Direct Power Converter Control for Buffer Capacitor Voltage Stability
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Solution Overview
Problem
Conventional direct power converters face challenges in maintaining stable both-end voltages due to variations in the electrostatic capacity of buffer capacitors, leading to errors in input current estimation and operational instability.
Innovation Solution
A direct-power-converter control device that includes a power buffer circuit with a discharge circuit and a charge circuit, utilizing a distribution factor to buffer power and an inverter controller to manage duties and voltages, ensuring the buffer capacitor's voltage remains stable despite capacity variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the electrostatic capacity of the buffer capacitor varies, then the both-end voltage varies significantly, but this leads to errors in input current estimation and operational instability
Solution Approach 1:
The control device continuously monitors the both-end voltage of the buffer capacitor and uses this feedback to dynamically adjust the reactor current command. By comparing the actual both-end voltage with the target voltage, the system generates corrective control signals that compensate for capacity variations, thereby maintaining accurate input current estimation and operational stability despite capacitor degradation or tolerance variations.
Solution Approach 2:
The system adapts to buffer capacitor capacity variations by dynamically changing the reactor current command parameter based on the measured both-end voltage. When the capacitor capacity changes, the control device modifies the reactor current command to maintain the desired both-end voltage, effectively compensating for the capacity variation without requiring physical replacement of the capacitor.
2Object-generated harmful factors
If a buffer capacitor is used to compensate for power ripple, then the power ripple is reduced, but the electrostatic capacity varies over time leading to voltage instability
Solution Approach 1:
The control device implements continuous feedback control by monitoring the both-end voltage and adjusting the reactor current command accordingly. This closed-loop control compensates for the natural capacity variation of the buffer capacitor over time, maintaining stable both-end voltage while the capacitor continues to effectively suppress power ripple from the full-wave rectifying circuit.
Solution Approach 2:
The system enables the buffer capacitor to continue serving its primary function of power ripple suppression while the control device automatically compensates for its capacity degradation. The capacitor maintains its voltage smoothing function, and the control system independently handles the stability issue through dynamic reactor current adjustment, allowing the capacitor to self-service without external intervention.
3Productivity
If the reactor current command is estimated based on maximum and minimum both-end voltage values, then the input current can be controlled, but variations in both-end voltage reduce estimation accuracy
Solution Approach 1:
Instead of relying solely on periodic maximum and minimum voltage measurements, the control device implements continuous feedback control by monitoring the both-end voltage in real-time and dynamically adjusting the reactor current command. This continuous adjustment maintains accurate input current estimation even when both-end voltage varies due to capacitor capacity changes, eliminating the need to wait for voltage extremes and improving responsiveness.
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 variations in both-end voltages, enhancing the stability and accuracy of input current estimation, even when the electrostatic capacity of the buffer capacitor changes, thereby maintaining operational reliability.
Implementation Method 1
the capacitor (hereinafter also referred to as a 'buffer capacitor'), which functions as a voltage source, drives a load together with a power supply voltage to compensate for the power ripple
Implementation Method 2
a technique that achieves a function of a boost chopper using a reactor and a switch to boost a voltage across a buffer capacitor
Data Source
Figure 1
Figure 2
Figure 3~4
AI summary
In a power buffer circuit included in a direct power converter, variations in voltage across a buffer capacitor are suppressed even when the electrostatic capacity of the buffer capacitor varies. A control device (10) includes a charge controller (103). The charge controller (103) includes an amplitude determining unit (103a), a charge command generating unit (103b), and a charging operation controller (103c). The amplitude determining unit (103a) determines an amplitude (Im) of a current to be input to a converter by performing at least proportional-integral control on a deviation (ΔVc) between a voltage (Vc) across the buffer capacitor and an average voltage command value (Vc*) that is a command value of an average of the voltage (Vc) across the buffer capacitor. The charge command generating unit (103b) determines a charge command (iL*) by multiplying by the amplitude (Im) a function (F(θ)) determined according to a discharge duty (dc), a rectifying duty (drec), and a distribution factor of power. The charging operation controller (103c) controls an operation of charging the buffer capacitor on the basis of the charge command (iL*).