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Control of High Speed Permanent Magnet Synchronous Motors Dong Le and Liping Zheng Calnetix Technologies, Inc. California, USA Motor & Drive System 2013 February 7-8, 2013 Orlando, Florida 1 Introduction Permanent Magnet Synchronous Motors are becoming more and more popular due to high performance. High performance PMSM controllers are still challenging when considering High Speed High efficiency High acceleration/deceleration Sensorless Robust to parameter changes Longer cables 2 Transformation Clarke’s Transformation [ f 0 ] [T 0 ][ f abc ] T 0 1 12 2 0 23 3 1 1 2 2 12 3 2 1 2 Park’s Transformation [ f dq ] [Tdq ( d )][ f ] cos sin Tdq ( ) sin cos 3 PWM Active Rectifier ADVANTAGES: Bi-directional flow Nearly sinusoidal current Regulation of power factor to unity Low harmonic distortion of current Controlled DC link voltage regardless of grid voltage (360-520 Vac) The motor may operate at full speed without field weakening by maintaining the DC link voltage above the voltage peak 4 Sensorless Flux Vector Control Virtual Flux Estimator: The voltage imposed by the line power in combination with the AC side inductors are assumed to be quantities related to a virtual motor Thus, R and L represent the stator resistance and stator leakage inductance of the virtual motor and the phase to phase line voltage Uab, Ubc, Uca would be induced by the virtual air gap flux. In other words, the integration of the voltages leads to a virtual line flux vector in stationary αβ coordinates L 5 Sensorless Flux Vector Control– Cont. ADVANTAGES Sensorless: •Simpler •Isolation between power and control circuits •Higher reliability and more cost effective Flux vector control: •Better noise immunity (use of integrator instead of differentiator). •Near sinusoidal current waveform •Better harmonic reduction (low pass filter in the integrator reduces nth harmonics by a factor of 1/k, and strongly reduce the high frequency ripple in the system) •Angle of virtual flux is less sensitive than angle of voltage vector to disturbances in line voltage •Simple algorithms •Good dynamic response •PLL is able to track the flux smoothly event through zero speed 6 Sensorless Flux Vector Control– Cont. Volt/Hz drive: Volt/Hz control of a machine is based on the principle of maintaining a constant magnetic flux in the motor The terminal voltage must increase roughly proportional to the applied frequency V/Hz drives typically add a low frequency voltage boost to increase starting torque capability V/Hz drives typically add a steady state slip compensation which increases with frequency based on current measurement to give better steady state speed regulation V/Hz drives may also add stability compensators to overcome mid frequency instabilities evident in highly efficient machines Volt/Hz works well on applications that the load is predictable, and does not change quickly such as fan loads For better torque control, flux vector control was developed. This technique controls not only the magnitude, but also the orientation of the AC excitation, thus the vector name. This is based on field orientation principles which state that: “If the current vector is controlled relative to the rotor flux vector, then the magnitude of the flux vector and the motor torque can be independently controlled. 7 Sensorless Flux Vector Control– Cont. Based on the DC link voltage Udc and the inverter switch state Sa, Sb, Sc of the rectifier input voltage 2 1 Us Udc ( Sa ( Sb Sc ) are estimated as follows 2 3 Us 1 2 Udc ( Sb Sc ) Then the virtual Flux ψL components are calculated in the stationary coordinates system: diL ) dt dt diL L (Us L ) dt dt And torque: L (Us L 3 n T * ( Iqs ds Ids qs ) 2 2 8 Sensorless Flux Vector Control– Cont. Sensor-less flux vector drives use direct field orientation to provide higher performance Instead of implying the orientation of the flux vector by satisfying the equations, the flux vector is directly measured from terminal electrical quantities of voltage and current The drive continuously integrates and solves the previous equations to obtain instantaneous measurements of the rotor flux vector and motor torque The inputs to the drive are the stator voltage and current vector The current vector is best directly measured, But the voltage can be deduced from a DC link voltage measurement and the PWM switching pattern 9 Sensorless Flux Vector Control– Cont. TOPOLOGY OF INNER LOOP FOR SENSORLESS FLUX VECTOR CONTROL 10 Sensorless Motor Control Block 11 Active Rectifier Control Block 12 Detection & Protection Ground fault detection Over/Under voltage, Over current Programmable DESAT As required for protecting power devices Line start lock-out Unit shall not motor/generator or put power back to GRID until commanded Over Temperature Provide caution signal for heat sink temperature to allow for controlled shutdown or fold back 13 Packaging Design Packaging design take into account Thermal performance Grounding scheme for noise immunity, EMI/EMC Accessibility/maintainability of the system Enclosure Design Features User friendly Provide Faraday cages for control logic to block electric field and electromagnetic radiation (RF) Meet customer design specification 14 IGBT Module SelectionLosses 15 IGBT Temperature Distribution Bi-Direction Power Electronics 17 Function Block Diagram 18 Function Block Diagram - Details 19 Active Rectifier Control Block ACTIVE RECTIFIER CONTROL BLOCK ic Vc ib Vb Udc load ia Va Sa Sc Sb UL Current measurement & Line voltage estimation IL UL PWM IL + Udc_ref k, Us Us V_reg d, q Usq d, q Usd Id_reg Iq_reg + - + Iq_ref Id_ref=0 20 Sensorless Motor Controller Block 21 Motor Control Simulation Simulink Simulation Model 22 Simulation Results Current Waveforms Current vs. time 200 Ia Ib Ic 150 Current (A) 100 50 0 -50 -100 -150 -200 0.425 0.43 0.435 Time(seconds) 0.44 0.445 23 Catch Spin Also caught flying catch - Synchronize the drive with the spinning motor 24 Test Double Pulse Test 25 Test Setup- Back to Back Operate system from 10 kW to 252 kW from/into grid 480VRMS P E MOTOR GEN P E Coupling 26 255kW Back To Back Testing Picture 27 Ground Systems Single Point A. Series (Common or Daisy Chain) B. Parallel(Separate) Multipoint Hybrid NOTE: Series or daisy chain should be avoid whenever possible to prevent common currents from developing voltage drops across their common reference. The concept of typing all the various subassemblies together to a central point via INDIVIDUAL WIRE is no longer acceptable. Such connection while working in very low frequency but tend to enhance cross talk between subassemblies for high frequency circuits. 1 BAD 2 3 1 PREFERED 2 3 28 How to Connect Circuit to Single Point Reference Rule is to Reduce Ground Loop Area Bad Example: Good Example: 29 Connect Equipment to Single Point Reference 30 Minimize Ground Loop Area BAD (LARGE GROUND LOOP AREA) vcc vcc gnd gnd GOOD (SMALL GROUND LOOP AREA) 31 Analog and Digital Ground analog section digital section 32 Conclusion Use PWM active rectifier instead of passive rectifier: Bi-directional power flow Nearly sinusoidal current Regulation of power factor to unity Controlled and regulated bus voltage regardless of grid voltage (360-520Vac) Use of virtual flux estimator instead of voltage estimator with Phase Lock Loop provides: Better noise immunity (use of integrator instead of differentiator) Better harmonic reduction Angle of virtual flux is far less sensitive than angle of voltage vector to disturbances in the line voltage. Simple algorithm Excellent dynamic responses Phase lock loop is able to track the flux smoothly event through zero speed Catchspin feature can synchronize the spinning motor. Proper grounding is very critical to have high performance motor control 33