JP4923938B2 - DC chopper - Google Patents

Description

  The present invention relates to a direct current chopper, and more particularly to a digital current control device.

  FIG. 5 shows a circuit configuration example of a conventional DC chopper. The DC power source 1 is used as a power source, the switch 2 is ON / OFF controlled at a constant frequency, and the battery 3 as a load is charged through the DC reactor. When the switch 2 is on, the charging current flows from the DC power source 1 to the battery 3 through the path of the reactor 4, and when the switch 2 is off, the electric energy stored in the reactor 4 is used as a power source. A charging current is passed through the battery 3 along the path. 6 is a smoothing capacitor.

  The chopper current control circuit controls the on / off ratio of the switch 2 by a digital control method, and controls the charging current of the battery 3. The current detector 7 detects the current of the reactor 4 and converts the detected current Is into a digital value Idet by the A / D converter 8, and the digital control circuit 9 converts the digital value Idet and the charging current command value (output current command value). And a PWM (pulse width modulation) waveform in which the on / off ratio is controlled in accordance with the deviation is used as the gate signal of the switch 2.

  FIG. 6 shows a control block diagram of the current control circuit of the chopper. In the A / D converter 8, the detection current Is is sampled by the sample hold circuit SH, and converted into a digital detection current Idet by the A / D conversion circuit. In the digital control circuit 9, a deviation between the detected current Idet and the charging current command (digital value) is obtained, and this deviation is digitally calculated by the controller PID, and this calculation result is used as an on / off command. A PWM signal is compared with a carrier wave to obtain a PWM waveform gate signal.

  In the DC chopper configured as described above, the current flowing through the reactor 4 by the on / off control of the switch 2 has a waveform including a ripple current component of the carrier frequency. Further, the charging current of the battery 3 is an average value of the reactor current. In order to control the charging current of the battery 3 according to the current command value, it is necessary to detect the average value of the reactor current at high speed and accurately.

  In the digital current control, the current is discretely sampled. However, as a technique for accurately detecting the average value of the reactor current, by sampling at the top of the carrier wave, it is possible to sample the average value that offsets the fluctuation due to the ripple current (for example, , See Patent Document 1).

This sampling method will be described with reference to FIG. In PWM modulation, an on / off gate signal of the switch 2 is generated by level comparison between a carrier wave and a signal wave, and the reactor current rises during the on period of the switch 2 by the gate signal, and the reactor current falls during the off period. Therefore, the reactor current waveform is a waveform including a ripple synchronized with the carrier wave signal, and the zero point of this ripple waveform is the timing of the peak of the carrier wave. Therefore, the average value of the reactor current can be accurately detected by sampling and holding the current detection signal Is at the vertex timing of the carrier wave.
JP 2004-15949 A

  In the above reactor current sampling method, in the case of the continuous current mode where there is no period in which the reactor current becomes zero as shown in FIG. 8, the average value of the reactor current is accurately detected by sampling the current at the top of the carrier wave. can do.

  However, as shown in FIG. 8, when the current discontinuous mode in which the charging current is small and the reactor current is zero is entered, the average value of the reactor current is detected even if the current is sampled at the top of the carrier wave. There is a problem that current control accuracy deteriorates.

  An object of the present invention is to provide a digital current control device capable of current control with high accuracy and high-speed response even when there is a period when the reactor current becomes zero.

  In order to solve the above-described problem, the present invention detects a current Idet2 from which a PWM carrier wave component included in the reactor current detection value Is is removed, and calculates a deviation between the low-frequency current component included in the reactor current detection value Is and the current Idet2. The detection current Idet is corrected, and the proportional integral derivative controller of the digital control circuit is separated into a proportional derivative controller and an integral controller. The proportional derivative control based on the detected current Idet and the current Idet2 are used as the basis. This is an integral control and has the following configuration.

(1) DC which obtains a chopper operation by a switch to be turned on / off and a direct current reactor, and performs PWM control of on / off of the switch by digital calculation based on a deviation between the detected current Idet of the reactor and an output current command A chopper,
A first A / D converter that samples the detected current Is of the reactor at a period synchronized with a carrier wave of PWM control and obtains an AD converted current Idet1;
An analog low-pass filter that extracts a low-frequency current component from the detected current Is of the reactor;
A second A / D converter that samples the current passing through the analog low-pass filter at a period synchronized with a PWM control carrier wave and obtains an A / D converted current Idet2;
A low-frequency current component is extracted from the current Idet1 by a digital low-pass filter, and a difference between the current and the current Idet2 is added to the current Idet1 to form the detection current Idet. And

(2) The digital control circuit
A proportional differential controller that performs a proportional differential operation on a deviation between the detected current Idet and the output current command;
An integration controller for integrating the deviation between the current Idet2 and the output current command;
And a PWM control unit for obtaining a PWM control signal of the switch based on a signal obtained by adding the control outputs of the two controllers.

  As described above, according to the present invention, the current Idet2 from which the PWM carrier wave component included in the reactor current detection value Is is removed is detected, and the detected current is detected by the deviation between the low frequency current component included in the reactor current detection value Is and the current Idet2. By correcting Idet, if current Is changes instantaneously, it is tracked by current Idet1, and the deviation of current control is suppressed by correcting the current Idet1 through a digital low-pass filter and current Idet2. Even when there is a period in which the reactor current becomes zero, current control can be performed with high accuracy and high-speed response.

  Further, the proportional integral derivative controller of the digital control circuit is separated into a proportional derivative controller and an integral controller, and by performing proportional derivative control based on the detected current Idet and integral control based on the current Idet2, Since the Idet that responds to the current Is at high speed is input to the proportional differential controller, high response characteristics can be realized, and at the same time, the current Idet2 that is obtained by detecting the current Is with high accuracy is input to the integral controller. Highly accurate current control can be realized.

(Embodiment 1)
A circuit configuration diagram of this embodiment is shown in FIG. 1, FIG. 2 is a control block diagram thereof, and FIG.

  1 is different from FIG. 5 in that an analog low-pass filter 10 and an A / D converter 11 are added to the current control circuit, and an arithmetic function is added to the digital control circuit 9. The analog low-pass filter 10 extracts a low-frequency current obtained by removing high-frequency components including the frequency component of the PWM carrier from the current Is of the reactor 4 detected by the current detector 7. The A / D converter 11 samples the low-frequency current extracted by the filter 10 at a period synchronized with the PWM control carrier wave, and performs A / D conversion. The digital control circuit 9 corrects the current Idet1 based on the current Idet1 converted by the A / D converter 8 and the low-frequency current Idet2 converted by the A / D converter 11 to obtain a detected current Idet of the reactor.

  In this correction process, as shown in FIG. 2, the low frequency component included in the current Idet1 is extracted by the digital low-pass filter LPF, and the difference between this and the current Idet2 obtained from the A / D converter 11 is obtained. The difference is added to the current Idet1, and this added value is used as the detection current Idet of the reactor current.

  In the current control circuit configured as described above, when correction processing is not performed, the current Idet1 is a digital current value sampled at the peak of the PWM carrier wave. However, as shown in FIG. 3, the current discontinuity is low. In the mode, the average value cannot be sampled, and the detection accuracy deteriorates. On the other hand, the current Idet2 is a current value sampled after passing through the analog low-pass filter 10, and has a high accuracy although the followability to the change of the reactor current is not good.

  Therefore, deviations occur in the currents Idet1 and Idet2 as shown in FIG. In order to eliminate this deviation, in the configuration of FIG. 2, the current Idet1 is corrected by the deviation between the current after passing through the digital low-pass filter LPF and Idet2, and used as the current detection value Idet input to the PID controller. Thus, the error included in the current Idet1 can be corrected.

  Here, each of the currents Idet1 and Idet2 has the following characteristics.

  Idet1 ... Although the detection accuracy is low, the responsiveness to the reactor current Is is high.

  Idet2 ... The response is slow, but the detection accuracy is high.

  Therefore, when the current Is changes instantaneously, it follows the current Idet1, and is steadily corrected by the value of the current Idet1 that has passed through the digital low-pass filter LPF and the correction by the current Idet2 extracted by the analog low-pass filter 10. In addition, it is possible to realize high-speed response and high-accuracy current control with suppressed current control deviation.

(Embodiment 2)
In the first embodiment, it is possible to improve the current control accuracy by adding a low-pass analog and digital filter and comparing the low-frequency detection current to improve the current control accuracy. The current control accuracy is only improved.

  In this embodiment, the current control accuracy is further improved by performing error correction in the controller of the digital control circuit.

  FIG. 4 shows a block diagram of current detection and current control for this purpose. 4 differs from FIG. 2 in that the controller PID is separated into a proportional differential controller PD and an integral controller I, and the proportional differential controller PD has a detection current Idet corrected by the same configuration as in the first embodiment. And the deviation of the charging current command is input to the integral controller I, and the deviation of the current Idet2 and the charging current command value is input to the integral controller I, and the outputs of both controllers PD and I are added to form a PWM control signal.

  According to the PID control of the present embodiment, the proportional differential controller PD can obtain an output that responds quickly to a change in the current Is, and can realize a highly responsive characteristic. At the same time, the integration controller I obtains an output that corrects the error of the current from which the ripple variation included in the current Is is removed, thereby realizing highly accurate current control.

  In addition, although Embodiment 1 and 2 show the case where it applies to a step-down chopper, a step-up chopper that controls the output current based on the detection of the reactor current by operating the chopper with a switch and a reactor that are switching-controlled at a constant frequency, etc. The same effect can be obtained by applying to a direct current chopper.

The circuit block diagram of the direct-current chopper which shows Embodiment 1 of this invention. FIG. 3 is a control block diagram of a current control circuit (first embodiment). FIG. 6 is a waveform diagram of each part in the reactor current discontinuous mode (first embodiment). The control block diagram of the current control circuit which shows Embodiment 2 of this invention. DC chopper circuit configuration example (conventional). Control block diagram of current control circuit of chopper (conventional). The waveform diagram of each part in the reactor current continuous mode. Each part waveform diagram in reactor current discontinuous mode.

Explanation of symbols

1 DC power supply 2 Switch 3 Battery (load)
4 DC reactor 7 Current detector 8, 11 A / D converter 9 Digital control circuit 10 Analog low-pass filter

Claims (2)

A DC chopper that obtains a chopper operation by a switch that is controlled on / off and a DC reactor, and that performs PWM control on the ON / OFF of the switch by digital calculation based on a deviation between the detected current Idet of the reactor and an output current command. And
A first A / D converter that samples the detected current Is of the reactor at a period synchronized with a carrier wave of PWM control and obtains an AD converted current Idet1;
An analog low-pass filter that extracts a low-frequency current component from the detected current Is of the reactor;
A second A / D converter that samples the current passing through the analog low-pass filter at a period synchronized with a PWM control carrier wave and obtains an A / D converted current Idet2;
A low-frequency current component is extracted from the current Idet1 by a digital low-pass filter, and a difference between the current and the current Idet2 is added to the current Idet1 to form the detection current Idet. DC chopper. The digital control circuit is:
A proportional differential controller that performs a proportional differential operation on a deviation between the detected current Idet and the output current command;
An integration controller for integrating the deviation between the current Idet2 and the output current command;
The DC chopper according to claim 1, further comprising: a PWM control unit that obtains a PWM control signal of the switch based on a signal obtained by adding control outputs of the two controllers.

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