Resonant controller#
Toolbox for a standard resonant controller. The ideal transfer function is:
with the resonant frequency \(\omega_R\) [[1]].
The implemented discrete time transfer function is created by impulse invariant discretization with delay compensation [[1] p. 1700] and is:
The resonant frequency is specified by \(\omega_R = h \cdot \omega_{el}\), with the order of the harmonic \(h\) to be controlled and the fundamental frequency \(\omega_{el}\). This method of discretization is chosen, as it is the most optimal among the methods discussed in [[1] p. 1710 f.] with reduced phase lag, improved stability and accurate location of the resonant peaks even for high frequencies.
Resonant-Controller#
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typedef struct uz_resonantController_t uz_resonantController_t#
Struct definition for uz_resonantController.
Description#
Struct to create a resonant controller instance.
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struct uz_resonantController_config#
Configuration struct for PI-Controller. Pass to init function. Accessible by the user.
Public Members
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float sampling_time#
SamplingTime of the PI-Controller in seconds. Must be greater than 0.0f
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float gain#
Gain of the resonant Controller
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float harmonic_order#
Order of harmonic to be controlled
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float fundamental_frequency#
Fundamental Frequency in rad/s
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float lower_limit#
Lower limit for the output limitation
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float upper_limit#
Upper limit for the output limitation. Must be greater than lower limit
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float antiwindup_gain#
Gain of anti-windup feedback
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float in_reference_value#
Input reference value
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float in_measured_value#
Input measured value
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float sampling_time#
Description#
Struct for the configuration of the resonant controller.
Init function#
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uz_resonantController_t *uz_resonantController_init(struct uz_resonantController_config config)#
init function for the resonant controller
- Parameters:
struct – uz_resonantController_config, config for the resonant controller
- Returns:
uz_resonant_controller*, pointer to the resonant controller
Example#
1int main(void) {
2
3 const struct uz_resonantController_config config_R = {
4 .sampling_time = 0.0001f,
5 .gain = 52.5f,
6 .harmonic_order = 2.0f,
7 .fundamental_frequency = 10.0f,
8 .lower_limit = -4.0f,
9 .upper_limit = 4.0f,
10 .antiwindup_gain = 10.0f,
11 .in_reference_value = 0.0f,
12 .in_measured_value = 0.0f,
13 };
14 uz_resonantController_t* R_controller_instance= uz_resonantController_init(config_R);
15}
Step function#
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float uz_resonantController_step(uz_resonantController_t *self, float in_reference_value, float in_measured_value, float fundamental_frequency)#
step function of the resonant controller, steps the controller once
- Parameters:
self – pointer to uz_resonantController_t* object
float – in_reference_value, input reference value for the controller
float – in_measured_value, input measured value for the controller
float – fundamental_frequency, current angular velocity for the controller
- Returns:
float outputvalue of the resonant controller
Example#
1int main(void) {
2 // step once
3 output = uz_resonantController_step(R_controller_instance, in_ref_value, in_measured_value, fundamental_fequency);
4}
Description#
Steps the resonant-controller. First the input values of the controller for the current time-step have to been set. With the step-function the new output value is calculated.
Warning
The step-function has to be called with the same sample time as specified in the input-struct of the resonant controller.
Get output function#
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float uz_resonantController_get_output(uz_resonantController_t *self)#
returns output of the resonant controller
- Parameters:
self – pointer to uz_resonantController_t* object
- Returns:
float output value
Description#
Function to get the output of the resonant controller after each step.
Reset function#
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void uz_resonantController_reset(uz_resonantController_t *self)#
reset function of the resonant controller
- Parameters:
self – pointer to uz_resonantController_t* object
- Returns:
void
Example#
1int main(void) {
2 uz_resonantController_reset(R_controller_instance);
3}
Description#
Resets the Resonant-Controller. The initial condition for the integrator and the output after the reset is 0.0f.
Set-Config function#
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void uz_resonantController_set_config(uz_resonantController_t *self, struct uz_resonantController_config config)#
sets config of resonant controller
- Parameters:
self – pointer to uz_resonantController_t* object
struct – uz_resonantController_config, new config for the resonant controller
- Returns:
void
Example#
1int main(void) {
2 config.lower_limit = -10.0f;
3 config.upper_limit = 10.0f;
4 config.harmonic_order= 7.0f;
5 uz_resonantController_set_config(R_controller_instance, config);
6}
Description#
Function to change the configuration of the resonant controller by passing a new or changed config struct to the controller.
Saturation and Anti-Windup#
The output of the controller is limited by the input values upper_limit and lower_limit.
As an anti-windup strategy the back calculation method is used.
The gain of the anti-windup feedback is given by the input value antiwindup_gain.
To disable the anti-windup strategy the feedback can be set to 0.
Set gain function#
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void uz_resonantController_set_gain(uz_resonantController_t *self, float gain)#
sets gain of resonant controller
- Parameters:
self – pointer to uz_resonantController_t* object
float – new gain
- Returns:
void
Description#
Function to set the gain of the controller without setting the complete config.
Set harmonic order function#
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void uz_resonantController_set_harmonic_order(uz_resonantController_t *self, float harmonic_order)#
sets harmonic order of resonant controller
- Parameters:
self – pointer to uz_resonantController_t* object
float – new harmonic order
- Returns:
void
Description#
Function to set the harmonic order of the controller without setting the complete config.