JP7677064B2 - Charging/discharging method and charging/discharging device - Google Patents

Description

The present invention relates to a charging/discharging method and a charging/discharging device.

An invention for centrally managing multiple power conditioners has been known for some time (Patent Document 1). The invention described in Patent Document 1 calculates the individual target power of each power conditioner and controls the individual output power of each power conditioner so that the calculated individual target power is achieved.

International Publication No. 2017/150376

However, when attempting to make power demand follow the target power using a discontinuously changing on-off power adjustment method such as the control described in Patent Document 1, it is not possible to match the power demand with the target power because the charging and discharging power is discontinuous, and there is a risk of chattering occurring due to continuing to control the discontinuous charging and discharging power thereafter.

The present invention was made in consideration of the above problems, and its purpose is to provide a charging/discharging method and a charging/discharging device that can prevent the occurrence of chattering.

A charging/discharging method according to one aspect of the present invention determines whether the command value indicates a variable power adjustment region in which the battery's charging/discharging power is changed continuously to charge/discharge, or an on/off power adjustment region, which is a power region lower than the variable power adjustment region and in which the charging/discharging power is changed discontinuously to charge/discharge, and if it is determined that the command value indicates the variable power adjustment region, charging/discharging is performed by changing the charging/discharging power continuously, whereas if it is determined that the command value indicates the on/off power adjustment region, charging/discharging is performed by changing the charging/discharging power discontinuously.

The present invention makes it possible to prevent chattering from occurring.

FIG. 1 is a schematic configuration diagram of a power system 1 according to an embodiment of the present invention. FIG. 2 is a graph showing the relationship between the command value and the output value. FIG. 3 is a flowchart showing an example of the operation of the command device 20. FIG. 4 is a flowchart showing an example of the operation of the power control device 30a. FIG. 5 is a graph showing the change in the command value over time. FIG. 6 is a graph showing the change in power over time. FIG. 7 is a flowchart showing an example of the operation of the command device 20. FIG. 8 is a graph showing the change in the command value over time. FIG. 9 is a graph showing the change in the command value over time.

Embodiments of the present invention will be described below with reference to the drawings. In the description of the drawings, identical parts are given the same reference numerals and the description will be omitted.

The power system 1 according to this embodiment will be described with reference to FIG. 1. As shown in FIG. 1, the power system 1 includes a power grid 10, a command device 20, and multiple power control devices 30a and 30b.

The power system 10 is a system that integrates power generation, transformation, transmission, and distribution to supply power to power receiving equipment. In FIG. 1, the power control devices 30a and 30b correspond to the power receiving equipment. The power control devices 30a and 30b are connected to the power system 10 via the command device 20 and receive power from the power system 10. The power control devices 30a and 30b may also transmit power to the power system 10 (this is called reverse flow). Although two power control devices 30a and 30b are shown in FIG. 1, three or more power control devices may be included. A predetermined range that includes the command device 20 and the power control devices 30a and 30b may form a smart grid. A smart grid is a power network that controls and optimizes power from both the supply and demand perspectives.

The command device 20 performs power control so that the power at the connection point with the power system 10 becomes the target power. As an example, the "target power" is set in advance based on the peak power demand, off-peak power demand, nighttime power, etc. in the above-mentioned smart grid. As shown in FIG. 1, the command device 20 includes a measurement unit 21, a command value calculation unit 22, and a command value transmission unit 23. The measurement unit 21 measures the power demand of the entire power system 1. The power demand of the entire power system 1 includes the power demand of the battery provided in the electric vehicle. A signal indicating the power demand measured by the measurement unit 21 is transmitted to the command value calculation unit 22. The command value calculation unit 22 calculates a command value based on the power demand measured by the measurement unit 21 and the target power input in advance. As an example, the command value is calculated by normalizing the difference between the target power and the power demand. The command value transmission unit 23 transmits the command value calculated by the command value calculation unit 22 to the power control devices 30a, 30b.

The power control device 30a (30b) is a computer (ECU: Electronic Control Unit) installed in an electric vehicle (EV). The power control device 30a (30b) mainly controls the charging and discharging of a battery installed in the electric vehicle. As shown in FIG. 1, the power control device 30a (30b) includes a power control unit 31a (31b), a charge/discharge output calculation unit 32a (32b), and a command value receiving unit 33a (33b). The command value receiving unit 33a (33b) receives a command value from the command device 20 and transmits it to the charge/discharge output calculation unit 32a (32b). The charge/discharge output calculation unit 32a (32b) calculates the charge/discharge output based on the acquired command value. The power control unit 31a (31b) controls the charging and discharging of the battery based on the charge/discharge output acquired from the charge/discharge output calculation unit 32a (32b). In the following, an electric vehicle equipped with the power control device 30a may be referred to as EV1, and an electric vehicle equipped with the power control device 30b may be referred to as EV2. In this embodiment, an "electric vehicle (EV)" is assumed to be a vehicle equipped with a motor as a power source and a battery that supplies power to the motor, but may also include a plug-in hybrid vehicle equipped with an internal combustion engine. In addition, the power control device 30a (30b) also includes a PCS (Power Control System) that controls a stationary battery.

Next, the relationship between the command value and the output value will be explained with reference to FIG. 2. In FIG. 2, the horizontal axis indicates the command value, and the vertical axis indicates the output value. The output value indicates the charging power of the electric vehicle. As described above, the electric vehicle receives power from the power grid 10, and conversely, transmits power to the power grid 10. FIGS. 2 to 6 explain the control when the electric vehicle is "charging," and FIGS. 7 to 9 explain the control when the electric vehicle is "discharging" (however, as will be described later, the explanation of FIGS. 7 to 9 also includes some of the control when the electric vehicle is "charging").

The minimum output value in FIG. 2 means the minimum output value related to the charging power, for example, 1 kW. The maximum output value means the maximum output value related to the charging power, for example, 3 kW. Reference numeral 40 indicates an on-off power adjustment region, and reference numeral 41 indicates a variable power adjustment region. In this embodiment, the command value includes two command values. The two command values are a "charge number command value" and a "charge amount command value". The "charge number command value" is a command value related to the number of charging units, and the "charge amount command value" is a command value related to the charge amount (also called charging power or charging output). In FIG. 2, the command values 0 to A indicate the "charge number command value", and the command values A to B indicate the "charge amount command value". The "on-off power adjustment region" indicated by reference numeral 40 is a region in which the power control unit 31a controls the charging of EV1 using an on-off power adjustment method. In the "on-off power adjustment method", the charging power is changed discontinuously. For example, when the command value is A, i.e., when the charging number command value is A, EV1 is controlled by the on-off power adjustment method, and as shown in FIG. 2, the battery of EV1 switches from charging off to charging on, and starts charging at the minimum output value (1 kW). Switching from charging off to charging on in this way means that the charging power is changed discontinuously. Note that "discontinuously changing the charging power" also includes switching from charging on to charging off.

The "variable power adjustment region" indicated by the reference numeral 41 is a region in which the power control unit 31a controls the charging of the EV1 using a variable power adjustment method. In the "variable power adjustment method", the charging power is changed continuously. For example, assume that the EV1 requests rapid charging. In this case, the power demand in the power system 1 increases due to this request. The command device 20 calculates a designated value in response to this request and transmits it to the EV1. At this time, assume that the command value transmitted increases from A to B. This means that the charge amount command value increases from A to B. The power control unit 31a changes the charging power continuously (increases in FIG. 2) in response to the increasing command value. Then, when the charge amount command value becomes B, the battery of the EV1 is charged at the maximum output value (3 kW). Thereafter, unless the command value changes, charging at the maximum output value continues as indicated by the reference numeral 42.

Next, an example of a method for controlling charging power performed by the command device 20 and power control devices 30a, 30b will be described with reference to Figures 3 to 6. Figure 3 is a flowchart showing an example of the operation of the command device 20. In step S101 of Figure 3, a target power is input to the command device 20. When the target power is input, initial values of the charging number command value and the charging amount command value are set. The initial values of the charging number command value and the charging amount command value are determined in advance. The process proceeds to step S103, where the measurement unit 21 measures the power demand of the entire power system 1. The process proceeds to step S105, where the command value calculation unit 22 calculates a command value based on the target power input in step S101 and the power demand measured in step S103. An example of a calculation formula for the charging amount command value is expressed by Equation 1. An example of a calculation formula for the charging number command value is expressed by Equation 2. In addition, the reason why the charging number command value does not change in Equation 2 is because at the time of step S105, it is not possible to determine whether the power at the connection point with the power grid 10 can be controlled to the target power using only the variable power adjustment method.

[Equation 1]
Charge amount command value=charge amount command value+α(target power−power demand) (1)
Here, α is a coefficient.

[Equation 2]
Charged unit count command value=Charged unit count command value (2)

The command value in step S107 indicates a "charge amount command value." In other words, the processing in step S107 means whether or not the charge amount command value is greater than an upper limit value. This upper limit value is determined in advance. "The charge amount command value is greater than the upper limit value" means that the power at the connection point with the power grid 10 cannot be controlled to the target power using only the variable power adjustment method. If the charge amount command value is greater than the upper limit value (YES in step S107), the processing proceeds to step S109, and the command value calculation unit 22 calculates the command value again. The calculation formula in step S109 is expressed by formula 3 and formula 4.

[Equation 3]
Charge amount command value=Upper limit of charge amount command value (3)

[Equation 4]
Charging unit number command value=charging unit number command value+β(target power−power demand) (4)
where β is a coefficient.

The process proceeds to step S111, where the command value transmission unit 23 transmits the command value calculated in step S109 to the power control devices 30a and 30b. If the charge amount command value is equal to or less than the upper limit (NO in step S107), the command value transmission unit 23 transmits the command value calculated in step S105 to the power control devices 30a and 30b.

Figure 4 is a flowchart showing an example of the operation of the power control device 30a (or the power control device 30b). In step S201 of Figure 4, the command value receiving unit 33a, 33b receives a command value transmitted from the command device 20. The command value in step S203 indicates a "charge number command value". In other words, the processing in step S203 means whether the charge number command value is greater than a threshold value. This threshold value means the priority of the electric vehicle connected to the power system 1. The priority is an index that is set in consideration of the SOC (STATE OF CHARGE) and the departure time of the electric vehicle. An electric vehicle with a higher priority can be charged before an electric vehicle with a lower priority. For example, assuming that there are five electric vehicles connected to the power system 1, the charge number command value is 3, and the priority of the electric vehicle itself is fourth, the processing in step S203 results in NO. In other words, the processing in step S203 results in NO, indicating that the first three vehicles can be charged, but the fourth and subsequent vehicles cannot be charged. It is assumed that the electric vehicles are capable of mutually grasping the priority of their own and other vehicles. In this example, the threshold value in step S203 is 4. If the answer is YES in step S203, the process proceeds to step S205, and the electric vehicle is charged with the charging output expressed by equation 5.

[Equation 5]
Charging output=γ(charging amount command value−threshold value) (5)
where γ is a coefficient.

If the answer is NO in step S203, the process proceeds to step S207, and the electric vehicle switches from the charging on state to the charging off state.

Figure 5 is a graph showing the change in command value over time. Reference numeral 50 indicates the "charged vehicle number command value" in this embodiment. Reference numeral 51 indicates the command value in the conventional technology. Reference numeral 52 indicates the "charged amount command value" in this embodiment. In Figure 5, the magnitude of the command value is shown as a standardized value from -10,000 to +10,000, but this is only an example and is not limited to this value. As shown in Figure 5, in this embodiment, unlike the conventional technology, the command value includes two different command values, the charged vehicle number command value and the charged amount command value. Figure 6 is a graph showing the change in power over time. Reference numeral 81 indicates "EV1 charging power", reference numeral 82 indicates "EV2 charging power", reference numeral 83 indicates "power demand", and reference numeral 84 indicates "target power". The horizontal axis of time is the same in Figures 5 and 6. Also, graph 1 in Figure 6 shows the change in power over time in the conventional technology. Graph 2 in Figure 6 shows the change in power over time in this embodiment.

First, graph 1 in FIG. 6 will be described. At time 3550 in graph 1, both EV1 and EV2 are not connected to the power grid 10. At time 3600, both EV1 and EV2 are connected to the power grid 10, and the power demand increases from 0 kW to 6 kW. Both EV1 and EV2 start charging at 3 kW. Here, since the power demand 83 (6 kW) exceeds the target power 84 (4 kW), a command value (command value 51 at time 3600 in FIG. 5) for reducing the charging power using the variable power adjustment method is sent to EV1 and EV2. EV1, which receives this command value, reduces the charging power 81 around time 3700. The reason why EV1 reduces the charging power before EV2 is because the priority of EV1 is lower than the priority of EV2. As described above, EV1 and EV2 are aware of the priority of their own and other vehicles. In graph 1, EV1 reduces the charging power 81, but before EV2 reduces the charging power using the variable power adjustment method, the command value received by EV1 enters the "on-off power adjustment region." As a result, before EV2 reduces the charging power using the variable power adjustment method, EV1 is controlled using the on-off power adjustment method. However, the on-off power adjustment method, which discontinuously changes the charging power, is unable to match the power demand 83 with the target power 84, and charging is repeatedly turned on and off, resulting in chattering as shown in graph 1.

Therefore, in this embodiment, before the command value received by EV1 enters the "on-off power adjustment region", EV2 reduces the charging power using the variable power adjustment method. That is, in this embodiment, the charging amount command value 52 is calculated to be close to 0 as shown at time 3600 in FIG. 5. Both EV1 and EV2 that receive this charging amount command value 52 reduce their charging power using the variable power adjustment method. After time 3600 in graph 2, EV1 first reduces its charging power using the variable power adjustment method. Then, just before time 3650, EV2 reduces its charging power using the variable power adjustment method. To repeat, the reason why EV1 reduces its charging power before EV2 is because the priority of EV1 is lower than the priority of EV2. As shown in graph 2 in FIG. 6, by both EV1 and EV2 reducing their charging power using the variable power adjustment method, it becomes possible to match the power demand 83 with the target power 84 after time 3700. In comparison with the conventional technology, in this embodiment, before the command value received by EV1 enters the "on-off power adjustment region," EV2 reduces the charging power using a variable power adjustment method, making it possible to match the power demand 83 with the target power 84, thereby preventing chattering as occurs in the conventional technology.

In the above embodiment, the control when EV1 and EV2 are "charging" has been described, but the present invention is also applicable to the case where EV1 and EV2 are "discharging". The control when EV1 and EV2 are "discharging" will be described with reference to Figs. 7 to 9. However, some of the controls described in Figs. 7 to 9 also include controls related to "charging". Fig. 7 is a flowchart showing an example of the operation of the command device 20. Fig. 8 shows the change over time in the command value when the charging power is suppressed and the discharging power is increased. In Fig. 8, the reference numeral 60 indicates the charge/discharge unit number command value. The reference numeral 61 indicates the charge/discharge amount command value. The reference numeral 62 indicates an area where the power demand is greater than the target power and the charge/discharge amount command value is greater than the lower limit of the charge amount command value, and indicates that the charge/discharge amount command value 61 decreases (the charging power is suppressed). The reference numeral 63 indicates an area where the power demand is greater than the target power and the charge/discharge amount command value is smaller than the lower limit of the charge amount command value, and indicates that the charge/discharge unit number command value 60 decreases (the charging power is suppressed). Reference numeral 64 indicates an area where the power demand is greater than the target power and the charge/discharge unit number command value is smaller than the lower limit of the charge unit number command value, and indicates that the charge/discharge amount command value 61 decreases (discharge power increases). Reference numeral 65 indicates an area where the power demand is greater than the target power and the charge amount command value is smaller than the lower limit of the discharge amount command value, and indicates that the charge/discharge unit number command value 60 decreases (charge power is suppressed).

Figure 9 shows the change in the command value over time when the discharge power is suppressed and the charge power is increased. In Figure 9, the reference numeral 70 indicates the charge/discharge unit number command value. The reference numeral 71 indicates the charge/discharge amount command value. The reference numeral 72 indicates an area where the power demand is smaller than the target power and the charge/discharge amount command value is smaller than the upper limit of the discharge amount command value, and the charge/discharge amount command value 71 increases (the discharge power is suppressed). The reference numeral 73 indicates an area where the power demand is smaller than the target power and the charge/discharge amount command value is larger than the upper limit of the discharge amount command value, and the charge/discharge unit number command value 70 increases (the discharge power is suppressed). The reference numeral 74 indicates an area where the power demand is smaller than the target power and the charge/discharge unit number command value is larger than the upper limit of the charge/discharge unit number command value, and the charge/discharge amount command value 71 increases (the charging power increases). The reference numeral 75 indicates an area where the power demand is smaller than the target power and the charging amount command value is larger than the upper limit of the charging amount command value, and the charging/discharging unit number command value 70 increases (the charging power increases).

The processing of steps S301, S303, and S323 in FIG. 7 is the same as steps S101, S103, and S111 in FIG. 3, so the description will be omitted. If the target power is equal to or less than the power demand (NO in step S305), the processing proceeds to step S309. In step S309, the "charge/discharge amount command value" and the "charge/discharge unit number command value" are calculated. The calculation formula for the "charge/discharge amount command value" is the same as formula 1 (however, "charge amount command value" is replaced with "charge/discharge amount command value"). The calculation formula for the "charge/discharge unit number command value" is the same as formula 2 (however, "charge unit number command value" is replaced with "charge/discharge unit number command value"). The predetermined relationship in step S311 indicates whether the charge/discharge amount command value calculated in step S309 is smaller than the lower limit value. If the charge/discharge amount command value calculated in step S309 is smaller than the lower limit value (YES in step S311), the processing proceeds to step S323. On the other hand, if the answer is NO in step S311, the process proceeds to step S313. If the charge/discharge unit number command value is smaller than the lower limit of the charge unit number command value (YES in step S313), the process proceeds to step S315, where the charge amount command value and the charge unit number command value are calculated. The calculation formula for the charge amount command value is expressed by Equation 6. The calculation formula for the charge unit number command value is the same as Equation 4.

[Equation 6]
Charging amount command value=Lower limit of charging amount command value (6)

If the answer is NO in step S313, the process proceeds to step S317. If the charge amount command value is smaller than the lower limit of the discharge amount command value (YES in step S317), the process proceeds to step S319, where the charge amount command value and the charge unit number command value are calculated. The calculation formula for the charge amount command value is expressed by Equation 7. The calculation formula for the charge unit number command value is expressed by Equation 8.

[Equation 7]
Charge amount command value=Charge amount command value (7)

[Equation 8]
Charging unit number command value=Lower limit of charging unit number command value (8)

If the answer is NO in step S317, the process proceeds to step S321, where the charge amount command value and the charge unit number command value are calculated. The calculation formula for the charge amount command value is expressed by Equation 9. The calculation formula for the charge unit number command value is the same as Equation 4.

[Equation 9]
Charge amount command value=Lower limit value of discharge amount command value (9)

If the target power is greater than the power demand (YES in step S305), the command value is calculated by processing areas 72 to 75 in Figure 9.

(Action and Effect)
As described above, the power control device 30a (or the power control device 30b) according to this embodiment provides the following advantageous effects.

The power control device 30a (charging/discharging device) receives a command value calculated based on the power demand measured within a predetermined range and a preset target power. An example of "within a predetermined range" refers to the entire power system 1. The command value is calculated by the command device 20. The command device 20 measures the power demand within a predetermined range, calculates a command value based on the measured power demand and a preset target power, and transmits the calculated command value to the power control device 30a. Depending on the received command value, the power control device 30a judges whether the power control device 30a is in a variable power adjustment region in which the charging/discharging power of the battery is continuously changed to charge/discharge, or in an on/off power adjustment region which is a power region lower than the variable power adjustment region and in which the charging/discharging power is discontinuously changed to charge/discharge. When the power control device 30a judges that the command value indicates the variable power adjustment region, it continuously changes the charging/discharging power to charge/discharge, while when it judges that the command value indicates the on/off power adjustment region, it discontinuously changes the charging/discharging power to charge/discharge. For example, as shown in FIG. 2, when the command value indicates the variable power adjustment region 41, the power control device 30a performs charging and discharging by continuously changing the charging and discharging power. On the other hand, when the command value indicates the on-off power adjustment region 40, the power control device 30a performs charging and discharging by discontinuously changing the charging and discharging power.

When a difference occurs between the target power and the power demand that is equal to or less than the minimum output value, in the on-off power adjustment method, it is difficult to match the power demand with the target power because the charging and discharging power is discontinuous. According to this embodiment, it is possible to match the power demand with the target power by the above-mentioned configuration. In the conventional technology, EV1 reduces the charging power 81, but before EV2 reduces the charging power with the variable power adjustment method, the command value received by EV1 enters the "on-off power adjustment region" (see graph 1 in FIG. 6). As a result, in the conventional technology, EV1 is controlled by the on-off power adjustment method before EV2 reduces the charging power with the variable power adjustment method. In the on-off power adjustment method, since the charging and discharging power is discontinuous, the power demand cannot be matched with the target power, and discontinuous on-off control is repeatedly executed thereafter, causing chattering. According to this embodiment, as shown in graph 2 in FIG. 6, the variable power adjustment method acts first, and by continuously changing the charging and discharging power, it is possible to match the power demand with the target power, and chattering as in the conventional technology is prevented. The determination unit and control unit correspond to the power control unit 31a (or the power control device 30b) in FIG. 1.

The command value includes two pieces of information: information for determining whether battery charging is on or off, and information for determining the magnitude of charging and discharging power. An example of "information for determining whether battery charging is on or off" is shown by reference number 50 in FIG. 5. An example of "information for determining the magnitude of charging and discharging power" is shown by reference number 52 in FIG. 5. In this way, in this embodiment, two pieces of information are used to determine whether the region is variable power adjustment or on-off power adjustment, so it is possible to apply the variable power adjustment method before the on-off power adjustment method.

The information for determining whether the battery is charged or not is changed when the charge/discharge power reaches the upper limit or the lower limit. An example of "the charge/discharge power is at the lower limit" is the charge/discharge power when the reference number 52 in FIG. 5 is minus 10,000. When the reference number 52 is minus 10,000, the information for determining whether the battery is charged or not (reference number 50) decreases. At this time, the command value indicates the on/off power adjustment region (change from charging on to charging off). An example of "the charge/discharge power is at the upper limit" is a state in which there are five electric vehicles connected to the power system 1, two of which are charging at the maximum output value, and the remaining three are not charging and have excess power. In this state, the third electric vehicle can start charging because there is excess power. At this time, the information for determining whether the battery is charged or not (command value) increases. For example, referring to FIG. 2, it increases from "0" to "A" (change from charging off to charging on). This causes the third electric vehicle to start charging.

Each of the functions described in the above embodiments may be implemented by one or more processing circuits. Processing circuits include programmed processing devices, such as processors that include electrical circuitry. Processing circuits also include devices, such as application specific integrated circuits (ASICs) or circuit components, arranged to perform the described functions.

As described above, an embodiment of the present invention has been described, but the descriptions and drawings that form part of this disclosure should not be understood as limiting this invention. Various alternative embodiments, examples, and operating techniques will become apparent to those skilled in the art from this disclosure.

30a, 30b Power control device, 31a, 31b Power control unit, 32a, 32b Charge/discharge output calculation unit, 33a, 33b Command value receiving unit

Claims (4)

A charging/discharging method for use in a charging/discharging device that receives a command value calculated based on a power demand measured within a predetermined range and a preset target power, comprising:
determining whether the power regulation region is a variable power regulation region in which the charge/discharge power of the battery is changed continuously to perform charging/discharging, or an on/off power regulation region which is a power region lower than the variable power regulation region and in which the charge/discharge power is changed discontinuously to perform charging/discharging, according to the command value;
A charging and discharging method characterized in that, when it is determined that the command value indicates the variable power adjustment region, charging and discharging are performed by continuously changing the charging and discharging power, while, when it is determined that the command value indicates the on-off power adjustment region, charging and discharging are performed by discontinuously changing the charging and discharging power. The charging/discharging method according to claim 1, characterized in that the command value includes two pieces of information: information for determining whether charging of the battery is on or off, and information for determining the magnitude of the charging/discharging power. 3. The method according to claim 2, wherein the information for determining whether the charge/discharge power is on or off is changed when the charge/discharge power reaches an upper limit or a lower limit. a receiving unit that receives a command value calculated based on a power demand measured within a predetermined range and a preset target power;
a determination unit that determines whether the received command value is in a variable power adjustment region in which charging and discharging are performed by continuously changing the charging and discharging power of the battery, or in an on-off power adjustment region which is a power region lower than the variable power adjustment region and in which charging and discharging are performed by discontinuously changing the charging and discharging power;
a control unit that, when it is determined that the command value indicates the variable power adjustment region, performs charging and discharging by continuously changing the charge/discharge power, and, when it is determined that the command value indicates the on-off power adjustment region, performs charging and discharging by discontinuously changing the charge/discharge power;
A charging/discharging device comprising:

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