Motor Control Using Zero-Phase Voltage to Cut Capacitor Ripple
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Solution Overview
Problem
Existing motor control techniques struggle to effectively reduce capacitor voltage ripples while minimizing increases in capacitor volume and switching loss, particularly in the overmodulation region where the modulation factor exceeds 1.15, due to complex calculations and inaccurate motor rotational position detection.
Innovation Solution
A motor control device that adjusts three-phase voltage commands using a zero-phase voltage based on the power factor of AC power, performing pulse width modulation to generate gate signals for the power converter, even in the overmodulation region, thereby reducing capacitor voltage ripples and switching losses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the electrostatic capacitance of the smoothing capacitor is increased to reduce capacitor voltage ripples, then the capacitor voltage ripple is reduced, but the capacitor volume increases
Solution Approach 1:
The patent changes the control parameter by introducing a zero-phase voltage command component that is superimposed on the three-phase voltage commands. This parameter change modifies the switching pattern of the power converter, thereby reducing capacitor voltage ripples without requiring an increase in capacitor electrostatic capacitance or volume
Solution Approach 2:
The patent applies periodic zero-phase voltage commands that are synchronized with the fundamental frequency of the AC output. By applying voltage commands at specific periodic intervals corresponding to the AC cycle, the patent reduces capacitor voltage ripples through timed switching actions rather than increasing capacitor size
2Object-affected harmful factors
If the switching frequency of the inverter is increased to reduce capacitor voltage ripples, then the capacitor voltage ripple is reduced, but the switching loss increases
Solution Approach 1:
The patent modifies the voltage command parameters by adding a zero-phase voltage component, which changes the switching instants and duty cycles of the power converter. This parameter adjustment reduces capacitor voltage ripples while maintaining the original switching frequency, thereby avoiding increased switching losses
Solution Approach 2:
The patent implements a control mechanism where the zero-phase voltage command is calculated based on the fundamental frequency components of the AC output voltage and current. This feedback-based approach optimizes the switching pattern to reduce capacitor voltage ripples without requiring higher switching frequencies that would increase switching losses
3Object-affected harmful factors
If the zero-phase voltage command is calculated using a complicated formula to reduce capacitor voltage ripple, then the capacitor voltage ripple is reduced, but the calculation cost increases
Solution Approach 1:
The patent segments the voltage command calculation into distinct components: the fundamental three-phase voltage commands and the zero-phase voltage command. The zero-phase voltage is calculated separately using a simplified formula based on fundamental frequency components, reducing the overall calculation complexity compared to a single complicated formula
Solution Approach 2:
The patent extracts the zero-phase voltage component from the overall voltage command system and calculates it independently using a simplified approach. By separating this component and calculating it based on fundamental frequency components rather than using a complicated comprehensive formula, the calculation cost is reduced while still achieving capacitor voltage ripple reduction
4Object-affected harmful factors
If the zero-phase voltage command is superimposed in the overmodulation region to reduce capacitor voltage ripple, then the capacitor voltage ripple is reduced, but the output voltage control accuracy deteriorates
Solution Approach 1:
The patent adapts the zero-phase voltage command calculation for the overmodulation region by using the power factor as a parameter. This parameter change allows the zero-phase voltage to be adjusted according to the operating condition, maintaining output voltage control accuracy while still reducing capacitor voltage ripples in the overmodulation region
Solution Approach 2:
The patent implements a dynamic control approach where the zero-phase voltage command is adjusted based on the modulation factor and power factor. In the overmodulation region, the system dynamically adapts the voltage command parameters to maintain control accuracy while reducing capacitor voltage ripples, rather than using a fixed superposition approach
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution effectively reduces capacitor voltage ripples and switching losses, allowing for a stable torque output and downsizing of the capacitor volume, especially in high-speed and high-torque regions.
Implementation Method 1
a gate signal generation unit that performs pulse width modulation on the three-phase voltage command and generates a gate signal for controlling an operation of the power converter
Implementation Method 2
The smoothing capacitor is connected to the power module in parallel with the DC power supply in order to suppress voltage ripples (capacitor voltage ripples) on the DC power supply side
Data Source
AI summary
A motor control device connected to a power converter that performs power conversion from DC power to AC power and controls driving of an AC motor that is driven by using the AC power includes a voltage command generation unit that generates a three-phase voltage command; and a gate signal generation unit that performs pulse width modulation on the three-phase voltage command and generates a gate signal for controlling an operation of the power converter, in which the voltage command generation unit adjusts the three-phase voltage command by using a zero-phase voltage based on a power factor of the AC power in an overmodulation region in which a modulation factor according to a voltage amplitude ratio between the DC power and the AC power exceeds a predetermined threshold value, and the gate signal generation unit generates the gate signal by performing pulse width modulation on the adjusted three-phase voltage command.