Relationship between EPS emergency power inverter switching time and switching reliability
This paper mainly describes the relationship between EPS emergency power inverter switching time and switching reliability.
EPS emergency power supply inverter switching time is determined by the EPS emergency power supply inverter switching design. The inverter has two working states: cold backup and hot backup. During cold backup, the control part of the inverter is only in working state, and the power part is in power-up standby state, but it does not start. During hot backup, the whole inverter is in normal operation, but does not bear the load. When the inverter is in hot backup, the minimum switching time is basically determined by the operation time of the switching device used, and when the inverter is in cold backup, the minimum switching time is also restricted by the inverter starting time. If the EPS emergency power supply with large power starts too fast, the inverter output transformer and low-pass filter will produce a large transient impact, and even damage the semiconductor power device, therefore, high-power inverters have soft start characteristics, and the greater the power, the slower the start. Milliseconds (ms) switching time can only use thyristor solid-state switching switch, and the inverter should be in a hot backup state and maintain phase lock with the mains. Applications with no harsh requirements on switching time are generally switched by mechanical switching switches, EPS emergency power supplies with smaller power are generally used power relays, and EPS emergency power supplies with larger power are generally used interlocked AC contactors or automatic switching switches. Compared with AC contactors, automatic switching switches are slower to operate, but because of the mechanical self-holding characteristics of switching switches, they have advantages in terms of long-term reliability for infrequent switching. There are generally five design methods.
(1) ATS dual power electromechanical conversion design: the conversion time is generally 1 ~ 3s, the inverter does not work when the mains is normal, and is in the cold start (also known as cold backup) state to be started.
(2) contactor type conventional conversion design: the conversion time is generally 1 ~ 3s, the inverter does not work when the mains is normal, and is in a cold state to be started.
(3) Thyristor type static high-speed conversion design: the conversion time is generally within ms level, and the inverter works without load when the mains is normal, and is in a hot backup state to be switched.
(4) Zero switching: equivalent to online UPS power supply (or conventional inverter) double conversion circuit design.
(5) Fast conversion design of relay type: the conversion time is generally 100 ~ 250ms, and the inverter works but does not carry a load when the mains is normal, and is in the hot backup state to be switched.