Converter Control Method for DC Voltage Stability
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Solution Overview
Problem
Existing converter control methods require voltage detection circuits, increasing size and cost, and suffer from overshoot issues during instantaneous voltage drops due to integrator interference, which complicates reliable DC voltage control and efficiency.
Innovation Solution
A converter control method that determines the DC voltage command value based on estimated multi-phase voltage components in a rotating coordinate system, eliminating the need for voltage detection and integrating feedback loops to prevent overshoot.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If voltage detection circuit is added to detect AC power source output voltage, then DC voltage control accuracy is improved, but device complexity and cost increase
Solution Approach 1:
The patent creates a mathematical model that copies the relationship between AC power source voltage and required DC voltage. Instead of directly measuring AC voltage, the system uses a predetermined relationship (copy) to determine the lower limit voltage based on detected AC current and power consumption, thereby avoiding the need for voltage detection circuit while maintaining control accuracy
Solution Approach 2:
The patent replaces the physical voltage detection circuit with a computational approach. By substituting the mechanical/electrical detection system with mathematical calculations based on current and power measurements, the system achieves the same control function without adding hardware complexity
2Measurement precision
If multiple integrators are used to control DC voltage and modulation rate, then control precision is improved, but system stability deteriorates due to interference during voltage recovery
Solution Approach 1:
The patent extracts the integration function from the modulation rate control and applies it only to the DC voltage control. By separating the control functions and removing the redundant integrator from modulation rate control, the system eliminates the interference that causes overshoot during voltage recovery while maintaining precise DC voltage control
Solution Approach 2:
The patent implements a feedback mechanism where the detected DC voltage is continuously compared with the command value, and the deviation is integrated to adjust the command value. This single feedback loop with integration provides stable control without the interference problems caused by multiple integrators operating simultaneously
3Reliability
If DC voltage set value is raised to ensure power factor of one, then power factor control is improved, but energy loss increases due to higher voltage stress on switching elements and reactor
Solution Approach 1:
The patent makes the DC voltage command value dynamic by continuously adjusting it based on the detected AC power source voltage (through current and power measurements). Instead of using a fixed high voltage setting, the system dynamically sets the minimum required voltage, thereby maintaining power factor control reliability while reducing unnecessary energy loss from excessive voltage stress
Solution Approach 2:
The patent changes the DC voltage parameter from a fixed value to a variable value that adapts to the actual AC power source conditions. By calculating and adjusting the command value based on detected voltage, current, and power, the system optimizes the voltage parameter to achieve the desired power factor with minimal energy loss
Data Source
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AI summary
A DC voltage is controlled in accordance with a variation of a power source voltage, without the need to detect an effective value of the power source voltage. A PI control section (702) performs a PI control on a deviation (ΔVdc) which is a difference between a DC voltage command (Vdc*) and a DC voltage command (Vdc), and outputs a d-axis current command value (Id*). A PI control section (704) performs a PI control on a deviation (ΔId) which is a difference between the d-axis current command value (Id*) and a d-axis current (Id), and outputs a d-axis voltage command value (Vd*). Based on the d-axis voltage command value (Vd*) and a q-axis voltage command value (Vq*), a PWM control section (709) outputs a switching control signal (G1) for controlling a switching operation of a converter. A voltage command computation section (710) generates the DC voltage command (Vdc*) based on the d-axis voltage command value (Vd*).