The air gap flux and the rotor speed are detected by processing the signal obtained from the summation of the stator phase voltages, Vs3. The DSP performs the integration of the third harmonic voltage signal to derive the third harmonic flux. In order to detect the rotor speed the signal Vs3 is processed by a switched capacitor band-pass filter (SCF), whose central frequency can be tuned over a wide range (from about 20 Hz to 4 kHz). The output of the filter is a variable amplitude sinusoidal wave. This wave has the same frequency as the rotor slot ripple . Two options are to detect the frequency of the SCF output signal: a Phase Locked Loop or a frequency to voltage converter (FVC).
5.3.2. Job Programmable Gate Arrays (FPGA)
A remarkable application of DSPs otherwise FPGAs is the sensorless control for high-speed applications in line with the performance off PWM handle schemes, which are categorized since unipolar and you may bipolar methods [twenty-four,51]. With regards to the PWM means made use of the control design might cause an excellent commutation impede into the fast applications while the PWM switching positivesinglestips and inverter commutation cannot be over independently. In case your commutation quick are synchronized into prevent of your PWM altering several months best commutation happens with any slow down. But as the commutating quick relies on the rotor position they will not generally correspond on the avoid off PWM period and unwanted commutation delay is actually brought. This problem are going to be beat of the controlling the voltage and you may volume independently because of the DC hook current handle strategy. So it manage shall be implemented having fun with good DSP otherwise FPGA dependent high-speed sensorless control setup .
Regular high speed applications where PWM procedure enforce is digital video clips disk (DVD) spindle possibilities, and is adopted using a beneficial FPGA, like the Altera Fold EPF6024AQC240-step three . The fresh controller includes a couple of main bits: this new PWM age group routine as well as the strength tool manage circuit. Contour 23 shows the device, using its an excellent FPGA, an excellent BLDC system, together with relevant source and you can feeling circuits . Only critical voltages from around three phases is actually sampled and you may fed to your the latest FPGA operator in order to calculate new commutation instants. This product results in extreme decrease in conduction losses and you can strength application, that is a little essential small fuel BLDCM pushes running on electric battery and you can/or which have limited dissipation room.
5.step three.step 3. Microprocessors (MP)
The lowest-costs sensorless manage strategy getting BLDC cars will be observed in the event the rotor status info is derived of the filtering singular motor-terminal-voltage, which leads to significant reduced components count of your own sensing circuit. Just like the conveyed in the Profile nine , merely a couple of three condition-windings is actually excited at once, and the third stage is open into the changeover periods between the good and bad apartment locations of your own back-EMF . Hence, all the engine critical voltages provides the right back-EMF suggestions that can be used to help you obtain the new commutation instants.
Cost saving is further increased by coupling the position sensing circuit with a single-chip microprocessor or DSP for speed control. Figure 24 shows a block diagram of the position detection circuit based on sensing all three motor terminal voltages for a BLDC motor. Each of the motor terminal voltages, referred to as the negative DC bus rail VA‘, VB‘ and VC‘ are fed into a filter through a voltage divider of a resistor network. This removes the DC component and high frequency contents that result from the PWM operation. The phase information is extracted from the back-EMF. The correction is based on measuring the elapsed time between the last two zero-crossing instants and converting it to frequency. This operation is achieved when the filtered voltage, VA”, is passed to a comparator to detect these zero-crossing instants, which are further sent to a microprocessor for phase-delay correction and generation of commutation signals. The microprocessor produces gate control signals for the inverter and may perform closed speed control with the motor speed information measured by the frequency of the detected signals .