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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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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