Content 4 Page 2.3.2 Semi-controlled Rectifi ers ..........................................................................................46 2.3.3 Fully-controlled Rectifi ers ...........................................................................................47 2.3.4 Active Front-End/Active Infeed .................................................................................48 2.4 Intermediate Circuit .................................................................................................................48 2.4.1 Variable Intermediate Circuit .....................................................................................49 2.4.2 Constant Intermediate Circuit ...................................................................................51 2.5 Inverter .........................................................................................................................................52 2.6 Modulation Principles .............................................................................................................55 2.6.1 Pulse Amplitude Modulation (PAM) ........................................................................55 2.6.2 Pulse with Modulation (PWM) ...................................................................................56 2.6.3 Asynchronous PMV .......................................................................................................59 2.6.3.1 SFAVM ................................................................................................................59 2.6.3.2 60° AVM .............................................................................................................62 2.7 Control Circuit and Methods ................................................................................................63 2.7.1 Simple Control Method ...............................................................................................65 2.7.2 Scalar Control with Compensation ..........................................................................66 2.7.3 Space Vector with and without Feedback ............................................................67 2.7.3.1 Space Vector (Open Loop) ..........................................................................67 2.7.3.2 Space Vector (Closed Loop) .......................................................................68 2.7.4 Open Loop and Closed Flux Vector Control .........................................................69 2.7.4.1 Flux Vector (Open Loop) .............................................................................69 2.7.4.2 Flux Vector (Closed Loop) ...........................................................................70 2.7.5 Servo Drive Control .......................................................................................................70 2.7.6 Control Conclusions ......................................................................................................71 2.8 Danfoss Control Principles .....................................................................................................71 2.8.1 Danfoss VVCplus Control Principle ..........................................................................72 2.8.2 Danfoss Flux Vector Control Principle ....................................................................76 2.9 Standards and Legislations ...................................................................................................77 3 Frequency Converters and Motors ..........................................................................................78 3.1 Basic Principles...........................................................................................................................78 3.1.1 U/f Operation and Field Weakening ........................................................................78 3.1.2 87 Hz Characteristics.....................................................................................................80 3.1.3 Running in Current Limit .............................................................................................82 3.2 Compensations ..........................................................................................................................82 3.2.1 Load-independent Start Compensations .............................................................83 3.2.2 Load-dependent Start Compensations .................................................................83 3.2.3 Load Compensations ....................................................................................................84 3.2.4 Slip Compensations ......................................................................................................84 3.2.5 PM Motor and SynRM compensations ...................................................................85