DSPIC33FJ128GP706-I/PT Microchip Technology, DSPIC33FJ128GP706-I/PT Datasheet - Page 75

• Manufacturer Part Number: DSPIC33FJ128GP706-I/PT
• Description: IC DSPIC MCU/DSP 128K 64TQFP
• Manufacturer: Microchip Technology
• Series: dsPIC™ 33Fr

Specifications of DSPIC33FJ128GP706-I/PT

• Program Memory Type: FLASH
• Program Memory Size: 128KB (128K x 8)
• Package / Case: 64-TFQFP
• Core Processor: dsPIC
• Core Size: 16-Bit
• Speed: 40 MIPs
• Connectivity: CAN, I²C, IrDA, LIN, SPI, UART/USART
• Peripherals: AC'97, Brown-out Detect/Reset, DMA, I²S, POR, PWM, WDT
• Number Of I /o: 53
• Ram Size: 16K x 8
• Voltage - Supply (vcc/vdd): 3 V ~ 3.6 V
• Data Converters: A/D 18x10b/12b
• Oscillator Type: Internal
• Operating Temperature: -40°C ~ 85°C
• Product: DSCs
• Data Bus Width: 16 bit
• Processor Series: DSPIC33F
• Core: dsPIC
• Maximum Clock Frequency: 40 MHz
• Number Of Programmable I/os: 85
• Data Ram Size: 16 KB
• Operating Supply Voltage: 3 V to 3.6 V
• Maximum Operating Temperature: + 85 C
• Mounting Style: SMD/SMT
• 3rd Party Development Tools: 52713-733, 52714-737, 53276-922, EWDSPIC
• Data Rom Size: 4096 B
• Development Tools By Supplier: PG164130, DV164035, DV244005, DV164005, PG164120, DM240001, DV164033
• Minimum Operating Temperature: - 40 C
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• For Use With: DM300024 - KIT DEMO DSPICDEM 1.1DV164033 - KIT START EXPLORER 16 MPLAB ICD2MA330012 - MODULE DSPIC33 100P TO 84QFPMA330011 - MODULE DSPIC33 100P TO 100QFPDM300019 - BOARD DEMO DSPICDEM 80L STARTERDM240001 - BOARD DEMO PIC24/DSPIC33/PIC32AC164327 - MODULE SKT FOR 64TQFPDV164005 - KIT ICD2 SIMPLE SUIT W/USB CABLE
• Eeprom Size: -
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

C.1
C.2
© 2009 Microchip Technology Inc.
OVERVIEW
SYNCHRONOUS SAMPLING AND QUASI-SYNCHRONOUS SAMPLING
Appendix C. Power Calculation Theory
This MCP3909 / dsPIC33F 3-Phase Energy Meter Reference Design is unique in that
all calculations are done in the frequency domain. This is easily realized using the DSP
engine core of the advanced 16-bit MCU, the dsPIC33F. In addition to performing direct
fourier transforms (DFTs) on all the input channel measurements, an additional
firmware function is included, quasi-synchronous sampling.
The fundamentals of quasi-synchronous sampling and corresponding methods for
measuring AC electrical parameters are discussed in this section. Typically, a
synchronous sampling method is used for measuring electrical parameters. The
method requires synchronization between sampling intervals and power grid
frequency. For these types of meter designs, an external hardware PLL circuit is used
to track power grid frequency, and the clock of the MCP3909 device is automatically
updated to change the sampling frequency. Since the PLL output frequency drops
behind the power grid frequency, a synchronous error exists in the system, and fully
synchronous sampling is hard to achieve. In addition, as non-sine waves exist in the
power grid, which may affect zero-crossing detection, when such conditions worsen, it
may cause PLL failure, preventing the system from working normally.
For the MCP3909 / dsPIC33F 3-Phase Energy Meter Reference Design presented
here, the dsPIC33F performs additionall calculations that eliminates the need for a
costly external PLL circuit. This quasi-synchronous sampling method has an
advantage in the engineering practice, which actually is periodic sampling, without
synchronizing with the power grid frequency. Therefore, the zero-crossing detection
and PLL circuit can be reduced to lower the hardware complexity. The tradeoff is the
increased software requirements of the system, easily realized using the powerful
dsPIC33F.
For DFT or FFT harmonic analysis of periodic signals, a Fourier transform may only
bring accurate spectrum analysis when the sampling points satisfy N > 2M for each line
cycle and strict synchronous sampling is realized. (Where M is the maximal harmonic
order of periodic signals, and N is the number of samples per line cycle).
Otherwise, if N ≤ 2M, it will cause spectrum aliasing. In addition, if strict synchronous
sampling cannot be realized, spectral-leakage will occur (the Hurdle Effect). However,
in the quasi-synchronous sampling method emplyed here, strict synchronization
between sampling intervals and the period of sampled signal is not guaranteed but is
overcome through post-processing and iteration of the collected data. To reduce the
error caused by this problem and to obtain better accuracy when measuring the
fundamental and harmonics of higher orders, an increase in the number of iterations
when processing data to improve accuracy is performed.
The iterations can effectively reduce the impact of synchronization error over the mea-
surement accuracy, and is one of the methods to realize accurate measurement of the
frequency and harmonics under steady-state conditions.
ENERGY METER REFERENCE DESIGN
MCP3909 / DSPIC33F 3-PHASE
DS51723A-page 75