As of MCAF R4, parameter customization is available through the Customize page of motorBench® Development Suite, which provides access to various parameters that affect code generation.
This section provides additional guidance for setting these parameters.
Please note: MCAF has been designed so that the default values for customizable parameters are applicable to most motors. In the event that it is unclear what to do, the best course of action is to use the default value of each parameter.
The following table describes these parameters briefly. Links to detailed guidance are included.
| Section | Parameter | Description |
|---|---|---|
| Estimators | Primary estimator | Selects which estimator is used for commutation and velocity feedback. |
| Estimators | Active estimators | Selects which estimators are active, in addition to the primary estimator used for commutation |
| Operating parameters | Minimum velocity | Determines minimum operating velocity |
| Operating parameters | Coastdown: Velocity threshold | Determines velocity threshold used to estimate when a motor stops |
| Operating parameters | Coastdown: Time | Determines time to wait until a motor stops |
| Operating parameters | Slew rate: max acceleration | Determines maximum velocity slew rate in motoring quadrants |
| Operating parameters | Slew rate: max deceleration | Determines maximum velocity slew rate in generating quadrants |
| Fault detection | Undervoltage margin | Determines undervoltage threshold margin |
| Fault detection | Overvoltage margin | Determines overvoltage threshold margin |
| Startup | Startup current | Determines current used during startup |
| Startup | Rampup time | Determines current rampup time during startup |
| Startup | Align time | Determines time to remain in the align state during startup |
| Startup | Min accel time | Determines minimum acceleration time during startup |
| Startup | Acceleration \(\alpha_1\) | Determines fast acceleration rate |
| Startup | Acceleration \(\alpha_0\) | Determines slow acceleration rate |
| Startup | Hold time | Determines time to remain in the hold state during startup |
| Startup | Speed threshold \(\omega_0\) | Determines speed threshold for switching to fast acceleration |
| Startup | Angle converge rate | Determines rate of angle convergence during closed-loop transition of classic startup |
| Startup | Startup algorithm | Selects startup method |
| Startup | Active damping: max amplitude | Determines maximum amplitude of active damping current |
| Startup | Active damping: max gain | Determines maximum gain of active damping |
| Startup | Active damping: speed threshold | Determines the minimum velocity to enable active damping |
| Overmodulation | D-axis limit | Determines the maximum d-axis voltage |
| Overmodulation | Q-axis limit | Determines the maximum q-axis voltage |
| AN1292 PLL | Time constant | Specifies the velocity estimation time constant |
| AN1292 PLL | Loop filter bandwidth | Specifies the loop filter bandwidth |
| Quadrature encoder | Lines | Specifies the number of lines of the encoder |
| Quadrature encoder | Index pulse present | Specifies whether an index pulse is present |
| Quadrature encoder | Tracking loop time constant | Determines bandwidth of tracking loop |
| Quadrature encoder | Synchronization method | Selects method of synchronizing encoder with back-emf |
| Quadrature encoder | Align angle shift | Determines angle shift between rampup and align states of startup |
| Quadrature encoder | Align initial angle | Determines initial angle used in rampup state of startup |
| Quadrature encoder | Align-and-sweep rate | Determines rotation rate during align state of startup, when using align-and-sweep method |
| Quadrature encoder | Align-and-sweep setup angle | Determines setup angle of align-and-sweep method, to allow transients to settle prior to measurements |
| Quadrature encoder | Pullout slip threshold | Determines rotor slip threshold used for detecting a pullout condition |
One position and velocity estimator must be chosen for use in commutation and velocity feedback.
Available estimators in MCAF R5:
New in version R5.
(Previously this choice was made on the Configure page in motorBench® Development Suite.)
In addition to the primary estimator, additional estimators may be selected. (Only the primary estimator is used for commutation and velocity feedback.)
Usage of more than one estimator — particularly the quadrature encoder, which has higher angle and velocity accuracy — is recommended for troubleshooting or validation purposes. Please note that this will increase CPU and memory requirements.
New in version R4.
Minimum velocity \(\omega_1\) was moved in MCAF R5 to the Customize page from the Configure page. It is used in MCAF in three ways:
New in version R5.
There are two interrelated coastdown parameters used to estimate the time required to bring the motor to a stop, before it can be safely restarted:
The resulting coastdown time is used in the STOPPING state before
proceeding to the STOPPED state.
New in version R5.
Maximum acceleration (in motoring quadrants) and deceleration (in generating quadrants) can be adjusted. Increasing the slew rates will increase the motor current required during acceleration or deceleration.
Determining maximum deceleration during regeneration must be done with some care: the motor drive converts mechanical energy into electrical energy, which must go somewhere, such as a battery or a dynamic brake resistor. Without a viable outlet for that energy, the DC link voltage will rise until the motor controller detects this and shuts down, or until one of the capacitors or transistors fails and dissipates this energy destructively.
New in version R5.
Determines the point at which the motor controller shuts down due to insufficient available voltage below its minimum operating voltage.
New in version R5.
Determines the point at which the motor controller shuts down due to excessive voltage above its maximum operating voltage.
New in version R5.
The startup sequence has numerous parameters that can be modified. These are shown in Figure 6.1.
Figure 6.1 Graph of current and electrical frequency in startup sequence. (The Weathervane startup algorithm is shown.)
Startup current amplitude \(I_{q0}\) represents a tradeoff between making startup robust (higher is better) and reducing power dissipation in the motor (lower is better). There’s not much value in reducing it below 0.5, which specifies half of maximum continuous current.
New in version R4.
Current rampup time \(t_r\) affects only the initial state of startup, in which current increases from zero to its maximum amplitude. The current rampup time should be slow compared to \(L/R\), so that it represents a smooth transition, but fast compared to the overall startup time.
New in version R4.
Some motors, especially those with large inertia and cogging torque, may start more reliably with align time \(t_{aln} > 0\). The default value of zero is sufficient in most cases.
New in version R5.
Increase the minimum acceleration time \(t_{acc}\) if a slower, less-aggressive startup is desired.
New in version R4.
Increase or decrease the acceleration rate \(\alpha_1\) to control the faster second phase of acceleration. Slower acceleration is generally less prone to cycle slips, but takes longer.
New in version R4.
Increase or decrease the acceleration rate \(\alpha_0\) to control the slower first phase of acceleration. (Note: this is normalized to \(\alpha_1\).) Slower acceleration is generally less prone to cycle slips, but takes longer.
New in version R4.
The hold time \(t_h\) controls how long the startup sequence
remains in the HOLD state where electrical frequency and current
are both held constant before transitioning to closed-loop commutation.
A value of zero is fine in most cases.
New in version R5.
Decreasing the velocity threshold \(\omega_0\) will switch to the faster second phase of acceleration sooner.
(Note that the threshold \(\omega_1\) is determined by the minimum velocity setting under Operating parameters.)
New in version R4.
The angle converge rate controls how fast the transition from open-loop to closed-loop commutation with the Classic startup method.
Some motors may require a lower value to ensure a smooth transition to closed-loop commutation, typically in the range of 0.1°/ms – 1.0°/ms.
New in version R5.
Classic is the algorithm provided in MCAF R1-R3. Weathervane transitions to closed-loop more quickly than the Classic algorithm.
New in version R4.
Controls the amplitude of active damping \(I_\Delta\). Reduce this value if startup is noisy or unstable. Set to zero to eliminate active damping completely.
New in version R4.
Controls the feedback gain of active damping. Reduce this value if startup is noisy or unstable.
New in version R4.
Determines the minimum velocity to enable active damping. Make sure to choose a velocity where the estimator is stable enough to be useful for active damping.
New in version R4.
See the section on overmodulation for more information.
Determines the maximum d-axis voltage. Leaving this at 1.0 is recommended.
New in version R4.
Determines the maximum q-axis voltage. A value between 1.05 and 1.25 is recommended. Larger values will allow higher output voltage amplitude, at the cost of higher distortion in output voltage and current.
The section on overmodulation behavior in the synchronous frame has more information on this subject.
New in version R4.
See the section on AN1292 Phase-locked Loop (PLL) for more information.
Determines the time constant \(\tau\) used for velocity estimation. This does not affect estimator stability, but it does impact the velocity control loop performance. Lower values of time constant let more noise through, but allow higher-bandwidth velocity loops. Higher values of time constant filter out more noise, but reduce the achievable velocity loop bandwidth.
New in version R5.
Determines the loop filter bandwidth \(\omega_1\) used for angle estimation in the PLL. (Note: this is a different value than the minimum operating velocity, also called \(\omega_1\))
Leaving this value at its default is recommended.
New in version R5.
See the section on quadrature encoder support for more information.
This should match the number of lines, or cycles per revolution (CPR), listed in the datasheet of the motor or encoder. The number of counts per revolution is 4× the number of lines.
New in version R4.
Select this option if an index pulse signal is present.
New in version R4.
Values in the 1 ms - 10 ms range are recommended. Smaller values will increase estimator bandwidth but allow more encoder quantization noise to appear in the velocity estimate. Larger values will decrease estimator bandwidth, along with the achievable velocity loop bandwidth, but will decrease the effect of encoder quantization noise.
Note: With MCAF R4, out-of-range errors in code generation will occur for certain combinations of motors with low speed ratings, and choices of tracking loop time constant. This is expected when \(\omega_{m1} \tau < \theta_L\) where \(\theta_L \approx 0.4\ \text{rad}\), where \(\omega_{m1}\) is the rated motor velocity in rad/s, and \(\tau\) is the tracking loop time constant. A viable workaround in most cases is to increase the tracking loop time constant, though this would reduce the velocity loop bandwidth.
For example, a motor with rated velocity of 2000 RPM ≈ 209 rad/s is likely to have out-of-range errors if the tracking loop time constant is less than approximately \(0.4 / 209 = 0.0019\) s or 1.9 ms.
New in version R4.
New in version R4.
This determines the align time used for back-emf synchronization. Systems with larger inertia may need longer times. Shorter times (less than 0.5 s) may be adequate for very low inertia systems.
New in version R4.
Increase this angle for systems with high cogging torque. Values of 30° - 60° are recommended.
New in version R4.
Controls the initial electrical angle used during the rampup state of startup. Some angles may be slightly more robust, but this must be determined empirically for a particular motor.
New in version R4.
4 counts per ISR is the fastest, and is adequate for most motors with low cogging torque. Decrease this value for motors with high cogging torque.
New in version R4.
This controls the setup angle prior to making commutation offset measurements. Smaller values may not leave enough time for transients to settle. Larger values will add more time for transients to settle. Increasing it for high-inertia systems may improve accuracy.
New in version R4.
This parameter controls the slip at which pullout offset is measured for determining commutation offset. Slip here is defined as the rate of change of difference in the angle of the stationary frame voltage vector \(V_{\alpha\beta}\) and the raw electrical position from the encoder. Good choices for this parameter depend on the motor’s mechanical properties, namely inertia \(J\), viscous damping \(B\), and friction torque \(T_{fr}\). The slip threshold may need to be increased for motors with low inertia, or decreased for motors with higher inertia. The recommended range for slip threshold is approximately 0.059 to 0.47 rad/s. (0.5× to 4× the default value)
New in version R4.