Abstract:
A power source system for supplying DC (direct current) power to a load, including first and second power source apparatuses and a control apparatus. The first power source apparatus is connected to an alternating current (AC) power source, and configured to convert AC power received from the AC power source to first DC power. The second power source apparatus is connected to a battery, and configured to convert power of the battery to second DC power. The control apparatus is connected to the first and second power source apparatuses, and configured to so control the first and second power source apparatuses that the DC power supplied to the load is the first DC power in a normal mode, the second DC power in a back-up mode, and a combination of the first and second DC power in an assist mode.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation application under 35 U.S.C. 120 of International Application PCT/JP2013/070644 having the International Filing Date of Jul. 30, 2013. The identified application is fully incorporated herein by reference. 
     
    
     TECHNICAL FIELD 
       [0002]    The present invention relates to a power source system that is configured by combining a power source unit and a battery unit, and is capable of supplying power greater than the total output of the power source unit to a load by supplying power from a battery unit temporarily, in other words, relates to a power source system having a power assist function. 
       BACKGROUND OF THE INVENTION 
       [0003]      FIG. 1  is a diagram showing the configuration of a power source system disclosed in Japanese Patent Application Publication No. 2013-046454 (hereinafter “JPA &#39;454”; see, e.g.,  FIG. 1 ,  FIG. 2 ). The power source system shown in  FIG. 1  is constituted by a three-phase commercial power source E, a DC (direct current) power source apparatus  501  and a load RL, and of these, the DC power source apparatus  501  is constituted by a power storage apparatus  60 , a plurality of DC power source apparatus units  1  to N, one charging/spare unit, and a monitoring unit  81  including an operational state determination unit  82 , an output voltage monitoring unit  83 , a droop operation control unit  84 , a charging voltage detection unit  85  and a constant-current charging control unit  86 . 
         [0004]    During a normal operation, the DC power source apparatus  501  operates n DC power source units  1  to N and supplies power to the load RL having constant power characteristics, and if there is a fault in any one of the DC power source units  1  to N, the charging/spare unit is used as a substitute unit for the unit suffering a fault. In the example illustrated, three-phase AC power is used as the input power source, but a configuration in which a single-phase AC power is used as the input source may also be used. 
         [0005]    When an AC input from the commercial power source E is lost due to a power outage, power is supplied to the load RL from a storage battery  61  via a diode DX 1 . Furthermore, in this DC power source apparatus  501 , the charging/spare unit, as well as being used as a spare power source unit, also serves as a charger for the storage battery  61 . 
         [0006]    When an output voltage is supplied to the load RL from the DC power source units  1  to N, since the charging/spare unit and the storage battery  61  are separated from the load RL side, a reverse bias voltage is applied to the diode DX 1 . 
         [0007]    The DC power source units  1  to N and the charging/spare unit have constant-current droop characteristics which limit the output current to a prescribed rated current (100% continuous rated current), in order to prevent damage to the units, during normal operation, and the constant-current droop characteristics can be switched temporarily to constant-power droop characteristics in the event of prescribed trigger conditions (conditions which are set in accordance with the operational state of the DC power source apparatus  501 ), for example, in the event of trigger conditions such as power source recovery after a power outage. 
         [0008]    A voltage sensor VT 1  detects the output voltage Vo (=load voltage VL) of the DC power source apparatus  501 . The voltage sensor VT 2  detects the charging voltage of the storage battery  61 . A current sensor CT 1  detects the charging current of the storage battery  61 . 
         [0009]    A monitoring unit  81  communicates with the DC power source units  1  to N and the charging/spare unit, and monitors the operational state of the DC power source units  1  to N and the charging/spare unit, as well as sending a control command signal (for example, a droop characteristics switching command signal) to the DC power source units  1  to N and the charging/spare unit. 
         [0010]    The operational state determination unit  82  receives input of operational state signals St 1  to StN from the DC power source units  1  to N, and receives input of an operational state signal Stc from the charging/spare unit. Consequently, the operational state determination unit  82  detects (determines) the operational state of the DC power source unit and the charging/spare unit, the occurrence of and recovery from faults, and restoration of power after a power outage, and the like. 
         [0011]    On the basis of the operational state signals received from the DC power source units  1  to N and the charging/spare unit, the operational state determination unit  82  determines whether the system is in a normal operational state in which all of the units are operating normally, for example, or a start-up state after restoration of power from a power outage, or a state of starting operation after recovering a DC power source unit that has suffered a fault. 
         [0012]    The output voltage monitoring unit  83  receives input of a voltage detection signal from the voltage sensor VT 1  and monitors the output voltage Vo of the DC power source apparatus  501 . Furthermore, the droop operation control unit  84  controls the droop characteristics of the DC power source units  1  to N and the charging/spare unit, in accordance with the state of operation of the DC power source units  1  to N and the charging/spare unit. Moreover, the charging voltage detection unit  85  receives an input of a voltage detection signal from the voltage sensor VT 2  and monitors the charging voltage of the storage battery  61 . 
         [0013]    The constant-current charging control unit  86  controls the charging/spare unit so as to perform a constant-current output operation, when carrying out constant-current charging from the charging/spare unit to the storage battery  61 . During the constant-current charging described above, the constant-current charging control unit  86  in the monitoring unit  81  performs constant-current charging to the storage battery  61  by controlling the output current of the charging/spare unit. In this case, the constant-current charging control unit  86  detects the charging current flowing to the storage battery  61  by the current sensor CT 1  and controls the output current of the charging/spare unit so as to become a prescribed constant current value. In the power source system disclosed in JPA &#39;454, a plurality of DC power source units are connected in parallel, the output line thereof is backed up by a battery during a power outage, and the droop characteristics of the power source unit are controlled so as to supply current at or above a rated current, temporarily. 
       BRIEF SUMMARY OF THE INVENTION 
       [0014]    In a power source system where the load is a server, or the like, in a data center, the consumed power changes in accordance with the amount of information processed by the server, etc. It is necessary to set a value exceeding the peak load as the rated power, for the power source capacity, but as a result of this, a problem arises in that the system operates for the majority of the time at an output significantly lower than the rating, the capacity of the power source equipment is excessively large in relation to the average power consumption, and the equipment costs become large. 
         [0015]    Meanwhile, a power source system which has a server as described above, or the like, normally has a battery back-up equipment which is provided for power outages. If a portion of the battery capacity is used, and a portion of the power is allocated to the battery during peak load, then the power source equipment capacity can be made smaller, theoretically. 
         [0016]    However, in the power source system disclosed in JPA &#39;454 which is illustrated in  FIG. 1 , the battery  61  is connected to a DC bus without passing via power control means, and the distribution of the power load cannot be controlled. When a charging/spare unit is provided, if the battery undertakes all of the power load during peak load, there is a risk that the amount of power provided for back up will be insufficient in the event that a power outage actually occurs, and furthermore, frequent full-load discharging of the battery is not desirable from the perspective of the battery life. 
         [0017]    This problem can be resolved by providing power control means on the battery side, but in this case also, if using a method wherein, for example, the full-load amount is detected and transmitted to a common control apparatus which determines the output distribution of the power source units and the battery unit and issues an instruction accordingly, in order to achieve appropriate distribution of the load between the power source unit group and the battery, it is necessary to transmit a continuous amount of data at high speed, and therefore, costs rise due to the increase in the number of components, and if a problem occurs in the common control apparatus, there is a risk of this obstructing the operation of all of the units. 
         [0018]    The present invention was devised in view of the foregoing circumstances, and provides a power source system whereby a distributed power load undertaken by a battery during peak load can be controlled appropriately, without providing a complicated common control apparatus and/or large-scale two-way communication means. 
         [0019]    Specifically, the present invention is a power source system in which the output units of one or more first power source apparatus which receives a supply of power from an AC or DC power source, adjusts the voltage to a uniform range and supplies the voltage to a load, and one or more second power source apparatus which receives a supply of power from a storage battery, adjusts the voltage to a uniform range and supplies the power to a load, are connected in parallel; 
         [0020]    wherein the power source system has three operation modes: a normal mode, a back-up mode and an assist mode, 
         [0021]    in the normal mode, power is supplied from the first power source apparatus when the AC or DC power source is healthy and the load is within the rated range of the power source system, 
         [0022]    in the back-up mode, power is supplied from the second power source apparatus when the AC or DC power source is suffering an outage, 
         [0023]    in the assist mode, a shortage of power is supplied from the second power source apparatus, when the load is greater than the sum of the rated output of the first power source apparatus, or the voltage of the AC or DC power source has fallen, or the number of operable apparatuses among the plurality of first power source apparatuses has fallen, 
         [0024]    the first power source apparatus and the second power source apparatus each have respectively independent voltage detection means, output current means for detecting the output current of the power source apparatus, and communication means for receiving instruction of the abovementioned three modes, and 
         [0025]    the power supply amount of the second power source system in the assist mode is adjusted by the output voltage of the power source system. 
         [0026]    According to the present invention, it is possible to distribute the power load undertaken by a battery at peak load, without providing a complicated common control apparatus or large-scale communication means, and the power source equipment capacity can be reduced. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0027]      FIG. 1  is a diagram showing a configuration of a conventional power source system disclosed in Patent Document JPA &#39;454. 
           [0028]      FIG. 2  is a block diagram showing an example of the configuration of a power source system relating to an embodiment of the invention. 
           [0029]      FIG. 3  is a diagram showing the configuration of power source units and battery units, including a control system, according to an embodiment of the present invention. 
           [0030]      FIG. 4  is a diagram illustrating the details of droop characteristics relating to an embodiment of the present invention. 
           [0031]      FIG. 5  is a diagram showing an example of the operation of a power source system relating to an embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0032]    Below, desirable embodiments of the present invention are described with reference to the drawings. 
         [0033]      FIG. 2  is a block diagram showing an example of the configuration of a power source system relating to an embodiment of the invention. The power source system relating to the embodiment of the present invention shown in  FIG. 2  is constituted by an AC (alternating current) power source  1 , a load  2 , power source units  3  to  5  which receive input of an AC power source  1  and supply a substantially constant voltage, for example, 12V, to the load  2 , and battery units  6  to  8  which supply power from a built-in battery. 
         [0034]    The power source units  3  to  5  and battery units  6  to  8  described above are connected in parallel to a common DC bus which is connected therebetween. The parallel number of power source units  3  to  5  and battery units  6  to  8  is shown as three each in  FIG. 2 , but is not limited to this number. 
         [0035]    The constituent elements of the power source units  3  to  5  may include AC/DC conversion circuits  10  to  12  and DC/DC conversion circuits  13  to  15 . Generally, an insulated input/output circuit is used for the DC/DC conversion circuits  13  to  15 . The constituent elements of the battery units  6  to  8  may include batteries  16  to  18 , and DC/DC conversion circuits  19  to  21 . The DC/DC conversion circuits  19  to  21  may be insulated or non-insulated circuits. Furthermore, the DC/DC conversion circuits  19  to  21  may carry out one-directional power conversion from the battery unit side to the DC bus side, and battery charging means (not illustrated) may be provided separately, but by adopting a circuit capable of bi-directional power conversion, the circuit can also serve as a charging circuit. 
         [0036]    The power source system relating to an embodiment of the present invention shown in  FIG. 2  operates in any one of normal mode, back-up mode and assist mode. Normal mode is a mode in which power is supplied to the load  2  by the power source units  3  to  5 . Back-up mode is a mode in which the battery units  6  to  8  supply power to the load  2  when there is a power outage of the AC power source  1 . Assist mode is a mode in which, when the power supplied to the load from the power source units  3  to  5  is insufficient, the power equivalent to the shortage is supplied by the battery units  6  to  8 . For example, this power source system operates in assist mode in cases where the power of the load  2  exceeds the total rated power of the power source units  3  to  5 , where the input voltage falls, without reaching a power outage, and sufficient power cannot be supplied, or where a portion of the power source units  3  to  5  are halted due to a fault, maintenance, or the like. The assist mode is described in further detail hereinafter. 
         [0037]    In general, the voltage of a battery falls with discharging. The amount of reduction in the voltage is greater, the larger the discharge current, and tends to increase as discharging progresses. The DC/DC conversion circuits  19  to  21  perform an operation for keeping the DC bus voltage substantially uniform, regardless of voltage change in the battery. 
         [0038]      FIG. 3  is a diagram showing the configuration of power source units and battery units, including a control system, according to an embodiment of the present invention.  FIG. 3  shows, as a representative example, a case where there is one power source unit and one battery unit, but it is possible to connect two or more of each of these units in a parallel arrangement, similarly to the configuration shown in  FIG. 2 . 
         [0039]    In  FIG. 3 ,  101 ,  102 ,  202  respectively indicate a voltage detector,  103  and  203  respectively indicate a current detector,  104  and  204  respectively indicate voltage command value setting means, and  105 ,  106 ,  205  and  206  respectively indicate an adder.  107  and  207  indicate a voltage regulator (Auto Voltage Regulator), which is constituted by a PI (proportional/integral) regulator (Proportional &amp; Integral Regulator), or the like. Furthermore  108 ,  208  indicate a current regulator (Auto Current Regulator), which is constituted by a PI (proportional/integral) regulator, or the like, similarly to the voltage regulator. 
         [0040]    In the power source unit  3  in  FIG. 3 , the output voltage is detected by the voltage detector  102 , and a current command value is output by the voltage regulator  107  by finding the differential between the output voltage and the voltage command value from the voltage command value setting means  104 . The current command value is large when the output voltage is insufficient and is small when the output voltage is excessively large. The differential between the current command value and the output current detected by the current detector  103  provided in the power source unit  3  is found, and the internal electromotive force of the DC/DC converter  13  is increased or decreased so as to make the differential approach 0. 
         [0041]    On the other hand, in the case of the battery unit  6 , the differential between the current command value output from the voltage adjuster  207  and the output current detected by the current detector  203  provided in the battery unit  6  is found, and the internal electromotive force of the DC/DC converter  19  is increased or decreased so as to make the differential approach zero. 
         [0042]    Furthermore, a limiter (not illustrated) is provided for the current command value when input to the current regulators  108 ,  208 , so as not to output a current exceeding the rated current, irrespective of the load. 
         [0043]    As shown in  FIG. 2 , in many cases, the power source system relating to an embodiment of the present invention uses a plurality of power source units and battery units in a parallel connection arrangement. In this case, control based on the droop characteristics of each unit is implemented in order to achieve a current balance in each of the units. 
         [0044]      FIG. 4  is a diagram illustrating the details of droop characteristics relating to an embodiment of the present invention. As shown in  FIG. 4 , the droop characteristics mean that the output voltage falls in accordance with the output current. When the output current of a particular unit is large, the current in that unit falls due to narrowing of the voltage as a result of the droop characteristics. As a result of this, the output currents of the units become balanced when the full-load current is a value close to the fraction of the parallel number. The range of variation of the output voltage due to this is constricted to the range of the output voltage accuracy which is defined by the apparatus specifications. 
         [0045]    The droop characteristics of the battery units  6  to  8  are described further here with reference to  FIG. 4 . Here, it is supposed that the voltage command value at zero load (indicated by the symbol “VOC” below) is switched between VO 1 , VO 2 , VO 3  in the battery units  6  to  8  in accordance with the operation mode. In order to simplify the explanation, the output ratings of the power source units  3  to  5  and the battery units  6  to  8  are the same, and the parallel number is the same. The rated value of the output current is taken to be 100%. 
         [0046]    The battery units  6  to  8  undertake the whole of the power load, when in the back-up mode. Therefore, the droop characteristics of the battery units  6  to  8  when in the back-up mode are set to be the same as the droop characteristics of the power source units  3  to  5  when in the normal mode (see  FIG. 4 , upper part). 
         [0047]    When in the assist mode, the VOC (voltage command value) is reduced to VO 2 , in such a manner that the output voltage value when the power source units  3  to  5  output 100% current and the output voltage value when the battery units  6  to  8  output 20% current become equal. For instance, when the input current of the load  2  is equivalent to 120% of the rated value, then the output current of the two units is balanced when the power source units  3  to  5  output 100% current, and the battery units  6  to  8  output 20% current, and the system is operated at this ratio. Thereby, unwanted discharging of the battery units  6  to  8  is avoided (see  FIG. 4 , middle part). 
         [0048]    When in the normal mode, the VOC (voltage command value) of the battery units  6  to  8  is reduced to the value VO 3 , which is lower than the output voltage value when the power source units  3  to  5  output 100% current. Accordingly, it is possible to avoid the occurrence of continuous discharging from the battery units  6  to  8 . On the other hand, when the power source units  3  to  5  deviate from the normal output range due to a sudden change in the load, or the like, then the amount of variation in the voltage can be suppressed by discharge from the battery units  6  to  8  (see  FIG. 4 , lower part). 
         [0049]    In  FIG. 4 , the current load distribution is adjusted by means of the voltage command value (VOC) at zero load, but it is also possible to adjust the current load by the amount of droop, in other words, the amount of reduction in the output voltage with respect to the output current. Alternatively, it is also possible to adjust the current load distribution by using both the voltage command value (VOC) at zero load and the amount of droop. 
         [0050]    Next, a method for setting the VOC in the battery units will be described with reference to  FIG. 3. 109  is power outage detection means which detects an input power outage.  110  is assist request generation means which outputs an assist request signal when the current command value in the power source unit is greater than a specific value, for example, the equivalent of 100% output.  210  is an assist cancellation request generation means for outputting a signal requesting cancellation of the assist mode when the current command value in the battery unit is lower than a specific value, for instance, 10%. 
         [0051]    When the power outage does not occur and there is no assist request, then the voltage command value setting means  204  sets the VOC (voltage command value) to VO 3 , and outputs the current command value according to the existing droop settings (see  FIG. 4 , lower part). When a power outage occurs, the voltage command value setting means  204  sets the VOC (voltage command value) to VO 1 , regardless of whether or not there is an assist request (see  FIG. 4 , upper part). When the assist request generation means  110  outputs an assist request without the occurrence of a power outage, then the voltage command value setting means  204  sets the VOC (voltage command value) to VO 2  (see  FIG. 4 , middle part). Therefore, the output from the battery units  6  to  8  is set to a prescribed ratio with respect to a load  2  which exceeds 100% of the rating. The fact that the current command value of the power source units  3  to  5  exceeds 100% does not necessarily mean that the input current of the load  2  exceeds 100%. When the voltage of the AC power source  1  falls without reaching a power outage, the AC/DC conversion units  10  to  12  of the power source units  3  to  5  cannot input current equal to or exceeding a specific level, and therefore the power is insufficient, as a result of which the output voltage falls. 
         [0052]    Furthermore, if one of the power source units  3  to  5  stops due to a fault, near to 100% load, or if any one of the power source units is removed for the purpose of maintenance, then the supply power is insufficient in the remaining units and the output voltage falls in a similar manner. 
         [0053]    The voltage regulator  107  of the power source units  3  to  5  increases the current command value in an attempt to restore this voltage fall, and therefore a current exceeding the rating is output (although a current exceeding the rating is not actually output due to the limiter described above). In cases of this kind as well, similarly to the description given above, an assist operation is performed by the battery units  6  to  8 , of course. 
         [0054]    When the output current of the power source units  3  to  5  falls to 100% or below, a current is output from the battery units  6  to  8 , up to 80%, under the settings described above. Discharge is performed from the battery units  6  to  8  in a region where an assist operation is not actually required, which is not desirable. The assist cancellation request generation means  210  serves to avoid this situation and, for instance, outputs an assist mode cancellation request signal to the assist request generation means  110 , when the output current of the battery units  6  to  8  is lower than 10%. The assist request generation means  110  determines that the total load current is equal to or less than 100% and cancels the assist request, when the output current of the host power source unit in this case is lower than 90%. When the output current of the host power source unit is not lower than 90%, then the assist mode is maintained (not cancelled), because if the assist mode is cancelled, there is a risk of a current shortage occurring due to current detection errors and/or imbalance between the units. 
         [0055]      FIG. 5  is a diagram showing an operation waveform of a power source system relating to an embodiment of the invention. When the load current increases and exceeds 100%, as shown in the upper half of  FIG. 5 , the output current of the power source units  3  to  5  is limited to 100% by the limiter, whereas when the system is in assist mode, the output from the battery units  6  to  8  is applied, as shown in the lower half of  FIG. 5 , and a current exceeding 100% is supplied. When the load current falls below 100%, the output current of the battery units  6  to  8  falls below 10%, and the output current of the power source units  3  to  5  falls below 90%, and therefore the assist mode is cancelled and all of the load current is supplied from the power source units  3  to  5 . 
         [0056]    The simplest method for switching mode when a plurality of power source units  3  to  5  and battery units  6  to  8  are connected in parallel to a DC bus is to adopt a wired OR method, or the like, and interpret that an assist request has been generated when an assist request has been issued by any one of the power source units  3  to  5 , and interpret that an assist cancellation request has been generated when all of the battery units  6  to  8  have issued an assist cancellation request. This is the safest method for avoiding output shortages, but if, for example, the range of error of the current detection and control is clear, then it is also possible to interpret that an assist request has been generated, when it can been determined that the range of output voltage drop is within a tolerable range, even while still waiting for the power source unit having the smallest output current to issue an assist request due to an imbalance in the parallel arrangement, or when all of the power source units  3  to  5  have issued an assist request. Alternatively, it is also possible to interpret that an assist request has been generated, when a prescribed number or prescribed proportion of the power source units  3  to  5  has issued an assist request. The same also applies to the assist cancellation request. 
         [0057]    Each unit outputs an assist request or assist cancellation request using a current command value, but may also output an assist request or assist cancellation request using an output current. 
         [0058]    According to the power source system relating to the embodiment of the present invention described above, a continuous amount, such as current or voltage, is transmitted between units or to an upper-level control apparatus, and complicated control for determining the presence or absence of an assist operation, and adjusting the assist amount in each battery unit, and the like, is not necessary, and therefore it is possible to achieve a desired operation with a configuration in which the signal transmission system and the control system are greatly simplified compared to a conventional method. 
       INDUSTRIAL APPLICABILITY 
       [0059]    The present invention can be applied to a power source apparatus for a communications apparatus or a power source apparatus for a large-scale computer.