Frequency domain analysis of capacitor voltage self-balance mechanism

According to the equivalent circuit of the 3L-NPC half-bridge inverter, the relationship between the capacitor current and the capacitor voltage difference is first analyzed from the perspective of frequency domain and time domain. Before the analysis, first assume that the capacity of the DC side capacitors Cdc1 and Cdc2 is large enough, the ripple amount of the […]

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NPC half-bridge inverter equivalent circuit

In small and medium power applications, half-bridge circuits are widely used due to their simple structure and few power devices. As current inverters mostly use the current instantaneous value control technology, the current instantaneous value control accuracy is high, and the system dynamic response is good. However, in the current-type instantaneous value control half-bridge inverter, […]

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Conductance increment and disturbance observation MPPT algorithm

Conductance incremental method Figure 1 shows the output characteristic curve of photovoltaic panels at a specific temperature and specific light intensity (ie, light intensity). Calculate dP/dU on the power/voltage curve, and use the relationship between dP/dU and 0 to determine the working state of the photovoltaic panel. When the photovoltaic panel is working in state […]

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Overview of Maximum Power Point Tracking (MPPT) control and constant voltage MPPT algorithm

In order to realize the maximum power tracking control, it is necessary to understand the output characteristics of the photovoltaic panel. Figure 1 shows the output characteristic curve of a certain type of photovoltaic panel under different lighting conditions. It can be seen from Figure 1 that the open circuit voltage of the photovoltaic panel […]

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The structure and design basis of LLCL filter

The structure of the LLCL filter The LLCL filter is a higher order filter. Its principle is to replace the capacitor C1 in the LCL filter with an LC resonant branch to achieve a better switching frequency harmonic filtering effect and reduce the volume. The inverter structure that adopts LLCL filter is shown as in Figure 1. […]

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Design example of LCL filter

A calculation method of ripple current was given in the design of a single inductance filter in the previous article, and another method of calculation of ripple current will be introduced here. Also considering that the prototype adopts the unipolar SPWM strategy, the expression of the bridge arm output voltage Uinv is Among them, M is […]

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The structure and design basis of LCL filter

The structure of the LCL filter The filtering capability of a single inductor is limited and the volume and loss are relatively large. However, the LCL type filter has the advantages of small size and low loss, and is widely used in grid-connected inverters. The grid-connected inverter structure using LCL filter is shown in Figure […]

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Overview of the network filter and the parameter design of L filter

Overview of the network filter The PWM modulation of the grid inverter leads to a large number of switching frequency and its multiplier harmonic voltages in the output voltage of the bridge arm, and finally leads to corresponding harmonic currents in the grid current. However, in order to make the grid-connected inverter friendly to the […]

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Leakage current suppression of three-phase grid-connected inverter

The previous article analyzed the analysis and improvement of leakage current analysis model, leakage current suppression methods and various topologies based on single-phase non-isolated photovoltaic grid-connected inverters, but the summarized leakage current model and suppression approach can also be analogized to a three-phase grid-connected inverter. Topology using inhibitory pathway A 1. Add an isolation transformer Like […]

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Construction of single-phase non-isolated bridge inverter topology

From the previous analysis, it is known that the suppression approach A is to increase the common-mode loop impedance and reduce the high-frequency leakage current in the case of high-frequency changes in the common-mode voltage. The suppression pathways B and C eliminate the high-frequency voltage of the common-mode loop to eliminate the leakage current. Compared […]

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