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Inverter Drive of the
Single Phase Induction Motor 4.1 Rotation Principle of th e Single Phase Induction Motor A Single Phase Induction Motor is an Induction Motor which drives a single phase current power supply as an input. Here, we will describe as an example, a capacitor inductio n motor that is driven by supplying current with phase difference to each of the2 coils th at are arranged at a position with90 [deg] shift, using a capacitor. Using a condenser, by flowing through each coil th e electric current which has a phase difference Block Diagram of a General Condenser Induction Motor is shown in figure4-1. Condenser Squirrel cage Rotator Auxiliary winding Main winding Single Phase Alternate current Voltage Figure4-1 Condenser Induction Motor Configuration Diagram The Condenser Induction Motor arranges the main winding and the auxiliary winding these2 sets of winding at an electrical angle by a phase difference of90 [deg]. A Conde nser is connected serially to an auxiliary winding. If a single phase alternating current source is connected here and since the condenser is connected to the current which flows into the auxiliary winding, in relation to the main winding it becomes about90 [deg] leading phase. Thereby, a rotating magnetic field of2 phase current is generated and the rotor rotates. RL/78G14 Inverter control of the single phase induction motor by RL78/G14 R01AN1658EJ0100 Rev.1.00 Page9 of49 2013.03.15 4.2 Inverter Drive method The Block Diagram at the time of carrying out an inverter drive of the single phase induction motor is shown in Figure4-2. Squirrel shaped Rotator Auxiliary winding Main winding W V U START RUN COM RL78/G14 Inverter Figure4-2 Inverter drive Block Diagram The3 Phase Output Port of an Inverter and winding of the Motor are connected. At this time, the Line Voltage of V-U is the main winding and the Line Voltage of W-U is a voltage applied to an auxiliary winding. For example, When a3 phase alternating current voltage of90 [deg] pha se difference as shown in figure4-3 is applied with an inverter,2 phase current of 90 [deg] phase difference can be created with a line voltage. 90[deg]90[deg] 90[deg] V phase U phase W phase W-U phase V-U phase [V] [deg] Figure4-3 3 Phase Voltage Waveform and Line Voltage Waveform of90 [deg] phase difference RL/78G14 Inverter control of the single phase induction motor by RL78/G14 MADD- Rev.1.00 Page10 of49 2012.12.07 The relation between a Phase Voltage and Line Volta ge can be considered with a Vector Diagram. If the condition of Figure4-3 is shown with a vector diagram, it becomes like figure4-4. W phase U phase V phase W-U phase V-U phase 90[deg] 90[deg] 90[deg] Figure4-4 Vector representation of3 phase voltage and line voltage of90 [deg] phase difference In this system, by adjusting the U Ph ase, V Phase and W Phase we can create the desired Line Voltage. Please refer the6.3 parameter adjustment method of each parameter adjustment method RL/78G14 Inverter control of the single phase induction motor by RL78/G14 R01AN1658EJ0100 Rev.1.00 Page11 of49 2013.03.15 4.3 False Sine wave Output by an Inverter A method to pseudo output the3 phase sine wave of Figure4-3 by using an inverter is explained. Compare a carrier waveform (Triangular wave) and command value voltage waveform (sine wave) and decide the pulse width of the output voltage. This method is called the Triangular Wave comparison method. A conceptual diagram of the triangular wave comparison is shown in figure4-5 Carrier Wave form Command Voltage Wave form Input Pulse Wave form ω t ω t Figure4-5 Triangular Waves Comparison Method Conceptual Diagram
