Power converter including a feedback control system
To provide a power converter which can maintain the stability and the response of the feedback control system, even if the frequency characteristic of the chopper circuit changes according to change of driving condition. A power converter is provided with a chopper circuit which has reactor and switching device; and a control circuit which changes a feedback value of duty ratio of the switching device so that a deviation between a target value of output voltage and a detection value of output voltage approaches to 0, wherein the control circuit changes a frequency characteristic of the feedback control, based on at least any two or more of information on the output voltage, information on an input voltage, and information on duty ratio.
1. A power converter comprising:
a chopper circuit that converts direct current (DC) power between an input terminal and an output terminal, and comprises a reactor, a switching device, an input capacitor connected at an input terminal side of the reactor and connected between a positive electrode side and a negative electrode side of the input terminal, a diode connected to an output terminal side of the reactor and the switching device, and an output capacitor connected to the diode and the switching device and connected between a positive electrode side and a negative electrode side of the output terminal;
a voltage detection circuit that detects an output voltage outputted from the output terminal; and
a control circuit that performs feedback control which changes a feedback value of duty ratio so that a deviation between a target value of the output voltage and a detection value of the output voltage approaches to 0, and controls on/off of the switching device by the feedback value of duty ratio,
wherein the control circuit changes a frequency characteristic of the feedback control, based on at least any two or more of information on the output voltage, information on an input voltage inputted into the input terminal, and information on duty ratio, and
wherein the control circuit is a digital control circuit, and
wherein in the feedback control, the control circuit performs at least integral control which integrates a value obtained by multiplying an integral gain to the deviation, and changes the feedback value of duty ratio; and
changes the integral gain based on at least any two or more of the information on the output voltage, the information on the input voltage, and the information on duty ratio, so that a gain crossover frequency of an open loop transfer function which combines a transfer function of the integral control and a transfer function of the chopper circuit becomes smaller than a resonance frequency of the chopper circuit.
2. The power converter according to claim 1 , wherein the control circuit is a digital control circuit, and
wherein the control circuit uses, as the information on the output voltage, the detection value of the output voltage or the target value of the output voltage; uses, as the information on the input voltage, a detection value of the input voltage detected by the voltage detection circuit or a setting value of the input voltage; and uses, as the information on duty ratio, the feedback value of duty ratio or a calculation value of duty ratio calculated based on the information of the output voltage and the information of the input voltage.
3. The power converter according to claim 1 ,
wherein the control circuit
calculates a gain of a proportional element in a transfer function of the chopper circuit representing change of the output voltage with respect to change of the duty ratio, based on at least any two or more of the information on the output voltage, the information on the input voltage, and the information on duty ratio; and
changes the integral gain according to a reciprocal of the gain of the proportional element, and a target value of a gain crossover frequency of an open loop transfer function which combined a transfer function of the integral control and a transfer function of the chopper circuit.
4. The power converter according to claim 3 , wherein the control circuit is a digital control circuit, and
wherein the control circuit sets the target value of the gain crossover frequency to a frequency smaller than a resonance frequency of the chopper circuit which is calculated based on any two or more of the information on the output voltage, the information on the input voltage, and the information on duty ratio.
5. The power converter according to claim 1 ,
wherein the power converter further comprises a current detection circuit that detects a current flowing through the reactor,
wherein the control circuit
by setting the information on the output voltage to Vout, setting a detection value of the current to ILd, setting a resistance value of the reactor to RL, setting the information on duty ratio to D, setting a target value of a gain crossover frequency of an open loop transfer function which combined a transfer function of the integral control and a transfer function of the chopper circuit to fco, and setting the integral gain to Ki, changes the integral gain by a calculation equation of
Ki=2π×fco×(1−D) 2 /(Vout×(1−D)−RL×ILd)
or
Ki=2π×fco×(1−D) 2 /(Vout×(1−D)).
6. A power converter comprising:
a chopper circuit that converts direct current (DC) power between an input terminal and an output terminal, and comprises a reactor, a switching device, an input capacitor connected at an input terminal side of the reactor and connected between a positive electrode side and a negative electrode side of the input terminal, a diode connected to an output terminal side of the reactor and the switching device, and an output capacitor connected to the diode and the switching device and connected between a positive electrode side and a negative electrode side of the output terminal;
a voltage detection circuit that detects an output voltage outputted from the output terminal; and
a control circuit that performs feedback control which changes a feedback value of duty ratio so that a deviation between a target value of the output voltage and a detection value of the output voltage approaches to 0 , and controls on/off of the switching device by the feedback value of duty ratio,
wherein the control circuit changes a frequency characteristic of the feedback control, based on at least any two or more of information on the output voltage, information on an input voltage inputted into the input terminal, and information on duty ratio, and wherein the control circuit is a digital control circuit, and
wherein in the feedback control, the control circuit performs at least differential control which differentiates a value obtained by multiplying a differential gain to the deviation, and changes the feedback value of duty ratio; and
changes a differential gain based on at least any two or more of the information on the output voltage, the information on the input voltage, and the information on duty ratio, so that a gain crossover frequency of an open loop transfer function which combines a transfer function of the differential control and a transfer function of the chopper circuit becomes larger than a resonance frequency of the chopper circuit.
7. The power converter according to claim 6 ,
wherein the power converter further comprises a current detection circuit that detects a current flowing through the reactor,
wherein the chopper circuit is provided with a smoothing capacitor just before the output terminal,
wherein the control circuit
by setting the information on the output voltage to Vout, setting a detection value of the current to ILd, setting a resistance value of the reactor to RL, setting an inductance of the reactor to L, setting the information on duty ratio to D, setting a capacity of the smoothing capacitor to Cout, setting a target value of a gain crossover frequency of an open loop transfer function which combines a transfer function of the differential control and a transfer function of the chopper circuit to fco, and setting the differential gain to Kd, changes the differential gain by a calculation equation of
Kd=2π×fco×L×Cout/(Vout×(1−D)−RL×ILd)
or
Kd=2π×fco×L×Cout/(Vout×(1−D)).
8. The power converter according to claim 6 ,
wherein the control circuit
calculates a gain of a second order integral element in a transfer function of the chopper circuit representing change of the output voltage with respect to change of the duty ratio, based on at least any two or more of the information on the output voltage, the information on the input voltage, and the information on duty ratio; and
changes the differential gain according to a reciprocal of the gain of the second order integral element, and a target value of a gain crossover frequency of an open loop transfer function which combines a transfer function of the differential control and a transfer function of the chopper circuit.
9. The power converter according to claim 8 , wherein the control circuit is a digital control circuit, and
wherein the power converter further comprises a current detection circuit that detects a current flowing through the reactor,
wherein the control circuit calculates a resonance frequency of the chopper circuit based on any two or more of the information on the output voltage, the information on the input voltage, and the information on duty ratio;
calculates a break frequency of the chopper circuit based on any two or more of the information on the output voltage, the information on the input voltage, and the information on duty ratio, and a detection value of the current; and
sets a target value of the gain crossover frequency to a frequency larger than the resonance frequency of the chopper circuit and smaller than the break frequency of the chopper circuit.
10. A power converter comprising:
a chopper circuit that converts direct current (DC) power between an input terminal and an output terminal, and comprises a reactor, a switching device, an input capacitor connected at an input terminal side of the reactor and connected between a positive electrode side and a negative electrode side of the input terminal, a diode connected to an output terminal side of the reactor and the switching device, and an output capacitor connected to the diode and the switching device and connected between a positive electrode side and a negative electrode side of the output terminal;
a voltage detection circuit that detects an output voltage outputted from the output terminal; and
a control circuit that performs feedback control which changes a feedback value of duty ratio so that a deviation between a target value of the output voltage and a detection value of the output voltage approaches to 0 , and controls on/off of the switching device by the feedback value of duty ratio, wherein the control circuit changes a frequency characteristic of the feedback control, based on at least any two or more of information on the output voltage, information on an input voltage inputted into the input terminal, and information on duty ratio, and wherein the control circuit is a digital control circuit, and
wherein the power converter further comprises a current detection circuit that detects a current flowing through the reactor,
wherein the control circuit calculates a resonance frequency of the chopper circuit based on any two or more of the information on the output voltage, the information on the input voltage, and the information on duty ratio;
calculates a break frequency of the chopper circuit based on any two or more of the information on the output voltage, the information on the input voltage, and the information on duty ratio, and a detection value of the current; and
when the resonance frequency is smaller than a determination frequency, changes control gain of the feedback control, so that a gain crossover frequency of an open loop transfer function which combines a transfer function of the feedback control and a transfer function of the chopper circuit becomes smaller than the resonance frequency, and exists in a frequency region where integral control included in the feedback control functions; and
when the resonance frequency is larger than the determination frequency, changes control gain of the feedback control, so that the gain crossover frequency of the open loop transfer function becomes larger than the resonance frequency and smaller than the break frequency, and exists in a frequency region where differential control included in the feedback control functions.
11. The power converter according to claim 10 , wherein the control circuit is a digital control circuit, and
wherein the control circuit calculates the resonance frequency of the chopper circuit, based on any two or more of the information on the output voltage, the information on the input voltage, and the information on duty ratio; and
changes number of break frequencies of a transfer function of the feedback control, according to whether the resonance frequency is smaller than or larger than the determination frequency.