User's Manual

HARSFEN0602
microseconds, which is about 160Hz.
The frequency is
frequency basic2
]15[CA
⋅ for CA[15] in the range [-4..4].
For example, with CA[15]=2 the frequency is about 40 Hz, whereas with CA[15]=-2
the frequency is about 640Hz
The selection rules for the parameters I and f are few and simple.
The torque I must be as large as possible, so as to reduce the relative effect of disturbance
torques (like cogging and friction) on the resulting waveform. Normally I is taken about 50% of
the continuous motor current.
The frequency f must be selected so that the amplitude of the position sine (See figure 1) will be
6 to 8 bits. The motor position can be analyzed accurately enough when the position sine
amplitude is 4 encoder bits or more. Slightly higher amplitude is set to prevent minor load
changes from disturbing the analysis. Larger position amplitudes will work, but the shaft
oscillation at the motor starting process will be unnecessarily large.
The frequency f must be so that in that frequency the load behaves inertially. This means that in
that frequency the phase angle
)f(
φ
is in the range of –140 to –220 degrees, and also that in this
frequency the amplitude function A(f) foes not have the high gradient of near resonance regions.
The algorithm will not function near to a resonant frequency, or in a low frequency where a
large viscous friction is present.
Specifying very high oscillation frequency (CA[15] equals –3 or –4) is not recommended, since
then not enough position samples are available for each sine cycle.
The composer program normally selects the parameters I and f at the “Establishing commutation” stage.
9.4.3 Method limitation
The algorithm presented in this paper is quite robust, and it is expected to work at most of the motor systems,
including systems with moderate backlash. The users of the algorithm must, however, be aware of its
limitations, which are as follows:
The encoder must have sufficient resolution – at least 256 counts per pole pair. For example, if a
motor has 3 pole pairs, a 256 lines (1000 counts/rev) will suffice, an encoder with 128 lines will
not.
The algorithm will not work with highly unbalanced systems. It is essential that the motor will
not accelerate significantly if no current is applied.
The algorithm will work only if the motor is not free to oscillate to both directions
The algorithm will not work too well if the motor static load is changed significantly. If the
static load is subject to significant changes, tune the algorithm with the highest possible load.
Namely, the inertia of the load must be no less than 40% from its value while the parameters of
the algorithm were tuned, and no more than 40% more than its value while the parameters of the
algorithm were tuned.
If the load inertia is to high, the preset torque level will not suffice to oscillate the motor shaft.
The algorithm will fail and the motor won’t start.
This has the consequence that the algorithm must be tuned with the load present
The algorithm assumes that in the in the excitation frequency, the motor and the load behaves
like an inertia. This assumption fails in one of the following cases:
The excitation frequency is a resonant frequency of the system
There is a large viscous (speed dependent) friction and the excitation frequency is so low, that
the phase of the transfer function between the torque and the acceleration is not in the range [-30
… 30] degrees.
If the found phase is out of range, the algorithm fails and the motor won’t start.
9.4.4 Protections