Pulse width modulation power converter and control method employing different sets of PID coefficients
In a Pulse Width Modulation power converter and control method, wherein one of the operating modes steady state or load transient is detected. For either of the two operating modes one set of PID coefficients is provided for the control law that controls the duty ratio command. In case a load transient is detected, the KP gain is selected adaptively. Operating mode detection is supported by oversampling the error signal.
1. A pulse width modulation power converter, comprising:
an output stage generating an output voltage according to a pulse width modulation signal and an input voltage by a switching element,
a source of an output voltage reference,
an analog digital converter connected to the output stage and to the source of the output voltage reference, sampling and amplifying a difference between the output voltage and the output voltage reference to generate an error signal,
a PID controller connected to the analog digital converter and to the switching element wherein the PID controller is configured by a set of PID coefficients, for determining a duty ratio, a pulse width modulator that generates the pulse width modulation signal according to the duty ratio,
a detector for detecting a steady state and a load transient,
wherein the pulse width modulation converter further comprises:
a memory for storing a first set of PID coefficients and a second set of PID coefficients,
a mode selector for selecting one of the first set of PID coefficients or the second set of PID coefficients for configuring the PID controller,
the first set of PID coefficients being selected in case the steady state is detected, and the second set of PID coefficients being selected in case the load transient is detected, wherein the detector for detecting the steady state and the load transient monitors the error signal and compares each value of the error signal to its predecessor by generating an error signal difference; and wherein a duty ratio difference of the duty ratio and its predecessor is computed, and, in case during an off-time of the pulse width modulation signal, the duty ratio difference exceeds a threshold, the pulse width modulator is triggered to start a new pulse width modulation period.
2. The pulse width modulation power converter according to claim 1 , wherein the comparing of each value of the error signal to its predecessor by generating the error signal difference comprises taking into account a second derivative of the error signal.
3. The pulse width modulation power converter according to claim 1 , further comprising a moving average filter for computing a moving average of the error signal.
4. The pulse width modulation power converter according to claim 1 , further comprising a storage unit for storing a plurality of nonlinear gain coefficients KP of the second set of PID coefficients and adaptively selecting a nonlinear gain Kp in case of load transient detection.
5. The pulse width modulation power converter according to claim 1 , wherein the analog digital converter is provided with a first clock frequency, the pulse width modulator is provided with a second clock frequency, and the first clock frequency is higher than the second clock frequency.
6. A control method for a power converter, comprising:
generating an output voltage according to a pulse width modulation signal and an input voltage;
generating an error signal by sampling the output voltage and differencing the sampled output voltage and an output voltage reference;
determining a duty ratio that defines a duty cycle of the pulse width modulation signal by a PID controlling algorithm;
generating the pulse width modulation signal by providing the duty ratio to a pulse width modulator;
detecting a steady state or a load transient,
selecting a first set of PID coefficients in case the steady state is detected and a second set of PID coefficients in case the load transient is detected, and wherein the step of detecting the steady state or the load transient comprises monitoring the error signal and comparing each value of the error signal to its predecessor by computing an error signal difference, and
computing a duty ratio difference of the duty ratio and its predecessor, and, in case, during an off-time of the pulse width modulation signal, the duty ratio difference exceeds a threshold, the pulse width modulator is triggered to start a new pulse width modulation period.
7. The control method according to claim 6 , wherein the step of comparing each value of the error signal to its predecessor by computing an error signal difference comprises taking into account a second derivative of the error signal.
8. The control method according to claim 6 , wherein the output voltage and/or the error signal is oversampled by sampling a plurality of error signals within one PWM period.
9. The control method according to claim 6 , wherein a moving average of the sampled error signal is computed.
10. The control method according to claim 6 , wherein a nonlinear gain KP is selected in case of load transient detection.