JP2012029538A - Charger - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a charger which can improve the accuracy of a charging voltage.SOLUTION: When a charging voltage is judged to be outside the range of a target voltage value, a charger (1) outputs a DAC value as a current command value for increasing or decreasing a charging current in order for the charging voltage to be within the target voltage value as a digital data of a normal minimum unit time width T to a D/A converter as a low impedance process when the charging current is more than a prescribed current value based on current information by a current sensor. The charger (2) outputs a DAC value as a current command value for increasing or decreasing the charging current in order for the charging voltage to be within the target voltage value and a current command value which exceeds the resolution of the digital data of the minimum unit time width T as a PWM signal which is converted into a pulse with a pulse width of a narrower time width tt than the minimum unit time width T to the D/A converter as a high impedance process when the charging current is less than the prescribed current value.

Description

  The present invention relates to a charging device that can charge a secondary battery with an output voltage obtained by converting an input voltage into voltage by chopper control.

  As a charging device that can charge a secondary battery with an output voltage obtained by converting an input voltage by chopper control, for example, there is a “charging circuit and charging method thereof” disclosed in Patent Document 1 below. In this type of charging circuit, a switching element is interposed between the input and output, and the chopper control for increasing or decreasing the charging current so that the charging voltage of the secondary battery approaches the target voltage by detecting the charging voltage or charging current with a sensor. This is done by switching elements.

JP 2007-288982 A

  However, according to the prior art disclosed in Patent Document 1, since a microcomputer is generally used for the control unit that performs charge control as described above, the current command value for controlling the charge current is digital data. Are often output. On the other hand, a chopper controller configured to be able to perform chopper control by switching charging current by a switching element often receives a control input signal as an analog voltage, and therefore a current command value from a microcomputer via a D / A converter. Receive. For this reason, for example, when the internal resistance of the secondary battery fluctuates, a problem as shown in FIG. 6 may occur.

  That is, as shown in FIG. 6A, when the internal resistance of the secondary battery is relatively low (for example, 0.67Ω), the charging voltage with respect to increase / decrease of the current command value (0.3 A / DAC value 1 bit). Is relatively small at 0.2 V per bit of the DAC value, so that when the charging voltage is lower than the target voltage value of 54 V, the current command value output from the microcomputer is increased by 1 bit (for example, , DAC value 29 (t1) → 30 (t2) → 31 (t3) → 31 (t4)...), And the charging voltage is set to the target voltage value of 54V.

  However, as shown in FIG. 6 (B), when the internal resistance of the secondary battery is relatively high (eg, 2.67Ω), charging with respect to increase / decrease of the current command value ((0.3 A / DAC value 1 bit)). Since the voltage change increases (0.8 V / DAC value 1 bit), for example, when the charging voltage is shifted by 0.4 V from the target voltage value, the current command value is increased or decreased by 1 bit (DAC value). 29 (t1) → 30 (t2) → 29 (t3) → 30 (t4) ...), the charging voltage is up and down (upper side 54.4V, lower side 53.6V) across the target voltage value (54V) The target voltage is not 54V.

  That is, in the conventional charging device, even if it is attempted to control the charging current in order to set the charging voltage to the target voltage value, the current command value needs to express a small value exceeding the resolution of the D / A converter. If the converter cannot accurately represent the charge current, the analog voltage value output from the D / A converter cannot accurately control the charging current. For this reason, there existed a problem that the precision of a charge voltage could fall.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a charging device that can improve the accuracy of the charging voltage.

  The present invention is a charging device capable of charging a secondary battery with an output voltage obtained by converting an input voltage by chopper control, the voltage sensor detecting the output voltage, and the output from the voltage sensor. Output voltage determining means for determining whether or not the output voltage is within a predetermined target voltage value range based on voltage information of the output voltage, and detecting a charging current of the secondary battery by the output voltage When the output voltage is determined not to be within the range of the target voltage value by the current sensor and the output voltage determining means, current information of the charging current output from the current sensor and the voltage information by the voltage sensor And a current command value for increasing or decreasing the charging current so that the output voltage falls within the range of the target voltage value as digital data having a predetermined time width. Charging current control means, a D / A converter for sequentially converting the digital data output from the charging current control means into an analog voltage value at a cycle shorter than the predetermined time width, and the D / A converter, A chopper control unit that performs the chopper control based on the analog voltage value output from the A conversion unit, and in a predetermined case, the charging current control means uses the current command value to determine the resolution of the digital data. Is output to the D / A converter as a PWM signal converted into a pulse width of a pulse accommodated within the predetermined time width.

  According to the present invention, when the charging voltage determining unit determines that the output voltage is not within the target voltage value range, the charging current control unit includes the current information of the charging current output from the current sensor and the voltage information from the voltage sensor. The current command value that increases or decreases the charging current so that the output voltage falls within the range of the target voltage value is output as digital data of a predetermined time width based on the Is output to the D / A converter as a PWM signal converted into a pulse width of a pulse accommodated within a predetermined time width. As a result, the current value information exceeding the resolution of the digital data is input as the current command value to the D / A converter as the PWM signal. It is possible to convert a “current command value based on current value information having a value exceeding the resolution” into an analog voltage value and output the analog voltage value from the D / A converter to the chopper controller. For this reason, the chopper controller can receive such a “current command value based on current value information having a value exceeding the resolution of digital data” as a current command value based on an analog voltage value.

  Further, the charging device of the present invention is as follows: "When the charging current is less than a predetermined current value based on the current information from the current sensor, the charging current control means sends the PWM signal to the D / A converter. It may be configured to output.

  According to this configuration, the charging current control means outputs a PWM signal to the D / A converter when the charging current is less than the predetermined current value based on the current information from the current sensor. As a result, when the charging current is less than the predetermined current value, that is, when the internal resistance of the secondary battery is relatively high, the charging current control means sends a “current according to the current value information whose value exceeds the resolution of the digital data” to the chopper control unit. "Command value" is output as a current command value based on an analog voltage value. That is, when it is necessary to control the charging current with high accuracy, the “current command value based on the current value information having a value exceeding the resolution of the digital data” can be output. Accordingly, the charging current control can be performed flexibly according to the internal resistance of the secondary battery, so that the charging current control can be made faster than the configuration in which such a current command value is always output.

  Regarding the setting of the predetermined current value, for example, the predetermined target voltage value is Vs, the rated maximum value of the charging current is Imax, the accuracy of the output voltage is Va, the decimal display value of the resolution by the D / A converter is DAmax, the predetermined value Assuming that the current value is Ith, the predetermined current value is expressed as Ith = (Vs / Va) × (Imax / DAmax). Thus, the predetermined current value can be arbitrarily set based on this equation.

  According to the present invention, current value information exceeding the resolution of digital data is input as a current command value to the D / A converter as a PWM signal, so that it could not be converted to an analog voltage conventionally. It is possible to convert “current command value based on current value information having a value exceeding the resolution of digital data” into an analog voltage value and output the analog voltage value from the D / A converter to the chopper controller. For this reason, the chopper controller can receive such a “current command value based on current value information having a value exceeding the resolution of digital data” as a current command value based on an analog voltage value. Therefore, for example, even when the internal resistance of the secondary battery is relatively high, the charging current can be chopper-controlled with high accuracy by the analog voltage value output from the D / A converter, so the charging voltage Accuracy can be improved.

It is a block diagram which shows the structural example of the charging device which concerns on embodiment of this invention. It is a flowchart which shows the flow of the charge control process by the charging device of this embodiment. 3A is a flowchart showing the flow of the low impedance process shown in FIG. 2, and FIG. 3B is a flowchart showing the flow of the high impedance process shown in FIG. FIG. 4A is an explanatory diagram illustrating a setting example of a charging voltage with respect to a DAC value by the charging device according to the present embodiment. FIG. 4A illustrates a case where the internal resistance of the secondary battery is relatively low, and FIG. If the resistance is relatively high. 5A is an explanatory diagram showing an example of the DAC value signal waveform output to the D / A converter by the high impedance processing shown in FIG. 3B, and FIG. 5B shows the DAC value signal waveform. It is explanatory drawing which shows the example of a setting of a charging voltage. FIG. 6A is an explanatory diagram illustrating an example of setting a charging voltage with respect to a DAC value according to the prior art. FIG. 6A illustrates a case where the internal resistance of the secondary battery is relatively low, and FIG. If it is expensive.

Hereinafter, an embodiment of a charging device of the present invention will be described with reference to the drawings.
First, the structural example of the charging device 10 which concerns on this embodiment is demonstrated based on FIG. FIG. 1 is a block diagram illustrating a configuration example of the charging device 10.

  As shown in FIG. 1, the charging device 10 can charge the secondary battery Batt with an output voltage obtained by converting the input voltage by chopper control, and mainly includes a transformer T, a rectifier DB, and a switching device. It is composed of an element SW, a coil L, a capacitor C, a current sensor CT, a voltage sensor VR, a control unit 20, and the like.

  That is, after the three-phase AC voltage supplied from the AC power source AC is stepped down by the transformer T, it is rectified into a DC voltage by the rectifier DB and used as an input voltage, which is used as the switching element SW, the coil L, the capacitor C, and the control. The voltage is stepped down by the step-down chopper circuit configured by the unit 20 and converted into an output voltage. In the present embodiment, for example, three-phase 200 V is supplied as the AC power supply AC, and this is stepped down to a predetermined target voltage value (for example, 120 V) by the step-down chopper.

  In the present embodiment, a lead storage battery is a target for charging as the secondary battery Batt. However, the secondary battery Batt is not limited to this as long as it is a rechargeable battery (storage battery). For example, a nickel cadmium battery, nickel hydrogen A battery, a lithium ion battery, etc. may be sufficient.

  The switching element SW is a switching transistor composed of a semiconductor element. In this embodiment, an IGBT (Insulated Gate Bipolar Transistor) is used. The IGBT reduces the increase in on-resistance due to the higher breakdown voltage than the MOSFET, but can switch at a higher speed than the bipolar transistor. Therefore, even if the input voltage from the rectifier DB is a high voltage exceeding 100 V, a large power is required. Enables high-speed switching.

  In this embodiment, the input voltage from the rectifier DB is applied to the collector (input terminal) of the IGBT that is the switching element SW, and the coil L is connected so that the switching output can be extracted from the emitter (output terminal) of the IGBT. Has been. Further, since the control terminal that can control the switching element SW is the gate of the IGBT, the output side of the chopper control unit 29 constituting the control unit 20 is connected to this.

  On the output side of the coil L, a capacitor C that forms an LC type LPF (Low-pass filter) together with the coil L is connected to SG (reference potential). Thus, the high-frequency noise component included in the switching output output from the switching element SW is removed, and the DC voltage, that is, the output voltage can be extracted from the capacitor C as the charging voltage of the secondary battery Batt.

  As described above, the step-down chopper circuit is configured by the switching element SW, the coil L, the capacitor C, and the control unit 20, but in this embodiment, the coil L is required because it is necessary to detect the charging current and the charging voltage of the secondary battery Batt. A current sensor CT is connected in series with the capacitor C, and a voltage sensor VR is connected in parallel with the capacitor C. Current information from the current sensor CT and voltage information from the voltage sensor VR are output to the control unit 20 as analog signals. A specific example of the current sensor CT is a current transformer with an amplifier, and a specific example of the voltage sensor VR is a voltage dividing resistor connected in series.

  Although not shown in FIG. 1, for example, by providing a snubber circuit between the input and output of the switching element SW and between the output and SG of the rectifying unit DB, a surge voltage that can be generated when the switching element SW is turned on and off. The damage of the semiconductor element (switching element SW or rectifying unit DB) due to can be suppressed.

  The control unit 20 includes a charge control unit 21, A / D conversion units 23 and 25, a D / A conversion unit 27, a chopper control unit 29, and the like. The charge control unit 21 is a digital circuit composed of a semiconductor memory, an input / output interface, and the like centering on a CPU (not shown). For example, a one-chip microcomputer corresponds to this. The semiconductor memory is composed of a RAM and an EEPROM, and a charge control process described later is realized by the CPU executing a charge control program stored in the EEPROM.

  The A / D converters 23 and 25 have a function of converting an analog signal into a digital signal, and are generally called an A / D converter or an ADC. In the present embodiment, the A / D conversion unit 23 is interposed between the charge control unit 21 and the current sensor CT, thereby converting the current information of the charging current based on the analog signal output from the current sensor CT into a digital signal. Output to the charging control unit 21, or the A / D conversion unit 25 is interposed between the charging control unit 21 and the voltage sensor VR, whereby the voltage information of the charging voltage by the analog signal output from the voltage sensor VR is obtained. It is converted into a digital signal and output to the charging control unit 21.

  The D / A converter 27 has a function of converting a digital signal into an analog signal, and is called a D / A converter or a DAC. In the present embodiment, the D / A conversion unit 27 is interposed between the charge control unit 21 and the chopper control unit 29, so that digital data (10-bit configuration) output from the charge control unit 21 (described later) The current command value by the DAC value) is converted into an analog control input signal and output to the chopper control unit 29.

  The chopper controller 29 can output a control signal to the gate of the switching element SW in accordance with an analog control input signal (current command value) input from the charge controller 21 via the D / A converter 27. It is. In general, a signal generator that can mainly generate a sawtooth waveform that repeats at a predetermined cycle, and a predetermined cycle having a pulse width according to the magnitude of the control input signal by comparing the sawtooth waveform with the control input signal. And a comparator that generates a PWM waveform. The PWM waveform is output to the switching element SW as a gate control signal.

  By configuring the control unit 20 in this way, a pulse waveform of a predetermined period having a pulse width according to the magnitude of the current command value is input to the gate of the switching element SW as a gate control signal. The SW performs a switching operation according to the PWM waveform by repeatedly performing an operation of conducting between the input and output (emitter-collector) for the time of this pulse width. As a result, a voltage having substantially the same waveform as the PWM waveform is output to the output (collector) side of the switching element SW, so that unnecessary high-frequency components are substantially eliminated by passing this through the LPF composed of the coil L and the capacitor C. A DC voltage close to the target value is obtained as an effective value. That is, a step-down chopper is possible.

  Next, the flow of the charging control process performed by the control unit 20 will be described with reference to FIGS. 2 is a flowchart showing the flow of the charging control process, and FIG. 3 shows the flow of the low impedance process (FIG. 3A) and the flow of the high impedance process (FIG. 3B). Has been. FIG. 4 is an explanatory diagram showing a setting example of the charging voltage with respect to the DAC value. Further, FIG. 5 is an explanatory diagram (FIG. 5A) showing an example of the DAC value signal waveform output to the D / A converter by high impedance processing, and an explanation showing an example of setting the charging voltage for the DAC value signal waveform. The figure (FIG. 5B) is shown.

  As described above, this charge control process is realized by the CPU executing the charge control program stored in the EEPROM, and automatically after the main power supply of the charging apparatus 10 is turned on. It is activated.

  As shown in FIG. 2, in the charging control process, when a main power supply (not shown) is turned on, a predetermined initialization process is first performed in step S101. In this process, the CPU constituting the charge control unit 21 clears the RAM work area and flags used for arithmetic processing and the like with predetermined values, and initializes each port corresponding to the input / output interface.

  In subsequent step S103, a charging voltage detection process is performed. This process acquires voltage information output from the voltage sensor VR. For example, the moving average value is calculated by the following algorithm using a task or process different from the main charging control process.

  For example, 512 times are measured during 50 mS (mS; millisecond, the same applies hereinafter), and the average value is stored for the last 800 mS. Then, after summing up the 16 data for the last 800 mS, and dividing by 16, a moving average value that fluctuates in real time is obtained. This suppresses the occurrence of errors due to other factors such as the influence of switching noise caused by the switching element SW and external noise. Thereby, the terminal voltage (charging voltage) of the secondary battery Batt connected to the charging device 10 can be accurately detected.

  After step S103, it may be determined whether or not the secondary battery Batt is connected to the charging device 10 based on the voltage information detected by the charging voltage detection process (S103). When it is determined that the secondary battery Batt is not connected, the charging control process is immediately terminated and a transition to a standby state is performed, thereby preventing a failure or failure due to a no-load state. It becomes possible.

  In step S105, based on the voltage information obtained in step S103, a process is performed to determine whether or not the terminal voltage of the secondary battery Batt is within the target voltage value range. In the present embodiment, when the nominal output voltage (for example, 120V) of the secondary battery Batt is set to the target voltage value and has a width of, for example, ± 2V, the “target voltage value range” is 118V to 122V. . That is, in this example, it is determined by step S105 whether it is between 118V-122V.

  If it is determined in step S105 that the voltage of the secondary battery Batt is within the target voltage value range (for example, 118V to 122V) (S105; Yes), the secondary battery Batt is currently charged. Since there is no need, the process returns to step S103 again to perform the charge voltage detection process. That is, as long as the voltage of the secondary battery Batt is within the range of the target voltage value, the voltage monitoring can be continuously performed by repeatedly performing the process of step S103 and the process of step S105.

  On the other hand, when it is not determined that it is within the range of the target voltage value (for example, 118V to 122V) (S105; No), the secondary battery Batt needs to be charged, so the process proceeds to the next step S107. To migrate. Note that a process for determining whether or not the voltage of the secondary battery Batt exceeds the target voltage value may be placed after step S105. This makes it possible to detect the secondary battery Batt that has fallen into an overcharged state.

  In step S107, a charging current detection process is performed. This process is to acquire current information output from the current sensor CT. Similar to the charge voltage detection process in step S103 described above, the switching element SW is obtained by obtaining a moving average value of the charge current that varies in real time. It is possible to suppress the occurrence of errors due to other factors such as the influence of switching noise due to the external noise and the like, and to accurately detect the charging current of the secondary battery Batt connected to the charging device 10.

  In the subsequent step S109, based on the current information obtained in step S107, the charging current of the secondary battery Batt is “greater than or equal to a predetermined current value” or “less than the predetermined current value” with respect to a predetermined current value set in advance. Processing to determine whether or not there is is performed. This “predetermined current value” is an index used for examining whether the internal resistance of the secondary battery Batt is relatively high or relatively low, and is calculated by the following equation (1). Can do.

        Ith = (Vs / Va) × (Imax / DAmax) (1)

  In the above equation (1), “Ith” is the predetermined current value, “Vs” is the target voltage value of the secondary battery Batt, “Imax” is the rated maximum value of the charging current, and “Va” is the accuracy of the charging voltage. , “DAmax” represents a decimal display value of resolution by the D / A converter 27.

  For example, in the above example, the target voltage value Vs of the secondary battery Batt is 120V, the rated maximum value Imax of the charging current is 280A, and the charging voltage accuracy Va is set to 1V. Further, as described above, since the digital data input to the D / A converter 27 has a 10-bit configuration, the maximum resolution is a decimal display value of 1024 (hereinafter, the decimal display value is expressed as “XXXXX”. (“d” is added to the end of the number as in “d”), but the resolution DAmax used in the region near the target voltage value (120 V) is “780 d”, which is used.

  When these values are substituted into the above equation (1), the predetermined current value Ith (= (120/1) × (280/780)) is 43.077A. That is, in this example, it is determined in step S109 whether or not the charging current of the secondary battery Batt detected in step S107 is greater than or equal to the predetermined current value 43A (or less than 43A).

  In the present embodiment, when the charging current of the secondary battery Batt is equal to or greater than the predetermined current value 43A (S109; “above”), it is determined that the internal resistance of the secondary battery Batt is relatively low, The process proceeds to low impedance processing in step S120.

  That is, when the charging current is greater than or equal to the predetermined current value 43A (S109; “above”), the internal resistance of the secondary battery Batt is as low as about 0.5Ω, for example, and is output from the D / A converter 27. The analog voltage value after conversion with respect to the current command value per bit of the digital data (DAC value) is also a relatively fine value. Therefore, in the chopper control unit 29 that performs chopper control by inputting the analog voltage value, as already described in the section “Problems to be solved by the invention”, the chopper control is performed as in the conventional case. The charging voltage can be brought close to the target voltage value without any problem. Therefore, the chopper control similar to the conventional one is performed in the low impedance processing in step S120.

  On the other hand, when the charging current is less than the predetermined current value 43A (S109; “less than”), it is determined that the internal resistance of the secondary battery Batt is relatively high. Transition.

  That is, when the charging current is less than the predetermined current value 43A (S109; “less than”), the internal resistance of the secondary battery Batt is as high as about 2Ω, for example, and the digital data output from the D / A conversion unit 27 The analog voltage value after conversion with respect to the current command value per bit of (DAC value) is also a relatively coarse value. Therefore, in the chopper control unit 29 that performs chopper control by inputting the analog voltage value, as described with reference to FIG. 6B in the column of [Problems to be solved by the invention] When the chopper control is performed, the charging voltage rises and falls across the target voltage value, so it is difficult to bring it close to the target voltage value. For this reason, information processing unique to the present invention, that is, high impedance processing in step S130 is performed.

  In addition, by modifying the above equation (1), as shown in the following equation (2), it becomes possible to obtain the resolution DAmax necessary for use in the region near the target voltage value.

        DAmax ≧ (Imax / Ith) × (Vs / Va) (2)

  For example, the predetermined current value Ith is set under the same conditions as described above (the target voltage value Vs (= 120 V) of the secondary battery Batt, the rated maximum value Imax (= 280 A) of the charging current, and the accuracy Va (= 1 V) of the charging voltage). When set to 10 A, the resolution DAmax (= (280/10) × (120/1)) required for use in the region near the target voltage value is “3660d”. That is, to determine whether to shift to the low impedance process (S120) or the high impedance process (S130) based on “10A” as the charging current flowing in the secondary battery Batt, at least the use region It is understood that it is necessary to select the D / A converter 27 (for example, 12 bits (= “4096d”)) having a resolution of “3660d”.

  From here, the flow of each process by step S120,130 is demonstrated. The flow of these information processing is shown in FIG. 3, and will be described with reference to FIG. First, the low impedance process (S120) for performing the same information processing as in the prior art will be described with reference to FIG.

  As shown in FIG. 3A, in the low impedance processing, first, in step S121, the current charging voltage of the secondary battery Batt is “greater than or equal to the target voltage value” or “less than the target voltage value” with respect to the target voltage value. Processing to determine whether or not That is, since the voltage information output from the voltage sensor VR is acquired in step S103, it is determined based on this whether the current charging voltage is “above the target voltage value” or “less than the target voltage value”. To do.

  If it is determined that the current charging voltage is “above the target voltage value” (S121; “above”), it is necessary to reduce the charging current in order to reduce the charging voltage. Transition. On the other hand, if it is determined that the value is “below the target voltage value” (S121; “less than”), it is necessary to increase the charging current in order to increase the charging voltage, and the process proceeds to the subsequent step S125. .

  In step S123, in order to reduce the charging current, a process of lowering the current digital data as the current command value output from the D / A converter 27 by 1 bit, that is, a process of reducing the DAC value by 1 bit is performed. On the other hand, in step S125, in order to increase the charging current, a process of increasing the current digital data as the current command value output from the D / A converter 27 by 1 bit, that is, a process of increasing the DAC value by 1 bit is performed.

  Specifically, as shown in FIG. 4A, for example, when the current charging voltage is 53.6 V when the target voltage value is 54 V, the charging current is increased to increase the charging voltage. . That is, the DAC value is increased from 29 by 1 bit to 30. As a result, the charging voltage rises by 0.2 V. By increasing the DAC value by 1 bit from 30 to 31 again by this process, the charging voltage increases by 0.2 V and reaches the target voltage value of 54.0 V (DAC) Value 29 (t1) → 30 (t2) → 31 (t3) → 31 (t4) → 31 (t5).

  On the other hand, as shown in FIG. 3B, even in the high impedance process, first, in step S131, whether the current charging voltage of the secondary battery Batt is “more than the target voltage value” with respect to the target voltage value or not. A process of determining whether the value is “less than” is performed. This process is performed based on the voltage information already acquired from the voltage sensor VR, as in step S121 of the low impedance process.

  If it is determined that the current charging voltage is “above the target voltage value” (S131; “above”), the process proceeds to the subsequent step S133 to lower the charging voltage, and “less than the target voltage value”. (S131; “less than”), the process proceeds to step S135 to increase the charging voltage.

  Steps S133 and 135 are greatly different from steps S123 and 125 by the low impedance processing in that the number of bits of the DAC value to be increased or decreased is less than 1 bit. That is, as shown in FIG. 3 (B) and FIG. 4 (B), by increasing / decreasing the DAC value that is basically increased / decreased for each bit by less than 1 bit (for example, by 1/4 bit), Numerical values smaller than 1 bit can be expressed.

  For example, as shown in FIG. 5A, the digital data as the DAC value is given meaning in the time axis direction. Specifically, since one bit represents a binary representation of “0” or “1”, “0” and “1” are set in the time axis direction with a time width tt smaller than the normal minimum unit time width T. Express. At this time, the wave height of the digital data as the DAC value is the value when “1”. Thus, for example, as shown in FIG. 5A, when the normal minimum unit time width T is set to 1S (1 second), 100 mS, which is 1/10 of the time width tt, is set as one slot. Ten of them are formed, and a PWM waveform is formed so that four values can be expressed in each slot. That is, the PWM waveform for 10 slots is accommodated within the normal minimum unit time width T.

  For example, as shown in FIG. 5 (A), after forming “1” only for the first 25 mS and then setting the remaining 75 mS to “0”, 1/4 (= 0.25) is obtained. Express. Further, as shown in β in the figure, after “1” is formed only for the first 50 mS, 2/4 (= 0.50) is expressed by setting the remaining 50 mS to “0”, and γ As shown, after forming “1” for the first 75 mS, the remaining 25 mS is set to “0” to express 3/4 (= 0.75).

  5A represents “0” which is 0/4 (= 0) by maintaining “0” for 100 mS from the beginning to the end, and ε in FIG. By maintaining “1” for 100 ms from the end to the end, “1” that is 4/4 (= 1) is expressed. That is, “0” and “1” generate a DAC value in the same manner as the conventional digital data representation.

  As a result, a value exceeding the resolution of the binary-represented digital data represented by the normal minimum unit time width T is set in the time axis direction by the pulse width of the PWM waveform accommodated in the normal minimum unit time width T. Since it is possible to superimpose and express it as a DAC value, by outputting such a DAC value to the D / A conversion unit 27, the D / A conversion unit 27 has the size of the current command value. A pulse waveform having the corresponding pulse width is output to the switching element SW as a gate control signal. In other words, “current command value based on current value information with a value exceeding the resolution of digital data” that could not be converted to analog voltage in the past is converted to an analog voltage value and output from the D / A converter to the chopper controller. It becomes possible to do.

  Therefore, in the switching element SW, by repeating the operation of conducting between the input and output (emitter-collector) for the time of this pulse width, the PWM waveform for 10 slots accommodated in the normal minimum unit time width T is obtained. In order to perform the switching operation in accordance with the secondary battery Batt, a DC voltage having an effective value according to a value expressed by four values (0.00, 0.25, 0.50, 0.75, 1.00) in the time axis direction is used as a charging voltage (output voltage). (Gray portion in each waveform shown in FIGS. 5A and 5B). Note that in the waveform example shown in FIG. 5B, the time width tt corresponding to 10 slots within the minimum unit time width T is omitted in 4 slots and expressed in the drawing. I want.

  As specific information processing for generating a PWM waveform with a time width tt of 10 slots within such a minimum unit time width T, for example, a timing four times faster than the output timing of a conventional DAC value (digital data) This is performed by outputting “1” and “0” as DAC values to the D / A converter 27 at a period of 100 mS (the present invention is a period of 25 mS). For example, in the case of α shown in FIG. 5A, using a counter that interrupts every 25 ms, the bit is raised and lowered in the order of “1” → “0” → “0” → “0” at the interrupt timing. As a result, the bit string of the generated PWM waveform is “1000b” (hereinafter, the binary display value is represented by adding “b” at the end of the number, such as “XXXB”).

  Further, in the case of β shown in the figure, in the order of “1” → “1” → “0” → “0”, similarly in the case of γ, “1” → “1” → “1” → “0” In this order, the bits are raised and lowered. Thus, the generated PWM waveform bit string is “1100b” in the case of β, and “1110b” in the case of γ. Note that “0000b” in the case of δ and “1111b” in the case of ε maintain “0” or “1” within the minimum unit time width T as in the conventional case. , “0” → “0” → “0” → “0”, or “1” → “1” → “1” → “1” in order of bit state control to α to γ This can be realized by the same information processing as the processing.

  In step S133, since the DAC value is reduced by ¼, the previous output value is stored, and the DAC value is reduced by ¼. For example, as shown in FIG. 5B, when the DAC value output last time is 29.75, the wave height of “29” is in the order of “1” → “1” → “1” → “0”. Since the output (1110b) is being performed, the DAC value is decreased by ¼, and output in the order of “1” → “1” → “0” → “0” at a wave height of “29” ( 1100b), the bit is raised and lowered for 10 slots (in FIG. 5B, only 4 slots are shown and 6 slots are omitted).

  If the DAC value that was output last time is 29, the output is (0000b) in the order of “0” → “0” → “0” → “0” at the wave height of “29”. Is reduced by ¼, the bit height is reduced by one step, and the bit height is set to “1” → “1” → “1” → “0” in that order (1110b). Is raised and lowered for 10 slots.

  On the other hand, in step S135, since the DAC value is increased by ¼, the previous output value is stored as in step S133, and the DAC value is increased by ¼. For example, as shown in FIG. 5B, when the DAC value output last time is 29.25, the wave height of “29” is in the order of “1” → “0” → “0” → “0”. Since the output (1000b) is being performed, the DAC value is increased by ¼ this time and output in the order of “1” → “1” → “0” → “0” at the wave height of “29” ( 1100b), the bit is raised and lowered for 10 slots (in FIG. 5B, only 4 slots are shown and 6 slots are omitted).

  When the previously output DAC value is 30, the DAC value is output in the order of “0” → “0” → “0” → “0” (0000b) at the wave height of “30”. Is increased by ¼, the bit height is increased by one step, and the bit is output in the order of “1” → “0” → “0” → “0” at that wave height (1000b). Is raised and lowered for 10 slots.

  As described above, according to the charging device 10 according to the present embodiment, when the control unit 20 determines in step S105 that the charging voltage is not within the target voltage value range (S105; No), (1) When the charging current is greater than or equal to a predetermined current value based on current information from the current sensor CT (S109; “above”), the charging current is set so that the charging voltage falls within the target voltage value range as a low impedance process (S120). The DAC value as a current command value for increasing or decreasing the value is output to the D / A converter 27 as normal digital data having a minimum unit time width T. On the other hand, (2) when the charging current is less than the predetermined current value based on the current information from the current sensor CT (S109; “less than”), the charging voltage is within the range of the target voltage value as high impedance processing (S130). The DAC value as the current command value that exceeds the resolution of the digital data of the minimum unit time width T with the current command value that increases or decreases the charging current so as to fall within the range of the pulse accommodated in the minimum unit time width T. The PWM signal converted into the pulse width is output to the D / A converter 27.

  Thus, in the case of (2) above, the DAC value exceeding the resolution of the digital data is input as the current command value to the D / A converter 27 as a PWM signal, so that it can be converted into an analog voltage conventionally. The “current command value based on the current value information having a value exceeding the resolution of the digital data” that has not been converted can be converted into an analog voltage value and output from the D / A converter 27 to the chopper controller 29. For this reason, the chopper control unit 29 can receive such a “current command value based on current value information having a value exceeding the resolution of digital data” as a current command value based on an analog voltage value. Even when the internal resistance is relatively high, the charging current can be chopper controlled with the analog voltage value output from the D / A converter 27 with high accuracy, so that the accuracy of the charging voltage can be improved. it can.

  In the charging device 10 described above, the step-down chopper control that makes the charging voltage (output voltage) lower than the input voltage is possible. However, the application of the present invention is not limited to this, and the charging voltage (output) The present invention can also be applied to step-up chopper control in which the voltage is higher than the input voltage, and the same operation and effect as in step-down chopper control can be obtained.

  In the charging device 10 described above, the DAC value is decreased or increased by 1/4 bit in the low impedance process (S130) by the charge control process (S133, 135), but the bits to be increased or decreased are further subdivided. (For example, 1 / n (n is an integer of 5 or more)). As a result, a larger amount of information can be superimposed as a DAC value in the time axis direction, so that the accuracy of the charging voltage can be further improved.

DESCRIPTION OF SYMBOLS 10 ... Charging apparatus 20 ... Control part 21 ... Charge control part 23, 25 ... A / D conversion part 27 ... D / A conversion part 29 ... Chopper control part AC ... AC power supply Batt ... Secondary battery C ... Capacitor CT ... Current sensor VR ... Voltage sensor DB ... Rectifier SW ... Switching element T ... Transformer L ... Coil

Claims (3)

A charging device capable of charging a secondary battery with an output voltage obtained by converting the input voltage by chopper control,
A voltage sensor for detecting the output voltage;
Output voltage determination means for determining whether or not the output voltage is within a range of a predetermined target voltage value based on voltage information of the output voltage output from the voltage sensor;
A current sensor for detecting a charging current of the secondary battery by the output voltage;
When the output voltage determining means determines that the output voltage is not within the range of the target voltage value, based on the current information of the charging current output from the current sensor and the voltage information by the voltage sensor. Charging current control means for outputting a current command value for increasing or decreasing the charging current as digital data having a predetermined time width so that the output voltage falls within the range of the target voltage value;
A D / A converter that sequentially converts the digital data output from the charging current control means into an analog voltage value at a cycle shorter than the predetermined time width, and outputs the analog voltage value;
A chopper control unit that performs the chopper control based on the analog voltage value output from the D / A conversion unit,
In a predetermined case, the charging current control means converts the current value information having a value exceeding the resolution of the digital data with the current command value into a pulse width of a pulse accommodated within the predetermined time width. And outputting to the D / A converter.   2. The charging current control means, when the charging current is less than a predetermined current value based on the current information from the current sensor, outputs the PWM signal to the D / A converter. The charging device described in 1. The predetermined target voltage value is Vs, the rated maximum value of the charging current is Imax, the accuracy of the output voltage is Va, the decimal display value of resolution by the D / A converter is DAmax, and the predetermined current value is Ith. Then, the predetermined current value is
The charging device according to claim 2, wherein Ith = (Vs / Va) × (Imax / DAmax).

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