UPS Static Switch Commutation Control
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Solution Overview
Problem
Conventional UPS operations using thyristor-type static switches face delays in commutation due to premature enabling of converter circuits, leading to extended transients and output deviations from specifications, as the converter may maintain the switch in an 'on' state for several milliseconds, causing low impedance conditions and prolonged specification violations.
Innovation Solution
Delaying the enabling of the converter circuit until the static switch has commutated to an off state by asserting a switch drive signal and using delay circuitry or current detection to prevent premature power application from the converter circuit, thereby allowing the switch current to decay rapidly and avoiding extended transients.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the converter circuit is enabled immediately after the static switch drive signal is deasserted, then the UPS can quickly transition to converter operation, but the static switch commutation is delayed and the output remains out of specification for an extended period
Solution Approach 1:
The patent applies preliminary action by enabling the converter circuit before the static switch has fully commutated. The converter is enabled after a predetermined time interval (e.g., 500 microseconds) following deassertion of the switch drive signal, but before the switch current has completely decayed. This preliminary enabling allows the converter to take over the load gradually as the switch commutates, preventing output specification violations while maintaining fast transition speed.
2Reliability
If the converter circuit is delayed until the static switch has fully commutated, then the output remains within specifications, but the transition to converter operation is prolonged and commutation delays increase
Solution Approach 1:
The converter circuit is enabled in advance during the commutation process rather than waiting for commutation to complete. This preliminary action reduces the effective commutation delay by having the converter ready to take over immediately as the switch current decays, rather than waiting for the entire commutation process to finish before enabling the converter.
Solution Approach 2:
The system uses self-service by monitoring the static switch current and automatically controlling the converter enablement timing. The converter is enabled based on the actual commutation progress detected through current sensing, allowing the system to self-regulate the transition timing without external intervention, optimizing both speed and reliability.
3Speed
If the converter circuit is enabled while the static switch is still conducting, then fast transition is achieved, but low impedance conditions and extended transients occur
Solution Approach 1:
The converter is enabled preliminarily during the commutation process rather than waiting for complete commutation or enabling immediately at drive signal deassertion. This timing optimization allows the converter to be ready to share the load as the switch commutates, preventing severe low impedance conditions while avoiding extended transients by not enabling too early.
Solution Approach 2:
The system changes the operational parameters by adjusting the converter enablement timing based on the commutation progress. By using a predetermined time interval (e.g., 500 microseconds) after drive signal deassertion, the system optimizes the parameter of converter enablement timing to balance transition speed with transient suppression, preventing harmful low impedance conditions.
Data Source
AI summary
A UPS is operated by deasserting a static switch drive signal, e.g., a gate signal to a thyristor, and then delaying provision of power from a converter circuit of the UPS, e.g., an inverter or other source of AC power, until after the switch has current commutated to an off state. For example, expiration of a predetermined time interval following deassertion of the switch drive signal may be detected, and the converter circuit may be enabled to drive the output of the UPS responsive to the detected expiration of the predetermined time interval. Alternatively, a current in the static switch may be detected, and the converter circuit may be enabled to drive the output of the UPS responsive to the detected current. The invention may be embodied as methods and apparatus.