15.1 Inverter Drive Basics15 -3(a)1 cycle 1 cyclePhase−Uvoltage signal PWM carrier signal Phase−U voltage signalSwitches(See Fig.15.2)Output frequenncy: HighOutput voltage: HighAverage output voltageS1,S3S4S2,ONONOutput frequenncy: LowOutput voltage: Low(b)Fig 15.3 Sine Wave PWM Control15.1.2 Inverter and Converter ConfigurationAs shown in Fig. 15.4, the configuration consists of a VS-656MR5 Converter, which rectifies a commer-cial power supply and converts it to direct current, a main circuit capacitor, which smooths the rectifiedvoltage, and a VS-626M5 Inverter, which converts the direct current to the required AC frequency. Theconverter switching element uses IGBT as used by the Inverter.3-phaseAC powersupplyVS-656MR5 ConverterACLP VS-626M5 InverterInductionmotorMain circuitcapacitorMain circuitcapacitorNFig 15.4 Inverter and Converter Configuration15.1.3 Squirrel Cage Induction Motor CharacteristicsThe squirrel cage induction motor characteristics are contrasted with the DC motor and the principle oftorque generation is explained below. Fig. 15.5 shows the model diagrams for each from the direction ofthe axis.Torque occurs in the DC motor using electromagnetic force proportional to the accumulated current thatflows in the armature winding, and the magnetic flux created by the magnetic field current. The torquegenerated in this way is easy to control because the magnetic field windings from which the magnetic cur-rent flows and the armature windings are independent.On the other hand, the squirrel cage induction motor consists of a rotator with a so-called “squirrel-cage”construction, and a stator with stator windings. When 3-phase alternating current flows through the statorwindings, a magnetic field of magnetic flux φm is generated. This is equivalent to the magnetic flux gener-ated by the DC motor magnetic field current.Magnetic flux φm can be expressed using the following formula. This current is called magnetized currentIm, and is almost equivalent to the unladen current of the squirrel-cage induction motor.Formula: φm = MIm15
