基于总分式控制的准Z源级联多电平光伏逆变器

doi:10.19595/j.cnki.1000-6753.tces.241832

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Abstract Each power unit of a cascaded multilevel inverter (CMI) can be controlled independently without capacitor voltage sharing problems, which is suitable for distributed photovoltaic power generation systems. By combining quasi-Z-source (QZS) with CMI, quasi-Z-source cascaded multilevel inverter (QZS-CMI) can achieve boost and inverter functions in a single stage without setting a dead zone and thus improve system efficiency. A master-division control strategy and a multi-carrier phase-shifted PWM (MPSPWM) method are proposed to reduce the total harmonic distortion (THD) of QZS-CMI grid-connected current and improve the system's dynamic response. Moreover, aiming at the problem of over-modulation when the power of each module is seriously unbalanced, this paper proposes a third harmonic injection control.
In the master-division control, the voltage outer-loop division controller uses PI control to achieve the stability of the DC-link voltage of each module. The grid-connected current master controller uses an improved deadbeat control (DBC), where the current deviation is corrected in a weighted form to fast-track the grid-connected current. Also, the MPSPWM prolongs the conduction time of two switches in the same bridge arm when the switching state changes. Accordingly, the shoot-through zero vector is inserted at the switching time to reduce the switching loss. However, suppose the system is over-modulated when the power is unbalanced. In that case, the third harmonic is injected into the modulation wave of the over-modulation module, and the reversed third harmonic is injected into the non-over-modulation modules. As a result, the modulation wave changes from a sine wave to a saddle wave. Thus, the system can operate normally without over-modulation.
A three-module cascaded seven-level topology is used for simulation and experiments. In the steady state, each DC-link voltage of the three modules is stable at about 70 V, and the QZS-CMI output voltage amplitude is about 210 V with seven levels. After being filtered, the output voltage has no phase difference to the current, where its power factor approaches 1.0, and the sine wave is revealed well at 50 Hz. Using the MPSPWM method, the shoot-through zero vector in a switching cycle is divided into four parts and inserted at the switching time on average to reduce the switching frequency. The traditional PR control's THD of the inverter output current is 2.84%, and the improved DBC is decreased to 0.86%. When the photovoltaic cell's output power changes, the inverter's output current can reach a steady state again within 0.005 s. The improved DBC can effectively suppress the harmonics and improve the response speed of the output current. When the power is seriously unbalanced, the output current is distorted, with a THD of 5.69%. After using the third harmonic injection control, the THD is suppressed to 0.91%.
The simulation and experiments concluded that: (1) The master-division control improves the overall power supply quality of the system. The improved DBC has a faster response speed than the traditional PR control, effectively suppressing the output current harmonics. (2) Using the proposed MPSPWM method, the switching frequency is effectively reduced, and the implementation scheme is simple. It is more suitable for QZS-CMI than simple boost modulation. (3) When the power is seriously unbalanced, the third harmonic injection control is adopted to ensure that each module photovoltaic cell is operating at the maximum power point and effectively prevent the occurrence of overmodulation.

Key words： Quasi-Z-source cascaded multilevel inverter multi-carrier phase-shifted PWM master-division control deadbeat control third harmonic injection

Received: 18 October 2024

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TM464

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	Jin Ningzhi
	Hou Jiaowei
	Sun Dongyang

Cite this article:

Jin Ningzhi,Hou Jiaowei,Sun Dongyang. Quasi-Z-Source Cascaded Multilevel Photovoltaic Inverter Based on Master-Division Control[J]. Transactions of China Electrotechnical Society, 2025, 40(20): 6699-6715.

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https://dgjsxb.ces-transaction.com/EN/10.19595/j.cnki.1000-6753.tces.241832 OR https://dgjsxb.ces-transaction.com/EN/Y2025/V40/I20/6699

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