Overview of the influence of closed-loop control on capacitor voltage balance

Previously, we analyzed the self-balancing characteristics of the 3L-NPC topology from the perspective of time domain and frequency domain under open-loop operation, that is, the modulated wave is symmetrical. In practical applications, the inverter must adopt closed-loop control to control the load current io or the load voltage uo. And in order to improve the stability […]

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Time domain analysis of capacitor voltage self-balance mechanism Part 2

This article analyzes the characteristics of the current ix(t) and its average value Ix(avg) from the midpoint of the capacitor arm when Vd=0 and Vd≠0. (1) Vd=0 Vd=0 means that the capacitor voltage is balanced. At this time, iinv(t) is denoted as iinv_b(t), and its expression is: Among them, φZmn is the impedance angle of Zeq, and […]

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Time domain analysis of capacitor voltage self-balance mechanism Part 1

The self-balancing characteristics of the half-bridge inverter can also be analyzed in the time domain. First, analyze the time constant τ of the capacitor voltage stability in the time domain, so as to qualitatively understand the self-balancing characteristics of the capacitor voltage; then, according to the two-variable Fourier decomposition, the factors of the capacitor voltage […]

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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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