Bypassable Variable Frequency Drives
A Variable Frequency Drive (VFD) completely eliminates the large starting inrush current of the compressor by ramping up frequency and voltage in a controlled time period. This prevents overload when on limited dockside power or a generator without causing noticeable voltage reductions throughout the rest of the yacht's electrical system. The bypassable VFD eliminates the starting inrush of current, then seamlessly disengages and reconnects the compressor to the main power once it is running at peak, thus eliminating all harmonic distortion and RFI. There is also no need for line filters and conditioners. In addition, it reconnects to the compressor just before compressor shutdown for a smooth stop. It accomplishes this with totally unique capabilities never before available in a marine HVAC system.
Before bypassing can take place, the VFD synchronizes the phase of its AC power sine wave with that of the main power source, a process called phase locking. Once phase lock occurs, the bypass is done by the opening and closing of a series of electrical switches, the timing of which is so precise that there is no interruption or overlap of current. For smooth compressor shutdown, the bypassed VFD will perform another pahse lock, then reconnect to the compressor by reversing the electrical switching. While in bypass mode, the VFD is available to connect to another compressor for ramp up or ramp down. One bypassable VFD cqn support up to four compressors, making it especially cost effective for chillers with two, three, or four stages. A display allows the user to monitor operation and faults.