tailieunhanh - HVAC and Dehumidifying Systems_12

Tham khảo tài liệu 'hvac and dehumidifying systems_12', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Simpo PDF Merge and Split UnregisteredVersion- http APPENDIX D Continued 4 High voltage spikes to motor windings. 5 Load dependent poor for multimotor applications. 6 Poor input power factor due to SCR converter section. VSI Design. The VSI drive is very similar to a CSI drive in that it also uses an SCR converter section to regulate DC bus voltage. Its inverter section produces a six-step output but is not a current regulator like the CSI drive. This drive is considered a voltage regulator and uses transistors SCR s or gate turn off thyristors GTO s to generate an adjustable frequency output to the motor. a VSI s have the following advantages 1 Basic simplicity in design. 2 Applicable to multimotor operations. 3 Operation not load dependent. b As with other types of drives there are disadvantages 1 Large power harmonic generation back into the power source. 2 Poor input power factor due to SCR converter section. 3 Cogging below 6 Hz due to square wave output. 4 Non-regenerative operation. Flux Vector PWM Drives a PWM drive technology is still considered new and is continuously being refined with new power switching devices and smart 32-bit microprocessors. AC drives have always been limited to normal torque applications while high torque low rpm applications have been the domain of DC drives. This has changed recently with the introduction of a new breed of PWM drive the flux vector drive. 190 Simpo PDF Merge and Split UnregisteredVersion- http APPENDIX D Continued b Flux vector drives use a method of controlling torque similar to that of DC drive systems including wide speed control range with quick response. Flux vector drives have the same power section as PWM drives but use a sophisticated closed loop control from the motor to the drive s microprocessor. The motor s rotor position and speed is monitored in real time via a resolver or digital encoder to determine and control the motor s actual speed torque and