Inverter Common-Mode Injection for Ripple Current and Switching Loss
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Solution Overview
Problem
Three-phase three-level inverters face challenges with large ripple currents on the direct current bus capacitor, leading to increased capacitor losses, temperature rise, and potential breakdowns, while existing common-mode voltage injection control methods either increase switching losses or require more capacitors, failing to meet both low ripple current and low switching loss requirements.
Innovation Solution
A method and apparatus for common-mode voltage injection control that adjusts common-mode voltages based on discontinuous pulse-width modulation (DPWM), model predictive control (MPC), and continuous pulse-width modulation (CPWM) modes, using real-time data to optimize ripple current and switching loss, reducing the number of bus capacitors and costs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the number of bus capacitors is reduced to lower cost, then device complexity and cost decrease, but ripple current and capacitor losses increase
Solution Approach 1:
The patent converts the harmful effect of common-mode voltage into a beneficial control mechanism. By intentionally injecting controlled common-mode voltage through selective PWM modulation, the system reduces ripple current magnitude and its harmful effects (capacitor losses, temperature rise) while using fewer capacitors, thereby transforming a potential problem into a solution.
Solution Approach 2:
The patent implements feedback control by continuously monitoring operating conditions (power factor, load level) and adjusting the common-mode voltage injection strategy accordingly. The controller uses feedback from the system state to select optimal modulation modes and parameters, ensuring that ripple current remains within acceptable limits even with reduced capacitor count.
Data Source
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AI summary
A common-mode voltage injection control method and apparatus for an inverter are provided. For the method and apparatus, a common-mode voltage for a DPWM mode is calculated based on three-phase port voltages and an output power command (S202); a common-mode voltage for an MPC modulation mode is calculated based on the direct current bus voltage, the three-phase port voltages, and the output power command (S204); a modulation proportion is determined based on a maximum phase voltage peak value of the three-phase port voltages, the direct current bus voltage, and a power factor of the output power command (S206); and a common-mode injection voltage is generated based on the common-mode voltage for the DPWM mode, the modulation proportion, and the common-mode voltage for the MPC modulation mode (S208). In this way, the common-mode voltages for the modulation modes and the modulation proportion for generating the common-mode injection voltage are adjusted according to the real-time state of the inverter, which is conducive to achieving the flexibility of the inverter under different operating conditions, and helps meet the requirements of both a relatively small ripple current of a direct current bus capacitor and a relatively small switching loss.