NXP MCSPTR2A5775E User Manual
MCSPTR2A5775E 3-phase PMSM Motor
NXP Semiconductors
Document Number: AN13038
Application Note
Rev. 0
,
10/2020
Contents
1. Introduction ........................................................................ 1
2. System concept ................................................................... 2
3. PMSM field-oriented control.............................................. 3
3.1. Fundamental principle of PMSM FOC ................... 3
3.2. PMSM model in quadrature phase synchronous
reference frame ...................................................................... 5
3.3. Output voltage actuation and phase current
measurement ......................................................................... 7
3.4. Rotor position/speed estimation .............................. 9
3.5. Field weakening .................................................... 10
4. Software implementation on the MPC5777E ................... 13
4.1. eTPU ..................................................................... 13
4.2. MPC5777E – Key modules for PMSM FOC control
17
4.3. MPC5775E Device initialization ........................... 19
4.4. Software architecture ............................................. 34
5. FreeMASTER and MCAT user interface ......................... 47
5.1. MCAT Settings and Tuning .................................. 48
5.2. MCAT application Control ................................... 51
6. Conclusion ........................................................................ 52
7. References ........................................................................ 52
Control Kit with MPC5775E
Featuring Motor Control Application Tuning (MCAT) Tool
by: NXP Semiconductors
1. Introduction
This application note describes the design of a 3-phase
Permanent Magnet Synchronous Motor (PMSM) vector
control drive with 3-shunt current sensing and resolver
position sensing. The design is targeted for automotive
motor control (MC) applications.
This design serves as an example of motor control design
using NXP family of automotive motor control MCUs
based on a 32-bit Power Architecture technology
optimized for a full range of automotive applications.
Following are the supported features:
• 3-phase PMSM speed Field Oriented Control.
• Current sensing with three shunt resistors.
• Application control user interface using
FreeMASTER debugging tool.
• Motor Control Application Tuning (MCAT) tool.
• Rotor position and speed measurement using
resolver transducer
System concept
MCSPTR2A5775E 3-phase PMSM Motor Control Kit with MPC5775E, Rev. 0, 10/2020
2 NXP Semiconductors
2. System concept
The system is designed to drive a 3-phase PM synchronous motor. The application meets the following
performance specifications:
• Targeted at the MPC5775E-EVB Evaluation Board (refer to dedicated user manual for
MPC5775E-EVB available at www.nxp.com). See References for more information
• S32 Design Studio (see References)
• MC33937 MOSFETs pre-driver with extensive set of functions and condition monitoring (see
References)
• Control technique incorporating:
o Field Oriented Control of 3-phase PM synchronous motor with resolver position sensor
o Closed-loop speed control with action period 1 ms
o Closed-loop current control with action period 100 µs
o Bi-directional rotation
o Flux and torque independent control
o Field weakening control extending speed range of the PMSM beyond the base speed
o Position and speed are computed by Enhanced Time Processing Unit eTPU
o Sensing of three-phase motor currents
o FOC state variables sampled with 100 μs period
• Automotive Math and Motor Control Library (AMMCLIB) - FOC algorithm built on blocks of
precompiled SW library (see section References)
• Use of eTPU Motor control function set to offload CPU
• FreeMASTER
o FreeMASTER software control interface (motor start/stop, speed setup)
o FreeMASTER software monitor
o FreeMASTER embedded Motor Control Application Tuning (MCAT) tool (motor
parameters, current loop, speed loop) (see section References)
o FreeMASTER software MCAT graphical control page (required speed, actual motor
speed, start/stop status, DC-Bus voltage level, motor current, system status)
o FreeMASTER software speed scope (observes actual and desired speeds, DC-Bus
voltage and motor current)
o FreeMASTER software high-speed recorder (reconstructed motor currents, vector control
algorithm quantities)
• DC-Bus over-voltage and under-voltage, over-current, overload and start-up fail protection
PMSM field-oriented control
MCSPTR2A5775E 3-phase PMSM Motor Control Kit with MPC5775E, Rev. 0, 10/2020
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Figure 1 MCSPTR2A5775E 3-phase PMSM Development Kit with MPC5775E
3. PMSM field-oriented control
3.1.
Fundamental principle of PMSM FOC
High-performance motor control is characterized by smooth rotation over the entire speed range of the
motor, full torque control at zero speed, and fast acceleration/deceleration. To achieve such control,
Field Oriented Control is used for PM synchronous motors.
The FOC concept is based on an efficient torque control requirement, which is essential for achieving a
high control dynamic. Analogous to standard DC machines, AC machines develop maximal torque
when the armature current vector is perpendicular to the flux linkage vector. Thus, if only the
fundamental harmonic of stator magnetomotive force is considered, the torque Te developed by an AC
machine, in vector notation, is given by the following equation:
Equation 1
where pp is the number of motor pole-pairs, is is stator current vector and ψs represents vector of the
stator flux. Constant 3/2 indicates a non-power invariant transformation form.
PMSM field-oriented control
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In instances of DC machines, the requirement to have the rotor flux vector perpendicular to the stator
current vector is satisfied by the mechanical commutator. Because there is no such mechanical
commutator in AC Permanent Magnet Synchronous Machines (PMSM), the functionality of the
commutator has to be substituted electrically by enhanced current control. This reveal that stator current
vector should be oriented in such a way that component necessary for magnetizing of the machine (flux
component) shall be isolated from the torque producing component.
This can be accomplished by decomposing the current vector into two components projected in the
reference frame, often called the dq frame that rotates synchronously with the rotor. It has become a
standard to position the dq reference frame such that the d-axis is aligned with the position of the rotor
flux vector, so that the current in the d-axis will alter the amplitude of the rotor flux linkage vector. The
reference frame position must be updated so that the d-axis should be always aligned with the rotor flux
axis.
Because the rotor flux axis is locked to the rotor position, when using PMSM machines, a mechanical
position transducer or position observer can be utilized to measure the rotor position and the position of
the rotor flux axis. When the reference frame phase is set such that the d-axis is aligned with the rotor
flux axis, the current in the q-axis represents solely the torque producing current component.
What further resulted from setting the reference frame speed to be synchronous with the rotor flux axis
speed is that both d and q axis current components are DC values. This implies utilization of simple
current controllers to control the demanded torque and magnetizing flux of the machine, thus
simplifying the control structure design.
Figure 2 shows the basic structure of the vector control algorithm for the PM synchronous motor. To
perform vector control, it is necessary to take following four steps:
1. Measure the motor quantities (DC link voltage and currents, rotor position/speed).
2. Transform measured currents into the two-phase orthogonal system (α, β) using a Clarke
transformation. After that transform the currents in α, β coordinates into the d, q reference frame
using a Park transformation.
3. The stator current torque (i
sq
) and flux (isd) producing components are separately controlled in d,
q rotating frame.
4. The output of the control is stator voltage space vector and it is transformed by an inverse Park
transformation back from the d, q reference frame into the two-phase orthogonal system fixed
with the stator. The output three-phase voltage is generated using a space vector modulation.
Clarke/Park transformations discussed above are part of the Automotive Math and Motor Control
Library set (see section References).
To be able to decompose currents into torque and flux producing components (isd, isq), position of the
motor-magnetizing flux has to be known. This requires knowledge of the accurate rotor position as
being strictly fixed with magnetic flux. This application note deals with the sensor based FOC control
where the position and velocity are obtained by position/velocity estimator executed by eTPU. Position
and speed are processed by eTPU co-processor that runs independently on system core.
PMSM field-oriented control
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Figure 2 Field oriented control transformations
3.2.
PMSM model in quadrature phase synchronous reference frame
Quadrature phase model in synchronous reference frame is very popular for field-oriented control
structures, because both controllable quantities, current and voltage, are DC values. This allows to
employ only simple controllers to force the machine currents into the defined states. Furthermore, full
decoupling of the machine flux and torque can be achieved, which allows dynamic torque, speed and
position control.
The equations describing voltages in the three phase windings of a permanent magnet synchronous
machine can be written in matrix form as follows:
Equation 2
where the total linkage flux in each phase is given as:
Equation 3
where Laa, Lbb, Lcc, are stator phase self-inductances and Lab=Lba, Lbc=Lcb, Lca=Lac are mutual
inductances between respective stator phases. The term ΨPM represents the magnetic flux generated by
the rotor permanent magnets, and θe is electrical rotor angle.
PMSM field-oriented control
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Figure 3 Orientation of stator (stationary) and rotor (rotational) reference frames, with current
components transformed into both frames
The voltage equation of the quadrature phase synchronous reference frame model can be obtained by
transforming the three phase voltage equations (Equation 2) and flux equations (Equation 3) into a two
phase rotational frame which is aligned and rotates synchronously with the rotor as shown in Figure 3.
Such transformation, after some mathematical corrections, yields the following set of equations:
Equation 4
where ωe is electrical rotor speed. It can be seen that Equation 4
represents a non-linear cross dependent system with cross-coupling terms in both d and q axis and back-
EMF voltage component in the q-axis. When FOC concept is employed, both cross-coupling terms shall
be compensated in order to allow independent control of current d and q components. Design of the
controllers is then governed by following pair of equations, derived from Equation 4 after
compensation:
Equation 5
Equation 6
Those equations describe the model of the plant for d and q current loop. Both equations are structurally
identical, therefore the same approach of controller design can be adopted for both d and q controllers.
The only difference is in values of d and q axis inductances, which results in different gains of the
controllers. Considering closed loop feedback control of a plant model as in either equation, using
α
β
d
q
ω
e
αβ frame – stator coordinates
dq frame – rotor coordinates
θ
e
i
S
i
Sd
i
Sq
i
Sα
i
Sβ
torque
component
flux
component
PM
PMSM field-oriented control
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standard PI controllers, then the controller proportional and integral gains can be derived, using a poleplacement method, as follows:
Equation 7
Equation 8
where ω0 represents the system natural frequency [rad/sec] and ξ is the Damping factor [-] of the current
control loop.
Figure 4 FOC Control Structure
3.3.
Output voltage actuation and phase current measurement
The 3-phase voltage source inverter shown in Figure 5 uses three shunt resistors (R38, R39, R40) placed
in three legs of the inverter as phase current sensors. Stator phase current which flows through the shunt
resistor produces a voltage drop which is interfaced to the AD converter of microcontroller through
conditional circuitry (refer to MCSPTR2A5775E Schematic available at nxp.com).
PMSM field-oriented control
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Figure 5 Three-phase DC/AC inverter with shunt resistors for current measurement
Figure 6 shows a gain setup and input signal filtering circuit for operational amplifier which provides the
conditional circuitry and adjusts voltages to fit into the ADC input voltage range.
Figure 6 Phase current measurement conditional circuitry
The phase current sampling technique is a challenging task for detection of phase current differences
and for acquiring full three phase information of stator current by its reconstruction. Phase currents
flowing through shunt resistors produces a voltage drops which need to be appropriately sampled by the
AD converter when low-side transistors are switched on. The currents cannot be measured by the shunt
resistors at an arbitrary moment. This is because the current only flows through the shunt resistor when
the bottom transistor of the respective inverter leg is switched on. Therefore, considering Figure 5, phase
A current is measured using the R38 shunt resistor and can only be sampled when the low side transistor
Q4 is switched on. Correspondingly, the current in phase B has to be measured when the low side
transistor Q5 is switched on, and the current in phase C can only be measured if the low side transistor
Q6 is switched on. To get an actual instant of current sensing, voltage waveform analysis has to be
performed.
Generated duty cycles (phase A, phase B, phase C) for two consecutive PWM periods are shown in
Figure 7. These phase voltage waveforms correspond to a center-aligned PWM with sine-wave
modulation. As shown in the following figure, (PWM period I), the best sampling instant of phase
PMSM field-oriented control
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current is in the middle of the PWM period, where all bottom transistors are switched on. However, not
all three currents can be measured at an arbitrary voltage shape. PWM period II in the following figure
shows the case when the bottom transistor of phase A is ON for a very short time. If the ON time is
shorter than a certain critical time (depends on hardware design), the current cannot be correctly
measured.
Figure 7 Generated phase duty cycles in different PWM periods
In standard motor operation, where the supplied voltage is generated using the space vector modulation,
the sampling instant of phase current takes place in the middle of the PWM period in which all bottom
transistors are switched on. If the duty cycle goes to 100%, there is an instant when one of the bottom
transistors is switched on for a very short time period. Therefore, only two currents are measured and the
third one is calculated from equation:
Equation 9
NOTE
MPC5775-EVB is using eTPU timer for generation the PWMs signals.
The default limit of the PWM duty cycle is 98% which allows in whole
range of duty cycle measure all three currents. This default setting and
also type of motor control modulation can be changed. Refer to eTPU
PWMM: Center-aligned PWM mode
3.4.
Rotor position/speed estimation
Different sensor type might require different approach to evaluate the speed and position of the motor.
The NXP approach for resolver systems utilizes an Angle Tracking Observer (ATO), see Figure 8 which
is based on the Phase Lock Loop technique. The ATO input is a position error between the position
given by the sensor and estimated ATO position. The PI controller in the ATO loop minimizes the input
error by adjustment of a control variable, in this case the control variable is equivalent to a motor speed.
Integration of the speed leads to the estimated position.
PMSM field-oriented control
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Figure 8 ATO for Resolver systems
The ATO for resolver system is characterized by the position error calculation. The observer error
corresponds to the following formula:
Equation 10
The coefficients of ATO PI controller, Integrator and filter can be tuned by MCAT tool. The ATO
function is a member of the motor control SW library (see References) and is available as
AMCLIB_TrackObsrv.
The alignment algorithm applies DC voltage to d-axis resulting full DC voltage applied to phase A and
negative half of the DC voltage applied to phase B, C for a certain period. This will cause the rotor to
move to "align" position, where stator and rotor fluxes are aligned. The rotor position in which the rotor
stabilizes after applying DC voltage is set as zero position. Motor is ready to produce full startup torque
once the rotor is properly aligned.
NOTE
MPC5775E-EVB is using eTPU for resolver feedback signal
demodulation. eTPU based resolver o digital converter is described in
chapter Software implementation on the MPC5777E.
3.5.
Field weakening
Field weakening is an advanced control approach that extends standard FOC to allow electric motor
operation beyond a base speed. The back electromotive force (EMF) is proportional to the rotor speed
and counteracts the motor supply voltage. If a given speed is to be reached, the terminal voltage must be
increased to match the increased stator back-EMF. A sufficient voltage is available from the inverter in
the operation up to the base speed. Beyond the base speed, motor voltages ud and uq are limited and
cannot be increased because of the ceiling voltage given by inverter. Base speed defines the rotor speed
at which the back-EMF reaches maximal value and motor still produces the maximal torque.
As the difference between the induced back-EMF and the supply voltage decreases, the phase current
flow is limited, hence the currents id and iq cannot be controlled sufficiently. Further increase of speed
would eventually result in back-EMF voltage equal to the limited stator voltage, which means a
complete loss of current control. The only way to retain the current control even beyond the base speed
is to lower the generated back-EMF by weakening the flux that links the stator winding. Base speed
PMSM field-oriented control
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splits the whole speed motor operation into two regions: constant torque and constant power, see the
following figure.
Figure 9 Constant torque/power operating regions
Operation in constant torque region means that maximal torque can be constantly developed while the
output power increases with the rotor speed. The phase voltage increases linearly with the speed and the
current is controlled towards its reference. The operation in constant power region is characterized by a
rapid decrease in developed torque while the output power remains constant. The phase voltage is at its
limit while the stator flux decreases proportionally with the rotor speed, see the following figure.
Figure 10 Constant flux/voltage operational regions
FOC splits phase currents into the q-axis torque component and d-axis flux component. The flux current
component Id is used to weaken the stator magnetic flux linkage ΨS. Reduced stator flux ΨS yields to
lower Back-EMF and condition of Field Weakening is met. More details can be seen from the following
phasor diagrams of the PMSM motor operated exposing FOC control without (left) and with FW (right),
Figure 11.
PMSM field-oriented control
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Figure 11 Steady-state phasor diagram of PMSM operation up to base speed (left) and above speed (right)
FOC without FW is operated demanding d-axis current component to be zero (Id=0) to excite electric
machine just by permanent magnets mounted on the rotor. This is an operation within constant torque
region (see Figure 9), since whole amount of the stator current consists of the torque producing
component Iq only (see Figure 11, left). Stator magnetic flux linkage ΨS1 is composed of rotor magnetic
flux linkage ΨPM, which represents the major contribution and small amount of the magnetic flux
linkage in q-axis LqIq produced by q-axis current component I
q
. Based on the Faraday’s law, rotor
magnetic flux linkage ΨPM and stator magnetic flux linkage ΨS1 produce back-EMF voltage
E
PM1=ωe1ΨPM
perpendicularly oriented to rotor magnetic flux ΨPM in q-axis and back EMF voltage
ES1=ω
e1ΨS1
perpendicularly oriented to stator magnetic flux ΨS1, respectively (see Figure 11, left). Both
voltages are directly proportional to the rotor speed ωe1. If the rotor speed exceeds the base speed, the
back-EMF voltage ES1=ω
e1ΨS1
approaches the limit given by VSI and Iq current cannot be controlled.
Hence, field weakening has to take place.
In FW operation, Id current is controlled to negative values to “weaken” stator flux linkage ΨS2 by -LdId
component as shown in Figure 11, right. Thanks to this field weakening approach, back-EMF voltage
induced in the stator windings ES2 is reduced below the VSI voltage capability even though E
PM2
exceeds it. Iq current can be controlled again to develop torque as demanded. Unlike the previous case,
this is an operation within constant power region (see Figure 9) where Iq current is limited due to Is
current vector size limitation (see Figure 11, right). In FW operation, stator magnetic flux linkage ΨS
consists of three components now: rotor magnetic flux linkage ΨPM, magnetic flux linkage in q-axis Ψq=
LqIq produced by q-axis current component Iq and magnetic flux linkage in d-axis Ψd= -LdId produced by
negative d-axis Id current component that counteracts to ΨPM.
There are some limiting factors that must be taken into account when operating FOC control with field
weakening:
• Voltage amplitude u_max is limited by power as shown in Figure 12, left
• Phase current amplitude i_max is limited by capabilities of power devices and motor thermal
design as shown in Figure 12, right
• Flux linkage in d-axis is limited to prevent demagnetization of the permanent magnets
q- axis
d- axis
IS= I
q
E
PM1
=
e1
PM
V
S1
S1
RS I
S
jXSI
S
q- axis
d- axis
I
S
I
q
I
d
V
S2
S2
RS I
S
jXSI
S
-LdI
d
I
MAX
I
MAX
ES2=
e2
S2
ES1=
e1
S1
LqI
q
LqI
q
VSI voltage capability
VSI voltage capability
E
PM2
=
e2
PM
PM
PM
e1
<
e2
E
PM1
< E
PM2
Software implementation on the MPC5777E
MCSPTR2A5775E 3-phase PMSM Motor Control Kit with MPC5775E, Rev. 0, 10/2020
NXP Semiconductors 13
Figure 12 Voltage (left) and current (right) limits for PMSM drive operation
NXP’s Automotive Math and Motor Control library offers a software solution for the FOC with field
weakening respecting all limitations discussed above. This library-based function is discussed in section
AMMCLIB integration.
4. Software implementation on the MPC5777E
4.1.
eTPU
The Enhanced Time Processing Unit (eTPU) is a programmable I/O controller with its own core and
memory system, allowing it to perform complex timing and I/O management independently of the CPU.
The eTPU is used as a co-processor, specialized for advanced timing functions, such as handle complex
engine control, motor control, and communication tasks independently of the CPU.
A new complex library of eTPU functions enabling the eTPU to drive motor control applications was
developed. This library represents a step forward compared to its predecessor – the motor control
function sets (set3 and set4). The new Motor Control eTPU Library benefits from NXP eTPU
development tools from CodeWarrior. The eTPU(2) Development Suite is based on Eclipse IDE and
includes the C and assembly compiler, simulator and debugger.
4.1.1.
eTPU PWMM:
The Motor Control PWM eTPU function (PWMM) uses either three eTPU channels to generate three
PWM output signals, or six eTPU channels to generate three complementary PWM output signal pairs,
used to drive a 3-phase electrical motor. One extra channel PWMM Master is used to synchronize all the
outputs and is responsible for all the necessary calculation. Master channel does not generate any
PWMM output, but the output is used for debugging and visualization of PWMM function processing.
An example of eTPU PWMM function can be seen on Figure 13.
Software implementation on the MPC5777E
MCSPTR2A5775E 3-phase PMSM Motor Control Kit with MPC5775E, Rev. 0, 10/2020
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Figure 13 Center aligned 3 phase PWM output with complementary channels and one Master channel
(PWMM).
Features:
• Generates three phases of PWM signals to drive an electrical motor.
• Based on the selected phase type, either single PWM outputs or complementary PWM pairs with
dead-time are generated for each motor phase.
• The PWM polarity can be separately configured for the base and the complementary PWM
outputs.
• The synchronous update of all PWM phases can happen either once or twice per PWM period:
o Frame update
o Frame and Center update (half-cycle update)
• The PWMM inputs are transformed into PWM output duty-cycles by a selected modulation. It
can be one of:
o Unsigned voltages
o Signed voltages
o Standard Space Vector Modulation
o Space Vector Modulation With O
000
Nulls
o Space Vector Modulation With O
111
Nulls
o Inverse Clark Transformation
o Sine Table Modulation
• There are four PWM modes supported. Switching between the PWM modes in run-time is also
supported:
o Left-aligned
o Right-aligned
o Center-aligned
o Inverted center-aligned
• The PWM period can be changed in run-time. The new period value is always applied at frame
update only, not at the center update.
Software implementation on the MPC5777E
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NXP Semiconductors 15
• Generation of short pulses can be limited by a minimum pulse width – a threshold for pulse
deletion.
4.1.2.
eTPU based Resolver to digital converter (RDC)
The Resolver Digital Interface eTPU function (RESOLVER) uses one eTPU channel to generate a 50%
duty-cycle PWM output signal to be passed through an external low-pass filter and used as a resolver
excitation signal. In the resolver position sensor, this excitation signal is modulated by sine and cosine of
the actual motor angle. The feedback Sine and Cosine signals are sampled by an on-chip ADC and the
conversion results can be transferred to eTPU DATA RAM by eDMA. Then, the eTPU function
RESOLVER can process the digital samples of resolver output signals. Motor angular position, angular
speed, a revolution counter, and diagnostics are results of the Sine and Cosine feedback signal
processing (see the following figure).
Figure 14 eTPU Resolver Digital Interface block diagram
Processing of the feedback signals is executed on a separate channel. Another channel is used to perform
linear extrapolation of the last updated position from ATO to any other time. This is important feature
since ATO updates come with a certain period (~50 µs) which most likely is not aligned with control
loop frequency.
Optionally, another eTPU channel can be used to process diagnostics either on the same eTPU engine
after the feedback signal processing is finished or on the other eTPU engine in parallel to the motor
angle and speed calculation. This enables the CPU application to read the new motor angle and, at the
same time, check the diagnostic results to ensure the motor angle is correct.
The Sine and Cosine analogue feedback signals need to be converted to a digital representation and
transferred to eTPU data RAM. This should be done independently of the CPU using an on-chip ADC
and eDMA. Although any of the ADC modules can be used, the described configuration adopts the
Sigma-Delta ADC (SDADC).
Software implementation on the MPC5777E
MCSPTR2A5775E 3-phase PMSM Motor Control Kit with MPC5775E, Rev. 0, 10/2020
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Two SDADC modules are used to continuously sample the Sine and Cosine signals in parallel (Figure
15). They are configured to obtain 32 samples of each signal per period instead of one sample at the
presumed peak as it is implemented in most of the SW resolver applications. This oversampling method
together with demodulation and filtration brings more robustness towards the induced noise.
Furthermore, the position is evaluated twice per resolver excitation period.
Figure 15 Oversampling and demodulation of Resolver feedback signals
4.1.3.
eTPU Analog Sensing function (AS)
The Analog Sensing eTPU function (AS) uses one eTPU channel to generate adjustable ADC trigger
pulses. On the selected eTPU channels the trigger signal generated by the AS function can be internally
routed to an ADC module. Using eDMA, the A/D conversion results can be moved back to the eTPU
data RAM for further processing by the AS eTPU function. Those pre-processed analog samples are
then available for consequential processing by e.g. an eTPU function handling the closed loop motor
control. It can run either independently with a given period (periodic mode) or it can be synchronized
with any other eTPU function (synchronized mode).
Features:
• Generates one or two adjustable trigger pulses per period:
o Frame pulse
o Center pulse
• Generates interrupts, DMA requests and eTPU links at none, one, or more of selected time-
positions:
o Frame pulse start
o Frame pulse end
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