JOHNSON CONTROLS
FORM 160.84-EG1 (617)
24
OptiSpeed Variable-Speed Drive
The new YORK OptiSpeed VSD is a liquid-cooled, insulated-gate, bipolar-transistor-
based (IGBT), pulse-width-modulated (PWM) rectifier/inverter in a highly integrated pack-
age. This package is small enough to mount directly onto the chiller. The power section of
the drive is composed of four major blocks: a three-phase AC-to-DC rectifier section with
an integrated input filter and precharge circuit, a DC link filter section, a three-phase DC
to AC inverter section, and an output sine filter-network.
An input disconnect device connects the AC line to an input filter and then to the AC-to-DC
three-phase PWM rectifier. The disconnect device can be a three-phase rotary disconnect
switch (standard), or an electronic circuit breaker (optional). The inductors in the input fil-
ter limit the amount of fault current into the VSD; however, for the additional protection of
the PWM rectifier’s IGBT transistors, semiconductor fuses are provided between the input
disconnect device and input filter. The three-phase PWM rectifier uses IGBT transistors,
mounted on a liquid-cooled heat sink and controlled at a high frequency, to convert AC
line voltage into a tightly regulated DC voltage. Additionally, the PWM rectifier shapes the
line current into an almost-sinusoidal waveform, allowing the VSD to produce low levels
of harmonic distortion while helping the building comply with the requirements of the IEEE
STD 519-1992, “IEEE Recommended Practices and Requirements for Harmonic Control
in Electrical Power Systems”. The PWM rectifier also contains a proprietary precharge
circuit, which keeps the inrush current into the VSD at a minimal value, well below the
nominal.
The DC Link filter section of the drive consists of one basic component, a bank of filter
capacitors. The capacitors provide an energy reservoir for use by the DC to AC inverter
section of the OptiSpeed Drive. The capacitors are contained in the OptiSpeed Power
Pole, as are the “bleeder” resistors, which provides a discharge path for the stored energy
in the capacitors.
The DC to AC PWM inverter section of the OptiSpeed serves to convert the DC voltage
to AC voltage at the proper magnitude and frequency as commanded by the OptiSpeed
Logic board. The inverter section consists of fast switching IGBT transistors mounted
on a liquid cooled heat sink. The OptiSpeed Power Pole is composed of the inverter
IGBT modules (with heat sink), the rectifier IGBT modules (with heat sink), the DC link
filter capacitor, the “bleeder” resistors, the laminated interconnecting buss bar, and the
OptiSpeed Gate Driver board. The OptiSpeed Gate Driver board provides the turn-on
and turn-off commands to the rectifier’s and inverter’s transistors. The OptiSpeed Logic
board determines when the turn-on, and turn-off commands should occur. Additionally,
the OptiSpeed logic board monitors the status of the OptiSpeed VSD system, generates
all OptiSpeed system faults (including the ground fault), and communicates with OptiView
control panel.
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