DC-AC Inverter Control for Unbalanced Loads
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Solution Overview
Problem
DC-AC inverters without individual regulation of positive and negative supplies experience load imbalances, leading to distortion and clipping when loaded with half-wave rectified loads, which increases complexity, cost, and size.
Innovation Solution
A control system with a high side and low side gate-controlled switch connected between a high supply line and a low supply line, utilizing an inverting driver with a feedback loop and a controller to regulate the DC voltage, preventing shoot-through conditions and minimizing distortion by selecting the optimal error signal for the DC-DC converter.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If individually regulated supplies with feedback from the load are used, then load imbalance and distortion are reduced, but cost and circuit complexity increase
Solution Approach 1:
The inverter leg is segmented into high side and low side switches with independent control drivers. Each driver (inverting driver 142 and non-inverting driver 144) independently controls one switch, allowing separate regulation of positive and negative supplies without requiring complex centralized feedback control for the entire leg.
Solution Approach 2:
The inverting driver incorporates feedback through its feedback input that receives a feedback signal from the output node. This local feedback mechanism enables the driver to sense output conditions and adjust its drive signal accordingly, maintaining load balance without requiring external regulated supplies.
2Reliability
If individually regulated supplies with feedback from the load are used, then distortion is reduced, but size and weight increase
Solution Approach 1:
The control circuitry is merged into the driver stage. The inverting driver and non-inverting driver are integrated within the inverter leg structure itself, eliminating the need for separate external regulated power supplies and feedback control circuits that would add weight.
Solution Approach 2:
The drivers are self-regulating through their feedback inputs that directly monitor their own output nodes. Each driver automatically adjusts its drive signal based on local conditions, eliminating the need for external weight-bearing regulation hardware.
3Reliability
If a driving voltage is applied to prevent shoot-through, then switch control reliability is improved, but device complexity increases
Solution Approach 1:
The inverting driver is designed to naturally produce a driving voltage that prevents shoot-through conditions before they can occur. The feedback mechanism detects potential shoot-through conditions and preemptively adjusts the drive signal to maintain proper switch timing and prevent simultaneous conduction.
Solution Approach 2:
The driver uses an inverting configuration where the feedback signal is inverted to produce the appropriate drive signal. This inversion naturally creates the driving voltage needed to prevent shoot-through while simplifying the control logic compared to direct control methods.
Data Source
AI summary
A three phase inverter consisting of three single phase legs using either switch mode or linear control is fed by a DC-DC converter to provide input output isolation. This requires that the DC-DC converter delivers equal positive and negative voltages to the single phase legs to allow each output to generate a high fidelity sine wave outputs to the load. By measuring the error voltages on the positive output, the negative output and the total output of the DC-DC converter it is possible to control a single duty cycle while maintaining all three output voltages within the limits required by the DC-AC phase legs. This significantly reduces the cost and complexity of the DC-DC converter and eliminates the need to use a fourth phase leg to generate the neutral connection for a three phase output.