Co-Owner Kappa Electronics www.kappaiq.com Counts V14 Clk0 z.o.h. PULSE(-1 1 0 0 0 {T_aperture} {1/Fs_pos} 100000) V7 Position_Command {2*pi/quadcounts} E18 i_sampled Pos_encoder POSITION REGULATOR VELOCITY OBSERVER Pos_vo Position_Error {P_pos/quadcounts} error_vo E1 {Speed_limit} max Clamp min V5 {-Speed_limit} {I_vo/Fs_speed} {P_vo} E6 E9 E10 {Kt_est} {B_vo/Jt_est} E15 V1 Torque^ Speed_command Radians/sec Clk0 SPEED REGULATOR {1/Jt_est} E13 V22 Clk1 z.o.h. {I_speed/Fs_speed} E2 {P_speed} PULSE(-1 1 {2*T_apert ure} 0 0 {T_aperture} {1/Fs_speed} 100000) {1/Fs_speed} E14 Acceleration^ CLAMPED INTEGRATOR E5 Speed_Error INTEGRATOR INTEGRATOR INTEGRATOR Clk0 max Clamp min {1/Fs_speed} E17 Clk1 Clk0 Clk0 Clamp min {I_limit} max V19 {-I_limit} 0.5 V16 Pos_vo E16 current PULSE(-1 1 {20uS + p/2 - T_aperture} 0 0 {T_aperture} {p} 100000) I_command CURRENT REGULATOR Range={2.2*I_limit}, bits=10 Speed^ PWM Speed M1- ADC i_sampled V3 Clk2 V4 B3 ADC Trigger V=I(L1)*Kt E4 {Kd} z.o.h. V6 {Kf} max Clamp min {I_current/Fs_current} E11 {P_current} E12 PULSE(-1 1 10uS 0 0 {T_aperture} {1/Fs_current} 100000) Motor Model (Pittman DC Servo Motor Model 14206 with 24V W inding) Damping Losses INTEGRATOR Current_Error L1 {L} V11 {-Kf} B1 V=I(L1) E3 {Kemf} R2 {Rt} Frict ion Motor Bearings and Brushes Clk2 V18 25 max Clamp min 25 V17 current Torque LOAD lock rotor {1/(Jmotor + Jload)} load torque V12 Load E7 V15 PWL(0 0 0.0999999 0 0.1 0.6) PWM Module Reload i.c. V13 To put motor on a dyno, set jumper to "lock rotor" and then use integrator i.c. voltage source to specify dyno speed. 0 z.o.h. MODULATION Quantize Range=50, levels=760 PULSE(-1 1 {20uS + p - T_aperture/2} 0 0 {T_aperture} {p} 100000) E8 PULSE(-24 24 20uS {p/2} {p/2} 0 {p} 1000 {30 / pi} i.c. PWM Carrier Radians Radians/sec Speed RPM 2016 Kappa Electronics Motor Control Training Series 2016 Kappa Electronics LLC Z -1 Z -1 Z -1 Z -1 Z -1 Z -1 -V th
Cycle-by-Cycle Current Limit From Amplifier Motor Current Dave s Motor Control Center PWMs come back on line automatically at the start of the next PWM cycle. Desired current limit + - To PWM Disable PWM Current limit 0 Pros: Cons: Great for robust hardware over-current protection. Can use on-board hardware comparator and fault inputs on most processors. Simple. No software required. Cost effective. Not good for control, since it regulates peak current, not average current. Unstable for duty cycles > 50% unless slope-compensation is used.
In-Line Current Sensing Dave s Motor Control Center i a PWM top PWM Bottom i b i c = -i a -i b Motor Phase Current Average Current Sample Sample Sample Sample Sample Synchronous ADC Sampling helps to filter the measured current anti-aliasing Noise free ADC sampling when the power transistor is not switching Current signal is ALWAYS visible Current can be sampled at TWICE the PWM frequency (null-vectors V0 AND V7) More expensive!
LEM Sensors Simplified schematic representation Hall Sensor - + 8A 7A I(L1) 6A 5A 4A 3A 2A 1A 0A -1A -2A -3A -4A -5A -6A -7A -8A 0.0ms 0.5ms 1.0ms 1.5ms 2.0ms 2.5ms 3.0ms 3.5ms 4.0ms 4.5ms 5.0ms Most popular in-line current sensing sensor. Excellent linearity (flux is zero, so permeability variations of core material do not affect the linearity of the reading). Frequency response all the way down to DC. Expensive
In-Line Current Sampling in Both V0 and V7 Measurements Carrier Voltage Modulation Phase Voltage Sample Pulses Phase Current
2-Shunt Current Sensing Dave s Motor Control Center Inverter Leg Shunts i c = -i a -i b PWM top PWM Bottom Motor Phase Current Average Current Shunt Resistor Signal Sample Sample Sample Synchronous ADC Sampling helps to filter the measured current anti-aliasing Noise free ADC sampling when the power transistor is not switching Current can be sampled at up to the PWM frequency (null-vector V0 only) Current samples are simultaneous. Not suitable for high power motors due to shunt power losses. Reading blackouts occur during high duty-cycle values In the d-q rotating reference frame: - Gain differences manifest as a 2X harmonic distortion - Offset errors manifest as a 1X harmonic distortion
Inverter Leg Current Sampling in V0 Only Measurements Carrier Voltage Modulation Measurement window is closing! Phase Voltage Sample Pulses Current Shunt Signal
3-Shunt Current Sensing Dave s Motor Control Center PWM top PWM Bottom Motor Phase Current Average Current Shunt Resistor Signal Sample Sample Sample Synchronous ADC Sampling helps to filter the measured current anti-aliasing Noise free ADC sampling when the power transistor is not switching Current can be sampled at up to the PWM frequency (null-vector V0 only) Current samples are simultaneous. 100% Modulation supported by switching between pairs of shunts. Extra shunt results in additional power loss. Channel gain differences can cause waveform discontinuities.
Selecting Shunt Pairs Based on V-angle Zone 1 Phase A Voltage High Zone 2 Phase B Voltage High Zone 3 Phase C Voltage High Zone 1 Phase A Voltage High Shunts B&C Shunts A&C Shunts A&B Shunts B&C 120 o 120 o 120 o 120 o Shunt selections are based on the voltage zones, not the current angles. Just a one percent gain change from one pair of shunts to the next represents a 41 count discrepancy on a 12-bit converter! Gain calibration may be required.
Phase Current Reconstruction from Single-Shunt Measurement Space Vector i bus Value i a i b i c V1 i a??? i b i c i a i bus V2 -i c i a i b The inverter can be driven to 8 states. V3 i b??? i c V1 = 100 V2 = 110 V3 = 010 V4 -i a - 6 voltage vectors V4 = 011 V5 = 001 V6 = 101 V5 i c - 2 null vectors V0 = 000 V7 = 111 1 = Top Switch is on 0 = Bottom Switch is on V6 -i b Assumes no ground currents in load
Single-Shunt Current Sensing Dave s Motor Control Center DC Bus Shunt Synchronous ADC Sampling helps to filter the measured current anti-aliasing Noise free ADC sampling when the power transistor is not switching Current can be sampled at SVM periodic rate (TWICE the PWM frequency). Lower power losses due to only one shunt. Only one current amplifier, so no waveform discontinuities due to gain mismatching. Only one shunt and one amplifier represents an economical solution. Op-amp must have much higher slew-rate characteristics. Shunt must be sampled during voltage vectors, NOT null vectors (timers required). ADC triggering is not fixed w.r.t. PWM waveform. (Timer scheduling). Current readings are skewed in time. Reading blackouts occur during similar duty cycles on two or more phases (next slide )
Current Sampling Blackout Problem Two current samples cannot be taken when: 1. voltage vector is crossing Space-vector boundary only one sample can be taken 1. Areas where voltage vector is crossing SV boundary 2. low modulation indexes sampling intervals are too short none of current samples can be taken 2. Low Modulation Index Source: Freescale Semiconductor
i a i b -i c Shunt Signal V a Single-Shunt Waveform Blackout Only c phase current reading available. V b V c Sample interval for b current V Bus PWM1 PWM3 PWM5 PWM2 i PWM4 PWM6
Single-Shunt Blackout Solutions Solution 1: Asymmetrical PWM Modified ON/OFF times Duty cycles preserved Source: STMicroelectronics
Single-Shunt Blackout Solutions Solution 2: Symmetrical PWM Double Pulse Split duty cycle into 2 pulses Duty cycles preserved 3-phase visibility! Source: STMicroelectronics
Single Supply Bipolar Current Sensing +V dd R +V dd R - + 10R +V dd rail-to-rail op amp with >20V/uS slew rate Good rail-to-rail performance > 15 MHz Gain-Bandwidth Product OPA320/2320 OPA350/2350 OPA365/2365 ADC in R 50 mw R R SENSE i bus Negative bus rail (V ss) I 0 reading is taken during V null vectors, and then stored.