Vacon OPT-A2 User Manual
Also see for OPTA1: User manual
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Introduction vacon • 324-hour support +358 (0)40 8371 150 • Email: vacon@vacon.com1. INTRODUCTION1.1 Operation principle of BCUWhen you want to slow down a running asynchronous motor fed by a frequency converter it turnsinto a generator, feeding energy back into the frequency converter. The energy increases the voltagein the DC-link. The frequency converter compensates for this increase by increasing the outputfrequency, decreasing the instantaneous slip and increasing the motor load. The deceleration is, inthis case, dependent on the power losses in the converter and in the motor. This is usually sufficientin most cases, for pumps, fans, conveyors etc. where the kinetic energy in the load is small or thebraking time is not critical.When you have to brake down the motor faster than the losses allow, you have to use BCU moduleand an external brake resistor (or resistors) for energy dissipation. The extra energy from the loadis turned into heat in the brake resistor. If the DC link voltage increases too much, the BCU turns onand discharges the capacitors through the brake resistor. Applications where dynamic braking isusually needed include centrifuges, cranes, some conveyors and drives requiring very fastreversing.Modules can be connected parallel with other BCU modules in order to increase braking capacity(Figure 1).In BCU application you can use either Analogue input or OPT-B8 option board for PT100 sensorconnection.Start-up sequence of BCU application has been illustrated in Figure 2.Figure 1. BCU in common DC bus system |
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