Photovoltaic Inverter Neutral Switching for Lower Modulation Loss
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Solution Overview
Problem
Existing photovoltaic inverters using a three-phase four-wire system are limited to sine wave pulse width modulation (SPWM) control, which hinders efficiency improvement.
Innovation Solution
A photovoltaic inverter with a three-phase bridge arm and a switching circuit connected to the neutral wire, allowing flexible switching between SPWM and common-mode voltage injection modulation modes, reducing switching losses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If SPWM control is used in a three-phase four-wire system, then the inverter can operate with proper neutral wire connection, but the efficiency is limited due to higher switching losses
Solution Approach 1:
The patent implements dynamic switching between SPWM and common-mode voltage injection modulation modes based on system conditions. The controller dynamically selects the optimal modulation mode, enabling the inverter to adapt its operation to minimize switching losses while maintaining proper neutral wire connection and system stability.
Solution Approach 2:
The patent changes the modulation mode parameter from fixed SPWM to a variable state that can switch between SPWM and common-mode voltage injection modulation. By changing this operational parameter dynamically, the system achieves reduced switching losses while maintaining adaptability through the switching circuit that controls neutral wire connection.
2Productivity
If common-mode voltage injection modulation is used, then switching loss is reduced and efficiency is improved, but the system requires blocking the neutral wire current loop which complicates the control system
Solution Approach 1:
The patent introduces a switching circuit as an intermediary component between the neutral wire and the load. This switching circuit acts as a mediator that can selectively block or connect the neutral wire current loop based on the selected modulation mode, thereby enabling common-mode voltage injection modulation without permanently complicating the overall system structure.
Solution Approach 2:
The control system complexity is managed through dynamic control of the switching circuit. The controller dynamically adjusts the switching circuit state (connected or blocked) according to the selected modulation mode, allowing the system to achieve high efficiency through common-mode voltage injection modulation only when needed, rather than maintaining constant complexity.
3Loss of energy
If the neutral wire current loop is blocked for common-mode voltage injection modulation, then switching loss is reduced, but the system loses the ability to handle interphase imbalance effectively
Solution Approach 1:
The patent implements dynamic switching between two operational states: when phases are balanced, the system blocks the neutral wire current loop to reduce switching losses; when interphase imbalance is detected, the system connects the neutral wire current loop to handle the imbalance effectively. This dynamic adaptation resolves the contradiction between loss reduction and reliability maintenance.
Solution Approach 2:
The control system incorporates feedback mechanisms to detect interphase balance status and dynamically adjust the switching circuit state accordingly. This feedback control ensures that the system maintains reliability by connecting the neutral wire when imbalance occurs, while achieving energy efficiency by blocking it during balanced operation.
Data Source
AI summary
A photovoltaic inverter and a control method thereof are provided. The photovoltaic inverter includes: a three-phase bridge arm, including an A-phase bridge arm, a B-phase bridge arm, and a C-phase bridge arm, where a midpoint of the A-phase bridge arm is electrically connected to an A-phase line, a midpoint of the B-phase bridge arm is electrically connected to a B-phase line, a midpoint of the C-phase bridge arm is electrically connected to a C-phase line, and a midpoint of any one of the A-phase bridge arm, the B-phase bridge arm, and the C-phase bridge arm is also electrically connected to a neutral wire through a freewheeling branch; and a switching circuit electrically connected between the neutral wire and a user side.