A Novel Method of Stabilizing the Vibration Velocity at the End of Piezoelectric Transducers - Advanced Research on Computer Education, Simulation and Modeling - page 42

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Fig. 3. Schematic of the asymmetric regulation-based ultrasonic power

The power system is composed by three parts, Main Circuit, Constant Current
Loop and Frequency Tracking Loop, which are partitioned by a dot-dash line.
The principle of Main Circuit is detailed below. V 1, D 1, L 1 and C 1 constitute the volt-
age adjustment circuit. Its output voltage U B provides variable working voltage for the
half-bridge converter circuit, which is constituted by V 2 and V 3. Moreover, the output
of the half-bridge converter circuit drives a transducer through a transformer TR.
The principle of Constant Current Loop is described. The transducer's current,
which is the input of Constant Current Loop, is sampled through resistance R3 and
sent to an Error Amplifier.

represents the increasing speed of U B , and the

τ = R C

A 4 4

smaller is, the faster the speed increases. decides the decreasing speed of

τ = R C

τ B 5 4

A

U B , and the smaller B is, the faster the speed decrease. The method proposed in this

paper makes sure that the decreasing speed of U B is much faster than the increasing
one by setting

τ

.
The principle of Frequency tracking is: the transducer's voltage is gained through
R 1 and R 2 , and its current value is sampled through R 3 . Their phase difference

τ >> τ

A B

in equation (4) is sent to Phase Comparator through two low-pass filters LPF 1 and
LPF 2 , and subsequently is used to regulate

θ ( ω )

U to realize frequency tracking.

θ

is set in this
work to realize the asymmetrical automatic steady speed control, which means that
the decreasing speed of U B is faster than the frequency tracking speed, and they both
are faster than the increasing speed of U B .

τ = R C stands for the speed of frequency tracking. τ >> τ >> τ

C 6 5 A C B

5 Simulation Experiments and Analysis

This section demonstrates the novel method by using the simulation-based analysis.
Parameters of the transducer with and without load is listed in Table 1.