Voltage Source Converter Pre-Control Unit Dynamics
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Solution Overview
Problem
Existing converter control methods experience undesirable control delays during transitions from one stationary operating point to another, especially due to time constants of the controller and the controlled system, making it difficult to quickly and reliably reach a new steady-state operating point, particularly after sudden changes in setpoint values.
Innovation Solution
The pre-control unit utilizes the impedance (R+jX) of a transformer connected between the converter and the AC voltage network to calculate step control variables, and the pilot control unit interrupts the transmission of reference variables from the control unit to the ignition unit, instead transmitting jump command variables based on transformer parameters, which improves control dynamics by calculating input signals using setpoint values and transformer parameters to accelerate the transition to a new steady-state operating point.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a standard proportional integral controller is used to control the inverter, then the controller is simple and reliable, but control delays occur during transitions between steady-state operating points
Solution Approach 1:
The feedforward control unit calculates the required change in reference input variables based on setpoint changes before the controller can respond. By computing the necessary voltage adjustments using the impedance relationship (ΔU = ΔI × Z) in advance, the system eliminates the delay inherent in traditional feedback controllers that must wait for errors to develop and then respond through their time constants.
Solution Approach 2:
The feedforward control unit acts as an intermediary between the setpoint specification and the ignition unit. It receives setpoint changes, calculates the appropriate reference input adjustments using transformer impedance parameters, and directly provides these adjusted values to the ignition unit, bypassing the slow feedback loop of the proportional integral controller for the initial transient response.
2Ease of operation
If the control unit generates reference values based on comparing actual values with setpoints through a proportional integral controller, then the control system is stable and easy to implement, but the transition to a new steady-state operating point is slow
Solution Approach 1:
The feedforward control unit performs preliminary calculations of the required reference input changes based on setpoint modifications and transformer impedance characteristics. This advance computation allows the system to immediately jump toward the new operating point without waiting for the gradual error-correction process of the proportional integral controller, significantly accelerating the transition speed while maintaining implementation simplicity.
3Speed
If the feedforward control unit calculates step control variables using transformer impedance parameters, then the control dynamics are improved and control delays are reduced, but the device complexity increases
Solution Approach 1:
The feedforward control unit serves as a dedicated intermediary component that handles the complex impedance-based calculations separately from the main proportional integral controller. This modular approach isolates the complexity to a specific function block while keeping the overall control system structure clear and maintainable, achieving improved control dynamics without overwhelming system-wide complexity.
Solution Approach 2:
The control system is segmented into two distinct functional parts: the feedforward control unit that handles dynamic transitions using impedance calculations, and the proportional integral controller that maintains steady-state operation. This segmentation allows each part to be optimized independently, with the feedforward unit providing fast transient response and the PI controller ensuring stable long-term operation, thereby managing overall system complexity.
Data Source
Figure 1~2
Figure 3
AI summary
The voltage source converter controlling device comprises an ignition unit. The ignition unit is connected with controlled power semiconductors of a voltage source converter. A control unit (3) is provided, which is connected at an input side with an actual value unified numbering system. Multiple measuring sensors are provided, which are connected at an output side with the ignition unit by a pre-control unit (9). The converter is connected to a direct current voltage circuit and an alternating voltage circuit with multiple phases. An independent claim is included for a method for controlling a voltage source converter.