Patent Publication Number: US-11380502-B2

Title: Electromagnetic switch control device

Description:
TECHNICAL FIELD 
     The present invention relates to an electromagnetic switch control device, and particularly, to an electromagnetic switch control device that controls opening and closing of an electromagnetic switch that is inserted between a power supply and a load and is connected to open and close a conductive path. 
     BACKGROUND ART 
     As illustrated in PTL 1, an operation coil drive device that calculates an impedance of an operation coil (inductive load) of an electromagnetic switch and performs control such that an appropriate current is supplied at the time of an opening and closing operation of the electromagnetic switch has been known. 
     CITATION LIST 
     Patent Literature 
     PTL 1: WO 2017/159070 A 
     SUMMARY OF INVENTION 
     Technical Problem 
     In a power supply system using an assembled battery in which a plurality of battery cells is connected in series or in parallel, when pulse control of an electromagnetic switch (inductive load) connected to an assembled battery and a load on the system side is performed, it is necessary to energize a holding current to be held by an electromagnetic switch in a closed circuit (hereinafter, also referred to as “on”) state. 
     When a contact resistance of an electrical contact (hereinafter, also referred to as a “contact portion” or simply a “contact”) in the electromagnetic switch increases, heat generation deteriorates at the time of the closed-circuit energization. As stated above, when the charge and discharge current of the assembled battery is energized in a state in which the contact resistance of the contact (hereinafter, also referred to as “contact resistance”) increases, there is a concern that the electromagnetic switch is welded and fails due to the heat generated by the contact. 
     In order to avoid such a failure, it is necessary to perform control such that an operation can be continued safely. In an unstable case in which an operation coil current does not satisfy a lower limit (hereinafter, also referred to as a “minimum holding current” or simply a “holding current”) for generating an electromagnetic force to reliably attract and maintain the contact even at the time of the closed-circuit energization control, since a contact pressure is not sufficient, an arc is caused at the contact, and thus the contact may be gradually damaged, and the contact resistance may be increased. In order to avoid such a situation, it is necessary to sufficiently secure the contact pressure by stably supplying the operation coil current as specified. 
     When an overload exceeding the supply capacity of the power supply system, the over-discharging of the battery, or causes thereof act together and the supply voltage drops, the operation coil current of the electromagnetic switch is reduced and becomes insufficient. As described above, this causes an increase in the contact resistance. To avoid this, it is necessary to suppress the decrease in the operation coil current. 
     Thus, when a control unit can detect in advance that the operation coil current is equal to or lower than a control lower limit (hereinafter, also referred to as a “holding current threshold value” or simply a “holding current”), it is effective to control so as not to fall below the holding current threshold value of the operation coil based on the detection result. For example, an on-duty of a switching element is controlled such that an operation coil current A does not fall below the holding current as long as the control is PWM control. In other words, control is performed in a direction in which the duty ratio of on or off approaches 100%, that is, such that an on time becomes longer than an off time. 
     However, the technology described in PTL 1 cannot predict a near-future value of the operation coil current. Accordingly, there is a problem that the control unit cannot detect in advance so as not to fall below the holding current threshold value of the operation coil and the decrease in the operation coil current cannot be suppressed. The present invention has been made to solve such problems, and an object of the present invention is to provide an electromagnetic switch control device capable of stabilizing a contact pressure by predicting ae near-future value of an operation coil current in advance and performing control such that the near-future value does not fall a holding current threshold value by a control unit. 
     Solution to Problem 
     In order to solve the above problems, the present invention is an electromagnetic switch control device that energizes a current value having a PWM-controlled duty ratio to an operation coil, and opens and closes an electrical contact by an electromagnetic force corresponding to the current value. The electromagnetic switch control device includes a current value prediction unit that estimates a near-future predicted current value by using a terminal voltage value of the operation coil, a control range determination unit that determines whether or not the estimated predicted current value is out of a range in which a current of the operation coil is holdable, and a PWM control unit that performs control such that the duty ratio is changed based on the predicted current value when the determination result of the control range determination unit is out of the range. 
     Advantageous Effects of Invention 
     Provided is an electromagnetic switch control device capable of stabilizing a contact pressure by predicting a near-future value of an operation coil current and performing control such that the near-future value does not fall below a holding current threshold value by a control unit. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a circuit diagram illustrating a schematic configuration of a battery-type power supply system using an electromagnetic switch control device (hereinafter, also referred to as “present device”) according to an embodiment of the present invention. 
         FIGS. 2A-2C  comprise a timing chart briefly illustrating PWM control in the present device of  FIG. 1 ,  FIG. 2A  illustrates opening and closing timings of a main switch  7 - 1 ,  FIG. 2B  illustrates opening and closing timings of a main switch  7 - 2 ,  FIG. 2C  illustrates opening and closing timings of a sub switch  8 . 
         FIG. 3  is a circuit diagram illustrating the present device of  FIG. 1  in more detail. 
         FIGS. 4A-4D  comprise a timing chart illustrating changes in a voltage and a current of an operation coil by the PWM control in the present device of  FIG. 1  and  FIG. 3 ,  FIG. 4A  illustrates a supply voltage Vcc,  FIG. 4B  illustrates a terminal voltage V of the operation coil,  FIG. 4C  illustrates a current value A of the operation coil, and  FIG. 4D  illustrates a duty ratio of the PWM control. 
         FIGS. 5A-5C  comprise a flowchart illustrating a processing procedure when the operation coil is controlled by the present device of  FIG. 1  and  FIG. 3 ,  FIG. 5A  illustrates pull-in processing,  FIG. 5B  illustrates voltage and current measurement and duty update processing, and  FIG. 5C  illustrates acquisition processing of a resistance R value and an inductance L value (hereinafter, abbreviated as “RL”). 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereinafter, an application example of the present device to a battery-type power supply system will be described with reference to the drawings.  FIG. 1  is a circuit diagram illustrating a schematic configuration of a battery-type power supply system (hereinafter, also referred to as “present system”) using the present device. As illustrated in  FIG. 1 , the present system includes a motor  1 , an inverter  2 , the present device  3 , an assembled battery  6 , main contactors (hereinafter, also referred to as “main switches” or “electromagnetic switches”)  7 - 1  and  7 - 2  (two switches are collectively  7 ), a precharge relay (hereinafter, also referred to as a “sub switch” or an “electromagnetic switch”)  8 , and a precharge resistor  9 . 
     The assembled battery  6  is configured such that a desired voltage is obtained in a whole assembled battery in which two battery modules  5  are connected in series. The battery module  5  is configured such that a desired half voltage is obtained in a unit in which four battery cells  4  as secondary batteries are connected in series. All the battery modules  5  and the battery cells  4  constituting the assembled battery  6  illustrated herein are connected in series with additive polarities, but are appropriately connected in series, in parallel, or in combination thereof depending on the application. 
     As described above, nine voltage measuring lines  12  are drawn out from electrode terminals in the eight battery cells  4  constituting the assembled battery  6  in the form of being connected in series with all additive polarities. These nine voltage measuring lines  12  are connected to the present device  3  including a microcomputer, and are configured to be able to monitor a charging or discharging status and other management items. The number of battery cells is not limited to eight, and the battery cells  4  may be appropriately connected in series or in parallel. The voltage measuring lines  12  having connection forms corresponding to various different monitoring purposes and management specifications may be connected to the present device  3 , but illustration and description thereof will be omitted. 
     The motor  1  is a load of the inverter  2 . The inverter  2  is a load of the assembled battery  6 . The assembled battery  6  is connected to the inverter  2  with a total of three electromagnetic switches including two main switches (electromagnetic switches)  7  and the sub switches (electromagnetic switch)  8  interposed therebetween. These three electromagnetic switches  7  and  8  can control a conductive state to either a closed or open circuit (on/off) by the present device  3 . 
     The main switch  7 - 1  is inserted in an electric circuit on a positive electrode side of the assembled battery  6  and has a function of instantly opening and closing for most of the current. The main switch  7 - 2  is inserted in an electric circuit on a negative electrode side of the assembled battery  6  and has a function of instantly opening and closing for a total current. On the other hand, the sub switch  8  is inserted in the same electric circuit on the positive electrode side as the main switch  7 - 1 , and has a function of opening and closing for a small current limited to some extent. The sub switch  8  is controlled to be turned on or off at an appropriate timing set by a general-purpose input/output (GPIO) to be described later. 
     The extent to which the current of the sub switch  8  is limited to a small value is defined by a resistance value of the precharge resistor  9  connected in series with the sub switch  8 . The sub switch  8  to which the precharge resistor  9  is connected in series is connected, as an inrush current prevention relay, in parallel to the main switch  7 - 1 . The present device  3  monitors the charging and discharging state of each of the individual battery cells  4  constituting the assembled battery  6 . As will be described later with reference to  FIG. 2 , the present device  3  controls the opening and closing of the main switches  7  and the sub switch  8  inserted between the assembled battery  6  and the inverter  2  at appropriate timings. 
     The electromagnetic switch control device (present device)  3  is a control device that energizes operation coils  16  and  17  of the electromagnetic switches  7  with a current value A having a PWM-controlled duty ratio (hereinafter, also simply referred to as a “duty ratio”) and opens and closes electrical contacts  13  of the electromagnetic switches  7  by an electromagnetic force corresponding to the current value A. The present device  3  includes a current value prediction unit  19 , a control range determination unit  20 , and a PWM control unit  21 . 
     The current value prediction unit  19  estimates a near-future predicted current value Y by using terminal voltages V 1  and V 2  (collectively V) of the operation coils  16  and  17 , respectively. The control range determination unit  20  determines whether or not the estimated predicted current value Y is out of a range in which the current of the operation coils  16  and  17  is holdable, that is, the electromagnetic force to maintain the contacts  13  in an attraction state is exhibitable and maintainable. 
     The PWM control unit  21  controls to change the duty ratio based on the predicted current value Y when the determination result of the control range determination unit  20  is out of the range in which the electromagnetic force is maintainable. Since the present device  3  is configured in this manner, the PWM control unit  21  can stabilize a contact pressure of the contacts  13  by predicting a near-future value X of the operation coil current A and performing control such that the near-future value does not fall below a holding current threshold value W. 
       FIG. 2  is a timing chart briefly illustrating PWM control in the present device of  FIG. 1 .  FIG. 2( a )  illustrates opening and closing timings of the main switch  7 - 1 ,  FIG. 2( b )  illustrates opening and closing timings of the main switch  7 - 2 , and FIG.  2 ( c ) illustrates opening and closing timings of the sub switch  8 . As illustrated in  FIG. 2 , when the assembled battery  6  is connected to the inverter  2 , the present device  3  limits such that an inrush current does not exceed an allowable current of the main switch  7  by the precharge resistor  9  by connecting the sub switch  8  earlier than the main switch  7 - 1  in order to prevent the inrush current. An electromagnetic switch power supply (contactor power supply)  10  is energized to the operation coils  16 ,  17 , and  18 , and thus, the present device  3  closes (on) each contact  13 . In contrast, when the energization is stopped (off), the contact is open by a spring (not illustrated). 
     More specifically, for example, in a hybrid vehicle or a storage battery vehicle, connection and disconnection (on/off) are supported between a DC power supply and a load. Thus, as illustrated in  FIG. 2 , the sub switch  8  is timing-controlled by the GPIO such that the sub switch closes at a timing slightly earlier than the main switch  7 - 1  when the switch is closed. By this timing control, an effect of protecting the contacts of the main switches  7  can be exhibited by precharging to relax the inrush current when a large-current DC electric circuit having a capacitor in the load is closed. 
     Next, a circuit configuration of the present device  3  will be described with reference to  FIG. 3 .  FIG. 3  is a circuit diagram illustrating the present device  3  of  FIG. 1  in more detail. In  FIG. 3 , the assembled battery  6  which is a power supply and the motor and the inverter  2  which are the loads are omitted, and the main part of the present device  3  is mainly constituted by a microcomputer control unit  11  which controls the main switches  7  and the sub switch  8 . A coil current contactor (coil switch or electromagnetic switch)  15  has a function of a main switch that simultaneously controls to energize the electromagnetic switch power supply (contactor power supply)  10  to all the operation coils  16  to  18 . However, it is assumed that the coil current contactor is constantly in an on state. 
     The control unit constituting the main part of the present device  3  is constituted by an RC filter circuit which is a combination of a resistor R and a capacitor C that set time constants T 1  and T 2  [seconds] and freewheeling diodes  41  and  42  in addition to switching elements  38  to  40  that are connected to the microcomputer control unit  11  and operate to be turned on or off. 
     The definitions of the time constant T [seconds] will be described later. 
     The microcomputer control unit  11  includes the current value prediction unit  19 , the control range determination unit  20 , PMW control units  21  to  23 , and A/D converters (ADCs)  24  to  30 . Of these components, the PMW control unit  21  is branched into the PWM control units  22  and  23  to perform independent operations. These components are not necessarily included in the microcomputer control unit  11 , and may have a scattered configuration. 
     Signals are input and output to and from the microcomputer control unit  11 . Signals are input and voltage and current values are input, as analog signals, to the ADCs  24  to  30 , and A/D conversion is performed on these signal so as to be suitable for the processing of the microcomputer. Thus, the ADCs  24 ,  25 ,  27 , and  29  form an operation coil voltage measurement circuit, and the ADCs  26 ,  28 , and  30  form an operation coil current measurement circuit. On the other hand, the PMW control units  21  to  23  output High and Low signals that turn on and off the switching elements  38  and  39 . The GPIO of the microcomputer control unit  11  outputs High and Low signals that turn on and off the switching element  40 . The switching elements  38  to  40  control the energization of the main switches  7 , the sub switch  8 , and the operation coils  16  to  18 , respectively. 
     As described above, the present device  3  forms a control function for appropriately turning on and off the electric circuit in a combination in which the battery-type power supply system formed by the assembled battery  6  constituted by the plurality of secondary batteries  4  connected in series, the loads that receive the supply of the power from the system, and the electromagnetic switches  16  to  18  inserted into current paths thereof. The present device  3  illustrates, for example, an embodiment adopted in the hybrid vehicle or the storage battery vehicle (not illustrated). The operation coil voltage measurement circuits (also referred to as the “ADCs”)  24 ,  25 , and  27  and voltage measurement filter circuits  31 ,  32 , and  33  are further connected to the assembled battery  6 . 
     The ADCs  24 ,  25 ,  27 , and  29  measure the terminal voltage V of the operation coils  16 ,  17 , and  18 . The voltage measurement filter circuits  31 ,  32 ,  33 , and  34  are low-pass filters provided between the operation coils  16 ,  17 , and  18  and the ADCs  24 ,  25 ,  27 , and  29 , and remove radio frequency components such as spike noise harmful to voltage measurement. Due to these configurations, the predicted current value Y that changes transiently can be calculated by using the terminal voltage V of the operation coils  16  and  17 , an impedance Z of the operation coils  16  and  17 , and the time constant T 1  of the voltage measurement filter circuits  31 ,  32 , and  33 . 
     The present device  3  further includes the operation coil current measurement circuits (ADCs)  26 ,  28 , and  30  and current measurement filter circuit  35 ,  36 , and  37 . The operation coil current measurement circuits  26 ,  28 , and  30  measure the current energized to the operation coils  16  and  17 . The current measurement filter circuits  35 ,  36 , and  37  are low-pass filters provided between the operation coils  16 ,  17 , and  18  and the operation coil current measurement circuits  26 ,  28 , and  30 , and remove radio frequency components such as spike noise harmful to current measurement. 
     The impedance Z is calculated by using the terminal voltage V, the time constant T 1  of the voltage measurement filter circuits  31 ,  32 , and  33 , the current value A, and the time constant T 2  of the current measurement filter circuits  35  and  36 . This impedance Z is calculated from the terminal voltage V of the operation coils  16  and  17  during an on period in which the duty ratio in the PWM control is 100% in order to set the contact in a closed circuit state, and the current value A. Impedance Z=terminal voltage V/current value A. The terminal voltages V 1  and V 2  and the current values A 1  and A 2  of the operation coils  16  and  17  are collectively abbreviated as the terminal voltage V and the current value A, respectively. 
     The microcomputer control unit  11  switches between on and off states of the sub switch  8  by turning on and off the switching element  40  with an output signal of either the High or Low signal from the GPIO. Similarly, the microcomputer control unit  11  switches between the on and off states of the main switches  7 - 1  and  7 - 2  by turning on and off the switching elements  38  and  39  with pulse control signals output from the PWM control units  21  to  23 . For example, when the switching elements  38  to  40  are constituted by NPN type transistors or the like, the current is energized to the operation coils  16  to  18  in a period in which the output signal of the microcomputer control unit  11  is High. 
     On the contrary, in order to set the main switches  7  and  8  to be surely in an off state by switching the output signal of the microcomputer control unit  11  from High to Low, it is necessary to quickly extinguish an exciting current in an opposite direction due to inductive components of those operation coils  16  to  18 . 
     The exciting current escapes as a reflux current passing through the freewheeling diodes  41  and  42 , and thus, the exciting current that tends to continue to flow through the operation coils  16  to  18  can be quickly extinguished. 
     Next, the duty control for the current A in an on period of the main switches  7 , that is, while being energized to the operation coils  16  and  17  will be described with reference to  FIGS. 4 and 5 . The operation coil  18  of the precharge relay (sub switch)  8  does not need to be duty-controlled. 
       FIG. 4  is a timing chart illustrating changes in the voltage and current of the operation coil due to the PWM control in the present device of  FIGS. 1 and 3 .  FIG. 4( a )  illustrates a supply voltage Vcc,  FIG. 4( b )  illustrates the terminal voltage V of the operation coil,  FIG. 4( c )  illustrates the current value A of the operation coil, and  FIG. 4( d )  illustrates the duty ratio of the PWM control. 
     Ideally, the supply voltage Vcc of  FIG. 4( a )  and the terminal voltage V of the operation coil in  FIG. 4( b )  are constantly maintained at constant levels as illustrated in the left half of each figure. However, as in the battery-type power supply system (the present system), in a power supply system using a battery, when there is a large load for supply capacity, even though there is constant voltage guarantee means, it is necessary to assume a voltage fluctuation (especially a drop) to some extent. 
     When the supply voltage Vcc drops as illustrated near a center in a horizontal direction of  FIG. 4( a ) , the near-future value is predicted based on a change direction of the measured value V due to the ADCs  24 ,  25 , and  27  as illustrated near the center in the horizontal direction of  FIG. 4( b ) . On the other hand, as illustrated in chronological order from left to right in  FIG. 4( d ) , the duty ratio of the PWM control is appropriately controlled by the microcomputer control unit  11  from 0 to 100% by internal arithmetic processing. 
     The current value A of the operation coil illustrated in  FIG. 4( c )  is controlled from 0 to 100% so as to follow the duty ratio of the PWM control. However, although there is a time delay, as will be described later, the duty ratio is controlled from 0 to 100% such that there is no excess or deficiency by the internal arithmetic processing while the microcomputer control unit  11  monitors the changes in the terminal voltage V and the current values A 1  and A 2  (collectively A) of the operation coils  16  and  17  illustrated in  FIGS. 4( b ) and 4( c ) . 
     More specifically, the following three types of operation modes &lt;1&gt; to &lt;3&gt; are executed for periods in chronological order from left to right in  FIG. 4 . 
     &lt;1&gt; A pull-in mode is a mode in which a duty ratio of 100% is output in order to reliably maintain the attraction state in a pull-in period immediately after the contact  13  is attracted (see  FIG. 5( a ) ). 
     &lt;2&gt; A holding current maintaining mode is a mode in which the current value A of the operation coils  16  and  17  is reduced by the PWM control in a normal operation period in which the attraction state of the contact  13  is maintained but is maintained by a holding current W that does not fall below a minimum required limit (see  FIG. 5( b ) ). 
     &lt;3&gt; An RL update period mode is a mode in which the PWM control duty is 100% in an RL update period for correcting the amount of drift of the impedance Z of the operation coils  16  and  17  in the electromagnetic switch  7  as in the pull-in period (see  FIG. 5( c ) ). 
     In the above mode &lt;1&gt;, when the main switch  7  is turned from off to on, the current value A is sharply increased to 100% by first setting the duty ratio to 100%. As a result, the contact  13  of the main switch  7  opened by an elastic force of a spring (not illustrated) is turned from off to on by being attracted (pulled in). In the above mode &lt;2&gt;, both the duty ratio and the current value A can be relaxed from 100% to near a closed-circuit holding current lower limit (holding lower limit) W in order to maintain the on state. 
     However, in this mode &lt;2&gt;, when the supply voltage Vcc and the terminal voltage V drop for some reason while the main switch  7  is maintained in the on state, the current value A required to maintain the main switch  7  in the on state falls below the holding lower limit value W, and thus, it is expected that the main switch is turned off unexpectedly. In order to avoid such an expected defect, the PWM control is performed such that the current value A greatly exceeds the holding lower limit W in the above mode &lt;2&gt;. 
     After the PWM control to counteract such a drop expectation, in the above mode &lt;3&gt;, a period in which a resistance value R and an inductance L value (abbreviated as “RL”) of the operation coils  16  and  17  in the electromagnetic switch  7  is updated is provided, and the duty ratio is set to 100% again and the current value A is raised to 100% only in this period. This RL update period will be described later with reference to  FIG. 5 . 
     The duty ratio of 0 to 100% which is illustrated in chronological order from left to right in  FIG. 4( d )  is controlled by the arithmetic processing performed by the PMW control units  21 ,  22 , and  23  formed inside the microcomputer control unit  11  illustrated in  FIG. 3 . As a result, PWM output signals as High and Low signals that turn on and off at a desired duty ratio and appropriately timing are output from the PMW control units  21  to  23 . 
       FIG. 5  is a flowchart illustrating a processing procedure when the operation coil is controlled in the present device of  FIGS. 1 and 3 .  FIG. 5( a )  illustrates pull-in processing,  FIG. 5( b )  illustrates voltage and current measurement and duty update processing, and  FIG. 5( c )  illustrates RL acquisition processing. 
     As illustrated in  FIG. 5( a ) , the pull-in processing has processing S 1  of setting the PWM output signal to duty 100%, processing S 2  of measuring voltage and current, processing S 3  of determining whether or not a transient response is completed, coil RL calculation processing S 4 , and processing S 5  of determining whether or not a pull-in time has elapsed. 
     Immediately after the main switch  7  is turned on, the control unit  11  sets a pull-in period in which the PWM output signal is set to the duty 100% output in order to secure a pull-in current for securely closing the main switch  7  (S 1 ). 
     Subsequently, while measuring the average current A of the operation coils  16  and  17  (S 2 ) so as not to fall below the closed-circuit holding current W of the main switch  7 , it is determined whether or not the transient response is completed (S 3 ). When the determination result in S 3  is No, the voltage and current measurement processing S 2  is continued as it is. When the determination result in S 3  is Yes, the coil RL calculation processing S 4  is performed. Subsequently, when the determination result of whether or not the pull-in time has elapsed in S 5  is No, the coil RL calculation processing S 4  is continued as it is. When the determination result in S 5  is Yes, the pull-in processing is ended. 
     As illustrated in  FIG. 5( b ) , the voltage and current measurement and duty update processing has voltage and current measurement processing S 6 , power supply (terminal) voltage near-future value calculation processing S 7 , coil current near-future value calculation processing S 8 , control range determination processing S 9 , PMW control duty recalculation processing S 10 , and PMW control output duty change processing S 11 . 
     In the voltage and current measurement processing S 6 , the terminal voltage V and the current value A of the operation coils  16  and  17  are measured. In the power supply voltage near-future value calculation (voltage prediction) processing in S 7 , the near-future voltage value X is calculated based on a situation in which the terminal voltage V is changed in the latest past. 
     In the coil current near-future value calculation (current prediction) processing S 8 , the near-future predicted current value Y flowing through the operation coils  16  and  17  is estimated based on the near-future voltage value X. 
     In the control range determination processing S 9 , it is determined whether or not the estimated predicted current value Y is below the threshold value W. 
     When the predicted current value Y falls below the threshold value W in S 9  (Yes in S 9 ), it is determined that the predicted current value is out of the range in which the current of the operation coils  16  and  17  is holdable. That is, it is determined that the predicted current value falls below the coil current value W of the minimum required to stably maintain the attraction state of the contact  13 . When the determination result in S 9  is No, the processing returns to S 6 . 
     When the determination result in S 9  is Yes, the processing proceeds to the PMW control duty recalculation processing S 10 . In S 10 , an optimum duty ratio is recalculated and obtained based on the predicted current value Y. Subsequently, the processing proceeds to the PMW control duty change processing S 11 , and the PWM output signal is output at the optimum duty ratio obtained in S 10 . 
     As illustrated in  FIG. 5(C) , the RL acquisition processing has PWM control duty 100% output processing S 12 , voltage and current measurement processing S 13 , determination processing S 14  of determining whether or not the transient response is completed, and coil RL calculation processing S 15 . Since S 12  to S 15  of  FIG. 5(C)  are equivalent to S 1  to S 4  of  FIG. 5(A) , the description thereof will be omitted. 
     In  FIG. 5(C) , a series of processing is ended when the coil RL calculation processing S 15  is ended. On the other hand, in  FIG. 5(A) , the pull-in time for the electromagnetic switch  7  to shift to the closed circuit state has elapsed, and thus, a state changes. That is, the processing is ended after the electromagnetic switch  7  shifts from the open circuit state to the closed circuit state. 
     When the supply voltage Vcc of the electromagnetic switch  7  fluctuates, a response delay (also referred to as a “primary delay”) is unavoidable in general PWM control of the prior art, and there may be a problem that the fluctuation cannot be countered. This primary delay is caused by a transient phenomenon defined by a time constant (hereinafter, a “RC time constant”, a “RL time constant”, or simply a “time constant”) T on which the resistor R, the capacitor C, or a coil L acts with respect to a DC power supply voltage E. 
     Such a transient phenomenon will not be illustrated, and the theory thereof may be briefly described. In the theoretical description, the power supply voltage E is simplified instead of the DC supply voltage Vcc. The power supply voltage E, the resistor R, the capacitor C, and the coil L, and a current I that gradually changes when the power supply voltage, the resistor, the capacitor, and the coil are energized, each terminal voltage, and the like can be numerically calculated by using well-known differential equations and natural functions. However, the description is simplified here, and it is illustrated that a certain degree of perspective can be obtained even with the simple definition of the time constant T to be described below. 
     The transient phenomenon defined by the time constant T is a phenomenon that occurs in a procedure of shifting from a certain steady state to the next steady state. More specifically, when the DC power supply E is connected to a series circuit having the capacitor C or the coil L with the resistor R interposed therebetween and the switch is turned on or off, the voltage and current I of each part of the circuit settle down to the next state while being gradually changed. 
     Here, as an example, a steady-state current value Is=E/R that shifts to the next steady state with respect to a maximum change width E of the voltage accompanying the change of the DC power supply E from off to on. It is assumed that the settled current value Is is defined as a steady-state value Is. A criterion for expressing a rate of change until the current value settles down is the time constant T. As the time constant T becomes smaller, the change becomes more sudden, and as the time constant T becomes larger, the slower the change. 
     In the present device  3 , the impedance Z is a transient variable obtained from the terminal voltage V of the operation coils  16  and  17  and the current value A flowing through the operation coils  16  and  17 , but can be regarded as a constant approximated over a predetermined period from a latest past to a present time. That is, after the time constant T is considered, the impedance can be regarded as a constant approximated as an impedance Z≈R=E/I. 
     This time constant T is defined as a time until the current value becomes about 0.63 times the steady-state value Is in a direction from off to on. On the contrary, the time constant T and the time until the current value becomes about 0.37 times a steady-state value I becomes are defined in a direction from on to off. 
     The time constant of the RC series circuit T=C·R [seconds], and the time constant of the RL series circuit T=L/R [seconds]. 
     The power supply voltage E, the resistor R, the capacitor C, and the coil L can be numerically measured in real time by combining with a measuring instrument or the microcomputer control unit  11 , and may be considered as known constants. However, since these constants have temperature characteristics, for example, when these constants are carried out in the hybrid vehicle, the storage battery vehicle, or the like, these constant are designed in consideration of the temperature characteristics. 
     In the calculation method of the RL values described above, may calculate the control duty may be calculated with a configuration in which the RL values are recorded as a map (table) inside the microcomputer control unit  11  in advance. 
     In the above &lt;2&gt;, after the contact  13  of the electromagnetic switch  7  is connected, the duty control is performed such that a certain current value A flows through the operation coils  16  and  17  in order to reduce power consumption. In the above &lt;2&gt;, when there is a sudden fluctuation in the terminal voltage V, since the operation coils  16  and  17  have the time constants T, current waveforms of the coil current A are delayed with respect to a waveform of the terminal voltage V. 
     When duty adjustment using the PMW control is performed based on the delayed current A in this manner, since it is necessary to anticipate that a delay occurs in the control, the coil current is controlled to a high current level by unnecessarily providing a margin for the threshold value W in the related art. As a result, there is a disadvantage that the power consumption for turning on the electromagnetic switch  7  increases. The present invention is to eliminate this disadvantage. 
     According to the present device  3  and the present method, the resistance value R and the inductance value L (RL values) of the operation coils  16  and  17  are calculated from a transient response waveform when the contact  13  is switched from off to on. A theory for calculation uses the fact that “the time constant T is defined as the time until the current value becomes about 0.63 times the steady-state value Is in the direction from off to on” and “the time constant of the RL series circuit T=L/R [seconds]”. 
     Based on the theory of the transient phenomenon described above, the resistance value R and the inductance value L (RL values) of the operation coils  16  and  17  can be calculated from the transient response waveform when the contact  13  is switched from off to on. The current fluctuation from the voltage waveform of the terminal voltage V is predicted based on the calculated RL values, and thus, even though there is a sudden fluctuation of the terminal voltage V, it can be fed back to the duty control without delay. 
     As a result, since the margin for the threshold value W can be set to be smaller than in the related art, the power consumption for turning on the electromagnetic switch  7  can be reduced. Since these RL values change depending on a temperature, for example, when the electromagnetic switch  7  is adopted in the hybrid vehicle or the storage battery vehicle, the RL values are calculated periodically in consideration of the temperature change while the vehicle is running, and thus, more precise control can be performed. 
     Modification Example 
     Next, a more realistic modification example will be briefly described. In this modification example, the basic operations to be illustrated below are the same as those of the present device  3  and the present method described above. That is, the terminal voltage V of the operation coils  16  to  18  is measured by the operation coil voltage measurement circuits (ADCs)  24 ,  25 ,  27 , and  29  of the microcomputer control unit  11  via the voltage measurement filter circuits  31  to  34 . 
     The microcomputer control unit  11  calculates the near-future value X of the terminal voltage V of the operation coils  16  and  17  from the acquired terminal voltage V. The near-future value Y of the current A corresponding to the present duty value is predicted based on the near-future voltage value X and the impedance Z. When the predicted near-future value Y is out of a predetermined control current range, the PWM control units  21  to  23  recalculate the duty, and switches a ratio between the on time and the off time of the switching elements  38  and  39 , that is, the duty ratio. Up to this processing, the modification example is the same as that of the present device  3  and the present method described above. 
     On the other hand, the features of the modification example are as follows. First, when the current value A flowing through the operation coils  16  and  17  drops, processing of determining whether or not the cause is a reflux current path of the operation coils  16  and  17 , for example, abnormal disconnection of the freewheeling diodes  41  and  42  and processing of determining whether or not the cause is the decrease in the terminal voltage V are executed. 
     As a result of the determination processing, when it is determined that the cause of the decrease in the current value A is the abnormal disconnection of the reflux current path or the decrease in the terminal voltage V, processing of increasing the control duty is executed in order to raise the operation coil current A to the holding current or more. As a result of the processing of increasing such a control duty, processing of determining whether or not the current of the operation coils  16  and  17  can be held is performed. 
     As a result of the processing, when it is predicted that the current of the operation coils  16  and  17  cannot be held, the microcomputer control unit  11  switches the duty value to 100% in order to cope with the significant decrease in the supply voltage Vcc of the electromagnetic switch  7 . When it is determined that the closed-circuit holding current lower limit W of the electromagnetic switch  7  cannot be maintained even with the duty 100%, the output of the signal that turns on to both the electromagnetic switches  17  and  18  is stopped. That is, when the current value falls below or is expected to fall below the threshold value W, in order to prevent a serious failure in which the contact  13  of the electromagnetic switch  7  is welded due to a decrease in a contact force in advance, a supply voltage decrease abnormality is diagnosed and the output of the on signal is stopped. 
     At this time, the microcomputer control unit  11  immediately stops the PMW control, and performs control such that the electromagnetic switches  7  and  8  are switched from on to off. When this modification example is adopted in the hybrid vehicle or the storage battery vehicle, the electromagnetic switches  7  and  8  can be prevented from being damaged by stopping a power running or regeneration operation in the vehicle. The electromagnetic switch  8  may be excluded from the protection target. 
     At this time, a true cause such as over-discharging of the battery that supplies the main power supply Vcc for driving needs to be investigated. When the cause is the over-discharge of the battery in the storage battery vehicle, the failure does not occur, and a fuel shortage in a gasoline vehicle or the like merely occurs. In that case, control is realized in which priority is given to preventing a serious failure in which the electromagnetic switch  7  is welded due to a decrease in contact force. From such an effect, the present invention is suitable for an application for the purpose of monitoring the charging and discharging state of the battery in the power supply system using the assembled battery as the power supply. 
     Next, the main points of the present invention will be described along with the scope of claims. 
     [1] 
     The electromagnetic switch control device (present device)  3  is a control device that energizes the current value A having the PWM-controlled duty ratio to the operation coils  16  and  17 , and opens and closes the electrical contact  13  of the electromagnetic switch  7  by the electromagnetic force corresponding to the current value A. The present device  3  includes the current value prediction unit  19 , the control range determination unit  20 , and the PWM control units  21  to  23 . 
     The current value prediction unit  19  estimates the near-future predicted current value Y by using the terminal voltage V of the operation coils  16  and  17 . The control range determination unit  20  determines whether or not the estimated predicted current value Y is out of the range in which the current of the operation coils  16  and  17  is holdable, that is, the electromagnetic force to maintain the contacts  13  in the attraction state is exhibitable and maintainable. 
     When the determination result based on the predicted current value Y of the control range determination unit  20  is out of the range in which the electromagnetic force is maintainable, the PWM control unit  21  performs control such that the duty ratio is changed based on the predicted current value Y. Since the present device  3  is configured in this manner, the PWM control unit  21  can stabilize the contact pressure of the contacts  13  by predicting the near-future value Y of the operation coil current A and performing control such that the near-future value does not fall below the holding current threshold value W. 
     [2] 
     In the present device  3 , it is preferable that the predicted current value Y is estimated by using the impedance Z of the operation coils  16  and  17 . That is, the microcomputer control unit  11  calculates the near-future value X of the terminal voltage V of the operation coils  16  and  17  from the acquired terminal voltage V. The near-future value Y of the current A corresponding to the present duty value is predicted based on the near-future voltage value X and the impedance Z. 
     [3] 
     In the present device  3 , the impedance Z is the transient variable obtained from the terminal voltage V of the operation coils  16  and  17  and the current value A flowing through the operation coils  16  and  17 , but can be regarded as the constant approximated over a predetermined period from the latest past to the present time. More specifically, after the time constant T is considered, the impedance can be regarded as the constant approximated as the impedance Z≈R=E/I. 
     This time constant T is defined as the time until the current value becomes about 0.63 times the steady-state value Is in the direction from off to on. On the contrary, the time constant T and the time until the current value becomes about 0.37 times a steady-state value I becomes are defined in a direction from on to off. Even the impedance Z calculated as the transient variable based on the theory of such a transient phenomenon can be approximated to the constant when the impedance is divided into a predetermined period from the latest past to the present time. 
     Accordingly, the predicted current value Y can be estimated by using the impedance Z of the operation coils  16  and  17 . 
     [4] 
     It is preferable that the constant that approximates the impedance Z is updated for each predetermined period in order to estimate the near-future predicted current value Y from the present time. The coil L, the resistor R, or the capacitor C forming the impedance Z can be numerically measured in real time by combining with the measuring instrument or the microcomputer control unit  11 , and may be considered as a known constant. However, since these constants have temperature characteristics, for example, when these constants are carried out in the hybrid vehicle, the storage battery vehicle, or the like, these constant are designed in consideration of the temperature characteristics. That is, it is preferable that the constant approximated from the non-constant impedance Z is updated for each predetermined period. 
     [5] 
     It is preferable that the present device  3  forms a control function for appropriately turning on and off the electric circuit in the combination in which the battery-type power supply system formed by the assembled battery  6  constituted by the plurality of secondary batteries  4  connected in series or in parallel, the loads that receive the supply of the power from the system, and the electromagnetic switches  16  to  18  inserted into current paths thereof. The assembled battery  6  is further connected to voltage measurement functions similar to the ADCs  24 ,  25 , and  27  and the voltage measurement filter circuits  31 ,  32 , and  33 . 
     The ADCs  24 ,  25 , and  27  measure the terminal voltage V of the operation coils  16  and  17 . The voltage measurement filter circuits  31 ,  32 , and  33  are provided between the operation coil  16  and  17  and the operation coil voltage measurement circuits (ADCs)  24 ,  25 , and  27 . It is preferable that the predicted current value Y is calculated by using the terminal voltage V of the operation coils  16  and  17 , the impedance Z of the operation coils  16  and  17 , and the time constant T 1  of the voltage measurement filter circuits  31 ,  32 , and  33 . 
     [6] 
     It is preferable that the assembled battery  6  is further connected to the operation coil current measurement circuits (ADCs)  26  and  28  and the current measurement filter circuits  35  and  36 . The operation coil current measurement circuits  26  and  28  measure the current energized to the operation coils  16  and  17 . The current measurement filter circuits  35  and  36  are provided between the operation coils  16  and  17  and the operation coil current measurement circuits  26  and  28 . 
     It is preferable that the impedance Z is calculated by using the terminal voltage V, the time constant T 1  of the voltage measurement filter circuits  31 ,  32 , and  33 , the current value A, and the time constant T 2  of the current measurement filter circuits  21  to  23 . 
     [7] 
     It is preferable that the impedance Z is calculated from the current value A and the terminal voltage V of the operation coils  16  and  17  in the on period in which the duty ratio in the PWM control is 100% in order to set the electrical contact  13  to be in the closed circuit state. Regarding this, in the RL update period mode of the above &lt;3&gt;, the mode in which the duty ratio of the PWM control is 100% in the RL update period for correcting the amount of drift of the impedance Z of the operation coils  16  and  17  in the electromagnetic switch  7  as in the pull-in period (see  FIG. 5( c ) ) is as described. 
     [8] 
     The electromagnetic switch control method (present method) is a control method for performing PWM control of the current value A flowing through the operation coils  16  and  17  of the electromagnetic switch  7  by the PWM control units  21  to  23  and opening and closing the electrical contacts  13  by the electromagnetic force corresponding to the energization of the PWM-controlled duty ratio. This method includes the voltage and current measurement processing S 6 , the current prediction processing S 8 , and the PWM control processing S 9  to S 11 . In the voltage and current measurement processing S 6 , the terminal voltage V and the current value A of the operation coils  16  and  17  are measured. 
     In the current prediction processing S 8 , the near-future predicted current value Y flowing through the operation coils  16  and  17  is estimated. In the PWM control processing S 9  to S 11 , when it is determined that the estimated predicted current value Y is out of the range in which the current of the operation coils  16  and  17  is holdable, the control is performed such that the duty ratio is changed based on the predicted current value Y. 
     In the present method, since the current value A flowing through the operation coils  16  and  17  of the electromagnetic switch  7  is controlled by such a procedure, the PWM control unit  21  predicts the near-future value Y of the operation coil current A by the current prediction processing S 8 , and performs control such that the estimated predicted current value Y does not fall below the holding current threshold value W by the PWM control processing S 9  to S 11 . Thus, the contact pressure of the contact can be stabilized. The operation coil current A can be reduced to the minimum necessary, and the control cycle can be reduced by the amount of precision control. 
     The present invention is not limited to the application of battery monitoring in the power supply system using the assembled battery as the power supply. In addition, the present invention is applicable to any application for controlling the opening and closing of the connection between the power supply and the load. 
     REFERENCE SIGNS LIST 
     
         
           1  motor 
           2  inverter 
           3  electromagnetic switch control device (present device) 
           4  battery cell 
           5  battery module 
           6  assembled battery 
           7  main contactor (main switch, electromagnetic switch) 
           8  precharge relay (sub switch) 
           9  precharge resistor 
           10  electromagnetic switch power supply (contactor power supply) 
           11  microcomputer control unit 
           12  voltage measuring line 
           13  contact 
           14  switching element 
           15  coil current contactor (coil switch, electromagnetic switch) 
           16 , 17 , 18  operation coil 
           19  current value prediction unit 
           20  control range determination unit 
           21  PMW control 
           24 , 25 , 27 , 29  operation coil voltage measurement circuit (ADC) 
           26 , 28 , 30  operation coil current measurement circuit 
           31 , 32 , 33 , 34  voltage measurement filter circuit (ADC) 
           35 , 36 , 37  current measurement filter circuit 
           41 , 42  freewheeling diode 
         A terminal voltage value 
         T 1  time constant (of voltage measurement filter circuit  31 ,  32 ,  33 ) 
         T 2  time constant (of current measurement filter circuit  35 ,  36 ) 
         W holding current (lower limit) threshold value 
         X near-future predicted voltage value 
         Y near-future predicted current value 
         Z impedance