Three-Phase Power Meter Solution

Transcription

1 Three-Phase Power Meter Solution FTF-SEG-F0475 Hui Ding Field Application Engineer M A Y TM External Use

2 Session Objectives Understand electricity meter block diagram and major functionalities. Familiarize with Kinetis M series MCUs, Photon features for metering application. Familiarize with Freescale 3PH AFE reference designs, HW/SW development tools and algorithms offering. Understand the components selection to guarantee meter accuracy, how to improve meter EMC performance. Understand meter calibration steps. External Use 1

3 Agenda Introduction to Electricity Metering Kinetis M Series MCUs Electricity Metering Algorithms Three-phase AFE Reference Design Power Meter Design-Accuracy Power Meter Design-EMC Power Meter Design-Calibration External Use 2

4 Electricity Meter Block Diagram MEASURE PROCESS DISPLAY Measure Electricity meters must measure phase voltages and phase currents consumed by connected load Measurement linearity of 0.1% over 2000:1 dynamic range. Shunt resistors, current transformers or Rogowski coils can be connected. Process Accurate calculation of the active and reactive energies Time keeping with accuracy better than 0.5s/day needed for billing purposes Tamper processing ensures security Load profiles and parameters storage Display LCD display allows visual inspection HMI (control button) allows system configuration IR / RF communication allows download of data for utility companies and automatic meter reading External Use 3

5 Agenda Introduction to electricity metering Kinetis M series MCUs Electricity metering algorithms Three-phase AFE reference design Power meter design-accuracy Power meter design-emc Power meter design-calibration External Use 4

6 Kinetis M series MCUs One Pager TM Core CM0+ core Up to 50MHz Separate FLL post-scalers for Flash and Core clocks. Dedicated PLL for ΣΔ modulator clock 4ch DMA Memory Protection Unit Single 32kHz Crystal operation MHz Crystal optional Security & Encryption Programmable 16/32-bit CRC IRTC w/ tamper detection 3 Tamper pins (operating on battery) Random Number Generator (NIST: SP800-90) AES Encryption (via software library) Memories Up to 128 KB Program Flash 16 KB SRAM Analog 4x24 bit ΣΔ after averaging (2xPGA) highly accurate supporting EN , EN , IEC , IEC and IEC , optimized for shunt sensor ( 50uOhm). 0.1% error in active and reactive energy over a dynamic range of 2000 to 1 Internal 1.2V reference voltage (33 ppm/ o C) 12-ch 16-bit SAR for auxiliary measurement 2x analog comparator Serial Communications 2x SPI 4x UART All combined with Quad Timer & HSCMP for IR 2 support ISO7816 All support flow control 2 I2C All UARTs and SPIs are 3V compatible while 1 UART and 1 SPI are both 3V and 5V compatible (open drain configuration) Peripheral XBAR Remapping peripheral IOs UART selection for IR Timer/PWM/Clock Quad Timer (total 4 universal timers) 2x PIT 1x Watchdog Timer (windowed, independently clocked) 1x EWM (External Watchdog Monitor) 1x LPTimer LCD Display Up to 288 segment LCD, up to 8 backplanes Wakeup Unit Group selected GPIOs (16), LPTIM, RTC (+tamper pins), HSCMP, SCI, Brownout and POR sources to wake up from Power Gated STOP mode GPIO Up to 68 with push pull, pull up/down select Up to 8 GPIO with filter Support for interruption on any edge Single cycle access for all GPIOs (Rapid GPIO) Power Modes & Clock Many low power modes supported 2.7V to 3.6V Operating voltage with AFE 1.71V to 3.6V Operating voltage without AFE 1.71V-3.6V IRTC VBAT supply 32kHz or 4 MHz internal clock source kHz crystal oscillator Package 100 LQFP, 64 LQFP and 44 LGA options -40 C ~ +85 C Temp x3 +/-250mV analogue I/O pads with 6kV PESD External Use 5 IPs with functionality specific to metering

7 Analogue Subsystem (Overview) 1.2V Voltage Reference Generates accurate reference voltage shared between PGA, SD ADC, SAR ADC and HSCMP 16-bit SAR ADC Conversion speed up to 818 ksps 12 single ended channels 4 result registers variety of triggering options 24-bit SD ADC and PGA Conversion speed up to 101 ksps on four channels Four SD ADC channels (two PGA) SW and HW triggering VREF ADC11.. ADC2 ADC1 ADC0 SD0 SD1 SD2 SD3 Kinetis M 1.2V VREF MUX PGA+SD PGA+SD SD SD 2x HSCMP 16-bit SAR ADC }{XBAR Phase shifter & Decimator Phase shifter & Decimator Phase shifter & Decimator Phase shifter & Decimator Kinetis M analogue and digital blocks allow realization most of electricity meter use-cases. High-Speed Comparator Two comparators, each with 6-bit DAC to provide selectable voltage reference Accepts a +/-250mV input signal range Inter-peripheral Crossbar Switch Allows programmable digital interconnections between specific modules 33 input x 33 output multiplexer Interrupt or DMA request Phase Shifter and Decimator Phase shift compensation with resolution of Hz line frequency Capability to connect external galvanic ally isolated SD modulators External Use 6

8 Low-Power Modes Typical Power Modes in an embedded system Run Wait Leading Dynamic Power ARM Cortex M0+ core Innovative low-power process technology (C90TFS) Low-power focused platform design Power Modes Run (AMO) VLPR (AMO) Wait (AMO) VLPW (AMO) Recovery Time us Target Typical Idd Range 2MHz 2MHz Stop Stop VLPS 4.31us 4.31us 312 ua 8.56 ua Freescale Adds Low Leakage Wake-up Unit Enables complete shut-down of core logic, including WIC, further reducing leakage currents in all low power modes Supports 16 external input pins and 5 internal modules as wakeup sources, extend the low power wakeup capability of internal modules to even lower power modes. VLLS3 VLLS2 VLLS1 143us 144us 239us 1.98 ua 1.24 ua 891 na Wakeup inputs are activated in VLLSx modes VLLS0 239us 357 na VBAT RTC operational on battery VDD/VDDA are not powered Standby Reset < 1 ua External Use 7

9 Kinetis M Series MCU Advantages for Electricity Metering Needs Computation Kinetis M Solution Lowest power Cortex-M0+ core (32x32 multiply in 1 cycle) up to 48MHz. Low Power Less than 124.4uA/MHz VLPR Current 1 Down to (POR disabled) 2 Low Power Boot with less then 2.33mA peak current 3 User Interface Communication Memory Scalability Time Keeping Analog Modules Security Up to 4x40 (8x36) segment LCD driver operating in all low power modes. Up to 4 UARTS, 2 SPIs and 2 IIC. From 64 KB to 128 KB of Flash. 16 KB of RAM Program longword execution time (65us) Auto compensated RTC with high speed calibration, 5 ppm accuracy, 0.88 ppm resolution of the 1Hz pulse output and operating in all low power modes. Highest linearity and resolution AFE with 4x24bit SD with 92 db SNR Low VREF gain drift over temperature of 33ppm/ o C Combined gain temperature drift of the PGA, SD ADC and Internal 1.2 VREF blocks (150ppm/ o C) High Speed 16-bit SAR ADC and CMP. Passive and active tamper pins. Random Number Generator (NIST: SP800-90) Robustness I/O pads withstanding 4 kv ESD and 6 kv PESD 1) Typ. 2 MHz core, system, bus clock, and 1 MHz flash clock. MCG configured for BLPE mode. All peripheral clocks disabled. 2) If independent RTC including 32 khz oscillator operates then device consumes additional 1.3uA from VBAT terminal. 3) Measured for 1.7ms linear supply voltage ramp with 3.26 V steady-state value; main function executed in 4.1 ms from applying supply voltage. External Use 8

10 Kinetis M Series MCU Selection for Electricity Metering 24 bit ƩΔ Part Number Package LCD Drive (Flash / Features Target APP ADCs AUX ADC SRAM) number MKM14Z64CHH bit pomkm14z128chh bit 44LGA (5x5mm 2 ) 44LGA (5x5mm 2 ) - 64 / 16 KB / 16 KB MKM33Z64CLH bit 64LQFP 8 x / 16 KB MKM33Z128CLH bit 64LQFP 8 x / 16 KB MKM33Z64CLL bit MKM33Z128CLL bit MKM34Z128CLL bit 100LQF P 100LQF P 100LQF P 8 x / 16 KB 8 x / 16 KB 8 x / 16 KB 5ppm RTC integrated, support harmonics function, cover 1PH/2PH/3PH meter design 5ppm RTC integrated, support harmonics function, cover 1PH/2PH/3PH meter design 5ppm RTC and LCD drive integrated,support harmonics function, cover 1PH/2PH/3PH meter design 5ppm RTC and LCD drive integrated,support harmonics function, cover 1PH/2PH/3PH meter design 5ppm RTC and LCD drive integrated,support harmonics function, cover 1PH/2PH/3PH meter design 5ppm RTC and LCD drive integrated,support harmonics function, cover 1PH/2PH/3PH meter design 5ppm RTC and LCD drive integrated,support harmonics function, cover 1PH/2PH/3PH meter design 1PH/2PH/3PH AFE/harmonics analyzing chip/smart plug/power monitor 1PH/2PH/3PH AFE/harmonics analyzing chip/smart plug/power monitor Low cost 1PH/2PH/3PH SOC power meter Low cost 1PH/2PH/3PH SOC power meter Low cost 1PH/2PH/3PH SOC power meter Low cost 1PH/2PH/3PH SOC power meter Low cost 1PH/2PH/3PH SOC power meter External Use 9

11 Agenda Introduction to electricity metering Kinetis M series MCUs Electricity metering algorithms Three-phase AFE reference design Power meter design-accuracy Power meter design-emc Power meter design-calibration External Use 10

12 Freescale Algorithms for Electricity Metering Electricity meter vendors require algorithms supporting calculations that adhere to either IEC/MID or ANSI C12 standards. Freescale offers algorithms that calculates metering quantities in either time or frequency domain Filter-based metering algorithm processes signals in time domain leverages IIR filters based on elementary 32/64-bit fractional arithmetic FFT-based metering algorithm processes signals in frequency domain leverages DFT computation based on elementary 32/64-bit fractional arithmetic An algorithm must be seen to be believed. - Donald Knuth External Use 11

13 Filter-based Metering Algorithm Block Diagram where: Fs is sampling frequency D3 is decimation ratio calculated as D1-D2+1 N is order of the Hilbert Transformation Filter. Executes when power meter is supplied from the mains Uses high-pass and low-pass IIR filters Hilbert filter is used for computing reactive power and energy Software configuration tool is available to setup structure, filter coefficients, and generate C-header file. Active energy counter updated at every calculation step. X /Fs For more information see AN4265 Calculation step External Use 12

14 FFT Metering Algorithm Block Diagram Where: N is number of samples RE is real part of the vector IM is imaginary part of the vector Number of samples (N) must be power-of-two (32,64,128,etc.) Ensures that processed samples represent full signal period Use linear interpolation technique to generate exactly power-of-two samples on a metering device with SD ADC for entire signal period. Sampling frequency must be at least 2x or higher than the maximum frequency included in input signal. For more information see AN4255 and AN4847 External Use 13

15 FFT Metering Algorithm - Computation Complex power (in Cartesian form) is defined as : N 1 2 k 1 N 1 2 I ( k) ji ( k) U ( k) ju ( k) I ( k) U ( k) I ( k) U ( k) ju ( k) I ( k) ju ( k) I ( k) RE IM RE IM k 1 RE RE IM IM IM RE RE IM Real part of complex power: Active power Imaginary part of complex power: Reactive power Root Mean Square computing (in Cartesian form) is defined as : I RMS U RMS N 1 2 k 1 N 1 2 k 1 I U 2 RE 2 RE ( k) I ( k) U 2 IM 2 IM ( k) ( k) Where: I RE (k),u RE (k) are real parts of k-th harmonics of input current/voltage I IM (k),u IM (k) are imaginary parts of k-th harmonics of input current/voltage External Use 14

16 Agenda Introduction to electricity metering Kinetis M series MCUs Electricity metering algorithms Three-phase AFE reference design Power meter design-accuracy Power meter design-emc Power meter design-calibration External Use 15

17 Three-Phase AFE Reference Designs Based On Kinetis KM14/KL36 MCUs Features 5 to 60A current range (Ib =5A,Imax=60A) 135 to 600V, 50/60 Hz voltage range Accuracy class: active power 0.5S, reactive power 2S 5ppm accuracy RTC over full temp range(-40~110 ) Hardware line frequency measurement Various low-power modes applicable for metering 8x32 segment LCD tamper meter cover monitoring with time stamp infrared hardware interface & 2 Isolated RS485 port LED pulse outputs (KWH, KVAH, MFUNC) Isolated electrical pulse outputs (KWH, KVAH, MFUNC) Xtrinsic 3-axis low power tilt sensor for electronics tamper detection (optional) Various external memory interface(eeprom,flash) Cost effective two layer PCB board & BOM EMC proven design (ESD ± 15kV, EFT ± 6KV) Software provided Application framework, Filter-based metering algorithms, FFT metering algorithms (optional) 44 LGA 5 x 5 mm 2 External Use 16

18 3-Phase Power Meter RD Performance Accuracy EMC FSL internal and third party test result: Passed over ± 6kv level EFT Passed over ± 15KV Contact ESD External Use 17

19 3-Phase Power Meter RD Resource Cost Resource Usage(3PH) Flash RAM CPU loading CAL Period Filter 34KB 4.3KB 75% 1200Hz FFT(interpolation) N=64 29KB 8KB 70% 50Hz FFT(synchronous) N=64 22KB 5KB 51% 50Hz External Use 18

20 Agenda Introduction to electricity metering Kinetis M series MCUs Electricity metering algorithms Three-phase AFE reference design Power meter design-accuracy Power meter design-emc Power meter design-calibration External Use 19

21 Meter design key point-accuracy 1 Current sensor 1.1 Shunt power capacity Should met the power capacity requirement under max current and sample signal threshold under min current. temp drift Should consider the temp drift affect overall meter accuracy under full temp. 1.2 CT/PT power capacity Ib/Imax should be considered to meet the metering voltage/current limit. ratio Ratio should be considered between sensor s original and second sides. accuracy CT/PT accuracy standard is critical for phase error and amplitude error. 1.3 Rogowski Coil Provides electrical isolation, could handle higher current. No DC or high current saturation and immune to magnetic tampering. Interference (far field) pickup - limited by design or shielding. External Use 20

22 Meter design key point-accuracy 2 Sampling circuit 2.1 R/C filter Hardware RC filter cut off frequency should be considered avoid higher frequency noise input to ADC ports. For differential SD ADC, should consider a stable common mode point, usually the common point is the system ground. 2.2 Resistor divider Temp drift of resistor is one key factor, it will directly impact the meter accuracy under full temp. Accuracy under normal temp is another factor which should be consist to meter calibration condition. 2.3 Sampling wirings Sampling wirings is quite critical to limit the noise coupling and channel crosstalk to guarantee the input signal integrity. 2.4 Protection circuit Do consider the affection of protection circuit leakage to the meter accuracy. External Use 21

23 Meter design key point-accuracy 3 Power supply 3.1 AC/DC AC/DC power supply quality such as ripple situation will affect DC supply directly. Keep safe distance between AC/DC and the MCU system. 3.2 DC/DC or LDO Both DC output will put into MCU VDD/VDDA directly, it will impact the MCU whole system noise level. 3.3 ADC VREF ADC VREF is the voltage reference to ADC, it could be MCU internal generated one or external one. ADC VREF performance will impact the ADC result directly, hence affect the metering accuracy. External Use 22

24 Meter design key point-accuracy 4 ADC performance bit SD ADC Operation Mode PGA Signal range (mv peak-peak) SNR OSR=2048) Current (ma) Normal ON 31 (gainx32) 64 (74) 4.0 Normal OFF bit SAR ADC External Use 23

25 Meter design key point-accuracy 5 Metering algorithm 5.1 Filter based algorithm Includes high-pass and low-pass IIR filters to calculate RMS. Includes Hilbert filter for computing reactive power and energy. Includes configurable coefficients used in typical metering case. Higher metering accuracy without harmonics function. 5.2 FFT algorithm Both synchronous and asynchronous sampling technique can be used in FFT algorithm calculation. The harmonics times depends on the CPU loading and sampling logic. Sampling frequency must be at least 2x or higher than the maximum frequency included in input signal. Guaranteed metering accuracy with harmonics function. External Use 24

26 Agenda Introduction to electricity metering Kinetis M series MCUs Electricity metering algorithms Three-phase AFE reference design Power meter design-accuracy Power meter design-emc Power meter design-calibration External Use 25

27 Meter design key point-emc 1 Auxiliary power supply 1.1 Power Supply Class Resistive and capacitive power supply. Switch Mode Power Supply. Industry Frequency Transformer Power Supply. 1.2 Advantage & Disadvantage Industry frequency transformer power supply is most favorable for getting better EMC performance, the disadvantage is it s bigger volume and lower voltage dynamic range. Resistive and Capacitive power supply is the most economic one, but it has limitation for the power load and most serious EMC challenge. Switch mode power supply is the trend for using in power meter, should choose fit components and assure good PCB layout to guarantee EMC performance. External Use 26

28 Meter design key point-emc 2 PCB layout 2.1 Keep Keep the layout in the right order: power ->GND->signal. Keep every signal line has GND in parallel especially the long wiring. Keep the bottom and top area under the MCU has relative overall GND plane. Keep all the components has safe distance away from the board edge. Keep all the VDD/VDDA power domain star connection and has decoupling/buck capacitor. 2.2 Avoid Avoid putting vias between bypass capacitor and MCU pins. Avoid no obvious current flow back loop. Avoid VDD/VDDA routing without through decoupling/buck capacitor. Avoid no enough space between isolation parts. External Use 27

29 Meter design key point-emc 3 Protection circuit 3.1 R/C R/C is the most cost effective components for improving EMC performance. 3.2 TVS TVS should be considered to the terminal lines and VDD/VDDA supply close the board edge etc. 3.3 NTC NTC should be used in series of lines to limit the current in EMC sensitive case. 3.4 Diodes Diodes to VDD or GND could be used for EMC sensitive lines such as sampling circuit. 3.5 Bead/inductor LC circuit is also one of the most effective way for improving EMC performance. External Use 28

30 Meter design key point-emc 4 MCU 4.1 MCU design MCU silicon design is also critical for getting better EMC performance. 4.2 MCU clock MCU clock configuration is effective for getting better EMC performance. 4.3 MCU pin configuration Pins unused suggest to configured to be GPIO output to improve EMC performance. 4.4 MCU /RESET /RESET pin EMC performance is lower than normal pins, configure it to be GPIO output can improve whole system EMC performance. External Use 29

31 Agenda Introduction to electricity metering Kinetis M series MCUs Electricity metering algorithms Three-phase AFE reference design Power meter design-accuracy Power meter design-emc Power meter design-calibration External Use 30

32 Meter design key point-calibration 1 Put meter on the calibration instrument 2 Set the calibration load value, example 220V,5A, PF 0.5L, then power up the board; External Use 31

33 Meter design key point-calibration 3 Download the binary file, then run image 4 Wait 45S for calibration finished, parameters automatically stored into flash External Use 32

34 Designing with Freescale Tailored live, hands-on training in a city near you 2014 seminar topics include QorIQ product family update Kinetis K, L, E, V series MCU product training freescale.com/dwf External Use 33

35 Freescale Semiconductor, Inc. External Use