Multilevel Inverter Gate Allocation for Capacitor Voltage Balance
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Solution Overview
Problem
Existing multi-level inverters face challenges in maintaining balance between the voltages of positive and negative electrode side capacitors in the DC bus circuit, leading to potential overvoltage and torque ripple due to imbalances caused by variations in voltage, frequency, or power factor.
Innovation Solution
A power conversion device with a control unit that includes a modulation factor computing unit, gate signal generator, and gate signal allocator to adjust the allocation of gate signals, ensuring balanced voltages between the positive and negative electrode side capacitors through alternating the on/off states of switching elements in switching legs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If triangular wave comparison PWM control is used with phase shifting for each level, then pulse generation for multi-level output is achieved, but capacitor voltage imbalance occurs between positive and negative electrode sides
Solution Approach 1:
The control unit monitors capacitor voltages on both electrode sides and dynamically adjusts the triangular wave phase shift amount based on the detected voltage imbalance, creating a closed-loop feedback system that maintains capacitor voltage balance while enabling multi-level pulse generation
Solution Approach 2:
The invention changes the phase shift parameter of the triangular wave dynamically based on capacitor voltage conditions. By adjusting the phase shift amount according to detected voltage imbalance, the system optimizes the pulse pattern to maintain capacitor voltage balance across different operating conditions
2Loss of energy
If switching control is optimized for uniform switching loss among power conversion units, then loss balance is improved, but capacitor voltage imbalance is not addressed
Solution Approach 1:
The control unit performs multiple functions simultaneously: it generates multi-level PWM pulses, manages switching loss distribution among power conversion units, and maintains capacitor voltage balance by dynamically adjusting triangular wave phase shifts, making the system universally capable of handling multiple control objectives
3Adaptability or versatility
If the inverter operates with variable voltage or frequency, then adaptability to different operating conditions is improved, but capacitor voltage imbalance increases due to asymmetric switching time periods
Solution Approach 1:
The system dynamically adjusts the triangular wave phase shift amount in real-time based on operating conditions (voltage, frequency, power factor) and detected capacitor voltage imbalance, enabling the inverter to maintain capacitor voltage balance across a wide range of variable operating conditions
Data Source
AI summary
A power conversion device includes an inverter, a control circuit and a series body. The control circuit includes a modulation factor computing unit that computes a modulation factor of the inverter based on the DC voltage and an output voltage command value, a gate signal generator that generates a gate signal necessary for on/off drive of the switching elements for generation of a pulse train based on comparison between the computed modulation factor and a carrier signal, and a gate signal allocator circuit that adjusts allocation of a gate signal such that a voltage of the positive electrode side capacitor and a voltage of the negative electrode side capacitor are balanced.