoint voltage is balanced, and repeat this process to maintain the midpoint voltage fluctuate within a small range. The invention can dynamically adjust the charging and discharging time of the capacitor according to the direction of the three-phase load current and the magnitude of the midpoint voltage, so that the midpoint voltage can quickly reach a balance and maintain a fluctuation within a small range.

The invention relates to a low frequency model prediction control method based on a hybrid modular multi-level current converter. Each bridge arm is equipped with N sub modules, namely, semi-bridge modules, and one full bridge module. The capacitor voltage of the full bridge module is assigned as a half of each sub module. The low frequency model prediction control method concretely includes taking upper and lower bridge arm module input number as a control variable, performing layering control on AC current, loop current and capacitor voltage of the sub modules and selecting the optimal switch state combination by utilizing an AC current index function; adjusting the sub module input number of the upper bridge and the lower bridge arms by adopting a loop current index function; determining the final sub module input number through combination with the working state of the full bridge module; and finally calculating the sub module input number difference of neighboring time points, adopting an optimization voltage-sharing strategy for realizing balance control of the capacitor voltage of the sub modules, so that the system switching frequency is reduced. The method is clear in physical model and does not need to consider complex parameter setting and weight index design. Digital control is easy to realize and optimizing computation workload is reduced.

The invention discloses a transformerless three-phase DC-AC converter for a DC microgrid, which comprises: at least two DC-AC conversion units, at least two DC-AC conversion units connected in parallel; wherein: two DC ‑AC conversion units are wrongly connected in parallel. In addition, the CPU can also be used to automatically control the DC-AC converter through PWM control technology. The transformerless three-phase DC-AC converter for the DC micro-grid of the present invention does not need to insert a transformer between the DC bus and the low-voltage power grid, and can allow the DC-AC converter to work in the best modulation rate range, improving the efficiency of the DC-AC converter. converter efficiency and reduced harmonic output.

The invention discloses a combined type inverter. The combined type inverter comprises input voltage, and a capacitor C1 connected between positive and negative electrodes of the input voltage in parallel, the positive electrode of the input voltage is connected with drain electrodes of an MOS tube Q1, an MOS tube Q3 and an MOS tube Q5 in parallel, a source electrode of the MOS tube Q1 is connected with a drain electrode of an MOS tube Q2, a source electrode of the MOS tube Q3 is connected with a drain electrode of an MOS tube Q4, a source electrode of the MOS tube Q5 is connected with a drain electrode of an MOS tube Q6, source electrodes of the MOS tube Q2, the MOS tube Q4 and the MOS tube Q6 are connected with the negative electrode of the input voltage; and a position between a source electrode of the MOS tube Q1 and the drain electrode of the MOS tube Q2 is connected between the source electrode of the MOS tube Q5 and the drain electrode of the MOS tube Q6 through an inductor L2, a capacitor C2 and an inductor L3 in sequence, a position between the source electrode of the MOS tube Q3 and the drain electrode of the MOS tube Q4 is connected between the source electrode of the MOS tube Q5 and the drain electrode of the MOS tube Q6 through an inductor L1, the capacitor C2 and the inductor L3 in sequence, and the capacitor C2 is connected with a load R1 in parallel.

The invention discloses a three-phase three-phase series-connected three-phase stepping alternating-current frequency conversion method. The main frequency conversion circuit is formed on the basis of the same circuit as the traditional three-phase three-phase three-phase series series thyristor alternating-current conversion method. Separate control, triggering a pair of thyristors in the positive group and the negative group simultaneously for each heavy circuit, so that the output terminal of the heavy circuit is connected with the input of one phase of the heavy circuit, and after a time interval related to the expected output frequency. The next time it is triggered, the heavy output terminal is connected to the input of the next phase. By continuously switching this connection relationship, the phase of the output voltage is continuously changed, thereby obtaining the effect of changing the overall output frequency. At the same time, by arranging the phase of the output voltage of each heavy circuit according to the needs, and adjusting the triggering time of each heavy thyristor, it can realize the output of AC power with a three-phase phase difference of 120° for use by three-phase motor loads. It has the advantages of low cost and high reliability.