Influence of low frequency harmonics of grid voltage and dead zone effect

1. The influence of low frequency harmonics of grid voltage The equivalent model of the grid-connected inverter is shown in Figure 1, in which the output voltage uinv of the bridge arm of the inverter is equivalent to a controlled voltage source (the specific form is related to the inverter control). Using the superposition theorem, […]

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Fundamental current tracking

In order to achieve a higher power factor, the fundamental tracking error of the incoming current must be resolved. This paper briefly introduces several fundamental current tracking control methods commonly used in L-filter grid-connected inverters 1. Proportional-integral (PI) regulator The form of the PI regulator is as follows: Among them, kp is the proportional gain, Ti is […]

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Stability of current control

Overview of current control techniques for single L filter grid-tied inverters The current control block diagram of the single-L filter grid-connected inverter is shown in Figure 1. The inverter bridge is simply equivalent to a proportional link with a gain of kPWM, and kPWM is the ratio of the DC side voltage to the amplitude […]

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Voltage sharing control strategy of half-bridge grid-connected inverter

In the grid-connected situation, considering the line impedance and the inductive and resistive impedance existing in the actual power grid, Zload is equivalent to resistive-inductive. Therefore, the model established above and the voltage sharing control strategy discussed are also applicable to the half-bridge grid-connected inverter, the only difference being that Zload is a relatively small resistive and […]

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Capacitor voltage balancing based on self balancing characteristics

According to the equalization control idea of class B, the equalization control method based on the self-balancing characteristic is discussed below. According to the effect of closed-loop control on the self-balancing characteristics of 3L-NPC, in order to satisfy the idea of B-type equalizing control, the closed-loop control needs to meet two conditions under the action […]

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Capacitor voltage deviation closed-loop control

Based on the above analysis, in the closed-loop control, if the regulator has no response to the DC component or the response to the DC component is small and does not destroy the self-balancing characteristics of 3L-NPC, the self-balancing characteristics of 3L-NPC can be used to achieve capacitor voltage balance control. According to the influence […]

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Specific analysis of the influence of closed-loop control on the modulation wave

The following will take proportional-integral PI regulator, proportional-resonant PR regulator and quasi-resonant QR regulator as examples to analyze the influence of closed-loop control on the modulation wave. (1) Gc(s) is the PI regulator, Gc(j0)→∞ Among them, kp>0, ki>0. The PI regulator controls the AC signal to have a static error, so the current error ie(t)=Ie·sin(ωst+θi)-Io(avg). At […]

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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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