An experimental set-up for the interior PMSM drive system has been built with the dSPACE DS1102 controller board. An experimental set-up for the drive system is shown in Fig. 5.4 and Fig. 5.5.
DC Generator
Torque Transducer
Prototype
IPMSM Encoder
Figure 5.4: Experimental set-up for the interior PMSM drive system
As shown in these figures, the experimental system consists of the following units:
• A PC for software programming, debugging and real-time control.
Figure 5.5: dSPACE DS1102 based integrated PMSM drive test platform
• A dSPACE DS1102 controller board for executing control programs, gener- ating control signals, performing A/D and D/A conversions, and communi- cating with the PC.
• A PWM voltage-source inverter for driving the interior PMSM.
• An integrated interface platform for performing logic operations, inverter control, buffering, isolation, protection, etc.
• The prototype interior PMSM with exterior incremental encoder for position sensing.
• Two current sensors for measuring the phase currents in two motor phases and voltage sensor for measuring the DC link voltage.
• A loading system for producing load torque to the interior PMSM.
• A torque transducer for measuring the actual motor torque.
TMS320C31 JTAG Interface
128K×32 Static RAM Zero wait state JTAG
Connector
Serial Interface
PCI BUS
Host Interface
Incremental Encoder Interface 1
TMS320P14 Digital I/O 16-bit ADC 1 16-bit ADC 2 12-bit ADC 3 12-bit ADC 4 12-bit DAC 1 12-bit DAC 2 12-bit DAC 3 12-bit DAC 4 Incremental Encoder Interface 2
Noise Filter
Noise Filter
Analog/Digital I/O Connector
26
Figure 5.6: Configuration of the controller board used for hardware implementation
5.3.1 DS1102 controller board
The dSPACE DS1102 controller board is specifically designed for the development of high-speed multi variable digital controllers and real-time simulations in various fields such as motor drives. The board consists of a floating-point DSP TMS320C31, a micro controller TMS320P14 acting as a slave-DSP for the digital I/O subsystem, A/D and D/A converters, and encoder interfaces.
The main DSP processes the numerically intensive algorithms at a speed of 60 MHz per instruction cycle. The slave-DSP performs digital I/O and PWM generation. The A/D converters convert the analog feedback signals of ± 10V into digital format so that the DSP can read in the measured quantity. Such conversions are used on the measured stator current or motor torque feedback signals. Conversely, the D/A converters convert the digital signals in the DSP into analog signals of ± 10V so that they can be displayed on an analog CRO. The encoder interface provides the interfacing of the DSP with the incremental encoder so that the output of the incremental encoder, which is in discrete pulses, can be quantized into digital form; hence, the data on the rotor-position is acquired.
The DS1102 controller board is designed like a PC expansion card so that it can be inserted into the PCI slot of the PC, together with the PC video card or sound card.
Using the appropriate software for communication between the PC and the DSP, users can debug the user-program that is loaded in the DSP (via C-programming and the Texas Instruments C-Compiler), tune the experimental parameters on-line or display the experimental variables in real-time.
5.3.2 PWM voltage source inverter
A 3-phase, 750 W PWM inverter is used as the power circuit for driving the PMSM.
The inverter used is called PowIRTrain (from International Rectifier), which com- bines all the power conversion and power control devices and circuitry that are required for building state-of-the-art AC drives into modules or assemblies. The PowIRTrain inverter consists of a 3-phase input rectifier, a 3-phase IGBT inverter with a braking switch, gate drive, power terminations, DC link capacitor with soft charge scheme, surge suppression, current/voltage/temperature sensing with asso- ciated protection circuits, system power supply and control interface. The PWM inverter of model IRPT2062C is used in the hardware implementation of the PMSM drive.
5.3.3 Integrated interface platform
In the implementation of the experimental PMSM drive set-up, it is necessary to provide a hardware interface between the motor drive and DSP-DS1102. The hardware interface has the following functions:
• Generating mid-symmetrical PWM signals using EX-OR gates.
• Generating six PWM signals that controls the six switches of the PWM in- verter.
• Incorporating dead-time in the PWM signals.
• Setting the over-current/over-voltage protections and RESET/STOP func- tions of the inverter.
• Buffering the pulse signals generated from the incremental encoder.
• Provide filtering of the measured current and torque signals.
Mid-symmetrical PWM Signals
EX-OR Setting
Dead- time
2às Opto- couplers
PWM_A2
From Stator Windings
Reset Stop Current/
Voltage Sensors
isa
isb
uiA
From Encoder Buffers
Encoder Interface
uiB
PWM_A1
PWM_B1 PWM_B2 PWM_C1 PWM_C2 PWM Inverter
ADC 1 ADC 2 PWM_0 PWM_1 PWM_2 PWM_3 PWM_4 PWM_5
DS1102 Interface
Break UFB
UREF
Reset Stop
IREF
Filter IFB
Motor & Encoder
Fault Display
ADC 3
ADC 4 usa,b
Figure 5.7: Interfacing the controller board with the control circuit
The block diagram of the peripheral interface circuit is shown in Fig. 5.7.
Signals of the six PWM channels, which are ch0 and ch1 for phase A, ch2 and ch3 for phase B, and ch4 and ch5 for phase C, are EX-ORed and become three mid-symmetrical PWM signals. Another three complementary signals are obtained
from three logic inverters. Proper ”dead time” is then incorporated into these six PWM signals to avoid ”mutual-ON” of the upper and lower switches on the same phase of the inverter. The opto-couplers transfer the six PWM signals and isolate the low-side circuit from the high-side circuit. The six PWM signals are inverted into ”low-active” signals as required by the inverter and then sent to the inverter.
Signals of ”Reset” and ”Stop” are also sent through opto-couplers to control the inverter. Voltage comparators are used to detect over voltage and over current.
”Fault” signals generated by the inverter and the voltage comparators are sent through opto-couplers to the low-side circuit to inhibit the transfer of the PWM signals. The installed current sensors and resistors convert the current signals into voltage signals for the use of A/D converters of DS1102. Signals from the incremental encoder are sent through buffers to shape the waveforms and to drive the encoder interface circuit of ds1102.
5.3.4 Current sensor
Sufficiently accurate measurements of the motor phase currents are essential to ensure high-performance in the PMSM drive system. In the experimental set- up, two current sensors are utilized to measure the phase-a and b currents. The measured currents are converted into voltage signals scaled to the range±10V by using resistors of appropriate resistances. These voltage signals are then fed into the A/D converters of the DS1102. In the PMSM experimental set-up, the LEM module LA 25-NP current sensors are used. The current sensors, resistors and the
power supply for the current sensor are included on the current sensor board.
5.3.5 Loading system
The PMSM drive loading system consists of a DC motor, an externally connected variable resistorRloadin series with the armature side of the DC motor which carries an armature current Ia and a DC power supply. Fig. 5.8 shows the configuration for the loading system.
Coupled to PMSM
+ E -
Rload
A
ωr
If
110 Vdc
φf
Ia
DC motor
(acting as generator)
Figure 5.8: Configuration for the interior PMSM loading system